AutoDrive Concept

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AutoDrive Concept

AutoDrive is a completely automated highway driving system. By 2030 all major

interstates in the US are expected to support "AutoDrive lanes" with completely

automated car and commercial vehicle driving. Any car updated for AutoDrive can enterthese lanes and enjoy speed limits of around 130 mph.

In this series of articles we will go through the design and development of this

remarkable technology.

AutoDrive Features

GPS based position determination for accurate steering of the car. GPS

position is used to accurately locate the vehicle's position on the map and then

steer the car according to the path specified by the map.

Inter Vehicle Signaling (IVS) is used for keeping track of neighboring vehicles.

IVS is used to detect speed changes and respond to lane change requests fromother vehicles.

Radar feed is used to identify objects in vicinity of the car. The main objective of

the radar is to detect non-vehicle objects that might be present on the highway.

The precision radar is capable of detecting objects that are more than 3 cm in

height.


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Map updates are obtained over a wireless internet connection. Most map

updates are obtained at the time of trip start. The maps are extremely detailed

and store information about the different lanes with an accuracy of +/- 1 cm.

Weather feed is used to adjust driving parameters according to the current

weather conditions.

Construction and road closure detection is implemented using IVS. An IVStransmitter is placed in a closed lane. Vehicles receive the IVS signal from the

transmitter and decide to change lanes.

GPS Based Position Determination

The current GPS position of the vehicle is the most important piece of information in the

AutoDrive system. A GPS receiver is fitted in all vehicles retrofitted with the AutoDrive

system. The salient features of the GPS system are:

GPS receiver used in the AutoDrive system has the accuracy of 1 cm. The current GPS position is constantly compared with the map coordinates to

determine the exact location of the vehicle.

Since the GPS position is accurate to 1 cm level, it is also used to steer the

vehicle so that it stays in the center of its lane.

Inter Vehicle Signaling (IVS)

IVS is used to adjust to speed changes and lane changes of the neighboring vehicles.

All vehicles broadcast the GPS position of their center and their dimensions interms of length and width and their speed. Vehicle type is also included in the

broadcast. The vehicles determine their neighboring vehicles by keeping track of

these broadcasts from vehicles that are within 100 feet. All broadcasts received

from vehicles outside the 100 feet radius are ignored. (Note that the 100 feet

check does not apply to IVS transmitters used for lane closures. See the section

on lane closures).

When a vehicle needs to change its lane, it sends a lane change request

message containing the direction if it is left or right, to the neighboring vehicles.

In response to a lane change request received from a neighbor or in response to

an obstruction on the road, a vehicle sends a braking request messagecontaining the deceleration rate to its neighbors.

IVS supports priority routing of emergency vehicles. If the broadcast received

from a neighboring vehicle indicates that it is an emergency vehicle, the vehicle

will automatically change lanes to make way for the emergency vehicle.

If a vehicle fails on the road, it broadcasts a speed of value zero thereby

indicating that it is crippled.


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Radar Feed

An AutoDrive vehicle has a radar installed. The radar monitors the presence of

obstructions other than vehicles like human beings, animals, fallen trees or rocks. The

radar feed is used to take appropriate lane and speed change actions to steer clear off

the obstructions.

Map Updates

Before the start of a journey, an AutoDrive vehicle downloads from the internet, the map

of the complete path from source to destination. This map has details up to the level of

number of lanes, their curvature etc. This map guides the AutoDrive vehicle to the

destination.

Weather FeedWeather updates about the path are constantly received during the journey. If extreme

weather conditions are detected, appropriate rerouting is carried out. This rerouting is

performed by obtaining map updates on the fly. Weather feed is also used to adjust

driving parameters like braking distance, wheel grip and radar visibility.

Construction and Road Closures

If a lane is closed for construction, an IVS transmitter is located at its center which

broadcasts its GPS position, width of the lane, the length of closure and a speed valueof zero. For example, if a one mile lane closure is required, an IVS transmitter is kept at

half mile and it broadcasts its length as 1 mile and speed as zero.

AutoDrive Architecture Design

Introduction

This document has been developed by the engineering contractor to define the softwarearchitecture of the AutoDrive system. The architecture document is based on the

requirements document mentioned in the references section.

Intended Audience

The intended audience for this document is:


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Subsystem design teams for the subsystems specified here.

AutoDrive Inc.

References

AutoDrive Software Requirements Document

Architecture Design

The software implementing the AutoDrive system will be divided into the following four

subsystems:

Inter Vehicle Signaling Subsystem will completely handle the Inter Vehicle Signaling

protocol. It will provide the Automatic Driving Subsystem (ADS) with information about

neighboring vehicles.

Obstruction Detection Subsystemwill interact with the Radar and inform ADS aboutobstructions on the road.

Position Mapping Subsystem will obtain the current GPS position and it will plot it on the

map and give information about lane curvature and speed limits. It will provide a driving

path information to ADS.

Automatic Driving Subsystem is the heart of the system. It obtains information from other

subsystems and uses it to operate the steering, brakes and the accelerator (gas paddle)

The software architecture and the interactions between the subsystems are shown in

the figure below. automatic transmission (often informally shortened to auto, and abbreviatedto AT) is amotor vehicletransmissionthat can automatically change gear ratios as the vehicle

moves, freeing the driver from having to shift gearsmanually. Similar but larger devices are alsoused for heavy-duty commercial and industrial vehicles and equipment.

Most automatic transmissions have a defined set of gear ranges, often with aparking pawl

feature that locks the output shaft of the transmission.Continuously variable transmissions

(CVTs), which are very different to conventional automatic transmissions, can change their'ratios' over a wider 'stepless' range, rather than between a set of fixed gear ratios. CVTs have

been used for decades in two-wheeled scooters; but have only seen use in a few automobile

models. Recently, however, CVT technology has gained greater acceptance among

manufacturers and customers, especially in Audi andNissan automobiles, and gas-electric hybridvehicles.

Some machines with limited speed ranges or fixed engine speeds, such as someforklift trucks

andlawn mowers, only use a torque converterto provide a variable gearing of the engine to the

wheels.

Contents
http://www.eventhelix.com/ThoughtProjects/AutoDrive/auto_drive_software_requirements.htmhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Inter%20Vehicle%20Signaling%20Subsystemhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Obstruction%20Detection%20Subsystemhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Obstruction%20Detection%20Subsystemhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Position%20Mapping%20Subsystemhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Automatic%20Driving%20Subsystemhttp://en.wikipedia.org/wiki/Motor_vehiclehttp://en.wikipedia.org/wiki/Motor_vehiclehttp://en.wikipedia.org/wiki/Transmissionhttp://en.wikipedia.org/wiki/Transmissionhttp://en.wikipedia.org/wiki/Gear_ratiohttp://en.wikipedia.org/wiki/Manual_transmissionhttp://en.wikipedia.org/wiki/Manual_transmissionhttp://en.wikipedia.org/wiki/Manual_transmissionhttp://en.wikipedia.org/wiki/Parking_pawlhttp://en.wikipedia.org/wiki/Continuously_variable_transmissionhttp://en.wikipedia.org/wiki/Continuously_variable_transmissionhttp://en.wikipedia.org/wiki/Audihttp://en.wikipedia.org/wiki/Nissanhttp://en.wikipedia.org/wiki/Hybrid_vehiclehttp://en.wikipedia.org/wiki/Hybrid_vehiclehttp://en.wikipedia.org/wiki/Hybrid_vehiclehttp://en.wikipedia.org/wiki/Forklift_truckhttp://en.wikipedia.org/wiki/Forklift_truckhttp://en.wikipedia.org/wiki/Lawn_mowerhttp://en.wikipedia.org/wiki/Lawn_mowerhttp://en.wikipedia.org/wiki/Torque_converterhttp://en.wikipedia.org/wiki/Torque_converterhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/auto_drive_software_requirements.htmhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Inter%20Vehicle%20Signaling%20Subsystemhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Obstruction%20Detection%20Subsystemhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Position%20Mapping%20Subsystemhttp://www.eventhelix.com/ThoughtProjects/AutoDrive/architecture_design.htm#Automatic%20Driving%20Subsystemhttp://en.wikipedia.org/wiki/Motor_vehiclehttp://en.wikipedia.org/wiki/Transmissionhttp://en.wikipedia.org/wiki/Gear_ratiohttp://en.wikipedia.org/wiki/Manual_transmissionhttp://en.wikipedia.org/wiki/Parking_pawlhttp://en.wikipedia.org/wiki/Continuously_variable_transmissionhttp://en.wikipedia.org/wiki/Audihttp://en.wikipedia.org/wiki/Nissanhttp://en.wikipedia.org/wiki/Hybrid_vehiclehttp://en.wikipedia.org/wiki/Hybrid_vehiclehttp://en.wikipedia.org/wiki/Forklift_truckhttp://en.wikipedia.org/wiki/Lawn_mowerhttp://en.wikipedia.org/wiki/Torque_converter


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having a selector (when worn) jump into Reverse from Low gear during engine braking

maneuvers.[citation needed]

Automatic transmissions have various modes depending on the model and make of thetransmission. Some of the common modes are:

Park (P)

This selection mechanically locks the output shaft of transmission, restricting

the vehicle from moving in any direction. A parking pawl prevents the

transmission from rotating, and therefore the vehicle from moving, although

the vehicle's non-driven roadwheels may still rotate freely. For this reason, it

is recommended to use the hand brake (or parking brake) because this

actually locks (in most cases) the rear wheels and prevents them from

moving. This also increases the life of the transmission and the park pin

mechanism, because parking on an incline with the transmission in park

without the parking brake engaged will cause undue stress on the parkingpin. An efficiently-adjusted hand brake should also prevent the car from

moving if a worn selector accidentally drops into reverse gear during early

morning fast-idle engine warm-ups.[citation needed]

A car should be allowed to come to a complete stop before setting the

transmission into park to prevent damage. Usually, park is one of only two

selections in which the car's engine can be started. In many modern cars and

trucks, the driver must have the foot brake applied before the transmission

can be taken out of park. The Park position is omitted on buses/coaches with

automatic transmission (on which a parking pawl is not practical), which must

be placed in neutral with the parking brakes set.

Most automobiles require P to be set on the selector lever before the internal

combustion engine can be started. This is typically achieved via a normally

open 'inhibitor' switch, which is wired in series with the starter motor

engagement circuit, and is only closed when P is selected, thus completing

the circuit (when the key is turned to the start position)

Reverse (R)

This engages reverse gear within the transmission, giving the ability for the

vehicle to drive backwards. In order for the driver to select reverse, theymust come to a complete stop,[dubious discuss] push the shift lock button in (or

pull the shift lever forward in the case of a column shifter) and select reverse.

Not coming to a complete stop can cause severe damage to the transmission.[citation needed] Many modern automatic transmissions have a safety mechanism in

place, which does to some extent prevent (but does not completely avoid)

inadvertently putting the car in reverse when the vehicle is moving forwards.

This mechanism usually consists of a solenoid-controlled physical barrier on
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either side of the Reverse position, which is electronically engaged by a

switch on the brakepedal. Therefore, the brake pedal needs to be depressed

in order to allow the selection of reverse. Some electronic transmissions

prevent or delay engagement of reverse gear altogether while the car is

moving.

Some shifters with a shift button allow the driver to freely move the shifter

from R to N or D, or simply moving the shifter to N or D without actually

depressing the button. However, the driver cannot put back the shifter to R

without depressing the shift button to prevent accidental shifting, especially

at high speeds, which could damage the transmission.

Neutral/No gear (N)

This disengages all gear trains within the transmission, effectively

disconnecting the transmission from the driven roadwheels, so the vehicle is

able to move freely under its own weight without the motive force from the

engine. This is the only other selection in which the vehicle's engine can be

started.

Drive (D)

This position allows the transmission to engage the full range of available

forward gear trains, and therefore allows the vehicle to move forward and

accelerate through its range of gears. The number of gear 'ratios' a

transmission has depends on the model, but they initially ranged from three

(predominant before the 1990s), to four and five speeds (losing popularity to

six-speed autos, though still favored by Chrysler and Honda/Acura).[citation needed]

Six-speed automatic transmissions are now probably the most common

offering, found in most Volkswagens and all Audis, BMWs and Mercedes,

Toyota Camry V6 models, the Chevrolet Malibu LTZ, Corvette, GM trucks,

Pontiac G8, and most newer model Ford/Lincoln/Mercury vehicles). However,

seven-speed autos are becoming available (found in Mercedes 7G gearbox),

as are eight-speed autos in the newer models ofLexus and BMW cars.

Some cars, when put into D, will automatically lock the doors or turn on the

daytime running lamps.[citation needed]

OverDrive (D, OD, or a boxed [D])

This mode is used in some transmissions to allow early computer-controlled

transmissions to engage the Automatic Overdrive. In these transmissions,

Drive (D) locks the Automatic Overdrive off, but is identical otherwise. OD

(Overdrive) in these cars is engaged under steady speeds or low acceleration

at approximately 35-45 mph (approx. 72 km/h). Under hard acceleration or

below 35-45 mph, the transmission will automatically downshift. Vehicles
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with this option should be driven in this mode unless circumstances require a

lower gear.

Second (2 or S)

This mode limits the transmission to the first two gear ratios, or sometimes

locks the transmission in second gear. This can be used to drive in adverse

conditions such as snow and ice, as well as climbing or going down hills in the

winter time. Some vehicles will automatically shift up out of second gear in

this mode if a certain rpm range is reached in order to prevent engine

damage.

Although traditionally considered second gear, there are other names used.

Chrysler models with a three-speed automatic since the late 1980s have

called this gear 3 while using the traditional names for Drive and Low.

First (1 or L [Low])

This mode locks the transmission in first gear only. It will not change to any

other gear range. This, like second, can be used during the winter season, or

for towing.

As well as the above modes there are also other modes, dependent on the manufacturer and

model. Some examples include;

D5

In Hondas and Acuras equipped with five-speed automatic transmissions, this

mode is used commonly for highway use (as stated in the manual), and usesall five forward gears. Lincoln LS also used a "D5" & "D4" in shiftgate....

D4

This mode is also found in Honda and Acura four- or five-speed automatics,

and only uses the first four gear ratios. According to the manual, it is used for

"stop and go traffic", such as city driving. Lincoln LS also used a "D5" & "D4"

in shiftgate....

D3 or 3

This mode is found in Honda, Acura and Pontiac four-speed automatics and

only uses the first three gear ratios. According to the manual, it is used for

"stop & go traffic", such as city driving.

S or Sport

This is commonly described as 'Sport mode'. It operates in an identical

manner as 'D' mode, except that the upshifts change much higher up the
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engine's rev range. This has the effect on maximising all the available engine

ouput, and therefore enhances the performance of the vehicle, particularly

during acceleration. This mode will also downchange much higher up the rev

range compared to 'D' mode, maximising the effects ofengine braking. This

mode will have a detrimental effect on fuel economy.

+ , and M

This is for the 'manual mode' selection of gears in certain automatics, such as

Porsche'sTiptronic. The M feature can also be found in Chrysler and General

Motors products such as the Dodge Magnum and Pontiac G6, as well as

Toyota's Camry, Corolla, Fortuner, Previa and Innova. Mitsubishi, meanwhile

does not have the M, and instead has the + and -, which is separated from

the rest of the shift modes; the same is true for some Peugeot products like

Peugeot 206. Meanwhile, the driver can shift up and down at will by toggling

the (console mounted) shift lever like a semi-automatic transmission. This

mode may be engaged either through a selector/position or by actuallychanging the gears (e.g., tipping the gear-down paddles mounted near the

driver's fingers on the steering wheel).

Winter (W)

In some Mercedes-Benz, BMW and General Motors Europe models, a 'Winter

mode' can be engaged so that second gear is selected instead of first when

pulling away from stationary, to reduce the likelihood of loss of traction due

to wheelspin on snow or ice.

Brake (B)

A mode selectable on some Toyota models. In non-hybrid cars, this mode lets

the engine do compression braking, also known as engine braking, typically

when encountering a steep downhill. Instead of engaging the brakes, the

engine in a non-hybrid car switches to a lower gear and slows down the

spinning tires. The engine holds the car back, instead of the brakes slowing it

down. For hybrid cars, this mode converts the electric motor into a generator

for the battery. It is not the same as downshifting in a non-hybrid car, but it

has the same effect in slowing the car without using the brakes.

[edit] Hydraulic automatic transmissions

The predominant form of automatic transmission ishydraulically operated; using a fluid

coupling ortorque converter, and a set ofplanetary gearsetsto provide a range of gear ratios.
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[edit] Parts and operation

A cut-away model of a torque converter

A hydraulic automatic transmission consists of the following parts:

Torque converter: A type offluid coupling, hydraulically connecting theengine to the transmission. It takes the place of a mechanical clutch, allowingthe transmission to stay 'in gear' and the engine to remain running whilst the

vehicle is stationary, without stalling. A torque converter differs from a fluidcoupling, in that it provides a variable amount of torque multiplication at lowengine speeds, increasing "breakaway" acceleration. This is accomplishedwith a third member in the "coupling assembly" known as the stator, and byaltering the shapes of the vanes inside the coupling in such a way as to curvethe fluid's path into the stator. The stator captures the kinetic energy of thetransmission fluid, in effect using the leftover force of it to enhance torquemultiplication.

Planetary gearset: A compound epicyclic planetary gearset, whose bands andclutches are actuated by hydraulic servos controlled by the valve body,providing two or more gear ratios.

Clutches and bands: to effect gear changes, one of two types of clutches orbands are used to hold a particular member of the planetary gearsetmotionless, while allowing another member to rotate, thereby transmittingtorque and producing gear reductions or overdrive ratios. These clutches areactuated by the valve body (see below), their sequence controlled by thetransmission's internal programming. Principally, a type of device known as asprag or roller clutch is used for routine upshifts/downshifts. Operating muchas a ratchet, it transmits torque only in one direction, free-wheeling or"overrunning" in the other. The advantage of this type of clutch is that iteliminates the sensitivity of timing a simultaneous clutch release/apply ontwo planetaries, simply "taking up" the drivetrain load when actuated, andreleasing automatically when the next gear's sprag clutch assumes thetorque transfer. The bands come into play for manually selected gears, suchas low range or reverse, and operate on the planetary drum's circumference.Bands are not applied when drive/overdrive range is selected, the torquebeing transmitted by the sprag clutches instead. Bands are used for braking;the GM Turbo-Hydramatics incorporated this.[citation needed]

Valve body: hydraulic control center that receives pressurized fluid from amain pump operated by the fluid coupling/torque converter. The pressurecoming from this pump is regulated and used to run a network of spring-loaded valves, check balls and servo pistons. The valves use the pump
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pressure and the pressure from a centrifugal governor on the output side (aswell as hydraulic signals from the range selector valves and the throttle valveor modulator) to control which ratio is selected on the gearset; as the vehicleand engine change speed, the difference between the pressures changes,causing different sets of valves to open and close. The hydraulic pressurecontrolled by these valves drives the various clutch and brake band

actuators, thereby controlling the operation of the planetary gearset to selectthe optimum gear ratio for the current operating conditions. However, inmany modern automatic transmissions, the valves are controlled by electro-mechanical servos which are controlled by the electronic engine control unit(ECU) or a separate transmission control unit (TCU). (See History andimprovements below.)

Hydraulic & lubricating oil: called automatic transmission fluid (ATF), thiscomponent of the transmission provides lubrication, corrosion prevention,and a hydraulic medium to convey mechanical power (for the operation ofthe transmission). Primarily made from refined petroleum, and processed toprovide properties that promote smooth power transmission and increaseservice life, the ATF is one of the few parts of the automatic transmission that

needs routine service as the vehicle ages.

The multitude of parts, along with the complex design of the valve body, originally made

hydraulic automatic transmissions much more complicated (and expensive) to build and repair

than manual transmissions. In most cars (except US family, luxury, sport-utility vehicle, andminivan models) they have usually been extra-cost options for this reason. Mass manufacturing

and decades of improvement have reduced this cost gap.

[edit] Energy efficiency

Hydraulic automatic transmissions are almost always less energy efficient than manual

transmissions due mainly to viscous and pumping losses; both in the torque converter and thehydraulic actuators. A relatively small amount of energy is required to pressurize the hydraulic

control system, which uses fluid pressure to determine the correct shifting patterns and operatethe various automatic clutch mechanisms.

Manual transmissions use a mechanical clutch to transmit torque, rather than a torque converter,

thus avoiding the primary source of loss in an automatic transmission. Manual transmissions also

avoid the power requirement of the hydraulic control system, by relying on the human musclepower of the vehicle operator to disengage the clutch and actuate the gear levers, and the mental

power of the operator to make appropriate gear ratio selections. Thus the manual transmission

requires very little engine power to function, with the main power consumption due to drag from

the gear train being immersed in the lubricating oil of the gearbox.

The energy efficiency of automatic transmission has increased with the introduction of the torque

converter lock-up clutch, which practically eliminates fluid losses when engaged. Modern

automatic transmission also minimize energy usage and complexity, by minimizing the amountof shifting logic that is done hydraulically. Typically, control of the transmission has been

transferred to computerized control systems which do not use fluid pressure for shift logic or

actuation of clutching mechanisms.
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The on road acceleration of an automatic transmission can occasionally exceed that of an

otherwise identical vehicle equipped with a manual transmission in turbocharged diesel

applications. Turbo-boost is normally lost between gear changes in a manual whereas in anautomatic the accelerator pedal can remain fully depressed. This however is still largely

dependent upon the number and optimal spacing of gear ratios for each unit, and whether or not

the elimination of spooldown/accelerator lift off represent a significant enough gain to counterthe slightly higher power consumption of the automatic transmission itself

[edit] History and improvements

Modern automatic transmissions can trace their origins to an early "horseless carriage" gearboxthat was developed in 1904 by the Sturtevant brothers ofBoston,Massachusetts. This unit had

two forward speeds, the ratio change being brought about by flyweights that were driven by the

engine. At higher engine speeds, high gear was engaged. As the vehicle slowed down and engine

RPM decreased, the gearbox would shift back to low. Unfortunately, the metallurgyof the timewasn't up to the task, and owing to the abruptness of the gear change, the transmission would

often fail without warning.

The next significant phase in the automatic transmission's development occurred in 1908 with

the introduction ofHenry Ford's remarkable Model T. The Model T, in addition to being cheapand reliable by the standards of the day, featured a simple, two speed plus reverseplanetary

transmission whose operation was manually controlled by the driver using foot pedals. The

pedals actuated the transmission's friction elements (bands and clutches) to select the desiredgear. In some respects, this type of transmission was less demanding of the driver's skills than

the contemporary, unsynchronized manual transmission, but still required that the driver know

when to make a shift, as well as how to get the car off to a smooth start.

In 1934, both REO and General Motors developed semi-automatic transmissions that were lessdifficult to operate than a fully manual unit. These designs, however, continued to use a clutchto

engage the engine with the transmission. The General Motors unit, dubbed the "Automatic

Safety Transmission," was notable in that it employed a power-shifting planetary gearbox thatwas hydraulically controlled and was sensitive to road speed, anticipating future development.

Parallel to the development in the 1930s of an automatically-shifting gearbox was Chrysler's

work on adapting the fluid couplingto automotive use. Invented early in the 20th century, the

fluid coupling was the answer to the question of how to avoid stalling the engine when thevehicle was stopped with the transmission in gear. Ironically, Chrysler itself never used the fluid

coupling with any of its automatic transmissions, but did use it in conjunction with a hybrid

manual transmission called "Fluid Drive" (the similarHy-Drive used atorque converter). Thesedevelopments in automatic gearbox and fluid coupling technology eventually culminated in the

introduction in 1939 of the General Motors Hydra-Matic, the world's first mass-produced

automatic transmission.

Available as an option on 1940 Oldsmobilesand laterCadillacs, the Hydra-Matic combined afluid coupling with three hydraulically-controlled planetary gearsets to produce four forward
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As computerised engine control units(ECUs) became more capable, much of the logic built into

the transmission's valve body was offloaded to the ECU. (Some manufacturers use a separate

computer dedicated to the transmission, but sharing information with the engine managementcomputer.) In this case, solenoids turned on and off by the computer control shift patterns and

gear ratios, rather than the spring-loaded valves in the valve body. This allows for more precise

control ofshift points, shift quality, lower shift times, and (on some newer cars) semi-automaticcontrol, where the driver tells the computer when to shift. The result is an impressive

combination of efficiency and smoothness. Some computers even identify the driver's style and

adapt to best suit it.

ZF Friedrichshafenand BMW were responsible for introducing the first six-speed (the ZF6HP26 in the 2002BMWE657-Series). Mercedes-Benz's 7G-Tronic was the first seven-speed

in 2003, with Toyota introducing an eight-speed in 2007 on theLexus LS 460. Mercedes-Benz

unveiled a conventional automatic transmission with the torque converter replaced with a lock-up clutch called the AMG SPEEDSHIFT MCT.[3]

[edit] Automatic transmission modelsSome of the best known automatic transmission families include:

General Motors Powerglide, "Turbo-Hydramatic" TH350, TH400 and 700R4,4L60-E, 4L80-E, HoldenTrimatic

Ford: Cruise-O-Matic, C4, C6, AOD/AODE, E4OD, ATX, AXOD/AX4S/AX4N Chrysler:TorqueFlite 727 and 904, A500, A518, 45RFE, 545RFE BorgWarner (later Aisin AW) ZF Friedrichshafen automatic transmissions Allison Transmission

Voith Turbo Aisin AW; Aisin AW is a Japanese automotive parts supplier, known for itsautomatic transmissions and navigation systems

Honda Nissan/Jatco Volkswagen Group - 01M Drivetrain Systems International (DSI) - M93, M97 and M74 4-speeds, M78

and M79 6-speeds

Automatic transmission families are usually based onRavigneaux, Lepelletier[disambiguation needed], orSimpsonplanetary gearsets. Each uses some arrangement of one or two central sun gears, and a

ring gear, with differing arrangements of planet gears that surround the sun and mesh with the

ring. An exception to this is the Hondamatic line from Honda, which uses sliding gears onparallel axes like a manual transmission without any planetary gearsets. Although the Honda isquite different from all other automatics, it is also quite different from an automated manual

transmission (AMT).

Many of the above AMTs exist in modified states, which were created by racing enthusiasts and

their mechanics by systematically re-engineering the transmission to achieve higher levels of
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tco_transmissionshttp://en.wikipedia.org/wiki/Volkswagen_Grouphttp://en.wikipedia.org/wiki/Volkswagen_01M_transmissionhttp://en.wikipedia.org/wiki/Ravigneaux_planetary_gearsethttp://en.wikipedia.org/wiki/Lepelletierhttp://en.wikipedia.org/wiki/Wikipedia:WikiProject_Disambiguation/Fixing_linkshttp://en.wikipedia.org/wiki/Epicyclic_gearinghttp://en.wikipedia.org/wiki/Hondamatichttp://en.wikipedia.org/wiki/Hondahttp://en.wikipedia.org/wiki/Automated_manual_transmissionhttp://en.wikipedia.org/wiki/Automated_manual_transmission


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performance. These are known as "performance transmissions". An example of a manufacturer

of high performance transmissions ofGeneral Motors and Ford transmissions is PerformaBuilt.

[edit] Continuously variable transmissions

Main article: Continuously variable transmission

A fundamentally different type of automatic transmission is the continuously variabletransmission orCVT, which can smoothly and steplessly alter itsgear ratioby varying thediameter of a pair ofbelt orchain-linkedpulleys,wheels or cones. Some continuously variable

transmissions use a hydrostatic drive - consisting of avariable displacement pump and a

hydraulic motor - to transmit power without gears. CVT designs are usually as fuel efficient asmanual transmissions in city driving, but early designs lose efficiency as engine speed increases.

A slightly different approach to CVT is the concept oftoroidal CVTorinfinitely variable

transmission (IVT) (from infinitely variable transmission). These concepts provide zero and

reverse gear ratios.

Some current hybrid vehicles, notably those ofToyota,Lexus and Ford Motor Company, havean "electronically-controlled CVT" (E-CVT). In this system, the transmission has fixed gears,

but the ratio of wheel-speed to engine-speed can be continuously varied by controlling the speed

of the third input to a differential using an electric motor-generator.

[edit] Manually controlled automatic transmissions

Most automatic transmissions offer the driver a certain amount of manual control over the

transmission's shifts (beyond the obvious selection of forward, reverse, or neutral). Thosecontrols take several forms:

Throttle kickdown

Most automatic transmissions include some means of forcing a downshift into

the lowest possible gear ratio if the throttle pedal is fully depressed. In many

older designs, kickdown is accomplished by mechanically actuating a valve

inside the transmission. Most modern designs use a solenoid-operated valve

that is triggered by a switch on the throttle linkage or by the engine control

unit (ECM) in response to an abrupt increase in engine power.

Mode selection

Allows the driver to choose between preset shifting programs. For example,

'Economy mode' saves fuel by upshifting at lower engine speeds, while 'Sport

mode' (aka Power or Performance) delays shifting for maximum acceleration.

The modes also change how the computer responds to throttle input.

Low gear ranges
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Conventionally, automatic transmissions have selector positions that allow

the driver to limit the maximum ratio that the transmission may engage. On

older transmissions, this was accomplished by a mechanical lockout in the

transmission valve body preventing an upshift until the lockout was

disengaged; on computer-controlled transmissions, the same effect is

accomplished electronically. The transmission can still upshift and downshiftautomatically between the remaining ratios: for example, in the 3 range, a

transmission could shift from first to second to third, but not into fourth or

higher ratios. Some transmissions will still upshift automatically into the

higher ratio if the engine reaches its maximum permissible speed in the

selected range.[citation needed]

Manual controls

Some transmissions have a mode in which the driver has full control of ratio

changes (either by moving the selector, or through the use of buttons or

paddles), completely overriding the automated function of the hydrauliccontroller. Such control is particularly useful in cornering, to avoid unwanted

upshifts or downshifts that could compromise the vehicle's balance or

traction. "Manumatic" shifters, first popularized by Porsche in the 1990s

under the trade nameTiptronic, have become a popular option on sports cars

and other performance vehicles. With the near-universal prevalence of

electronically controlled transmissions, they are comparatively simple and

inexpensive, requiring only software changes, and the provision of the actual

manual controls for the driver. The amount of true manual control provided is

highly variable: some systems will override the driver's selections under

certain conditions, generally in the interest of preventing engine damage.

Since these gearboxes also have a throttle kickdown switch, it is impossible

to fully exploit the engine power at low to medium engine speeds.[dubiousdiscuss]

[citation needed]

Second gear takeoff

Some automatics, particularly those fitted to larger capacity or high torque

engines, either when '2' is manually selected, or by engaging a "winter

mode", will start off in second gear instead of first, and then not shift into a

higher gear until returned to D. Also note that as with most American

automatic transmissions, selecting "2" using the selection lever will not tell

the transmission to be in only 2nd gear, rather, it will simply limit the

transmission to 2nd gear after prolonging the duration of 1st gear through

higher speeds than normal operation. The 2000-2002 Lincoln LS V8 (the 5-

speed automatic withoutmanumatic capabilities (as opposed to the optional

sport package w/ manu-matic 5sp) started in 2nd gear during most starts

both in winter and summer by selecting the "D5" transmission selection notch

in the shiftgate (For fuel savings), whereas "D4" would always start in 1st
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gear. This is done to reduce torque multiplication when proceeding forward

from a standstill in conditions where traction was limited - on snow or ice

covered roads for example.

Some automatic transmissions modified or designed specifically fordrag racing may also

incorporate a transmission brake, or "trans-brake," as part of a manual valve body. Activated byelectrical solenoid control, a trans-brake simultaneously engages the first and reverse gears,locking the transmission and preventing the input shaft from turning. This allows the driver of

the car to raise the engine RPM against the resistance of the torque converter, then launch the car

by simply releasing the trans-brake switch.
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.

The roles played by the subsystems in the above figure are described in terms of inputs

and outputs of the subsystem.

Inter Vehicle Signaling Subsystem

Inputs

Inter Vehicle Signaling information obtained from other vehicles


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Current GPS position is obtained from the Position Mapping Subsystem to keep track of

neighboring vehicles

Lane and speed change requests from the Automatic Driving Subsystem for

transmission to other vehicles

Outputs

Neighboring vehicle information is passed to the Obstruction Detection Subsystem.

Lane and speed change requests to other vehicles

The following outputs are passed to Automatic Driving Subsystem:

o Neighboring vehicle information

o Lane and speed change requests from other vehicles

Obstruction Detection Subsystem

Inputs

Radar feed is obtained from the vehicle radar. This information corresponds to the 360

degree sweep around the vehicle.

Current GPS position is obtained from the Position Mapping Subsystem to keep track of

neighboring obstructions

Neighboring vehicle information is obtained from the Inter Vehicle Signaling Subsystem.

This information is used to filter out IVS vehicles from the obstruction list sent to

Automatic Driving Subsystem. This way the system will never confuse a vehicle with an

obstruction.

Outputs

Current obstruction list is passed to the Automatic Driving Subsystem.

Position Mapping Subsystem

Inputs

Current GPS position is obtained from the GPS Receiver

Map updates and weather feeds are obtained over the internet. Mapping information is

used to compute a path for the vehicle. This is done by plotting the current position on

the map and following the detailed lane level map

Outputs

Current GPS information is made available to the IVS and Obstruction Detection

Subsystems

Travel path and plan with complete information about direction changes, speed changes

etc. is passed to Automatic Driving Subsystem


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Automatic Driving Subsystem

Inputs

Lane and speed change requests from the IVS Subsystem. This information will be used

to control the brakes, steering and accelerator to implement the request.

Obstruction List is obtained from the Obstruction Detection Subsystem. This information

is used to steer clear off any unexpected obstructions on the highway.

Travel path and plan obtained from the Position Mapping Subsystem. This information

will be used to keep the vehicle in the center of its lane while traveling towards the

destination. Lane changes will also be made to exit or enter highways.

Outputs

Accelerator (Gas Paddle) is instructed to speed the vehicle

Brakes are applied to slow down or stop the vehicle

Steering is used to change vehicle direction

Dashboard is kept updated with AutoDrive actions. This is to keep the passengers

posted about the functioning of the AutoDrive system.

Purpose of an Automatic Transmission

Location of the automatic transmission.

Just like that of a manual transmission, the automatic transmission's primary job is to allow theengineto operate in itsnarrow range of speeds while providing a wide range of output speeds.

Without a transmission, cars would be limited to onegear ratio, and that ratio would have to be selected to allow thecar to travel at the desired top speed. If you wanted a top speed of 80 mph, then the gear ratio would be similar tothird gear in most manual transmission cars.
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You've probably never tried driving a manual transmission car using only third gear. If you did, you'd quickly find outthat you had almost no acceleration when starting out, and at high speeds, the engine would be screaming alongnear the red-line. A car like this would wear out very quickly and would be nearly undriveable.

So the transmission uses gears to make more effective use of the engine'storque, and to keep the engine operatingat an appropriate speed. When towing or hauling heavy objects, your vehicle's transmission can get hot enough toburn up the transmission fluid. In order to protect the transmission from serious damage, drivers who tow should buy

vehicles equipped with transmission coolers.

The key difference between a manual and an automatic transmission is that the manual transmission locks andunlocks different sets ofgears to the output shaft to achieve the various gear ratios, while in an automatictransmission, the same set of gears produces all of the different gear ratios. The planetary gearset is the device thatmakes this possible in an automatic transmission.

Let's take a look at how the planetary gearset works.

The Planetary Gearset

From left to right: the ring gear, planet carrier, and two sun gears

When you take apart and look inside an automatic transmission, you find a huge assortment of parts in a fairly smallspace. Among other things, you see:

An ingenious planetary gearset

A set of bands to lock parts of a gearset

A set of three wet-plate clutches to lock other parts of the gearset

An incredibly odd hydraulic system that controls the clutches and bands

A large gear pump to move transmission fluid around

The center of attention is the planetary gearset. About the size of a cantaloupe, this one part creates all of the

different gear ratios that the transmission can produce. Everything else in the transmission is there to help theplanetary gearset do its thing. This amazing piece of gearing has appeared on HowStuffWorks before. You mayrecognize it from the electric screwdriverarticle. An automatic transmission contains two complete planetary gearsetsfolded together into one component. SeeHow Gear Ratios Workfor an introduction to planetary gearsets.

Any planetary gearset has three main components:

The sun gear

The planet gears and the planet gears' carrier
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The ring gear

Each of these three components can be the input, the output or can be held stationary. Choosing which piece playswhich role determines the gear ratio for the gearset. Let's take a look at a single planetary gearset.

Planetary Gearset RatiosOne of the planetary gearsets from our transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. Wecan get lots of different gear ratios out of this gearset.

Input Output Stationary CalculationGear

Ratio

A Sun (S)Planet

Carrier (C)Ring (R) 1 + R/S 3.4:1

B PlanetCarrier (C)

Ring (R) Sun (S) 1 / (1 + S/R) 0.71:1

C Sun (S) Ring (R)Planet Carrier

(C)-R/S -2.4:1

Also, locking any two of the three components together will lock up the whole device at a 1:1 gear reduction. Noticethat the first gear ratio listed above is a reduction -- the output speed is slower than the input speed. The second isan overdrive -- the output speed is faster than the input speed. The last is a reduction again, but the output directionis reversed. There are several other ratios that can be gotten out of this planetary gear set, but these are the onesthat are relevant to our automatic transmission. You can try these out in the animation below:

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Animation of the different gear ratios related to automatic transmissionsClick on the buttons on the left in the table above.

So this one set of gears can produce all of these different gear ratios without having to engage or disengage anyother gears. With two of these gearsets in a row, we can get the four forward gears and one reverse gear ourtransmission needs. We'll put the two sets of gears together in the next section.

This automatic transmission uses a set of gears, called a compound planetary gearset, that looks like a singleplanetary gearset but actually behaves like two planetary gearsets combined. It has one ring gear that is always theoutput of the transmission, but it has two sun gears and two sets of planets.

Let's look at some of the parts:

How the gears in the transmission are put togetherLeft to right: the ring gear, planet carrier, and two sun gears

The figure below shows the planets in the planet carrier. Notice how the planet on the right sits lower than the planeton the left. The planet on the right does not engage the ring gear -- it engages the other planet. Only the planet onthe left engages the ring gear.

Planet carrier: Note the two sets of planets.

Next you can see the inside of the planet carrier. The shorter gears are engaged only by the smaller sun gear. Thelonger planets are engaged by the bigger sun gear and by the smaller planets.


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Inside the planet carrier: Note the two sets of planets.

The animation below shows how all of the parts are hooked up in a transmission.

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Move the shift lever to see how power is transmitted through the transmission.

First GearIn first gear, the smaller sun gear is driven clockwise by the turbine in the torque converter. The planet carrier tries tospin counterclockwise, but is held still by the one-wayclutch(which only allows rotation in the clockwise direction) andthe ring gear turns the output. The small gear has 30 teeth and the ring gear has 72, so the gear ratio is:

Ratio = -R/S = - 72/30 = -2.4:1
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So the rotation is negative 2.4:1, which means that the output direction would be opposite the input direction. But theoutput direction is really the same as the input direction -- this is where the trick with the two sets of planets comes in.The first set of planets engages the second set, and the second set turns the ring gear; this combination reverses thedirection. You can see that this would also cause the bigger sun gear to spin; but because that clutch is released, thebigger sun gear is free to spin in the opposite direction of the turbine (counterclockwise).

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JavaScript or it is disabled.

Move the shift lever to see how power is transmitted through the transmission

Second GearThis transmission does something really neat in order to get the ratio needed for second gear. It acts like twoplanetary gearsets connected to each other with a common planet carrier.

The first stage of the planet carrier actually uses the larger sun gear as the ring gear. So the first stage consists of thesun (the smaller sun gear), the planet carrier, and the ring (the larger sun gear).

The input is the small sun gear; the ring gear (large sun gear) is held stationary by the band, and the output is theplanet carrier. For this stage, with the sun as input, planet carrier as output, and the ring gear fixed, the formula is:

1 + R/S = 1 + 36/30 = 2.2:1

The planet carrier turns 2.2 times for each rotation of the small sun gear. At the second stage, the planet carrier acts

as the input for the second planetary gear set, the larger sun gear (which is held stationary) acts as the sun, and thering gear acts as the output, so the gear ratio is:

1 / (1 + S/R) = 1 / (1 + 36/72) = 0.67:1

To get the overall reduction for second gear, we multiply the first stage by the second, 2.2 x 0.67, to get a 1.47:1reduction. This may sound wacky, but if you watch the video you'll get an idea of how it works.


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Third GearMost automatic transmissions have a 1:1 ratio in third gear. You'll remember from the previous section that all wehave to do to get a 1:1 output is lock together any two of the three parts of the planetary gear. With the arrangementin this gearset it is even easier -- all we have to do is engage the clutches that lock each of the sun gears to the

turbine.

If both sun gears turn in the same direction, the planet gears lockup because they can only spin in oppositedirections. This locks the ring gear to the planets and causes everything to spin as a unit, producing a 1:1 ratio.

By definition, an overdrive has a faster output speed than input speed. It's a speed increase -- the opposite of areduction. In this transmission, engaging the overdrive accomplishes two things at once. If you read How TorqueConverters Work, you learned about lockup torque converters. In order to improve efficiency, some cars have amechanism that locks up the torque converter so that the output of the engine goes straight to the transmission.

In this transmission, when overdrive is engaged, a shaft that is attached to the housing of the torque converter (whichis bolted to the flywheel of the engine) is connected by clutch to the planet carrier. The small sun gear freewheels,and the larger sun gear is held by the overdrive band. Nothing is connected to the turbine; the only input comes fromthe converter housing. Let's go back to our chart again, this time with the planet carrier for input, the sun gear fixed

and the ring gear for output.

Ratio = 1 / (1 + S/R) = 1 / ( 1 + 36/72) = 0.67:1

So the output spins once for every two-thirds of a rotation of the engine. If the engine is turning at 2000 rotations perminute (RPM), the output speed is 3000 RPM. This allows cars to drive at freeway speed while the engine speedstays nice and slow.

Reverse GearReverse is very similar to first gear, except that instead of the small sun gear being driven by the torque converter

turbine, the bigger sun gear is driven, and the small one freewheels in the opposite direction. The planet carrier is

held by the reverse band to the housing. So, according to our equations from the last page, we have:

Ratio = -R/S = 72/36 = 2.0:1

So the ratio in reverse is a little less than first gear in this transmission.

Gear RatiosThis transmission has four forward gears and one reverse gear. Let's summarize the gear ratios, inputs and outputs:

Gear Input Output Fixed Gear Ratio

1st 30-tooth sun 72-tooth ring Planetcarrier

2.4:1

2nd30-tooth sun

Planet

carrier36-tooth ring 2.2:1

Planet carrier 72-tooth ring 36-tooth sun 0.67:1
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Total 2nd 1.47:1

3rd30- and 36-tooth

suns72-tooth ring 1.0:1

OD Planet carrier 72-tooth ring 36-tooth sun 0.67:1

Reverse 36-tooth sun 72-tooth ringPlanet

carrier-2.0:1

After reading these sections, you are probably wondering how the different inputs get connected and disconnected.This is done by a series of clutches and bands inside the transmission. In the next section, we'll see how these work.

Clutches and Bands in an AutomaticTransmission

In the last section, we discussed how each of the gear ratios is created by the transmission. For instance, when wediscussed overdrive, we said:

In this transmission, when overdrive is engaged, a shaft that is attached to the housing of the torque converter (whichis bolted to the flywheel of the engine) is connected by clutch to the planet carrier. The small sun gear freewheels,and the larger sun gear is held by the overdrive band. Nothing is connected to the turbine; the only input comes fromthe converter housing.

To get the transmission into overdrive, lots of things have to be connected and disconnected by clutches and bands.The planet carrier gets connected to the torque converter housing by a clutch. The small sun gets disconnected from

the turbine by a clutch so that it can freewheel. The big sun gear is held to the housing by a band so that it could notrotate. Each gear shift triggers a series of events like these, with different clutches and bands engaging anddisengaging. Let's take a look at a band.

BandsIn this transmission there are two bands. The bands in a transmission are, literally, steel bands that wrap aroundsections of the gear train and connect to the housing. They are actuated by hydraulic cylinders inside the case of thetransmission.


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One of the bands

In the figure above, you can see one of the bands in the housing of the transmission. The gear train is removed. Themetal rod is connected to the piston, which actuates the band.

The pistons that actuate the bands are visible here.

Above you can see the two pistons that actuate the bands. Hydraulic pressure, routed into the cylinder by a set ofvalves, causes the pistons to push on the bands, locking that part of the gear train to the housing.

The clutchesin the transmission are a little more complex. In this transmission there are four clutches. Each clutch isactuated by pressurized hydraulic fluid that enters a piston inside the clutch. Springs make sure that the clutch
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releases when the pressure is reduced. Below you can see the piston and the clutch drum. Notice the rubber seal onthe piston -- this is one of the components that is replaced when your transmission gets rebuilt.

One of the clutches in a transmission

The next figure shows the alternating layers of clutch friction material and steel plates. The friction material is splinedon the inside, where it locks to one of the gears. The steel plate is splined on the outside, where it locks to the clutchhousing. These clutch plates are also replaced when the transmission is rebuilt.

The clutch plates

The pressure for the clutches is fed through passageways in the shafts. The hydraulic system controls which clutchesand bands are energized at any given moment.

When You Put the Car in ParkIt may seem like a simple thing to lock the transmission and keep it from spinning; but there are actually somecomplex requirements for this mechanism:

You have to be able to disengage it when the car is on a hill (the weight of the car is resting on themechanism).

You have to be able to engage the mechanism even if the lever does not line up with the gear.


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Once engaged, something has to prevent the lever from popping up and disengaging.

The mechanism that does all this is pretty neat. Let's look at some of the parts first.

The output of the transmission: The square notches are

engaged by the parking-brake mechanism to hold the car still.

The parking-brake mechanism engages the teeth on the output to hold the car still. This is the section of thetransmission that hooks up to the drive shaft -- so if this part can't spin, the car can't move.

The empty housing of the transmission with the parking brake

mechanism poking through, as it does when the car is in park


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Above you see the parking mechanism protruding into the housing where the gears are located. Notice that it hastapered sides. This helps to disengage the parking brake when you are parked on a hill -- the force from the weight ofthe car helps to push the parking mechanism out of place because of the angle of the taper.

This rod actuates the park mechanism.

This rod is connected to a cable that is operated by the shift lever in your car.

Top view of the park mechanism

When the shift lever is placed in park, the rod pushes the spring against the small tapered bushing. If the parkmechanism is lined up so that it can drop into one of the notches in the output gear section, the tapered bushing willpush the mechanism down. If the mechanism is lined up on one of the high spots on the output, then the spring will


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push on the tapered bushing, but the lever will not lock into place until the car rolls a little and the teeth line upproperly. This is why sometimes your car moves a little bit after you put it in park and release the brake pedal -- it hasto roll a little for the teeth to line up to where the parking mechanism can drop into place.

Once the car is safely in park, the bushing holds down the lever so that the car will not pop out of park if it is on a hill.






The output of the transmission: The square notches are

engaged by the parking-brake mechanism to hold the car still.



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The empty housing of the transmission with the parking brakemechanism poking through, as it does when the car is in park





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When the shift lever is placed in park, the rod pushes the spring against the small tapered bushing. If the parkmechanism is lined up so that it can drop into one of the notches in the output gear section, the tapered bushing willpush the mechanism down. If the mechanism is lined up on one of the high spots on the output, then the spring willpush on the tapered bushing, but the lever will not lock into place until the car rolls a little and the teeth line upproperly. This is why sometimes your car moves a little bit after you put it in park and release the brake pedal -- it hasto roll a little for the teeth to line up to where the parking mechanism can drop into place.








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The output of the transmission: The square notches areengaged by the parking-brake mechanism to hold the car still.


The empty housing of the transmission with the parking brake

mechanism poking through, as it does when the car is in park



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When the shift lever is placed in park, the rod pushes the spring against the small tapered bushing. If the parkmechanism is lined up so that it can drop into one of the notches in the output gear section, the tapered bushing willpush the mechanism down. If the mechanism is lined up on one of the high spots on the output, then the spring willpush on the tapered bushing, but the lever will not lock into place until the car rolls a little and the teeth line upproperly. This is why sometimes your car moves a little bit after you put it in park and release the brake pedal -- it hasto roll a little for the teeth to line up to where the parking mechanism can drop into place.


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AutoDrive Concept

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