Automotive Terminology & Definitions

a control device that delivers mechanical action in response to a vacuum or electrical signal; anything that the engine control computer uses to do something, such as trigger fuel injection or fire a spark plug. Most actuators on a computercontrolled engine system are activated by grounding their circuits rather than by actively powering them, since that protects the computer from short circuits.

in automotive terminology, a substance added to a liquid, such as engine oil, transmission fluid, gear oil or coolant to enhance its properties.

select shift manual (SSM) and auto shift manual (ASM) use a combination of auto-clutch and shift-by-wire electronic control system technology to provide the customer a fun-to-shift experience along with significant fuel economy improvements over a base manual transmission. The Select Shift Manual mode allows a customer to command gear changes according to his/her personal preference like a conventional manual transmission. The Auto Shift Manual mode provides the customer automatic gear shifting much like an automatic transmission.

the oil that is used in an automatic transmission.

a transmission that changes forward gears automatically.

an enclosure for the differential and drive axles.

a rotating shaft that rotates another part, such as a wheel.

a friction-reducing bearing that uses a series of steel balls held between inner and outer bearing races such as in a roller clutch.

in an automatic transmission, a device used to prevent members of a planetary gearset from rotating.

the machined surface of a bearing assembly against which the needles, balls or rollers ride. The outer race is also called a cup.

part that supports and reduces friction between a stationary and moving part or two moving parts.

connects the engine to the transmission and encloses the clutch assembly. It also provides mounting points for part of the clutch release mechanism.

the most common type of universal joint used. Consists of a center cross, four bearing cups, each containing a set of needle roller bearings, grease seals and snap rings.

part used to retain the axle shaft in a drive axle assembly

the part of a clutch that receives the driving motion from the flywheel and pressure plate assembly and transmits that motion to the transmission input shaft.

the friction material on a clutch disc.

also known as the release fork. The device which moves the throwout (release) bearing, activating the pressure plate.

in an automatic transmission, an assembled series of clutch friction discs and clutch plates that are alternately layered.

the part of a clutch assembly that is used to hold the driven disc against the flywheel. The pressure plate is composed of a cover and coil springs, driving disc and release levers, or a diaphragm spring.

a sealed ball or roller bearing unit that rides on a sleeve over the transmission input shaft, and acts on the pressure plate to disengage the clutch disc when the clutch release mechanism is applied. Also called a throwout bearing.

see 'clutch release bearing'.

in a manual transmission, a device that allows the driver to engage and disengage the engine from the drivetrain; in an automatic transmission, a device capable of both holding and turning members of a planetary gearset; a device used to engage and disengage and A/C compressor.

in a transmission, where all gears are constantly in contact and turning with one another.

a continuously variable transmission is an automatic that can select any desired drive ratio within its operating range. Unlike a traditional three-, four-, or fivespeed automatic transmission the CVT is an "infinite speed" transmission, the CVT continually selects an optimum overall drive ratio between engine and drive wheels for all operating conditions, whether accelerating or cruising. Unlike conventional automatics, there are no perceptible shifts. During maximum acceleration, the drive ratio Is adjusted to maintain peak engine horsepower. At a constant vehicle speed, the ratio is set to maintain an engine rpm which will support the required power. A CVT provides smooth, fast acceleration and high cruising efficiency with the convenience of an automatic transmission.

a set of different size gears incorporated in one casting, used in a manual transmission.

enclosure for the differential and ring and pinion gears. Can be removable or integral part of axle housing. Also called differential housing.

housing for the differential pinion gears and side gears. Mounting point for ring gear.

gears that are meshed with the differential side gears and rotate on the differential pinion shaft inside the differential case.

a shaft mounted inside the differential case, provides support and pivot for the differential pinion gears.

gears that are meshed with the pinion gears inside the differential case and splined to the axle shafts.

gear assembly that transmits power from the driveshaft to the wheels; allows the outside wheel to turn faster than the inside when cornering.

downward gear engagement in which the input shaft and output shaft are locked together; the gearing in a drivetrain in which one turn of the crankshaft equals one turn of the wheels.

two cardan universal joints connected by a yoke; also called a constant velocity (CV) joint.

a Rzeppa type plunger CV-joint used on the inboard side of the interconnecting shaft.

a peg or pin which fits into corresponding holes used for holding two parts together or to locate two parts in a set position.

a gear that drives or provides power for other gears in a planetary gearset.

see 'driveshaft angle'.

all of the parts connecting the engine to the drive axle.

the installation angle of the driveshaft off the true horizontal; also called driveline angle.

transfers power from the transmission to the differential on a rear-wheel drive vehicle. Consists of a hollow metal tube with universal joints at each end, each of which is attached to yokes at the transmission and differential.

all of the components that generate power and transfer it to the vehicle's wheels.

an electronic automatic transmission utilizes an electronic control module to signal when to shift. The module also determines when to lock and unlock the torque converter. By controlling these functions electronically rather than mechanically, the transmission can be tuned for better driveability.

the amount of axial or end-to-end movement in a shaft due to clearance in the bearings; the regulated movement of a component, usually a shaft, during operation.

in mechanical terms, wear of a component that exceeds designed limits; wear caused by overloading a part that is in an out-of-balance condition, resulting in lower-than-normal life expectancy of the part being subjected to the adverse operating condition.

aluminum or cast iron enclosure for the transmission output shaft and bearings, speedometer drive and driven gears. Provides support for driveshaft slip yoke.

a projecting rim or collar on a component used for holding it in place, giving it strength or guiding it into place or attaching it; a part mounted on the pinion gear that provides the mounting point for the rear universal joint of the driveshaft.

a cast iron or steel wheel mounted to the end of the crankshaft; helps to smooth the engine's power delivery, the teeth around its circumference provide an engagement for the starter, and it provides the mounting points for the pressure plate and friction surface for the clutch disc.

system that supplies power to both the front and rear wheels of the vehicle when activated.

the measurable travel in a mechanical device between the time force is applied and work is accomplished; looseness in a linkage between the start of application and the actual movement of the device, such as the movement in the steering wheel before the wheels start to turn.

distance a clutch pedal moves before it begins to take up slack in the clutch linkage; essentially the same as free play, usually applied to shaft movement.

a mechanical device that engages the driving member to impart motion to a driven member in one direction but not the other; in automotive terms, a device that permits the driveshaft to continue turning when its speed exceeds that of the crankshaft, thus allowing free coasting with the gear train engaged.

the entire drivetrain is located at the front of and drives the front wheels of the vehicle.

system where the weight of the vehicle is supported by the axle housing and the axle bearing is located outside of the axle housing; most often used on trucks.

in a manual transmission, where gears are changed using synchronizers.

number of teeth per given unit of pitch diameter. Gear pitch is determined by dividing the number of teeth by the pitch diameter of the gear.

the number of revolutions a driving gear must turn to rotate the driven gear through one revolution. Numerical value determined by dividing the number of teeth on the driven gear by the number of teeth on the driving gear; the ratio between the number of teeth on meshing gears.

when a smaller gear drives a larger gear, there is a speed reduction but an increase in torque.

a toothed wheel, disc, etc. designed to mesh with another or with the thread of a worm; used to transfer or change motion.

the change in line pressure that takes place as a result of an increase in vehicle speed.

a device used on non-electronic automatic transmissions, which regulates the operation of the shift valves inside the valve body according to vehicle speed.

a gear in which the teeth are cut so as to form a spiral; gear with teeth that are cut at an angle or are spiral to the gear's axis of rotation.

differential gearset where any one pinion gear tooth contacts all ring gear teeth.

bevel-cut gear in a system in which the driven gear is not in the same plane as the drive gear. A type of spiral, beveled ring and pinion gearset in a differential. Hypoid gears mesh below the ring gear centerline.

the shaft that is splined to the clutch disc and transfers power from the engine into the transmission; the shaft to which torque is applied, usually carrying the drive gear or gears.

exerts pressure on the inserts in a synchronizer assembly.

a part of the synchronizer assembly that fits between the hub and sleeve, also called key or plate. The insert spring pushes the inserts into the sleeve, helping to center the sleeve on the hub.

a type of differential that uses clutches to supply a major portion of the drive torque to the wheel that has better traction when one wheel is slipping,

in an automatic transmission, the hydraulic pressure of the fluid after it leaves the pump and is regulated by the pressure regulator.

an axle on which the wheels are firmly affixed, with the axle driving the wheels.

in an automatic transmission, pressure that is regulated in the hydraulic system.

to fit closely together or interlock, as the fit of gear teeth.

an anti-friction device that consists of a number (usually a large number) of thin rollers riding within races.

a switch that prevents starter engagement if the transmission is in another gear besides Park or Neutral.

differential gearset in which one drive pinion gear tooth contacts only three ring gear teeth after several rotations.

device used to remove heat from the engine or transmission oil. There are oil-to-air coolers and oil coolers that are incorporated into the vehicle's cooling system.

the original manufacturer of a vehicle or engine.

outer part of a bailor roller bearing that provides a surface for the balls or rollers to rotate. Can be integral with the bearing or a separate part.

when a previously round hole or bore has different diameters when measured at different points due to wear or distortion.

the shaft that delivers the power that has come through the transmission or transaxle.

a gear assembly that outputs more shaft revolutions than were input.

a clutch that locks in one direction and overruns or freewheels in the other.

the smaller, drive gear of the ring and pinion gearset; one of the gears inside the differential that rotates on the differential pinion shaft; rotates around the sun gear in a planetary gearset.

the smaller of two meshing gears.

houses the pinion gears in a planetary gearset.

a gear system consisting of three primary components: a sun gear, a planetary pinion carrier and a ring or internal gear.

on vehicles with computer control systems, the main computer that determines engine operation based on sensor inputs and by using its actuator outputs. The PCM may also control transmission operation.

the driving member of the clutch assembly. Coil springs or a diaphragm spring in the pressure plate exert pressure on the clutch disc, holding it against the flywheel.

system where the driveline drives the rear wheels of the vehicle. Most often the engine is located in the front of the vehicle and a transmission and drive shaft connect to a drive axle, however there are also systems where the entire drive line is located toward the rear of the vehicle.

see 'clutch release bearing'.

a gear used to reverse the direction of power in a transmission.

the larger, driven gear of the ring and pinion gearset; the largest member in a planetary gearset, also known as the internal gear or annulus. The internal teeth of the gear mesh with and rotate on the planetary pinions.

torque converter oil flow associated with the coupling stage of operation.

a part, usually made of rubber or plastic, installed around a moving part or shaft to prevent leaks.

system where the axle bearing is located inside the axle housing and the weight of the vehicle is supported by the axle.

a device in a manual transmission that moves the synchronizer assembly sleeve, in response to movement from the shift linkage.

the parts of transmission shift linkage that transfer motion from the driver-controlled gear shift lever to the shift forks.

the lever operated by the driver to shift the transmission. The shifter is attached directly to internal linkage in the transmission or it is mounted on the outside of the transmission or on the frame or vehicle floor, and connected to the transmission or trans axle by external linkage rods or cables.

a device that is connected to the release bearing in a hydraulic clutch system. When the clutch pedal is depressed, hydraulic fluid flows from the master cylinder through the hydraulic fluid line to the slave cylinder. Pressure in the system causes the slave cylinder to act on the release bearing, disengaging the clutch

a driveline component that is splined to the transmission output shaft and connected to the driveshaft front U-joint. Allows in and out movement on the transmission extension housing in response to rear suspension movement.

condition caused when a driving part rotates faster than a driven part.

grooves cut into the outside or inside surface of a component to enable it to fit with another component having corresponding grooves. Commonly used to keep a component secured on a rotating shaft.

a type of overrunning clutch.

the reservoir that holds the oil for the pump.

a type of clutch assembly used in a manual transmission to shift gears. Consists of a hub splined to the main shaft, inserts (keys) and insert springs, outer sleeve and blocking rings. There are grooves machined into the sleeves to capture the shift forks, which transfer the motion from the gearshift linkage. The sleeve moves along the splined inner hub in response to the shift fork, forcing the blocking ring against the gear cone and then, when the gear is at the same speed, slides over the blocking ring and gear engagement teeth, locking the gear to the synchronizer hub and shaft.

see 'clutch release bearing'.

a bearing that separates rotating parts from each other and non-rotating parts, and absorb thrust loads; a bearing with side surfaces that controls the fore and aft movement of a shaft.

a device located inside the torque converter that mechanically links the engine and transmission together.

a fluid coupling device used to transfer engine torque from the crankshaft to the transmission.

the tendency of many front -wheel-drive vehicles with half-shafts of unequal length, to turn somewhat from the desired direction when accelerating, especially in a curve, or when decelerating in a curve.

attached to or connected to the transmission in a four-wheel drive vehicle. Transfers power to both front and rear axles.

the computer that controls the transmission.

transfers the engine's power to the driveshaft and the rear wheels. Contains a series of gears that provide torque multiplication, so the vehicle can be moved from a standstill and also cruise at highway speeds at lower engine rpms.

perpendicular or at a right angle to a front-to-back centerline.

a type of CV-joint consisting of a spider, which is splined to the interconnecting shaft of the halfshaft, three rollers that turn on needle roller bearings located between the spider and rollers, a housing, or yoke, that is part of the stub shaft, and a boot. Used on the inboard side of the halfshaft.

a joint that allows the drives haft to transmit torque at different angles as the suspension moves up and down.

a device used to vary line pressure according to engine load in an automatic transmission.

in an automatic transmission, the housing that contains most of the valves used for transmission operation.