ASE A2 Glossary

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  • a

  • Accumulator (Transmission)
    A spring-loaded device used to dampen pressure fluctuations within the hydraulic system. The accumulator prevents shock loads by slowing the application rate of a clutch or band.
  • Actuator (Transmission)
    A computer controlled output device that provides mechanical action in response to an electrical signal. An electronic pressure control valve is an example of an actuator.
  • Apply Side
    Refers to the side of a piston on which force or pressure is exerted.
  • b

  • Band
    A circular brake that wraps around a drum to stop the rotation of a planetary gear component. Bands are hydraulically operated by servos.
  • Barometric Pressure
    Atmospheric pressure expressed in terms of 'inches of mercury.'
  • Battery Capacity Test
    A test used to determine a battery's ability to handle a sustained high-current load for a period of 15 seconds. When tested at 80¡F, a good battery will maintain a terminal voltage of at least 9.6V for the duration of the test.
  • c

  • Chamfer
    A beveled edge.
  • Clutch Pack
    A series of alternately stacked metal and composition plates.
  • Coefficient Of Friction
    A measurement equal to the force required to slide an object across a surface divided by the weight of the object.
  • Coolant
    A blend of water and ethylene glycol-based antifreeze. A 50/50 mixture provides freeze protection down to -34¡F (-37¡C), and raises the boiling point to 265¡F (129¡C) when used in a system with a 15-psi pressure cap.
  • d

  • Data Link Connector (DLC)
    The computer interface connector that accepts a scan tool; typically located below the instrument panel.
  • Drive Member
    A gear that transmits power to other members of a planetary gearset.
  • Duty Cycle
    The ON-time of a controlled device expressed as a percentage.
  • f

  • Friction Modifiers
    Additives used to enhance an oil's lubricating properties.
  • g

  • Gear Pump
    An internal/external gear pump whose gears are separated by a crescent-shaped boss.
  • i

  • Impeller
    The rear half of the torque converter shell that drives the turbine. The impeller is also called a pump.
  • k

  • KOEO
    Key on, engine off
  • kPa (kilopascals)
    6.895 kPa = 1 psi
  • m

  • Manifold Absolute Pressure (MAP) Sensor
    An electronic device that converts intake manifold pressure into an electrical signal. In some electronic transmission/transaxles, the computer uses the signal from the MAP sensor to adjust line pressure according to changes in altitude.
  • Manual Valve
    A spool valve operated by the shift linkage. The manual valve directs hydraulic pressure to the appropriate location to apply bands and clutches.
  • n

  • Neutral Safety Switch
    An electrical device used to open the starter circuit when the transmission/transaxle is in gear.
  • o

  • Orifice
    A precisely machined hole that controls the flow of fluid.
  • p

  • Pascal's Law
    A discovery made by a sixteenth century scientist that proved that liquid is non-compressible, and that a force applied to the top of a liquid in a closed container is exerted equally in all directions.
  • Porosity
    Minute holes in a casting that result when air bubbles form during the casting process.
  • Preload
    The load applied to a bearing to eliminate looseness.
  • Pulse Width Modulated
    A computer command signal that allows a controlled device to be cycled on and off many times per second to achieve a specific output.
  • r

  • Ravigneaux Gear Train
    Also known as a compound gear train, it consists of a single internal gear that houses two sets of planetary pinions mounted on a common carrier along with two sun gears.
  • Reaction Member
    The part of a planetary gearset that is kept stationary so that output motion can occur.
  • Rotary Flow
    The oil flow that takes place in a torque converter when the impeller and turbine reach the coupling point.
  • Rotor Pump
    A type of internal/external gear pump that utilizes rounded-toothed gears or lobes.
  • s

  • Servo
    A hydraulically activated piston used to apply a band.
  • Simpson Gear Train
    A gear train composed of two simple planetary gearsets linked by a common sun gear.
  • Slip
    Refers to the difference in speed between the impeller and turbine in a torque converter.
  • Spool Valve
    A valve with a series of raised lands used to direct the flow of fluid throughout the valve body and transmission/transaxle case passages.
  • Sprag
    A 'dogbone' shaped holding element used in one style of overrunning clutch.
  • Stall Speed
    An engine's maximum rpm with the transmission/transaxle in gear and the brakes applied.
  • t

  • Throttle Position (TP) Sensor
    A potentiometer that converts the movement of the throttle plate into an electrical signal. On an electronic transmission/transaxle, the computer uses the TP signal to regulate line pressure and shift points.
  • Throttle Valve
    A spool valve that adjusts line pressure based on changes in engine load. The throttle valve is typically operated by a cable-actuated pushrod or plunger. In older transmissions that do not use a TV cable, the throttle valve is controlled by the vacuum modulator.
  • Throttle Valve (TV) Pressure
    The hydraulic pressure applied to the boost side of the pressure regulator and the downshift side of the shifts valves.
  • Transmission Range (TR) Switch
    A device that indicates the selected gear to the on-board computer. The starter interrupt switch (neutral safety) is typically incorporated into the TR switch.
  • Turbine
    The part of a torque converter positioned in the front half (engine side) of the shell but not connected to it. The turbine drives the transmission/transaxle input shaft.
  • v

  • Viscosity
    An oil's resistance to flow.
  • Vortex Flow
    A swirling oil flow that occurs between the impeller and turbine during torque multiplication.