Dictionary of Automotive:

Any people have contributed something of their knowledge to this dictionary, providing material, reading and checking definitions and offering advice. Amongst the many. I would like to acknowledge the following by name:  

For "A"

A-pillar 

Α-post Structural member forming the forward corner of the cab or passenger compartment. In structural analysis, the post may be assumed to include adjacent (contingent) parts of the door frame.

 

ABS (anti-lock brake system)

ABS relay valve Electrically actuated pneumatic valve that controls the air pressure in the brakes of an anti-lock braking system during braking.

 

accelerator 

Pedal by which the fuel flow to the engine is controlled, depression of the pedal causing the vehicle to accelerate. 

accelerator heel point(AHP)

 Assumed point of contact of driver's heel with floor when foot is placed on the un-depressed accelerator. 

accelerator pump 

Carburetion pumping system that introduces additional flow of fuel into the carburetor choke on acceleration, particularly when it accelerating from lower speeds. 

accumulator

(1) Rechargable electrical storage battery. Obsolescent term. 

(2) An hydraulic accumulator.

 

Ackermann angle 

The angle between the planes of the steered wheels of a vehicle, particularly when steering lock is applied. The angle would usually be measured in the horizontal plane. 

Ackermann steer angle

(1) The mean angle through which the steered wheels 

of a vehicle are turned to turn the vehicle to a given radius.

 (2) The angle whose tangent is the wheelbase divided by the radius of turn. 

active restraint

Occupant restraint system requiring manipulation by wearer, as for example a seat belt. 

adhesion 

Grip between road and tire, proportional to the static coefficient of friction. 

adiabatic engine

Engine in which combustion heat loss to coolant is minimized, a greater portion of the thermal value of the fuel being converted to useful work.

adiabatic engine process

 

advanced ignition

Maladjustment of ignition timing in a spark ignition engine whereby the spark occurs before its optimum setting.

aerial  (US:  antenna)  

  Wire  or  rod,  often   retractable,  for  receiving  radio  signals.

 aerodynamic  noise 

  Noise generated  by the  flow  of  air around  and through  a  vehicle   due   to   its   forward   motion.

 aerofoil  (US: airfoil)   

 Streamlined  planar  shape,  such  as  a  wing  intended  to  produce  positive  or  negative  lift, or  otherwise  derive  some  effect  from  the  flow  of  air.

  afterburner   

 Device  that  completes  the  combustion  of  incompletely  burned  exhaust  products  within  the  exhaust  system.   

aftercooler    

Heat  exchanger  that  cools the  induction  air  before  it enters  the  cylinders  of  an  engine.

 agglomerator  

  Device  such  as  a  separator  or  trap  for  removing  water  from  fuel  or  oil.  

  aggregate   body    Commercial   vehicle   truck   body   for   the   conveyance   of   aggregates,   ballast   and   similar   bulk   materials,   usually   equipped   with   tipping  gear.

  aiming   

 Adjustment   of  direction   of  beam   of  lamps  to  meet  highway   or   legislative  requirements.

  air-assisted  hydraulic  brake  

  Commercial  vehicle  braking  system  in  which  the  master  cylinder  of  a hydraulic  braking  system  is actuated  by  pneumatic  pressure    or    vacuum.    Also    air-over-hydraulic    brake;   vacuum-assisted   hydraulic  brake;  vacuum-over-hydraulic  brake.

  air  bag   

 Passive  vehicle  occupant  restraint  system  in  which  on  impact  the  rapid  inflation  of  a bag  fitted  in  iht  fascia  region  restrains  the  body  above  torso  level  and  prevents  direct  contact  with  the  vehicle  structure.

 air  bellows  

  Usually  cylindrical  or  torose  rubber  vessel  or  sleeve  which,  when  filled  with  a  compressed  gas  or  air,  acts  as  a  compression  spring.  Mainly  used  in  commercial  vehicle  or  trailer  suspensions.  See  also  air  spring;  air  suspension; gas  spring. 

 air bleed  passage (UK:  compensating jet)  

  Jet  or passage  in  a carburetor with a branch  to atmosphere  through  which  air  is drawn  and introduced  into  the  fuel   flow   at   high   flow  rates,  thus   preventing   over-richness.    

 air brake

   Brake  in which the  force  that  actuates the brake mechanism  is  provided  by compressed  air  acting on  a diaphragm  within  a brake  chamber  or  servo.  Used  mainly  in commercial  vehicles.

 air  cell     

 A  small  chamber,  located  in  the  cylinder  head  particularly  of  an  indirect injection engine,  in which combustion  is initiated. The burning  fuel  charge passes through  a throat to the main combustion chamber.  Also swirl chamber, antechamber;  Comet  head;  indirect  injection;  Lanova;  pre-chamber.

Air Check Valve 

One-way valve in a pulse air injection system to prevent return of exhaust gases to induction system. 

air cleaner 

Any device such as a porous paper or wire mesh filter that prevents airborne particles from entering air-breathing machinery.

 air compressor

Machine for delivering compressed air, as for example to an air brake system. 

air-cooled

Cooled by the passage of air as opposed to water, etc. Describes engines in which combustion heat is lost mainly through finning.

 air dam

Aerodynamically shaped transverse extension or spoiler below front bumper which reduces drag created by vehicle under body. 

 air dryer 

 Device for removing moisture from air, but particularly from the compressed air of a commercial vehicle braking system.

 air-fuel delivery ratio

Mass ratio of air to fuel inducted by an engine. 

air horn 

 (1) Audible warning device in which sound is produced by a blast of air through a reed or resonator.

 (2) Engine induction tract leading from air filter or cleaner to a carburetor or intake manifold (US informal)

air-injection 

 Addition of an air stream under pressure, but particularly to an exhaust system to promote combustion of un-burned hydrocarbons and conversion of carbon monoxide to carbon dioxide.

 air-lift axle 

 Pneumatically operated lift axle of tandem axle commercial vehicle undercarriage. In some examples lifting or lowering are achieved by manipulation of pressure in the air bellows of an air suspension.

 air-line 

 Pressure or vacuum resisting tubing or piping for connecting the components of a pneumatically operated system.

air-line connector 

Plug and socket for making connections within a pneumatic system.

 air shift PTO 

Pneumatically actuated power take-off.

 air strainer 

An air filter or air cleaner .

. airless injection 

 Fuel injection by mechanical pressure only. The normal method of injection in a diesel engine. Also called solid injection.

 alternator 

Alternating current electrical generator.

ambulance 

Vehicle for conveying the sick or injured.

anchorage 

 Point of a vehicle structure to which a non-structural stress carrying item is attached, as for example a seat belt, or seat.

 . annulus

(1) A ring shaped component. 

 (2) The annular internally toothed wheel of an epicyclic gearbox or planetary transmission. Also annulus gear; internal gear; ring gear. 

annulus gear

A spur gear in the form of an internally or externally toothed ring. See also annulus; ring gear. 

 antenna (UK: aerial)

Wire or rod, often retractable, for receiving radio signals.

 anti-dive 

Suspension geometry that reduces or prevents nose-down pitching on braking.

anti-lock braking system

System that automatically controls wheel slip or prevents sustained wheel-locking on braking. 

antiknock additive 

 Compound such as tetraethyl lead added to a gasoline fuel to reduce the tendency to detonation and thereby increase the Octane Number. 

Antiknock Index 

 Measure of the anti-knock properties of a gasoUne fuel, particularly in North America where it is defined by half the sum of the Research Octane Number and Motor Octane Number. 

antiper-colator

Valve or channel through which excess vapors can be vented, as from a carburetor.

anti-roll bar 

 Transverse torsion bar attached to a vehicle underside to couple the vertical displacements of nearside and offside wheels and so reduce the vehicle's displacement in roll. Use of term roll-bar is discouraged as this is used in a different context. Also stabilizer.

anti-sail bar 

 Horizontal bar to restrain deflection in service of an anti-spray flap or mudflap.

 anti-spin regulation

Control or prevention of wheelspin or wheelslip under power, normally by electronic sensing in conjunction with anti-lock braking. Also ASR.

anti-spray flap 

Flexible flap or curtain attached behind roadwheel to reduce roadspray.

 anti-vibration mounting 

 Flexible mounting, as for an engine or other mechanical item, that reduces the transmission of noise and vibration from the mounted item to a structure such as a vehicle chassis.  

antifreeze

A chemical, such as ethylene glycol, added to the cooling water of an engine to depress the freezing point for winter operation. 

antipercolator

Tube and orifice in carburetor through which fuel vapor can escape from main jet tube to prevent over-enrichment due to vapor pressure.

apex seal

Gas seal to epitrochoidal surface in a Wankel engine.

apron 

Downward panel extension, usually transversely mounted at front of a vehicle, to reduce drag resulting from disorderly flow under the vehicle. Also air dam; underbumper apron. 

artic

An articulated vehicle, usually a goods vehicle tractor unit with semi-trailer.

articulated bus 

 Usually single-decker bus with central articulation and accommodation for passengers in tractor and trailer units.

articulated vehicle 

 An articulated vehicle is a vehicle which has a permanent or semi-permanent pivot joint in its construction, allowing the vehicle to turn more sharply. There are many kinds of articulated vehicles, from heavy equipment to buses, trams and trains. Steam locomotives were sometimes articulated in that the driving wheels.

auto-ignition Continued running of a spark ignition engine after the ignition has been switched off. Also dieseling; running-on.

autocar

A passenger car (archaic). A motor vehicle, but especially a passenger coach.

autocycle 

Light motorcycle with pedals for assisting the motor on starting and on inclines. Obsolescent. The forerunner of the moped.

Autogas 

Liquefied petroleum gas motor fuel.Also LPG. 

automatic

Vehicle with automatic transmission (informal).

automatic choke 

Thermostatically operated choke valve in carburetor inlet tract, closed when engine is cold and opening automatically as engine or induction air temperature rises.

 automatic gearbox (US: automatic transmission)

Geared transmission unit in which gear ratios are automatically selected and engaged without driver intervention. See also preselector.

 automatic levelling system Suspension system that automatically adjusts front and rear ride heights to compensate for changes in axle load.

 automatic speed control

Device or system capable of maintaining selected vehicle speed in changing road conditions. See also cruise control.

automatic transmission (1) (UK: automatic gearbox)

Transmission system in which gear ratios are selected and engaged automatically, though usually with provision for the driver to manually override the selection. (2) An automatic continuously variable transmission such as a belt with expanding pulley. See also Hayes transmission; preselector; Variomatic transmission.

 automatic wear adjuster 

Device that automatically compensates an actuating system for wear in the item being operated, such as a clutch or brakes. automobile (UK: passenger car) Self-propelled or motorized land vehicle. 

auxiliary brake

Any brake that serves in addition to the main braking system of a vehicle. See  also engine brake; exhaust brake; retarder. 

auxiliary driving lamp

Lamp intended to provide illumination forward of the vehicle and to supplement the upper beam of a standard headlamp system. See also fog lamp. 

auxiliary gearbox 

 Gearbox used in conjunction with a main change speed gearbox to provide an extra range of speeds, as for example by providing a 2:1 reduction in addition to normal gearbox speeds. Also auxiliary transmission.

See also range-change; splitter transmission.

auxiliary pressure

(1) Additional control pressure within an automatic transmission regulator control unit, normally to modify the response of the regulator valve to supply pressure. 

 (2) Any additional hydraulic or pneumatic pressure that influences the response of a control system. auxiliary transmission See auxiliary gearbox.

axle 

Horizontal transverse shaft or beam with spindles on which road wheels are mounted. See also dead axle; fully floating axle; half-shaft; live axle; stub-axle; trans-axle.

trans-axle

axle bearing

Any bearing that supports an axle or half shaft.

 axle camber 

 Wheel camber achieved in a beam dead axle by convex curvature of the axle.

axle casing (US: axle housing) 

Rigid non-rotating casing that carries an axle or half shaft. 

axle fore-and-aft shake 

 Longitudinal oscillatory motion of an axle.

 axle lift

Mechanism for raising and lowering a lift axle of a commercial vehicle.

axle side shake 

 Lateral oscillatory motion of an axle of a moving vehicle. 

axle sleeve 

 Tubular casing of a live or dead axle shaft.

axle spindle 

 Shaft machined to carry wheel bearings and seals and with means for securing the wheel to the axle.

axle tramp 

 (1) Form of wheel hop on live axles in which the left and right hand wheels hop in opposite phase.

 (2) Resonant oscillation of an axle/suspension system, usually due to axle wind-up of an insufficiently damped suspension during heavy acceleration. The term is also used to describe a similar effect on vehicles without a beam axle.

axle weight

Static weight imposed on the highway by one axle.

axle wind-up

(1) Torsional deflection of an axle shaft, as due to sudden application of power or brakes. 

(2) Rotation of an axle casing due to flexure of semi-elliptical springs in reacting torsional loads.

 (3) Oscillatory motion of an axle about the horizontal transverse axis through its center of gravity. See also axle tramp.