Auto Glossary: A
Welcome to our auto glossary, an alphabet-organized list of the most commonly used terms in the automotive world. We hope it will help you understand some of the more advanced topics found on our site.
Please let us know if you believe we've missed something or simply want something added to the glossary.
Glossary Terms Filed Under: A
Vehicles have two A-pillars, one on either side of the front windshield. The A-pillar usually supports the roof of a vehicle and is located in front of the driver. On convertible models it also represents the main roll-over protection, and is among the strongest body parts.
Adaptive Air Suspension
Created by Audi engineers, the Adaptive Air Suspension is an electronically controlled air suspension system coupled with continuously adaptive damping. Originally an Audi A8-only feature, it is now available for the Q7 SUV also. Each of the vehicle's wheels have air suspension struts which are being electronically controlled by a central control unit which takes its data from sensors on the axles and acceleration sensors on the body.
Making necessary changes in milliseconds, the computer controls the damping force at each individual wheel, thus minimizing uncomfortable body movements when the car is braking, cornering or even driving off-road (in Q7's case).
Another advantage of the AAS system is the body self-levelling feature, making the vehicle's suspension height remain constant irrespective of the load it is carrying. Also, the Adaptive Air Suspension allows the driver to directly influence the suspension characteristics like height and comfort settings as individually preferred.
Active Body Control
The active suspension system Active Body Control (ABC) was developed by Mercedes-Benz in an effort to combine active safety and handling with ride comfort. Using high-pressure hydraulic servos, a multitude of sensor and high-performance microprocessors, ABC adapts the suspension and damping settings to different driving situations.
Computer-controlled hydraulic servos are mounted in the spring struts between the coil springs and the body, and are used to develop additional forces which act on the suspension and damping to control the car's body motion on the horizontal. Designed to control body vibrations in a range of frequency of up to 5 Hz, ABC reduces to a minimum caused is designed to control body vibrations in the frequency range up to 5 Hz - the kind of vibrations typically caused by uneven road surfaces, braking and cornering.
Mercedes-Benz engineers have used passive gas-pressure shock absorbers and coil springs which can be tuned in real time and independently to provide a good ride quality no matter the road conditions. In its latest generation on the S, CL and SL-Klasse models, ABC virtually eliminates body roll and pitch when accelerating, braking or cornering. Like most active suspension systems nowadays, ABC has different preset settings which can be chosen by the driver at the flick of a switch.
Automatic Braking Differential
The Automatic Braking Differential (ABD) system was co-developed by Bosch and Porsche in order to counteract unnecessary wheel spin by one of the driving wheels. In essence, ABD is an electronic locking differential that uses the brakes and inputs from the Anti-lock Braking System sensors to simulate "the lock" of one of the wheels in case of hard acceleration or during a high-speed maneuver.
On most car models, the ABD does not substitute for a real locking differential, but is a supplementary system which provides better directional stability and more traction on less-than-ideal road surfaces by applying braking power to any slipping wheel during acceleration.
Antilock Braking System
Originally developed for aircraft braking systems in the first half of the twentieth century, the Antilock Braking System (ABS) is essentially used to improve stability during braking and in some cases it can even shorten braking distances altogether. Appearing in various mechanical forms before, the first modern electronic four-wheel ABS system was co-developed by Mercedes-Benz and Bosch.
In cars without ABS, during hard braking the wheels lock, thus making impossible for the car to be steered and the vehicle most likely skids into the obstacle the driver is trying to avoid. The ABS prevents wheel lock-up during braking maneuvers by using sensors which can determine if any wheel is slowing down more than the others and computer-controlled valves which can limit the pressure delivered to each brake cylinder on demand. The whole system is controlled via a master ECU (Electronic Control Unit).
Since the ABS constantly pumps the brakes during a braking maneuver the driver can concentrate on steering the car while applying constant pressure on the brake pedal, without fear of losing control of the car's direction. Also, while braking on uneven surfaces (left tires on gravel and right ones on tarmac, for example) the ABS can keep the car's stability under control.
Adaptive Cruise Control
With the help of a laser or a radar sensor, the Adaptive Cruise Control (ACC) system recognizes preceding vehicles, calculates their speed and keeps the distance required by automatically acting on the brakes and/or engine power.
ACC can scan the area in front of the vehicle in order to determine the distance to the vehicle ahead. The information gathered by the sensors and/or radar is used to warn the driver if he/she is tailgating or to maintain an automatic safety distance to the vehicle by cutting engine power or activating brakes if necessary.
Some ACC systems can actually get the vehicle to a complete halt without any driver intervention in case they're detecting an impending impact with the object in front of the car.
Automatic Climate Control
The Automatic Climate Control is an air-conditioning unit which can automatically set the temperature desired by the driver without being influenced by the outside temperature or other factors. The most advanced climate control systems nowadays use different sensors and can take into account outside temperature, the sun rays' intensity and even the angle on which they're setting on the car in order to automatically regulate the temperature requested by the driver.
Active Cornering Enhancement
A feature first found on Land Rover vehicles, the Active Cornering Enhancement (ACE) is a system that reduces body roll during cornering. A pair of accelerometers are used to detect the angle of body lean and to instruct the ACE computer to counteract these movements by applying pressure to the vehicle's torsion bars via actuators which are hydraulically controlled.
On the Land Rover Discovery, the ACE system can counteract up 1 g of lateral acceleration in less than a tenth of a second, thus helping the vehicle become more stable and responsive during hard cornering.
Advanced Compatibility Engineering
The Advanced Compatibility Engineering (ACE) body structure is the name given to a passive safety technology available on most modern Honda vehicles. It is essentially a structure designed to disperse collision forces away from the passenger space inside the cabin in case of a crash. This is done while the damage to other vehicles involved is also minimized. This is accomplished by utilizing different grades of steel and also well thought crumple zones distributed around the passenger area.
Attention Control System
The Attention Control System (ACS) consists of a camera installed in the cockpit to monitor the driver’s blinking movements. The development of this system is aimed at eliminating the risk of driver inattentiveness, by constantly keeping track of the frequency and duration of eyelid movement. If the computer connected to the camera perceives the driver to be at risk of sleepiness at the wheel, the system can warn him ahead of time. Similar technologies are currently being developed by Lexus, Mercedes-Benz and Volvo.
Active Suspension Technology
The Active Suspension Technology is a definition for any suspension system which can modify its settings in real time to control body motion in response to any road abnormality or during cornering, braking or acceleration. These type of systems usually respond to inputs from either the road or the driver using different sensors. At least in theory, a vehicle equipped with an active suspension can provide both a comfortable and firm ride, thus keeping a perfect balance between smoothness and good road handling.
Automatic Distance Control
The Automatic Distance control (ADC) technology is similar with the DISTRONIC system from Mercedes-Benz. It is in essence a combination between Cruise Control and a radar based speed control system. When activated, the speed control system can make the car keep a constant distance to another vehicle in front independent of driver input.
If the radar determines an impending frontal crash is unavoidable it emits a collision warning and then automatically slows down the car to avoid it. Newer generations are actually able to bring the vehicle to a full stop behind the car ahead if necessary.
Adjustable height shoulder belt
ADJUSTABLE HEIGHT SHOULDER BELT
A belt that usually has an anchor point with assorted slot positions, allowing the car occupants to individually adjust the safety belt to fit their size and/or height.
Adaptive Damping System
The AIRMATIC suspension system from Mercedes-Benz combines the pneumatic suspension with an Adaptive Damping System (ADS), which can individually adjust the shock absorbers forces to match the vehicle's payload, the state of the road surface and even the driving style.
The system comprises of a steering angle sensor, three accelerometers on the vehicle body, the ABS speed sensors on each wheel and a brake pedal sensor. These constantly measure the lateral and longitudinal acceleration of the car during driving. From this data, the ADS Electronic Control Unit calculates the optimal damper setting for each individual wheel and transmits the signals to special actuator valves located on the gas-pressure shock absorbers.
These valves are able to switch between different preset damping characteristics during the blink of an eye, thus switching from comfort to sporty mode at the touch of a button.
Aerodynamics are a very important part of automotive design, since it singlehandedly can influence by a high margin factors like fuel consumption, noise levels, top speed and undesired lift forces experienced by any vehicle at high speed. A more streamlined car will have a lower drag coefficient, thus increasing its mileage, its top speed and also lower wind noise levels.
On the other hand, there has to be a balance between a clean aerodynamic shape that can also provide downforce at very high speeds. High performance cars use different types of spoilers, integrated bodykits and diffusers to create venturi effects and improve the vehicle's road grip. Almost all aerodynamic elements on modern cars were inspired by the aviation industry and are designed using wind tunnels and computer simulations.
Active Front-lighting System
The Active Front-lighting system (AFS) can redirect the headlamp units individually on a horizontal direction during vehicle cornering. All is made in accordance with steering angle and vehicle speed, and is assisted by a computer which determines the angle it needs to rotate the headlamps. An early purely mechanical version of the system appeared in the 1950's on the Citroen DS.
The airbag is also called a "Supplementary Restraint System", and in short it consists of an inflatable bag or envelope which keeps the occupants from hitting any hard parts of the vehicle's interior during a crash. In case of a collision, cars equipped with airbags give a much better chance of survival for its occupants, but ONLY when seat belts are worn - hence the "supplementary" part.
The way it works is pretty simple in theory: in case of a sudden deceleration (such as a crash) accelerometers within the car's body trigger the ignition of a gas generator propellant to inflate a nylon fabric bag very rapidly (under 1 tenth of a second). The airbag has small vent holes on its side in order to allow the propellant gas to be slowly expelled from it just as the occupant pushes against the bag.
Most airbag equipped vehicles have several accelerometers and/or gyroscopic sensors to help sense various types of impacts. The different signals from these sensors are fed into a microcomputer which can determine the angle of impact and even the severity of the collision taking place. Depending on the result of these calculations, the airbags ECU will decide if the airbag deployment is necessary or not.
Airbag Electronic Control Unit
The Airbag ECU uses information gathered from deceleration sensors usually located in the crumple zones of a vehicle. Within just 15 milliseconds of any impact, the information is already processed by the ECU, therefore it can determine if there is really a need for airbag deployment, whether they should be triggered in stages (in the case of modern multistage airbags) or whether only the seat belt limiters should come into force or not.
Instead of a conventional suspension and damping system with coil springs and gas-pressure shock absorbers, some Mercedes-Benz models are equipped with AIRMATIC, a system which combines a pneumatic suspension with the Adaptive Damping System (ADS).
All of its components mainly consist of pneumatic lines, pneumatic suspension struts on all wheels, an air compressor, a central air reservoir, solenoid valves and actuators, a central ECU and various pitch and yaw sensors on the vehicle's body. Everything is connected via a CAN (Controller Area Network) databus and fed to a multitude of microprocessors which decide the suspension's behaviour during different driving maneuvers and road surfaces.
Automatic Locking Differential
The Automatic Locking Differential improves handling during acceleration in curves or when one of the driving wheels is on a surface with a different grip coefficient than the others. In short, it ensures the best rotational speed for each of the driving wheels, thus preventing loss of the car's dynamics during evasive maneuvers or potentially dangerous situations like driving with a lateral set of wheels on a slippery surface.
This is done by "locking" both wheels on a driving axle together as if they were on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack of it) available to either wheel individually, making it a very efficient solution for off-roading if found on an all-wheel driven vehicle.
Automatic Locking Retractors
Automatic Locking Retractors allow the safety belt to be pulled in one motion until fastened, then operates as a ratchet, thus preventing further extension. On most safety belts you will hear a faint clicking sound that indicates the belt is locked and ratcheting in. The Automatic Locking Retractors on belts help to keep the occupants in place in the event of a frontal collision or during hard braking.
Aufrecht Melcher Grossaspach
AMG is short for Aufrecht Melcher Grossaspach, and is the tuning arm of Mercedes-Benz. The company was founded in 1967 by former Mercedes engineer Hans-Werner Aufrecht and his business partner Erhard Melcher in a small German town named Grossaspach. The name originated from each of the two partner's family names and the town in which they started the business.
Currently no longer located in Grossaspach, but in Affalterbach - AMG started off by designing and testing Mercedes-Benz racing engines and after a few years expanded their business into building bespoke road cars, also based upon the tri-star vehicles.
Until the mid '80's there were no official tie-ups between the two companies, but then AMG started to supply the Stuttgart brand with aftermarket alloy wheels and various styling products. Mercedes-Benz took a majority stake in AMG in 1999 and a full ownership in 2005, and has now transformed AMG into its in-house tuner.
Active Noise Cancellation
The Active Noise Cancellation system is designed to implement an acoustically adaptive algorithm that cancels the unwanted sound by generating an anti-sound (or anti-noise) of equal amplitude and opposite phase. The original sound and the anti-sound acoustically combine, resulting in the cancellation of both sounds, thus improving the acoustical comfort in the vehicle.
Angle of Approach
ANGLE OF APPROACH
When viewing the side of a vehicle, the angle of approach is the angle between the ground and a line running from the front tire to the low est-hanging component directly ahead (which is usually the front bumper). The intensity of this angle gives an indication of how steep a ramp can the vehicle negotiate without suffering damage to its undercarriage.
Angle of Departure
ANGLE OF DEPARTURE
When viewing a vehicle from its side, the angle of departure is the angle between the ground and a line running from the rear tires to the lowest-hanging component directly behind them (which is usually the rear bumper). Similar to the approach angle only backwards, the departure angle indicates a vehicle's ability to drive off a ramp or some other obstacle without damaging the rear part of its undercarriage.
Acoustic Parking System
The Acoustic Parking System (APS) uses ultrasonic sensors installed at the rear as well as at the front of a vehicle to make parking easier. Using information from the sensors, a microprocessor calculates how far is the car from an obstacle. An intermittent warning tone or lights on a display are usually used to give the driver warning of an impending impact with any object caught by the ultrasonic sensors' sight.
Active Roll Mitigation
Active Roll Mitigation (ARM) is similar with Land Rover's Active Cornering Enhancement (ACE). This system is also able to react when the vehicle becomes light on one side in a fast corner, only in a different way. The ARM system only uses the braking system to stabilize the vehicle, by providing very short brake bursts on individual wheels, following information gathered from rollover and ABS wheel sensors.
Advanced Restraint Systems
Advanced Restraint Systems are a safety technology designed to improve the efficiency of safety items during a crash. A combination of sensors in the cockpit monitor everything from the occupant's height, the seating position, safety belt usage and the vehicle's deceleration to control the airbag deployment and the belt forces during a crash. The data gathered from sensors and accelerometers is gathered and provided to a computer which uses this information to decide which safety restraints (belt limiters and multistage airbags) should be deployed and with how much force.
Anti Skid Control
The Anti Skid Control (ASC) keeps the driving wheel spin within the optimum range during hard acceleration or on slippery surfaces. The system uses information taken from the ABS sensors which monitor the rotational speed of the wheels and can intervene by individually applying the brakes or even cutting the engine power to the driving wheels until the wheel spin is counteracted.
Therefore, regardless of how hard the driver presses the gas pedal, the ASC system intervening on the engine power and on the brakes controls the car's acceleration with maximum possible efficiency, ensuring that none of the driving wheels will spin excessively.
Audi Space Frame
The first generation of the Audi A8 is the first car with an aluminium body built according to the Audi Space Frame principle. The ASF is a high-strength aluminium frame structure into which the panels are integrated so that they also perform a load-bearing function. The main advantage of this solution, especially on a heavier car is the low weight combined with better stiffness. Audi engineers say that the A8 would weight at least 15% more if it had a comparable steel frame.
Acceleration Slip Regulation
ASR prevents the driving wheels from spinning unnecessary while on slippery surfaces, or when the power coming from the engine is too much for ensuring good traction (unnecessary wheel spin). It also improves directional control with better traction during high speed cornering. Developed by Mercedes-Benz in the 1980's, the system uses the ABS speed sensors to calculate if one of the driving wheels is spinning faster than the other and automatically actuates its individual brake sufficient enough for it to regain grip (or arrive at the same speed as the other driving wheel).
Active Service System
Engines are equipped with a microcomputer that monitors the aging of the motor oil via data transmitted by sensors and calculates an individualized maintenance plan for the engine. A digital indicator in the cockpit notifies the driver of the number of kilometers remaining before the next maintenance check.
All engines fitted in newer Mercedes' are equipped as standard with the Active Service System ASSYST, which registers the varying operating loads individually and takes these into account for scheduling engine maintenance.
On the basis of sensor-derived data such as oil level, oil temperature, coolant temperature, engine speed, road speed and engine load, a microcomputer calculates the actual load on the engine oil and works out a servicing schedule for the engine which reflects this and announces the driver.
Active Tilt Control
The Active Tilt Control is a technology used by some SUVs belonging to brands from the Ford Motor Company. Like other similar systems, ATC is used primarily for controlling body lean while the vehicle is cornering. A mounted accelerometer gives a lateral acceleration signal to a control module, which in turn directs pressure from pumps to hydraulic cylinders that replace the stabilizer bar links. The hydraulic cylinders wind up the stabilizer bars, thus minimizing the vehicle's body lean during hard cornering.
Adaptive Transmission Control
The Adaptive Transmission Control system is found only on automatic and sequential transmissions and is based on a fuzzy-logic processor which can recognize individual styles of driving and adapts transmission shift parameters accordingly. It usually uses a microprocessor to read data from various sensors, and with the help of a complex algorithm it decides when to upshift or downshift.
It is very helpful especially since the fuzzy logic processor allows it to actually memorize the driver's driving habits or "learn" the environment conditions (for example, on slippery surfaces it will change gears more rarely).
Active Transfer Torque System
The Active Torque Transfer System (ATTS) is basically Honda's example of a Limited Slip Differential (LSD), since is also used to transfer as much as 80% of the engine torque to the outside driving wheel. By using information gathered from multiple sensors, including yaw rate, steering angle and lateral acceleration, ATTS can transfer torque to the wheel with the greatest traction.
The term All Terrain Vehicle is usually used to describe small open motorized vehicles with three or four wheels that are designed for off-road use. The versions with four wheels are also called quad-bikes or just quads.
Assisted or automatic parking
A number of car companies have started to offer automatic parking features on their models nowadays. In theory, as the vehicle equipped like this passes a parking spot, the system ascertains the dimensions of the available space and if any obstacles might be in the way. Once it has evaluated this sensory data, it automatically calculates the ideal parking maneuver and it either lateral parks itself or requires gas and brake pedal input form the driver. This is done by using parking sensors on every side of the car and a microprocessor which in some cases can also control steering, braking and acceleration during the parking maneuver.
An automobile is a self-propelled wheeled vehicle that carries its own means of propulsion and is used for transport on land.
Active Valve Control System
The Active Valve Control System (AVCS) is a variable valve timing engine technology used by Subaru. Using similar ideas as Honda's VTEC, the system squeezes the best performance from the engine while also minding emission standards. It works by varying the timing of the intake valves and adjusting the positions of the camshafts based on inputs from various sensors in the powertrain. This increases the power output especially on higher rpms without sacrificing fuel consumption.
All Wheel Drive
Sending power to every one of the vehicle's wheels all the time, or only when needed, through active or non-active differentials or a transfer case.
All Wheel Steering
All Wheel Steering is a system that turns the rear wheels in the same direction as the front wheels to aid in high-speed cornering. Other similar systems turn the rear wheels in the opposite direction as the front to aid in low speed maneuvering and/or parking.
Axle articulation is the ability of a vehicle's axle to move in a different direction vertically relative to the chassis or the other axle/s. Most American pick-up trucks have axle articulation as a standard feature to help on rough roads.
The axle ratio is the proportion between a vehicle's driveshaft rotation and its driving wheel axle. For example, a 3:1 axle ratio means that the driveshaft turns three times for every rotation of the driving wheels. By changing a vehicle's axle ratio, you may change its towing capacity, but this also depends on the engine's power, naturally.
Active Yaw Control
The Active Yaw Control is a Mitsubishi developed system that stabilizes the yaw moment during hard cornering. By simulating a torque differential between the right and left driving wheels, the AYC system on the Mitsubishi EVO models improves cornering performance and lateral stability on most surfaces.