TSB : Automotive Terminology & Definitions

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ACTIVE SUSPENSION SYSTEM active suspension systems move each wheel up and down to control body motion in response to road abnormalities. The system responds to inputs from the road and the driver. With an active suspension, a vehicle can simultaneously provide the smooth ride of a soft suspension along with the superior handling associated with a firm suspension. ACTIVE TILT CONTROL active tilt control winds up the stabilizer bars in the front and rear suspension to resist body lean while cornering. Because active control is used only as needed, vehicle spring rates and stabilizer bar stiffness can be reduced, improving normal ride characteristics. In addition, this system has potential to increase low-speed, off-road traction on 4WD vehicles. ACTIVE VARIABLE RATIO STEERING electronically provides variable steering ratios. A computer is linked with the vehicle stability control system to aid in directional stability of the vehicle. As the vehicle travels down the highway, road surfaces and wind gusts can affect the vehicle directional stability. The car may wander a little or dart to one side, as many who have met a tractor-trailer unit on a windy day have experienced. Sensors on the car detect this sudden unintentional movement and the computer will stabilize the car by moving the Active Steering electric motor and steering gear. The driver doesn't turn the steering wheel at all. AIR SPRING a suspension device made up of a flexible bladder containing compressed air. The air spring takes the place of a :onvent;onal coil or leaf spring. Air is supplied by an on-board ;ompressor, usually with auxiliary equipment to sense vehicle leight and modify the pressure in the air spring as needed. AIR SUSPENSION instead of steel coil or leaf springs, some vehicles have a bellows-like unit at each corner that contains pressurized air. As a rule, air suspensions can produce a softer ride. ALIGNMENT an adjustment to bring parts or components into a line or proper coordination. ALL-WHEEL DRIVE the method of providing traction to any of the wheels of a vehicle, as conditions require. Depending on the system, it may be full-time or part-time. ANTI-ROLL BAR see 'stabilizer bar'. ASPECT RATIO the relationship between the height of a tire from bead to tread, and the tread width, usually expressed as a percentage of the tread width. AUTOMATIC RIDE CONTROL automatic ride control adjusts vehicle shock absorber resistance (damping) in response to driver inputs such as steering and braking and for changes in road surface. During maneuvers such as hard braking or quick lane changes, the system increases suspension damping to improve dynamic stability. Damping is automatically decreased during steady driving, so that bumps and potholes are absorbed rather than being transmitted to the occupants. Some systems also allow the driver to select suspension settings: soft, normal or firm (sport). AXIAL LOAD a type of load placed on a bearing that is parallel to the axis of the rotating shaft. AXIAL PLAY movement of a component parallel to the axis of rotation. AXIAL round, on or along an axis; having the same direction or being parallel to the axis of rotation. AXIS a real or imaginary straight line on which or around which an object rotates. BALANCE a condition of equal weight distribution within a component or among components; the act of equalizing the weight distribution, such as balancing a tire or an engine's reciprocating assembly. BALL JOINT a suspension component that provides a pivot point, allowing the steering knuckle to move up and down as well as turn. In response to steering input. The ball fits into a socket housing that is attached to the control arm and the stud on the other end of the ball is attached to the steering knuckle. A dust cover is installed over the ball and socket assembly to keep dirt out and lubricant in. BEAD the steel reinforced inner edge of a tire, which fits inside and seals against the wheel rim. BOOT protective rubber cover with accordion pleats used to contain lubricants and exclude contaminating dirt, water and grime, located at each end of the rack-and- pinion assembly and FWD CV-joints. BUMP STEER a steering problem in which a vehicle tends to the left or the right after a bump, without steering wheel input from the driver. This is usually caused by some steering misalignment or damage that permits change of toe when the suspension works up and down. BUSHING a liner, usually removable, for a bearing; an anti-friction liner used in place of a bearing; a type of bearing that is used to support rotating shafts. CAMBER the attitude of a wheel/tire assembly in which, when viewed from the front, the distance between the tops and bottoms of the tires are different. If the distance between the tops is greater than between the bottoms, positive camber is present. If the distance between the tops is less than between the bottoms, negative camber is present. CASTER angle formed between the kingpin axis and a vertical axis as viewed from the side of the vehicle. Caster is considered positive when the top of the kingpin axis is behind the vertical axis, that is, tilted toward the rear of the vehicle. CENTER LINK a steering linkage component which attaches the Pitman arm to the idler arm, tie-rod or crosslink. COIL SPRING spring steel rod wound into a coil that supports the vehicle's weight while allowing suspension movement. COLLAPSIBLE STEERING COLUMN a steering column that is designed to collapse, to prevent the column from heavily impacting the driver during an accident. CONSTANT VELOCITY (CV) JOINT a flexible coupling between two shafts that allows each shaft to maintain the same speed regardless of operating angle. CONTROL ARM a suspension component that connects the vehicle frame to the steering knuckle or axle housing and allows the up and down movement of the wheels. COTTER PIN. a safety component made from soft steel, used to keep a nut from loosening on a bolt or stud. The cotter pin is inserted through a hole in the bolt or stud and through slots in the nut (see 'castellated nut'), then the ends of the cotter pin are spread to lock it in position. CROSSMEMBER part of the vehicle frame structure, arranged transversely and attached to the frame rails at each side of the vehicle. Can be removable or welded in place. DAMPEN to slow or reduce oscillations or movement. DEAD AXLE a load-supporting axle that does not transmit power; an axle that does not rotate, but merely forms a base on which to attach the wheels. DIRECTIONAL STABILITY the ability of a car to travel in a straight line on a flat surface with a minimum of driver control. DIRECTIONAL TIRE tire with a tread pattern that is designed to give maximum traction by removing water from under the tread in such a way as to minimize the risk of aquaplaning. Directional tires must be installed to turn in a specific direction. DOWNFORCE negative aerodynamic lift. DRAG COEFFICIENT drag divided by the product of dynamic pressure and projected area. A factor representing the drag acting on a body (as an automobile or airfoil). DRAG LINK a steering linkage component that connects the pitman arm and the steering arm. DRAG horizontal aerodynamic retarding force on a vehicle parallel to the relative wind direction. DYNAMIC BALANCING balancing a part while it is in motion. ELECTRICALLY POWERED STEERING electrically powered steering uses an electric motor to drive either the power steering hydraulic pump or the steering linkage directly. The power steering function is therefore independent of engine speed, resulting in significant energy savings. ELECTRONIC AIR SUSPENSION electronic air suspension provides the comfort of riding on air with adjustable spring rates and capability to change ride height and load-carrying ability. Under normal driving conditions, an electronic air suspension vehicle rides at the same height as a traditionally sprung vehicle. With a heavy load, ride height is increased automatically. On current vehicles, the suspension lowers the ride height by 20 mm at highway speeds for improved aerodynamics, with about 2 percent better fuel economy. Lower ride height also can improve on-center feel of steering due to the change in suspension geometry and increased caster angle. ELECTRONIC LEVEL CONTROL. a suspension system that uses air springs to maintain vehicle ride height. Height sensors are used to signal a control unit when the vehicle is riding low or high. In response to this signal, compressed air is either sent to or vented from the air springs. HALFSHAFT transfers power from the transaxle to the front wheels on a front-wheel drive vehicle. Also used on some vehicles with rear-wheel drive and independent rear suspension to transfer power from the differential to the rear wheels. Consists of a stub shaft that is splined into the differential side gear, another stub shaft that is splined into the wheel hub, an interconnecting shaft, and two CV-joints, which connect the interconnecting shaft to the stub shafts. HARMONIC VIBRATION periodic motion or vibration along a straight line. The severity depends on the frequency or amplitude. HEIGHT SENSOR a component used in an air suspension system to signal a control unit when the vehicle is riding low or high. In response to this signal, compressed air is either sent to or vented from the air springs. HUB mounting point for the wheelan an axle or spindle; the part of the synchronizer assembly that is splined to the transmission shaft; the center part of a wheel, gear, etc., that rides on a shaft. IDLER ARM a conventional steering system component consisting of an arm that swivels in a bushing on a shaft, which is attached to the frame. The idler arm is mounted on the right side of the vehicle and is the same length and set at the same angle as the Pitman arm. Its function is to hold the right end of the center link level with the left end, which is moved by the pitman arm, and transfer the steering motion to the right side tie-rod. INCLUDED ANGLE the sum of the angle of camber and steering axis inclination; the sum of two intersecting angles. INDEPENDENT SUSPENSION a suspension in which each wheel can travel up and down without directly affecting the position of the opposite wheel. INTEGRAL POWER STEERING a power steering system in which the power cylinder and control valve are contained in one housing. INTELLIGENT VEHICLE HIGHWAY SYSTEM (IVHS) the Intelligent Vehicle Highway System (IVHS) provides a variety of information to the vehicle and driver through cooperation of automotive electronics, communications, controls and systems engineering technologies. IVHS has two areas of interest to car and truck makers: (1)telematics and (2)active safety warning and control systems. Several features are: Telematics: Navigation systems Traffic messaging Emergency messaging and security tracking (e.g. RESCU - Remote Emergency Satellite Cellular Unit) Short range communications/ automatic toll collection Active Safety Warning and Control Systems Collision warning/avoidance - Backup and parking aids - Side vision aid - Vision enhancement - (all weather/night vision) - Adaptive cruise control - Lane departure control INTERACTIVE VEHICLE DYNAMICS (IVD) interactive Vehicle Dynamics is designed to minimize loss of vehicle control due to loss of traction. The IVD system could be activated when a vehicle is taking a turn too quickly or when encountering an icy patch. JAM NUT a locknut. KINGPIN the pivot shaft for the steering knuckle on most early axles and some modern heavy-duty axles. KNUCKLE the suspension component that connects the upper and lower control arms or the strut and lower control arm. On rear wheel drive vehicles, it usually incorporates the front wheel spindle and on front wheel drive vehicles it has an opening where the halfshaft passes through. A steering arm is attached to the knuckle, where the tie-rod end is connected. Also called a steering knuckle. LANE-DEPARTURE WARNING SYSTEM Issues a warning when the vehicle edges off course and reaches the highway lane markers. Introduced on the 2005 Infiniti FX and available on the 2006 Infiniti M45, the system developed by Iteris can detect lane dividers even in rainy weather. It delivers a noticeable sound when the vehicle starts to move into an adjacent lane, whether due to inattention, drowsiness or distraction. LATERAL RUNOUT side-to-side movement or wobble in a wheel or tire. LEAF SPRING a suspension spring consisting of a single flat plate made of steel or composite material or several steel plates bundled together. LOW TIRE PRESSURE WARNING a low tire pressure warning system alerts the driver if the air pressure in a tire becomes too low. Typically, a light on the instrument panel will be illuminated to warn of the low-pressure condition. MACPHERSON STRUT the principal device in the suspension of the same name, in which the spring, shock absorber and sometimes the steering knuckle are combined in a single unit. MEMORY STEER a steering condition where the steering wheel and wheels want to return to a position other than center. This can be caused by tightening rubber bonded socket tie-rod ends when the steering wheel is not centered, binding in the upper strut mounts, or binding in a steering component or ball joint. ON-CAR BALANCING the practice of spinning a wheel on the car to balance the wheel and all other rotational components together. PARALLELOGRAM STEERING LINKAGE a type of conventional steering linkage consisting of a pitman arm, center link, idler arm and tierod assemblies to connect to the steering knuckles. The pitman arm, center link and idler arm form three sides of a parallelogram. PITMAN ARM a steering system component mounted on the steering box shaft and transfers the gearbox motion to the steering linkage. PLUNGER JOINT the inboard CV-joint on a halfshaft, so called because the joint moves in and out in response to the suspension's up and down movement, which causes the distance between the transaxle and the wheel to change. The movement takes place within the joint, with the tripod rollers or double offset ball bearings moving in and out on elongated grooves in the yoke or outer race. PRESS FIT when a part is slightly larger than a hole it must be forced together with a press. PULL a steering condition where the vehicle driver has to maintain constant pressure on the steering wheel to keep the vehicle moving straight. RACK-AND-PINION STEERING a type of steering mechanism that replaces the pitman arm, center link and idler arm on gearbox steering. The steering column ends in a pinion gear that moves the driven rack to the left and right. The rack ends contain ball studs connected to the outer tie-rod ends and steering knuckles. RADIAL LOAD load applied at 90 degrees to an axis of rotation. RADIAL RUNOUT the out-of-roundness ot a wheel or tire. RADIAL branching out in all directions from a common center; perpendicular to the shaft or bearing bore. RADIUS ARM a suspension component that is connected to a twin I-beam or solid axle at one end and to the vehicle frame through bushings at the other. The radius arm braces the I-beam or axle and keeps it at a right angle to the vehicle frame. REAR WHEEL STEERING a system used on a some vehicles to change the toe of the rear wheels to either steepen a sharp turn or enhance cornering on a shallower, faster one. RIDE HEIGHT the dimension between a fixed point on the vehicle and the pavement. The fixed point varies according to vehicle and manufacturer. Also called vehicle height. ROLLING RESISTANCE retarding force, parallel to the direction of travel, caused by tire resistance along the ground. RUNOUT wobble or deflection beyond a rotating part's normal plane of movement. SAI see 'steering axis inclination', SCRUB RADIUS the distance between the point at which the tire's vertical centerpoint intersects the road, and th