DICTIONARY OF AUTOMOTIVE TERMS - "Un"
- Unbalance:
- A condition of wheels which are not balanced. Also see tire unbalance
- Unburnt hydrocarbons:
- Pollutant (basically petrol vapor) released into the atmosphere as an exhaust gas, due to incomplete combustion
- Uncluttered:
- An orderly, neat instrument panel that is free of irrelevant detail
- UNC thread:
- Acronym for Unified National Coarse thread; one of the screw threads used on British cars. See national coarse thread. Compare UNF thread
- Underbody:
- The underside of a car.
Commonly called the floor pan. Usually made up of several smaller panels joined
together to form a single unit and reinforced on the underside by floor pan cross
bars.
Also see PVC underbody treatment
- Underbody coating:
- A coating of the underbody of a vehicle, usually with organic coating materials (plastic, wax, bitumen-based products), to protect it from mechanical damage and corrosion
- Underbody protection:
- A coating of the underbody of a vehicle, usually with organic coating materials (plastic, wax, bitumen-based products), to protect it from mechanical damage and corrosion
- Underbody sealing compound:
- See underseal
- Underbody structure:
- The structural members and flat panels of the bodywork on the chassis. Also called substructure
- Underbody treatment:
- See PVC underbody treatment
- Underbrake:
- To run farther into the turns than normal without applying much brake
- Undercarriage:
- See underbody structure
- Undercharge:
- A term referring to a system low on refrigerant, resulting in improper cooling.
- Undercoat:
- All of the products used to prepare the surface to receive color coats (primers, surfaces, putties, sealers, etc.).
- A rustproof coating with sound-deadening properties applied to the underbody
- Undercoating:
- The material sprayed on the underside of the automobile, under the hood, trunk lid, etc. which is designed to deaden sound and prevent the formation of rust.
- Undercoats:
- See undercoat.
- Undercure:
- A condition in which the vulcanization or curing has not been adequate.
- Degree of cure less than optimum. May be evidenced by tackiness, softness, off-color, or inferior physical properties of an adhesive.
- Undercut:
- A depression at the toe of the weld which is below the surface of the base metal.
- Underfilm corrosion:
- See creepage
- Underfloor:
- The underside of a car
- Underfloor mid-engine:
- A design, introduced on the Toyota Previa minivan, where the engine is located below the passenger compartment, between front and rear
- Underframe:
- The underbody backbone of a car, both for unitary or chassis designs
- Underhead collar:
- A washer fitted under the head of a bolt or screw
- Underhood area:
- The engine compartment
- Underinflated tire:
- A tire which has too little air in it, causing increased wear at the tread edge
- Underinflation:
- Insufficient air pressure in a tire for the amount of load carried.
- Underpowered:
- A description of a vehicle with an engine that provides less power than is necessary for acceptable performance; especially noticeable when accelerating, passing, or going uphill
- Underseal:
- A rustproof coating with sound-deadening properties applied to the underbody.
- To apply underseal.
Also See:
PVC underseal coating
undercoat
- Underseal coating:
- See pvc underseal coating
- Under seat panel:
- See seat well
- Undershield:
- A body accessory panel made from tough, oil-resistant plastic for fitting on cars that do not have a standard wheel housing panel. It is designed to protect the upper inside area of the fender and the door hinge area from splashes of water and mud deposits; it is also used as standard equipment on some modern cars to replace the traditional steel wheel housing panel
- Underside:
- The lower side of the underbody, i.e., the surfaces that face the road surface
- Underside panelling:
- A smooth cover on the underside of a car for improving aerodynamics below the vehicle, e.g., on the Porsche 911 and 928
- Under sill panel:
- A separate closing panel or section used on cars where the inner sill or side member consists of several separate parts; it forms the bottom of the inner sill and connects the sill area to the floor panel
- Undersize grind:
-
A type of brake shoe arcing that produces a lining with a constant thickness
ground to a radius slightly smaller than that of the brake drum.
- Undersize tire:
- The use of a tire having insufficient carrying capacity for the load. Also replacing original-equipment tire size with a smaller size of sufficient capacity, thus reducing unladen weight.
- Underslung:
- Suspended below a supporting member, e.g., of a chassis suspended below the axles
- Underslung frame:
- A frame design of the pre-war era whose characteristic feature is that the frame members run below the axles
- Undersquare engine:
- See under square engine
- Under square engine:
- An engine in which the bore diameter is smaller than the length of the stroke. Also called long stroke engine
- Under-square engine:
- An engine in which the bore diameter is smaller than the length of the stroke.
- Understeer:
- The tendency for a vehicle, when negotiating a corner, to turn less sharply than the driver intends. The front end wants to run wide in a turn. To correct this problem, the suspension needs to be stiffer in the front or softer in the rear. A front-engine vehicle has a natural tendency to plow straight ahead on turns (i.e., understeer) unless its suspension is adjusted to counteract it. Sometimes called "push." Also see roll understeer
- Undertray:
- The bottom panel of multi-layer or complex underbody panel assemblies, which faces the road surface
- Undertread:
- See breaker. A cushioning layer between the belt layers and the tread in radial tires.
-
Underwriters Laboratories, Inc. (UL):
- An independent testing organization that sets safety standards for electric
motor and other electrical equipment
- Unequal-length wishbone suspension:
- A double wishbone suspension system in which the upper wishbone is shorter than the lower one, with both converging slightly at the wheel hub; reduces tire wear due to variations in track and camber angle when cornering
- Unequal wishbones:
- A colloquial term for unequal-length wishbone suspension
- UNF thread:
- Unified National Fine thread; one of the screw threads used on British cars. See national fine thread. Compare UNC thread
- Unibody construction:
- A manufacturing process where sheet metal body parts are combined with stress-bearing elements to form the body and chassis as a single piece, as opposed to attaching body parts to a frame.
Also See:
unitized construction
unitary construction
-
Unicrown fork:
- A mountain bicycle fork blades which curve in at the top and are welded to the
steerer instead of fitting into a fork crown (there is no fork crown on a unicrown
fork)
- Unicycle:
- A one-wheel cycle having pedals attached to the axle and a saddle attached to the upper end of the fork tubes.
- Unidirectional flow scavenging:
- A scavenging process of two-stroke engines. One of the characteristic features is that the flow of fresh charge does not follow a path opposed to that of the burnt charge; scavenging and exhaust ports are not located at the same stroke end of the piston but rather are staggered, i.e., the fresh charge flows along the length of the cylinder without its direction being reversed. This process is widely used in large engines, e.g., for ships
- Uniflow scavenging:
- A scavenging process of two-stroke engines. One of the characteristic features is that the flow of fresh charge does not follow a path opposed to that of the burnt charge; scavenging and exhaust ports are not located at the same stroke end of the piston but rather are staggered, i.e., the fresh charge flows along the length of the cylinder without its direction being reversed. This process is widely used in large engines, e.g., for ships
- Unified National Coarse thread:
- See UNC thread
- Unified National Fine thread:
- See UNF thread
- Uniform corrosion:
- Corrosion occurring over the entire exposed surface. The opposite is localized corrosion
- Union:
-
A hydraulic coupling that connects two brake lines.
-
Union Cycliste International:
- (UCI) International governing body of professional and amateur bicycle racing
- Union nut:
- A nut used to secure the connection between pipes or rods
- Uni-servo brake:
- A servo brake with one single-end wheel cylinder and two
self-energizing brake shoes
- A drum brake that has servo action in the forward direction only.
- Uni-servo drum brake:
- A servo-action drum brake that has servo action only when the vehicle is braked in a forward direction.
- Unit:
- See:
airbag unit
enrichment unit
inflator unit
lamp unit
light unit
metering unit
-
Unitary construction:
- A modern chassis layout with no separate frame, using the sheet metal parts of
the vehicle body or floorpan as structural members which also carry all suspension
parts; introduced by Citroën in 1934 and by GM/Opel Olympia in 1935. Also called monocoque
- Unitary system:
- A heating/cooling system factory assembled in one package and usually designed for conditioning one space or room.
- Unit body:
- Unit body: Type of body/frame construction in which the body of the vehicle, its floor plan and chassis form a single structure. Such a design is generally lighter and more rigid than a vehicle having a separate body and frame.
- Unit construction:
- Integrated unit consisting of the engine and gearbox within the same casing
- United States Council for Automotive Research:
- (USCAR) an organization founded by Chrysler, Ford, and General Motors to strengthen the technology base of the domestic automotive industry through research and co-operation.
- Unit engine:
- A term used for motorcycles where engine and gearbox are accommodated in one common housing
- Unitized construction:
- A type of body construction that doesn't require a separate frame to provide structural strength or support for the car's mechanical components. A unitized body can employ monocoque construction, or it can utilize strong structural elements as an integral part of its construction.
- Unitized transmission:
- A transmission (also "unit transmission") that is an integral part of the engines bottom end.
- Universal:
- See:
ball universal
cardan universal
hardy-spicer universal joint
hooke universal
impact swivel ball universal joint
Rzeppa-type universal joint
-
Universal cable:
- A shift or brake cable that is designed to fit all types of levers; on each
end is a different lead end and you cut off the one you do not need.
- Universal Japanese Motorcycle:
- (UJM) during the 1970s, the Japanese became so identified with the four-cylinder standard-style motorcycle that this term described them.
- Universal joint:
(UJ) A flexible double-pivoted joint that allows driving power to be carried through two shafts that are at an angle to each other. It consists of two Y-shaped yokes and a cross-shaped member called the spider. The four arms of the spider are assembled into bearings in the ends of the two yokes. With the normal cross-and-two-yoke universal joint there is some change in speed when the driveshaft and the driven shaft are at an angle to each other. The change in speed occurs because the driven yoke and driven shaft speed up and then slow down twice with every revolution of the drive line. The greater the angle between the drive and driven shafts, the greater the speed variation. To eliminate this speed variation, which results in increased wear of the affected parts, constant velocity joints are used on many cars. In front drive vehicles, it is called the constant velocity joint. Also
called "Hooke joint" or "cardan joint."
Also See:
ball universal joint
constant velocity universal joint
hardy-spicer universal joint
impact swivel ball universal joint
Rzeppa-type universal joint
- Universal joint socket:
- A socket with universal joint to reach into cramped working areas
- Universally jointed shaft:
- See cardan shaft
- Universal motor:
- Electric motor which will operate on either ac or dc.
- Universal spark plug socket:
- A spark plug socket with universal joint for reaching hard-to-get-at spark plugs
- Unladen weight:
- The actual weight of a vehicle or combination with no payload. See tare weight.
- Unleaded gas:
- Gasoline which has no tetraethyl lead. See lead free.
- Unleaded gasoline:
- See unleaded gas.
- Unloaded radius:
- See free radius.
- Unloader:
- See self-unloader
- Unloader valve:
- See delivery valve
- Unmanned machinery spaces:
- Engine room or space fitted with sensors and controls for monitoring and responding to machinery operating conditions. This makes it unnecessary for personnel to be present in the space at all times
- Unobtanium:
- A coined word describing a bicycle or accessory made from expensive, high-tech material. A play on "unobtainable" and "titanium."
- An object that is in a place that is impossible to retrieve but continues to rattle around (e.g., a weld flashing that has come off inside a bicycle tubing)
- Unseating:
- See bead unseating
- Unsprung mass:
- See unsprung weight
- Unsprung weight:
- This refers to all parts of the vehicle that are not supported by the
suspension system, wheels, tires, etc.
High unsprung weight makes suspension movement more difficult to control.
Also See:
sprung weight
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