| Parallel
steering |
Another
term for Four-wheel steering. See Four-wheel steering |
|
|
| Parking
brake |
See
Emergency brake. |
|
|
| Particulates |
The
non-gas portion of an engine's exhaust that includes small particles
of soot, carbon and other compounds. There are EPA particulate standards
that automobile engines must meet. Diesel engines produce a high
amount of particulate emissions. |
|
|
| Parting
line |
A
line on a cast part where the molds came together. |
|
|
| Passenger
cell |
The
structure that makes up and surrounds the passenger compartment
sometimes called The Cage. Engineers strive to increase the strength
and crashworthiness of the passenger cell in modern vehicles. During
a collision, it should resist deformation and allow doors to open
so passengers can quickly exit. |
|
|
| Passive
restraint |
Devices
designed to limit movement of people's body in an automobile without
any input from passengers in order to reduce the risk of injury
in the event of a collision. Seat belts, headrests and air bags
are common examples. |
|
|
| Passive
safety |
Features
built into an automobile that are designed to protect passengers
in the event of a collision. Includes passive restraint systems,
energy absorbing steering wheel and column, padded knee bolsters
and front/rear crush zones. |
|
|
| Pawl |
A
pivoting or spring-loaded tooth that limits movement, like in a
ratchet. Automatic transmissions used a pawl for the "park"
position. When placed in "park", the pawl slides into
a notch on a drum inside the transmission and prevents the gear,
and thus, wheels from moving. |
|
|
| PCV |
See Positive
Crankcase Ventilation.
|
|
|
| Pedal |
A
floor-mounted foot controls used to remotely operate brakes, clutch
and throttle. Some vehicles use a foot-controlled emergency brake
also. |
|
|
| Pedal
effort |
The
amount of energy required to push a vehicle's pedals (brake, clutch
& gas). |
|
|
| Pedal
feedback |
Motion
or vibration transmitted back through the pedals. Usually associated
with brakes. |
|
|
| Pentroof
combustion chamber |
A
combustion chamber design that has a "wedge" or sloped
appearance to it. |
|
|
| Photochemical
smog |
See
smog |
|
|
| Pickup
truck |
A
vehicle that features an bed or open box for hauling loads and a
cab for seating two or three passengers. Pickup trucks have become
extremely popular due to there versatility and ruggedness. The come
in come in many designs; extended cab, four-door, short box, long
box, two-wheel drive and four-wheel drive. As popularity has risen
and pickup trucks are more and more being driven by commuters rather
than construction workers and farmers, manufacturers have adopted
a more car-like suspension. Pickup trucks also come in different
classes; compact, mid-sized and full-sized trucks. Compact trucks
often come with four or six cylinder engines while full-sized pickup
trucks can have eight and even ten cylinder engines. |
|
|
| Pillarless |
A
chassis design where the traditional B-pillar has been omitted leaving
an unobstructed view between front and rear sideglass windows. Usually
done for styling reasons. Can be a four-door design such as was
used by several full-sized mid-sixties sedans, or a two-door design
where the glass from the front door meets glass from the rear quarter
window. On a four-door design, there is often a B-pillar that protrudes
from the chassis to mount the doors but does not extend above the
doors. |
|
|
| Pilot
bearing |
A
bearing that is placed in the rear of the crankshaft that supports
the transmission's front input shaft. Used with manual transmissions.
The bearing can be a ball or needle bearing, or brass bushing. Not
used with automatic transmissions. |
|
|
| Pilot
production |
A
new assembly plant, or modified assembly process where production
occurs in order to monitor and evaluate new machines and construction
processes/techniques. Vehicle construction is generally slow but
the focus is on monitoring and tweaking the machines and assembly
process for a period before going into full production. Pilot car
are generally not offered for sale to the general public but are
kept by the manufacturer and evaluated for quality control purposes.
|
|
|
| Ping |
Another
term for Detonation. See Detonation. |
|
|
| Pinion
gear |
A
small gear with few teeth that meshes with a larger gear or rack.
In an automobile, a small pinion gear is found in a Rack and
pinion steering, inside many starter motors, and inside a live
rear axle (differential). |
|
|
| Piston |
A cylindrical
object used in several locations in the typical automobile to
create mechanical motion. In an engine, pistons are used in the
cylinders to convert the energy of expanding combusted gasses
into mechanical motion. The pistons are connected to the crankshaft
by connecting rods.
In the brake
system, tiny pistons are used in the master brake cylinder to
pressurize hydraulic fluid. Pistons are used in wheel cylinders
and disc brake calipers at each wheel to transfer the hydraulic
pressure back into mechanical motion which produces braking.
|
|
|
| Piston
displacement |
See
Displacement. |
|
|
| Piston
pin |
A
cylindrical tubular metal pin that connects an engine's piston to
a connecting rod. |
|
|
| Piston
pin bushing |
A
small bushing that fits inside the small end of the connecting rod
(end which attaches to the piston) and serves as a bearing for the
piston pin. |
|
|
| Piston
rings |
Thin
metal rings that fit in grooves around the the outside of pistons
and form a seal between the piston and the cylinder wall. Automotive
engines typically use three rings per piston - the top two rings,
compression rings, prevent expanding combusting gasses from leaking
past the piston into the crankcase. The bottom ring is an oil control
ring which prevents crankcase oil from getting into the cylinder.
On small engines such as lawn mower engines only one compression
ring is sometimes used. |
|
|
| Piston
skirt |
See
Skirt. |
|
|
| Piston
slap |
An
undesirable engine noise caused by a worn piston (or worn cylinder
walls). If the engine's cylinder walls or the piston is worn, the
piston can bounce side-to-side in the cylinder as it travels up
and down. Typically sounds like a muffled, hollow slapping noise.
Greater tendency to occur when the engine is cold but can go away
once the piston warms up and expands to fit the cylinder better. |
|
|
| Pitch |
1. The forward
and rearward rocking motion in an automobile, like caused when
brakes are applied or shocks are worn.
2. The distance
between threads on a bolt; Thread pitch.
|
|
|
| Pitman
arm |
A
short, heavy-duty arm that comes off the steering box and attaches
to steering linkages. Connects to the pitman shaft of the steering
box and converts rotary shaft motion into lateral motion which moves
the wheels side-to-side. Removing a pitman arm typically requires
a pitman arm puller. |
|
|
| Pitman
arm puller |
A
tool designed specifically for removing pitman arms. The typical
pitman arm pullers resembles a small gear puller but is usually
nonadjustable and very heavy-duty in construction - pitman arms
often require significant force to remove. |
|
|
| Planetary
gears |
A
unique gear design where a central gear (the sun gear) is
surrounded by two or three smaller planet gears. The planet
gears spin on their own axis and their teeth mesh with the sun gear
and teeth of another gear, a ring gear, which surrounds them. Holding
one of the gear elements motionless produces different ratios on
the other gears. Planetary gears are used widely in automotive transmissions,
particularly overdrive transmissions. |
|
|
| Plan
view |
An
overhead view of an object; looking at an object from above. |
|
|
| Platform |
The
basic chassis structure, frame or foundation of a vehicle. Often
manufacturers produce several different models based on a common
chassis platform but change some structural components and outer
body panels. Many steering and driveline components are shared among
different models of the same platform which reduces manufacturing
costs. General Motors "J" and "X" body cars
are a good example as is the Chrysler "K" car which was
used as the basis of several automobile models and minivans. |
|
|
| Plenum |
A
chamber where air or gas is combined or travels. An engine's intake
manifold contains a plenum where the air/fuel mixture travels to
the cylinders. |
|
|
| Plexiglass |
Clear
plastic panels that are often used in place of glass particularly
for racing. A trade name by Dow Chemicals. |
|
|
| Plies |
Wide
layers of reinforcing fabric used inside tires to provide strength
and durability to the tread and sidewall areas. Typically made of
cord, fiberglass and steel. Several plies, also called belts, are
and laid down in different orientations to each other. A typical
passenger car tire may have four plies (layer of belts) while truck
tires may have from 6 to 20+ plies. More plies yield a sturdier
tire capable of carrying heavier loads. |
|
|
| Plow |
Same as Understeer.
The tendency for a vehicle to want to travel straight ahead during
a curve. Requires extra effort to turn the vehicle.
Also, can
apply to a snow plow which can be mounted to a pickup truck.
|
|
|
| Plug |
See
Sparkplug. |
|
|
| Plus
fitments |
A
tire and wheel fitting system designed to help owners determine
tire/wheel size and combinations when switching to high performance
tires. When switching to low-profile high-performance tires using
the same wheels, outside wheel diameter changes which can throw
off the speedometer and vehicle computer system, not to mention
overall vehicle appearance. To switch to a low profile tire yet
keep the same overall tire diameter, rim size must be increased.
Plus 1 fitment means increasing rim diameter on size (14" to
15"). If very high-performance tires are purchased it might
require stepping up two rim sizes; Plus 2 (eg. 14" to 16")
to maintain the same overall wheel diameter. |
|
|
| Ply
rating |
An
index of a tire's strength that was at one time related to the number
of plies used in tire construction. However, modern materials have
different material strengths which can compensate for reduced plies
so the ply rating is no longer strictly represented by the number
of plies in a tire. |
|
|
| P-metric |
A tire rating
system adopted in 1976 by U.S. tire manufacturers. An example
is P195/75R14. The first letter "P" stands for passenger
and would be suitable as a passenger car tire. 195 is the tire's
section width in millimeters (sidewall-to-sidewall). 75 is the
tire's aspect ratio (the ratio of section height to section width).
R designates the tire as a radial tire. The last number identifies
the wheel diameter it will fit. A letter preceding the construction
type would indicate it's speed rating. LT stands for light truck
tire.
The metric
rating system used in Europe does not require the use of a P (passenger)
but does require a speed rating designation.
|
|
|
| Pneumatic
tire |
A
tire which is filled with air. |
|
|
| Pneumatic
tools |
Air
Tools. Tools which use compressed air rather than electricity to
function. |
|
|
| Pneumatic
trail |
A
phenomenon where a tire's contact patch is move slightly rearward
of it's center. Caused by rolling and other dynamic forces. |
|
|
| Points |
Shortened
term for breaker points. See Breaker points. |
|
|
| Pollution |
Harmful
exhaust emissions that lead to smog, acid rain and other environmentally
damaging conditions. See Exhaust emissions. |
|
|
| Polyellipsoid |
Having
two or more elliptical lobes or shapes. |
|
|
| Pop-off
valve |
A
valve rarely used in automobiles that limits pressure to a certain
level. If pressure is exceeded the valve "pops-off". Used
in racing engines on turbo chargers and superchargers to limit boost. |
|
|
| Poppet
valve |
The
type of mushroom-shaped valve used in almost all automobile engines
for intake and exhaust valves. Called a poppet valve because it
"pops" open. |
|
|
| Pop
rivet |
A
small metal fastener useful because it can be installed quickly
from one side of an object or panel. The fastener has a hollow metal
core where a shaft with a ball on the end is pulled through. As
the shaft/ball is pulled through it expands the cylinder to fit
tight in the hole. The metal shaft is designed to break off once
tight and enough pressure is applied. |
|
|
| Porpoising |
A
ride condition where a vehicle's nose rises and falls rhythmically
over a series of bumps. Worn shocks increase porpoising. |
|
|
| Port |
See Exhaust or Intake port. |
|
|
| Port
fuel injection |
A
fuel injection system where the fuel is sprayed directly into the
intake ports near the intake valves. See Fuel injection. |
|
|
| Positive
camber |
An
alignment term where the top of the wheels are tilted outward (from
vertical) away from the vehicle. An undesirable condition. |
|
|
| Positive
Crankcase Ventilation (PVC) |
An
emission control system used on nearly every vehicle in which crankcase
vapors are recirculated back into the combustion chamber, usually
through the PVC valve into the engine's intake, and reburned rather
than be discharged into the atmosphere. Also known as Closed Crankcase
Ventilation system. |
|
|
| Positive
offset |
The
position of the tire's center (where the rubber meets the ground)
in relation to the axis which the wheels are steered (line from
upper ball joint or strut through lower ball joint to ground). Positive
offset is where the steering axis line is inside the center of the
tire's contact area on the ground. Installing wider rims generally
increases offset because it moves the tire's footprint further away
from the steering axis. |
|
|
| Pound-feet |
A
unit which engine torque is measured by. The twisting force is measured
in pounds. |
|
|
| Pounds
per Square Inch (PSI) |
A
unit of measure of pressure. For example, passenger car tires are
generally require 35 psi of air pressure. |
|
|
| Pour
point |
A
term used by the oil industry which is the lowest temperature that
an oil will flow. Indicates an oil's ability to flow and lubricate
in cold weather. Multiviscocity oils (10W 30) have lower pour point
than single weight oils (eg. SAE30). |
|
|
| Power |
The rate
at which work is done. Most common measurements used in the United
States is ft-lb/sec and horsepower.
Also refers
to automotive accessories such as power assist steering, power
windows/seats that reduce input effort.
|
|
|
| Power
antenna |
An antenna
which telescopes by way of an electric motor, usually when the
radio is switched on and retracts when the car is shut off or
radio is no longer in use; for purposes of styling and to prevent
damage to an antenna.
Although
there are several designs, the most common electric antennas have
several relatively loose-fitting stainless steel sections that
telescope outward and collapse into a compact size. A rigid, yet
flexible steel or nylon strip is wrapped around a reel and is
securely attached to the inside of the uppermost telescoping antenna
section. When activated by an electric switch (either manually
or part of the radio switch) an electric motor unreels the steel
or nylon strip which forces the top antenna section upward telescoping
all sections in the process.
|
|
|
| Power-assisted
brakes |
See
Power brakes (below). |
|
|
| Power-assisted
steering |
See
Power steering (below) |
|
|
| Power
band |
The
range of rpm's where an engine delivers the majority of it's peak
power. Usually begins below the engine's torque peak and extends
to it's power peak. |
|
|
| Power
brakes |
A
brake system that uses engine vacuum or hydraulic power to help
the driver apply the brakes using less force than would otherwise
be necessary. The typical system uses a brake booster which uses
engine intake vacuum and valves to help apply the brakes as the
pedal is pushed. |
|
|
| Power
curve |
A
graphical representation of an engine's power relative to it's speed
as measured on a dynamometer. Power output is measured on a dynamometer
at various speeds and plotted on a graph. Rpm is typically horizontally
and power output, vertically. The main purpose is for comparing
engine modifications or comparing different engine outputs. Kilowatts
is used in place of horsepower in Europe. |
|
|
| Power
door locks |
A
standard or optional feature on automobiles that allows passengers
to lock/unlock doors with an electrical switch rather than moving
mechanical levers. Solenoids are mounted to the door locking mechanism
inside each door and connected via wires to the battery and a switch.
The main attraction of power door locks is being able to lock/unlock
all doors from one conveniently located switch, or remotely from
an infrared remote control. |
|
|
| Power
inverter |
An
electrical device which can be used to step up voltage to higher
voltages. Typically used in automobiles to operate 110V appliances
from a 12V power source. |
|
|
| Power
peak |
The
maximum power output of an engine; the highest point on a power
curve. |
|
|
| Power
plant |
Another
term for a vehicle's engine. |
|
|
| Power
seats |
Seats
which contain small electric motors and a unique frame below the
seat to move the position of the seat by electrical means. Power
seats offer a wider range of adjustment than manually adjusted seats.
6-way power seats can adjust the pitch of the front or rear of the
lower seat, it's height, and forward/back position. Some vehicles
have 10-way power seats which control the pitch of the seat back. |
|
|
| Power
steering |
A steering
system which uses hydraulic pressure to reduce steering effort.
The main components of a power steering system include a hydraulic
pump (commonly called the power steering pump), which is
mounted to the engine and driven by a belt driven off it's crankshaft;
a power steering fluid reservoir which can be integral with the
pump, or mounted elsewhere in the engine compartment, the steering
box or steering rack; hydraulic lines which connect all the components
together; and hydraulic fluid, commonly referred to as power steering
fluid. Dextron III, a type of hydraulic fluid which is commonly
used in automatic transmissions, is frequently used as power steering
fluid.
The engine-driven
pump forces pressurized hydraulic fluid through hydraulic lines
to the steering box (or steering rack). When the steering wheel
is turned, valves inside the steering box or steering rack increase
hydraulic pressure to one side or chamber to help turn the wheels.
Power steering is also referred to as power-assisted steering.
Also see, Recirculating ball-and-nut steering, and Rack-and-pinion
steering.
|
|
|
| Power
stroke |
The
third stroke in a four-stroke motor. Combustion of an air/fuel mix
in the combustion chamber (basically a small explosion) forces the
piston downward from it's highest point in the cylinder to it's
lowest point. During the power stroke, the intake and exhaust valves
are both closed. Called the "power stroke" because it
is the only stroke that produces power; all other strokes consume
power. |
|
|
| Power
train |
The
components in an automobile that produce and transmit power to the
wheels. Includes the engine, transmission, differential and driveshafts. |
|
|
| Power
valve |
A
vacuum or mechanically operated valve in a carburetor that adds
additional fuel to the engine when the throttle is wide open. On
many carburetors it is a plunger or rubber diaphragm that squirts
extra gas into the airstream when the pedal is pressed to the floor. |
|
|
| Power
windows |
A
standard or optional feature on many automobiles which allows passengers
to lower side windows through the use of an electric switch rather
than cranking a lever. Inside each door, an electric motor is mounted
to the window regulator. The motors are connected to the battery
and an electric switch via wires. The main advantages of power windows
include reduced lowering effort, one-touch lowering/raising feature,
allowing the driver to open/close any window from one convenient
location and safety -- reducing driver distraction. |
|
|
| Prechamber
injection |
See
Fuel injection. |
|
|
| Preignition |
Combustion
in the cylinder that occurs before ignition spark (from spark plug)
occurs. An undesirable condition which can damage pistons if allowed
to persist. Caused by carbon deposit buildup in the combustion chamber,
unusually hot conditions or unusually high combustion chamber pressures.
|
|
|
| Preload |
Adding
weight or pressure to a part to give it certain operating characteristics,
such a adding weight to a ball joint to reduce looseness, etc. |
|
|
| Press-fit |
Fitting
parts together by pressing in rather than using fasteners. Many
automotive parts such as bearings, bushings and suspension parts
(ball joints) are pressed into parts with machined bores with a
hydraulic press. |
|
|
| Pressure |
Force
per unit area. Expressed in measurements such as pounds per square
inch and kilograms per square centimeter. |
|
|
| Pressure
cap |
Another
term for Radiator cap. Radiator caps on modern vehicles are spring
loaded and have a valve that opens to allow fluid to escape if pressure
becomes too high and allows air/coolant to enter if a vacuum is
created. By keeping the coolant under pressure the boiling temperature
of the coolant is raised allowing the motor to operate at higher
and more efficient temperatures. Most caps have pressures that range
from 10-15 lbs. |
|
|
| Pressure
gauge |
A gauge used
to measure air or fluid pressure. Typical automotive pressure
gauges include: Tire pressure gauge, Boost gauge (for turbo or
super chargers) and oil pressure gauge. Race cars also often have
fuel pressure gauges.
Also see
Tire pressure gauge.
|
|
|
| Pressure
plate |
See
Clutch pressure plate |
|
|
| Pressure
relief valve |
A
one-way valve that opens when internal pressure exceeds a set pressure
limit to relieve internal pressure and reduce the risk of damage.
A radiator cap has a pressure relief valve as does an engine's oiling
system. |
|
|
| Primary
brake shoe |
The
forward or leading shoe in a drum brake system that begins the process
of self-energization when the brakes are applied. Self-energization
in the brake system is the the process of producing more pressure
to the brake shoes than the pressure applied by the hydraulic system
itself. How this works is, when both brake shoes are pushed outward
against the brake drum, the friction of the shoes against the spinning
drum creates a twisting motion on the shoes. They become "cocked"
inside the drum which forces the shoes against the drum with even
greater pressure. The primary shoe, sometimes called the leading
shoe essentially pushes the trailing shoe even harder against the
drum. The twisting force that causes amplification of brake forces
is called servo action. |
|
|
| Primary
circuit |
Low-voltage
current that flows from the battery to the primary coils of the
coil, through the breaker points and back to the battery.
Also, the
main passages in a carburetor where fuel flows to the jets.
|
|
|
| Profile |
See
Aspect Ratio. |
|
|
| Programmable
read-only memory (PROM) |
A
type of memory chip used in vehicle computers that contains pre-programed
information that cannot be changed. Aftermarket PROMS are available
to increase engine performance by changing certain fuel and ignition
characteristics. |
|
|
| Progressive-rate
springs |
Suspension
springs in which spring pressures vary throughout compression. Engineers
vary wire diameter and distance between coils in an effort to compensate
for increased vehicle loads and to strike a balance between a smooth
ride over small bumps yet firm control over large bumps. |
|
|
| Progressive
transmission |
A
transmission design used in vintage automobiles where the operator
was required to shift through all gears in sequence. Shifting down
also required shifting from fourth gear to third, to second and
finally back to first gear. |
|
|
| PROM |
See
Program Read Only Memory. |
|
|
| Propane |
A
liquefied gas which can be burned in engines. Some municipalities
use propane in their fleet vehicles to reduce fuel and maintenance
costs. See Liquefied petroleum gas. |
|
|
| Propeller
shaft |
Another
term for driveshaft. See Driveshaft. |
|
|
| Proving
ground |
A
facility where prototype vehicles are tested by manufacturers usually
before they go into production. Proving grounds try to duplicate
the kinds of terrain that a vehicle would be driven in daily. Drivers
put many miles on test vehicles to uncover design and manufacturing
weaknesses so they may be corrected before the vehicle goes into
production. Usually includes roads of a variety of quality, water
splash areas, skid pad test area, and off-road obstacles for testing
trucks and sport utility vehicles. |
|
|
| PTO |
Stands
for Power Take Off ; an additional output shaft separate from the
main output shaft (that drives the wheels), which can be used to
drive accessories. Allows the engine to directly drive hydraulic
pumps or shafts which can be used for operating hydraulically tiltable
beds, a winch or other devices. Found on the the transmissions of
large trucks and on the transfer case of some pickups. |
|
|
| Pull |
An
undesirable handling condition where a vehicle wants to steer in
one particular direction. When the steering wheel is left go, the
vehicle will quickly and automatically head in the same direction.
Usually caused by improper wheel alignment, worn steering bushings,
improper tire inflation or dragging brakes. |
|
|
| Pulley |
A
wheel with a V-shaped groove around it's outer edge in which a belt
can run and drive accessories. Modern automobiles use serpentine
belts which are wider and contain many grooves that provide greater
traction. |
|
|
| Pulsed
air injection |
See
Air injection system. |
|
|
| Pulsed
injection |
An
injection system that pulses fuel injectors as a way of metering
fuel to an engine. This method sends fuel to the cylinder at a precise
time - when the intake valve opens. In another popular injection
system, Continuous flow injection (e.g.. throttle-body injection),
fuel flow through the injectors is continuous when the motor is
running. |
|
|
| Pump
octane |
See
Octane number. |
|
|
| Push |
An
undesirable handling characteristic where the vehicle tends to want
to plow straight ahead around a corner. Also called Understeer. |
|
|
| Push
bar |
See
Grille guard. |
|
|
| Push-pull
suspension |
A
somewhat complicated suspension design used in racing where inboard
mounted spring/shock units are actuated by a linkage system. The
main purpose of this design is to move the springs and shocks away
from the wheel in order to reduce aerodynamic drag. |
|
|
| Pushrod |
A
long thin rod used in overhead valve engines that is connected between
and transfers motion from the camshaft lifters in the center of
the motor to the valve train at the top of the cylinder heads. The
rods on most engines are hollow so pressurized oil can flow from
the lifters to the top of the motor and lubricate the rocker arms.
|
|
|
| Push-rod
suspension |
See
Push-pull suspension. |
|
|
| Pyrometer |
An
instrument to measure high temperatures. Commonly used in racing
to check tire temperatures. |
