have more than one path to flow from the negative
PISTON HEAD--The portion of the piston above the
to the positive terminal.
top ring.
PARKING BRAKE--See HAND BRAKE.
PISTON LANDS--The portion of the piston between
the ring grooves.
PASCAL'S LAW--A pressure applied to a confined
fluid at rest is transmitted with equal intensity
PISTON PIN--The cylindrical or tubular metal pin
throughout the fluid.
that attaches the piston to the connecting rod; also
called wrist pin.
PCV (POSITIVE CRANKCASE VENTILA-
PISTON RING--One of the rings fitted into grooves
TION)--A system that removes gasoline and
in the piston. There are two types: compression
water vapors from the engine crankcase to prevent
rings and oil control rings.
excessive crankcase pressure and contamination of
the engine oil supply.
PISTON ROD--See CONNECTING ROD.
PERIOD--The time required for the completion of
PITMAN ARM--The arm that is a part of the steering
one cycle.
gear. It is connected by linkage to the wheel
steering knuckle.
PERIPHERY--The outside surface, especially that of
a rounded object or body.
PLANETARY GEARS--A set of gears having a set of
pinions rotating around a central gear (called a sun
PERMANENT MAGNET--A piece of steel or alloy
gear).
in which molecules are so aligned that the piece
continues to exhibit magnetism without application
P I V O T I N C L I N AT I O N -- S e e K I N G P I N
of external influence.
INCLINATION.
PHASE--The angular relationship between two
PLIES--Layers of rubber-impregnated fabric that
alternating currents or voltages when the voltage or
make up the body of a tire.
current is plotted as a function of time.
PNEUMATICS--Engineering science pertaining to
PICKUP COIL--A device used in automotive
gaseous pressure and flow.
electronic ignition systems that sends electrical
PORT--An internal or external terminus of a passage
pulses to a control unit.
in a component.
PILOT--A short plug at the end of a shaft to aline it
POSITIVE--A term designating the point of higher
with another shaft or rotating part.
electrical potential when the potential difference
PING--A metallic rattling sound produced in the
between two points is considered.
combustion chamber resulting from air-fuel
POTENTIAL--A characteristic of a point in an
mixture exploding rather than burning evenly.
electric field or circuit indicated by the work
PINION--The smaller of two mating or meshing
necessary to bring a unit positive charge from
infinity; the degree of electrification as compared
to some standard (the earth, for example).
PINTLE ASSEMBLY--A swivel-type assembly used
to engage with a lunette for towing equipment.
POTENTIAL DIFFERENCE--The arithmetical dif-
ference between two electrical potentials; same as
PIPE--A type of fluid line whose dimensions are
electromotive force, electrical pressure, or voltage.
designated by nominal (approximate) outside
diameter and wall thickness.
POTENTIAL ENERGY--The energy a substance
has because of its position, its condition, or its
PISTON--In an engine, the cylindrical part that moves
chemical composition.
up and down in the cylinder.
POUR POINT--The lowest temperature at which a
PISTON BOSS--An enlarged area around the piston
liquid will flow under specified conditions.
pin hole.
POWER STEERING--A steering system that uses a
PISTON DISPLACEMENT--The volume displaced
fluid to produce an assisting hydraulic pressure on
by the piston as it moves from the bottom to the top
the steering linkage, thus reducing the steering
of the cylinder in one complete stroke.
effort on the part of the driver.
AI-17
