Ch 44 Motive Power Types

Vane-type phaser

A cam phaser that uses vanes inside to allow oil pressure to push against and change cam timing as it is turning.

Dual overhead cam (DOHC)

A design that. in a V-engine, includes four cams, also called a twin cam engine.

Phaser

A device that is able to shift camshaft timing while the camshaft is turning. This device takes the place of the standard timing belt pulley or timing chain gear.

Valve lifter

A device that transfers motion from the cam lobe to a pushrod or directly acts on the valve and spring, depending on if the cam is in the engine block or the cylinder head; sometimes called a tappet.

Inert Gas

A gas that will not react chemically.

Fulcrum

A half-round bearing that the rocker moves on as a bearing surface.

Parasitic loss

A loss of engine efficiency caused by internal friction, inefficient breathing, etc.

Valve face

A machined surface on the back of the valve head; this area seals onto the valve seat in the cylinder head.

Rotary engine

A non-reciprocating engine with a rotor and housing instead of pistons.

Volumetric efficiency

A ratio, given as a percentage, of the amount of air actually inducted at a given engine speed at full throttle compared to the internal engine displacement. For a normally aspirated engine (with-out supercharging or turbocharging), an engine's volumetric efficiency may peak at around 85%. Peak engine torque is developed at peak volumetric efficiency.

Coil bind

A result of excessive valve lift. When the coils of the spring touch each other, the spring breaks, flattening the cam lobe and bending the pushrod.

Reed valve

A small flexible metal plate that covers the inlet port of a two-stroke engine and opens and closes to let air and fuel into the crankcase.

Pushrod

A tubular rod that stands between the tappet and the rocker arm in an overhead valve engine; the pushrod transfers cam motion to the rocker arm.

Overhead cam (OHC) engine

An I-head engine with the camshaft located on top of the cylinder head rather than in the block.

Flathead engine

An L-head engine with valves in the block.

Horsepower

An amount of work performed in a given time.

Atkinson cycle

An engine cycle that uses a longer effective exhaust stroke than intake stroke to reduce exhaust emissions. This type of engine is widely used in hybrid-electric vehicles.

Miller cycle

An engine cycle that uses a longer exhaust stroke than intake stroke through delayed closing of the intake valve. This engine uses a supercharger to pressurize air into the cylinder when needed.

Cam-in-block engine

An engine in which the camshaft is located in the engine block rather than on the cylinder head.

Internal combustion engine

An engine that burns a fuel internally and creates movement due to thermal expansion of gases.

Freewheeling engine

An engine that has enough clearance between the piston and the valves so that in event the timing belt or chain breaks, the valves that are hanging all the way open will not contact the piston thus preventing engine damage.

Interference Engine

An engine that has minimum clearance between the valves and the pistons during normal operation; in the event that the timing belt or chain breaks, the open valves will be contacted by the piston and bend the valves, possibly breaking the piston.

Spark ignition (SI) engine

An engine that relies on an electrical spark to ignite the air and fuel mixture.

External combustion engine

An engine that runs on heat applied externally to the cylinder. For example: the steam engine.

Four-stroke engine

An engine that uses four strokes— intake, compression, power, and exhaust—to complete its cycle.

Two-stroke engine

An engine that uses only two strokes to complete its running cycle.

Piston engine

An engine that uses pistons that move when expanding gases from combustion press against them.

Valve guide

An insert in the cylinder head through which the valve stem passes and moves.

Compression-ignition (CI) engine

An internal combustion engine that uses the heat of compression to ignite the compressed air-fuel mixture.

Reciprocating motion

An up-and-down motion within the cylinder.

Tappet

Another name for a valve lifter. Tappets may be flat or have rollers to ride on the cam lobes.

Keepers

Locking devices that keep the valve retained by the valve spring seat.

After top dead center

Position of the piston once it has moved beyond top dead center.

Block deck

The "top" of the engine block and cylinder bore where the cylinder head is bolted on.

Duration

The amount of time the valve stays open, given in degrees of rotation of the crankshaft.

Torque

The amount of twisting force applied in a turning application, usually measured in foot-pounds.

Lift

The amount the valve will open. The more the valve lifts off its seat, the more air can get into and out of the engine.

Piston Skirt

The area below the ring groove area of the Piston that prevents the piston cocking and becoming jammed in the cylinder bore.

Epitrochoid curve

The circular movement around the perimeter of another circle. This is the movement that the rotary engine uses to ensure that the rotor stays in contact with the housing.

Piston clearance

The clearance between the piston and the cylinder wall that allows for lubricating oil to reduce friction.

Force

The effort to produce a push or pull action.

Cam

The egg-shaped lobe machined to a shaft used to cause opening and closing of the valves of a four-stroke cycle engine.

Powertrain control module (PCM)

The electronic "brain" controlling the engine and related systems. The PCM handles more tasks than the former ECM (engine control module) used on earlier emission-controlled vehicles.

Valve margin

The flat surface on the outer edge of the valve head between the valve head and the valve face.

Rocker arm

The fulcrum that transfers pushrod endwise motion to the valve stem.

Flywheel

The heavy, circular flat plate that keeps the engine rotating when power is not produced, such as on the exhaust, intake, and compression strokes.

Cylinder bore

The hole in the engine block that the piston fits into.

Ignition

The lighting of the fuel and air mixture in the combustion chamber.

Cam lobe centerline

The location of the cam lobe in relation to top dead center of the engine in degrees.

Ring lands

The metal between the ring grooves that supports the rings as the piston moves.

Alloy

The mixture of materials to make a substance at has properties different from the original materials. Aluminum alloy has silica added to make it perform better than pure aluminum.

Stroke

The movement of an object in a straight line. The piston sees four strokes during one combustion cycle in a four-stroke cycle engine, meaning it moves up and down twice each during a cycle.

Cam lobe separation

The number of degrees between the centerline of the intake lobe and the centerline of the exhaust lobe; this with cam duration determines the amount of valve overlap.

Throw

The offset area of the crankshaft where the connecting rod bolts on.

Drive cycle

The operating range of an engine from startup until shutdown when finished performing its job.

Camshaft

The part of the engine that activates the valve train by using lobes riding against lifters.

Bottom dead center (BDC)

The position of the piston at the end of its stroke when it is closest to the crankshaft.

Before top dead center (BTDC)

The position of the piston when it has not yet reached top dead center.

Top dead center (TDC)

The position of the piston when it is farthest from the crankshaft.

Column inertia

The principle that as a column of air flows, it creates inertia, which keeps air flowing until its inertia energy is spent; sometimes referred to as a "ram effect" when using tuned intake or exhaust systems.

Scavenging

The process of removing burned gases from the cylinder through the use of moving airflow pulling or extracting the gases out.

Lobe

The raised portion on a camshaft; used to lift the lifter and open the valve.

Pulse width modulation (PWM)

The rapid yet variable on-time signal used to smoothly actuate output devices like solenoids, lights, etc.

Power

The rate or speed at which work is done.

Piston pin boss

The reinforced area of the piston Where the piston wrist pin attaches the piston to the connecting rod.

Blow-by gas

The result of combustion gases leaking past the compression rings and getting into the crankcase.

Work

The result of force creating movement.

Cam lobe ramp

The rise of the lobe from the base circle to the top of the lobe, which is where the valve starts to lift, on the side opposite of where it starts to close.

Base circle

The rounded bottom part of the camshaft (off the lobe) where the valves remain closed or at rest.

Valve stem

The shaft that is attached to the valve head and provides the sliding surface for the valve in its guide as it opens and closes.

Engine displacement

The size of the engine given in cubic inches, cubic centimeters, and liters. It is found by multiplying the piston displacement by the number of cylinders the engine has. Sometimes called "swept volume."

Power stroke

The stroke during which combustion is pushing the piston from top dead center to bottom dead center in the cylinder. This stroke is where power is produced.

Exhaust stroke

The stroke of piston during which the exhaust valve is open and the piston is moving from bottom dead center to top dead center to push exhaust gas out of the cylinder.

Compression stroke

The stroke of the piston during which air and fuel is being compressed into a small area prior to ignition.

Intake stroke

The stroke of the piston from top dead center to bottom dead center during which the intake valve is open and air is pulled into the cylinder.

Valve overlap

The time, usually expressed in degrees of crankshaft rotation, during which both the intake valve and the exhaust valve are open at the same time.

Piston stroke

The up or down motion the piston makes from one limiting position to the other.

Piston displacement

The volume of air that is moved by the piston from bottom dead center to top dead center.

Compression ratio (CR)

The volume of the cylinder with the piston at bottom dead center as compared to the volume of the cylinder at top dead center, given in a ratio such as 9:1 CR