Load on stationary vehicle

Load on stationary vehicle

What are the Forces on a Moving Car?

The forces acting on a moving car are thrust and drag
as well as the same forces that act on a stationary car.

Drag is the force of air resistance (a form of friction)
pushing against the front of the car while it is moving.

Thrust is the force pushing the car forwards. Thrust comes from the engine turning the wheels.

How do Wheels make a Car go Forwards?

Tyres on the wheels push backwards against the road as they try to turn, causing an equal and opposite force which pushes the car forwards.

The tyres must have good grip (a high friction)
so that they do not slide on the road surface.

If the forces of thrust and drag are equal,
then the forces are balanced and
the car will move with a constant velocity.

If the forces of thrust and drag are not equal, then
the forces are unbalanced and the car will accelerate.
The car will get faster if thrust is bigger than drag,
and slower if the drag is bigger than the thrust.

Crankshaft position sensor

Crankshaft Position Sensor

The functional objective for the crankshaft position sensor is to determine the position and/or rotational speed (RPM) of the crank. Engine control unit use the information transmitted by the sensor to control parameters such as ignition timing and fuel injection timing. The sensor output can also be related to other sensor data including the cam position to derive the current combustion cycle, this is very important for the starting of a four stroke engine. The Crankshaft Position Sensor (CPK) is always located somewhere on the engine in close proximity to the crankshaft, usually near the harmonic balancer or in the engine block aligned with a toothed wheel connected to the crankshaft. The CPK provides the data that is used to compute the engine's revolutions per minute (RPM), which is essential for proper transmission gear selection in relationship to vehicle speed and load.

Failure Symptoms

• There are three primary engine malfunction symptoms that may be indicators of CPK malfunction. If the vehicle engine is experiencing cylinder misfires, the CPK may not be providing the computer with accurate information on piston position. If the vehicle hesitates during acceleration, the CPK may not be providing cylinder position data to the computer fast enough to fire the appropriate cylinder to accelerate the vehicle in response to driver input. The most serious indication of CPK malfunction is intermittent start, and eventually no start. When the sensor fails, the computer will register a malfunction code and illuminate the check engine light on the instrument panel. There may be an indication of sensor failure due to defective electrical connections such as high resistance, or an open condition in the circuit going to the sensor or returning to the vehicle engine control module.

oxygen sensor

Introduction
The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as it exits the engine. Monitoring oxygen levels in the exhaust is a way it gauges the fuel mixture. The sensor tells the ECU if the fuel mixture is burning rich (less oxygen) or lean (more oxygen).

The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is caoted on the outside with a porous layer of platinum.Inside the bulb are two strips of platinum that serve as electrodes or contacts.Between the electrodes is a solid-state electrolyte made up of a zirconic ceramic material that acts like a galvanic battery electrolyte under certain conditions. When the sensing element is cold, the zirconia material behaves similar to an insulator . At elevated temperatures, the zirconia material performs more like a semiconductor, and can generate a characteristic voltage output on the sensor connections. The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Newer-style O2 sensors breathe through their wire connectors and have no vent hole. This is why grease should never be used on O2 sensor connectors because it can block the flow of air.

Automobiles: Air brake system

Automobiles: Air brake system: "Air Brake system Compressed air brake systems are typically used on heavy trucks and buses . The system consists of service brakes, parking..."

Air brake system

Air Brake system

Compressed air brake systems are typically used on heavy trucks and buses . The system consists of service brakes, parking brakes, a control pedal, an engine-driven air compressor and a compressed air storage tank. Compressed air brake system used both disc or drum brake arrangement. Most types of truck air brakes are drum units, though there is an increasing trend towards the use of disc brakes in this application. The air compressor air draws filtered air from the atmosphere and forces it into high-pressure reservoirs at around 120 PSI. Most heavy vehicles have a gauge within the driver's view, indicating the availability of air pressure for safe vehicle operation, often including warning tones or lights. Setting of the parking/emergency brake releases the pressurized air pressure in the lines between the compressed air storage tank and the brakes, thus actuating the (spring brake) parking braking hardware. An air pressure failure at any point would apply full spring brake pressure immediately.

Brakes are applied by pushing down the brake pedal. (It is also called the foot valve.) Pushing the pedal down harder applies more air pressure. Letting up on the brake pedal reduces the air pressure and releases the brakes. Releasing the brakes lets some compressed air go out of the system, so the air pressure in the tanks is reduced. It must be made up by the air compressor. Pressing and releasing the pedal unnecessarily can let air out faster than the compressor can replace it. If the pressure gets too low, the brakes won't work.These large vehicles also have an emergency brake system, in which the compressed air holds back a mechanical force (usually a spring) which will otherwise engage the brakes. Hence, if air pressure is lost for any reason, the brakes will engage and bring the vehicle to a stop.

A compressed air brake system is divided into a supply system and a control system. The supply system compresses, stores and supplies high-pressure air to the control system as well as to additional air operated auxiliary truck systems (gearbox shift control, clutch pedal air assistance servo, etc.).

Component of air brake system

Air Compressor

The air compressor pumps air into the air storage tanks (reservoirs). The air compressor is connected to the engine through gears or a v-belt. The compressor may be air cooled or may be cooled by the engine cooling system. It may have its own oil supply or be lubricated by engine oil. If the compressor has its own oil supply, check the oil level before driving.

Air Compressor Governor

The governor controls when the air compressor will pump air into the air storage tanks. When air tank pressure rises to the "cut-out" level (around 125 pounds per-square-inch or "psi"), the governor stops the compressor from pumping air. When the tank pressure falls to the "cut-in" pressure (around 100 psi), the governor allows the compressor to start pumping again.

Air Storage Tanks

Air storage tanks are used to hold compressed air. The number and size of air tanks varies among vehicles. The tanks will hold enough air to allow the brakes to be used several times, even if the compressor stops working.

Air Tank Drains

Compressed air usually has some water and some compressor oil in it, which is bad for the air brake system. For example, the water can freeze in cold weather and cause brake failure. The water and oil tend to collect in the bottom of the air tank. Be sure that you drain the air tanks completely. Each air tank is equipped with a drain valve in the bottom. There are two types:

· Manually operated by turning a quarter turn or by pulling a cable. You must drain the tanks yourself at the end of each day of driving. See Figure 5.1.

· Automatic--the water and oil are automatically expelled. These tanks may be equipped for manual draining as well.

Automatic air tanks are available with electric heating devices. These help prevent freezing of the automatic drain in cold weather

Alcohol Evaporator

Some air brake systems have an alcohol evaporator to put alcohol into the air system. This helps to reduce the risk of ice in air brake valves and other parts during cold weather. Ice inside the system can make the brakes stop working.

Check the alcohol container and fill up as necessary, every day during cold weather. Daily air tank drainage is still needed to get rid of water and oil. (Unless the system has automatic drain valves.)

Safety Valve

A safety relief valve is installed in the first tank the air compressor pumps air to. The safety valve protects the tank and the rest of the system from too much pressure. The valve is usually set to open at 150 psi. If the safety valve releases air, something is wrong. Have the fault fixed by a mechanic.

The Brake Pedal

You put on the brakes by pushing down the brake pedal. (It is also called the foot valve or treadle valve.) Pushing the pedal down harder applies more air pressure. Letting up on the brake pedal reduces the air pressure and releases the brakes. Releasing the brakes lets some compressed air go out of the system, so the air pressure in the tanks is reduced. It must be made up by the air compressor. Pressing and releasing the pedal unnecessarily can let air out faster than the compressor can replace it. If the pressure gets too low, the brakes won't work.

Foundation Brakes

Foundation brakes are used at each wheel. The most common type is the s-cam drum brake. The parts of the brake are discussed below.

Brake Drums, Shoes, and Linings. Brake drums are located on each end of the vehicle's axles. The wheels are bolted to the drums. The braking mechanism is inside the drum. To stop, the brake shoes and linings are pushed against the inside of the drum. This causes friction, which slows the vehicle (and creates heat). The heat a drum can take without damage depends on how hard and how long the brakes are used. Too much heat can make the brakes stop working.

S-cam Brakes. When you push the brake pedal, air is let into each brake chamber. Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake camshaft. This turns the s-cam (so called because it is shaped like the letter "S"). The s-cam forces the brake shoes away from one another and presses them against the inside of the brake drum. When you release the brake pedal, the s-cam rotates back and a spring pulls the brake shoes away from the drum, letting the wheels roll freely again. See Figure 5.2.

Wedge Brakes. In this type of brake, the brake chamber push rod pushes a wedge directly between the ends of two brake shoes. This shoves them apart and against the inside of the brake drum. Wedge brakes may have a single brake chamber, or two brake chambers, pushing wedges in at both ends of the brake shoes. Wedge type brakes may be self-adjusting or may require manual adjustment.

Disc Brakes. In air-operated disc brakes, air pressure acts on a brake chamber and slack adjuster, like s-cam brakes. But instead of the s-cam, a "power screw" is used. The pressure of the brake chamber on the slack adjuster turns the power screw. The power screw clamps the disc or rotor between the brake lining pads of a caliper, similar to a large c-clamp.

Wedge brakes and disc brakes are less common than s-cam brakes.

Supply Pressure Gauges

All vehicles with air brakes have a pressure gauge connected to the air tank. If the vehicle has a dual air brake system, there will be a gauge for each half of the system. (Or a single gauge with two needles.) Dual systems will be discussed later. These gauges tell you how much pressure is in the air tanks.