Shock absorbers reduce the effect of traveling over rough ground, leading to improved ride quality and increase in comfort. While shock absorbers serve the purpose of limiting excessive suspension movement, their intended sole purpose is to dampen spring oscillations. Shock absorbers use valving of oil and gasses to absorb excess energy from the springs. Spring rates are chosen by the manufacturer based on the weight of the vehicle, loaded and unloaded. Some people use shocks to modify spring rates but this is not the correct use. Along with hysteresis in the tire itself, they dampen the energy stored in the motion of the unsprung weight up and down. Effective wheel bounce damping may require tuning shocks to an optimal resistance.
Spring-based shock absorbers commonly use coil springs or leaf springs, though torsion bars are used in torsional shocks as well. Ideal springs alone, however, are not shock absorbers, as springs only store and do not dissipate or absorb energy. Vehicles typically employ both hydraulic shock absorbers and springs or torsion bars. In this combination, "shock absorber" refers specifically to the hydraulic piston that absorbs and dissipates vibration.
2012年10月9日星期二
Different Types of Chassis
Ladder Chassis
This is the earliest kind of chassis. From the earliest cars until the early 60s, nearly all cars in the world used it as standard. Even in today, most SUVs still employ it. Its construction, indicated by its name, looks like a ladder - two longitudinal rails interconnected by several lateral and cross braces. The longitude members are the main stress member. They deal with the load and also the longitudinal forces caused by acceleration and braking. The lateral and cross members provide resistance to lateral forces and further increase torsional rigidity.
Monocoque
Monocoque is a one-piece structure which defines the overall shape of the car. While ladder, tubular space frame and backbone chassis provides only the stress members and need to build the body around them, monocoque chassis is already incoporated with the body in a single piece,In fact, the "one-piece" chassis is actually made by welding several pieces together.
Monocoque chassis also benefit crash protection. Because it uses a lot of metal, crumple zone can be built into the structure.Another advantage is space efficiency. The whole structure is actually an outer shell, unlike other kinds of chassis, therefore there is no large transmission tunnel, high door sills, large roll over bar etc.
There are many disadvantages as well. It's very heavy, thanks to the amount of metal used. As the shell is shaped to benefit space efficiency rather than strength, and the pressed sheet metal is not as strong as metal tubes or extruded metal, the rigidity-to-weight ratio is also the lowest among all kinds of chassis bar the ancient ladder chassis. Moreover, as the whole monocoque is made of steel, unlike some other chassis which combine steel chassis and a body made of aluminium or glass-fiber, monocoque is hopelessly heavier than others.
ULSAB Monocoque
As tougher safety regulations ask for more rigid chassis, traditional steel monocoque becomes heavier than ever. As a result, car makers turned to alternative materials to replace steel, most notable is aluminium .more and more cars use aluminium in body panels like bonnet and boot lid, suspension arms and mounting sub-frames.
Backbone Chassis
Backbone chassis is very simple: a strong tubular backbone (usually in rectangular section) connects the front and rear axle and provides nearly all the mechnical strength. Inside which there is space for the drive shaft in case of front-engine, rear-wheel drive layout like the Elan. The whole drivetrain, engine and suspensions are connected to both ends of the backbone. The body is built on the backbone, usually made of glass-fibre.
Sway bar
A sway bar is usually a torsion spring that resists body roll motions. It is usually constructed out of a wide, U-shaped steel bar that connects to the body at two points, and at the left and right sides of the suspension. If the left and right wheels move together, the bar rotates about its mounting points. If the wheels move relative to each other, the bar is subjected to torsion and forced to twist. Each end of the bar is connected to an end link through a flexible joint. The sway bar end link in turn connects to a spot near a wheel or axle, permitting forces to be transferred from a heavily-loaded axle to the opposite side.
Wheel bearings
Wheel bearing are one of the most crucial components of a car's
suspension. They are usually located in the hub (the part that the
brakes and wheels are attached to) or even the brake drum or rotor
itself. Wheel bearings allow the wheel to rotate freely as the car
travels down the road. Most cars have an inner and an outer bearing on
each wheel.
Wheel Bearing Problems
Problems with wheel bearings arise from wear, which can be caused by a variety of factors. Bearings are protected from dirt and debris by oil seals. If these seals fail and dirt finds its way into the bearing, damage can occur to the bearing and the race. Another factor can be long-term wear, affecting the bearings' ability to function properly. If a bearing falls apart completely, it can render the car undriveable and dangerous. The brakes will not function correctly and the wheel will not stay in its proper orientation.
Symptoms
Symptoms of a bad bearing are noisy rubbing as the car is driven and that usually gets louder as speeds increase. If the bearings are very worn, another symptom can be vague steering, vibrating suspension and darty behavior from the suspension as the wheel moves unevenly around the bearing.
Maintenance
Bearings can be checked by jacking up the car and pushing on the wheel. If there is excessive movement of the wheel on the spindle, it's probably the bearing. Wheel-bearing maintenance is relatively simple but time-consuming, since the wheel, brakes and hub need to be removed. Once the bearing is visible, check the bearings for wear and the races for any scratches or wear. Clean everything thoroughly and repack the bearings with a generous amount of bearing grease. This should be done every 20,000 to 30,000 miles.
Replacement
Replacing bearings can be time-consuming, but most accomplished home mechanics can do the job. It involves removing the wheel, brake and hub. Once the hub is off, the bearing races are removed and new ones pressed in. This is usually the most difficult part. Once the bearings are packed and installed, everything is reinstalled in the reverse of removal. Refer to a workshop manual for detailed instructions about your car's model. This should be done every 40,000 to 50,000 miles.
Warning
A destroyed wheel bearing can result in a vehicle that is difficult to control. If you suspect that your bearings are bad, do not drive the vehicle until it is fixed or you know it is safe.
- Grease cap
- Cotter pin (Always replace)
- Lock ring
- Nut
- Thrust washer
- Outer wheel bearing
- ABS wheel speed sensor rotor (Only on vehicles with ABS)
- Brake drum
- Stub axle
- Socket-head bolt
- ABS wheel speed sensor (Only on vehicles with ABS)
- Backing plate with brake shoes
- Dished washer
- Hex bolt
Wheel Bearing Problems
Problems with wheel bearings arise from wear, which can be caused by a variety of factors. Bearings are protected from dirt and debris by oil seals. If these seals fail and dirt finds its way into the bearing, damage can occur to the bearing and the race. Another factor can be long-term wear, affecting the bearings' ability to function properly. If a bearing falls apart completely, it can render the car undriveable and dangerous. The brakes will not function correctly and the wheel will not stay in its proper orientation.
Symptoms
Symptoms of a bad bearing are noisy rubbing as the car is driven and that usually gets louder as speeds increase. If the bearings are very worn, another symptom can be vague steering, vibrating suspension and darty behavior from the suspension as the wheel moves unevenly around the bearing.
Maintenance
Bearings can be checked by jacking up the car and pushing on the wheel. If there is excessive movement of the wheel on the spindle, it's probably the bearing. Wheel-bearing maintenance is relatively simple but time-consuming, since the wheel, brakes and hub need to be removed. Once the bearing is visible, check the bearings for wear and the races for any scratches or wear. Clean everything thoroughly and repack the bearings with a generous amount of bearing grease. This should be done every 20,000 to 30,000 miles.
Replacement
Replacing bearings can be time-consuming, but most accomplished home mechanics can do the job. It involves removing the wheel, brake and hub. Once the hub is off, the bearing races are removed and new ones pressed in. This is usually the most difficult part. Once the bearings are packed and installed, everything is reinstalled in the reverse of removal. Refer to a workshop manual for detailed instructions about your car's model. This should be done every 40,000 to 50,000 miles.
Warning
A destroyed wheel bearing can result in a vehicle that is difficult to control. If you suspect that your bearings are bad, do not drive the vehicle until it is fixed or you know it is safe.
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