1、英文资料 Suspension Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose contributing to the cars roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicl
2、e occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations,etc. These goals are generally at odds, so the tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much a
3、s possible, because all the forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different. Leaf springs have been around sin
4、ce the early Egyptians. Ancient military engineers used leaf springs in the form of bows to power their siege engines, with little success at first. The use of leaf springs in catapults was later refined and made to work years later. Springs were not only made of metal, a sturdy tree branch could be
5、 used as a spring, such as with a bow. Horse drawn vehicles By the early 19th century most British horse carriages were equipped with springs； wooden springs in the case of light one-horse vehicles to avoid taxation, and steel springs in larger vehicles. These were made of low-carbon steel and usual
6、ly took the form of multiple layer leaf springs.1 The British steel springs were not well suited for use on Americas rough roads of the time, and could even cause coaches to collapse if cornered too fast. In the 1820s, the Abbot Downing Company of Concord, New Hampshire developed a system whereby th
7、e bodies of stagecoaches were supported on leather straps called thoroughbraces, which gave a swinging motion instead of the jolting up and down of a spring suspension (the stagecoach itself was sometimes called a thoroughbrace) Automobiles Automobiles were initially developed as self-propelled vers
8、ions of horse drawn vehicles. However, horse drawn vehicles had been designed for relatively slow speeds and their suspension was not well suited to the higher speeds permitted by the internal combustion engine. In 1903 Mors of Germany first fitted an automobile with shock absorbers. In 1920 Leyland
9、 used torsion bars in a suspension system. In 1922 independent front suspension was pioneered on the Lancia Lambda and became more common in mass market cars from 1932.2 Important properties Spring rate The spring rate (or suspension rate) is a component in setting the vehicles ride height or its lo
10、cation in the suspension stroke. Vehicles which carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke). Heavier springs are also used in performance applications where the loading conditio
11、ns experienced are more extreme. Springs that are too hard or too soft cause the suspension to become ineffective because they fail to properly isolate the vehicle from the road. Vehicles that commonly experience suspension loads heavier than normal have heavy or hard springs with a spring rate clos
12、e to the upper limit for that vehicles weight. This allows the vehicle to perform properly under a heavy load when control is limited by the inertia of the load. Riding in an empty truck used for carrying loads can be uncomfortable for passengers because of its high spring rate relative to the weigh
13、t of the vehicle. A race car would also be described as having heavy springs and would also be uncomfortably bumpy. However, even though we say they both have heavy springs, the actual spring rates for a 2000 lb race car and a 10,000 lb truck are very different. A luxury car, taxi, or passenger bus
14、would be described as having soft springs. Vehicles with worn out or damaged springs ride lower to the ground which reduces the overall amount of compression available to the suspension and increases the amount of body lean. Performance vehicles can sometimes have spring rate requirements other than
15、 vehicle weight and load. Mathematics of the spring rate Spring rate is a ratio used to measure how resistant a spring is to being compressed or expanded during the springs deflection. The magnitude of the spring force increases as deflection increases according to Hookes Law. Briefly, this can be s
16、tated as where F is the force the spring exerts k is the spring rate of the spring. x is the displacement from equilibrium length i.e. the length at which the spring is neither compressed or stretched. Spring rate is confined to a narrow interval by the weight of the vehicle,load the vehicle will ca
17、rry, and to a lesser extent by suspension geometry and performance desires. Spring rates typically have units of N/mm (or lbf/in). An example of a linear spring rate is 500 lbf/in. For every inch the spring is compressed, it exerts 500 lbf. A non-linear spring rate is one for which the relation betw
18、een the springs compression and the force exerted cannot be fitted adequately to a linear model. For example, the first inch exerts 500 lbfforce, the second inch exerts an additional 550 lbf (for a total of 1050 lbf), the third inch exerts another 600 lbf (for a total of 1650 lbf). In contrast a 500
19、 lbf/in linear spring compressed to 3 inches will only exert 1500 lbf. The spring rate of a coil spring may be calculated by a simple algebraic equation or it may be measured in a spring testing machine. The spring constant k can be calculated as follows: whered is the wire diameter, G is the spring
20、s shear modulus (e.g., about 12,000,000 lbf/in or 80 GPa for steel), and N is the number of wraps and D is the diameter of the coil. Wheel rate Wheel rate is the effective spring rate when measured at the wheel. This is as opposed to simply measuring the spring rate alone. Wheel rate is usually equa
21、l to or considerably less than the spring rate. Commonly, springs are mounted on control arms, swing arms or some other pivoting suspension member. Consider the example above where the spring rate was calculated to be 500 lbs/inch, if you were to move the wheel 1 inch (without moving the car), the s
22、pring more than likely compresses a smaller amount. Lets assume the spring moved 0.75 inches, the lever arm ratio would be 0.75 to 1. The wheel rate is calculated by taking the square of the ratio (0.5625) times the spring rate. Squaring the ratio is because the ratio has two effects on the wheel ra
23、te. The ratio applies to both the force and distance traveled. Wheel rate on independent suspension is fairly straight-forward. However, special consideration must be taken with some non-independent suspension designs. Take the case of the straight axle. When viewed from the front or rear, the wheel
24、 rate can be measured by the means above. Yet because the wheels are not independent, when viewed from the side under acceleration or braking the pivot point is at infinity (because both wheels have moved) and the spring is directly inline with the wheel contact patch. The result is often that the effective wheel rate under cornering is different from what it is under acceleration and braking. This variation in wheel rate may be minimized by locating the spring as close to the wheel as possible. Roll couple percentage
