Automobile Transmissions and Power Steering Automobiles, trucks, bus, and tractors all depend on transmissions to deliver power from the engine to the wheels, The gasoline and diel engines that power the vehicles cannot be connected directly to the wheels, becau the engines must keep turning at a certain ed to keep
from stalling. Also, different amount of torque (turning force) must be delivered to the wheels at
different times. A large amount of force is needed to get a car moving from a standstill. Less force is needed to keep the car moving once it is rolling. Going up a hill of driving at high speed requires still other amount of force. It is the job of the transmission to deliver the particular
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amount of force that is needed. The transmission also allows a motor vehicle to back up
-----gasoline and diel engines can run in only one direction, but the transmission can rever the
direction of the force. And when a car stops, the transmission lets the engine keep running without moving the wheels.
The heart of any transmission——even an automatic one—is a t of gears. Gears do not
change the power of an engine, but they can increa the torque by decreasing the speed. They can
also increa the speed by decreasing the torque.
The automobile transmission us a ries of gears which enables the engine to continue to
vehicle’’s speed is altered. Setting an automobile in operate at maximum efficiency when the vehicle
vehicle’’s weight. This motion requires a large amount of power to overcome the inertia of the vehicle
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process requires high engine speed, needed for high power, and a gradual increa in a vehicle’s
speed to avoid a jerky start. To do this, a low gear ratio is allows the crankshaft to revolve veral times in order to turn the real axle once. The low gear ratio is ud for starting, climbing steep slops, and other situations in which maximum power is required .As power needs are reduced, a cond, higher gear ratio is ud which rotates the rear axle with fewer revolutions of the crankshaft. As the car’s speed increas, successively higher gear ratios are ud until the drive from the engine to the rear wheels pass through the transmission without reduction. Two principle types of transmission are ud, manual and automatic.
The manual transmission system permits the driver to lect the desired gear ratio by
manipulating a shift lever. Besides the forward speed gears, additional gearing is incorporated to
permit the vehicle to operate in rever. Manually operated pasnger car transmission ud in the United States and Canada usually have there speeds forward and one in rever. Trucks, tractors, bus, and other heavy-duty vehicles have as many as 10 forward speeds and 2 in rever. The units are basically five-speed transmissions with a two-speed auxiliary gearbox. Transmission that are to be shifted with the vehicle in motion incorporate synchromesh units to prevent gears from clashing as they are meshed. The synchromesh unit synchronizes the speed of the gears so that they revolve at the same speed as they slide into engagement.
The automatic transmission system changes gear ratios automatically in respon to changes
in engine speed or throttle tting. The u of automatic transmissions incread tremendously
breathingafter World War Ⅱ, and they are installed in more than half of the automobile produced in the United States. Automobiles equipped with an automatic transmission have a control lever which allows the driver to lect neutral, low, drive, and rever. The engine is started in neutral, and the lever is moved to “drive
drive”” position the drive”” for normal operation when moving forward. In “drive
vehicles can accelerate from rest to maximum speed by simply depressing the accelerator. The
low”” position prevent the transmission from shifting out of the lower gear ratios.
“low
It is ud for climbing steep grades, in mud, or at other tomes when maximum power is
park”” position, which locks the transmission to prevent a parked car needed. Some units have a “park
from rolling. The automatic transmission makes it easier to drive a car, but it is less efficient than a manually shifted unit and increa gasoline consumption. For this reason, the automatic transmission is not as common in Europe, where economy of operation is a prime sales factor.
Four basic types of automatic transmissions have been developed to the point where they have been installed in production vehicles. The first consists of a standard mechanical transmission and clutch which is automatically shifted by pneumatic, hydraulic or electric power units. The cond type us a hydraulic torque converter plus a planetary gear system to increa engine torque. The third system combines a hydraulic coupling with an automatically shifted mechanical gearbox to provide torque amplification. The fourth type us one or more stages of hydraulic torque conversion to provide torque multiplication.
Automatic transmission shift in respon to signals from speed nsing and throttle position nsors. The units incorporating hydraulic torque converters u the hydraulic fluid, under pressure, to engage and dingage planetary gear trains.
Power steering system 也是汽车重要的一部分，
ambleThe car of today is larger and heavier than earlier cars; the tyres are wider, further apart and inflated to lower pressures .In addition, the trend of development has been to place more than half the weight on the front wheels, especially the weight of the engine , which itlf is larger and heavier than in the early days.
To make cars easier to steer, the gear ratio in the steering box at the end of the steering column was changed to that turning the wheel required less torque, but this incread the number of turns of the steering wheel required on modern cars without power steering compared to 2.5 or 3 turns for cars built before 1940. Modern cars with power steering only require about three turns.
Power assisted steering was first developed in the 1920s; one of the first devices was developed by an engineer at Pierce Arrow, an American make of luxury cars. The Cadillac division of General Motors was going to offer power steering as optional equipment on some models in the early 1930s,
but the depression interfered with development. During World War Ⅱ power steering was fitted to military vehicles; in 1952 Chrysler began offering it , and it is now standard equipment on many of the biggest American cars .
Electric devices were tried , but power steering today is always hydraulic , with oil pressure of perhaps 1000 psi (70kg/cm2) maintained by a pump driven by the engineer of the car . The system is a rvomechanism, or rvo loop, which makes a correction to compensate for the torque applied to the steering wheel by the driver. It consists of an actuator and a control valve. The actuator is a hydraulic cylinder with a piston, or ram, which is free to travel in either direction from the center. The function of the control valve is to respond to the torque from the steering wheel by actuating smaller valves at each end of the cylinder. The system is designed to assist the steering linkage, rather than to replace it, and it does not do all of the work of steering , but leaves some of it for the driver. Thus if the hydraulics fail the car can still be steered , though with greater effort, and at all times the feel of the road is mechanically transmitted from the front wheels to the hands of the hands of the driver on the steering wheel, an esntial element of safe driving. The power steering makes a positive contribution to safe driving in that if the driver hits a small obstacle in the road or has a flat tyre at speed, the power unit makes it easier to keep the car under control. Many large cars fitted with wide, stiff radial ply tyres would be nearly impossible to steer
fbi warning是什么意思at parking speeds without power steering.
Hydrostatic systems, designed for off-the-road vehicles, are exception to some of this, becau they dispen with the steering column and the steering box , and the steering wheel and the steered wheels are connected only by hydraulic tubes or hos.
The power steering system includes a rervoir to hold the oil. Oil pressure is always provided when the engine is running, but when the system is at rest, that is when the steering wheel is not being turned, equal pressure is available to each side of the piston in the actuator, so that it does not move.
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There are basically two types of power steering system: tho which have the control valve located within the steering box, in which ca it is usually a rotary valve, and tho in which the valve is integral with actuator, when it is an axial spool valve.
汽车传动系与动力转向装置
轿车、卡车、公交车以及拖拉机都靠汽车传动系将动力从发动机输送到车轮上。为机动车辆提供动力的汽油或柴油发动机不能直接与车轮相连，因为发动机必须以一定的速度运转以防熄火停车。必须以
一定的速度运转以防熄火停车。而且，而且，而且，在不同的时刻，在不同的时刻，在不同的时刻，需要由不同大小的需要由不同大小的力矩（旋转力）传递到车轮上。当车辆从静止开始运动的时候需要较大的力矩，而一旦启动后要维持车辆行走则需要较小的力矩。当车辆以比较高的速度爬坡的时候，还需要额外的驱动力。传动系的作用就是在需要的时候传递特定大小的力矩。传动系统也能够使机动车辆后退——虽然汽油或者柴油发动机只能够按一个方向旋转，方向旋转，但是传递系统可以改变力矩的方向。但是传递系统可以改变力矩的方向。但是传递系统可以改变力矩的方向。当车辆停止运动时，当车辆停止运动时，当车辆停止运动时，传动系统能传动系统能够使发动机保持运动而车轮不运动。够使发动机保持运动而车轮不运动。
即使是自动的，任何一个汽车传动系统的核心都是一系列齿轮装置。齿轮不改变发动机的功率大小，但它可以通过降低转速来增大转矩；也可通过减小转矩来提高转速。来提高转速。
汽车传动系是用一系列齿轮，在车速改变时，该系统能使发动机继续以最高效率运转。起动汽车需要大功率以克服车辆本身的惯性。启动过程要求发动机的转速高，即大功率所必需的转速，同时还要求汽车逐步加速，以免造成颠簸起动。为此，低速比可使曲轴传动数周而后轮轴只转一周。低速比可使曲轴传动数周而后轮轴只转一周。低速比用于起动，低速比用于起动，低速比用于起动，爬陡坡及爬陡坡及其他需要大功率的场合。其他需要大功率的场合。当功率需要减小时，当功率需要减小时，当功率需要减小时，就用较高的变速比，就用较高的变速比，就用较高的变速比，此变速比使曲此变速
比使曲轴以较少的转数带动后轮轴。轴以较少的转数带动后轮轴。随着车速的增大，随着车速的增大，随着车速的增大，要继续地使用更高的变速比，要继续地使用更高的变速比，要继续地使用更高的变速比，直直至发动机到后轮轴的传动经过传动装置时无需减速为止。传动装置主要由两类：手动的和自动的。手动的和自动的。
手动传动系要求驾驶员熟练地操纵变速杆以选择所需的变速比。汽车一般除装有前进变速齿轮外，还有辅助齿轮装置，以便倒车。在美国和加拿大，客车的手动传动系有三个前进档和一个倒车档。手动传动系有三个前进档和一个倒车档。卡车、卡车、拖拉机、拖拉机、公共汽车及其他重型车公共汽车及其他重型车辆都有十个前进挡和两个倒车档。这些机构主要有五速传动机构和一个二速辅助齿轮箱。那些使汽车在行进中可变速的传动系都装有同步齿轮变速机构，以防止齿轮啮合时碰撞。齿轮啮合时碰撞。同步齿轮变速机构使齿轮速度同步，同步齿轮变速机构使齿轮速度同步，同步齿轮变速机构使齿轮速度同步，这样，这样，这样，在这些齿轮进入啮在这些齿轮进入啮合时，能同速转动。合时，能同速转动。
自动传动系随发动机的速度变化或调速气门的变化而自动地改变速比。第二次世界大战后，应用自动换挡的车辆迅速增加。美国现今生产的汽车多半都装有
自动换挡装置。装自动换挡的汽车都有一操纵杆，驾驶员可用它选择空挡、低速、行驶和倒车速度。
发动机以空挡起动，操纵杆移至“行驶”挡为正常向前运行。挂“行驶”挡时，只要踩下加速踏板，汽车便可从静止加速到最大速度。低档位置可防止变速机构变速超出较低的变速比范围。置可防止变速机构变速超出较低的变速比范围。
fragrance抵挡用于爬陡坡、泥路或者其他需要大功率的场合。有的车还装有“停车”挡，它可锁住变速机构以防止已停止的汽车溜动。使用自动换挡装置使驾车更加容易，然而，它没有手动变速效率高，而且汽车油耗量增大。因此自动变速机构在欧洲用的并不普遍，因为在那里经济实惠是汽车销售的首要因素。在欧洲用的并不普遍，因为在那里经济实惠是汽车销售的首要因素。
现已研制处四种基本自动换挡装置，并已达到在汽车上安装使用的程度。第一种是标准的机械传动装置及靠气传动。液力或电力装置自动换挡的离合器。第二种是液力变矩器加行星齿轮机构，以增加发动机的扭矩。第三种是把液力联轴器与自动换挡机械齿轮箱结合在一起以增大扭矩。第四种是用一级或多级的液力变矩器以增大扭矩。变矩器以增大扭矩。
自动换挡是随着来自速度传感器和调速气门位置传感器的变化而变速的。自动换挡是随着来自速度传感器和调速气门位置传感器的变化而变速的。该该装置与液力变矩器相合并，利用高压液流使行星齿轮啮合或分离。装置与液力变矩器相合并，利用高压液流使行星齿轮啮合或分离。
动力转向装置也是汽车上重要的一部分，现今的汽车比早期的汽车大得多也重的多。为了降低压力，
加宽了轮胎，也加大了轮胎间距，并给轮胎充了气。此外，汽车的发展趋势主要是把一多半的重量，特别是发动机的重量，由前轮承受，发动机本身也比早期的既大又重。发动机本身也比早期的既大又重。原来如此日语
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为使汽车容易转向，改变了转向柱末端转向箱的传动比，结果只需较小的扭矩转动方向盘。然而，这与1940年以前制造的汽车需要两周半或三周的传数相比，现在无动力转向装置的转向盘所需的转数增加了，而有动力转向装置的现代汽车其转数只需三周左右。 动力转向装置早在20世纪20年代首次研制出来；最初的装置之一是由皮尔斯埃罗汽车长的一位工程师、美国豪华汽车制造商研制出来的。在20世纪30年代初期，美国通用汽车公司卡迪莱克汽车分部打算提供动力转向装置作为某些型号汽车的备选装置，但是经济萧条妨碍了其发展。在第二次世界大战期间，动力转向装置曾装在军用车辆上。1952年克莱斯勒公司开始提供这种装置。现在这种动力转向装置是美国许多大型汽车的一种标准配置。置。
虽然曾经试过电动装置，但现在用的动力转向装置常是液压的，由汽车发动机驱动一台泵，该泵使油压维持在1000泵/平方英寸（700公斤/平方厘米）。该高贵的意思
