动力转向机构
动力转向机是利用外部动力协助司机轻便操作转向盘的装置。随着Zui近汽车发动机马力的增大和扁平轮胎的普遍使用，使车重和转向阻力都加大了，动力转向机构越来越普及。转向助力不应是不变的，因为在高速行驶时，轮胎的横向阻力小，转向盘变得轻飘，很难捕捉路面的感觉，也容易造成转向过于灵敏而使汽车不易控制。在高速时要适当减低动力，但这种变化必须平顺过度。
（一）液压式动力转向装置液压式动力转向装置重量轻，结构紧凑，利于改善转向操作感觉，但液体流量的增加会加重泵的负荷，需要保持怠速旋转的机构。
（二）电动式动力转向装置电动式动力转向装置是Zui新形式的转向装置，由于它节能，故受到人们的重视。它是利用蓄电池转动电机产生推力。由于不直接使用发动机的动力，大大降低了发动机的功率损失(液压式Zui大损失5-10马力)，且不需要液压管路，便于安装。尤其有利于中置发动机后轮驱动的汽车。但目前电动式动力转向装置所得动力还比不上液压式，只限用于前轮轴轻的中置发动机后驱动的汽车上。
（三）电动液压式动力转向装置即由电机驱动转向助力泵并由计算机控制的方式，它集液压式和电动式的优点于一体。因为是计算机控制，转向助力泵不必经常工作，节省了发动机的功率。这种方式结构紧凑，便于安装布置，但液压产生的动力不能太大，适用排量小的汽车。
制动系简介
汽车制动系统的构造组成及作用
汽车上用以使外界（主要是路面）在汽车某些部分（主要是车轮）施加一定的力，从而对其进行一定程度的强制制动的一系列专门装置统称为制动系统。其作用是：使行驶中的汽车按照驾驶员的要求进行强制减速甚至停车；使已停驶的汽车在各种道路条件下（包括在坡道上）稳定驻车；使下坡行驶的汽车速度保持稳定。
制动系工作原理图
对汽车起制动作用的只能是作用在汽车上且方向与汽车行驶方向的外力，而这些外力的大小都是随机的、不可控制的，汽车上必须装设一系列专门装置以实现上述功能。
分类：
（1）按制动系统的作用
制动系统可分为行车制动系统、驻车制动系统、应急制动系统及辅助制动系统等。用以使行驶中的汽车降低速度甚至停车的制动系统称为行车制动系统；用以使已停驶的汽车驻留原地不动的制动系统则称为驻车制动系统；在行车制动系统失效的情况下，保证汽车仍能实现减速或停车的制动系统称为应急制动系统；在行车过程中，辅助行车制动系统降低车速或保持车速稳定，但不能将车辆紧急制停的制动系统称为辅助制动系统。上述各制动系统中，行车制动系统和驻车制动系统是每一辆汽车都必须具备的。
（2）按制动操纵能源
制动系统可分为人力制动系统、动力制动系统和伺服制动系统等。以驾驶员的肌体作为唯一制动能源的制动系统称为人力制动系统；完全靠由发动机的动力转化而成的气压或液压形式的势能进行制动的系统称为动力制动系统；兼用人力和发动机动力进行制动的制动系统称为伺服制动系统或助力制动系统。
（3）按制动能量的传输方式
制动系统可分为机械式、液压式、气压式、电磁式等。采用两种以上传能方式的制动系称为组合式制动系统。
制动系统一般由制动操纵机构和制动器两个主要部分组成。
1） 制动操纵机构
制动系统
产生制动动作、控制制动效果并将制动能量传输到制动器的各个部件，如图中的2、3、4、6，以及制动轮缸和制动管路。
2）制动器
产生阻碍车辆的运动或运动趋势的力(制动力)的部件。汽车上常用的制动器都是利用固定元件与旋转元件工作表面的摩擦而产生制动力矩，称为摩擦制动器。它有鼓式制动器和盘式制动器两种结构型式。
Power steering mechanism
The power steering gear is a device that uses external power toassist the driver to operate the steering wheel easily. With therecent increase of engine horsepower and the widespread use of flattires, the vehicle weight and steering resistance have increased,so the power steering mechanism is more and more popular. It isworth noting that the steering power should not be constant,because when driving at high speed, the tire's lateral resistanceis small, the steering wheel becomes light, it is difficult tocapture the feeling of the road, and it is also easy to cause thesteering too sensitive and make the car difficult to control. So weshould reduce the power properly at high speed, but the change mustbe smooth and excessive.
（1） Hydraulic power steering device the hydraulic power steeringdevice is light in weight and compact in structure, which isconducive to improving the sense of steering operation, but theincrease of liquid flow will increase the load of the pump, so itis necessary to maintain the idle rotation mechanism.
（2） Electric power steering device electric power steeringdevice is the latest form of steering device, because it isenergy-saving, so people pay attention to it. It uses the batteryto rotate the motor to generate thrust. Because the power of theengine is not used directly, the power loss of the engine isgreatly reduced (the maximum loss of hydraulic type is 5-10horsepower), and the hydraulic pipeline is not needed, which isconvenient for installation. In particular, it is conducive to themiddle engine rear wheel drive vehicles. However, at present, thepower of electric power steering device is not as good as that ofhydraulic type, so it is only used in the vehicle with light frontaxle and middle engine and rear drive.
（3） The electric hydraulic power steering device is the way thatthe power pump is driven by the motor and controlled by thecomputer. It integrates the advantages of the hydraulic type andthe electric type. Because of the computer control, the powersteering pump does not have to work frequently, saving the power ofthe engine. This method is compact in structure and easy to installand arrange, but the power generated by hydraulic pressure cannotbe too large, so it is suitable for cars with smalldisplacement.
Introduction to brake system
Structure and function of automobile brake system
A series of special devices used to make the outside world(mainly the road surface) exert certain force on some parts of thecar (mainly the wheels), so as to carry out a certain degree offorced braking on the car are collectively referred to as thebraking system. Its function is: to make the driving car decelerateor even stop according to the driver's requirements; to make thestopped car park stably under various road conditions (including onthe ramp); to keep the speed of the car running downhillstable.