Drive and gear reducer
driving wheel position form. Now the passenger car of drive are: the precursor, rear-drive, front drive, drive, four-wheel drive, middle middle post after flooding, rwd.
(1) the precursor
    Front engine, front wheel drive, the drive type most cars more popular, but the trucks and buses basically do not use the type of. This arrangement at present mainly in the engine by widely used car below 2.5L. Previa car layout is generally the transverse engine layout, the bridge is connected with the gear design compact drive.
    The advantage of omitting the drive shaft device, reduce weight, the structure is compact; the effective use of the engine compartment space, driving the indoor space more spacious, and helps to reduce the floor height, improve the ride comfort; the engine to the drive wheels, high efficiency of power transmission, good fuel economy; engine assembly front front axle, increase the load, improve the handling stability and braking direction stability of passenger car running at high speed; the rear suspension system.
    The disadvantages of starting, accelerating and climbing, wheel load reduction, resulting in
loss of traction; the front axle is steering axle, and drive axle, structure and complex process, high cost of manufacture, repair and maintenance difficulties; front axle load and axle load is after, front wheel and steering wheel, the front wheel poor working conditions, tire life is short.
(2) lead after flooding
    Front engine, rear wheel drive, this is one of the most traditional driving pattern.    Most of domestic trucks, cars (especially the senior car) and some buses are using this drive type, but the type of small car is very few.
    The advantages in good road starting, accelerating and climbing, increased driving wheel load (i.e., driving wheel attached pressure), the traction performance is superior to the precursor form; the axle load distribution is uniform, so it has good handling stability and ride comfort, and to prolong the service life of tire; the engine, clutch and transmission assembly near the cab, simplifies the operation mechanism of the layout; the steering wheel is a driven wheel, steering mechanism is simple in structure, easy to repair.
    The defects due to the use of drive shaft device, not only increase the weight, transmissi
on efficiency and reduce power transmission system, affect the fuel economy; longitudinal engine, gearbox and transmission shaft assembly layout, the cab space decreases, affecting ride comfort;
(3) front drive
    Front drive refers to the automobile front engine, and is a four wheel drive, used for high performance cars or SUV, advantages of using in the car is handling high, and used in off-road vehicle is through.
    The advantages of easy to slide in the snow or on the road when driving, the front stretch the body, to ensure stability; auto radiator is arranged at the front of the car, good radiation condition, the engine can get enough cooling; trunk is arranged in the rear of the car, so there is enough space in the trunk.
The disadvantages of 4WD and front steering need constant velocity universal joint, the mechanism and the more complex manufacturing processes. Once involved in a head-on collision, because of its engine and its attached
suv越野车By the gear, shaft, bearing, gear and synchronizer is composed of casing and other.
(1) gear
Helical gear reducer gear has axial force, but still with its smooth running, low noise, long service life and outstanding advantages has been widely used, and more to match transmission form normally engaged helical gear synchronizer gear sleeve shift or to. Spur gear is used only for some transmission gear and a reverse gear.
(2) the transmission shaft
    The transmission shaft work in bear torque and moment, normal mesh was deformed shaft will affect the gear, large noise, reduce the service life. Structural shape axis should ensure that the strength and rigidity, also should consider the gear, synchronizer and bearing installation, fixed, it also has a close relationship with the process.
    The first shaft and gear are made into a whole, its length is determined by the axial dimension of the clutch assembly, spline in the unity of the spline size and clutch disc hub considerations, generally by the rectangular spline gear side centering, tooth movably matched.
    Second shaft made ladder, in order to facilitate the installation of gear, but the section siz
e should not differ very much. The circlip for location of each gear is simple, but unable to bear large axial force, and the rotating parts end are sliding, so only for automobile transmission light and below. Mounted on the shaft spline synchronizer gear seat should adopt the involute spline and big diameter centering. When a reverse sliding gear gear, spline shaft with second corresponding rectangle spline and movable fit, and grinding centering diameter and tooth side. The intermediate shaft for rotating and supported on the two ends of the rolling bearing. A gear on the shaft often and made into a whole, and other gear is connected with the shaft key, which is convenient for replacing the. The fixed shaft is only play the role of the optical axis. And the body is light pressure combined with locking plate for axial positioning. Stiffness is mainly supported by the conjoined gear on the structure to ensure. The conjoined gear is supported by a needle or cylindrical roller bearings on the fixed shaft.
(3) reducer
bearing with cylindrical roller bearings and needle roller bearings. Heavy vehicles are often using smaller, larger capacity, can bear high load and improve the tapered roller bearing gr
ace axes.
    The first shaft front bearing deep groove ball bearing, deep groove ball bearing outer ring of bearing with stop groove, because it can bear radial load, axial load is also affected by outward. After bearing seat hole should be the first shaft gear through, in order to facilitate folding.
    Second shaft bearing with needle or cylindrical roller bearings, the back-end using with single-row deep-groove ball bearing dynamic slot. Some cars are often set up auxiliary support in the rear end of the shaft extension second. And the choice of deep groove ball bearing.
    Rotary shaft front end the use of cylindrical roller bearing, bearing with the stop of deep groove ball bearing groove. The middle of the axial to offset each other, offset in part by the end of the bearing. Intermediate shaft bearing radial size is often affected by the center distance limitation of size, help sometimes using cylindrical roller bearing without inner ring.
    Constant mesh gear second to the shaft supported by a needle bearing, sliding sleeve is also useful. The former compared with the latter, with high precision, small friction and spla
sh lubrication, which can meet the requirement of advantages, but on the precision of size matching, surface roughness and hardness requirements
驱动方式及减速器的传动机构
驱动方式，是指发动机的布置方式以及驱动轮的数量、位置的形式。现在乘用车的驱动方式有：前置前驱、前置后驱、前置四驱、中置后驱、中置四驱、后置后驱、后置四驱。
（1）前置前驱
发动机前置、前轮驱动，这是绝大多数轿车比较盛行的驱动型式，但货车和大客车基本上不采用该型式。这种布置形式目前主要在发动机排量为2.5L以下的乘用车广泛应用。前置前驱轿车的布局一般都是将发动机横向布置，与设计紧凑的变速驱动桥相连。
优点  省略了传动轴装置，减轻了车重，结构比较紧凑；有效地利用了发动机舱的空间，驾驶室内空间更为宽敞，并有利于降低地板高度，提高乘坐舒适性；发动机靠近驱动轮，动力传递效率高，燃油经济性好；发动机等总成前置，增加前轴的负荷，提高了轿车高速行驶时的操纵稳定性和制动时的方向稳定性；简化了后悬架系统。
    缺点  启动、加速或爬坡时，前轮负荷减少，导致牵引力下降；前桥既是转向桥，又是驱动桥，结构及工艺复杂，制造成本高、维修保养困难；前桥负荷较后轴重，并且前轮又是转向轮，故前轮工作条件恶劣，轮胎寿命短。
（2）前置后驱
发动机前置、后轮驱动，这是一种最传统的驱动型式。国内外大多数货车、部分轿车(尤其是高级轿车)和部分客车都采用这种驱动型式，但采用该型式的小型车则很少。
优点  在良好的路面上启动、加速或爬坡时，驱动轮的负荷增大(即驱动轮的附着压力增大)，其牵引性能比前置前驱型式优越；轴荷分配比较均匀，因而具有良好的操纵稳定性和行驶平顺性，并有利于延长轮胎的使用寿命；发动机、离合器和变速器等总成临近驾驶室，简化了操纵机构的布置；转向轮是从动轮，转向机构结构简单、便于维修。
缺点  由于采用传动轴装置，不仅增加车重，同时降低动力传动系的传动效率，影响了燃油经济性；纵置发动机、变速箱和传动轴等总成的布置，使驾驶室空间减小，影响乘坐舒适性；
（3）前置四驱
前置四驱是指汽车发动机前置，并且是四轮驱动，多用于高性能轿车或者SUV，用在轿车上的优点就是操控性高，而用在越野车上则是通过性更强。
优点  在积雪或易滑路面上行驶时，靠前轮牵拉车身，有利于保证方向稳定性；汽车散热器布置在汽车前部，散热条件好，发动机可得到足够的冷却；行李箱布置在汽车后部，所以有足够大的行李箱空间。
缺点  前置四驱并转向需要等速万向节，其机构和制造工艺较为复杂。一旦发生正面碰撞事故，因其发动机及其附件损失较大，维修费用高。
（4）中置后驱
中置后驱即发动机中置、后轮驱动，发动机置于座椅之后、后轴之前，大多数高性能跑车和超级跑车都采用这种型式。
优点  可获得最佳的轴荷分配，操纵稳定性和行驶平顺性较好；发动机临近驱动桥，无需传动轴，从而减轻车重，具有较高的传动效率。
缺点  发动机的布置占据了车厢和行李箱的一部分空间，通常，车厢内只能安放2个座椅；对发动机的隔音和绝热效果差，乘坐舒适性有所降低。
（5）中置四驱
中置四驱即发动机中置、四轮驱动，与中置后驱一样，高性能跑车和超级跑车都采用这种型式。不过相比中置后驱，中置四驱的操控性以及过弯极限要更强。
优点  重量集中，车身平摆方向的惯性力矩小，转弯时，转向盘操作灵敏，运动性好。
缺点  后排地板中央有突起；在雪地或易滑路面上启动加速时，后轮推动车身，易发生甩尾现象。
（6）后置后驱
后置后驱即发动机后置、后轮驱动(Rear—engine Rear—drive，简称RR），是目前大、中型客车流行的布置型式，而现代乘用车采用后置发动机的仅有保时捷911系列和Smart fortwo。
应用在乘用车上，后置发动机可以说是没有任何优点，由于后部的重量过大，在快速过弯时，整车的抓地需求绝大部分交付给了后轮，此时后轮的负担是很大的，因此一旦后轮因为速度过高，或者路况较差等原因打滑，后轮就会失控，导致无法让车辆保持既定运行轨迹。
减速器的传动机构
由齿轮，轴，轴承，啮合或同步器及壳体等组成。
（1）齿轮
斜齿轮减速机圆柱齿轮虽有轴向力，但仍以其运转平稳，噪声低，寿命长的突出优点而得到普遍采用，且多以常啮合斜齿轮的传动形式配以同步器或啮合套换档。直齿圆柱齿轮仅用于一些变速器的一档和倒档。