Axle

Author: QQ Rush

Link: https://zhuanlan.zhihu.com/p/653013512

Source: Zhihu

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The axle (also known as the axle) is connected to the frame (or load-bearing body) through suspension, and its two ends are equipped with wheels. Its function is to transmit the forces and moments in all directions between the frame (or load-bearing body) and the wheels. According to the different suspension structures, the axle can be divided into two types: integral and disconnected. When non independent suspension is used, the middle of the axle is a rigid solid or hollow beam, and this type of axle is called an integral axle; The detachable axle is a movable joint structure that is used in conjunction with independent suspension. According to the function of the wheels on the axle, the axle can be further divided into four types: steering axle, drive axle, steering drive axle, and support axle. Among them, both the steering axle and the support axle belong to the driven axle. Generally, cars use the front axle as the steering axle, while the rear axle or the middle and rear axles are the drive axles. Some modern sedans and off-road vehicles have a steering drive axle on the front axle, and a single axle drive three axle vehicle (6x2 car) has a middle axle (or rear axle) as the drive axle, while the rear axle (or middle axle) is the supporting axle. The drive axle has been introduced in Chapter 18, and the supporting axle has the same functions and structure as the steering axle, except that it cannot turn. Therefore, this section mainly describes the integral and disconnected steering axles and steering drive axles. 1、 A steering axle is a device that uses the steering knuckles in the axle to allow the wheels to deflect at a certain angle, in order to achieve the steering of a car. It not only bears vertical loads, but also longitudinal and lateral forces, as well as the moments caused by these forces. The steering axle is usually located at the front of a car, so it is also commonly referred to as the front axle. The overall steering axle structure of various vehicle models is basically the same, mainly consisting of a front beam and steering knuckles. Taking the front axle of Dongfeng EQ1090E car (Figure 20-1) as an example, this will be explained. As the main component, the front beam 12 is forged from steel, and its cross-section is I-shaped to improve bending strength. To improve torsional strength, the two ends are slightly square. Two widened surfaces were machined in the middle to support the steel plate spring - spring seats (not shown in the figure). Bending downwards in the middle allows the engine position to be lowered, thereby lowering the center of gravity of the car, expanding the driver's field of view, and reducing the angle between the transmission shaft and the output shaft of the transmission. There are two bold parts at both ends of the front beam, which are fist shaped and have through holes. The main pin 10 is inserted into this hole. Fix the main pin in the punch hole with a threaded wedge-shaped locking pin to prevent it from rotating. The two ears with pin holes on steering knuckle 5 are connected to the fist of the front beam through the main pin, allowing the front wheels to deflect a certain angle around the main pin and turn the car. In order to reduce wear, a bronze bushing 7 is pressed into the pin hole of the steering joint. The lubricating oil groove on the bushing is cut through at the upper end, and lubricating grease is injected into the nozzle installed on the steering joint. For the sake of flexible and lightweight steering, a thrust roller bearing 11 is installed between the lower ear of the steering knuckle and the front beam fist. An adjusting shim 8 is installed between the ear and the fist of the steering knuckle to adjust the gap between them. On the upper ear of the left steering knuckle, there is a flange integrated with the steering knuckle arm 9, and on the lower ear, there is a flange integrated with the steering trapezoidal arm. Both flanges have a rectangular key, so there are keyways that match them on both upper and lower ears of the left steering knuckle. The steering knuckle is connected to the steering knuckle arm and trapezoidal arm through rectangular keys and double headed bolts with conical sleeves. Install a strip shaped rubber sealing gasket between the keyway end faces. The wheel hub 2 is supported on the journal at the outer end of the steering knuckle by two tapered roller bearings 3 and 4. The tightness of the bearing can be adjusted by adjusting the nut (installed on the outer end of the bearing). Cover the outer end of the wheel hub with a stamped metal cover. The inner side of the wheel hub is equipped with oil seal 6. If the oil seal leaks oil, the outer oil deflector is still sufficient to prevent lubricating oil from entering the brake, and there is a square flange on the steering joint near the main pin hole to fix the brake base plate. The front axle of the Liberation CA1091 car is similar to the above structure, as shown in Figure 20-2. Figure 20-3 shows the steering axle of Beijing BJ1040 car. The front beam 2 is formed by welding the fist shaped parts 7 at both ends with a seamless steel pipe, and this structure does not require large forging equipment to forge the front beam. The main thrust bearing 5 adopts ball bearings, which can make the steering control light. Lubricating grease can be injected through the ear oil nozzle on the steering joint, and enters the friction surface between the main pin and the bushing through the axial and radial oil holes in the main pin 8, providing lubrication. The steering knuckle arm 3 is connected to the trapezoidal arm and fixed on the lower ear of the steering knuckle, which simplifies the structure of the steering knuckle. The wheel angle limit screw 6 is used to limit the maximum wheel angle. The detachable steering axle is widely used in sedans and micro buses, and it is configured with independent suspension to form a high-performance steering axle. Due to its effective reduction of non sprung mass, the height of the engine's center of mass is lowered, thereby improving the driving smoothness and handling stability of the car. Figure 20-4 shows the structural diagram of JL6360 detachable steering axle. The disconnected steering axle (front axle) mainly consists of wheel 1, shock absorber 2, upper pivot assembly 3, buffer spring 4, steering knuckle 5, large ball pin assembly 6, lateral stabilizer assembly 7, left and right trapezoidal arms 8 and 13, main steering arm 11, middle arm 15, left and right tie rods 10 and 12, cantilever assembly 14, etc. Among them, some parts are also composed of steering and front suspension. The middle arm, main steering arm, and cantilever are all welded structures made of thin steel plates. The main steering arm is connected to the middle arm through bolts and rubber bushings (see Figure 20-5). The left and right steering trapezoidal arms are connected to the cantilever assembly 14 using a large head ball pin assembly 6. This disconnected steering axle, like the aforementioned integral steering axle, should not only have the function of carrying and transmitting force, but also have the function of achieving steering. It is coordinated with the steering gear and uses the longitudinal rod 16, main steering arm 11, middle arm 15, left and right tie rods, and left and right trapezoidal arms shown in Figure 20-4 to deflect the wheels and achieve vehicle steering.