What Is a Segmental Bridge?

The drive axle is a mechanism at the end of the drive train that changes the speed and torque from the transmission and transmits them to the drive wheels. The drive axle is generally composed of a main reducer, a differential, a wheel transmission and a drive axle housing. The steering drive axle also has a constant velocity universal joint. In addition, the transaxle must withstand the vertical, longitudinal and lateral forces acting on the road and the frame or body, as well as braking torque and reaction forces.

The drive axle is a mechanism at the end of the drive train that changes the speed and torque from the transmission and transmits them to the drive wheels. The drive axle is generally composed of a main reducer, a differential, a wheel transmission and a drive axle housing. The steering drive axle also has a constant velocity universal joint. In addition, the transaxle must withstand the vertical, longitudinal and lateral forces acting on the road and the frame or body, as well as braking torque and reaction forces.

main decelerator

Differential

Half axis

Axle housing

Expand

Chinese name

Drive axle

Foreign name

driving axle

Classification

Non-disconnected and disconnected

Make up

Main reducer, differential, axle shaft, axle housing, etc.

Use

Car construction

Basic function

Increase torque, reduce speed, change the direction of torque transmission

Drive axle function

The drive axle is at the end of the power train. Its basic functions are: The engine torque transmitted from the universal transmission is transmitted to the drive wheels through the main reducer, differential, half shaft, etc., to reduce the speed and increase the torque. Change the transmission direction of the torque through the bevel gear pair of the main reducer; The differential effect of the wheels on both sides is achieved through the differential to ensure that the inner and outer wheels turn at different speeds; Moment effect. ^[1]

Drive axle design

The drive axle design should meet the following basic requirements:

1. The main reduction ratio should be selected to ensure that the car has the best power and fuel economy.

2. The external dimensions should be small to ensure the necessary ground clearance. It mainly means that the size of the main reducer is as small as possible.

3. The gears and other transmission parts work smoothly with low noise.

4. High transmission efficiency under various speeds and loads.

5. Under the condition of ensuring sufficient strength and stiffness, the quality should be small, especially the unsprung mass should be as small as possible to improve the ride comfort of the car.

6. Coordinate with the movement of the suspension steering mechanism. For the steering drive axle, it should also coordinate with the movement of the steering mechanism.

7. Simple structure, good processing technology, easy manufacture, convenient disassembly and adjustment.

Drive axle classification

There are two types of drive axles: non-disconnected and disconnected.

Non-disconnecting

When driving wheels with non-independent suspension, a non-disconnecting drive axle should be selected. Non-disconnected drive axle is also called integral drive axle. Its half-shaft sleeve and main reducer shell are rigidly connected with the axle shell to form an integral beam, so the half-shafts on both sides and the drive wheel oscillate in relation to each other. The components are connected to the frame. It consists of an axle housing, a main reducer, a differential, and a half shaft.

Disconnected

The drive axle adopts an independent suspension, that is, the main reducer shell is fixed on the frame, and the side axles and drive wheels on both sides can move relative to the vehicle body in the transverse plane are called disconnected drive axles.

In order to cooperate with the independent suspension, the main reducer housing is fixed on the frame (or body), the drive axle housing is segmented and connected by a hinge, or there is no other drive axle housing except the main reducer housing. In order to meet the needs of the drive wheels to independently jump up and down, universal joints are used to connect the segments of the half shaft between the differential and the wheels.

Drive axle structure

According to the structure, the drive axle can be divided into three categories:

1. Central single-stage reduction drive axle

It is the simplest type of drive axle structure, and it is the basic form of drive axle. It is dominant in heavy trucks. Generally, when the main transmission ratio is less than 6, the central single-stage reduction drive axle should be used as much as possible. The central single-stage reducer tends to adopt a hyperbolic spiral bevel gear, the driving pinion gear is supported by a riding type, and a differential lock device is available for selection.

2. Central two-stage reduction drive axle

In the domestic market, there are mainly two types of central two-stage drive axles: the design of the rear axle of a type of truck, such as Eaton series products, reserves space in the single-stage reducer in advance. When compared, a cylindrical planetary gear reduction mechanism can be installed to change the original central single-stage to a central two-stage drive axle. This reform has a high degree of "three transformations" (ie, serialization, generalization, and standardization). All bevel gears can be used universally, the diameter of the bevel gear remains the same; another type, such as Rockwell series products, when the traction and speed ratio are to be increased, the first stage bevel gear needs to be modified and then installed into the second stage cylindrical spur gear Or the helical gear becomes the required central two-stage drive axle. At this time, the axle housing can be used universally, the main reducer is not universal, and the bevel gear has 2 specifications. Because the above-mentioned central two-stage reduction bridges are all models derived from a series of products when the speed ratio of the central single-stage bridge exceeds a certain value or the total traction mass is large, they are difficult to be transformed into front drive axles. Certainly limited; therefore, in general, two-stage reduction axles generally do not develop as a basic drive axle, but exist as a drive axle derived from a special consideration.

3.Central single-stage, wheel-side reduction drive axle

Wheel-side reduction drive axles are widely used in off-highway and military vehicles such as oil fields, construction sites, and mines. Current wheel-side reduction bridges can be divided into two categories: one is a conical planetary gear-type wheel-side reduction bridge; the other is a cylindrical planetary gear-type wheel-side reduction drive bridge. The conical planetary gear wheel side reduction bridge is a wheel side reducer composed of a conical planetary gear transmission. The wheel side reduction ratio is a fixed value of 2, and it generally forms a series with the central single-stage bridge. In this series, the central single-stage bridge is still independent and can be used alone. When the output torque of the bridge needs to be increased to increase the traction force or the speed ratio, the central main reducer can be changed without adding the central main reducer. The conical planetary gear reducer can become a two-stage bridge. The difference between this type of bridge and the central two-stage reduction bridge is that the torque transmitted by the half shaft is reduced, and the increased torque is directly added to the wheel side reducer at the two shaft ends, which has a higher degree of "three transformations". However, because this type of bridge has a fixed reduction ratio of 2 at the wheel edge, the size of the central main reducer is still large, and it is generally used for on-road and off-road military vehicles. Cylindrical planetary gear type wheel side reduction bridge, single-row, ring gear fixed cylindrical planetary gear reduction bridge, the general reduction ratio is between 3 and 4.2. Because the reduction ratio of the wheel side is large, the speed ratio of the central main reducer is generally less than 3, so that the large bevel gear can take a smaller diameter to ensure that the heavy truck requires clearance from the ground. This type of bridge is larger in quality and more expensive than a single-stage reducer, and has gear transmission in the wheel valley. It can generate a large amount of heat and cause overheating when driving on the road for a long time. Therefore, as a road vehicle drive bridge, it Not as good as the central single-stage reduction bridge.

Drive axle composition

The drive axle is mainly composed of a main reducer, a differential, a half shaft and a drive axle housing.

main decelerator

The main reducer is generally used to change the transmission direction, reduce the speed, increase the torque, and ensure that the car has sufficient driving force and appropriate speed. There are many types of main reducers, including single-stage, double-stage, double-speed, and wheel-side reducers.

1) Single-stage main reducer

A device that reduces speed by a pair of reduction gears is called a single-stage reducer. Its simple structure and light weight make it widely used in light and medium-duty trucks such as Dongfeng BQl090.

2) Two-stage main reducer

For some heavy-duty trucks, a larger reduction ratio is required. If a single-stage main reducer is used, the diameter of the driven gear must be increased, which will affect the ground clearance of the drive axle. Therefore, two decelerations are used. It is often called a two-stage reducer. The two-stage reducer has two sets of reduction gears to achieve two deceleration and increase torque.

In order to improve the meshing smoothness and strength of the bevel gear pair, the first reduction gear pair is a spiral bevel gear. The secondary gear pair is a helical cylindrical gear.

The driving bevel gear rotates, which drives the driven bevel gear to rotate, thereby completing the first-level deceleration. The second-stage deceleration of the driving cylindrical gear and the driven bevel gear rotate coaxially and drive the driven cylindrical gear to perform the second-stage reduction. Since the driven spur gear is mounted on the differential case, when the driven spur gear rotates, the wheels are driven by the differential and the half shaft.

Differential

The differential is used to connect the left and right half shafts, which can make the wheels on both sides rotate at different angular speeds while transmitting torque. Ensure the wheels are rolling normally. Some multi-axle driven cars are also equipped with a differential in the transfer case or between the shafts of the through transmission, which is called an inter-axle differential. Its role is to make a differential effect between the front and rear drive wheels when the car is turning or driving on uneven roads.

Domestic cars and other types of cars basically use symmetric bevel gear ordinary differentials. The symmetrical bevel gear differential consists of planetary gears, half-shaft gears, planetary gear shafts (cross shafts or a direct shaft), and differential housings.

Most cars use a planetary gear differential. A common bevel gear differential consists of two or four bevel planetary gears, planetary gear shafts, two bevel half-shaft gears, and left and right differential housings.

Half axis

The half shaft is a solid shaft that transmits the torque from the differential to the wheels to drive the wheels to rotate and propel the car. Because the installation structure of the hub is different, the stress of the axle is also different. Therefore, the semi-shaft is divided into three types: full-floating, semi-floating, and 3 / 4-floating.

1) Full floating axle

Generally, large and medium-sized cars adopt full floating structure. The inner end of the half shaft is connected to the half shaft gear of the differential with a spline, and the outer end of the half shaft is forged with a flange, and is connected with the hub by bolts. The wheel hub is supported on the axle sleeve by two tapered roller bearings located far apart. The axle sleeve is press-fitted into the rear axle housing to form a drive axle housing. With this type of support, there is no direct connection between the half shaft and the axle housing, so that the half shaft only bears driving torque without bearing any bending moment. This half shaft is called a "full floating" half shaft. By "floating" is meant that the axle is not subject to bending loads.

Full-floating half-shaft, the flange is integrated with the shaft at the outer end. But there are also trucks that make flanges as separate parts and spline the outer ends of the axles. Therefore, the two ends of the half shaft are splined, which can be used by changing the head.

2) Semi-floating half shaft

The inner end of the semi-floating half shaft is the same as the full-floating one, and it does not bear bending and twisting. The outer end is directly supported on the inner side of the axle housing by a bearing. This type of support will subject the outer end of the axle to bending moments. Therefore, in addition to transmitting torque, this half-sleeve also partially receives bending moments, so it is called a semi-floating half shaft. This type of structure is mainly used in passenger cars.

The picture shows the drive axle of the Hongqi CA7560 premium sedan. The inner end of the semi-axis is not subject to bending moments, but the outer end must bear the full bending moment, so it is called a semi-floating support.

3) 3/4 floating axle

The 3/4 floating axle is subjected to bending moments between semi-floating and full-floating. There are not many applications for this type of axle, and it is only applied to some small sleeping cars, such as the Warsaw M20 car.

Axle housing

1) Integral axle housing

The integral axle housing is widely used because of its good strength and rigidity performance, which facilitates the installation, adjustment and maintenance of the main reducer. Integral axle housings can be divided into monolithic casting, mid-section cast-in steel pipe, and steel plate stamping and welding due to different manufacturing methods.

2) Segmented drive axle housing

The segmented axle housing is generally divided into two sections, and the two sections are connected into one by bolts. Segmented axle housings are easier to cast and machine.