Graduation Design (Dissertation) of Wuhan University of Technology

College (Department): School of International Education

Specialty amp; Class: GJ13202

Student name: Chen Yibo

Tutor: Han Aiguo

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Chapter 1.Overview of Mechanical Transmission Design

Chapter 2. Layout of transmission mechanism

2.1 Analysis of transmission mechanism layout

2.2 Component structure scheme analysis

2.2.1 Gear

2.2.2 Gear shift mechanism

2.2.3 Transmission bearing

Chapter 3 Selection of main parameters of transmission

3.1Transmission gear number determination and each gear transmission ratio assignment

3.1.1 Determines the maximum and minimum gear ratio

3.1.2 Determine each gear ratio

3.4 Allocation of gear teeth number

3.5 Calculation of each gear parameters

3.5.1Gear parameter before modification

3.5.2 Calculation of Displacement Gear Parameters

Chapter 4.Verification of gear strength

4.1 Selection principle of gear material

4.2 Calculation of each shaft torque

4.3 Gear strength check

4.3.1 Calculation and check of gear bending stress

4.3.2 Calculation and Checking of Contact Stress of Gear

Chapter 5. Structural design and strength check of shaft

5.1 Structural design of shafts

5.2 Calculation of axle load and analysis of dangerous section

5.2.1 Calculation of axle load

5.2.2 Calculation sketch of shaft and dangerous section location analysis

5.3 Strength check of shaft

5.3.1 Stiffness check of shaft

5.3.2 Strength checking of shafts

6 Synchronizer design

6.1 Determination of synchronizer main dimensions

6.2 Determination of main parameters of synchronizer ring

6.3 synchronizer spline parameter determination and calculation

6.4 Conclusion

Reference

Chapter 1.Overview of Mechanical Transmission Design

The car can adapt to various complicated conditions through changing different gear ratios of transmission, so that small torque range and speed internal combustion engine can be widely used in cars. There are neutral gear, reverse gear and forward gear in transmission to meet torque and speed requirements in different conditions. The neutral gear allows the engine to start smoothly, and cut off the engine power output timely when there is no need for power; the reverse gear allows the car to turn back to meet the demand for parking and driving in narrow spaces; the forward gear is the normal running gear of the automobile, so that the vehicle can obtain various speed and torque, and at the same time, the power of the engine is fully utilized, so that the power and fuel economy of the automobile are balanced. Transmission design, in the final analysis, is to speed up the engine and torque range, and to make it well controlled. In general, the design of the transmission needs to meet the following basic design requirements:

1. when the car gets enough power, it ensures the best fuel economy
2. power can be interrupted and transmitted at any time, so neutral gear is necessary
3. A car can travel backwards in a narrow space, so reverse gear is necessary
4. The gear shift process should be stable, and the impact and noise of the gear must be as small as possible. Therefore, gear speed synchronization measures are necessary, such as using synchronizer
5. The transmission must be reliable, which can not appear to take off the gear, simultaneously hangs more than two gear positions and other dangerous condition.
6. The transmission ratio of each gear should be reasonable. Besides, the power output device should be set up so that the power of the engine can be output externally when needed
7. The efficiency of the transmission should be high enough to ensure that the engine's power can reliably drive heavy truck.
8. when the transmission meets the basic function, it should make it lighter and reduce its volume as much as possible, thus reducing the cost of production and maintenance

With the development of the automotive industry, many types of transmission structures are used in modern automobiles, but their basic structure are approximately the same. For many large freight cars in order to obtain more continuous transmission ratio, transmission requires more gears, so some transmission is additionally provided with an auxiliary gearbox in the transmission based on a common, in order to obtain more gears, so as to meet the demand for the use of heavy vehicles. For this type of transmission, after removing the secondary gearbox, it can also be used on occasions where there is little demand for the number of gear. Generally, the transmission is composed of two parts, the power transmission mechanism and the control mechanism. In recent years, the application of electric control and hydraulic control system enables the driver to control and utilize the engine more accurately through the control of the transmission.

The manual five speed transmission design parameters are as follows

Table 1.1 Parameters of the Transmission

Chapter 2. Layout of transmission mechanism

The mechanical transmission is not only simple in structure, low in manufacturing and maintenance cost, but also reliable in operation and high in transmission efficiency. Therefore, it is widely used in many automobiles.

2.1 Analysis of transmission mechanism layout

1. Fixed shaft transmission

(1) twin-shaft transmission

Compared with the intermediate-shaft transmission, the twin-shaft transmission has simpler structure and less number of shafts and bearings, so the twin-shaft transmission is smaller in size and lower in manufacturing cost. In addition, twin-shaft transmission power is transmitted only by a pair of meshing gears, so the efficiency is high. But due to restrictions on the structure, the twin-shaft transmission cannot set direct gear, so the gear drive is very noisy when the transmission working on high-speed gear. Moreover, the two axle transmission cannot obtain a large transmission ratio under the condition of little distance between the input and output shafts. The input shaft and the output shaft of the two shaft transmission gear rotate at opposite speed, while the intermediate shaft type transmission has the first shaft and the output shaft turned the same, and can be provided with a direct gear, thereby reducing the working noise of the high gear shift.