Matching of AMT transmission and gas engine on bus

With the continuous improvement of urban bus driving comfort, economy and environmental protection requirements, the development of transmission system technology, that is, the automation of shifting and clutch operation, is the trend of the times. In developed countries and regions, such as Western Europe, urban-operated buses Almost all matched hydraulic automatic transmission (AT). Although the current domestic bus matching manual transmission is still the mainstream, the application of the new automatic transmission technology has become more and more extensive. In the long run, the city bus will surely achieve full shift automation. Taking into account the differences in market demand, choosing the right transmission automation technology route is the only way to accelerate this process.

Due to its structural characteristics, the ZF's six-speed mechanical automatic transmission AS Tronic Lite is particularly suitable for automation from manual transmissions, especially for customers who are sensitive to the cost of ownership and use. Figure 1 shows the basic structure of the AS Tronic Lite transmission.

Because the basic transmission is a six-speed manual transmission and the clutch is a common dry clutch, the intelligent electronic control system can realize the automation of shifting and clutch operation, which can effectively avoid the driver's misoperation and achieve the driving level of the skilled driver. Can give users the following obvious advantages:

1) Realize automatic shifting and reduce the labor intensity of the driver.

2) The initial procurement cost is low.

3) Compared with the manual transmission of the same configuration, the fuel consumption of the vehicle can be reduced by about 3% to 5% by eliminating the adverse effect of the driver's operation on fuel consumption.

4) Extend the clutch life by 2 to 3 times compared to the manual transmission.

5) Avoid the impact of the wrong operation on the transmission system, protect the transmission system, and reduce the failure rate of related components.

6) Reduce the dependence on the driver's driving skills and save the cost of driver training. Inexperienced drivers can also achieve better results.

7) Maintenance is easier than AT.

In 2008, ZF Suzhou first introduced AS Tronic Lite products on Shanghai buses, and fully verified the reliability and economy of the system through the operation of different working conditions. Since 2010, AS Tronic Lite has started to apply in bulk in Suzhou, and has become the standard configuration for new buses purchased in Suzhou. So far, it has maintained more than 700 units in the domestic market. In addition to the domestic market, the transmission has also become a new highlight of domestic automakers' export projects, and is exported to Taiwan, Eastern Europe and other markets in batches. From the perspective of vehicle configuration, it can be applied to cities or buses between 9 and 12 meters. In addition, in addition to a large number of mature applications with imported engines such as Cummins, the transmission has been successfully matched with mainstream domestic diesel engines such as Yuchai, Weichai, Shangchai and Xichai, and has achieved good results.

In the past two years, natural gas engine technology has been greatly developed due to the advantages of energy saving, economy and environmental protection. The output of alternative fuels, especially natural gas engine buses, has grown by leaps and bounds (see Figure 2).

Figure 2 Production of natural gas engine passenger cars

Both natural gas engines and AMT technologies are characterized by energy saving and consumption reduction. The matching power systems will effectively exert their respective advantages and achieve the best results. The simulation results of economic and environmental performance are as follows:

1) Reduce fuel costs, about 35% lower than diesel vehicles.

2) Reduce exhaust pollution, reduce CO2 emissions by about 1/3, and reduce hydrocarbon emissions by 4/5.

The huge economic advantage has attracted widespread attention in the market, and the market demand for this dynamic matching has become stronger and stronger. However, from the perspective of the structure and performance characteristics of the gas engine, this matching is facing a huge technical challenge. A detailed comparison of the characteristics of diesel engines and gas engines is given in the attached table.

Comparison of diesel engine and gas engine characteristics

During the operation of the transmission, both clutch control and shift control require accurate data on the current vehicle state. The accuracy of the engine's torque and speed signals is especially important. After the data is processed by the transmission controller, the transmission needs to be controlled in a specific process. The engine's speed and torque reach the target value to successfully complete the clutch or shifting action, so the engine's response time and accuracy are critical to the performance and reliability of the transmission. It can be seen from the attached table that compared with diesel engines, there is a big gap between gas engines and data transmission accuracy and response performance. This requires an engine and transmission supplier to work closely together to optimize their systems and interfaces, starting with control strategy optimization and fine calibration to optimize vehicle performance.

The specific optimization direction is as follows: On the one hand, according to the characteristics and requirements of AMT, assist engine manufacturers to optimize engine control: reduce the error between actual torque and CAN line broadcast torque; improve engine response speed and accuracy; reduce engine under low speed and small throttle opening The speed of the fluctuations. On the other hand, the AMT clutch control strategy and shift strategy are optimized based on gas engine characteristics.

(1) Optimized shifting strategy? Higher shifting point (compared with diesel engine), guarantees power; avoids engine speed oscillation zone after downshifting, especially in the case of air conditioning; reduces engine torque and slow speed response The impact of the increase, improve shift comfort.

(2) Optimize clutch control? Clutch self-learning strategy adjustment to avoid impact on gas engine start; optimize clutch control in sudden braking and coasting mode.

Since 2009, ZF and domestic gas engine suppliers have carried out many rounds of theoretical simulation calculations, verifications, bench tests and vehicle road tests. For the optimization of working conditions, the company finally realized high-volume applications in 2011. And achieved good market feedback. More than 300 buses matching natural gas engines and ZF AS Tronic Lite have been operating on the market so far, and their ride comfort has reached or approached the level of diesel engine vehicles, which is significantly lower than diesel engine vehicles. The user's operating costs and significant environmental advantages.

The use of AMT transmission-matched gas engines can bring significant economic benefits to customers in the commercial vehicle sector and reduce pollutant emissions. The scope of application will be extended from current urban buses to long-haul road passenger cars and medium- and heavy-duty trucks. With good market prospects and huge market potential.