Modeling and Simulation of a New Type Hydraulic System on CVT

Abstract

CVT (Continuously Variable Transmission) is the ideal transmission for vehicle, for it can provide better fuel economy than other transmissions by enabling the engine to run at its most efficient revolutions area for a range of vehicle speeds. And hydraulic system is the core of CVT. This chapter presents the new design hydraulic system of CVT which focus on its efficiency. According to the CVT test carried out by Bosch Group, the pump takes the largest part in CVT’s fuel consumption. In hydraulic system of traditional CVT, pump is driven directly by engine. So its flow rate is proportional to the engine speed. We need to consider the extreme working conditions when we develop the requirement to its flow rate/power. And to satisfy the extreme conditions means to overflow on the other conditions and that costs much loss. Therefore, in traditional powertrain, the fuel consumption of CVT takes 8 % of the vehicle fuel consumption. The primary goal of this chapter is to improve the efficiency of CVT to further reduce its fuel consumption by developing the new hydraulic system. We designed a new hydraulic system for CVT, it separates the control oil and the lubricating oil. According to the vehicle performance requirement, we determined the parameters of hydraulic system. In order to verify the efficiency of this hydraulic system also to optimize its parameters, a simulation model for hydraulic system, CVT and vehicle was built up with MATLAB and SIMULINK environment. Simulations were performed under typical driving conditions such as start up, instant acceleration and vehicle run cycle, and the pressure, flux characteristics of the hydraulic system together with the whole vehicle fuel consumption were obtained. The results indicated that compared with the traditional hydraulic system, the new one has more efficiency and therefore can lower the fuel consumption of the vehicle. Through reducing the clamping force, the efficiency of CVT can also be improved. However, due to the limitation of time, the topic is not included in this research. Also, we didn’t develop the real hydraulic module to verify the system we designed. And in the future, we will develop the hydraulic module and apply it on CVT to test it’s performance on CVT test rig. All in all, this chapter introduced a new hydraulic system which separates the control oil and the lubricating oil. And through simulation, the efficiency of the new hydraulic system was proved. This research has important value for improving the efficiency of CVT.

F2012-C04-009