This article describes a new transmission control system for off-highway dump trucks with small electro-hydraulic control valves which are individually equipped for each clutch. The new system mainly improves shift shocks by generating suitable clutch pressure curves while shifting.
This system has some important technical points.
The first one is the mechanism of the small electro-hydraulic control valve. It has two spools. One spool controls clutch pressure, and another controls oil flow and senses oil pressure. This valve recognizes the moment at which the clutch pack is filled up. It enables us to control not only the pressure curves of clutches, but also the timing of engagement and disengagement of clutches.
Next technical point is that every clutch is equipped with one valve. Since one valve holds the pressure of a clutch which is being disengaged until another clutch, which is controlled by another valve, is filled up, we can keep driving torque while shifting. We developed so called “Torque-continuous shifting”.
The last point is that the clutch pressure is controlled according to driving condition by an electronic control system. Using this system, we can easily get the most suitable clutch pressure for any driving condition. One drawback of using electronic system is that it is a little troublesome for mechanics to repair or to do trouble shooting. To make the repairwork easier, we provided a self diagnosis system, which also memorizes troubles in the past in a non-volatilize random access memory.
This system has been already applied to our off-highway dump trucks since 1988, and has received good reputation.