VRS Function
The spool rod in VFS is not duty cycled like one of PWM, it minutely vibrates at the range between the control port and exhaust port to control the hydraulic pressure. That is, it uses the equilibrium effect between the spring force and the magnetic force, the spring force is mechanical characteristics decided at the stage of design and the magnetic force is controlled by TCM. This electrical magnetic force is proportional to the current. So TCM will control the current.
In case of VFS valve, the electrical' time constant' is considered to decide the frequency for the current not to be fluctuated even though turns on or off the input signal. The electrical' time constant' is much more fast than one of mechanical so the frequency of VFS is extremely higher than the conventional PWM type.
Scheme 258
Scheme 259
The reducing pressure will be supplied to the 'Supply' port of the VFS valve on the above illustration to control the line pressure.
Scheme 260
As same as one of Alpha or Beta automatic transaxle system, this reducing valve length can be adjusted by rotating the screw on the picture. As you rotate the screw toward clockwise by 90°, the reducing pressure will increase about 1.0bar. However, the reducing pressure is used just as a ' supply pressure' for the solenoid valves (except Low & Reverse, Reduction and Damper Clutch control solenoids), so this may not be handled to rotate in the field service shop. VFS is operated based on the ' supply pressure' and it outputs the ' control pressure' to control the regulator valve indirectly. While developing the VFS system, the line pressure was used as a ' supply pressure' for VFS and other solenoid valves but it has been changed into additional ' reducing pressure' because the line pressure is variably changed by VFS so the control pressure becomes unstable and some hydraulic pressure oscillation occurred. That is why the reducing pressure has been added in the hydraulic circuit of VFS system for both 4th and 5th speed A/T.
Scheme 261
Scheme 262
The reducing pressure is about 6.5bar and this value does not be changed regardless of the driving or engine load condition. Be sure that the conventional line pressure is used for the ' supply pressure' of Low & Reverse, Reduction solenoid because the variable line pressure is not available at reverse range.