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.

Fig 1: Identifying VFS And ATF Temp Sensor

Courtesy of KIA MOTORS AMERICA, INC.

Characteristics of Bosch VFS:

Supply pressure : 700~1600kPa

Control pressure: typically 600~0 kPa

Current range: typically 0~1,000 mA

Dither frequency: Up to 600 Hz

Dimension: 32 mm protrusion reach 42 mm

Fig 2: Identifying Supply Port Of VFS Valve

Courtesy of KIA MOTORS AMERICA, INC.

The reducing pressure will be supplied to the' Supply' port of the VFS valve on the above illustration to control the line pressure.