Kia Carnival (2009+). Manual — part 301

VFS (Variable Force Solenoid)

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

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.

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

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

Reducing pressure

Function

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 solen), 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

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.

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.

HYDRULIC PRESSURE TABLE

Under the constant current amount of VFS (200mA), the line pressure will become as below table. Be sure that the
following data can be achieved by specific special facility or device to check the performance of A/T assembly (not on
the vehicle), however we can refer the maximum pressure value according to each element.

Solenoid valve Duty(

％)

Measured Element

Pressure kPa(Psi)

LR

2ND

UD

OD

RED*

0

100

0

100

0

LR

1030±20(149±3)

60

!

!

!

!

520±40(75±6)

75

!

!

!

!

230±40(33±6)

100

!

!

!

!

0

100

0

0

100

0

2ND

1030±20(149±3)

!

60

!

!

!

550±40(80±6)

!

75

!

!

!

220±40(32±6)

!

100

!

!

!

0

100

100

0

0

0

OD

1030±20(149±3)

!

!

!

60

!

520±40(75±6)

!

!

!

75

!

210±40(30±6)

!

!

!

100

!

0

100

100

0

0

0

UD

1030±20(149±3)

!

!

60

!

!

470±40(68±6)

!

!

75

!

!

170±40(25±6)

!

!

100

!

!

0

100

0

100

0

100

DIR*

0

75

!

!

!

!

270±40(39±6)

60

!

!

!

!

540±40(78±6)

0

!

!

!

!

1030±20(149±3)

Measuring condition:

1. PG-A (Input speed): 2,500rpm
2. Manual valve position: D
3. DCC Solenoid duty: 0

％

N-P