Operating pressure - RA27007229110X(27-9110)
- General
The following pressures are governed for controlling the hydraulic system and for operating the shift elements:
Operating pressure
RA reduced pressure or oil flow
SR lubricating pressure
M1 modulating pressure (dependent on the vacuum)
M2 modulating pressure (dependent on speed)
S1 full throttle control pressure (constant)
S2 control pressure (dependent on load)
S3 kick-down control pressure (dependent on control pressure S2)
R governor pressure
VR boosted governor pressure
SD shift pressure
The working pressure operates the multiple-disc brake B3, the brake bands and clutches.
This pressure is governed by the working pressure system. The pressure level is adapted to the particular operating state irrespective of the quantity of oil supplied from the primary or secondary pump. This enables the primary pump capacity to be kept as low as possible and high transmission efficiency to be achieved.
The working pressure is always the highest pressure in the hydraulic system. All the other pressures are derived from this maximum pressure and reduced by control valves to a lower pressure level.
The quantity is controlled by the discharge edges (h) and (j). As soon as the control valve (26) deflects to the left, the excess pumped quantity of oil is passed primarily over the discharge edge (h) to the lubricating system. The remaining excess oil flows, depending on pump speed and oil temperature, over the discharge edge (j) and the nozzle (D) back to the suction side of the primary pump.
The following operating states are allowed for:
- control in basic pressure range (deceleration)
- control under engine load
The working pressure system is influenced by:
- position of accelerator pedal
- vehicle speed
- selector level position
- gear engaged
The following elements form the working pressure system:
- working pressure control valve (28)
- basic pressure control valve (26)
- two-way ball valve(14)
- two-way ball valve(15)
- modulating pressure relief valve (25)
- non-return valve with restriction (81)
The working pressure control valve (26) determines the level of the working pressure.
This pressure varies:
- It rises by the force of the pressure in the spring chamber which, together with the spring force, acts to the right.
- Is reduced by the forces which act to the left at the control surfaces (f), (g), (l) and (m).
The basic pressure control valve (16) governs a basic pressure when a low modulating pressure "M2" exists. This pressure is derived in the basic pressure range from the working pressure "A1/AR" or governor pressure "R" and passed to the spring chamber of the valve (26).
- Control in basic pressure range (deceleration)
Working pressure system shown in selector level position "D" 2nd gear and partial throttle
The basic pressure range designates the operating state of the transmission in which the modulating pressure is zero or very low.
Reverse gear basic pressure
Working pressure "AR" flows through the two-way ball valve (15), the control edge (e) and two-way ball valve (14) to the spring chamber of the working pressure control valve (26). This pressure also acts at the annular surface (c) of the basic pressure control valve (16) and pushes the latter to the left into the govern position against the force of its spring. As a result, the inlet of the working pressure "AR" is closed at the control edge. The valve (16) controls a high pressure as the end face surface (d) is pressureless in reverse gear. The annular surface (f) and the end face surface (m) at the valve (26) are likewise pressureless. A high and constant working pressure is maintained.
1st gear basic pressure, position "2" Control as described in "Reverse-gear basic pressure".
Variations:
- Inlet → working pressure "A1"
- The end face surface (m) of the valve (26) is pressurized in addition to the annular surface (l), which results in a lower operating pressure being controlled than in reverse gear.
2nd gear basic pressure, position "2" The governor pressure "R" which increases with vehicle speed passes to the spring chamber of the valve (26). The force of the governor pressure at the annular surface (16) is, in the absence of working pressure, and at the end face surface (d) not high enough to push the valve (16) to the left into the govern position.
The valve (26) governs a working pressure which increases with the governor pressure.
- Control under engine load
1st and 2nd gear basic pressure, positions "D" and "3"
Governor pressure "R" passes to the spring chamber of the valve (26). Working pressure "AD" is switched to the end face surface (d) of the valve (16). The rising governor pressure at the annular surface (c) pushes the valve (16) to the left into the govern position, supported by the working pressure at the end face surface (d). The working pressure initially increases with the governor pressure and is then maintained at the constant level.
3rd and 4th gears basic pressure, position "D"
Control as described for 1st and 2nd gear basic pressure, position "D" and "3". In addition, the annular surface (g) at the valve (26) is pressurized which results in a lower working pressure than in 1st and 2nd gear.
Basic pressure in position "N"
A constant working pressure is governed at the working pressure control valve (26) as a result of the force of the pressure at the annular surface (l) which acts against the force of the spring. All other control surfaces are pressureless.
Diagram "control at full throttle" (maximum modulating pressure). At lower modulating pressures, the curves are shifted down, but not lower than for basic pressure control.
When the throttle is opened, modulating pressure "M2" is governed. This pressure passes to the two-way ball valve (14) and through the restriction (B) to the annular surface (f). As soon as the modulating pressure "M2" becomes higher than the pressure governed by the valve (16), the ball valve (14) shifts upward and modulating pressure "M" passes to the spring chamber of the valve (26). The pressure at the annular surface (f) acts in the direction of low working pressure.
Reverse gear working pressure
Only the annular surface (11) is pressurized at valve (26). A high working pressure is governed. At low vehicle speed or low governor pressure, the working pressure is raised in line with the pressure pattern of modulating pressure "M2".
Working pressure in 1st and 2nd gear
The annular surface (l) and the end face surface (m) at the valve (26) are connected to the working pressure. The working pressure which is governed is lower than the pressure in reverse gear. This pressure is raised in the lower vehicle speed range in accordance with torque converter adaptation.
Working pressure in 3rd and 4th gear
The annular surface (g) at the valve (26) is additionally pressurized. This results in a lower pressure than in 1st and 2nd gear. The pressure pattern is the same.