Transmission control, function

P27.19-2260-76

Exploded view

1 Carrier

2 Electrical connection

3 Twin-pipe vane-type oil pump

4 Valve body

5 Intermediate panel

6 Slide valve housing

7 Regulating valve for torque converter lockup clutch

8 Regulating valve for supply pressure limiter

9 Regulating valve for valve supply

10 Regulating valve lubrication

11 Limp-home mode shift valve 1

12 Regulating valve for secondary pressure

13 Regulating valve for auxiliary pressure

14 Limp-home mode shift valve 2

15 Regulating valve for supply pressure

16 Regulating valve for clutch control

17 Shift valve for radiator bypass

Y3/9y2 CVT secondary-control solenoid valve

Y3/9y3 CVT clutch control solenoid valve

Y3/9y4 CVT control solenoid valve for torque converter lockup clutch

Y3/9b3 CVT primary rpm sensor

Y3/9b4 CVT secondary rpm sensor

Y3/9b5 CVT output rpm sensor

Y3/9n1 Continuously variable transmission control unit

Y3/9y1 CVT primary-control solenoid valve

Function requirements for transmission control, general

 Circuit 87 ON

Transmission control, general

In the electronically-regulated, continuously variable, automatic transmission (CVT), all transmission functions and transmission components are combined in a single assembly module (CVT electric controller unit (Y3/9)).

The CVT electric controller unit contains:

- CVT control unit with integrated temperature sensor and oil pressure sensor for supply pressure

- CVT primary, secondary and output rpm sensor

- CVT primary and secondary control solenoid valve

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- CVT clutch control solenoid valve and CVT control solenoid valve for torque converter lockup clutch

- Oil pressure sensor for secondary pressure

- Valve housing with 12 slide valves

- Valve housing with selector valve

- Selector lever slider for detection of positions "P, R, N, D"

Transmission control function sequence

The function sequence is subdivided into the following steps:

 Basic shift program function sequence

 Electronic and hydraulic transmission control function sequence

 Variables, function sequence

 Oil supply, function sequence

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Basic shift program function sequence

The basic shift program contains the gear ratio regulation, designed for:

- Empty vehicle

- Warm operating condition

- Level road

- Sea level

The gear ratio regulation is adapted according to:

- Vehicle load

- Change in driving resistance

- Pedal movement

The CVT control unit (Y3/9n1) monitors and shifts depending on:

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- Vehicle speed

- Selector lever position

- Transmission mode selection

- Signals on engine compartment CAN (CAN-C)

Electronic and hydraulic transmission control function sequence

The electronic part calculates the actuation currents required for controlling the control solenoid valves. The control solenoid valves then convert the actuation currents into oil pressure.

The hydraulic control distributes the oil of the twin-pipe vane-type oil pump to the following consumers depending on the oil pressures:

- Primary pulley set

- Secondary pulley set

- Reverse gear set

- 2-channel torque converter

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Variables, function sequence

The following variables are relevant for the driving strategy:

- Road gradient

- Payload

- Driving resistance

- Accelerator pedal movement

- Shifting frequency

- Vehicle longitudinal and lateral acceleration

Through recognition of the influencing variables the correct gear ratio for the vehicle is selected for each operating condition and for every driver command. The CVT electric controller unit actuates the control solenoid valve for the CVT torque converter lockup clutch and thus influences the oil pressure in the torque converter lockup clutch (slip control), taking the following parameters into consideration:

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- Engine load

- Vehicle speed

- Vehicle acceleration

- Transmission oil temperature

- Frictional power entry

- Aging effects of hydraulics and mechanics

Oil supply, function sequence

The oil feed for cooling and lubrication of the hydraulic elements is performed using a twin-pipe vane-type oil pump with two irrespective, pressure-regulated outputs. Additionally, the demand-based pressure control at the outputs allows a reduction in fuel consumption.

The twin-pipe vane-type oil pump has a nominative pressure range of 4.5 to 67.0 bar and an rpm range of 740 to 7000 rpm

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The CVT control unit regulates via the control solenoid valves the required oil pressure taking the following parameters into account:

- Engine load

- Wheel speed

- Accelerator pedal position

- Selector lever position

- Transmission mode switch

- Internal sensors for rotational speed, oil temperature and oil pressure

The required oil pressure for the primary and secondary pulley sets and the contact pressure of the thrust link belt are regulated by the CVT secondary control solenoid valve via the secondary pressure valve. The hydraulic pressure application of the pulley sets axially displaces the moveable pulleys. This in turn enables the contact pressure of the thrust link belt and the gear ratio to be continuously varied.

The oil pressure sensor forwards the current oil pressure (secondary pressure) to the CVT control unit.

Prioritization of the variator control guarantees each driving situation a reliable contact pressure of the thrust link belt and any slip of the thrust link belt is avoided.

The torque converter lockup clutch, reverse gear set and primary pulley set are regulated by a separate control solenoid valve:

- CVT primary-control solenoid valve

- CVT clutch control solenoid valve

- CVT control solenoid valve for torque converter lockup clutch