Electronic-hydraulic control for automobile drive systems with automatic gear shifting

Electronic-hydraulic control device of an automatic automobile transmission in which all of the solenoid valves (12) and pressure control valves (6, 7, 8, 9, 10, 11) are de-energized when the electronic control device fails and in which a lower gear, preferably third gear, is automatically selected when a lower gear has been previously engaged, and a higher gear, preferably fifth gear, is selected when a higher gear has been engaged previously. The control valves (20, 21, 23) have surfaces of different dimensions that can be controlled jointly or individually to permit a variety of valve characteristic curves.

FIELD OF THE INVENTION

The invention relates to an electronic-hydraulic control device of an automatic automobile transmission in, which frictional clutches or brakes that can be engaged or released are controlled to shift individual gears by pressurizing the actuators depending on the operating parameters of the automobile transmission and a drive motor as well as on devices for influencing the gear shift operation and/or drive program.

BACKGROUND OF THE INVENTION

An electronic-hydraulic control device of an automatic automobile transmission of the type described above is known from EP 0 440 748 B1. In this control system a control valve is associated with each actuating device and the solenoid valves and shifting valves, which are used to drive the control valves can perform multiple functions. The control device of this transmission control has a fault-monitoring device in which an associated solenoid valve or pressure control valve is controlled in such a way when the error signal appears that the automobile transmission is in idle at least phasewise. An automobile must be able to continue traveling even if there is a defect in the electronic control.

SUMMARY OF THE INVENTION

The goal of the invention is to create an electronic-hydraulic transmission control for an automatic transmission, preferably a six-speed transmission, in which the clutches or brakes of the transmission can be controlled by an electronic control device and in which an emergency gear is automatically selected if the electronic control device fails, which is designed such that when traveling in the upper transmission speeds ( 4 to 6 ), a higher gear is selected in case of failure, and during travel in the lower speeds ( 1 to 3 ), a shift is made to a lower gear in the event of a defect.

This goal is achieved by a type-compliant electronic-hydraulic transmission control with the characterizing features of the main claim in which the clutches or brakes can be controlled directly by the electronic control device by driving electrical pressure control valves or electrical solenoid valves which in turn control hydraulic valves that pressurize the clutches or brakes depending on the control pressure of the electrical pressure control valves. The solenoid valves or electrical pressure control valves in the de-energized state always assume a predetermined position in which the emergency gear is selected by corresponding valve combinations. This is necessary since even when the electronic control device fails, travel must still be possible. By the solenoid valves and electrical control valves assuming a predetermined position in the de-energized state in an emergency case, the clutch or brake to be engaged for the emergency gear is not subjected to a controlled pressure but to the full system pressure. In order to prevent thermal loading of the emergency gear clutches, the shift from the previous gear to the emergency gear must not be too high. For this reason, the control valves are switched so that in case of a previously used upper gear, preferably the fourth to sixth gear, in case of an upper gear, the fifth gear is selected, and during travel in the lower gears, preferably one to three, a shift is made to a lower gear, preferably the third gear. Reverse can be selected directly during the emergency operation by shifting the selector lever. Since gears can no longer be shifted when traveling in an emergency gear, it is possible that when the fifth gear is engaged as the emergency gear, the vehicle can no longer start in this fifth gear, for example after braking at a traffic light. By lowering the system pressure shortly to zero, for example by switching off the combustion engine, the control valves are switched so that when re-starting the combustion engine, the third gear is automatically selected when the electronic control device is defect. Since this electronic-hydraulic transmission control is preferably used for a six-speed automatic transmission, the control valves controlling the clutches and brakes are designed with two different valve characteristic curves. This is necessary since in a six-speed automatic transmission, the clutches or brakes must be operated at different speeds in order to shift gears in combination with other clutches or brakes. Thus a clutch is actuated in both the third and fifth gear for engaging the gears. However, since the torque on the clutch in a lower gear is different from the torque of the same clutch in an upper gear, it is necessary to subject the actuator of this clutch to different pressures depending on the speed selected.

Depending on the gear combination, the control valves are either pressurized by only one surface or, if a second valve characteristic curve is required, the control valves are pressurized by another surface, with the surface of one pressurized side being different from the other side. This results in a different clutch pressure while the control pressure remains the same.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 : This transmission diagram shows a six-speed planetary-type transmission in which drive shaft 1 is driven by a combustion engine, not shown. Drive shaft 1 is connectable with drive shaft 2 by clutches A, B, E and brakes C and D. The shifted clutches or brakes for the corresponding gears are shown in FIG. 2 .

FIG. 2 : In the table shown it is evident which clutches and brakes must be closed to engage the specific gears.

FIG. 3 : A pump 3 is driven by a combustion engine, not shown, that supplies the system pressure for the electronic-hydraulic transmission control. The system pressure is regulated by system pressure valve 4 . When the selector is moved into a forward travel position, depending on the parameters of the combustion engine and the automatic transmission, the electrical control pressure valves 6 , 7 , 8 , 9 , 10 , 11 and solenoid valves 12 are controlled, as shown by the table in FIG. 4 . For example, if the second gear is engaged, pump 3 supplies the control with pressure medium through channel 13 at a predetermined level. controlled by the system pressure valve. The reverse valve 15 is controlled by channel 14 connecting channel 16 with channel 17 . The electronic control device checks that the gear selection is permitted and then controls the electrical pressure control valves 6 , 8 , and 11 . In this state, emergency travel valve 18 and shift valve 19 are in their initial positions. Control valve 20 is switched and clutch A is closed. This selects the second gear. If a defect in the electronic control device occurs in gears 1 to 3 , solenoid valves 12 and electrical pressure control valves 6 , 7 , 8 , 9 , 10 , 11 are de-energized. Since pressure control valve 7 is deenergized, electrical pressure control valve 7 is switched by its spring so that control valve 23 is controlled through channel 22 and clutch B closes without feedback control. Since reverse valve 15 is still pressurized, channel 17 is connected with channel 16 and the pressure acting on the actuator of clutch B is passed through emergency travel valve 18 to control valve 20 . Control valve 20 is thus pressurized so that clutch A remains closed. Likewise, valve 24 is switched and channel 25 is pressurized by channel 16 . Shift valve 19 is controlled so that the connection is switched from channel 26 to channel 27 while channel 28 has zero pressure. Consequently, control valve 29 is switched and clutch D is opened with zero pressure. This ensures that if the electronic control device fails in one of the lower gears, the third gear is automatically engaged in an emergency situation. If a failure in the electronic control device occurs when one of the upper gears is engaged, electronic pressure control valves 6 , 7 , 8 , 9 , 10 , 1 1 and solenoid valves 12 are de-energized. As described above, electrical pressure control valve 7 is switched by its spring and clutch B is closed. When one of the upper speeds 4 , 5 , and 6 is engaged, solenoid valve 12 is energized during normal operation of the electronic control device.

For this reason, When a fault occurs in the electronic control device, the emergency travel valve 18 is still pushed against its spring. Since in its de-energized state the electrical pressure control valve 9 is controlled so that channel 26 is pressurized and switching valve 19 remains controlled since valve 24 is controlled by reverse valve 15 , the pressure from channel 26 works on the differential surface in emergency travel valve 18 holding emergency travel valve 18 in its lower position. Control valve 30 is controlled by channel 27 and emergency travel valve 18 so that clutch E remains closed. This ensures that when there is a fault in the electronic control device and an upper gear is engaged, anautomatic shift to fifth gear is made. If the vehicle is fully stopped while in this engaged fifth emergency gear, it is no longer possible under certain conditions to produce sufficient torque in fifth gear to start again. For this reason, the system pressure must be interrupted for a short time, which can be accomplished by shutting off the combustion engine or by manually switching another valve. Emergency travel valve 18 then enters its initial position and third gear is automatically engaged again when the engine restarts and the driving position is selected.

In another embodiment of the invention, the control valves associated with the clutches and brakes can be pressurized on both sides. However they have different surfaces on the two sides so that it is possible to produce a first valve characteristic curve by pressurizing one surface and to produce a second valve characteristic curve by pressurizing a second surface and a first surface. This is necessary since certain clutches or brakes are used at several speeds, for example, clutch C is pressurized in gears 2 and 6 .

REFERENCE NUMERALS

1 input drive shaft

2 output drive shaft

4 system pressure valve

6 electrical pressure control valve

7 electrical pressure control valve

8 electrical pressure control valve

9 electrical pressure control valve

10 electrical pressure control valve

11 electrical pressure control valve

18 emergency travel valve

19 switch valve

20 control valve

21 control valve

23 control valve

29 control valve

30 control valve

A clutch

B clutch

C brake

D brake

E clutch