The invention relates to a method and device for actuating a motor vehicle clutch device and for control or regulation of the transmissible input torque and the frictional power of the clutch device, especially for a reversing clutch device placed in a vehicle power train which contains a continuously variable ratio transmission.
A hydrostaic mechanical power split transmission with continuously variable ratio and a reversing clutch device consisting of a multi-disk clutch for forward motion and a multi-disk clutch for reverse motion on the transmission output has been disclosed in WO 97/01049. By alternatively using the two clutches Kv and Kr, the direction of travel of the vehicle can be reversed at low speeds. For example, this means that the clutch Kr is closed already with pressure modulation while the vehicle still moves forward. Starting from a specific modulation pressure, the formerly closed clutch Kv opens and the forward moving vehicle decelerates until parked, via the clutch Kr, and then accelerated in reverse direction of travel. The actually adjusted ratio of the transmission remains constant during the reversal operation. It will only be changed again after the reversal via the clutches Kv and Kr has terminated. Thereby obtaining with great shifting comfort and quick reverse gear shifting without interrupting the traction force of the power train of the vehicle.
The invention can be implemented with the known power split transmission and for, but not limited to, agricultural vehicles such as farm tractors and other tractors.
The vehicle input torque transmissible by a clutch in clutch-slip operation depends upon the adjustment of a clutch pedal of a vehicle and on the nature of the road. The so-called inch function (possibility of slip operation of the clutch) allows for the continuous variation of the input torque transmissible by the clutch, in the instant example, the reversing clutch device, through the driver with the aid of the clutch pedal position. The quantitatively regulated limitation of the input torque during practical utilization of the vehicle is indispensably needed, such as when starting on slippery soil or when docking on other equipment.
The rotation angle sensor on the clutch pedal or on a separate inch pedal produces a stress which corresponds to the pedal position and is processed in an electronic control unit. The tension is then converted to the inch effect which is between 0% and 100%. A 100% inch effect means that the reversing clutch device is open and a 0% inch effect means reversing clutch device is closed and that the input train is also closed.
In known tractor transmissions, the clutch pressure and thus the maximum transmissible input torque between 0 bar and a maximum value such as of 18 bars, are adjusted according to the inch effect. Like in the tractor transmissions already known, a rotational speed difference of more or less magnitude would appear over the reversing clutch device (through drive degree) according to the motor rotational speed, adjusted transmission ratio and the slowed down input torque on the output side of the reversing clutch device. The adjusted clutch pressure and the differential rotational speed between the input side and the output side of the reversing clutch device are a measure for the frictional power appearing in the reversing clutch device.
In the transmissions known, the reversing clutches are dimensioned for heavy loads so that burn out will occur under permanent operation with the inch function. To make permanent operation with slipping clutches at all driving speeds possible, new methods are needed to implement the use without limitations of the inch effect and at the same time to protect the clutches.
According to the invention, the problem is solved for a vehicle power train containing a transmission with continuously variable ratio and a clutch device utilizable in the slip operation, by providing a valuable possibility of operating the clutch device in friction-slip operation for a longer time than in the known driving systems without the clutch friction elements burning out or requiring an especially oversized clutch.
This problem is solved according to the invention by the characteristic features of Claim 1.
An essential idea of the invention consists in preventing too high frictional power or overheating of the clutch device not by changing the clutch closing pressure and/or the slipping time when opening and/or closing the clutch device, but by a predetermined automatic limitation, control or regulation of the rotational speed difference between the input side and the output side of the clutch device by an adequate control or regulation of the ratio of the transmission or of the rotational speed of the prime mover according to a predetermined parameterizable value or according to a parameterized value range, or according to the temperature and/or the frictional power of the clutch device. In this invention, the differential rotational speed of the clutch device is preferably modulated by varying the transmission ratio in the inch operation. In tractors or other mobile machines, so-called PTO motor, rotational speeds are often constantly in demand so that the needed variation of the motor rotational speed excludes itself. The frictional power can be measured in different ways or calculated by an electronic control device. The automatic calculation can be carried out according to the rotational speed difference between the input side and the output side of the clutch device, to clutch closing pressure and/or to the torque transmitted by the clutch device.