Method for warming-up a pneumatic clutch actuator

Abstract

A method for controlling a pneumatic actuator (1) of a transmission having at least one sealing element (6, 7), arranged between two elements (2, 3) of the clutch actuator (1) that move relative to one another, and within a specifiable operating temperature range in which leakproofness of the clutch actuator (1) is ensured. The clutch actuator (1) is acted upon with compressed air from an air supply system for actuating a shifting and/or starting clutch arranged between a drive aggregate and a transmission. In order to warm up the clutch actuator (1), if a temperature of the clutch actuator (1) is lower then a glass transition temperature of the at least one sealing element (6, 7), the drive aggregate is operated at a higher rotational speed compared to the idling speed of the drive aggregate.

Claims

1. A method for warming up a pneumatic clutch actuator of a transmission having at least one sealing element arranged between two elements of the clutch actuator that are moveable relative to one another, the method comprising: within a specifiable operating temperature range in which leakproofness of the clutch actuator is ensured, acting upon the clutch actuator with compressed air from an air supply system for actuation of a shifting and a starting clutch arranged between a drive aggregate and a transmission, and if a temperature of the clutch actuator is lower than a glass transition temperature of the at least one sealing element, operating the drive aggregate at a rotational speed compared with an idling speed of the drive aggregate.

2. The method according to claim 1, further comprising operating the drive aggregate at a maximum permissible rotational speed, with respect to a temperature of the drive aggregate.

3. The method according to claim 1, further comprising reducing the rotational speed of the drive aggregate when either the temperature of the clutch actuator or a temperature of the at least one sealing element, arranged between the two elements of the clutch actuator that move relative to one another, exceeds the glass transition temperature.

4. The method according to claim 1, further comprising, if the temperature of the clutch actuator is lower than the glass transition temperature of the at least one sealing element, acting upon the clutch actuator with compressed air from the air supply system.

5. The method according to claim 4, further comprising preheating the compressed air supplied to the clutch actuator by a through-flow heater arranged in the air supply system.

6. The method according to claim 4, further comprising discontinuing the supply of compressed air from the air supply system, when the temperature of either the clutch actuator or the at least one sealing element, arranged between the two elements of the actuator that move relative to one another, exceeds the glass transition temperature.

7. The method according to claim 4, further comprising discontinuing the supply of compressed air from the air supply system when a maximum permissible switched-on time of an electro-pneumatic switching valve of the air supply system is reached.

8. The method according to claim 1, further comprising deducing a degree of leakproofness of either the clutch actuator or the sealing element with reference to a pulse frequency at which inlet valves of the air supply system are controlled in order to actuate the clutch actuator, and a determined position of the clutch actuator while the clutch actuator is being acted upon by pressure.

9. A control unit designed to carry out the method for warming up a pneumatic clutch actuator according to claim 1.

10. A computer program product with program code modules stored on a computer-readable data carrier, for carrying out the method according to claim 1 when the computer program product is run on a computer or an appropriate computer unit of a control unit of the pneumatic clutch actuator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred further developments emerge from the subordinate claims and the following description. An example embodiment of the invention, to which it is not limited, is explained in greater detail with reference to the drawing, which shows:

(2) FIG. 1: A pneumatic clutch actuator of a transmission, and

(3) FIG. 2: A diagram in which temperature variations of the clutch actuator are shown as a function of time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) FIG. 1 shows a pneumatic clutch actuator 1 for opening and closing a shifting and/or starting clutch in the form of a central release device arranged between a drive aggregate and a transmission. In this case the clutch actuator 1 comprises a cylinder 3 with an annular cylinder body. In the cylinder 3 is arranged a piston 2 that can move axially along a rotational axis 9 of the shifting and/or starting clutch on a guide-tube 12. The piston 2 is in the form of an annular piston and carries a release bearing 8, which co-operates with a pressure plate 11 of the shifting and/or starting clutch. The pressure plate 11 can for example be in the form of a membrane spring.

(5) Between the piston 2 and the cylinder 3 is arranged an outer sealing element 6 and between the piston 2 and the guide-tube 12 is arranged an inner sealing element 7. In this case the sealing elements 6, 7 are in the form of elastomer groove rings.

(6) Furthermore, between the piston 2 and the cylinder 3 is arranged a spring 5, which pushes the piston 2 away from the cylinder 3 and therefore applies a defined load on the piston 2 and the release bearing 8, without the clutch actuator 1 being acted upon by compressed air. Accordingly, the spring 5 is also called a pre-load spring.

(7) The position of the piston 2 can be detected by a path sensor 10. To detect the temperature of the clutch actuator 1, a temperature sensor (not shown here) can be used.

(8) The clutch actuator 1 is actuated and moved to the left in the plane of the figure, when from an aft supply system (not shown) of a motor vehicle compressed air is supplied to a pressure chamber 4 between the piston 2 and the cylinder 3.

(9) When the clutch actuator 1 is not actuated, the shifting and/or starting clutch arranged between the drive aggregate and the transmission is dosed. If the temperature falls below a glass transition temperature of the sealing elements 6, 7, these and therefore the clutch actuator 1 as well are no longer leakproof and the starting and/or shifting clutch cannot be opened by the clutch actuator 1, or only incompletely so. To warm up the clutch actuator 1 the drive aggregate of the motor vehicle then has to be operated at an idling rotational speed for a longer time. During this, the release bearing 8 lightly prestressed by the spring 5 is warmed by the waste heat emitted. Indirectly, therefore, the piston 2 and the sealing elements 6, 7 are also warmed. As soon as the sealing elements 6, 7 reach a temperature above the glass transition temperature of the sealing elements 6, 7, the sealing elements fulfill their sealing function and the clutch actuator 1 is ready to operate. Since the gradient at which the temperature of the sealing elements 6, 7 rises is very shallow, at low temperatures the warm-up process can take a correspondingly long time. For the driver of the vehicle this results in unacceptably long waiting times.

(10) According to the invention, it is therefore provided that the drive aggregate is operated at a rotational speed higher compared with the idling speed of the drive aggregate, when a temperature of the clutch actuator 1 is lower than a glass transition temperature of the at least one sealing element 6, 7. This actively influences the warming-up process and the warming of the pneumatic sealing elements 6, 7 to above their glass transition temperature can be made much quicker.

(11) The higher the rotational speed at which the drive aggregate and consequently also the pressure plate 11 of the shifting and/or starting clutch in contact with the release bearing 8 are operated, the more rapidly is the release bearing 8 prestressed by the spring 5 warmed up by the waste heat given off. The clutch actuator 1, and thus also the transmission and the motor vehicle, are therefore ready for operation at an earlier time.

(12) If the clutch actuator 1 is already being acted upon with compressed air from the air supply system when the temperature of the clutch actuator 1 is lower than a glass transition temperature of the at least one sealing element 6, 7, the warming up process of the clutch actuator can be accelerated further.

(13) By acting upon the pressure chamber 4 with pressure, despite the imperfectly leakproof condition the piston 2 of the clutch actuator 1 undergoes an axial movement in the direction toward the pressure plate 11 of the shifting and/or starting clutch. This increases the load acting on the release bearing 8. Since the drive aggregate is already being operated at an elevated rotational speed, the pressure plate 11 of the shifting and/or starting clutch also rotates at the elevated speed of the drive aggregate. Due to the higher load on the release bearing 8 and the elevated rotational speed of the drive aggregate the release bearing 8 consequently warms up more quickly, and along with the release bearing 8 so too do the piston 2 and the sealing elements 6, 7 arranged between the piston 2 and the cylinder 3, and the piston 2 and the guide-tube 12.

(14) Alternatively or in addition to the detection of the temperature of the clutch actuator 1 by a temperature sensor, the temperature of the clutch actuator 1 or the temperature of the piston 2 of the clutch actuator 1 can also be determined. Since the load acting on the release bearing 8 is proportional to the release path that can be covered by the piston 2 due to the action of pressure, by virtue of path signals picked up by the path sensor 10 the load acting on the release bearing 8 can be deduced. From the known load on the release bearing 8 a temperature gradient can be determined, with which the piston 2 of the clutch actuator 1 warms up. Finally, by integrating the temperature gradient produced over time in each case, the warming behavior of the piston 2 of the clutch actuator 1 and therefore the temperature of the piston 2 and the temperature of the sealing elements 6, 7 can be deduced.

(15) FIG. 2 shows a schematic diagram in which temperature variations of the clutch actuator 1 are shown as a function of time. The temperature in C. is plotted along the ordinate and the time t along the abscissa. As examples, temperature variations are shown which are produced at the piston 2 of the clutch actuator 1 during a warm-up phase of the transmission or the motor vehicle. When the temperature is below a glass transition temperature of the sealing elements 6, 7, which is indicated in this case as around 18 C., the sealing elements and thus also the clutch actuator are not leakproof and the starting and/or shifting clutch cannot be opened by means of the clutch actuator 1, or only incompletely so. Only when the glass transition temperature has been reached or exceeded can the sealing elements 6, 7 and therefore also the clutch actuator 1 be operated again. In this example a warm-up phase is started at time t1 at an assumed temperature of 30 C.

(16) The continuous line T_n1 shows a time variation of the temperature of the piston 2 of the clutch actuator 1 during a warm-up phase in which the drive aggregate is operated at an idling speed, for example of 600 r/min, and the clutch actuator 1 is not acted upon by compressed air. The gradient with which the temperature of the piston increases is very shallow, such that the glass transition temperature is not reached until a time t4 and the warming-up process takes a correspondingly long time.

(17) The broken line T_n2 shows a time variation of the temperature of the piston 2 of the clutch actuator 1 during a warm-up phase in which the drive aggregate is operated at a rotational speed higher compared with the idling speed of the drive aggregate but the clutch actuator 1 is again not acted upon by compressed air. In this case, for example, the drive aggregate can be operated at a rotational speed of 850 r/min. Since the warm-up process is actively influenced by the elevated rotational speed of the drive aggregate, warming of the piston 2 of the clutch actuator 1 to a temperature above the glass transition temperature can be substantially accelerated. In this case the glass transition temperature is reached already after a time t3.

(18) The dot-dash line T_1 shows a time variation of the temperature of the piston 2 of the clutch actuator 1 during a warm-up phase in which, in addition to the elevation of the rotational speed of the drive aggregate, the clutch actuator 1 is also acted upon by compressed air from the air supply system. This can further accelerate the warming-up process of the clutch actuator, so that the glass transition temperature is already reached at an earlier time t2.

INDEXES

(19) 1 Actuation means, clutch actuator 2 Piston 3 Cylinder 4 Pressure chamber 5 Pre-load spring 6 Outer sealing element 7 Inner sealing element 8 Release bearing 9 Rotational axis 10 Path sensor 11 Pressure plate 12 Guide-tube