METHOD FOR CONTROLLING A PNEUMATIC ACTUATOR

Abstract

A method for controlling a pneumatic actuator (1) of a transmission having at least one sealing element (6, 7) that is arranged between two elements (2, 3) of the actuator (1) that move relative to one another, and within a specifiable operating temperature range in which a leakproofness of the actuator (1) is ensured. The pneumatic actuator is acted upon with compressed air from an air supply system for actuating a transmission component. When a temperature of the actuator (1) is below a glass transition temperature of the at least one sealing element (6, 7), the actuator (1) is acted upon with pre-heated compressed air from the air supply system to warm up the at least one sealing element (6, 7) above the glass transition temperature.

Claims

1-7. (canceled)

8. 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 actuator (1) that move relative to one another, and within a specifiable operating temperature range in which a leakproofness of the actuator (1) is ensured, and the actuator (1) being acted upon by compressed air, from an air supply system, for actuating a transmission component, the method comprising: when a temperature of the actuator (1) is below a glass transition temperature of the at least one sealing element (6, 7), acting upon the actuator (1) with compressed air from the air supply system.

9. The method according to claim 8, further comprising preheating the compressed air supplied to the actuator (1) by a through-flow heater arranged in the air supply system.

10. The method according to claim 8, further comprising discontinuing the supply of compressed air from the air supply system when either the temperature of the actuator (1) or a temperature of the at least one sealing element (6, 7), arranged between the two elements (2, 3) of the actuator (1) that move relative to one another, exceeds the glass transition temperature.

11. The method according to claim 8, 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.

12. The method according to claim 8, further comprising deducing a degree of leakproofness of either the actuator (1) or the sealing element (6, 7) with reference to a pulse frequency at which inlet valves of the air supply system are controlled in order to actuate the actuator (1), and a determined position of the actuator (1) while the actuator is being acted upon by pressure.

13. A control unit for controlling a pneumatic actuator (1) of a transmission, wherein the control unit has means for carrying out the method according to claim 8.

14. A computer program product with program code modules stored on a computer-readable data carrier, for carrying out the method according to claim 8 when the computer program product is run on a computer or an appropriate computer unit of a control unit of the pneumatic clutch actuator.

15. A method for controlling a pneumatic actuator (1) of a transmission having a pair of sealing elements (6, 7) arranged between two elements (2, 3) of the actuator (1) that move relative to one another, within a specifiable operating temperature range of the pair of sealing elements (6, 7), a leakproofness of the actuator (1) is ensured, and the actuator (1) being acted upon by compressed air, from an air supply system, for actuating a transmission component, the method comprising: when a temperature of the actuator (1) is below a glass transition temperature of the pair of sealing elements (6, 7), acting upon the actuator (1) with pre-heated compressed air from the air supply system to warm the pair of sealing elements (6, 7) to a temperature above the glass transition temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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 drawings, which show:

[0028] FIG. 1: A pneumatic actuator of a transmission, and

[0029] FIG. 2: A diagram in which temperature variations of the actuator are shown as a function of time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The pneumatic actuator 1 shown in FIG. 1 is a clutch actuator 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The clutch actuator 1 is actuated and moved to the left in the plane of the figure, when from an air 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.

[0035] When the clutch actuator 1 is not actuated, the shifting and/or starting clutch arranged between the drive aggregate and the transmission is closed. 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.

[0036] Thus, according to the invention it is provided that the clutch actuator 1 is already acted upon by compressed air from the air supply system when a temperature of the clutch actuator 1 is lower than a glass transition temperature of the at least one sealing element 6, 7.

[0037] This actively influences the warm-up process and a warming of the pneumatic sealing elements 6, 7 to a temperature above their glass transition temperature can be substantially accelerated. Accordingly, the clutch actuator 1 and thus too the transmission and the motor vehicle are ready to operate at an earlier time.

[0038] Due to the action of pressure in the pressure chamber 4, despite the imperfect sealing 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. If the drive aggregate is already in operation, then the pressure plate 11 of the shifting and/or starting clutch also rotates at the rotational speed of the drive aggregate. Consequently, owing to the increased load on the release bearing 8, the release bearing 8 is warmed more quickly and, with the release bearing 8, so too are the piston 2 and the sealing elements 6, 7 respectively between the piston 2 and the cylinder 3 and between the piston 2 and the guide-tube 12.

[0039] 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.

[0040] 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. For example, 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.

[0041] The continuous line T_1 shows a time variation of the temperature of the piston 2 of the clutch actuator 1 when the clutch actuator 1 is not actuated during the warm-up phase. The gradient with which the temperature of the piston 2 increases is very shallow, so the glass transition temperature is not reached until a time t3 and the warming-up process takes a correspondingly long time.

[0042] The broken line T_2 shows a time variation of the temperature of the piston 2 of the clutch actuator 1 when, during the warm-up phase, the clutch actuator 1 is already acted upon with compressed air. Since the warming-up process is actively influenced by the action of pressure, the warming up 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 already reached at a time t2.

INDEXES

[0043] 1 Actuation means, clutch actuator [0044] 2 Piston [0045] 3 Cylinder [0046] 4 Pressure chamber [0047] 5 Pre-load spring [0048] 6 Outer sealing element [0049] 7 inner sealing element [0050] 8 Release bearing [0051] 9 Rotational axis [0052] 10 Path sensor [0053] 11 Pressure plate [0054] 12 Guide-tube