Actuator system for hydraulic actuation

Abstract

An actuator system for hydraulic actuation of a clutch comprises a master cylinder with a master piston, a readjustment container for containing hydraulic fluid, a connection opening between the readjustment container and the master cylinder, where a degree of openness of the connection opening is dependent on the position of the master piston, and a hydraulic actuator to control a position of the master piston. In an actuator system, a control device for controlling the hydrostatic actuator is also provided, such that a speed of motion of the master piston is high while the connection opening is wide open, and low while the connection opening is open a little. In a method according to the disclosure, a position of the master piston is detected, and the actuator is controlled at different speeds depending on the position or the degree of openness.

Claims

1. A method for controlling an actuator system for hydraulic actuation of a clutch, wherein the actuator system has a master cylinder with a master piston, a readjustment container to receive hydraulic fluid, a connection opening between the readjustment container and the master cylinder, a hydrostatic actuator to control a position of the master piston and a control device to control the hydrostatic actuator, and a degree of openness of the connection opening is dependent on the position of the master piston, the method comprising the steps of: controlling the actuator at a first constant speed, while the connection opening is fully closed by the master piston; and, controlling the actuator at a plurality of speed steps in a sequence to displace the master piston to fully open the connection opening, wherein: an initial speed step begins at a point at which the master piston begins to open the connection opening; and, each speed step in the sequence of the speed steps increases over a respective speed step preceding said each speed step in the sequence.

2. The method of claim 1, wherein the speed of movement when the connection opening is only partially open is lower than when the connection opening is closed.

3. The method of claim 1, further comprising the steps of: moving the master piston into an opening position in which the connection opening is partially opened; determining that a pressure of the hydraulic fluid is decreasing to an ambient pressure more slowly than predetermined; adjusting the opening position so that the degree of openness of the connection is enlarged; and, moving the master piston past a closed position in which the connection opening is completely closed in order to actuate the clutch.

4. The method of claim 3, further comprising the steps of: determining that a contact point of the master piston at which the clutch begins to engage is shifted in the direction of the closed position of the master piston at which the connection opening is just closed.

5. The method of claim 4, further comprising the steps of: moving the master piston in the direction of a decreasing degree of openness; determining the closed position at which the connection opening is just closed, on the basis of a pressure pattern of the hydraulic fluid.

6. An actuator system for hydraulic actuation of a clutch, comprising: a master cylinder with a master piston; a readjustment container to receive hydraulic fluid; a connection opening between the readjustment container and the master cylinder, wherein a degree of openness of the connection opening is dependent on a position of the master piston; and, a hydraulic actuator for controlling a position of the master piston, and including a control device, wherein: the control device is for controlling the hydraulic actuator in such a way that the master piston is moved at a plurality of speed steps in a sequence; a final speed step in the sequence terminates at a point at which the master piston fully closes the connection opening; each speed step in the sequence of the speed steps decreases over a respective speed step preceding said each speed step in the sequence; the control device is for controlling the hydraulic actuator such that the master cylinder is moved at a first constant speed while the connection opening is fully closed; and, the first constant speed follows the final speed step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments are disclosed, by way of example only, with reference to the accompanying drawings in which corresponding reference symbols indicate corresponding parts, in which:

(2) FIG. 1 is a schematic view of an actuator system for hydraulic actuation of a clutch;

(3) FIG. 2 is a diagram of the correlations between a position and a maximum speed of movement of a master piston in the actuator system from FIG. 1;

(4) FIG. 3 is a diagram of a correlation between the position of a master piston and a pressure of hydraulic fluid in the actuator system from FIG. 1; and,

(5) FIG. 4 is an enlarged view of the correlation shown in FIG. 3.

DETAILED DESCRIPTION

(6) At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects.

(7) Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure.

(8) Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure.

(9) FIG. 1 shows an actuator system 100 for hydraulic actuation of a clutch 105. The clutch 105 is intended for controlled engagement or interrupting of a flow of power in a drivetrain, in particular of a motor vehicle. In a preferred embodiment, a plurality of clutches 105 are provided in the drivetrain, where at every point in time a maximum of one of the clutches is completely engaged.

(10) The actuator system 100 comprises a master cylinder 110, in which a master piston 115 is accommodated, a slave cylinder 120, in which a slave piston 125 is accommodated, a pressure line 130 for fluid connection of the cylinders 110 and 120, and a readjustment container 135, which can be fluidly connected to the master cylinder 110, depending on a position of the master piston 115 by means of a connection opening 140 in the master cylinder 110. In the readjustment container 135, the master cylinder 110, the pressure line 130 and the slave cylinder 120 there is a hydraulic fluid 145. The readjustment container 135 is not sealed pressure-tight relative to an environment, so that the hydraulic fluid 145 in the readjustment container 135 is at ambient pressure, in general an ambient air pressure.

(11) In the depicted embodiment, it is assumed that a pressure of the hydraulic fluid 145 can be elevated by moving the master piston 115, in order to engage the clutch 105 or to produce a flow of power through the clutch 105 in the drivetrain. An inverted arrangement, in which the clutch 105 is engaged by means of spring force when the pressure of the hydraulic fluid 145 drops, is also possible.

(12) The master piston 115 can be moved by means of a hydrostatic actuator 150, by shifting the position of the master piston 115 in the master cylinder 110 by means of the actuator 150. To that end, the actuator 150 preferably includes a spindle drive 155 to convert a rotational into a linear position, a drive motor 160 to provide the rotational position, and a control device 165, which may also be provided separate from the actuator 150. The control device 165 is preferably connected to a first sensor 170 to determine a temperature in the region of the hydraulic fluid 145, and/or to a second sensor 175 to determine a pressure of the hydraulic fluid 145 in the region of the pressure line 130.

(13) In order to disengage and engage the clutch 105 in a normal operation, the actuator 150 is addressed to move the master piston 115 in the master cylinder 110 in such a way that the connection opening 140 is closed, and the requisite pressure of the hydraulic fluid 145 for disengaging or engaging is provided through the position of the master piston 115. If the master piston 115 is in a position in which the pressure of the hydraulic fluid 145 is low in normal operation, then the master piston 115 in FIG. 1 can be moved still further to the left, in order to at least partially release the connection opening 140 in conjunction with a so-called sniffing procedure, and to enable an exchange of hydraulic fluid 145 between the master cylinder 110 and the readjustment container 135. The sniffing procedure may be necessary if a temperature of the hydraulic fluid 145 has changed since a previous sniffing procedure. By means of the sniffing procedure the actuator system 100 is recalibrated hydraulically or mechanically, in order to establish a predetermined correlation between the position of the actuator 150 and the position of the clutch 105.

(14) FIG. 2 shows correlations 200 between a position and a maximum speed of movement of the master piston 115 of the actuator system 100 from FIG. 1; the left-hand area depicts functionally a section of the master cylinder 110 with the master piston 115 and the connection opening 140. In the right-hand area at the top a correlation is depicted between the position of the master piston 115 in the vertical direction and the time in the horizontal direction. Further down in the right-hand area, three alternative patterns of movement speeds of the master piston 115 in the master cylinder 110 are depicted. Broken lines simplify assignments between segments of the three depictions.

(15) In normal operation, the upper edge of the master piston 115 in FIG. 2 is in a zero position 205, in which the slave cylinder 120 is under a minimum pressure. In order to actuate the clutch 105, the master piston 115 is moved upward from the zero position 205 in FIG. 2. For sniffing, the master piston 115 on the other hand is moved downward into a closed position 210, in which the connection opening 140 is still completely closed. The master piston 115 is then moved further past the closed position 210 into an opening position 215, in which the connection opening 140 is released sufficiently to the readjustment container 135. In the depiction in FIG. 2, the opening position 215 is depicted with a maximum possible degree of openness of the connection opening 140, without restriction of the generality. In other embodiments, the opening position 215 can also be defined further above with reference to the depiction in FIG. 2. The opening position 215 can also be variably definable, in order to allow an optimized sniffing procedure.

(16) According to the disclosure, the speed of movement of the master piston 115 is controlled depending on its position in the master cylinder 110. A pattern 220 explains the correlation between speed of movement and position of the master piston. In a first time segment 225 the sniffing is prepared, by moving the master piston 115 from the zero position 205 into the closed position 210. In a second time segment 230 the master piston 115 is moved further in the direction of the opening position 215, so that the connection opening 140 is partially opened and a degree of openness of the connection opening 140 then increases. In a third time segment 235 the master piston 115 is held in the opening position 215. The greatest part of the pressure equalization between the interior space of the master cylinder 110 and the readjustment container 135 takes place in this segment. After that, in a segment 240, the connection opening 140 is closed again by means of the master piston 115, until the master piston 115 has reached the closed position 210. The movement in segment 240 preferably corresponds to the time-reversed procedure in segment 230. In a fifth time segment 245 the master piston 115 is moved again from the closed position 210 into the zero position 205. This segment corresponds to the time-reversed segment 225.

(17) While the speed of movement of the master piston 115 is high in segment 225, when the connection opening 140 is fully closed, the speed of movement is lower in segment 230, when the connection opening 140 is between fully closed and fully open. In one embodiment the speed of movement can also be controlled on the basis of a temperature of the temperature sensor from FIG. 1, in particular in segment 230. If the temperature is high, then the speed of movement can be higher than when the temperature is low, in order to take account of a temperature-dependent viscosity of the hydraulic fluid 145.

(18) Three alternative exemplary speed patterns 250, 255 and 260 explain a speed control of the master piston 115, which depends on the degree of openness of the partially released connection opening 140. Outside of the segments 230 and 240, in which the connection opening 140 is either completely open or completely closed, a suitable speed of the master piston 140 can be achieved in a known way.

(19) In the first pattern 250, the speed of movement of the master piston 115 in segment 230 is below that in segment 225, the speed of movement in segment 230 being constant.

(20) In the second pattern 255, the speed of movement of the master piston 115 in segment 230 increases in a straight line as the degree of openness of the connection opening 140 rises. The speed of the master piston 115 at the opening position 215 can be as high as the speed in segment 225, or also lower.

(21) In the third pattern 260, the speed of the master piston 115 in segment 230 is controlled in multiple segments, each with constant speed, depending on the degree of openness of the connection opening 140. The result is the step-like speed pattern 260 which is shown. Here two, three or more constant speeds of the master piston 115 can be controlled one after the other.

(22) In other embodiments, still other speed patterns of the master piston 115 are possible in segment 230. In an exemplary embodiment, the speed pattern is consistent.

(23) In the fourth segment 240, the master piston 115 is preferably moved at a speed which, as shown, corresponds to the respective pattern in segment 230 in reversed time sequence.

(24) FIG. 3 shows a correlation 300 between the position of the master piston 115 and a pressure of the hydraulic fluid 145 of the actuator system in FIG. 1. A pressure of the hydraulic fluid 145 is depicted in the vertical direction, and a position of the master piston 115 in the horizontal direction. The correlation shown is exemplary, and the indicated scale values are examples.

(25) A first pattern 305 corresponds to a movement of the master piston 115 in the positive direction, i.e., toward the right in FIG. 3, while a second pattern 310 corresponds to a movement of the master piston 115 in the negative direction, i.e., toward the left in FIG. 3. The different patterns 305, 310 result during a clutch actuation from a hysteresis effect based on friction in the real actuator system 100 in FIG. 1.

(26) At a position of the master piston 115 at approximately 10 mm there is a contact point 315, at which an actuation of the clutch 105 begins or ends, i.e., a frictional lock is engaged by means of the clutch 105 when the hydrostatic actuator 150 is actuated, or is interrupted as the actuation decreases. To be able to precisely control the disengaging or engaging of the clutch 105, it is necessary to know the contact point 315 as precisely as possible in reference to the position of the master piston 115. If the hydraulic fluid 145 warms up after the connection opening 140 was closed during a sniffing procedure, the patterns 305 and 310 shift to the left. A shifting of this sort may also have other causes, for which reason the shifting cannot yet be compensated for solely on the basis of the temperature of the hydraulic fluid 145. Instead, the shifting can be eliminated by freeing the hydraulic fluid 145 of over- or under-pressure when the master piston 115 is moved into the sniffing position in segment 230 in FIG. 2.

(27) FIG. 4 shows an enlarged detail of the correlation shown in FIG. 3. Here the closed position 210 is assumed to be in the position 1.0 mm. However, the closed position 210 lies within an uncertainty zone 405, since an elevated pressure in the region of the closed position 210, for example, may result in a deformation of a seal at the connection opening 140, so that the actual closed position 210 during operation of the actuator system 100 may vary in its position relative to the master cylinder 110.

(28) In order to place the opening position 215 at a position of the master piston 215 at which an adequate release of the connection opening 140 is just guaranteed, various approaches may be followed. In a first variant, the pressure of the hydraulic fluid 145 is observed in the opening position 215. If the pressure drops more slowly than a predetermined speed to the pressure in the readjustment container 135, then the opening position 215 is set further to the left in FIG. 4. This change relates to an internal parameter of the control device 165.

(29) In a second variant, the opening position 215 can be adjusted on the basis of a temperature of the hydraulic fluid 145, so that the opening position 215 corresponds to a smaller degree of openness when the hydraulic fluid 145 is hot than when the hydraulic fluid 145 is cold.

(30) To ensure further that no unacceptably high pressure of the hydraulic fluid 145 remains in the pressure line 130 when the connection opening 140 in segment 240 in FIG. 2 is closed, the pressure sensor 175 from FIG. 1 may also be used in order to adjust the closed position 210 accordingly. In one embodiment, the closed position 210 may be adjusted if the master piston 115 is positioned below, or in FIG. 4 to the left of the depicted uncertainty zone 405, and a predetermined threshold value 410 for the pressure is exceeded.

(31) It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

LIST OF REFERENCE NUMBERS

(32) 100 actuator system 105 clutch 110 master cylinder 115 master piston 120 slave cylinder 125 slave piston 130 pressure line 135 readjustment container 140 connection opening 145 hydraulic fluid 150 hydrostatic actuator 155 spindle drive 160 drive motor 165 control device 170 first sensor 175 second sensor 200 correlation 205 zero position 210 closed position 215 opening position 220 pattern 225 first segment 230 second segment 235 third segment 240 fourth segment 245 fifth segment 250 first speed pattern 255 second speed pattern 260 third speed pattern 300 correlation 305 first pattern 310 second pattern 315 contact point 405 uncertainty zone 410 threshold value