Method for operating a hydrostatic actuator system

Abstract

A hydrostatic actuator system includes an electric motor for delivering a hydraulic fluid via a piston unit. The actuator system is operating using a method in which a change in volume caused by a temperature change is sensed by a pressure measurement. The method reliably identifies a state of the transfer of the hydraulic fluid from a planetary roller transmission compartment into the master piston. The pressure measurement is continuously evaluated, and, in the event of a negative signal of the pressure measurement, suction of the hydraulic fluid by a planetary roller transmission lying in the hydraulic fluid between the electric motor and the piston unit into the piston unit is recognized and a fault signal is output.

Claims

1. A method for operating a hydrostatic actuator system, in which an electric motor is used for delivering a hydraulic fluid in the actuator having a piston unit, in which a change in volume of the hydraulic fluid caused by a temperature change is sensed by a pressure measurement, wherein the pressure measurement is continuously evaluated, wherein, in the event of a negative signal of the pressure measurement, suction of the hydraulic fluid by a planetary roller transmission lying in the hydraulic fluid between the electric motor and a spindle into the piston unit is recognized and a fault signal is output, and in which a sniffing action is triggered on the basis of the fault signal to eliminate a shift in a characteristic curve.

2. The method according to claim 1, wherein the fault signal is output if the negative signal of the pressure measurement lasts for a predetermined period of time.

3. The method according to claim 1, wherein the negative pressure signal is less than −0.2 bar.

4. The method according to claim 2, wherein the predetermined time period is at least 0.3 seconds.

5. The method according to claim 1, wherein a position signal of the actuator is continuously monitored and the fault signal is output when the actuator moves back from a high actuator position to a low actuator position.

6. The method according to claim 5, wherein the continuous evaluation of the pressure signal and the position signal takes place during a diagnostic process which is carried out in response to a predetermined ambient temperature.

7. The method according to claim 1, wherein the sniffing action is immediately initiated in response to the fault signal.

8. An actuator system comprising: a spindle; a master cylinder; a piston within the master cylinder and axially fixed to the spindle; an electric motor driving the spindle via a planetary transmission, the planetary transmission being encased in a sleeve; a pressure sensor within the sleeve; and a controller programmed to evaluate a signal from the pressure sensor and output a fault signal in response to a negative pressure.

9. The actuator system according to claim 8, wherein the fault signal is output if the negative pressure lasts for a predetermined period of time.

10. The actuator system according to claim 9, wherein the predetermined time period is at least 0.3 seconds.

11. The actuator system according to claim 9, wherein the fault signal is output in response to the negative pressure being less than −0.2 bar.

12. The actuator system according to claim 8, further comprising a spindle position sensor and wherein the fault signal is output when the actuator moves back from a high actuator position to a low actuator position.

13. The actuator system according to claim 12, wherein the controller evaluates the pressure signal and a position signal during a diagnostic process which is carried out in response to a predetermined ambient temperature.

14. The actuator system according to claim 8, wherein a sniffing request is triggered on the basis of the fault signal.

15. The actuator system according to claim 14, wherein a sniffing process is immediately initiated in response to the fault signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The method allows for numerous embodiments. One of these embodiments will be explained in more detail with reference to the figure shown in the drawing, wherein:

(2) FIG. 1 shows a schematic diagram of a hydraulic actuator for carrying out the method,

(3) FIG. 2 shows an exemplary embodiment of the movement of the master and slave cylinders at low temperatures,

(4) FIG. 3 shows an exemplary embodiment of the movement of the master cylinder of the actuator system at room temperature.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic diagram of a hydraulic actuator for carrying out the method. The hydraulic clutch actuator 1 comprises a control unit 2, which controls an electric motor for actuating the clutch actuator 1. The control device 2 is designed as a module which is connected to a hydraulic module 3. When the position of the clutch actuator 1 changes, a spindle 4 can be moved on both sides along an axial actuator path. The spindle 4 is driven by the electric motor, which has a stator 5. A rotor 6 is mounted radially inside the stator 5 and is in engagement with the spindle 4 via a planetary roller transmission (not shown). The planetary roller transmission is encased in a sleeve 7. At the end 4.1 of the spindle 4 facing away from the control unit 2, a pressure piece 8 is attached which acts (not shown) on an element of a hydraulic path, such as a master cylinder. Bellows 11, which protect the actuator 1 from contamination, extends between the pressure piece and the hydraulic module 3.

(6) The distance covered by the clutch actuator 1 along the actuator path is detected by a multi-turn angle sensor 9 over several revolutions of the spindle 4. A pressure sensor 10, which is arranged in the hydraulic path, detects a change in volume of a hydraulic fluid that fills the hydraulic path and also the planetary roller transmission.

(7) Diagnostic software is implemented in the control device 2 of the actuator system 1, which continuously evaluates the pressure signal and the signal from the multi-turn angle sensor. In particular, the pressure signal is observed over an extended period of time. As can be seen from FIG. 2, in which the movement of the master and slave cylinders arranged in the hydraulic path are shown at low temperatures, such as −40° C., the slave cylinder actuating a clutch or a transmission (curve A) cannot follow the position of the master cylinder (curve B) when moving from a high actuator position to a lower actuator position. Particular attention is drawn to the different scaling of the master cylinder position and the slave cylinder position. When the master cylinder moves from the high position to the lower position, a pressure below 0 bar is quickly reached, as can be seen in curve C. This pressure below 0 bar corresponds to a pressure below 1 bar atmospheric pressure. The negative pressure in the master cylinder can have an effect on the seal, for example by folding it over or similar, and the hydraulic fluid can inadvertently penetrate from the planetary roller transmission chamber into the master cylinder. This state will be referred to as “inflating” in the following.

(8) If the negative pressure signal is present for a period of, for example, 0.5 seconds below a predetermined pressure threshold of, for example, −0.2 bar, the “inflating” state is recognized. The control signal sets an “inflating” fault signal to true. When this fault signal is output, an increased sniffing request is output.

(9) The sniffing request distinguishes between four states: no sniffing, sniffing if possible, urgent sniffing, or sniffing now.

(10) This sniffing request can be triggered depending on the length of the period during which the pressure p is below 0 bar. It must be taken into account here that the possible shift in the characteristic curve of the clutch actuator 1, depending on the driving strategy of the vehicle, can only be eliminated in the distant future by a sniffing process. Since the clutch actuator 3 can heat up considerably at low temperatures, depending on the use of the clutch, as a result of the operation of the clutch and therefore an expansion of the hydraulic fluid is to be expected, a sniffing process is immediately triggered by the fault signal.

(11) In FIG. 3, a position of the master cylinder at an ambient temperature of 20° is indicated, at which a pressure change below 0 bar can only be seen very briefly in curve C.

LIST OF REFERENCE SIGNS

(12) 1 Hydraulic clutch actuator 2 Control unit 3 Hydraulic module 4 Spindle 5 Stator 6 Rotor 7 Sleeve 8 Pressure piece 9 Multi-turn angle sensor 10 Pressure sensor 11 Bellows