Method for operating an electrically actuable feed pump in a hydraulic circuit

Abstract

A method for operating an electrically actuable feed pump in a hydraulic circuit, which draws in fluid from a fluid sump with a normal supplying of fluid. The fluid circulated in the hydraulic circuit can be returned back, and air is sucked in at least partially with an undersupply of fluid. The electric motor is integrated in a control circuit, which is provided with a control unit, which actuates the electric motor based on an actual rotational speed and a setpoint rotational speed with an actuation rotational speed. The evaluation unit compares the actual rotational speed to a reference rotational speed and in particular always with an identical current consumption. The evaluation unit then determines based on the comparison whether a fluid undersupply is present.

Claims

1. A method for operating an electrically actuable feed pump comprising: an electric motor in a hydraulic circuit, which draws in a normal supply of fluid from a fluid sump, wherein the fluid circulated in the hydraulic circuit can be fed back into the fluid sump, wherein air intake occurs at least partially during a fluid undersupply condition, wherein the electric motor is integrated with a control circuit, which is provided with a control unit, which actuates the electric motor on the basis of an actual rotational speed and of a target rotational speed, wherein the control unit is associated with an evaluation unit for detection of the fluid undersupply condition, which is provided with a filling state model unit, wherein the evaluation unit compares the actual rotational speed of the electric motor to a reference rotational speed at an equivalent current consumption in order to detect the fluid undersupply condition, wherein the equivalent current consumption is correlated with the reference rotational speed, wherein the filling state model unit maintains a predictive model which generates a predicted fluid level of the fluid sump based on input data, the input data of the predictive model comprising a time variable and an occurrence of at least one event which exerts influence on an actual fluid level of the fluid sump, and wherein an evaluation of the feed pump for detection of the fluid undersupply condition is carried out only upon the fulfillment of a test condition in which the predictive model predicts a predicted fluid level of the fluid sump that is above a specified level.

2. The method according to claim 1, wherein the electric motor of the feed pump is provided with a current limit for overload protection, by which an actual current consumption of the electric motor is limited to a maximum current consumption, wherein a maximum normal supply rotational speed is determined from a rotational speed corresponding to the actual rotational speed of the electric motor which occurs when the electric motor is supplied with the maximum current consumption and the feed pump is provided with a normal fluid supply without the intake of air, and wherein, during a fluid undersupply condition, the target speed is set to be greater than the maximum normal supply rotational speed.

3. The method according to claim 2, wherein the evaluation unit is provided with a comparison unit which compares the actual rotational speed of the electric motor with the reference speed, wherein the fluid undersupply condition is determined to be present when the actual rotational speed of the electric motor is greater than the reference speed, wherein the actual rotation speed of the motor is that which occurs when the motor is supplied with the maximum current consumption, wherein the reference speed is a correlating maximum normal supply rotational speed.

4. The method according to claim 3, wherein the comparison unit is associated with a rotational speed constancy unit, by which it is detected whether the electric motor is operated at a constant actual rotational speed, wherein the comparison between the actual rotational speed of the electric motor and the maximum normal supply rotational speed is carried out only if the rotational speed constancy unit determines the electric motor is operated at the constant actual rotation speed.

5. The method according to claim 3, wherein, after checking for fluid undersupply, the target speed is reset from a testing speed, and the evaluation unit is deactivated.

6. The method according to claim 2, wherein the maximum normal supply rotational speed is determined empirically by the evaluation unit, and the maximum current consumption and a correlating maximum normal supply rotational speed are stored as a pair of values in the evaluation unit, wherein a plurality of the pair of values are stored, each pair of values being respectively associated with a different operating temperature.

7. The method according to claim 2, wherein in order to provide the electric motor with the maximum current consumption, a target rotational speed for the electric motor is set by the control circuit to a speed which exceeds an anticipated maximum rotational speed at the maximum current consumption, so that performance deviations of the feed pump from a reference feed pump may be taken into consideration.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention and its advantageous embodiments and further developments, as well as their advantages, will now be explained with reference to the figures, which show the following:

(2) FIG. 1 shows a partial block diagram of a hydraulic system of a dual clutch drive of a motor vehicle; and

(3) FIG. 2 shows a basic system architecture of the evaluation unit for detecting a fluid undersupply.

DETAILED DESCRIPTION OF THE FIGURES

(4) FIG. 1 shows a highly simplified block diagram of a hydraulic system of a dual clutch transmission of a motor vehicle. A hydraulic cylinder 23 of the clutch K1 as well as a hydraulic cylinder 23 of actuators 22 are actuated by means of the hydraulic system. The actuators 22 are for examples dual synchronizer clutches, by means of which the gear shifts are operated in the dual clutch transmission. As shown in FIG. 1, the hydraulic system is provided with a high-pressure circuit H as well as with a low-pressure circuit N. In the high-pressure circuit H, all the hydraulic cylinders 23 of separating clutches connected in it (only clutch K1 is shown in FIG. 1), as well as the actuators 22 are impacted via a pressure accumulator 25 with a storage pressure p.sub.s. For this purpose, a pressure accumulator, which is connected to a main line 27, is guided via a branch line 31, not described further, to the hydraulic cylinders 23. In the branch lines 31 are arranged respective control valves 35, which can be controlled via a central control device 39. The hydraulic system shown in FIG. 1 will be described only to the extent required to understand the invention. Therefore, the hydraulic system is provided with a feed-hydraulic pump 53, which is connected on the suction side to an oil sump 55. The feed-hydraulic pump 53 can be controlled for charging the pressure accumulator 25 via an electric motor 57 by the control unit 39. In addition, the feed-hydraulic pump 53 is arranged together with a cooling hydraulic pump 59 on a common drive shaft 60, which can be controlled by the electric engine 57. The cooling hydraulic pump 59 is also connected on the suction side to the oil sump and on the pressure side it is connected to a low pressure circuit N.

(5) As is further apparent from FIG. 1, the components connected in the respective hydraulic circuits N, H are in each case hydraulically connected via the return lines to the oil sump 55, so that the hydraulic oil circulated in the hydraulic circuit N, H is returned again into the oil sump 55 and it is collected there while an actual filling state FS.sub.act is being formed.

(6) As shown in FIG. 1, the motor actuation is carried out by means of a rotational speed circulation control circuit R, in which in addition to the control unit 39 is integrated also a current measuring device 75, which detects an actual current consumption I.sub.act of the electric motor 57, as well as a rotational speed sensor 77 which detects an actual rotational speed n.sub.act of the electric motor 57. On the input side of the control unit 39 is created a setpoint rotational speed n.sub.setp, which together with the actual current consumption I.sub.act and the actual rotational speed n.sub.act form the basis for determining an actuate rotational speed n.sub.actuate by means of which the control unit actuates the electric motor 57.

(7) The electric motor 57 is provided with supply pumps 53, 59 which are in current practice used as an overload protection with a current limit, which is set with the actual current consumption I.sub.act of the electric motor 57 to a limiting maximum current consumption I.sub.max.

(8) As is further apparent from FIG. 1, the control circuit R is connected in terms of signal propagation via a signal line 78 to an evaluation unit 79, by means of which an oil undersupply can be detected in the hydraulic circuit N, H. If such an oil undersupply is generated, the evaluation unit 79 generates a warning message W in a signal generation module 84 (FIG. 2), by means of which an oil undersupply can be indicated.

(9) The evaluation unit 79, which will be described later and which is used to test for undersupplying of oil, uses in this case the following facts: a maximum normal supply rotational speed n.sub.max,N is established for a normal fluid supply without air intake and with a maximum current consumption I.sub.max as a maximum normal supply rotational speed n.sub.max,N. In contrast to that, a rotational speed n.sub.act is established, which is greater than the maximum normal supply n.sub.max,N, with a fluid undersupply and with at least partial air intake as well as with a maximum electric motor current consumption I.sub.max.

(10) The basic program architecture as well as the mode of operation of the evaluation unit 79 are indicated in FIG. 2. Accordingly, the evaluation unit 79 is provided with a filling state model unit 81, which detects events exerting an influence on the current filling state FS.sub.act in the oil sump 55, such as for example a time period during the vehicle was turned off, or an operating temperature. The filling state unit 81 determines as a function of these events a temporal model filling state profile FS.sub.m(t), which recreates the temporal actual filling state profile FS.sub.act(t).

(11) In order to obtain a meaningful test result, the actual test for oil undersupply is carried out only when a testing condition is verified, namely the condition that the temporal model filling state profile F.sub.Sm(t) must be greater than or equal to a predefined test filling state FS.sub.test. The testing for an oil undersupply can be in addition also associated with another test condition, wherein the condition of a predetermined traveling distance, for example 500 km, must be also fulfilled. For this purpose, in the evaluation unit can be integrated also a suitably designed delay unit. If these testing conditions are fulfilled, a comparison unit 80 and a program module 82 are then actuated in the following process step with a trigger signal S.sub.T.

(12) The setpoint rotational speed n.sub.setp is then set in the program module 82 to a greatly increased test speed n.sub.test, which is substantially greater than a rotational speed that can be represented with the maximum current consumption I.sub.max of the control circuit R. In this manner it is ensured that the electric motor 57 is operated with a maximum current consumption I.sub.max during the test for an oil undersupply.

(13) In addition, if the trigger signal S.sub.T is present in the comparison unit 82, the actual rotational speed n.sub.act to be set is compared to a maximum normal supply rotational speed n.sub.max,N. The comparison 80 unit is associated with a rotational speed constant unit 83, by means of which it is detected whether the electric motor 57 is operated at a constant actual rotational speed n.sub.act. The comparison mentioned above is carried out only if the rotational speed constant is present in the comparison unit 80.

(14) The maximum normal supply rotational speed n.sub.max,N, which is to be set with a normal supplying of fluid, without air intake and with maximum current consumption I.sub.max of the electric motor, is determined empirically and it is stored together with the maximum current consumption I.sub.max as a pair of values in the evaluation unit 79. As is evident from FIG. 2, a plurality of such value pairs are stored in the evaluation unit 79, which are respectively associated with different operating temperatures T.sub.B. In this manner, the comparison unit 80 can determine with interpolation of the maximum normal supply rotational speed n.sub.max,N that is required as a reference rotational speed in a characteristics diagram, by means of which the fluid temperature and the actual current can be indicated.

(15) When an actual rotational speed n.sub.act is present, which is greater than the maximum normal supply rotational speed n.sub.max,n, an oil undersupply is detected in the comparison unit 80. In this case, the signal generation module 84 will generate the warning signal W, by means of which the oil undersupply can thus be indicated.

(16) As shown in FIG. 2, the comparison unit 80 is connected with a signal line 85 to the signal generation module 84. A return line 85 is branched from the signal line 85 to the filling state unit 81 and to the delay module 87.

(17) After the test for an oil undersupply has been carried out via the return line 86, the filling state model unit 81 resets again the rotational speed requirement in the program module 82 from the text rotational speed n.sub.test to the setpoint rotational speed n.sub.setp. In addition, the delay module 87 is activated.