Vehicle and method for operating a clutch as a starter element

Abstract

A vehicle, in the drivetrain of which a clutch, in particular a wet-running multi-disc clutch, is connected as a starter element between an internal combustion engine and a transmission, having a clutch controller, which, as a function of current driving operation parameters, determines a setpoint clutch torque and actuates a clutch actuator with a manipulated variable correlating with the setpoint clutch torque, in order to set at the clutch an actual clutch torque, which manipulated variable is determined as a function of the setpoint clutch torque and of a coefficient of friction stored in the clutch controller in an actuation unit of the clutch controller, and having an engine controller, which determines an actual engine rotational speed and an actual engine torque, and, in a stationary state of the vehicle with the internal combustion engine running, regulates the actual engine rotational speed to a predefined idling rotational speed.

Claims

1. A vehicle, comprising: a drivetrain of which a clutch, in particular a wet-running multi-disc clutch, is connected as a starter element between an internal combustion engine and a transmission, having a clutch controller, which, as a function of current driving operation parameters, determines a setpoint clutch torque and actuates a clutch actuator with a manipulated variable correlating with the setpoint clutch torque, in order to set at the clutch an actual clutch torque, which manipulated variable is determined as a function of the setpoint clutch torque and a coefficient of friction stored in the clutch controller in an actuation unit of the clutch controller, and having an engine controller, which determines an actual engine rotational speed and an actual engine torque, and, in a stationary state of the vehicle with the internal combustion engine running, regulates the actual engine rotational speed to a predefined idling rotational speed, wherein an adaptation device is assigned to the clutch controller, and, in the presence of a stationary state of the vehicle with the internal combustion engine operating in the idling mode, starts a coefficient-of-friction adaptation operation, in which, as a function of a checking clutch torque and a checking coefficient of friction, a checking manipulated variable is applied to the clutch actuator, and, in fact, is applied with an increase in the actual engine torque to a checking engine torque, while maintaining the actual engine rotational speed that is regulated to the idling rotational speed, and wherein the adaptation device has an analysis unit, which, from the checking engine torque, from the checking manipulated variable, and from the idling engine torque that is produced in the stationary state of the vehicle with a completely opened or disengaged clutch, calculates an adapted coefficient of friction, which can be stored in the clutch controller instead of the checking coefficient of friction.

2. The vehicle according to claim 1, wherein the manipulated variable acting on the clutch actuator is calculated from the following equation: $\Delta p=\frac{M_{K,\mathrm{soll}}}{\mu \times K_{\mathrm{geo}}},$ where M.sub.K,soll : setpoint clutch torque μ : coefficient of friction K.sub.geo : constant.

3. The vehicle according to claim 1, wherein, in the coefficient-of-friction adaptation operation, a torque difference between the checking engine torque and the idling engine torque corresponds to an actual clutch torque applied to the clutch, which correlates with the checking clutch torque output by the clutch controller.

4. The vehicle according to claim 3, wherein, in the analysis unit of the adaptation device, the adapted coefficient of friction is calculated from the following equation: ${\mu }_a=\frac{\Delta M}{\Delta p_{pr\stackrel{\mathrm{.Math.}}{u}f}\times K_{\mathrm{geo}}},$ where ΔM : torque difference between checking engine torque M.sub.M,prüf and idling engine torque M.sub.Leerlauf Δp.sub.prüf : checking manipulated variable, correlated with checking clutch torque M.sub.K,prüf, K.sub.geo : constant.

5. The vehicle according to claim 1, wherein the coefficient-of- friction adaptation operation is carried out automatically in a driving mode, provided that a detection unit of the adaptation device records a stationary state of the vehicle with the internal combustion engine operating in the idling mode.

6. The vehicle according to claim 1, wherein, in the coefficient-of- friction adaptation operation, the checking coefficient of friction read out in the actuation unit, together with a plurality of other checking coefficients of friction, forms at least one start characteristic diagram stored in tabular form, which can be spanned in a multi-axis characteristic diagram, and in which the coefficients of friction are stored, in particular empirically, as a function of a clutch slippage and a clutch torque, and, in particular, a plurality of such characteristic diagrams are stored as a function of different cooling oil temperatures and/or volumetric flows.

7. The vehicle according to claim 6, wherein, in the adaptation operation, the adapted coefficient of friction calculated in the analysis unit replaces the checking coefficient of friction corresponding thereto in the start characteristic diagram, and the remaining coefficients of friction in the start characteristic diagram can be adjusted to the adapted coefficient of friction, in particular by interpolation or by estimation, and, can be adjusted with the formation of an adapted characteristic diagram.

8. The vehicle according to claim 7, wherein the adapted characteristic diagram is formed with a parallel shift of the start characteristic diagram along a coefficient of friction axis to the adapted coefficient of friction in the characteristic diagram.

9. The vehicle according to claim 6, wherein, in addition, in each adaptation operation, a current oil temperature and a current oil volumetric flow are recorded, and, as a function of thereof, in one of the plurality of such characteristic diagrams, which are stored in the clutch controller, the adapted coefficient of friction replaces the corresponding checking coefficient of friction.

10. The vehicle according to claim 5, wherein the coefficient-of-friction adaptation operation is carried out automatically in the stationary state of the vehicle, for which a creep torque is applied to the clutch, in order to make possible an instantaneous startup after the release of a vehicle brake, wherein the creep torque corresponds to the checking setpoint torque used in the coefficient-of-friction adaptation operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantageous embodiments and enhancements as well as the advantages thereof will be explained in detail below on the basis of drawings.

(2) Shown are:

(3) FIG. 1 in a highly simplified block diagram, the drivetrain with assigned clutch controller for automatic actuation of a wet-running multi-disc clutch as a starter element;

(4) FIG. 2 a characteristic diagram, from which a coefficient of friction can be read as a function of the clutch slippage and the clutch torque, in order to calculate the manipulated variable acting on the clutch actuator;

(5) FIG. 3 a view corresponding to FIG. 1 with an additional adaptation device; and

(6) FIG. 4 a view corresponding to FIG. 3 for illustration of the adaptation operation.

DETAILED DESCRIPTION

(7) Shown in the FIG. 1, in a highly simplified way, is a drivetrain of a motor vehicle, in which an internal combustion engine 1 can be driven, with intermediate connection of a starter element 3 to a vehicle transmission 5. The internal combustion engine 1 can be actuated via an engine controller 7, which, in the driving mode, determines an actual engine rotational speed as well as an actual engine torque, and, in a stationary state of the vehicle, regulates the actual engine rotational speed to a predefined idling rotational speed n.sub.Leerlauf (FIG. 3). In FIG. 1, the starter element 3 is a wet-running multi-disc clutch, which can be actuated electrohydraulically via a clutch controller 9. For this purpose, the multi-disc clutch 3 has a ring piston as a clutch actuator 11, which is in signal connection with the clutch controller 9 via a hydraulic system 13 and an actuation unit 15.

(8) In driving mode, as a function of current driving operation parameters, the clutch controller 9 calculates a setpoint clutch torque M.sub.K,soll, which, in the actuation unit 15, is converted to a set pressure Δp correlating therewith. The set pressure Δp acts on the clutch actuator 11 in order to adjust an actual clutch torque M.sub.K,ist, which matches the setpoint clutch torque M.sub.K,soll that was calculated using the clutch controller 9, in the multi-disc clutch 3.

(9) The manipulated variable Δp is determined in the actuation unit 15 as a function of the setpoint clutch torque M.sub.K,soll and as a function of a coefficient of friction μ stored in the clutch controller 9 and, in fact, is determined by means of the following equation:

(10) $\Delta p=\frac{M_{K,\mathrm{soll}}}{\mu \times K_{\mathrm{geo}}},$
where

(11) M.sub.K,soll setpoint clutch torque μ coefficient of friction K.sub.geo constant.

(12) In FIG. 1, the actuation unit 15 is in signal connection with a database 17. Stored in the database 17 diagrams are coefficients of friction μ, in a plurality of coefficient-of-friction characteristic, only one of which is shown in FIG. 1. By way of example, in FIG. 2, such a coefficient-of-friction characteristic diagram K is spanned in a multi-axis characteristic field diagram as a closed envelope surface. In the characteristic diagram of FIG. 2, it is possible to determine respectively assigned coefficients of friction μ, as a function of a clutch slippage Δn and a clutch torque M.sub.K. The coefficient-of-friction characteristic diagram shown in FIG. 2 is applicable for a predefined cooling oil temperature as well as a predefined cooling oil volumetric flow m. In the database 17, a plurality of such coefficient-of-friction characteristic diagrams are stored as a function of different cooling oil temperatures T.sub.öl and cooling oil volumetric flows.

(13) The characteristic diagram K illustrated in FIG. 2 was set at the factory and is based, for example, on empirical determination. By way of example, in the database 17 for a clutch slippage Δn of 1500 rpm and for a setpoint clutch torque of 200 Nm in FIG. 2, a coefficient of friction μ that lies at about 60% is determined. This coefficient of friction μ is read out in FIG. 1 in the actuation unit 15 in order to compute the manipulated variable Δp correlating with the setpoint clutch torque M.sub.K,soll.

(14) Described below, on the basis of FIGS. 3 and 4, is an adaptation operation, with which the characteristic diagram K shown in FIG. 2 can be adapted to a current torque transmission behavior of the multi-disc clutch 3: For carrying out the adaptation operation, an adaptation device 19 is assigned to the clutch controller 9 in FIG. 3. Said adaptation device starts the coefficient-of-friction adaptation operation in the presence of a stationary state of the vehicle with the internal combustion engine 1 operating in the idling mode. Generated in the clutch controller 9 in the coefficient-of-friction adaptation process is a checking clutch torque M.sub.K,prüf (that is, in FIG. 4, a creep torque of 15 Nm). In the characteristic diagram of FIG. 4, as a function of the checking clutch torque M.sub.K,prüf and the current slippage Δn (that is, the idling rotational speed), a checking coefficient of friction μ.sub.prüf is determined and read out at the actuation unit 15. The manipulated variable 15 calculates from it a checking manipulated variable Δp.sub.prüf, with which the clutch actuator 11 is actuated.

(15) Based on the actuation of the clutch actuator 11 with the checking manipulated variable Δp.sub.prüf, there occurs in FIG. 3 an increase in the actual engine torque to a checking engine torque M.sub.M,prüf, while maintaining, however, the actual engine rotational speed that is regulated to the idling rotational speed n.sub.Leerlauf.* In a subtraction element 21 of the adaptation device 19, a torque difference ΔM, which is obtained in a stationary state of the vehicle with a completely opened or disengaged multi-disc clutch 3, is determined from the checking engine torque M.sub.M,prüf* and the idling engine torque M.sub.Leerlauf.

(16) The torque difference ΔM determined in the subtraction element 21 corresponds to an actual clutch torque of the multi-disc clutch 3 that is set by actuation with the checking manipulated variable Δp.sub.prüf and matches the setpoint clutch torque M.sub.K,soll. By means of the torque difference ΔM, an adapted coefficient of friction μ.sub.a is calculated in an analysis unit 23 and, in fact, is calculated by means of the following equation:

(17) ${\mu }_a=\frac{\Delta M}{\Delta p_{pr\stackrel{\mathrm{.Math.}}{u}f}\times K_{\mathrm{geo}}},$
where ΔM torque difference between the checking engine torque M.sub.M,prüf and the idling engine torque M.sub.Leerlauf; Δp.sub.prüf checking manipulated variable, which correlates with the checking clutch torque M.sub.K,prüf.

(18) The adapted coefficient of friction μ.sub.a calculated in the analysis unit 23 is transmitted to the database 17 and is stored there in the database 17 instead of the checking coefficient of friction μ.sub.Prüf.

(19) The adaptation operation illustrated above is carried out automatically in the driving mode, provided that a detection unit of the adaptation device 19 records a stationary state of the vehicle, in which the internal combustion engine 1 is operated in the idling mode, such as, for example, in a stationary state of the vehicle at a traffic light, for which, in the stationary state of the vehicle, a creep torque is applied to the multi-disc clutch 3, in order to make possible an instantaneous startup after the release of the vehicle brake, with the creep torque corresponding to the checking setpoint torque M.sub.K,prüf used in the adaptation operation.

(20) As can be seen from FIG. 3, the adapted coefficient of friction μ.sub.a calculated in the adaptation operation in the analysis unit 23 replaces the checking coefficient of friction μ.sub.prüf corresponding to it in the start characteristic diagram K (FIG. 4). The remaining coefficients of friction in the start characteristic diagram K are adjusted, in particular by interpolation, to the calculated adapted coefficient of friction μ.sub.a, as a result of which an adapted characteristic diagram K.sub.a (partially indicated in FIG. 4) is obtained. In a variant with a reduced computational time, the adapted characteristic diagram K.sub.a can be shifted with a parallel shift of the start characteristic diagram K along a coefficient-of-friction axis in the characteristic diagram to the calculated adapted coefficient of friction μ.sub.a, as it is indicated in FIG. 4.