Method for preventing stalling of an internal combustion engine of a motor vehicle

Abstract

A method for preventing stalling of an internal combustion engine of a motor vehicle, wherein the motor vehicle has at least one internal combustion engine, at least one automatically controlled clutch, and at least one transmission, wherein a drive shaft of the internal combustion engine can be coupled to a transmission input shaft of the transmission by means of the clutch to transmit torque, wherein the clutch is disengaged if a calculated rotational speed value of the drive shaft is less than a certain threshold value, and wherein the rotational speed value is calculated, in particular continually or continuously, as a function of a determined, current rotational speed of the drive shaft and as a function of a determined, current speed gradient of the drive shaft.

Claims

1. A method for preventing stalling of an internal combustion engine of a motor vehicle, the motor vehicle comprising at least one internal combustion engine, at least one automatically controlled clutch, and at least one transmission, wherein a drive shaft of the internal combustion engine is adapted to be coupled to a transmission input shaft of the transmission via the clutch to transmit torque, wherein the clutch is designed as part of an automatic transmission or part of an automatic dual-clutch transmission, the method comprising: calculating a rotational speed value continually or continuously as a function of a determined, current rotational speed of the drive shaft and as a function of a determined, current speed gradient of the drive shaft; determining a current temperature of the clutch; determining a response time of the clutch as a function of the temperature of the clutch via a control and/or regulation device of the motor vehicle; and calculating the rotational speed value from a sum of the determined, current rotational speed of the drive shaft and the product of the current speed gradient of the drive shaft and the response time of the clutch; and disengaging the clutch if the calculated rotational speed value of the drive shaft is less than a certain threshold value.

2. The method according to claim 1, wherein the response time of the clutch is read out from a characteristic map stored in the control and/or regulation device of the motor vehicle, in particular from a saved data table.

3. The method according to claim 1, wherein the response time of the clutch is calculated by a model stored in the control and/or regulation device of the motor vehicle.

4. The method according to claim 1, wherein the clutch is actuated by a hydraulic fluid, and wherein the temperature of the clutch is measured and/or determined with the aid of the hydraulic fluid.

5. The method according to claim 1, wherein the response time of the clutch has values between 1 s at ?35? C. and 0.03 s at 90? C.

6. The method according to claim 1, wherein a disengagement offset is read out from a characteristic map stored in the control and/or regulation device of the motor vehicle or is calculated by a model stored in the control and/or regulation device of the motor vehicle, wherein the threshold value is calculated from the difference between a specified, certain target idle speed of the drive shaft and the disengagement offset, or wherein the disengagement offset is subtracted mathematically from the target idle speed.

7. The method according to claim 1, wherein the correspondingly implemented stall protection of the internal combustion engine is not deactivated again until after a specific time following a startup of the motor vehicle and/or following a gear change of the transmission.

8. The method according to claim 1, wherein the clutch is not engaged again after a disengagement of the clutch until the speed gradient assumes positive values.

9. The method according to claim 8, wherein an engagement offset is read out from a characteristic map stored in the control and/or regulation device of the motor vehicle or is calculated by means of a model stored in the control and/or regulation device of the motor vehicle, wherein the clutch is not engaged again after a disengagement of the clutch until the determined, current rotational speed of the drive shaft is greater than the difference between the specified, certain target idle speed of the drive shaft and the engagement offset, or wherein the engagement offset is subtracted mathematically from the target idle speed in this case.

10. The method according to claim 9, wherein a value of the engagement offset is less than a value of the disengagement offset.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 is a graph of the rotational speed of the drive shaft as a function of time, in a schematic representation, and

(3) FIG. 2 is a dependence of the response time of the clutch on the temperature of the clutch, in tabular form.

DETAILED DESCRIPTION

(4) The method for preventing stalling of an internal combustion engine of a motor vehicle or the sequence of this method can be understood on the basis of the schematic representation of the graph of the rotational speed n of the drive shaft of the internal combustion engine as a function of the time t in FIG. 1.

(5) The motor vehicle has at least one internal combustion engine, at least one automatically controlled clutch, and at least one transmission, in particular that is automatically controlled, in particular an automatic transmission. A drive shaft of the internal combustion engine can be coupled to a transmission input shaft of the transmission by means of the clutch to transmit torque. In particular, the clutch is designed as part of an automatic transmission, in particular as part of an automatic dual-clutch transmission.

(6) The clutch is disengaged if a calculated rotational speed value n.sub.CALC of the drive shaft is less than a certain threshold value S. The calculated rotational speed value n.sub.CALC, which does not correspond to the current speed of the drive shaft is calculated, in particular continually or continuously, as a function of a determined, current rotational speed n.sub.AKT of the drive shaft and as a function of a determined, current speed gradient dn/dt of the drive shaft.

(7) Continually or continuously in this context can mean, in particular, that a calculated rotational speed value n.sub.CALC is present at all times, precisely so that a stalling can be avoided at all times.

(8) Usually, the current rotational speed n.sub.AKT of the drive shaft is determined with the aid of speed sensors, which supply measurement signals at discrete angular positions of the drive shaft, and thus at discrete time intervals, wherein these discrete time intervals are so small, however, that a continuous signal can then be assumed here in the sense of reliable avoidance of stalling.

(9) A current temperature T of the clutch is determined, in particular is measured. A certain response time Z of the clutch is likewise determined as a function of the determined temperature T of the clutch, in particular by means of a control and/or regulation device of the motor vehicle. The rotational speed value n.sub.CALC is calculated from the sum of the determined, current rotational speed n.sub.AKT of the drive shaft and the product of the current speed gradient dn/dt of the drive shaft and the response time Z of the clutch. This relationship can be represented as a formula as follows:

(10) $n_{\mathrm{CALC}}=n_{\mathrm{AKT}}+\frac{d_n}{d_t}?Z$

(11) A risk of the internal combustion engine stalling is present when, in particular, the rotational speed n of the drive shaft decreases. When the rotational speed n of the drive shaft decreases, the speed gradient dn/dt has negative values, so that the calculated rotational speed value n.sub.CALC is then less than the determined, current rotational speed n.sub.AKT of the drive shaft. At the current, first time t.sub.1, the response time Z is then in the future or extends into the future. It is assumed that the torque decreases linearly with the slope characterized by the speed gradient dn/dt after actuation of the clutch and until the response time Z has elapsed at a second time t.sub.2 that likewise is in the future. Up until the time t.sub.1, the curve of the rotational speed n represented in FIG. 1 corresponds to the values of the rotational speed determined up to that point. From the time t.sub.1 onward, the curve of the rotational speed n is shown that would result if the motor vehicle were to continue to be operated under the same conditions as at the time t.sub.1, in particular without stall avoidance and without the associated disengagement of the clutch, wherein the rotational speed n would then drop to the value zero, which would then mean precisely the stalling of the internal combustion engine.

(12) The response time Z of the clutch is read out from a characteristic map stored in the control and/or regulation device of the motor vehicle, in particular from a table. Such a characteristic map, in particular the table, is represented in FIG. 2. The table here schematically shows different temperatures T.sub.1 to T.sub.n and/or temperature ranges T.sub.1 to T.sub.n, wherein a particular response time Z.sub.1 to Z.sub.n is associated with each temperature or each temperature range.

(13) The current temperature T is then compared with the temperatures T.sub.1 to T.sub.n or with the temperature ranges T.sub.1 to T.sub.n by means of the control and/or regulation device, and the associated response time Z.sub.1 to Z.sub.n is then determined in this way.

(14) Alternatively, it is possible that the response time Z of the clutch is calculated by means of a model stored in the control and/or regulation device of the motor vehicle.

(15) The clutch usually can be actuated by means of a hydraulic fluid. The current temperature T of the clutch is therefore measured and/or determined with the aid of the hydraulic fluid, in particular. However, the use of clutch actuators, which can be actuated electrically, for example, is also possible.

(16) The response time Z of the clutch has values between 1 s at ?35? C. and 0.03 s at 90? C.

(17) A disengagement offset ?.sub.1 is read out from a characteristic map stored in the control and/or regulation device of the motor vehicle or is calculated by means of a model stored in the control and/or regulation device of the motor vehicle. The disengagement offset ?.sub.1 can be applied in this case. The certain threshold value S is then calculated, in particular from the difference between a specified, certain target idle speed n.sub.0 of the drive shaft and the disengagement offset ?.sub.1. In particular, the disengagement offset ?.sub.1 is subtracted mathematically from the target idle speed no. This relationship can be represented as a formula as follows: S=n.sub.0??.sub.1

(18) Additional parameters that, in particular, have an effect on the stalling of the internal combustion engine can be taken into account by means of the disengagement offset ?.sub.1.

(19) The stall protection of the internal combustion engine can be deactivated, in particular only after a certain time following a startup of the motor vehicle and/or following a gear change of the transmission. Furthermore, the stall protection can also be activated during the entire operating period of the motor vehicle.

(20) The clutch is not engaged again after implementation of the stall protection or after a disengagement of the clutch, in particular until the speed gradient dn/dt assumes positive values.

(21) An engagement offset ?.sub.2 is read out from a characteristic map stored in the control and/or regulation device of the motor vehicle or is calculated by means of a model stored in the control and/or regulation device of the motor vehicle. This engagement offset ?.sub.2 can consequently also be applied. The clutch is not engaged again after a disengagement of the clutch until the determined, current rotational speed of the drive shaft n.sub.AKT is greater than the difference between the specified, certain target idle speed n.sub.0 of the drive shaft and the engagement offset ?.sub.2. In particular, the engagement offset ?.sub.2 is subtracted mathematically from the target idle speed n.sub.0 in this case.

(22) A value of the engagement offset ?.sub.2 is less than a value of the disengagement offset ?.sub.1. This relationship can be represented as a formula as follows: ?.sub.2<?.sub.1

(23) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.