Method for operating a drive train of a motor vehicle in an inclined position

Abstract

A method for operating a drive train of a motor vehicle in an inclined position, in particular an agricultural or municipal utility vehicle. A connection between a prime mover and at least one drive axle of the motor vehicle is automatically disconnected as part of a function upon actuation of a service brake for stopping the motor vehicle monitored by at least one sensor. To avoid uncontrolled backward rolling, provision is made that a maximum brake pressure applied to achieve or maintain the standstill of the motor vehicle is determined and monitored by continually measuring a brake pressure applied by the service brake. Upon the brake pressure falling below the maximum brake pressure minus a pre-definable pressure difference, the function is automatically deactivated and thus the connection is automatically re-established between the prime mover and the at least one drive axle.

Claims

1. A method of operating a drive train of a motor vehicle in an inclined position, wherein, upon actuation of a service brake monitored by at least one sensor for stopping the motor vehicle, a connection between a prime mover and at least one drive axle of the motor vehicle is automatically disconnected as part of a function, the method comprising: determining and monitoring a maximum brake pressure applied to achieve or maintain standstill of the motor vehicle by continually measuring a service brake pressure applied by the service brake; and automatically deactivating the function, if the service brake pressure falls below the maximum brake pressure minus a predeterminable pressure difference, and thus automatically re-establishing the connection between the prime mover and the at least one drive axle.

2. The method according to claim 1, further comprising detecting the actuation of the service brake by a sensor assigned to a brake circuit of the service brake.

3. The method according to claim 1, further comprising detecting the actuation of the service brake by monitoring an operating state of at least one brake light switch.

4. The method according to claim 1, further comprising adapting an amount of the pressure difference to the determined maximum brake pressure.

5. The method according to claim 1, further comprising performing a selection of the pressure difference based on an assignment to different maximum brake pressures stored in a table.

6. The method according to claim 1, further comprising effecting the disconnection and also a re-establishment of the connection between the prime mover and the at least one drive axle of the motor vehicle by a starting element located between the prime mover and a motor vehicle transmission.

7. A control unit for a drive train of a motor vehicle, the control unit comprising: a first device for regulating a function for operating the drive train of the motor vehicle in an inclined position, wherein upon actuation of a service brake for stopping the motor vehicle, which is monitored by at least one sensor, the first device disconnects a connection between a prime mover and at least one drive axle of the motor vehicle as part of the function, the first device determining and monitoring a maximum braking pressure 4 applied to achieve or maintain a standstill of the motor vehicle by continuously measuring a service brake pressure applied by the service brake, and the first device automatically deactivates the function if the service brake pressure falls below the maximum brake pressure, minus a pre-definable pressure difference, and thus automatically re-establishes the connection between the prime mover and the at least one drive axle.

8. The control unit according to claim 7, wherein the control unit facilitating automatic disconnection of the connection between the prime mover and the at least one drive axle when the service brake is actuated, the control unit further facilitating determining and monitoring of the maximum brake pressure the control unit also facilitating automatic re-connection of the connection between the prime mover and the at least one drive axle if the service brake pressure falls below the maximum brake pressure minus the predeterminable pressure difference, and the at least one sensor for monitoring the actuation of the service brake is arranged in a brake circuit of the service brake.

9. The control unit according to claim 7, wherein a computer program product implementing a routine for deactivating the function by corresponding control commands stored in software of the computer program product.

10. The control unit according to claim 9, wherein the computer program product is stored on a computer-readable data storage medium.

11. A method of operating a drive train of a motor vehicle in an inclined position, the method comprising: actuating a service brake for stopping the motor vehicle and monitoring a brake pressure applied by the service brake with at least one sensor; automatically disengaging, with a control unit, a connection between a prime mover and at least one drive axle of the motor vehicle as part of a function; continually measuring the brake pressure applied by the service brake to determine and monitor a maximum brake pressure at which standstill of the motor vehicle is achieved or maintained; if the control unit determines that the brake pressure applied by the service brake falls below the maximum brake pressure, minus a predeterminable pressure difference, automatically deactivating the function and automatically reengaging the connection between the prime mover and the at least one drive axle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Advantageous embodiments of the invention, which are explained below, are shown in the drawings. In the drawings:

(2) FIG. 1 shows a schematic view of a drive train of a motor vehicle;

(3) FIG. 2 shows a flow chart of a method of operating the powertrain of FIG. 1 in accordance with a preferred embodiment of the invention;

(4) FIG. 3 shows a characteristic curve of a pressure difference; and

(5) FIG. 4 shows a characteristic of a brake pressure as a function of time from the start of a braking operation to the start of a driving-off process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) FIG. 1 shows a schematic view of a drive train 1 of a motor vehicle, which is preferably an agricultural or municipal commercial vehicle and more preferably a farm tractor. The drive train 1 comprises a prime mover 2, which is designed as an internal combustion engine and can be connected to a motor vehicle transmission 4 downstream at its output side via an intermediate starting element 3. While the starting element 3 is preferably in the form of a dry or wet friction clutch, the motor vehicle transmission 4 is, in particular, a manual transmission.

(7) As can be further seen in FIG. 1, the output side of the motor vehicle transmission 4 is connected to an axle transmission 5 of a drive axle 6, wherein the axle transmission 5 is used to allocate a translated drive motion of the prime mover 2 to two drive wheels 7 and 8 arranged on the drive axle 6 via the motor vehicle transmission 4. A wheel brake 9 and 10 of a service brake 11 of the motor vehicle is allocated to the respective the drive wheels 7 and 8, at the actuation of which the relevant drive wheel 7 and 8 is braked. The drive wheels 7 and 8 can also be braked independently of each other to increase maneuverability of the motor vehicle. The actuation or release of the service brake 11 results in an actuation of brake light switches 19 a, 19b associated with the brake pedal mechanism. The actuation states of the two wheel brakes 9 and 10 can be checked on the basis of actuation states S.sub.R,Brems and S.sub.L,Brems of the relevant brake light switch 19a, 19b.

(8) The prime mover 2, the starting element 3, the motor vehicle transmission 4, the axle transmission 5 and also the service brake 11 are each assigned a respective control unit 12 or 13 or 14 or 15 or 16, which are integrated with further control unitsnot shown herein a data bus system 17 of the motor vehicle and which communicate with each other. In this case, the control unit 12 controls the prime mover 2; while an automated opening and closing of the starting element 3 can be controlled by means of the control unit 13. In addition to this automated operation of the starting element 3, there is also the option of manually opening and closing the starting element 3 according to the specifications of the driver of the vehicle, for which purpose the control unit 13 is in communication with a clutch pedalnot shown here.

(9) The control unit 14 is associated with the motor vehicle transmission 4 and can regulate it in the manner of an automated manual transmission, wherein there is also the option of performing operations according to the specifications of the driver in a manual shifting mode. Finally, the control unit 15 is assigned to the axle transmission 5 on the drive axle 6 and the control unit 16 is assigned to the service brake 11 and to a pressure sensor 18 associated to the brake circuit of the service brake 11, which is set up to continuously record a brake pressure p.sub.Brems.

(10) As a special feature, the control unit 13 can be used to implement the automated opening and closing of the starting element 3 as part of a function to prevent the motor vehicle from creeping forward by disconnecting the connection between the prime mover 2 and the motor vehicle transmission 4. A timely re-establishment of the connection between the prime mover 2 and the motor vehicle transmission 4 by closing the starting element 3 can be used, if the motor vehicle at the beginning of the release of the service brake 11 is in an inclined position, i.e. on a downwards or upwards slope, to prevent unwanted movement against the desired direction of travel. To detect that the service brake 11 is released and a start is desired at an early stage, the control unit 13 controls the starting element 3 in accordance with the method illustrated in the flowchart of FIG. 2:

(11) At the beginning of the method, it is first queried in a step S1 whether the function was deactivated manually by the vehicle driver. If that is true, the initial state will be resumed and nothing will be done until the vehicle driver cancels the deactivation.

(12) On the other hand, if the result in step S1 is true, a transition is made to a step S2, in which various conditions are queried. In step S2 a query is executed whether a brake pressure p.sub.Brems detected by the pressure sensor 18 is greater than a limit p.sub.Grenz, which corresponds to the actuation of the service brake 11. In this case, the limit p.sub.Grenz can also have the value zero. Alternatively or additionally, the actuation states of the two wheel brakes 9 and 10 are queried in step S2, for which purpose the respective actuation state S.sub.R,Brems and S.sub.L,Brems of the respective brake light switches 19a, 19b is checked. If the condition required in step S2 is satisfied, the program skips to step S3, whereas in the negative case, the program returns to the state of step S2.

(13) In step S3, the starting element 3 is opened automatically and in this way the connection between the prime mover 2 and motor vehicle transmission 4 is disconnected. Furthermore, in step S3, a maximum brake pressure p.sub.Max is determined, which was applied to bring the motor vehicle to a standstill. The maximum brake pressure p.sub.Max is determined by a continuous detection of the brake pressure p.sub.Brems, which is applied by the service brake 11 until the standstill of the motor vehicle is achieved or subsequently to maintain the standstill of the motor vehicle. After the maximum brake pressure p.sub.Max has been determined, step S4 is entered.

(14) In step S4, the program checks whether if the brake pressure is below the previously determined maximum brake pressure p.sub.Max minus a predefinable pressure difference amount p. If it is exceeded, then the system proceeds to a step S5, while in the negative case, it returns to step S4. As long as the brake pressure does not fall below the maximum brake pressure p.sub.Max minus the pressure difference amount p, the brake pressure p.sub.Brems applied by the service brake 11 is sufficiently large to keep the motor vehicle in its current standstill position. Accordingly, it is inferred therefrom that there is no wish to drive off. If the brake pressure falls below the maximum brake pressure p.sub.Max minus the predetermined pressure difference amount p, this is interpreted as the incipient release of the service brake 11 by relieving a brake pedal to initiate the driving-off process.

(15) In step S5, the starting element 3 is closed automatically and in this way the connection between the prime mover 2 and motor vehicle transmission 4 is re-established. Due to the early initiation of the driving-off process, subsequently an undesired movement of the motor vehicle, in particular located in an inclined position, against the desired direction of travel is prevented. Subsequent to step S5, the function is ended.

(16) FIG. 3 shows an exemplary characteristic curve 20 for the pressure difference amount p, on which the decision in step S4, if the service brake 11 is being released, is based. One or more of these characteristics 20 may be stored in the control unit 13. It is also conceivable to store a freely parameterizable table in order to enable the adaptation between the maximum brake pressure p.sub.Max determined based on a sensor and the pressure difference p.

(17) FIG. 4 shows an exemplary brake pressure curve 21 of a brake pressure detected by the pressure sensor 18 as a function of the time from the start of a braking operation to the start of a driving-off operation. Upon passing the limit p.sub.Grenz at a time t1, which corresponds to a brake pressure of zero bar in the illustrated exemplary embodiment, thereby fulfilling the condition in step S2, the remainder of the brake pressure p.sub.Brems is detected during the braking operation. Upon reaching the standstill of the motor vehicle at time t2, the maximum brake pressure p.sub.Max is determined, which was or is applied by the service brake 11 to bring the motor vehicle to a standstill or hold it there. The release of the service brake 11 at time t3 results in a drop in the brake pressure p.sub.Brems. If the brake pressure p.sub.Brems falls below the previously determined maximum brake pressure p.sub.Max minus the pressure difference amount p, the starting element 3 is automatically closed in accordance with step S5 and thus the connection between the prime mover 2 and the motor vehicle transmission 4 is re-established.

REFERENCE NUMERALS

(18) 1 drive train 2 prime mover 3 starting element 4 vehicle transmission 5 axle transmission 6 drive axle 7 drive wheel 8 drive wheel 9 wheel brake 10 wheel brake 11 service brake 12 control unit 13 control unit 14 control unit 15 control unit 16 control unit 17 data bus system 18 pressure sensor 19a, 19b brake light switch 20 pressure difference characteristic 21 braking pressure curve p.sub.Brems brake pressure p.sub.Grenz limit p.sub.Max maximum brake pressure p pressure difference S.sub.R,Brems operating state brake light switch S.sub.L,Brems operating state brake light switch