METHOD OF OPERATING THE POWER TRAIN OF A VEHICLE

Abstract

A method of operating a drive-train of a vehicle having a drive engine, a motor vehicle transmission, at least one drive axle and a further axle that can be engaged to drive. In context of a function, a connection between the drive engine and the at least one drive axle of the vehicle is automatically interrupted, and the function is automatically activated when certain conditions exist. For the activation of the function, a service brake of the vehicle must be actuated and, as a condition, the vehicle must be stopped. To check whether operation of the vehicle in the all-wheel mode is necessary, when the function is carried out, a brake pressure is determined and, if the brake pressure exceeds a brake pressure limit value, the driving engagement of the further axle is carried out automatically as the function is deactivated for re-starting the vehicle.

Claims

1-12. (canceled)

13. A method for operating a drive-train (1) of a motor vehicle comprising a drive engine (2), a motor vehicle transmission (4), at least one drive axle (6), and a further axle (18) that is drivingly engagable, the method comprising: automatically interrupting, in a context of a function, a connection between the drive engine (2) and the at least one drive axle (6) of the motor vehicle, the function being automatically activated when certain conditions exist, and the certain conditions for activating the function comprising activation of a service brake (11) of the motor vehicle and braking the vehicle to rest, determining a brake pressure (p.sub.Brems) when the function is carried out, and if the brake pressure (p.sub.Brems) exceeds a brake pressure limit value (p.sub.Grenz), automatically carrying out the driving engagement of the further axle (18) as the function is deactivated for re-starting the motor vehicle.

14. The method according to claim 13, further comprising, if a speed limit (v.sub.Anfahr) is exceeded after re-starting, automatically interrupting the driving connection of the further axle (18).

15. The method according to claim 13, further comprising parameterizing the brake pressure limit value (p.sub.Grenz) as a function of a mode of operation of the motor vehicle.

16. The method according to claim 15, further comprising determining the mode of operation of the motor vehicle by recognizing components that are connectable to the motor vehicle and which increase a total weight of the motor vehicle.

17. The method according to claim 16, further comprising control-technologically connecting the components to the motor vehicle by a bus system (17).

18. The method according to claim 13, further comprising detecting the brake pressure (p.sub.Brems) of at least one brake circuit of the service brake system (11).

19. The method according to claim 13, further comprising effecting a separation and re-establishment of the connection between the drive engine (2) and the at least one drive axle (6) of the motor vehicle via a starting element (3) located between the drive engine (2) and the motor vehicle transmission (4).

20. The method according to claim 13, further comprising using a clutch unit (21) to control engagement of the further axle (18).

21. The method according to claim 13, further comprising using one of an agricultural or a municipal utility vehicle as the motor vehicle.

22. A control unit (13) for a drive-train (1) of a motor vehicle comprising: a device for regulating a function for separating a connection between a drive engine (2) and at least one drive axle (6) of the vehicle, the device being designed for automatically controlling a clutch unit (21) for drivingly connecting a further axle (18) to the drive engine (2) and a motor vehicle transmission (4), the device activating a function in the drive-train (1) which brings about a separation of a connection between the drive engine (2) and the at least one drive axle (6) of the vehicle, a service brake (11) of the vehicle being actuatable and the vehicle being braked to a rest to activate the function, and when carrying out the function, a brake pressure (p.sub.Brems) being applied to the service brake for braking the vehicle to the rest, the brake pressure being determinable, and the further axle (18) being automatically engaged when the brake pressure exceeds a brake pressure limit value (p.sub.Grenz).

23. The control unit (14) according to claim 22, wherein the control unit carries out a method of operating the drive-train (1) of the vehicle, the method including: automatically interrupting, in a context of the function, the connection between the drive engine (2) and the at least one drive axle (6) of the vehicle, the function being automatically activated when certain conditions exist, and the certain conditions for activating the function including activating the service brake (11) and braking the vehicle to rest; determining the brake pressure (p.sub.Brems) when the function is carried out; and, if the brake pressure (p.sub.Brems) exceeds the brake pressure limit value (p.sub.Grenz), carrying out the driving engagement of the further axle (18) automatically as the function is deactivated for re-starting the motor vehicle.

24. The control unit (14) according to claim 23, in combination with a computer program product by which the method of operating the drive-train (1) of the vehicle can be carried out, wherein a routine for activating the function by corresponding control commands stored by software means is implemented.

25. The control unit (14) and the computer program product according to claim 24, in combination with a data carrier on which the computer program product is stored.

26. A method of operating a drive-train of a motor vehicle, the vehicle having a drive engine, a transmission, at least one drive axle and a further axle that is drivingly engagable, the method comprising: determining, via a control unit, whether a service brake of the motor vehicle has been actuated and whether the vehicle is braked to a stop; automatically activating a function, via the control unit, if the service brake is actuated and the vehicle is braked to a stop; in a context of the function, automatically disengaging a starting element to interrupt a connection between the drive engine and the at least one drive axle of the vehicle; determining, via the control unit, a brake pressure when the function is carried out; comparing, via the control unit, the determined brake pressure to a brake pressure limit value; and if the brake pressure exceeds the brake pressure limit value, once the function is deactivated, automatically engaging a clutch to drivingly connect the further axle for re-starting the motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] An advantageous embodiment of the invention, which is explained below, is illustrated in the figures, which show:

[0024] FIG. 1: A schematic representation of a drive-train of a motor vehicle;

[0025] FIG. 2: A flow chart of a method for operating the drive-train of FIG. 1, corresponding to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] FIG. 1 shows a schematic representation of a drive-train 1 of a motor vehicle, which is preferably an agricultural or municipal utility vehicle and more preferably still an agricultural tractor. The drive-train 1 comprises a drive engine 2 in the form of an internal combustion engine which, on a drive output side, can be connected by way of an intermediate starting element 3 to a downstream motor vehicle transmission 4. While the starting element 3 is preferably a dry-running or wet-running friction clutch, the motor vehicle transmission 4 is in particular a manual transmission.

[0027] As can also be seen from FIG. 1, on its drive output side the motor vehicle transmission 4 is connected to an axle transmission 5 of a drive axle 6 so that by way of the axle transmission 5 drive movement of the drive engine 2, geared by the motor vehicle transmission 4, is distributed to two drive wheels 7 and 8 of the drive axle 6. Associated with each of the drive wheels 7 and 8 is a respective wheel brake 9 or 10 of a service brake system 11 of the motor vehicle, which when actuated, brakes the drive wheel 7 or 8 concerned. In this case the drive wheels 7 and 8 can be braked independently of one another so as to increase the maneuverability of the motor vehicle.

[0028] In addition an axle 18 that can be drivingly engaged is provided, which has wheels 19, 20. In this drive-train 1, the axle 18 can be connected by a controllable clutch unit 21 in such manner that both the drive wheels 7, 8 of the drive axle 6 and the wheels 19, 20 of the further axle 18 are driven. The clutch unit 21 can be in the form of an electronically controlled frictional disk clutch.

[0029] The drive engine 2, the starting element 3 and the clutch unit 21, the motor vehicle transmission 4, the axle transmission 5 and also the service brake system 11 are in each case associated with respective control units 12 or 13 or 14 or 15 or 16, which are connected with further control unitsnot shown in greater detail hereby a data bus system 17 of the motor vehicle and which communicate with one another. In this case the control unit 12 regulates the drive engine 2, while by means of the control unit 13 an automated opening and closing of the starting element 3 and, independently of the control of the starting element 3, opening and closing of the clutch unit 21 can be regulated. Besides this automated operation of the starting element 3, however, the starting element 3 can also be optionally opened and closed in accordance with the wishes of the driver of the vehicle, for which purpose the control unit 13 is connected to a clutch pedalnot shown further here. The clutch unit 21 can also be controlled manually in accordance with a driver's wish, in order when necessary to enable all-wheel operation of the motor vehicle.

[0030] The control unit 14 is associated with the motor vehicle transmission 4 and can regulate it in the manner of an automated change-speed transmission, such that in this case too it is possible to carry out shifting operations in a manual mode in accordance with the driver's wishes. Finally, the control unit 15 is associated with the axle transmission 5 and with a rotational speed sensor 22, and the control unit 16 is associated with the service brake system 11. The control unit 16 receives from at least one pressure sensor 23 signals for evaluation, which signals indicate the brake pressure p.sub.Brems applied.

[0031] In the context of a function, the control unit 13 can bring about the automated opening and closing of the starting element 3, in order to obtain a start-stop function of the motor vehicle by separating the connection between the drive engine 2 and the motor vehicle transmission 4. For this, the existence of at least one condition is checked, which condition is a prerequisite for the automatic opening of the starting element 3. This condition is the actuation of the service brake 11, which among other things can be detected by monitoring the brake pressure p.sub.Brems. Furthermore the control unit 13 can control the clutch unit 21 as a function of the brake pressure p.sub.Brems which, respectively, would be or is applied for braking the motor vehicle to a stop or for holding the motor vehicle. Depending on the brake pressure p.sub.Brems detected at the time, the operating situation of the motor vehicle is concluded in order to control the clutch unit 21 appropriately for the operating situation concerned, i.e. to decide whether to drivingly engage the axle 18 for re-starting. In this way it is possible to avoid an operating situation in which, when the motor vehicle is re-started, slipping of the drive wheels 7, 8 takes place since the traction is too low because the axle 18 has not been engaged. For this, the control unit 13 regulates the starting element 3 and the clutch unit 21 in accordance with the method represented in FIG. 2:

[0032] At the beginning of the process, in a step S1 it is questioned whether the function for the automated opening and closing of the starting element 3 is activated. If not, the process returns to the beginning and no further action is taken.

[0033] On the other hand if the result in step S1 is positive, the process advances to a step S2. In step S2 the existence of at least one condition is checked, which is a prerequisite for the automatic opening of the starting element 3. This includes the actuation of the service brake 11, which among other things can be detected by monitoring the brake pressure p.sub.Brems. The actuation or release of the service brake 11 results in an actuation of brake light switches associated with a brake pedal mechanism. The actuation conditions of the two wheel brakes 9 and 10 can be checked with reference to the actuation conditions of the respective brake light switches and taken into account as a further condition which is a prerequisite for the triggering of the function for opening the starting element 3. In addition, in step S2 it is questioned whether a rotational speed n.sub.Mot of the drive engine is lower than a rotational speed limit value n.sub.Mot. Another condition in step S2 is whether a vehicle speed v.sub.Fahr is lower than a limit value v.sub.Grenz, which initiates the determination of the brake pressure p.sub.Brems applied by the service brake 11. If all the conditions specified in step S2 are fulfilled, the process progresses to a step S3, whereas otherwise the process reverts to before step S2.

[0034] In step S3 the starting element 3 is automatically opened and thereby the connection between the drive engine 2 and the motor vehicle transmission 4 is separated. In addition, in step S3 the brake pressure p.sub.Brems, or its variation is evaluated by the control unit 16, which pressure has been applied to brake the motor vehicle to rest or is being applied to hold the motor vehicle. From this it can be concluded whether for example the motor vehicle is on an incline and/or whether it is towing a trailer, particularly a fully loaded one.

[0035] Thereafter, in a step S4 it is checked whether the brake pressure p.sub.Brems evaluated by the control unit 16 exceeds a specifiable brake pressure limit value p.sub.Grenz. With reference to the comparison of the brake pressure p.sub.Brems with the specifiable brake pressure limit value p.sub.Grenz, it is concluded whether the vehicle is on an incline and/or whether the vehicle or a trailer it is towing are fully loaded. If the brake pressure limit value p.sub.Grenz has been exceeded, then in the next step S5 the clutch unit 21 is automatically controlled in order to connect the axle 18 drivingly into the drive-train 1 so that the wheels 18, 19 are also driven. The process then advances to a step S6, whereas in the opposite case the process jumps directly from step S4 to step S6.

[0036] In step S6 it is checked whether the driver of the vehicle has indicated a wish to close the starting element 3 by the automatic deactivation of the function or by virtue of a manual control action, in order to be able to start the motor vehicle. If the result in step S6 is positive, then in a step S7 the starting element 3 is closed so that the drive engine 2 and the motor vehicle transmission 4 are connected to one another.

[0037] During the starting process the actual driving speed v.sub.Fahr is monitored and sent to the control unit 13 by way of the bus system 17. In step S8 the driving speed v.sub.Fahr is compared with a limit value v.sub.Anfahr of the vehicle speed, which is generally different from the limit value v.sub.Grenz. The specifiable or variable limit value v.sub.Anfahr is for example stored in the control unit 12 or 14. If the limit value v.sub.r, is exceeded by the actual driving speed v.sub.Fahr, then in step S9 the clutch unit 21 is controlled by the control unit 13 in such manner that the driving connection to the axle 18 is automatically interrupted and the all-wheel drive is therefore automatically discontinued. In the opposite case the process reverts to before step S8 and the engagement remains in place. After the step S9, the function then ends.

[0038] By virtue of the design according to the invention, of a method for operating a drive-train of a motor vehicle, in the context of an automatic function the traction during a starting process can be increased by the automatic engagement of the further axle of the motor vehicle in order to avoid slipping of the drive wheels, in that by checking the brake pressure it can be concluded whether the motor vehicle is on an incline and/or whether the motor vehicle or a trailer are fully loaded.

INDEXES

[0039] 1 Drive-train [0040] 2 Drive engine [0041] 3 Starting element [0042] 4 Motor vehicle transmission [0043] 5 Axle transmission [0044] 6 Drive axle [0045] 7 Drive wheel [0046] 8 Drive wheel [0047] 9 Wheel brake [0048] 10 Wheel brake [0049] 11 Service brake [0050] 12 Control unit [0051] 13 Control unit [0052] 14 Control unit [0053] 15 Control unit [0054] 16 Control unit [0055] 17 Data bus system [0056] 18 Axle [0057] 19 Wheel [0058] 20 Wheel [0059] 21 Clutch unit [0060] 22 Rotational speed sensor [0061] 23 Pressure sensor [0062] n.sub.Mot Rotational speed [0063] n.sub.Grenz Rotational speed limit value [0064] p.sub.Brems Brake pressure [0065] p.sub.Grenz Brake pressure limit value [0066] v.sub.Fahr Vehicle speed [0067] v.sub.Grenz Limit value of the vehicle speed [0068] v.sub.Anfahr Limit value of the vehicle speed