Method and control unit for operating a drivetrain of a motor vehicle comprising a power take-off

Abstract

A method for operating a drive-train of a motor vehicle. The drive-train having a transmission connected between a drive aggregate and a drive output. A hydrodynamic starting element is connected between the drive aggregate and transmission. The starting element includes a converter and converter lock-up clutch. A Power Take-Off (PTO) can be coupled to the drive aggregate on the drive aggregate side to take up drive torque delivered by the drive aggregate. In order to determine the torque taken up by the PTO, the lock-up clutch is operated in a rotational-speed-regulated manner at least when the PTO is coupled to the drive aggregate in order to set a defined target slip at the lock-up clutch. As a function of the actuation pressure of the lock-up clutch required for setting the target slip when the PTO is coupled, the torque taken up by the PTO is determined.

Claims

1. A method for operating a drive-train of a motor vehicle, the drive-train having a drive aggregate, a transmission connected between the drive aggregate and a drive output, a hydrodynamic starting element connected between the drive aggregate and the transmission, and the hydrodynamic starting element having a converter and a converter lock-up clutch connected parallel to the converter, the drive-train further having a power take-off that is couplable on a drive aggregate side to the drive aggregate, in order to take up drive torque delivered by the drive aggregate, the method comprising: to determine a torque taken up by the power take-off, operating the converter lock-up clutch in a rotational-speed-regulated manner at least when the power take-off is coupled to the drive aggregate, in order to set a defined target slip at the converter lock-up clutch, and determining the torque taken up by the power take-off as a function of an actuation pressure of the converter lock-up clutch required for setting the target slip while the power take-off is coupled.

2. The method according to claim 1, further comprising operating the converter lock-up clutch in the rotational-speed-regulated manner both with the power take-off coupled and with the power take-off decoupled, determining the torque taken up by the power take-off as a function of the actuation pressure of the converter lock-up clutch required for setting the target slip when the power take-off is coupled, and as a function of the actuation pressure of the converter lock-up clutch required for setting the target slip when the power take-off is decoupled.

3. The method according to claim 1, further comprising determining a first torque at the converter lock-up clutch as a function of the actuation pressure of the converter lock-up clutch required for setting the target slip at the converter lock-up clutch when the power take-off is coupled.

4. The method according to claim 3, further comprising calculating the first torque, at the converter lock-up clutch, from the following equation:
M.sub.1=p.sub.1*A*μ*r in which M.sub.1 is the first torque, p.sub.1 is the actuation pressure of the converter lock-up clutch when the power take-off is coupled, A is the friction surface area of the converter lock-up clutch, μ is the coefficient of friction of the converter lock-up clutch, and r is the friction radius of the converter lock-up clutch.

5. The method according to claim 3, further comprising determining the torque taken up by the power take-off from a difference between a second torque and the first torque, and the second torque at the converter lock-up clutch being determined as a function of the actuation pressure of the converter lock-up clutch required for setting the target slip at the converter lock-up clutch when the power take-off is decoupled.

6. The method according to claim 3 further comprising determining the torque taken up by the power take-off from the difference between a torque delivered by the drive aggregate and the first torque.

7. The method according to claim 1, further comprising determining a second torque at the converter lock-up clutch as a function of the actuation pressure of the converter lock-up clutch required for setting the target slip at the converter lock-up clutch when the power take-off is decoupled.

8. The method according to claim 7, further comprising calculating the second torque at the converter lock-up clutch from the following equation:
M.sub.2=p.sub.2*A*μ*r in which M.sub.2 is the second torque, p.sub.2 is the actuation pressure of the converter lock-up clutch when the power take-off is decoupled, A is the friction surface area of the converter lock-up clutch, μ is the coefficient of friction of the converter lock-up clutch, and r is the friction radius of the converter lock-up clutch.

9. The method according to claim 1, further comprising carrying out shifts in the transmission as a function of the torque taken up by the power take-off.

10. A control unit for operating a drive-train of a motor vehicle, the control unit operating a converter lock-up clutch of the drive-train in a rotational-speed-regulated manner in order to determine a torque taken up by a power take-off, in order to set a defined target slip at the converter lock-up clutch, the drive-train having a drive aggregate, a drive output and a transmission connected between the drive aggregate and the drive output, and a clutch, for engaging the power take-off, is located between the drive aggregate and the converter lock-up clutch, wherein, as a function of an actuation pressure of the converter lock-up clutch required for setting the defined target slip when the power take-off is coupled, the control unit determines the torque taken up by the power take-off.

11. The control unit according to claim 10, wherein the control unit is designed to carry out a method for operating the drive-train, the drive-train having a hydrodynamic starting element connected between the drive aggregate and the transmission, and the hydrodynamic starting element having a converter and a converter lock-up clutch connected parallel to the converter, the drive-train further having the power take-off that is couplable on a drive aggregate side to the drive aggregate, in order to take up drive torque delivered by the drive aggregate, wherein to determine the torque taken up by the power take-off, operating the converter lock-up clutch in a rotational-speed-regulated manner at least when the power take-off is coupled to the drive aggregate, in order to set the defined target slip at the converter lock-up clutch, and determining the torque taken up by the power take-off as a function of the actuation pressure of the converter lock-up clutch required for setting the defined target slip while the power take-off is coupled.

12. A method for operating a motor vehicle drive-train having a drive aggregate, a transmission connected between the drive aggregate and a drive output, a hydrodynamic starting element connected between the drive aggregate and the transmission, the hydrodynamic starting element having a converter and a converter lock-up clutch connected parallel to the converter, and the drive train further having a power take-off that is couplable, on a drive aggregate side thereof, to the drive aggregate in order to take up drive torque delivered by the drive aggregate, the method comprising: operating the converter lock-up clutch in a rotational-speed-regulated manner at least when the power take-off is coupled to the drive aggregate, determining torque taken up by the power take-off as a function of an actuation pressure of the converter lock-up clutch while the power take-off is coupled to the drive aggregate, and setting a defined target slip at the converter lock-up clutch based on the torque taken up by the power take-off while the power take-off is coupled to the drive aggregate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred further developments emerge from the subordinate claims and the description that follows. Example embodiments of the invention, to which it is not limited, will be explained with reference to the sole drawing.

(2) The sole drawing schematically illustrates an example drive-train of a motor vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) In a very schematic manner the sole drawing shows a drive-train 1 of a motor vehicle, wherein the drive-train 1 comprises a drive aggregate 2 and a transmission 4 connected between the drive aggregate 2 and a drive output 3.

(4) The transmission 4 is an automatic or automated change-speed transmission, in which gear changes and therefore shifts are carried out automatically or in an automated manner.

(5) The drive-train 1 also comprises a hydrodynamic starting element 5 connected between the drive aggregate 2 and the transmission 4. The hydrodynamic starting element 5 comprises a converter 6 with a pump wheel 6A and a turbine wheel 6B. In addition the hydrodynamic starting element 5 has a converter lock-up clutch 7 which is connected parallel to the converter 6.

(6) The drive-train 1 of the sole drawing also comprises a power take-off 8. Such a power take-off 8 is also denoted as a PTO (Power Take-Off). The power take-off 8 can be coupled by a clutch 9 to a shaft of the drive aggregate 2, in the sole drawing to the output shaft of the drive aggregate 2. Such a power take-off 8 is a power take-off 8 that can be coupled on the drive aggregate side.

(7) When the clutch 9 is open the power take-off 8 is decoupled from the drive aggregate 2. On the other hand, when the clutch 9 is closed the power take-off 8 is coupled to the drive aggregate 2. When the power take-off 8 is coupled, the power take-off 8 takes up torque from the output shaft of the drive aggregate 2, so that less torque is then available at the transmission 4.

(8) To determine the torque taken up by the power take-off 8, the converter lock-up clutch 7 is operated in a rotational-speed-regulated manner, specifically with the help of a control unit 10. During the rotational-speed-regulated operation of the converter lock-up clutch 7, a defined target slip is set at the converter lock-up clutch 7, and in the context of the present invention this takes place with the power take-off 8 coupled and preferably also with the power take-off 8 decoupled.

(9) In order to set the target slip at the converter lock-up clutch 7 when the power take-off 8 is coupled, a first actuation pressure is needed. In order to set the defined target slip when the power take-off 8 is decoupled from the drive aggregate 2, a second actuation pressure is needed at the converter lock-up clutch. As a function of these actuation pressures the torque taken up by the power take-off 8 can be determined.

(10) As a function of the actuation pressure of the converter lock-up clutch 7 required for setting the target slip at the converter lock-up clutch 7 when the power take-off 8 is coupled, a first moment or torque at the converter lock-up clutch 7 is determined, preferably from the following equation:
M.sub.1=p.sub.1*A*μ*r
in which M.sub.1 is the first torque, p.sub.1 is the actuation pressure of the converter lock-up clutch when the power take-off is coupled, A is the friction surface area of the converter lock-up clutch, μ is the coefficient of friction of the converter lock-up clutch and r is the frictional radius of the converter lock-up clutch.

(11) As a function of the actuation pressure of the converter lock-up clutch 7 required for setting the target slip at the converter lock-up clutch 7 when the power take-off 8 is decoupled, a second moment at the converter lock-up clutch 7 is determined, preferably from the following equation:
M.sub.2=p.sub.2*A*μ*r
in which M.sub.2 is the second torque, p.sub.2 is the actuation pressure of the converter lock-up clutch when the power take-off is decoupled, A is the friction surface area of the converter lock-up clutch, μ is the coefficient of friction of the converter lock-up clutch 7 and r is the frictional radius of the converter lock-up clutch 7.

(12) As a function of these two torques, the torque taken up by the power take-off 8 can be determined, namely from the difference between the second torque at the converter lock-up clutch 7 when the power take-off is decoupled from the drive aggregate 2 and the first torque at the converter lock-up clutch 7 when the power take-off 8 is coupled to the drive aggregate 2.

(13) The value of the torque taken up by the power take-off 8, determined in this way, is preferably stored in the control unit 10 so that thereafter the control unit 10 can carry out shifts in the transmission 4 taking into account the torque taken up by the power take-off 8, namely when, while carrying out shifts, the power take-off 8 is coupled to the drive aggregate 2 by closing the clutch 9.

(14) It is also possible to compare the first torque at the converter lock-up clutch 7 determined while the power take-off 8 is coupled to the drive aggregate 2, with the torque delivered by the drive aggregate 2.

(15) The torque taken up by the power take-off 8 can also be determined from the difference between the moment or torque delivered by the drive aggregate and the first moment or torque required during rotational speed-regulated operation of the converter lock-up clutch 7 for setting the target slip while the power take-off 8 is coupled. The motor torque delivered by the drive aggregate 2 can be transmitted to the control unit 10 from a motor control unit by way of a CAN data bus.

(16) The invention further relates to a control unit 10 designed to carry out the method according to the invention. The control unit 10 operates the converter lock-up clutch 7 in a rotational-speed-regulated manner and determines an actuation pressure of the converter lock-up clutch 7, which during the rotational-speed-regulated operation, is required in order to set the defined target slip at the converter lock-up clutch 7. This takes place at least with the power take-off 8 coupled to the drive aggregate 2 and preferably also while the power take-off 8 is decoupled from the drive aggregate 2. When this is done with the power take-off both coupled and decoupled, the control unit 10 can determine the torque taken up by the power take-off 8 from the corresponding actuation pressures and, as a function of those actuation pressures, by calculating a difference between them. The motor torque delivered by the drive aggregate 2 can also be transmitted to the control unit 10 by some other control unit, in order to calculate the torque taken up by the power take-off 8 by computing a difference between the motor torque and the torque at the converter lock-up clutch 7 which is determined when the power take-off 8 is coupled to the drive aggregate 2.

(17) The control unit 10 is preferably the transmission control unit. This has means for carrying out the method according to the invention. The means include hardware-side means and software-side means.

(18) The hardware-side means are data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention, i.e. at least with the converter lock-up clutch 7.

(19) In addition the hardware-side means include a memory for data storage and a processor for data processing.

(20) The software means consist of program modules which are implemented in the control unit 10 for carrying out the method according to the invention.

INDEXES

(21) 1 Drive-train 2 Drive aggregate 3 Drive output 4 Transmission 5 Starting element 6 Converter 6A Pump wheel 6B Turbine wheel 7 Converter lock-up clutch 8 Power take-off 9 Clutch 10 Control unit