METHOD FOR STARTING OFF A MOTOR VEHICLE

Abstract

A method for starting off a motor vehicle, wherein the motor vehicle has a drive train, which comprises a hybrid drive unit, a transmission and an accelerator pedal, by means of which a driver can set a driver's desired torque, wherein during the starting off of the motor vehicle the hybrid drive unit is regulated to a total drive torque greater than the driver's desired torque in a first operating phase.

Claims

1. A method for starting off a motor vehicle, wherein the motor vehicle has a drive train, which comprises a hybrid drive unit, a transmission and an accelerator pedal, by means of which a driver can set a driver's desired torque, wherein during the starting off of the motor vehicle the hybrid drive unit is regulated to a total drive torque greater than the driver's de-sired torque in a first operating phase.

2. The method as claimed in claim 1, wherein the hybrid drive unit is regulated to a total drive torque corresponding to the driver's desired torque in a second operating phase.

3. The method as claimed in claim 1, wherein the hybrid drive unit comprises an internal combustion engine and an electric machine, wherein the total drive torque is formed by addition of a first drive torque of the internal combustion engine and a second drive torque of the electric machine.

4. The method as claimed in claim 3, wherein the internal combustion engine is regulated to a first target drive torque during the first operating phase, wherein the first target drive torque corresponds to the driver's desired torque.

5. The method as claimed in claim 3, wherein the electric machine is regulated to a second target drive torque in the first operating phase, wherein the second target drive torque is less than the driver's desired torque.

6. The method as claimed in claim 5, wherein the electric machine is regulated to a zero torque during the second operating phase, namely after the internal combustion engine has reached the first target drive torque and/or the electric machine has reached the second target drive torque.

7. The method as claimed in claim 5, wherein the electric machine is regulated to a generator torque during the second operating phase, namely after the internal combustion engine has reached the first target drive torque and/or the electric machine has reached the second target drive torque.

8. The method as claimed in any of claims 2, characterized in that wherein the second operating phase lasts at least as long as the first operating phase.

9. The method as claimed in any of claims 3, wherein, if the driver's desired torque changes during the first operating phase, the second drive torque of the electric machine is increased or reduced in accordance with the change.

10. The method as claimed in any of claims 3, wherein, if the driver's desired torque changes during the second operating phase, the first drive torque of the internal combustion engine is increased or reduced in accordance with the change.

11. The method as claimed in any of claims 3, wherein the internal combustion engine is started within the first operating phase.

Description

DRAWINGS

[0038] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.

[0039] FIG. 1 shows time curves of torques when starting off with the method according to the invention.

[0040] FIG. 2 shows the curve of the torque and of the power of an electric machine against the vehicle speed.

[0041] FIG. 3 shows an illustrative drive train for carrying out the method according to the invention.

[0042] The method according to the invention described below is applied to a motor vehicle having a (hybrid) drive train 9 comprising an internal combustion engine 10, an electric machine 11, namely a 48V machine, a dual clutch transmission 12 and an accelerator pedal (FIG. 3). In the present exemplary embodiment, the hybrid drive unit thus has an internal combustion engine 10 and an electric machine 11. However, it is also conceivable to apply the method according to the invention to some other combination of drive units or drive techniques.

[0043] FIG. 1 shows time curves of torques, i.e. the torque Y in newton meters [Nm] against the time X in seconds [s], when starting off a motor vehicle.

[0044] The curve of the driver's desired torque is illustrated as a line 1. Line 2 shows the time curve of a total drive torque of the hybrid drive unit. Line 3 shows the time curve of a first drive torque of the internal combustion engine 10. Line 4 shows a time curve of a second drive torque of the electric machine 11. Marking 5 shows a first target drive torque of the internal combustion engine 10. Marking 6 shows a second target drive torque of the electric machine 11. The zero torque of the electric machine 11 is indicated by marking 7.

[0045] The curve of the individual drive torques 3, 4 and thus of the total drive torque 2 is dependent on the driver's desired torque 1. The driver selects the driver's desired torque 1 via an accelerator pedal, which can be actuated by the driver. By means of a control unit, the driver's desired torque 1 specified by the driver via the accelerator pedal is sensed, and the starting-off process is controlled. At least one characteristic, by means of which the starting off of the motor vehicle is regulated, is stored in the control unit. That Is to say that the starting off of the motor vehicle is determined by at least one stored characteristic.

[0046] The starting-off process is subdivided into two operating phases, namely into a first operating phase A and a second operating phase B. The first operating phase A starts at time t1 and ends at time t2. The second operating phase starts at time t2 and ends at time t3. The entire starting-off process thus starts at a time t1 and ends at a time t3. In the present exemplary embodiment, the two operating phases A, B last for substantially equal length.

[0047] The total drive torque 2 represents the sum of the first drive torque 3 of the internal combustion engine 10 and the second drive torque 4 of the electric machine 11.

[0048] At time t1, the first drive torque 3 of the internal combustion engine 10 and the second drive torque 4 of the electric machine 11 and thus the total drive torque 2 are equal to zero. During the first operating phase A, the first drive torque 3 of the internal combustion engine 10 is regulated to a first target drive torque 5, which corresponds to the driver's desired torque 1. In addition, during the first operating phase A, the second drive torque 4 of the electric machine 10 is regulated to a second target drive torque 6, which is less than the driver's desired torque 1. At time t2, the first target drive torque 5 and the second target drive torque 6 are reached. The resulting total drive torque 2 of the hybrid drive unit is excessive with respect to the driver's desired torque 1, in particular at time t2. After the first target drive torque 5 and the second target drive torque 6 have been reached, the second operating phase B starts, namely at time t2. In the second operating phase B, the second drive torque 4 of the electric machine 11 is regulated to a zero torque 7. Alternatively, the electric machine 11 can also be switched immediately to a no-load state. The first drive torque 3 of the internal combustion engine 10 is further regulated to the level of the driver's desired torque 1 in the second operating phase B. At time t3, the second drive torque 4 of the electric machine 11 corresponds to the zero torque 7, and the first drive torque 3 of the internal combustion engine 10 corresponds to the driver's desired torque 1. This results in a total drive torque 2 of the hybrid drive unit corresponding to the driver's desired torque 1 at time t3.

[0049] FIG. 2 shows the characteristic curve of the torque Y in newton meters [Nm] of the electric machine 11 and of the power Y′ in watts [W] of the electric machine 11 against the motor vehicle speed X′ in kilometers per hour [km/h] or the rotational speed of the electric machine 11 at different power requirements (dashed lines 8′, 8″, 8″′). In this case, a first dashed line 8′ represents a power requirement which is higher than a second dashed line 8″ and a third dashed line 8″′, which means that the power to be controlled is already achieved at low speeds/rotational speeds. Although the decreasing torque curve 4′ of the electric machine 11 is specified by a substantially parabolic curve, the maximum torque 4″ that can be set can be limited section-by-section by an intervention in the control of the electric machine 11, such as, for example, by a current limitation. The electronics can thereby be protected against overload in the event of a high power requirement, in particular during starting off, and efficient operation of the electric machine 11 can be ensured. Normally, the maximum torque 4″ that can be set is kept constant by the intervention in the control of the electric machine 11, namely until the torque follows the characteristic torque curve 4′.

[0050] By an intervention in the control of the electric machine 11, in particular in the case of a 48V machine, a comparatively higher torque is called up during starting off, thus enabling an increased total drive torque 2 to be established in the hybrid drive train 9.

[0051] Compliance with a maximum torque 4″ of the electric machine 11 that is to be set is regarded as a mandatory requirement here. The second target drive torque 6 is therefore limited by a maximum second target drive torque. In other words, an increased load on the electronics of the electric machine 11 is to be permitted for a short time by optimized control.

[0052] The maximum second target drive torque preferably results from the expected time duration of the first operating phase A, that is to say the time duration which is necessary to accelerate the first target drive torque 5 of the internal combustion engine 10 to the driver's desired torque 1. In order to be able to achieve and maintain the maximum possible torque 4″ over this time range, the maximum second target drive torque is adapted to the characteristic torque curve 4′ in such a way that the second target drive torque 6 of the electric machine 11 can be set to a constant value without a torque drop within operating phase A and/or operating phase B.

[0053] Furthermore, the second target drive torque 6 can be brought to the maximum possible second target drive torque, independently of the driver's desired torque 1, during starting off of the motor vehicle. In other words, the electric machine 11 supports the hybrid drive train 9 with the highest possible power when starting off, irrespective of the driver's desired torque 1 demanded.

LIST OF REFERENCE DESIGNATIONS

[0054] 1 driver's desired torque [0055] 2 total drive torque [0056] 3 first drive torque (of the internal combustion engine) [0057] 4 second drive torque (of the electric machine) [0058] 4′ torque curve (of the electric machine) [0059] 4″ maximum torque (of the electric machine) that can be set [0060] 5 first target drive torque (of the internal combustion engine) [0061] 6 second target drive torque (of the electric machine) [0062] 7 zero torque [0063] 8′ first dashed line [0064] 8″ second dashed line [0065] 8′″ third dashed line [0066] 9 (hybrid) drive train (for a motor vehicle) [0067] 10 internal combustion engine [0068] 11 electric machine [0069] 12 dual clutch transmission [0070] A first operating phase [0071] B second operating phase [0072] X time in seconds [s] [0073] X′ motor vehicle speed in kilometers per hour [km/h] [0074] Y torque in newton meters [Nm] [0075] Y′ power in watts [W]