The present invention relates to a method for operating a vehicle, in particular a hybrid vehicle, at least one of the axles of the vehicle being driven by a drive unit causing the vehicle to be accelerated at a predefined setpoint torque, in that a partial drive torque is transferred to at least one axle and the wheels coupled to it as well as a device for implementing the method.
A generic device is discussed in DE 35 42 059 C1. In the discussed manner, the vehicle has a main drive axle capable of being driven by an internal combustion engine. In the case of increased slip of the wheels of the main drive axle, the wheels of an engageable supplemental drive axle may be driven automatically using a separate supplemental drive unit, in particular an electric motor.
In this connection, a setpoint torque of the vehicle, which is set, for example, by a driver by operating an accelerator pedal in the vehicle, is distributed to the two axles of the vehicle. When negotiating curves where the steering of the vehicle is turned, the effect occurs that the torque acting on the steered wheels contributes more to the acceleration of the vehicle than the torque acting on the unsteered wheels. In the case that high, counteracting torques are present on both axles, only a change of the steering angle would undesirably change the setpoint torque of the vehicle. This would be unpleasantly noticeable for the driver.
A method for operating a vehicle having the features described herein has the advantage that the set setpoint torque is actually implemented by the vehicle's driving behavior even when negotiating curves. Due to the fact that, when negotiating a curve, the partial drive torque of the steered and/or unsteered axle is corrected in such a way that the vehicle is accelerated at the predefined setpoint torque, the different lever relationships of the wheels of the steered and the unsteered axle are compensated.
Advantageously, the partial drive torque of the steered and/or the unsteered axle is corrected as a function of a distance of the wheels to the center of rotation of the vehicle. When negotiating a curve as a result of the turned steering, the different lengths of the lever arms of the wheels to the center of rotation of the vehicle at an equal wheel torque cause an acceleration impact of varying strength on the vehicle, which results in a different effect on the vehicle's steered and unsteered axle and accordingly a differentiated acceleration behavior of the vehicle. This differentiated acceleration behavior is compensated reliably.
In one embodiment, the partial drive torque of the steered and/or the unsteered axle is corrected as a function of a steering angle of the wheels of the steered axle. The described compensation is usable both for hybrid drives and also in all-wheel drives and conventional drives.
Advantageously, the predefined setpoint torque is determined and broken down into partial drive torques of the steered and the unsteered axle, at least one partial drive torque being corrected as a function of the steering angle of the wheels of the steered axle and the partial drive torques subsequently being transferred to the steered and the unsteered axle. Since the setpoint torque is distributable in any manner between the steered and unsteered axle, the compensation always takes place consistent with the drive request made by the driver. In this connection, the steered and the unsteered axle and accordingly the wheels may be driven both positively and negatively.
In one embodiment, the partial drive torques are distributed to the wheels of the steered and unsteered axle as a function of an operating state of the vehicle. The partial drive torques may thus be distributed to the steered and the unsteered axle as a function of a charge of battery. For example, when an electric motor is used as a drive unit, the electric motor operated by the battery may be used for driving the one axle when the battery is at a full charge, while the battery may be charged by a drive unit driving the other axle, for example, an internal combustion engine, when the charge is low.
In one refinement, the correction of the partial drive torques is made as a function of a reference point which refers to the steered or the unsteered axle or to a position between the steered and the unsteered axle. The result is that the axle selected as the reference point is regarded as a correctly set axle. As a function of this reference point, the drive torques of the other axles are then corrected as a function of the drive through a curve.
Advantageously, the unsteered axle is determined as the reference point for the predefined setpoint torque, the partial drive torque of the steered axle being reduced as a function of the steering angle of the wheels of the steered axle after the distribution of the drive torques. This process minimizes the required computational power of the system, since the relationships between the predefined setpoint torque, the steering angle and the corrected partial drive torques may be read out simply from a table or a characteristic curve.
In one embodiment, the steered axle is selected as the reference point for the predefined setpoint torque, the partial drive torque of the unsteered axle being increased as a function of the steering angle of the steered wheels. This causes the driving torques on both axles to be compensated.
Advantageously, a position between the steered and the unsteered axle is selected as the reference point for the predefined setpoint torque, the partial drive torque on the steered axle being reduced and the partial drive torque on the unsteered axle being increased.
In another refinement, the exemplary embodiments and/or exemplary methods of the present invention relates to a device for operating a vehicle, in particular a hybrid vehicle, in which at least one of the axles of the vehicle is driven by a drive unit causing the vehicle to be accelerated at a predefined setpoint torque, in that a partial drive torque is transferred to at least one axle and the wheels coupled to it.
In order to always set the setpoint torque of the vehicle in such a way that it consistently agrees with the driver's request, a correcting arrangement is provided which, when negotiating a curve, correct the partial drive torque of the steered and/or the unsteered axle in such a way that the vehicle is accelerated at the predefined setpoint torque. As a result, the set setpoint torque is actually implemented by the vehicle's driving behavior when negotiating curves. This reliably prevents a maloperation of the vehicle due to a difference in the strength of forces acting on the wheels of the steered and the unsteered axle.
In one embodiment, the correcting arrangement corrects the partial drive torque of the steered and/or the unsteered axle as a function of a distance of the wheels to the center of rotation of the vehicle.
Advantageously, a control unit determines the predefined setpoint torque and divides it into partial drive torques of the steered and the unsteered axle, the partial drive torques being corrected as a function of an angle of the wheels of the steered axle, and the partial drive torques subsequently being transferred to the steered and the unsteered axle. The wheel torques of the wheels of the unsteered and/or the steered axle are corrected and set according to the calculations of the control unit. Correcting the wheel torques causes the requested acceleration or deceleration of the vehicle to be achieved.
In one embodiment, the control unit is connected to a first drive unit for activating the steered axle and a second drive unit for activating the unsteered axle. This makes it possible to set the partial drive torques which are transferred from the drive units to the particular wheels of the axles in a simple way.
In one refinement, the first drive unit is designed as an internal combustion engine and the second drive unit is designed as an electric motor. In the case of such axle hybrid vehicles in particular, a different acceleration effect of the front and rear wheels of the vehicle is reliably prevented when the steering is turned.
Numerous specific embodiments are allowed according to the present invention and will be elucidated in greater detail with reference to the figures in the drawings.
Identical features are denoted by identical reference numerals.
Engine control unit 1 has a memory 3, in which characteristic curves and tables are stored, which are necessary for the control and regulation of the vehicle's drive.
Furthermore, engine control unit 1 is connected to a steering angle sensor 4 which detects the steering angle selected by the driver. Moreover, engine control unit 1 is connected directly to internal combustion engine 5 which drives a first axle 7 via a first gear unit 6, both drive wheels 8, 9 being situated on first axle 7. First axle 7 is a steered axle, which means that the steering movements performed by the driver on the steering wheel are transferred to front wheels 8, 9 of the vehicle.
Engine control unit 1 is furthermore connected to an electric motor control unit 10 which activates an electric motor 11. Electric motor 11 is connected via a second gear unit 12 to a second, unsteered axle 13 of the vehicle which drives rear wheels 14 and 15 of the vehicle.
When the vehicle is driven straight ahead, the setpoint torque input by the driver is distributed to steered axle 7 and unsteered axle 13, so that the sum of the wheel torques of wheels 8, 9; 14, 15 is equal to the setpoint torque. When negotiating curves, this constellation changes.
Longer lever arms 16, 17 of steered axle 7 cause front wheels 8, 9 of the vehicle to be accelerated faster than rear wheels 14, 15 at an identical torque. It is possible for this difference to amount to approximately 30% when front wheels 8, 9 are fully turned. This means that a torque of, for example, 100 Nm on unsteered axle 13 accelerates the vehicle as quickly as front wheels 8, 9 of steered axle 7 when a torque of 70 Nm acts on it.
In the case of an axle hybrid as represented in
If the driver now turns front wheels 8, 9 fully and the compensation described according to the exemplary embodiments and/or exemplary methods of the present invention is not used, the sum derived from the axle torque of steered axle 7 and the axle torque of unsteered axle 13 remains at −10 Nm. However, since wheels 8, 9 of steered axle 7 have, as explained, a significantly longer lever arm 16, 17, the vehicle is abruptly accelerated if the accelerator pedal position is unchanged.
If engine control unit 5 switches internal combustion engine 5 off while negotiating curves, the −10 Nm requested by the driver is delivered exclusively by the wheels of unsteered axle 13, causing the vehicle to be decelerated abruptly again.
The method prevents such effects, which will be explained in greater detail below with reference to
In block 100, engine control unit 1 detects the input of a setpoint torque which is divided into partial drive torques and distributed to the front and rear axle, for example as a function of a charge state of a high voltage battery which drives electric motor 11. The steering angle is detected in block 110.
In block 120, the partial drive torque of unsteered axle 13 is considered to be correct. The partial drive torque of steered axle 7 is reduced by a factor of 1 as a function of the measured steering angle. In a particularly simple embodiment, the factor is determined from the cosine of the steering angle of the wheels on the steered axle.
Alternatively, the setpoint torque will be based on a point between axles 7, 13. The reference point may, for example, lie on the front seat bench in the area of the driver seat, which improves the sense of acceleration for the driver. The partial drive torque on unsteered axle 13 is increased as a function of the steering angle, while the partial drive torque on the unsteered axle is reduced as a function of the steering angle.
In block 130, the partial drive torques determined in block 120 are output to steered axle 7 and unsteered axle 13.
Number | Date | Country | Kind |
---|---|---|---|
10 2009 002 586.3 | Apr 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP2010/052292 | 2/23/2010 | WO | 00 | 1/6/2012 |