DE102017101367A1 - Anti-slip regulation in an electric vehicle - Google Patents

Abstract

In a method for controlling a traction drive (1,2) of an electric vehicle, which is driven by at least two electric traction motors, of which at least one is arranged as a right traction drive motor on a right side of the vehicle and left drive motor on a left side of the vehicle a drive axle and the be controlled independently of each other with different speeds of a controller, the controller when cornering the wheels of the vehicle sides with a steering wheel radius of the respective wheel corresponding speed, the control of the traction motors is carried out respectively via a torque control (4) and a slippage of a Travel drive motor over a maximum slip threshold a deceleration by recuperation in an energy storage.

Description

The invention relates to a method for traction control in an electric vehicle. In particular, the invention relates to a method for controlling a traction drive of an electric vehicle, which is driven by at least two electric traction motors, of which at least one is arranged as right traction drive motor on a right side of the vehicle and left drive motor on a left side of the vehicle a drive axle and independently can be controlled by a controller at different speeds, the controller when cornering the wheels of the vehicle sides with a steering wheel radius of the respective wheel corresponding speed controls.

In vehicles with electric drive highly dynamic drive systems are known, which represent an electrical differential effect by at least two electric motors. The prerequisite for this is that the motor shafts are not mechanically coupled. It is also known to use in such vehicles as additional functions an electric differential lock (EDS) to increase the stability, for example, in an electric vehicle as a motor vehicle in traffic.

Further additional functions are known as traction control (ASR), intelligent differential lock (EDS) or electronic stability control (ESC / ESP), which are used to increase the sensitivity or precision of the vehicle handling and / or to increase the energy efficiency of the drive system. Electronic differential locks, which minimize the need for hardware resources in a cost-optimized drive system, are desirable.

In the prior art electrical differentials are known, which operate on the basis of a torque control. Such a conventional electric differential, for example, has the same functionality as a mechanical differential, providing for compensation of rotational speeds between the two wheels of an axle. When driving straight ahead, the wheels of both sides turn synchronously, so that no differential effect occurs. When cornering, the wheels rotate at different speeds, the wheel is driven at the outer radius with a higher and the other at a lower speed. In a conventional differential, the same torque is applied to the wheels on the left and right sides, respectively.

Such a differential works stably and accurately when there is even adhesion to the wheels on both sides. A disadvantage of this prior art, however, that as soon as a wheel loses liability, as may occur, for example, in the rain or ice, this wheel is spinning. In this case, the vehicle loses not only traction but also its stability when driving straight ahead and steering.

In order to increase the stability of the vehicle in such situations, so-called dynamic differential locks are often used, which reduce the energy supply of the affected electric motor to reduce the wheel slip. Common names for such systems in the literature are EDS, ASR, IEDS, ESC or ESP, which are increasingly used in motor vehicles for road traffic. In practice, predominantly torque controls are used in these dynamic differential locks to control the power supply, because this type of control is much more dynamic than, for example, a speed control.

Disadvantages of this prior art are various aspects. For example, a speed measurement or a speed sensor is needed to detect a wheel slip. Also, the precision of the traction control is not very large because the algorithm used to control the scheme some sizes that can not be accurately determined while driving. This includes, for example, the effective radius of the wheel and the possible momentary frictional force of the wheel on the road. However, with lower traction control precision, other systems, such as ABS, must be adjusted so as not to erroneously interfere with driveability.

There is also no adjustment of the control characteristics to dynamic properties of the torque control loop, no adjustment of the behavior over time in the sense of a synthesis or improvement of the dynamic properties. Nor can a prognosis be made that would enable a proactive ASR or traction control.

Therefore, it may happen that in the case of rain or ice, for example, in a four-wheel drive vehicle drives an axis because of insufficient precision of the scheme, while the other brakes. Likewise, this can be the case between the sides of an axis. It comes to unwanted vibration due to unwanted, constant changes in the operating mode, which affect the efficiency of the drive and also has a negative effect on the life of the drive units.

From the DE 10 2011 005 107 A1 is a dynamic traction control known at a A vehicle with two driven axles redirects torque from one axle to another as soon as a wheel slips.

The present invention is therefore an object of the invention to provide an anti-slip control in an electric vehicle, which avoids the aforementioned problems and with the improved traction control is made possible.

This object is achieved by an anti-slip regulation in the electric vehicle with the features of the independent claim 1 solved. Advantageous developments of the invention are specified in the subclaims.

The object is achieved in that in a method for controlling a traction drive of an electric vehicle which is driven by at least two electric traction motors, of which at least one arranged as a right traction drive motor on a right side of the vehicle and left drive motor on a left side of a drive axle is and can be controlled independently of each other with different speeds of a controller, the controller when cornering the wheels of the vehicle sides with a steering wheel radius of the respective wheel corresponding speed controls, the control of the traction motors is done in each case via a torque control and a slippage of a Travel drive motor via a maximum slip threshold is a deceleration by recuperation in an energy storage.

Advantageously, there is a precise traction control and this does not intervene during a steering operation, as long as the adhesion does not break off and the actual torque of the left and the right side are identical or almost identical, if the wheels run on their respective steering wheel radius with different radius a curved line. The torque control is very dynamic, as it can have an additional solution-specific feedback and reduces the time constant in the control loop. Also, in an active traction control by the specification of a desired torque, for example by the operation of an accelerator pedal or accelerator pedal, and a corresponding actual torque recuperation is achieved much faster than in an antiskid based alone on a speed comparison. In principle, the feedback can take place here in any form of electrical energy storage, but in particular in a traction battery of a battery-electrically powered vehicle.

A change in the angular velocity is slower, as it depends heavily on the inertia of the drive system. Therefore, in the proposed method according to the invention, a speed control during the traction control is not used, as is often used, for example, for an electrical conversion of a differential lock, in which a kind of electrical wave is simulated on the basis of a speed and position control, brought into line become. This results in an energy saving, since during the slip through the average wind speeds are lower by the highly dynamic control and the recuperation. Compared to prior art systems, drivability and comfort for the driver are increased and lower vibrations result during traction control. The stability of the vehicle is increased without the need for additional hardware resources and associated costs. Particularly advantageous is the proposed method in very light vehicles and vehicles in which it can come to a high Durchschlupfrate the drive wheels. Examples of this include recreational vehicles such as Gocarts, which have so far been powered mainly by gasoline-powered engines. Advantageously, in addition to a first operating state without slippage of the wheels, in particular when driving straight ahead, and a third operating state with a slippage above the maximum slip threshold, in a second operating state, a reduction of the torque of a slipping wheel without recuperation.

Exceeding the maximum slip threshold may be determined by determining the power difference between the vehicle sides.

The determination of the power difference in the right-hand and left-hand drive trains or traction drive motors is very dynamic and precise, since it can be calculated as a product of torque and speed. The slip threshold, however, by no means simply corresponds to a speed difference. For example, with only a very slowly rotating wheel on one side of the vehicle and a "spinning" drive wheel on the other side of the vehicle due to the large speed difference this page will record a much higher performance and a power balance that takes into account the different speeds at the same torque is violated. Advantageously can then be dispensed with a speed measurement, since with active traction control, a magnitude of the calculated power is highly dynamically set towards zero, so that a correct comparison of the performance of both Pages in a very precise traction control process can be achieved.

In one embodiment of the method, the drive of the traction drive motors via a two-quadrant control.

In the first quadrant, a linear characteristic can be used.

As a result, there is a constant gain in the first quadrant, which corresponds to the forward direction of rotation in a traction drive motor. This results in a maximum sensitivity and precision of traction control.

Advantageously, a non-linear characteristic is used in the second quadrant.

In particular, here a non-linear characteristic can be used, which is closer to the properties of a system with a two-step control. Such a design results in a very high dynamics and precision of traction control.

The traction motors can be three-phase, DC or reluctance motors.

Further advantages and details of the invention will be explained in more detail with reference to the embodiment shown in the schematic figure. Here, the figure shows a drive train 1 for a right drive motor and a drive train 2 for a left drive motor. The torque is specified 3 , for example by an accelerator pedal. This torque 3 is in a torque control 4 set higher than all external torques in a block torque load 17 be joined together. The difference between the actual torques at the output of a torque control loop 4 and the torque load 17 determined together with an inertia factor 5 in particular the mechanical rotational inertia 1 / J of the drive train 1 represents, and an integrator 6 the acceleration, speed or deceleration of the vehicle.

A speed sensor 7 determines the speed of the traction drive motor, the speed of the vehicle also by a possible transmission 8th and a rolling radius 9 of the drive wheel is defined.

A transfer function 10 forms the feedback of the torque control 4 and is not active in a straight-ahead driving without speed difference between the two sides of the vehicle, because the output power is identical in both drive trains 1,2.

The drive powers are produced as a product by a multiplier 12 from torque 11 and speed of the speed sensor 7 determined. In a comparator 16 is a power balance .DELTA.P between the two drive trains 1,2 determined. When ΔP equals zero, the nonlinear antislip controls become 13 . 14 are not activated and are passive, ie their output signal is zero. The actual torque of the torque control 4 is positive in this mode and corresponds to torque control in a first quadrant.

In contrast to a first operating state described above rotate in a second operating state when cornering, the drive wheels at different speeds. The wheel in the larger steering wheel radius is driven a little faster and the other slower. The power in the two drive strands 1.2 changes and at the output of the comparison 16 ΔP does not equal zero. It becomes an allowable power difference according to a characteristic 13 and / or characteristic 14 Are defined

It becomes a permissible performance difference 15 given, in which a possible wheel slip remains below a maximum slip threshold. Within this second operating range, there is no false intervention of the feedback by the transfer function 10 ,

If due to a reduced traction and as a result of a reduced external torque it comes to a slippage of a drive wheel, the power increases at the output of the multiplier 12 at. Once the allowable values of the current account are violated, the comparator 16 a positive output signal and the control loop of the torque control 4 builds the actual torque in the drive train 1 from. The drive wheel brakes in the first quadrant through the existing load 17 to prevent slippage of the wheel.

If the burden 17 and the resulting braking effect is insufficient, the speed continues to increase and the power of the powertrain increases 1 , The power balance between the drive trains 1.2 is even less favorable, which is due to the feedback to a negative actual torque. In this third operating state, a recuperation of the electrical energy into, for example, a traction battery of the vehicle takes place in the second quadrant. A defined Rekuperationsgrad, corresponding to an amplitude of the output signal of the torque control 4 , thereby ensuring an optimal braking effect in the drive train one, so that after a short time with high dynamics, the power balance between the drive trains 1.2 is again at a value that a slip below the maximum slip threshold corresponds.

During a differential lock function in this second quadrant mode, the multiplier provides 12 no performance. On this basis, a decision is made as to whether the drive wheel of the drive train 2 forcibly decelerated to optimize stability control. In this case, in the comparator 16 checked whether the drive power is large. When the drive power in the second drive train 2 at the output the level -ΔP in the curve 14 falls below, a deceleration is required. The intensity of the deceleration depends on the amplitude of the output signal.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011005107 A1 [0010]

Claims (7)

A method for controlling a traction drive (1,2) of an electric vehicle, which is driven by at least two electric traction motors, of which at least one is arranged as a right traction drive motor on a right side of the vehicle and left drive motor on a left side of the vehicle a drive axle and independently can be controlled by a controller at different speeds, the control when cornering the wheels of the vehicle sides with a steering wheel radius of the respective wheel corresponding speed controls, characterized in that the control of the traction motors each via a torque control (4) and at a Slipping a traction drive motor over a maximum slip threshold is a deceleration by recuperation in an energy storage. Method according to Claim 1 , characterized in that in addition to a first operating state without slippage of the wheels, in particular when driving straight ahead, and a third operating state with a slippage above the maximum slip threshold, in a second operating state, a reduction of the torque of a slipping wheel without recuperation. Method according to Claim 1 or 2 , characterized in that the exceeding of the maximum slip threshold value is determined by a determination of the power difference between the vehicle sides. Method according to one of Claims 1 to 3 , characterized in that the control of the traction drive motors via a two-quadrant control. Method according to Claim 4 , characterized in that in the first quadrant a linear characteristic is used. Method according to Claim 4 or 5 , characterized in that in the second quadrant, a non-linear characteristic is used. Method according to one of Claims 1 to 6 , characterized in that the traction motors are three-phase, DC or reluctance motors.

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