DEVICE AND METHOD FOR OPTIMIZING THE ELECTRICAL POWER GENERATED BY AN ELECTRIC MACHINE IN THE COASTING MODE OF A VEHICLE

Abstract

A device for optimizing the electrical power generated by an electric machine in the coasting mode of a vehicle includes a module for computing a total regenerative torque or a variable proportional thereto, on the basis of which the electric machine is operated in generator mode. The module is configured to: compare the wheel slip that is present at at least one wheel of the vehicle to a predefined threshold value; reduce the total regenerative torque by a small amount when the ascertained wheel slip is less than the predefined threshold value; and increase the total regenerative torque by a small amount when the ascertained wheel slip is greater than the predefined threshold value. The reduction or increase takes place iteratively with multiple successive iteration steps.

Claims

1. A device for optimizing electrical power generated by an electric machine in a coasting mode of a vehicle, the device comprising: a processor, wherein the processor is configured to: compare a wheel slip that is present at at least one wheel of the vehicle to a predefined threshold value; iteratively reduce, in a plurality of successive iteration steps, a total regenerative torque or a variable proportional to the total regenerative torque by a reduction amount when the ascertained wheel slip is less than the predefined threshold value; and iteratively increase, in a plurality of successive iteration steps, the total regenerative torque or the variable by an increase amount when the ascertained wheel slip is greater than the predefined threshold value; wherein the electric machine is operable in a generator mode based on the total regenerative torque or the variable.

2. The device of claim 1, wherein the processor is configured to: ascertain, based on absolute values of the reduction amounts or increase amounts ascertained in the individual iteration steps, a correction value with which a predefined allowable regenerative torque is corrected; and ascertain the total regenerative torque or variable based on the corrected allowable regenerative torque.

3. The device of claim 2, wherein the processor is configured to: determine the allowable regenerative torque in a first coasting phase of the vehicle; store the determined allowable regenerative torque; and in a subsequent coasting phase, use the stored allowable regenerative torque as a starting value for correcting the total regenerative torque or variable.

4. The device of claim 2, wherein the processor is configured to determine the total regenerative torque or variable by adding the allowable regenerative torque and the correction value.

5. The device of claim 2, wherein the allowable regenerative torque is determined as a function of various driving state variables.

6. The device of claim 1, wherein the processor is connected to a control electronics system that is configured to control the electric machine.

7. A method for optimizing electrical power generated by an electric machine in a coasting mode of a vehicle, the method comprising: comparing a wheel slip that is present at at least one wheel of the vehicle to a predefined threshold value; iteratively reducing, in a plurality of successive iteration steps, a total regenerative torque or a variable proportional to the total regenerative torque by a reduction amount when the ascertained wheel slip is less than the predefined threshold value; and iteratively increasing, in a plurality of successive iteration steps, the total regenerative torque or variable by an increase amount when the ascertained wheel slip is greater than the predefined threshold value; wherein the electric machine is operable in a generator mode based on the total regenerative torque or the variable.

8. The method of claim 7, wherein the method is interrupted and a different regenerative torque is set when a vehicle stability program is active.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0016] The FIGURE is a schematic illustration of a system for recuperation of electrical energy in the coasting mode of a vehicle, according to an example embodiment of the present invention.

DETAILED DESCRIPTION

[0017] In the FIGURE, an electric machine 13 of a vehicle is shown which is operated in generator mode in a coasting phase of the vehicle, and which converts the kinetic energy that is released during deceleration of the vehicle into electrical energy. In generator mode, electric machine 13 generates a drag torque, which has a decelerating effect on the associated wheel(s).

[0018] The magnitude of the drag torque exerted by electric machine 13 is set by a power electronics system 12. For controlling electric machine 13, power electronics system 12 can vary, for example, an excitation voltage of electric machine 13 or a phase angle between the current and the voltage. Various methods for modifying the generator power of an electric machine are well known from the related art.

[0019] Power electronics system 12 at its input is connected to a module 1 for optimizing the electrical power generated by electric machine 13. At its output, stated module 1 outputs a total regenerative torque M.sub.R,ges or a variable proportional thereto which represents total regenerative torque M.sub.R,ges, and on the basis of which the generator power of electric machine 13 is then set.

[0020] Module 1 can be, for example, an arbitrary control unit or some other control device which processes software that ascertains above-mentioned total regenerative torque M.sub.R,ges.

[0021] In the example embodiment illustrated in the FIGURE, total regenerative torque M.sub.R,ges is ascertained as follows in principle: a so-called allowable regenerative torque M.sub.R,zul is initially specified which forms the basis for the subsequent computation of total regenerative torque M.sub.R,ges. Allowable regenerative torque M.sub.R,zul can be predefined by a characteristic map 5, for example, which takes into account various driving state variables, for example a rotational speed n.sub.G present at the gearbox output, a wheel speed n.sub.wheel, surroundings conditions such as temperature or wetness, etc. Allowable regenerative torque M.sub.R,zul ascertained based on characteristic map 5 is corrected with a correction value M.sub.R,korr that is continually recomputed in an iterative method.

[0022] In the illustrated example embodiment, allowable regenerative torque M.sub.R,zul and cumulative correction value M.sub.R,korr are added at a node 6. The result is then multiplied by the factor 1 (block 7) in order to obtain total regenerative torque M.sub.R,ges having the physically correct algebraic sign. The multiplier is schematically denoted by reference numeral 8.

[0023] A check is made in block 9 as to whether the vehicle is in coasting mode. As long as the driver is depressing accelerator pedal FP, the corresponding driver input torque specified by the driver at accelerator pedal FP is output by a block 10. If the driver does not depress accelerator pedal FP and the vehicle is thus in coasting mode, block 10 outputs the previously computed total regenerative torque. For the case that the vehicle stability program (ESP) is active, at a subsequent node 11 a torque that is requested by vehicle stability program ESP is added to the torque that is output by block 10. The resulting variable is then supplied to an inverter 12, which accordingly controls electric machine 13.

[0024] Above-mentioned correction value M.sub.R,korr that is added to allowable regenerative torque M.sub.R,zul is a cumulative (positive) value that is ascertained in an iterative method and recomputed and stored in each iteration step. In the illustrated example embodiment, correction value M.sub.R,korr is likewise a positive value, and is ascertained essentially as follows: a comparison is made in step 2 as to whether the wheel slip present at at least one wheel is greater than a predefined threshold value SW, or whether vehicle stability program ESP is active. If one of the two conditions is met, a small reduction value M.sub.R is output, which is then processed by a learning algorithm 4, which ascertains a new correction value M.sub.R,korr based on previous correction value M.sub.R,korr and reduction value M.sub.R. When the vehicle is in coasting mode and wheel slip occurs, for example, correction value M.sub.R,korr is decremented, for example, by an amount per time increment. This takes place until the wheel slip has become less than threshold value SW.

[0025] A comparison is made in step 3 as to whether wheel slip S present at at least one wheel is less than a predefined threshold value SW, and whether at the same time vehicle stability program ESP is switched off. If both conditions are met, a small increase value +M.sub.R is output, which is then processed by a learning algorithm 4, which once again ascertains a new correction value M.sub.R,korr based on previous correction value M.sub.R,korr and increase value +M.sub.R. When the vehicle is in coasting mode and no wheel slip S occurs, correction value M.sub.R,korr is incremented, for example, by a corresponding amount per time increment. This takes place until a wheel slip S occurs that is greater than threshold value SW. The generator portion of a vehicle deceleration thus becomes continuously larger, and the portion from the service brake becomes correspondingly smaller, as the result of which the efficiency of the vehicle can be increased.

[0026] Last cumulative correction value M.sub.R,korr within a coasting phase of the vehicle is preferably stored by learning algorithm 4 as a new correction value M.sub.R,korr as a function of the operating point. In a new coasting phase of the vehicle, most recently stored correction value M.sub.R,korr can be used as a new starting value for correcting total regenerative torque M.sub.R,ges.