METHOD FOR CONTROLLING A DRIVE SYSTEM FOR AN AXLE OF A MOTOR VEHICLE

Abstract

The invention relates to a method for calibrating a drive system (1) for an axle (2) of a motor vehicle (3); wherein the drive system (1) has at least one drive unit (4), a drive shaft (5) driven by the drive unit (4), a first output shaft (6) and a second output shaft (7), as well as a first clutch (8) connecting the drive shaft (5) to the first output shaft (6) and a second clutch (9) connecting the drive shaft (5) to the second output shaft (7).

Description

The present invention relates to a method for regulating a drive system for an axle of a motor vehicle. The drive system comprises at least one drive unit (e.g. an electric machine or an internal combustion engine), a drive shaft driven by the drive unit, a first output shaft and a second output shaft (of the common axis), as well as a first clutch connecting the drive shaft to the first output shaft and a second clutch connecting the drive shaft to the second output shaft. Furthermore, a control unit is provided at least for regulating the clutches (optionally for additionally regulating the drive unit and for determining rotational speeds of the drive shaft and of the output shafts). The clutches are associated with the output shafts of a common axle.Drive systems of this type are provided, for example, for the forwarding and the division, as required, of a torque provided by the drive unit. Such a drive system is known, for example, from DE 10 2007 030 091 A1.DE 10 2015 118 759 A1 discloses a method for controlling a drive torque of a drive train arrangement.DE 10 2007 056 174 B3 discloses a micro-slip control of a clutch which is arranged between an engine and a transmission. The slip control automatically adjusts the torque transmitted by a clutch to the torque provided by the drive unit.EP 2 353 916 A1 is directed to a method for controlling a clutch arrangement.It is an object of the present invention to provide a control system for a drive system in which the wheels of an axle can be connected to a common drive shaft via respective clutches of their own.This is contributed by a method according to the features of claim 1. Advantageous further developments are the subject of the dependent patent claims. The features individually listed in the patent claims can be combined with one another in a technically expedient manner and can be supplemented by explanatory facts from the description and details from the figures, wherein further embodiment variants of the invention are shown.A method for regulating a drive system for an axle of a motor vehicle is proposed. The drive system has at least one drive unit, a drive shaft driven by the drive unit, a first output shaft and a second output shaft, as well as a first clutch connecting the drive shaft to the first output shaft and a second clutch connecting the drive shaft to the second output shaft, and further a control unit for regulating the clutches. The clutches can be operated at least at certain operating points (in particular continuously during the operation of the motor vehicle) with a micro-slip control, in which a rotational speed difference between the input shaft and the output shaft of more than zero revolutions per minute and of at most 50 revolutions per minute, in particular at most 20 revolutions per minute, is set at the respective clutch.The method has at least the following steps: a) establishing a driving state of the motor vehicle, wherein at least the following driving states are detected or determined: straight-ahead driving and cornering in traction operation; b) selecting and applying a control strategy for each clutch, wherein the control strategy is different for different driving states.A micro-slip control system comprises, which at the clutch at as far as possible each time a rotational speed difference of greater than zero revolutions per minute is set. In this case, too great a rotational speed difference should be avoided because frictional heat is generated by the slip in the clutch. This frictional heat can lead to overloading of the clutch.The micro-slip control makes it possible in particular for the torque demanded by the drive unit via the clutch always to correspond exactly to the transmittable torque between a wheel and the roadway. Furthermore, a coordination of the motor vehicle or of the drive system can be simplified, because the torque requirement always adjusts according to the slip present. A parameterization of controllers can thus be omitted.The control of the drive system can thus be effected independently of the actuation of the drive unit. This is particularly advantageous when an operating strategy (e.g. a hybrid strategy for driving a hybrid motor vehicle) is provided by other manufacturers (than the manufacturer of the control unit regulating the clutches).Straight-ahead travel comprises in particular a movement of the motor vehicle along a (substantially) straight route (i.e. no travel along a curve). In this case, there is in particular no (predeterminable, maximum steering angle of a steering wheel or of a steering wheel or of the wheels. Straight-ahead travel also includes, in particular, routes whose radius of curvature is greater than 500 meters.In contrast, cornering comprises a movement of the motor vehicle along a curved route (i.e. no travel along a straight route). In this case, in particular, a (predeterminable, minimum) steering angle of a steering or of a steering wheel is present. Cornering comprises in particular curves whose curve radius is less than 1000 meters, in particular at most 500 meters.A delimitation of straight-ahead travel and cornering can be predefined via the (ascertained) angle of turn and / or the curvature or curvature radius of the route, wherein a predefinable delimitation value for cornering defines a greater angle of turn and / or a smaller curvature radius in relation to the straight-ahead travel. This delimiting value can be variably adjustable and / or predefinable.In the case of a motor vehicle, coasting is the driving state in which, in the event of a non-disconnected frictional connection (for example, when the clutch is not engaged), the drive unit is dragged by the motor vehicle, that is to say is kept in rotational movement.In contrast, traction mode refers to the driving state in which the drive unit drives the motor vehicle.A control strategy can comprise a specific setting and / or a specific function or operating mode of a clutch. A plurality of control strategies may be stored and retrievable on at least one storage medium.It is possible that (automatically and / or directly) after detecting one of the predefined driving states, a control strategy which is assigned to this detected driving state is selected and applied (for the duration of this driving state) for the clutch.In particular, the method for regulating a drive system is provided, in which two clutches are provided on a common axle of the motor vehicle, wherein a wheel of the motor vehicle is connected to the drive unit of the motor vehicle in a torque-transmitting manner via each of the two clutches. The two clutches may replace the otherwise usual differential by which different speeds of the wheels may be compensated.The construction of such clutches and drive systems can be described as follows. For example, multiplate clutches can be used as clutches in which outer plates are connected to a plate outer carrier and inner plates are connected to a plate inner carrier in a rotationally fixed manner and each plate carrier is connected to the drive shaft or the respective output shaft in a rotationally fixed manner. As a result of a clamping force acting in an axial direction being applied (as a result of the actuating pressure), the plates, in other clutches the friction partners, are brought into contact with one another, so that a torque can be transmitted from the drive shaft via the clutch to the respective output shaft.At least one of the two clutches can be a hydraulically actuated clutch; preferably, the two clutches are used. In a hydraulically actuated clutch, the actuation pressure is transmitted to the clutch via a hydraulic fluid. The hydraulic fluid can be pressurized by a pump (also electrically operable).At least one of the two clutches can be an electrically actuated clutch; preferably, the two clutches are. In an electrically actuated clutch, the actuating pressure is generated directly by an electric machine, for example by a ramp arrangement rotatable via the machine.In particular, as a result of the actuation of each of the clutches, a respective wheel of the common axle of the motor vehicle can be connected to the drive unit in a torque-transmitting manner.At least one clutch is preferred, in particular both clutches are a multiplate clutch.In particular, the axle is steerable via a steering system (e.g. comprising a steering wheel, e.g. actuatable by a driver in order to deflect the wheels of the axle), which steering system has a steering drive (e.g. a power steering system or the like) for actuating the steering system. During cornering in traction operation, the steering drive is subjected to a restoring torque for restoring the steering system to the straight-ahead driving state.As a result of the micro-slip control, a torque of the drive unit can be transmitted in a known distribution to the wheels of the axle. At any time, the torques transmitted via the respective clutch are known. From a difference of these torques it can be derived in particular the restoring torque with which the steering should be (additionally) acted upon in order to return the steering back into the non-deflected state (straight-ahead travel).It has been observed that, when setting a torque difference at the wheels of an axle (for example in the case of locking differentials, or also in the case of axles with two controllable clutches, in which the wheel on the outside of the curve is locked by the clutch; or else as a result of the micro-slip control), the effect can occur in traction operation that a restoring torque of the wheels acting on the steering, which restoring torque automatically resets the steering without setting a torque difference or without a micro-slip control, is now no longer present. Therefore, as a result of the differential torque on the steered axle, which is generated, for example, by the micro-slip control, the situation can now occur that a steering system remains in the turned-in state (when the user releases the steering wheel, for example, i.e., when the steering system is automatically steered), or even changes further toward a deflected position.In particular, the restoring torque is determined as a function of at least one steering angle of the steering system and of a differential torque, the differential torque being the difference between a first torque transmitted via the first clutch and a second torque transmitted via the second clutch.The steering is preferably automatically set or transferred via the restoring torque (i.e. without intervention by a user) into the driving state of straight-ahead travel.In particular, a first control strategy for the driving state of straight-ahead driving comprises a mutually independent micro-slip control for the first clutch and for the second clutch. This means in particular that each clutch is controlled by itself, in particular for example (exclusively) as a function of the slip in the respective clutch (that is to say in particular slip between inner plate carrier and outer plate carrier of the respective clutch). In this case, the torque set at the one clutch is ignored, in particular by the other clutch, and therefore in particular has no direct influence on its regulation.The first control strategy for the driving state straight-ahead travel is preferably applied in the forward gear (movement of the motor vehicle toward the front) and in the reverse gear (movement of the motor vehicle in the opposite direction, i.e. toward the rear).In particular, at least the following driving state is additionally detected: cornering in coasting operation.In particular, a second control strategy for the driving state of cornering in coasting mode comprises a micro-slip control for the clutch on the inside of the curve, wherein the clutch on the outside of the curve is controlled as a function of the clutch on the inside of the curve, so that a first torque T 1 transmitted by the clutch on the outside of the curve corresponds to the second torque T 2 of the clutch on the inside of the curve, which second torque is changed by a factor K. Thus, in particular, the following applies:In particular, a third control strategy for the driving state of cornering in traction mode comprises a micro-slip control for the clutch on the outside of the curve, wherein the clutch on the inside of the curve is controlled as a function of the clutch on the outside of the curve, so that a first torque T 1 transmitted by the clutch on the inside of the curve corresponds to the second torque T 2 of the clutch on the outside of the curve, which second torque is changed by a factor K. Thus, in particular, the following applies:In the second and third control strategy, one clutch is controlled via the micro-slip control, the respective other clutch being operated (exclusively) as a function of the clutch controlled by this micro-slip control.For the second and third control strategy, a factor K is set in each case for converting the torque. The factor K can be determined in the same way for both control strategies.The factor K is in particular not a constant, but rather has a value between zero and 1 which varies as a function of parameters. In special cases, such as, for example, starting on a roadway which has a first coefficient of friction for one wheel of the axle and a different second coefficient of friction for the other wheel, the factor can also be greater than 1.Such a special case comprises, for example, cornering in traction operation, wherein the wheel on the outside of the curve is located on an ice surface (with a very low coefficient of friction). In this case, the wheel on the inside of the curve (or the clutch on the inside of the curve) must also be able to transmit a significantly greater torque, since otherwise the motor vehicle would remain stationary. Here, the factor can also be between 1 and 10.In particular, the factor is determined as a function of at least one of the following parameters:• a steering angle of a steering (e.g. a steering wheel) of the motor vehicle;• a speed of the motor vehicle;• a minimum differential torque between an inner wheel and an outer wheel;• a differential yaw rate (difference between a yaw rate measured on the motor vehicle and the yaw rate of the motor vehicle which is theoretically present on account of the steering movement; a determination is possible with the differential yaw rate as to whether understeering or oversteering is present);• a torque of the drive shaft;• a rotational speed difference between the wheels of the axle (e.g. inner wheel and outer wheel).In particular, by the actuation of each clutch, a respective wheel of the common axle of the motor vehicle can be connected to the drive unit in a torque-transmitting manner.The drive unit is preferably an electric machine (or an internal combustion engine). In particular, the electric machine (or the internal combustion engine) can be the only drive unit used to drive the motor vehicle. In particular, a second driven axle can also be present, wherein a further drive unit is preferably provided for driving the second axle (e.g. an internal combustion engine or a further electric machine)In particular, in the case of the micro-slip control, a torque difference between the drive shaft and the output shaft of more than zero revolutions per minute and of at most 5 revolutions per minute is set at the respective clutch.A motor vehicle is also proposed, at least having a drive system for at least one axle of the motor vehicle. The drive system has at least one drive unit, a drive shaft driven by the drive unit, a first output shaft and a second output shaft, as well as a first clutch connecting the drive shaft to the first output shaft and a second clutch connecting the drive shaft to the second output shaft, and further a control unit for regulating the clutches, wherein the drive system is regulated with the described method according to one of the preceding patent claims. The control unit is in particular suitably designed and / or set up or executes the method for carrying out the method.Between the drive unit and the output shafts, a transmission with a variable transmission ratio can be arranged. Variable transmission means in particular that there is not a single constant transmission, but that the transmission can be changed, e.g. in steps or also continuously.Alternatively, no transmission or a transmission with a single fixed transmission ratio can be arranged between the drive unit and the output shafts.In particular, the two clutches for transmitting torques are arranged on an axle of a motor vehicle, so that by actuating the first clutch a first wheel of an axle and by actuating the second clutch a second wheel of the same axle of the motor vehicle is connected to the drive unit in a torque-transmitting manner. The clutches are therefore in particular not a clutch of a motor vehicle which is arranged between the drive unit and a shiftable transmission of the motor vehicle.In particular, the axle is steerable via a steering system (e.g. comprising a steering wheel, e.g. actuatable by a driver in order to deflect the wheels of the axle), which steering system has a steering drive (e.g. a power steering system or the like) for actuating the steering system. The steering system can be deflected starting from an non-deflected state (e.g. straight-ahead travel), so that a steering angle greater than zero angle degree is present.Furthermore, the method can also be executed by a computer or with a processor of a control unit.Accordingly, a system for data processing (in particular a control device or part thereof) is also proposed, which comprises a processor which is adapted / configured in such a way that it executes the method or part of the steps of the proposed method.A computer-readable storage medium may be provided which comprises instructions which, when executed by a computer / processor, cause the computer to execute the method or at least part of the steps of the proposed method.The embodiments of the method can be transferred in particular to the motor vehicle, the system, the storage medium or the computer-implemented method and vice versa.As a precautionary measure, it should be noted that the numerical words used here ("first", "second",... ) are primarily (only) used for distinguishing a plurality of articles, sizes or processes of the same type, that is to say in particular do not necessarily specify a dependence and / or sequence of these articles, sizes or processes with respect to one another. If a dependence and / or sequence is required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described configuration.The invention and the technical field are explained in more detail below with reference to the figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other constituent parts and findings from the present description and / or figures. Identical reference numerals designate identical objects, so that explanations from other figures can be used additionally if appropriate. They show schematically: FIG. 1 : a motor vehicle having a drive system for driving a respective wheel of the motor vehicle; FIG. 2 : shows a further motor vehicle; FIG. 3 : an axle of the motor vehicle according to FIG. 2, which is controlled using the first control strategy; FIG. 4 : the axle according to FIG. 3, which is controlled using the third control strategy; and FIG. 5 : the axle according to FIG. 3, which is controlled using the second control strategy; FIG. 6 : shows a driven and steerable axle which is controlled using the third control strategy.FIG. 1 shows a motor vehicle 3 having a drive system 1 for driving a first wheel 16 and a second wheel 17 of a common axle 2 of the motor vehicle 3, respectively. the drive system 1 comprises a drive unit 4, an input shaft 5 driven by the drive unit 4, a first output shaft 6 and a second output shaft 7, as well as a first clutch 8 connecting the input shaft 5 to the first output shaft 6, and a second clutch 9 connecting the input shaft 5 to the second output shaft 7.A drive system 1 is shown here, in which two clutches 8, 9 are provided on a common axle 2 of the motor vehicle 3, wherein a wheel 16, 17 of the motor vehicle 3 is connected to the drive unit 4 of the motor vehicle 3 in a torque-transmitting manner via each of the two clutches 8, 9. The two clutches 8, 9 replace an otherwise customary differential 18 (shown here on the other axle of the motor vehicle), by means of which different rotational speeds of the wheels can be compensated.A transmission 19 is arranged between the drive unit 4 and the output shafts 6, 7.FIG. 2 shows a further motor vehicle 3. Here, the drive unit 4 transmits the torque directly via the input shaft 5 to the axle 2 or via the first clutch 8 to the first output shaft 6 and via the second clutch 9 to the second output shaft 7. The valves 22, 23 are controlled in a controlled manner by a pump 21 driven by a pump motor 20.FIG. 3 shows an axle 2 of the motor vehicle 3 according to FIG. 2, which is controlled using the first control strategy 11.For the driving state of straight-ahead travel, the first control strategy 11 comprises a mutually independent micro-slip control for the first clutch 8 and for the second clutch 9.FIG. 4 shows the axle 2 according to FIG. 3, which is controlled using the third control strategy 13. Reference is made to the explanations relating to FIG. 3.The third control strategy 13 comprises, for the driving state of cornering in traction operation, a micro-slip control for the clutch on the outside of the curve (here second clutch 9), wherein the clutch on the inside of the curve (here first clutch 8) is controlled as a function of the clutch on the outside of the curve (second) 9, so that a first torque transmitted by the clutch on the inside of the curve (first) 8 corresponds to the second torque of the clutch on the outside of the curve (second) 9, which second torque is changed by a factor. The steering system 15 has a steering angle 14, so that the (first) wheel 16 on the inside of the curve and the (second) wheel 17 on the outside of the curve can be determined.FIG. 5 shows the axle 2 according to FIG. 3, which is controlled using the second control strategy 12. Reference is made to the explanations relating to FIGS. 3 and 4.The second control strategy 12 comprises, for the driving state of cornering in coasting operation, a micro-slip control for the clutch on the inside of the curve (here the first clutch 8), wherein the clutch on the outside of the curve (second) 9 is controlled as a function of the clutch on the inside of the curve 8, so that a first torque transmitted by the clutch on the outside of the curve 9 corresponds to the second torque of the clutch on the inside of the curve 8, which second torque is changed by a factor.In the case of the second control strategy 12 and third control strategy 13, in each case one clutch 8, 9 is controlled by means of the micro-slip control (in each case identified by a dotted line in FIGS. 4 and 5 ), wherein the respective other clutch 9, 8 is operated as a function of the clutch 8, 9 controlled by this micro-slip control.FIG. 6 shows a driven and steerable axle 2 which is controlled using the third control strategy 13. Reference is made to the explanations relating to FIG. 4.The third control strategy 13 comprises a micro-slip control for the driving state of cornering in traction operation. The steering system 15 has a steering angle 14, so that the (first) wheel 16 on the inside of the curve and the (second) wheel 17 on the outside of the curve can be determined.In the present case, the axle 2 is steerable via a steering system 15 (e.g. comprising a steering wheel, e.g. actuatable by a driver in order to deflect the wheels 16, 17 of the axle 2) which has a steering drive 24 (e.g. a power steering system or the like) for actuating the steering system 15. The steering system 15 can be deflected starting from an non-deflected state (e.g. straight-ahead travel, or steering angle 14 of zero angle degree), so that a steering angle 14 greater than zero angle degree is present.During cornering in traction operation, the steering drive 24 is acted upon by an additional restoring torque 25 (which is dependent on the differential torque on the steered axle) for restoring the steering 15 to the straight-ahead driving state.List of reference characters1 Drive system 2 Axle 3 Motor vehicle 4 Drive unit 5 Drive shaft 6 First output shaft 7 Second output shaft 8 First clutch 9 Second clutch 10 Control unit 11 First control strategy 12 Second control strategy 13 Third control strategy 14 Angle of engagement 15 Steering 16 First wheel 17 Second wheel 18 Differential 19 Transmission 20 Pump motor 21 Pump 22 First valve 23 Second valve 24 Steering drive

Claims

Method for regulating a drive system (1) for an axle (2) of a motor vehicle (3), wherein the drive system (1) has at least one drive unit (4), a drive shaft (5) driven by the drive unit (4), a first output shaft (6) and a second output shaft (7) and a first clutch (8) connecting the drive shaft (5) to the first output shaft (6) and a second clutch (9) connecting the drive shaft (5) to the second output shaft (7) and further a control unit (10) for regulating the clutches (8, 9); wherein the clutches (8, 9) can be operated at least at specific operating points with a micro-slip regulation, in which a rotational speed difference between the drive shaft (5) and the output shaft (6, 7) of more than zero revolutions per minute and of at most 50 revolutions per minute is set at the respective clutch (8, 9); wherein the method comprises at least the following steps: a) establishing a driving state of the motor vehicle (3), wherein at least the following driving states are detected: straight driving and cornering in traction mode; b) selecting and applying a control strategy (11, 12, 13) for each clutch (8, 9), wherein the control strategy (11, 12, 13) is different for different driving states; wherein a first control strategy (11) is defined for the straight driving state; wherein additionally at least the following driving state is detected: cornering in coasting mode; wherein a second control strategy (12) for the driving state of cornering in coasting mode comprises a micro-slip control for the clutch (8, 9) on the inside of the curve, wherein the clutch (9, 8) on the outside of the curve is controlled as a function of the clutch (8, 9) on the inside of the curve, so that a first torque transmitted by the clutch (9, 8) on the outside of the curve corresponds to the second torque of the clutch (8, 9) on the inside of the curve, which second torque is changed by a factor; or wherein a third control strategy (13) for the driving state of cornering in traction mode comprises a micro-slip control for the clutch (9, 8) on the outside of the curve, wherein the clutch (8, 9) on the inside of the curve is controlled as a function of the clutch (9, 8) on the outside of the curve, so that a first torque transmitted by the clutch (8, 9) on the inside of the curve corresponds to the second torque of the clutch (9, 8) on the outside of the curve, which second torque is changed by a factor.Method according to Patent Claim 1, wherein the axle (2) is steerable via a steering system (15) which has a steering drive (24) for actuating the steering system (15); wherein, during cornering in traction operation, the steering drive (24) is subjected to a restoring torque (25) for restoring the steering system (15) towards the straight-ahead driving state.Method according to Patent Claim 2, wherein the restoring torque (25) is determined as a function of at least one angle of lock (14) of the steering (15) or of a differential torque, wherein the differential torque is the difference between a first torque transmitted via the first clutch (8) and a second torque transmitted via the second clutch (9).Method according to one of the preceding patent claims 2 and 3, wherein the steering system (15) is automatically set into the straight-ahead driving state via the restoring torque (25).Method according to one of the preceding patent claims, wherein the first control strategy (11) comprises independent micro-slip control for the first clutch (8) and for the second clutch (9) for the straight-ahead driving state.Method according to Patent Claim 5, wherein the first control strategy (11) is used for the driving state of straight-ahead travel in the forward gear and in the reverse gear.Method according to one of the preceding patent claims, wherein the factor is determined as a function of at least one of the following parameters: • a steering angle (14) of a steering system (15) of the motor vehicle (3); • speed of the motor vehicle (3); • minimum differential torque between an inner wheel (16) and an outer wheel (17); • differential yaw rate; • torque of the drive shaft (5); • differential rotational speed of the wheels (16, 17) of the axle (2).Method according to one of the preceding patent claims, wherein by the actuation of each clutch (8, 9), a respective wheel (15, 16) of the common axle (2) of the motor vehicle (3) can be connected to the drive unit (4) in a torque-transmitting manner.Method according to one of the preceding patent claims, wherein the drive unit (4) is an electric machine.Method according to one of the preceding patent claims, wherein in the case of the micro-slip control at the respective clutch (8, 9) a torque difference between the drive shaft (5) and the output shaft (6, 7) of more than zero revolutions per minute and of at most 5 revolutions per minute is set.Motor vehicle (3) at least having a drive system (1) for at least one axle (2) of the motor vehicle (3), wherein the drive system (1) has at least one drive unit (4), a drive shaft (5) driven by the drive unit (4), a first output shaft (6) and a second output shaft (7) and also a first clutch (8) connecting the drive shaft (5) to the first output shaft (6) and a second clutch (9) connecting the drive shaft (5) to the second output shaft (7) and furthermore a control unit (10) for regulating the clutches (8, 9), wherein the drive system (1) can be operated with a method according to one of the preceding patent claims.

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