Control unit and method for torque distribution during a load change

Abstract

Method for torque distribution during a load change from a positive torque range to a negative torque range for a motor vehicle (10), wherein the motor vehicle (10) has a first torque source (12) by which a first torque (26) is provided, and a traction motor (20) by which a second torque (28) is provided, wherein after determining that the torque distribution is to be changed, the first torque (26) is reduced from the positive torque range to torque neutrality with a first gradient, wherein the second torque (28) of the traction motor (20) is controlled into the negative torque range with a predetermined second gradient at a predetermined load change time (t1) before the torque neutrality of the first torque (26) is reached, until a predetermined load change range (32) of the traction motor (20) has been traversed.wherein the second moment (28) is continued into the negative moment region with a third gradient after passing through the load change region (32), wherein the first moment source does not contribute a negative moment, and wherein the third gradient is steeper than the second gradient.

Description

[0001] The invention relates to a method for torque distribution during a load change from a positive torque range to a negative torque range for a motor vehicle, wherein the motor vehicle has a first torque source that provides a first torque and a traction motor that provides a second torque. Furthermore, the invention relates to a control unit configured to carry out the method and to a motor vehicle having such a control unit.

[0002] Disturbing load change effects such as vibrations or noise arise in vehicles with combustion engines, hybrid drives, or electric drives when the requested torque changes rapidly, particularly the desired torque requested by the driver via the accelerator and / or brake pedal, which determines the vehicle's propulsion. Therefore, it is common practice to implement abrupt torque changes, for example, due to a sudden change in the accelerator pedal position, with a time delay using a filter, for example, with the help of a predetermined torque gradient limitation. Depending on the control structure, the torque can be viewed at various reference points, for example as wheel torque, in particular as the total torque of all driving wheels, or as clutch torque (transmission input torque).

[0003] The vibrations are primarily caused by elasticities in the drivetrain, which create a system susceptible to vibration, as well as nonlinearities in the drivetrain, for example, gear flank changes. Such nonlinearities are particularly evident when the torque on the corresponding component changes sign, as gears, for example, then switch from one contact surface to another. A similar effect is the tilting of the engine in its mounts when the clutch torque changes sign, which is related to the nonlinear characteristics of the engine mounts. Zero crossings of torques at certain positions in the drivetrain in positive or negative directions can therefore lead to particularly pronounced load change effects, which the driver perceives as disturbing.

[0004] DE 10 2015 015 691 A1 discloses a method for operating a motor vehicle with at least one drive device and a separately drivable first and second axle. The method comprises the steps: (i) detecting a first actual value of a first torque at the first axle and a second actual value of a second torque at the second axle, (ii) specifying a first setpoint value for the first torque and a second setpoint value for the second torque, (iii) predicting a change time until the first torque reaches the first setpoint value as a function of the first actual value and the first setpoint value, (iv) determining a maximum gradient for the second torque as a function of the quotient of the difference between the second setpoint value and the second actual value as the numerator and the change time as the denominator,(v) determining a target gradient for the second torque as a function of the second target value and the second actual value, (vi) controlling the drive device and / or at least one torque distribution device to provide the second torque as a function of the target gradient if its value is smaller than the value of the maximum gradient, and otherwise as a function of the maximum gradient.

[0005] The object of the present invention is to improve the torque distribution during a load change so that load change effects are reduced.

[0006] This object is achieved by the independent patent claims. Advantageous developments of the invention are disclosed in the dependent patent claims, the following description, and the figures.

[0007] The invention is based on the idea that, while the positive torque contribution of a first torque source, in particular an internal combustion engine, is reduced, the torque of the second torque source, which is preferably a traction motor, is already controlled to a slightly negative torque, for example, via a ramp, with the gradient of the second torque source being selected to be particularly low in the region near the zero crossing. Thus, the part of the drive train relevant to the traction motor is already preloaded, and the load change effects can be reduced.

[0008] The invention provides a method for torque distribution during a load change from a positive torque range to a negative torque range for a motor vehicle, wherein the motor vehicle has a first torque source by which a first torque is provided and a traction motor by which a second torque is provided.In the method, which can be controlled in particular by a control unit, after determining that the torque distribution is to be changed, the first torque is reduced from the positive torque range with a first gradient to a torque neutrality, wherein the second torque of the traction motor is controlled into the negative torque range with a predetermined second gradient at a predetermined load change time before the torque neutrality of the first torque is reached, until a predetermined load change range of the traction motor is passed through, wherein the second torque is continued into the negative torque range with a third gradient after passing through the load change range, wherein the first torque source does not provide a negative torque contribution, wherein the third gradient is steeper than the second gradient.In particular, the third gradient can then be continued up to a driver desired torque which is to be set for the second torque.

[0009] In other words, the transition from the positive to the negative torque range, which can be initiated by a driver of the motor vehicle, occurs by reducing the positive torque contribution of the first torque source to zero in a first step, i.e., reducing the first torque to torque neutrality. If the torque neutrality of the first torque source is approximately achieved, the second torque of the traction motor can be controlled, preferably following a ramp, with a second gradient into the negative torque range at a predetermined load change time before this torque neutrality is reached, in order to generate the desired negative driver input.The second gradient can be selected to be so low that, during load changes, the traction motor passes through a predetermined load change range close to the zero crossing and then preferably remains in this state with a slight negative torque until the first torque from the first torque source reaches torque neutrality. By controlling the second torque into the negative torque range, the traction motor is preloaded. Subsequently, the second torque can be controlled further into the negative range using a third gradient that is steeper than the second gradient until the target value required for the driver's request is reached.

[0010] The respective gradient refers to the rate by which the respective torque changes. Thus, the rule that the third gradient is steeper than the second gradient means that the absolute value of the gradient of the third gradient into the negative torque range is greater than the absolute value of the gradient of the second gradient into the negative torque range. The respective gradients do not have to be constant, but can be specified, for example, via a table, depending on the current torque value.

[0011] The motor vehicle can, for example, be a purely electrically powered motor vehicle, such that both the first torque source and the traction motor are embodied as electric motors. Particularly preferably, the motor vehicle can be embodied as a hybrid vehicle, which means that, in addition to the traction motor, the first torque source is embodied as an internal combustion engine. A traction motor is understood to mean an electric motor that can drive the motor vehicle purely electrically, in particular generating propulsion in the positive torque range and deceleration, in particular recuperation, in the negative torque range. The first and / or second torque can be a wheel torque, in particular a wheel sum torque, a clutch torque and / or an axle torque of the respective torque source.

[0012] The load change range refers to the range of the load change transition near the zero crossing of the traction motor, in which the preloading of the traction motor is completed. Specifically, the load change range is the range where the tooth flanks of the gear stages of the traction motor are in contact on the appropriate side. This load change range can be different for each motor vehicle and is therefore preferably predetermined individually for each motor vehicle. In other words, it is predetermined how far into the negative torque range the traction motor must be controlled for the respective motor vehicle in order to complete the preloading.

[0013] By placing the traction motor in a state with low negative torque while further reducing the positive torque contribution from the first torque source, it is possible to preload the traction motor around the torque zero crossing or torque neutrality area, allowing for a rapid buildup of negative torque. This has the advantage of achieving high drivetrain dynamics during load change transition while simultaneously avoiding disruptive load change effects, enabling a good combination of dynamics and driving comfort. Preloading the traction motor generally increases the dynamics of the buildup of negative torque, since, for example, the tooth flanks of a gear stage are already in contact on the correct side.

[0014] The invention also includes embodiments which provide additional advantages.

[0015] One embodiment provides that the load change time and the second gradient are specified such that the passage through the predetermined load change range by the second torque is completed when the first torque reaches torque neutrality. In other words, the times for the torque neutrality of the first torque and the completion of the passage through the load change range of the second torque coincide. This embodiment results in the advantage that the load change time and the second gradient can be precisely specified in order to coordinate the passage through the load change range with the torque neutrality of the first torque. This makes it possible to increase the dynamics of the drive train by achieving a particularly smooth transition of the first torque source to torque neutrality, avoiding load change effects by the traction motor.

[0016] Another embodiment provides for the control of the second torque into the negative torque range through recuperation. This means that the traction motor can be controlled into the negative torque range through recuperation, allowing electrical energy to be recovered from the kinetic energy of the vehicle. This embodiment offers the advantage of allowing a faster transition to recuperation, for example, by avoiding the use of the friction brake, thereby reducing overall fuel consumption.

[0017] A further embodiment provides that the reduction of the first torque to torque neutrality is slowed to the extent that the second torque is built up. In other words, when the second torque is controlled into the negative torque range, the first gradient is flattened by the amount of the second gradient. This allows for a particularly smooth transition of the first torque source to torque neutrality, which can counteract possible load change effects from the range of the first torque source. Furthermore, a specific advantageous gradient for the sum of the two torques can be maintained.

[0018] In an advantageous embodiment, it is provided that the second torque, if it is in a positive torque range, is reduced before the first torque to torque neutrality or to a small torque, which represents the upper limit of the load change range, before it is controlled into the negative torque range at the time of the load change. In particular, if the second torque is in a higher positive torque range than the first torque, the second torque can be brought to torque neutrality with a steeper gradient. If the second torque is in the positive torque range with a smaller amount than the first torque, it can preferably be provided that it is initially reduced to torque neutrality or to the upper limit of the load change range in parallel to the first torque, in particular with the first gradient, before it is controlled into the negative torque range at the time of the load change.This design offers the advantage that the second torque can be biased into the negative torque range before the first torque reaches neutrality, thus avoiding disruptive load-change effects. Furthermore, recuperation can begin sooner, saving fuel.

[0019] In a further embodiment, the first torque source is an internal combustion engine. This means that the motor vehicle is a hybrid vehicle that has an internal combustion engine as the first torque source and the traction motor as the second torque source. In particular, the hybrid vehicle can have a parallel hybrid drive according to one of the categories P0 to P4.

[0020] Preferably, the first torque source is decoupled and / or deactivated from a drivetrain of the motor vehicle upon reaching torque neutrality. For example, a clutch can be opened to disconnect the first torque source, in particular to disconnect the combustion engine, which can subsequently also be shut down without generating a load change effect. Thus, the first torque source does not provide a negative torque contribution, which increases energy recovery through recuperation of the traction motor.

[0021] In a further embodiment, the first torque source comprises an electric motor. In other words, the first torque source, particularly in the case of an internal combustion engine, can comprise an additional electric motor (starter generator) that contributes to the first torque. Alternatively, the first torque source can also be another traction motor, thereby making the motor vehicle fully electric.

[0022] A further aspect of the invention relates to a control unit for a motor vehicle, wherein the control unit is designed to carry out a method according to one of the preceding embodiments. In particular, the control unit can be designed to, upon determining that a torque distribution is to be changed, reduce the first torque from the positive torque range to a torque neutrality using a first gradient and to control the second torque of the traction motor at a predetermined load change time before the torque neutrality of the first torque is reached using a predetermined second gradient into the negative torque range until a predetermined load change range of the traction motor has been passed through, and to continue the second torque after passing through the load change range using a third gradient into the negative torque range, wherein the third gradient is steeper than the second gradient.For this purpose, the control unit can, for example, generate control signals that can be sent to the first torque source and / or the traction motor to make the appropriate adjustments. This aspect of the invention offers the same advantages and possible variations as the method.

[0023] According to the invention, a motor vehicle with a control unit according to the preceding aspect is also provided.

[0024] The invention also includes further developments of the control device according to the invention which have features as have already been described in connection with the further developments of the method according to the invention.

[0025] For this reason, the corresponding developments of the control device according to the invention are not described again here.

[0026] The invention also includes combinations of the features of the described embodiments.

[0027] An embodiment of the invention is described below. It shows: Fig. 1 shows a schematically illustrated motor vehicle according to an exemplary embodiment; Fig. 2 a schematically illustrated motor vehicle according to a further exemplary embodiment; Fig. 3 Moment distribution diagram.

[0028] The exemplary embodiment explained below is a preferred embodiment of the invention. In the exemplary embodiment, the described components of the embodiment each represent individual, independently considered features of the invention, which also further develop the invention independently of one another and are thus also to be considered as components of the invention, either individually or in a combination other than that shown. Furthermore, the described embodiment can also be supplemented by further features of the invention already described.

[0029] In the figures, functionally identical elements are provided with the same reference numerals.

[0030] In Fig. 1 shows a schematically illustrated motor vehicle 10 according to an exemplary embodiment. In this exemplary embodiment, the motor vehicle 10 can be a hybrid vehicle, with an internal combustion engine 12 and a starter generator 14 on the front axle 16 of the motor vehicle, wherein the internal combustion engine 12 and the starter generator 14 are combined as a first torque source that provides a first torque. The hybrid vehicle, which in this exemplary embodiment is designed as a category P4 hybrid, can have a traction motor 20 on the rear axle 18. The total wheel torque can in principle be distributed arbitrarily between the front and rear axles 16, 18, so that when the total wheel torque changes, the axle torques on the front and rear axles 16, 18 can exhibit zero crossings at different times.Relative non-linearities include, for example, gear stages in the reduction gear on the rear axle 18 as well as transmission gear stages or the characteristics of the engine block bearing on the front axle 16.

[0031] Another exemplary embodiment of the motor vehicle 10 is shown in Fig. 2, where Fig. 2 The motor vehicle 10 is designed as a Category P3 hybrid with a traction motor 20 with a gear stage behind the transmission 23, as well as the combustion engine 12 and a starter generator 14 upstream of the transmission 23. In this case, the clutch torque (transmission input torque corresponds to the sum of the combustion engine torque, the starter generator torque, and any losses of mechanically driven ancillary units) and the torque of the traction motor 20 can exhibit zero crossings at different times. Nonlinearities in the transmission can generate load change effects when the clutch torque passes through zero. Edge changes in the gear stage can generate load change effects when the torque in the gear stage of the traction motor 20 changes sign.

[0032] The Fig. 1 and Fig. The motor vehicles 10 shown in Figure 2 are only exemplary embodiments, and the motor vehicle can also be designed as a P2 or P2.5 hybrid or as a purely electrically powered vehicle.

[0033] The entirety of the combustion engine 12 and starter generator 14 and / or mechanically driven auxiliary units is hereinafter referred to as the first torque source, which provides a first torque. Accordingly, the traction motor 20 represents a second torque source, which provides a second torque. In general, the second torque source may also have multiple torque contributions, for example, multiple traction motors whose torques are added together.

[0034] During a load change, particularly from a positive torque range or propulsion torque to a negative torque range, disruptive load change effects may occur, which may be caused primarily by elasticities in the drive train and non-linearities in the drive train, particularly flank changes of gears. In order to reduce and preferably avoid these load change effects, a control unit 22 may be provided that controls the torque distribution during the load change. This method, which is carried out by the control unit 22, is described below with the aid of the Fig. 3 explained.

[0035] In Fig. 3 the time course t is shown on the respective x-axis and the (total) wheel torque M on the y-axis. In the upper half of the diagram the Fig. Figure 3 shows the driver's command 24 or the driver's desired torque. The driver's command 24 represents the total wheel torque to be set in the motor vehicle 10, which can be achieved, for example, by changing the accelerator pedal setting and / or applying the brake.

[0036] The lower half of the diagram shows the wheel torque contributions of the first torque source 12, 14, hereinafter referred to as the first torque 26, and the wheel torque contribution of the traction motor, hereinafter referred to as the second torque 28. The sum of the wheel torque contributions preferably results in the total wheel torque M, which corresponds to the driver command 24.

[0037] To implement the method and avoid load change effects, the control unit 22 can, following the driver's command 24, reduce the first torque 26, which is in a positive torque range, with a first gradient or a first gradient in order to achieve torque neutrality (M=0) for the first torque. Shortly before the first torque 26 reaches torque neutrality, the second torque 28 can be controlled into the negative torque range with a predetermined second gradient at a time t1, which is predetermined as the load change time t1. The second gradient is preferably predetermined such that the load change of the traction motor 20 begins gently, without causing load change effects due to an excessively rapid change in the torque.Thus, the traction motor 20 is brought into a state with a low negative torque, while the positive torque contribution of the first torque source 12, 14 is further reduced. Preferably, at the load change time t1, the reduction of the first torque 26 is also slowed to the same extent as the second torque 28 is built up, which occurs in the region 30 of the . Fig. 3, so that the sum of the torque contributions continues to correspond to the driver request 24.

[0038] The second gradient of the second torque 28 and the load change time t1 are preferably selected such that a predetermined load change range 32 is passed through precisely when the first torque source 26 reaches torque neutrality. The load change range 32 indicates the torque threshold at which the load change of the traction motor 20 is completed. Once the torque neutrality of the first torque 26 has been reached and the load change range 32 has been passed through by the second torque 28, the second torque 28 can be further guided into the negative torque range with a third gradient, which is indicated in the range 34 and which is preferably steeper than the second gradient, in order to correspond to the driver command 24. The control of the second torque 28 into the negative torque range can preferably be carried out by means of recuperation in order to thus obtain energy recovery.Furthermore, after the torque neutrality of the first torque 26 has been reached, the first torque source 12, 14 can preferably be decoupled and / or deactivated from a drive train of the motor vehicle 10 in order to save fuel.

[0039] Overall, the examples show how the invention can be used to control torque distribution, particularly in hybrid vehicles, to avoid disruptive load change effects. List of reference symbols 10 motor vehicle 12 combustion engine 14 Starter generator 16 front axle 18 Rear axle 20 Traction motor 22 Control unit 23 gearboxes 24 Driver request torque 26 first moment 28 second moment 30 torque range 32 load change range 34 torque range t1 load change time

Claims

[1] Method for torque distribution during a load change from a positive torque range to a negative torque range for a motor vehicle (10), wherein the motor vehicle (10) has a first torque source (12) by which a first torque (26) is provided, and a traction motor (20) by which a second torque (28) is provided, wherein after determining that the torque distribution is to be changed, the first torque (26) is reduced from the positive torque range with a first gradient to a torque neutrality, wherein the second torque (28) of the traction motor (20) is controlled at a predetermined load change time (t1) before the torque neutrality of the first torque (26) is reached with a predetermined second gradient into the negative torque range until a predetermined load change range (32) of the traction motor (20) has been passed through,wherein the second torque (28) is continued into the negative torque range after passing through the load change range (32) with a third gradient, wherein the first torque source does not provide a negative torque contribution, wherein the third gradient is steeper than the second gradient. [2] Method according to claim 1, wherein the load change time (t1) and the second gradient are predetermined such that the passage through the predetermined load change range (32) by the second torque (28) is completed when the first torque (26) reaches torque neutrality. [3] Method according to one of the preceding claims, wherein the control of the second torque (28) into the negative torque range is carried out by recuperation. [4] Method according to one of the preceding claims, wherein the reduction of the first moment (26) to the moment neutrality is slowed down to the extent that the second moment (28) is built up. [5] Method according to one of the preceding claims, wherein the second torque (28), if it is in a positive torque range, is reduced before the first torque (26) to the torque neutrality or a small torque, which represents an upper limit of the load change range, before it is controlled into the negative torque range at the load change time (t1). [6] Method according to one of the preceding claims, wherein the first torque source is an internal combustion engine (12). [7] Method according to one of the preceding claims, wherein the first torque source is decoupled and / or deactivated from a drive train when torque neutrality is reached. [8] Method according to one of the preceding claims, wherein the first torque source comprises an electric motor (14). [9] Control unit (22) for a motor vehicle (19), wherein the control unit is designed to carry out a method according to one of the preceding claims. [10] Motor vehicle (10) with a control unit (22) according to claim 9.

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