Control for the distribution of drive power

Abstract

A multi-engine motor vehicle having a front axle (2) and a rear axle (5), wherein the front axle (2) is drivable by at least one first motor (4) and the rear axle (5) is drivable by at least one second motor (7), wherein a control unit (8, 9) is provided which is configured to determine a distribution with which a requested total drive power is divided between a first drive power for the front axle (2) and a second drive power for the rear axle (5) and to control the at least one first motor (4) and the at least one second motor (7) according to the distribution, wherein the control unit (9) is further configured to check whether the motor vehicle (1) is understeering or oversteering and, in the event of understeering, to shift the distribution towards the rear axle (5) and, in the event of oversteering, to shift the distribution towards the front axle (2), characterized in thatthat a limit value is provided for the lateral acceleration of the motor vehicle (1), and when the limit value is exceeded, a current yaw rate deviation is stored as a first value, wherein the control unit is configured to carry out a control for the distribution of the drive power based on the first value.

Description

[0001] The invention relates to a multi-engine motor vehicle with a front axle and a rear axle, wherein the front axle is driven by at least one first motor and the rear axle is driven by at least one second motor. A control unit is provided which is configured to determine a distribution which divides the total requested drive power between a first drive power for the front axle and a second drive power for the rear axle and controls the at least one first motor and the at least one second motor according to the distribution. The front axle and the rear axle are not connected to one another by a mechanical connection, such as a shaft.

[0002] The distribution of drive power between the first and second motors has typically been based solely on the requested acceleration. For high accelerations, torque is increased on the rear axle and decreased on the front axle. In normal driving situations with lower acceleration values, however, more torque is applied to the front axle.

[0003] When cornering, however, this can lead to the distribution of drive power causing instability of the vehicle, so that a stability control system (ESC) must restore the stability of the vehicle by braking individually at each wheel and reducing the overall drive power.

[0004] DE 10 2011 006 813 A1 discloses a system for distributing drive power to the front and rear axles of a vehicle. An electronic control unit is configured to increase the torque supplied to the rear axle in an understeer condition and to increase the torque supplied to the front axle in an oversteer condition.

[0005] From DE 10 2016 102 004 A1 a method is known in which the distribution of the torque to the front axle and the rear axle is based on a slip angle, a measured and / or a desired yaw rate.

[0006] A method for distributing drive torque between an internal combustion engine and an electric motor is known from DE 10 2004 049 324 A1. This method takes into account the requirements of vehicle dynamics control.

[0007] Another method for distributing drive torque to the driven wheels is disclosed in DE 10 2007 051 590 A1. To reduce the tendency to understeer or oversteer, the drive torque is distributed during cornering in such a way that a differential torque is created that counteracts the understeer or oversteer tendency.

[0008] DE 10 2009 045 418 A1 discloses a method for adjusting the drive torque on two axles, wherein a variable influencing driving stability is monitored and a change in the drive torque is made when a permissible value range is exceeded.

[0009] The object of the invention is therefore to improve the stability of the vehicle when cornering.

[0010] The object is achieved according to the invention in that the distribution of the drive power is adjusted accordingly before instability of the vehicle occurs.

[0011] For this purpose, the control unit is further configured to check whether the vehicle is understeering or oversteering during cornering. In the event of understeering, it shifts the distribution toward the rear axle, and in the event of oversteering, it shifts the distribution toward the front axle. The invention is not limited to two-axle motor vehicles. Rather, a front axle and a rear axle are understood to mean any axles arranged one behind the other, regardless of the arrangement of a third or additional axle.

[0012] In a preferred embodiment of the invention, the control unit is configured to detect understeer and / or oversteer by exceeding a lateral acceleration threshold and a yaw rate deviation threshold. The difference between an actual yaw rate of the vehicle, measured, for example, by a yaw rate sensor, and a reference yaw rate from a vehicle model is calculated as the yaw rate deviation and compared with the yaw rate deviation threshold. The vehicle model can be a single-track model, for example. The expected yaw rate is determined as the reference yaw rate, particularly from the steering angle, vehicle speed, and vehicle geometry. Furthermore, a lateral acceleration of the vehicle, determined, for example, by an acceleration sensor, is compared with the lateral acceleration threshold.The threshold values ​​can be set so low that a stability system (ESC) does not intervene.

[0013] According to the invention, a limit value is provided for the lateral acceleration of the vehicle. If the limit value is exceeded, the current yaw rate deviation is stored as the first value, and the control unit is configured to implement a control for the distribution of the drive power based on the first value. The limit value of the lateral acceleration is selected such that the vehicle still has sufficient stability. Accordingly, the yaw rate deviation at this point in time is still considered acceptable, and the vehicle state with such a yaw rate deviation is still stable. The value of the yaw rate deviation can therefore be used as the basis for a control for the distribution of the drive power.

[0014] In a particularly preferred embodiment of the invention, the control unit comprises a PID controller configured to control the distribution of the drive power. The PID controller has an input variable with a setpoint and an output variable. The current yaw rate deviation is used as the input variable, which is controlled to a setpoint based on the first value. The distribution of the drive power between the front axle and the rear axle is used as the controlled variable. A PID controller (proportional-integral-derivative controller) consists of a P element, an I element, and a D element and can achieve the set setpoint particularly reliably and without overshoot.

[0015] In a further particularly preferred embodiment of the invention, the control system has a hysteresis. The control system is activated when the yaw rate deviation exceeds the first value and deactivated when the yaw rate deviation falls below a second value, wherein the second value is less than the first value by a hysteresis value. Either a fixed hysteresis value can be stored in the control unit, which is subtracted from the first value, or, for example, a proportion can be stored so that the first value is multiplied by a factor less than 1 to obtain the second value. The hysteresis ensures that the control system is not activated and deactivated very frequently when the input value fluctuates slightly around the target value.

[0016] In another particularly preferred embodiment of the invention, the control system is configured to control the yaw rate deviation to the second value. This means that the second value is provided to the control system as a setpoint. After activation, the control system therefore attempts to reach the lower deactivation value. Once this is the case, the control system is deactivated and only reactivated when the higher first value is reached again.

[0017] In another particularly preferred embodiment of the invention, a coefficient of friction between a tire of the vehicle and the vehicle surface is estimated, and based on the coefficient of friction, a maximum lateral acceleration of the vehicle is determined at which vehicle stability is lost because the tire loses grip on the surface. From the maximum lateral acceleration, a value less than the maximum lateral acceleration is determined and used as the limit value for the lateral acceleration. For this purpose, a fixed value can again be subtracted or a multiplication by a factor less than 1 can be performed. Thus, the limit value of the lateral acceleration is still within a range in which the vehicle can be stably controlled.

[0018] In another particularly preferred embodiment of the invention, the coefficient of friction is continuously determined, and the limit value for lateral acceleration is dynamically adjusted during the course of the journey. This also allows the distribution of drive torque to be instantly adapted to changing surface conditions, ensuring vehicle stability.

[0019] In another particularly preferred embodiment of the invention, a value between 50% and 90%, preferably between 60% and 80% of the maximum lateral acceleration is used as the limit value for the lateral acceleration. The vehicle is thus controlled within a stability range that is well away from an unstable range, allowing the motor vehicle to always be controlled safely.

[0020] In another particularly preferred embodiment of the invention, the control unit is configured to shift the distribution of drive power toward the front axle when the vehicle is oversteering and the yaw rate deviation is greater than a target value, in particular the second value. The magnitude of the yaw rate can be considered in each case, since the sign of the yaw rate depends on the installation position of the yaw rate sensor on the one hand and on the direction of the curve, whether a left or right turn is being negotiated.

[0021] In a further particularly preferred embodiment of the invention, the control unit is configured to shift the distribution of the drive power towards the rear axle when the vehicle is understeering and the yaw rate deviation is greater than the target value, in particular the second value.

[0022] In a preferred embodiment of the invention, the motor vehicle has an input device, in particular an accelerator pedal, for detecting the requested drive power.

[0023] In an alternative embodiment of the invention, a virtual driver is provided for autonomous control of the vehicle. This driver is configured to determine the required drive power and transmit it to the control unit as the requested drive power. This allows the stability improvement to be easily applied to autonomous vehicles.

[0024] The problem is further solved by a method for distributing the drive power of a vehicle between a front axle driven by a first motor and a rear axle driven by a second motor. During cornering, the method checks whether the vehicle is understeering or oversteering. In the case of understeering, the distribution is shifted toward the front axle, and in the case of oversteering, the distribution is shifted toward the rear axle. According to the invention, the following steps are performed: - Check whether a limit value for the lateral acceleration of the vehicle is exceeded and - If the limit is exceeded, save the current yaw rate deviation as a first value.

[0025] In a preferred embodiment of the method, the following steps are further carried out: - Determining a second, lower, value, for example by subtracting a predetermined hysteresis value from the first value or by multiplying by a factor less than 1 - Controlling the distribution of drive power to the front axle and the rear axle in such a way that the yaw rate deviation corresponds to the second value by - in the case of an oversteering vehicle, if the yaw rate deviation is greater than the second value, the distribution of the drive power is shifted towards the front axle and - in the case of an understeering vehicle, if the yaw rate deviation is greater than the second value, the distribution of the drive power is shifted towards the rear axle.

[0026] Further features, advantages, and possible applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features, both individually and in any combination, are part of the subject matter of the invention, regardless of their summary in the claims or their references. Fig. 1 shows schematically a motor vehicle according to the invention, Fig. 2 shows schematically the data flow of a method according to the invention, Fig. 3 shows schematically an oversteering vehicle, Fig. 4 shows the vehicle of the Fig. 3 during active control, Fig. 5 shows schematically an understeering vehicle, Fig. 6 shows the vehicle of the Fig. 5 during active control, Fig. 7 shows the vehicle of the Fig. 3 to 6 according to the regulation,

[0027] The motor vehicle 1 of Fig. 1 has a drive with several electric motors 4, 7. Alternatively, one or both of the motors 4, 7 can be designed as internal combustion engines. The first motor 4 drives a front axle 2 of the motor vehicle 1 with two front wheels 3. The second motor 7 is arranged on a rear axle 5 with two rear wheels 6 and drives them. The front axle 2 and the rear axle 5 are not mechanically coupled to one another, and the two motors 4, 7 can be controlled independently of one another, whereby the drive power or the torque at the front axle 2 and the rear axle 5 can be adjusted independently of one another.

[0028] The total drive power, requested, for example, by a driver using an accelerator pedal, is distributed by an engine control system 8 when driving straight ahead between the front axle 2 with the first motor 4 and the rear axle 5 with the second motor 7. The distribution of the drive power can depend in particular on the accelerator pedal position and can be selected with regard to energy efficiency. In addition, the invention provides a control unit 9 which checks whether the motor vehicle 1 is understeering and / or oversteering when cornering. In this case, the control unit 9 can determine a distribution of the total drive power between the first motor 4 and the second motor 7 and transmit this to the engine control system 8. Alternatively, the control unit 9 can control the first motor 4 and the second motor 7 directly.

[0029] As in Fig. As shown in Figure 2, the control unit of motor vehicle 1 has a lateral acceleration sensor 10 and a yaw rate sensor 11. A computing unit 16 of control unit 9 calculates a vehicle model from which a reference yaw rate is determined based on vehicle speed, steering angle, vehicle-specific parameters, etc. Control unit 9 compares the actual yaw rate, as determined by yaw rate sensor 11, with the reference yaw rate and determines yaw rate deviation 13 as the difference between the actual yaw rate and the reference yaw rate. Alternatively, yaw rate deviation 13 can be transmitted to control unit 9 from another control unit, for example, an ESC control unit.

[0030] If the yaw rate deviation 13 exceeds a yaw rate deviation threshold and at the same time the lateral vehicle acceleration exceeds a lateral threshold, oversteering vehicle 1 (see Fig. 3) or understeering vehicle 1 (see Fig. 5). Oversteering of vehicle 1, for example, is detected by the fact that the actual yaw rate 11 is greater in magnitude than the reference yaw rate. Understeering of vehicle 1, on the other hand, is detected by the fact that the actual yaw rate 11 is smaller in magnitude than the reference yaw rate.

[0031] In the control unit 9, a limit value for the lateral acceleration is also stored in the memory unit 15. This can be identical to the lateral threshold value, or stored as an additional variable and thus also have a different value. The control unit 9 receives the measurement data from the lateral acceleration sensor 10 and compares it with the lateral limit value in a check 12. As soon as the lateral acceleration exceeds the lateral limit value, the current yaw rate deviation 13 is determined and stored in a memory unit 15. This value is used as the first value, namely the activation threshold 17, for the control system 14. Since this value corresponds to the current yaw rate deviation 13, the control system 14 is also activated at the same time.This means that the distribution of drive power between the front axle 2 and the rear axle 5 is no longer carried out independently by the engine control unit 8, but is determined by the control unit 9 and transmitted to the engine control unit 8. From the first value 17, a second value is also determined as the deactivation threshold 18. This is set, for example, to 80% of the activation threshold in order to implement hysteresis behavior. This means that the control 14 is deactivated at a lower value and activated at a higher value in order to avoid constant activation and deactivation of the control 14. The deactivation threshold is fed to the PID controller 14 as a setpoint, which varies the distribution of drive power between the front axle 2 and the rear axle 5 such that the yaw rate deviation 13 approaches the setpoint 18.

[0032] In the case of an oversteering vehicle, Fig. 3 the driver's command 20, which indicates the desired driving line, as determined from the steering wheel position, vehicle speed, and vehicle geometry. The lateral forces 22 on the front axle 2 are significantly smaller than the lateral forces 23 on the rear axle 5, and a yaw moment acts on the vehicle 1, so that the actual driving line 21 deviates from the driver's command, causing the vehicle 1 to turn more sharply than desired.

[0033] Through the inventive intervention of the control of the drive torque between the front axle 2 and the rear axle 5, more torque is applied to the front axle 2 and less torque to the rear axle 5, so that the lateral force 22 on the front axle 2 becomes greater than the lateral force 23 on the rear axle 5. As a result, the yaw moment acting on the vehicle 1 is inverted and the actual driving line 21 approaches the driver's request 20.

[0034] After the intervention, the actual driving line 21 corresponds to the driver's request 20 and the lateral forces 22, 23 on the front axle 2 and the rear axle 5 are equal, as in Fig. 7 is shown.

[0035] The case of an understeering vehicle 1 is in the Fig. 5. The lateral force 22 on the front axle 2 is greater than the lateral force 23 on the rear axle, and a left-hand yaw moment acts on the vehicle 1. The actual driving line 21 therefore deviates from the driver's desired 20, with the vehicle steering only slightly to the right. The control shifts the drive torque from the front axle 2 to the rear axle 5, reducing the lateral force on the front axle and increasing it on the rear axle 5. This results in a right-hand yaw moment 24, and the actual driving line 21 approaches the driver's desired 20. After the control has ended, the lateral forces on the front axle 2 and the rear axle are equal again, and the actual driving line 21 corresponds to the driver's desired 20, as shown in Fig. 7 is shown.

[0036] Thus, by distributing the drive forces between the front and rear axles, the stability of the vehicle can be improved before an ESC system intervenes. List of reference symbols: 1 motor vehicle 2 front axle 3 front wheel 4 first engine 5 Rear axle 6 rear wheel 7 Second engine 8 Engine control 9 Control unit 10 Accelerometer 11 Yaw rate sensor 12 Review 13 Yaw rate deviation 14 PID controllers 15 storage unit 16 computing unit 17 Activation threshold 18 Deactivation threshold 20 Driver request 21 Actual driving line 22 Lateral forces front axle 23 Lateral forces rear axle 24 Yaw moment

Claims

[1] Multi-engine motor vehicle having a front axle (2) and a rear axle (5), wherein the front axle (2) is drivable by at least one first motor (4) and the rear axle (5) is drivable by at least one second motor (7), wherein a control unit (8, 9) is provided which is configured to determine a distribution with which a requested total drive power is divided between a first drive power for the front axle (2) and a second drive power for the rear axle (5) and to control the at least one first motor (4) and the at least one second motor (7) according to the distribution, wherein the control unit (9) is further configured to check whether the motor vehicle (1) is understeering or oversteering and, in the event of understeering, to shift the distribution towards the rear axle (5) and, in the event of oversteering, to shift the distribution towards the front axle (2). characterized bythat a limit value is provided for the lateral acceleration of the motor vehicle (1), and when the limit value is exceeded, a current yaw rate deviation is stored as a first value, wherein the control unit is designed to carry out a control for the distribution of the drive power based on the first value. [2] Multi-engine motor vehicle according to claim 1, characterized by in that the control unit (9) is configured to detect understeering and / or oversteering by exceeding a lateral acceleration threshold value and a yaw rate deviation threshold value, wherein the difference between a yaw rate of the motor vehicle (1) and a reference yaw rate from a vehicle model is calculated as a yaw rate deviation and compared with the yaw rate deviation threshold value. [3] Multi-engine motor vehicle according to one of the preceding claims, characterized bythat the control unit (9) has a PID controller (14) which is designed to control the distribution of the drive power. [4] Multi-engine motor vehicle according to one of the preceding claims, characterized by in that the control has a hysteresis, wherein the control unit (9) is designed to activate the control when the yaw rate deviation reaches and / or exceeds the first value and to deactivate it when the yaw rate deviation reaches and / or falls below a second value, wherein the second value is smaller than the first value by a predetermined hysteresis value. [5] Multi-engine motor vehicle according to claim 4, characterized by that the control is set up to control the yaw rate deviation to the second value. [6] Multi-engine motor vehicle according to one of the preceding claims, characterized bythat a coefficient of friction between a tire (3, 5) of the motor vehicle (1) and a vehicle ground is estimated and, based on the coefficient of friction, a maximum lateral acceleration of the motor vehicle (1) is determined at which the adhesion between the tire (3, 5) and the vehicle ground is lost and a value smaller than the maximum lateral acceleration is used as the limit value for the lateral acceleration. [7] Multi-engine motor vehicle according to claim 6, characterized by that the coefficient of friction is continuously determined and the limit value for lateral acceleration is dynamically adjusted during the course of the journey. [8] Multi-engine motor vehicle according to one of claims 6 and 7, characterized by that a value between 50% and 90%, preferably between 60% and 80% of the maximum lateral acceleration is used as the limit value for the lateral acceleration. [9] Multi-engine motor vehicle according to one of the preceding claims, characterized bythat the control unit (9) is designed to shift the distribution of the drive power towards the front axle (2) when the motor vehicle (1) is oversteering and the yaw rate deviation is greater than a control setpoint. [10] Multi-engine motor vehicle according to one of the preceding claims, characterized by that the control is designed to shift the distribution of the drive power towards the rear axle (5) in the event of an understeering motor vehicle (1) and a yaw rate deviation greater than the target value. [11] Multi-engine motor vehicle according to any preceding claim, characterized by that an input device, in particular an accelerator pedal, is provided for detecting the requested drive power. [12] Multi-engine motor vehicle according to any preceding claim, characterized bythat a virtual driver is provided for the autonomous control of the motor vehicle (1), which is designed to determine a required drive power and to transmit it as requested drive power to the control unit (9). [13] Method for distributing a drive power of a vehicle to a front axle (2) driven by a first motor (4) and a rear axle (5) driven by a second motor (7), characterized bythat when cornering, it is checked whether the motor vehicle (1) is understeering or oversteering and in the event of understeering the distribution is shifted towards the front axle (2) and in the event of oversteering the distribution is shifted towards the rear axle (5), wherein a limit value for the lateral acceleration of the motor vehicle (1) is provided, and it is checked whether a limit value for the lateral acceleration of the motor vehicle (1) is exceeded, and if the limit value is exceeded, a current yaw rate deviation is stored as a first value, wherein the control unit is set up to carry out a control for the distribution of the drive power based on the first value. [14] Method according to claim 13, characterized by that the following steps are also carried out: - Determining a second value less than the first value - Controlling the distribution of the drive power to the front axle (2) and the rear axle (5) in such a way that the second value is used as the target value for the yaw rate deviation, whereby - in the case of oversteering of the vehicle, if the yaw rate deviation is greater than the second value, the distribution of the drive power is shifted towards the front axle (2) and - in the case of an understeering vehicle, if the yaw rate deviation is greater than the second value, the distribution of the drive power is shifted towards the rear axle (5).

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