DE102020204991A1 - Control for the distribution of the drive power - Google Patents

Abstract

The invention relates to a multi-engine motor vehicle having a front axle and a rear axle, the front axle being drivable by at least one first motor and the rear axle being drivable by at least one second motor, a control device being provided which is set up to determine a distribution, with which a requested total drive power is divided into a first drive power for the front axle and a second drive power for the rear axle and to control the at least one first motor and the at least one second motor according to the distribution. In order to improve the stability of the vehicle, the control unit is also set up to check whether the vehicle is understeering or oversteering and to shift the distribution in the direction of the rear axle in the event of understeer and to shift the distribution in the direction of the front axle in the event of oversteer.

Description

The invention relates to a multi-engine motor vehicle with a front axle and a rear axle, the front axle being driven by at least one first motor and the rear axle being driven by at least one second motor, a control device being provided which is set up to determine a distribution, which divides the entire required drive power into 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.

The distribution of the drive power to the first motor and the second motor has so far typically been carried out solely on the basis of the requested acceleration. The torque on the rear axle is increased for large accelerations and decreased on the front axle. In normal driving situations with lower acceleration values, on the other hand, a greater torque is applied to the front axle.

When cornering, however, this can mean that the distribution of the drive power leads to instabilities in the vehicle, so that a stability system (ESC) has to restore the stability of the vehicle through individual brake interventions and a reduction in the total drive power.

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

The object is achieved according to the invention in that the distribution of the drive power is adjusted accordingly even before the vehicle becomes unstable.

For this purpose, the control unit is also set up to check whether the vehicle is understeering or oversteering when cornering and to shift the distribution in the direction of the rear axle in the event of understeer and to shift the distribution in the direction of the front axle in the event of oversteer. The invention is not limited to two-axle motor vehicles. Rather, a front axle and a rear axle are to be understood as any axles that are arranged one behind the other, regardless of the arrangement of a third or further axles.

In a preferred embodiment of the invention, the control device is set up to recognize understeering and / or oversteering when a lateral acceleration threshold value and a yaw rate deviation threshold value are exceeded. The difference between an actual yaw rate of the vehicle, which is measured for example by means of 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 value. The vehicle model can be a single-track model, for example. In particular, the yaw rate to be expected is determined as the reference yaw rate from the steering angle, vehicle speed and vehicle geometry. Furthermore, a lateral acceleration of the vehicle, which is determined for example by means of an acceleration sensor, is compared with the lateral acceleration threshold value. The threshold values can be selected so low that a stability system (ESC) does not yet intervene.

In a further preferred embodiment of the invention, a limit value for the lateral acceleration of the vehicle is provided, the current yaw rate deviation being stored as the first value when the limit value is exceeded and the control device is set up to regulate the distribution of the drive power based on the first value perform. The limit value of the lateral acceleration is selected so that the vehicle still has sufficient stability. Correspondingly, the yaw rate deviation is still to be regarded as acceptable at this point in time 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 a basis for a regulation for the distribution of the drive power.

In a particularly preferred embodiment of the invention, the control device has a PID controller which is set up to regulate 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, which is regulated to a setpoint based on the first value, is used as the input variable. The distribution of the drive power to the front axle and the rear axle is used as the control variable. A PID controller (proportional-integral-derivative controller) consists of parts of a P-element, an I-element and a D-element and can reach the setpoint particularly safely and without overshooting.

In a further particularly preferred embodiment of the invention, the regulation has a hysteresis. The regulation is activated when the yaw rate deviation exceeds the first value and deactivated when the yaw rate deviation falls below a second value, with the second value is one hysteresis value less than the first value. Either a fixed hysteresis value can be stored in the control unit, which is subtracted from the first value, or, for example, a portion can be stored so that the first value is multiplied by a factor less than 1 in order to obtain the second value. The hysteresis ensures that the control is not activated and deactivated very often if the input value fluctuates slightly around the setpoint.

In a further particularly preferred embodiment of the invention, the regulation is set up to regulate the yaw rate deviation to the second value. This means that the control is provided with the second value as a setpoint. After activation, the control therefore tries to reach the lower deactivation value. As soon as this is the case, the regulation is deactivated and only activated again when the higher first value is reached again.

In a further particularly preferred embodiment of the invention, a coefficient of friction between a tire of the vehicle and a vehicle surface is estimated and, based on the coefficient of friction, a maximum lateral acceleration of the vehicle is determined at which the vehicle stability is lost because the tire loses its grip on the surface. A value smaller than the maximum lateral acceleration is determined from the maximum lateral acceleration and used as a limit value for the lateral acceleration. For this purpose, a fixed value can be deducted again or a multiplication with a factor smaller than 1 can be carried out. The limit value of the lateral acceleration is therefore still in a range in which the vehicle can be steered in a stable manner.

In a further particularly preferred embodiment of the invention, the coefficient of friction is continuously determined and the limit value for the lateral acceleration is adapted dynamically during the course of the journey. As a result, the distribution of the drive torques is instantaneously adapted to changing surface conditions and the stability of the vehicle is ensured.

In a further 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 in a stability range that is a long way from an unstable range, so that the motor vehicle can always be safely controlled.

In a further particularly preferred embodiment of the invention, the control device is set up to shift the distribution of the drive power in the direction of the front axle when the vehicle is oversteering and if the yaw rate deviation is greater than a setpoint value, in particular the second value. The amount 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 curve is being driven.

In a further particularly preferred embodiment of the invention, the control device is set up to shift the distribution of the drive power in the direction of the rear axle in the event of an understeering vehicle and a yaw rate deviation greater than the setpoint value, in particular the second value.

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

In an alternative embodiment of the invention, a virtual driver is provided for autonomous control of the vehicle, which is set up to determine a required drive power and to transmit it to the control unit as the requested drive power. This means that the stability improvement can also be easily applied to autonomous vehicles.

The object is also achieved by a method for distributing a drive power of a vehicle to a front axle driven by a first motor and a rear axle driven by a second motor Shifts towards the front axle and shifts the distribution towards the rear axle in the event of oversteer.

• - Überprüfen ob ein Grenzwert für die laterale Beschleunigung des Fahrzeugs überschritten wird und
• - Bei einem Überschreiten des Grenzwerts, Speichern der aktuellen Gierratenabweichung als erster Wert
• - Bestimmen eines zweiten, niedrigeren, Werts, beispielsweise durch Subtraktion eines vorbestimmten Hysteresewerts von dem ersten Wert oder durch Multiplikation mit einem Faktor kleiner 1
• - Regeln der Verteilung der Antriebsleistung auf die Vorderachse und die Hinterachse derart, dass die Gierratenabweichung dem zweiten Wert entspricht, indem
• - bei übersteuerndem Fahrzeug bei einer Gierratenabweichung größer als der zweite Wert die Verteilung der Antriebsleistung in Richtung der Vorderachse verschoben wird und
• - bei untersteuerndem Fahrzeug bei einer Gierratenabweichung größer als der zweite Wert die Verteilung der Antriebsleistung in Richtung der Hinterachse verschoben wird.

In a preferred embodiment of the method, the following steps are carried out:

• - Check whether a limit value for the lateral acceleration of the vehicle is exceeded and
• - If the limit value is exceeded, the current yaw rate deviation is saved as the first value
• - Determination of 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
• - Regulating the distribution of the 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
• - If the vehicle is oversteering and the yaw rate is greater than the second value, the distribution of the drive power is shifted in the direction of the front axle and
• - If the vehicle is understeering and the yaw rate is greater than the second value, the distribution of the drive power is shifted in the direction of the rear axle.

• 1 zeigt schematisch ein erfindungsgemäßes Kraftfahrzeug,
• 2 zeigt schematisch den Datenfluss eines erfindungsgemäßen Verfahrens,
• 3 zeigt schematisch ein übersteuerndes Fahrzeug,
• 4 zeigt das Fahrzeug der 3 während aktiver Regelung,
• 5 zeigt schematisch ein untersteuerndes Fahrzeug,
• 6 zeigt das Fahrzeug der 5 während aktiver Regelung,
• 7 zeigt das Fahrzeug der 3 bis 6 nach der Regelung;

Further features, advantages and possible applications of the invention can also be found in the following description of exemplary embodiments and the drawings. All of the features described and / or shown in the figures, both individually and in any combination, are part of the subject matter of the invention, regardless of how they are summarized in the claims or their references.

• 1 shows schematically a motor vehicle according to the invention,
• 2 shows schematically the data flow of a method according to the invention,
• 3 shows schematically an oversteering vehicle,
• 4th shows the vehicle of the 3 during active regulation,
• 5 shows schematically an understeering vehicle,
• 6th shows the vehicle of the 5 during active regulation,
• 7th shows the vehicle of the 3 until 6th according to the regulation;

The car 1 the 1 has a drive with several electric motors 4th , 7th on. Alternatively, either or both of the motors 4th , 7th be designed as an internal combustion engine. The first engine 4th drives a front axle 2 of the motor vehicle 1 with two front wheels 3 at. The second engine 7th is on a rear axle 5 with two rear wheels 6th arranged and drives them. The front axle 2 and the rear axle 5 are not mechanically coupled to each other and the two motors 4th , 7th can be regulated independently of one another, which means that the drive power or the torques on the front axle 2 and the rear axle 5 can be set independently of each other.

A total drive power requested, for example by a driver by means of an accelerator pedal, is provided by an engine control when driving straight ahead 8th on the front axle 2 with the first engine 4th and the rear axle 5 with the second engine 7th distributed. The distribution of the drive power can depend in particular on the position of the accelerator pedal and be selected with regard to energy efficiency. In addition, according to the invention, there is a control device 9 provided, which checks when cornering whether the motor vehicle 1 understeer and / or oversteer. In this case the control unit can 9 a distribution of the entire drive power to the first motor 4th and the second motor 7th determine and send this to the engine control 8th to transfer. Alternatively, the control unit 9 the first engine 4th and the second motor 7th drive directly.

As in 2 shown, has the control unit of the motor vehicle 1 a lateral acceleration sensor 10 and a yaw rate sensor 11 on. In one arithmetic unit 16 of the control unit 9 a vehicle model is calculated from which a reference yaw rate is determined based on vehicle speed, steering angle, vehicle-specific parameters, etc. The control unit 9 compares the actual yaw rate as determined by the yaw rate sensor 11 is determined with the reference yaw rate and determines the yaw rate deviation 13th as the difference between the actual yaw rate and the reference yaw rate. Alternatively, the yaw rate deviation 13th the control unit 9 from another control device, for example an ESC control device.

When the yaw rate deviation 13th exceeds a yaw rate deviation threshold value and at the same time the lateral vehicle acceleration exceeds a lateral threshold value, the vehicle is oversteering 1 (please refer 3 ) or understeering vehicle 1 (please refer 5 ) went out. Oversteering of the vehicle 1 is recognized, for example, by the fact that the actual yaw rate 11 is greater in amount than the reference yaw rate. Understeering of the vehicle 1 is recognized by the fact that the actual yaw rate 11 is smaller in terms of amount than the reference yaw rate.

In the control unit 9 is in the storage unit 15th In addition, a limit value for the lateral acceleration is stored. This can be identical to the lateral threshold value, or it can be 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 them in a review 12th with the lateral limit value. As soon as the lateral acceleration exceeds the lateral limit value, the current yaw rate deviation becomes 13th determined and in a storage unit 15th deposited. This value is used as the first value, namely as the activation threshold 17th , for the scheme 14th used. Because this value is the current yaw rate deviation 13th corresponds to the scheme 14th activated at the same time. That means the distribution of the drive power to the front axle 2 and the rear axle 5 is no longer independent by the engine control 8th made, but by the control unit 9 determined and the engine control 8th transmitted. From the first value 17th a second value is also used as the deactivation threshold 18th certainly. This is set to 80% of the activation threshold, for example, in order to implement a hysteresis behavior. That is, the scheme 14th is deactivated at a lower value and activated at a higher value in order to continuously activate and deactivate the control 14th to avoid. The deactivation threshold is assigned to the PID controller 14th supplied as a setpoint, which determines the distribution of the drive power between the front axle 2 and rear axle 5 varies such that the yaw rate deviation 13th the setpoint 18th approaching.

In the event of a vehicle oversteering, shows 3 the driver's request 20th , which indicates the desired driving line as it can be determined from the steering wheel position and the vehicle speed as well as the vehicle geometry. The side forces 22nd on the front axle 2 are much smaller than the side 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 request and the vehicle 1 turns more than desired.

The inventive intervention in the regulation of the drive torque between the front axle 2 and the rear axle 5 gets more torque on the front axle 2 and less torque on the rear axle 5 given so that the lateral force 22nd on the front axle 2 becomes greater than the lateral force 23 on the rear axle 5 . This inverts it on the vehicle 1 effective yaw moment and the actual driving line 21 approaches the driver's wish 20th at.

After the end of the intervention, the actual driving line corresponds 21 the driver's request 20th and the side forces 22nd , 23 on the front axle 2 and the rear axle 5 are the same as in 7th is shown.

The case of an understeering vehicle 1 is in the 5 shown. The side force 22nd on the front axle 2 is greater than the serial force 23 on the rear axle and a counterclockwise yaw moment acts on the vehicle 1 . The actual driving line 21 therefore deviates from the driver's request 20th by turning the vehicle only slightly to the right. The control generates drive torque from the front axle 2 on the rear axle 5 shifted, which reduces the side force on the front axle and on the rear axle 5 is increased. This results in a clockwise yaw moment 24 and the actual driving line 21 approaches the driver's wish 20th at. After the end of the regulation, the side forces are on the front axle 2 and the rear axle is the same again and the actual driving line 21 corresponds to the driver's demand 20th , as in 7th is shown.

By distributing the drive forces to the front axle and the rear axle, the stability of the vehicle can thus be improved before an ESC system intervenes.

List of reference symbols

1

Motor vehicle

2

Front axle

3

Front wheel

4th

first engine

5

Rear axle

6th

Rear wheel

7th

Second engine

8th

Engine control

9

Control unit

10

Accelerometer

11

Yaw rate sensor

12th

Verification

13th

Yaw rate deviation

14th

PID controller

15th

Storage unit

16

Arithmetic unit

17th

Activation threshold

18th

Deactivation threshold

20th

Driver request

21

Actual driving line

22nd

Lateral forces on the front axle

23

Lateral forces on the rear axle

24

Yaw moment

Claims (15)

Multi-engine motor vehicle having a front axle (2) and a rear axle (5), the front axle (2) being drivable by at least one first motor (4) and the rear axle (5) being drivable by at least one second motor (7), with a Control device (8, 9) is provided, which is set up to determine a distribution with which a requested total drive power is transferred to a first drive power for the front axle (2) and a second drive power for the rear axle (5) is divided and to control the at least one first motor (4) and the at least one second motor (7) according to the distribution, characterized in that the control unit (9) is further set up to check whether the motor vehicle (1) is understeering or oversteering and to shift the distribution in the direction of the rear axle (5) in the event of understeering and to shift the distribution in the direction of the front axle (2) in the event of oversteer. Multi-engine motor vehicle according to Claim 1 , characterized in that the control unit (9) is set up to detect understeering and / or oversteering when a lateral acceleration threshold value and a yaw rate deviation threshold value are exceeded, the difference between a yaw rate of the motor vehicle (1) and a reference yaw rate from a vehicle model as the yaw rate deviation is calculated and compared to the yaw rate deviation threshold. Multi-engine motor vehicle according to Claim 1 or 2 , characterized in that a limit value for the lateral acceleration of the motor vehicle (1) is provided, and when the limit value is exceeded, a current yaw rate deviation is stored as the first value, the control device being set up to regulate the distribution of the drive power based on the perform the first value. Multi-engine motor vehicle according to Claim 3 , characterized in that the control device (9) has a PID controller (14) which is set up to regulate the distribution of the drive power. Multi-engine motor vehicle according to one of the Claims 3 until 4th , characterized in that the regulation has a hysteresis, the control device (9) being set up to activate the regulation when the yaw rate deviation reaches and / or exceeds the first value and to deactivate it when the yaw rate deviation reaches a second value and / or falls below, wherein the second value is smaller than the first value by a predetermined hysteresis value. Multi-engine motor vehicle according to Claim 5 , characterized in that the regulation is set up to regulate the yaw rate deviation to the second value. Multi-engine motor vehicle according to Claim 3 until 6th , characterized in that a coefficient of friction between a tire (3, 5) of the motor vehicle (1) and a vehicle surface is estimated and, based on the coefficient of friction, a maximum lateral acceleration of the motor vehicle (1) is determined at which the grip between tires (3 , 5) and vehicle ground is lost and a value smaller than the maximum lateral acceleration is used as the limit value for the lateral acceleration. Multi-engine motor vehicle according to Claim 7 , characterized in that the coefficient of friction is continuously determined and the limit value for the lateral acceleration is dynamically adapted during the course of the journey. Multi-engine motor vehicle according to one of the Claims 7 and 8th , characterized in 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. Multi-engine motor vehicle according to one of the Claims 3 until 9 , characterized in that the control unit (9) is set up to shift the distribution of the drive power in the direction of the front axle (2) when the motor vehicle (1) is oversteering and when the yaw rate deviation is greater than a setpoint value of the control system. Multi-engine motor vehicle according to one of the Claims 3 until 10 , characterized in that the control is set up to shift the distribution of the drive power in the direction of the rear axle (5) when the motor vehicle (1) is understeering and when the yaw rate deviation is greater than the target value. Multi-engine motor vehicle according to one of the preceding claims, characterized in that an input device, in particular an accelerator pedal, is provided for recording the required drive power. Multi-engine motor vehicle according to one of the preceding claims, characterized in that a virtual driver is provided for autonomous control of the motor vehicle (1), which is set up to determine a required drive power and to transmit it to the control unit (9) as the requested drive power. 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 in that when cornering it is checked whether the motor vehicle ( 1) understeer or oversteer and in the case of understeer the distribution is shifted in the direction of the front axle (2) and in the event of oversteer the distribution is shifted in the direction of the rear axle (5). Procedure according to Claim 14 , characterized in that the following steps are carried out: - Check whether a limit value for the lateral acceleration of the motor vehicle (1) is exceeded and - If it is exceeded, store the current yaw rate deviation as the first value - Determine a second value less than the first value - Control of 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 Drive power is shifted in the direction of the front axle (2) and - if the vehicle is understeering, if the yaw rate deviation is greater than the second value, the distribution of the drive power is shifted in the direction of the rear axle (5).

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