DE102023202245A1 - Method for controlling regenerative braking operation - Google Patents

Abstract

A method for controlling regenerative braking in a motor vehicle comprises the steps
a) estimating (S2) a maximum permissible acceleration (a _K ) of the motor vehicle;
b) estimating (S5) a transverse acceleration (a _y ) resulting from negotiating a curve;
c) limiting (S7, S8) the longitudinal deceleration (at) resulting from regenerative braking with the aid of an electric machine (1) operated as a generator when negotiating the curve in such a way that the total acceleration (a total) resulting from the transverse acceleration (a _y ) and the longitudinal deceleration ( _at ) does not exceed the maximum permissible acceleration (a _K ).

Description

The present invention relates to a method for controlling regenerative braking operation in a motor vehicle.

In drive technology, the term recuperation refers to the technical process for recovering energy during braking or when the fuel supply is cut off.

During recuperation, an electric machine in generator mode is driven by the rolling wheels, thus converting the vehicle's kinetic energy into electrical energy.

Out of US 5 915 801 A is a hybrid vehicle with an internal combustion engine and an electric motor in which the recuperation during electric operation is dosed in such a way that it simulates the braking torque that the internal combustion engine would generate during combustion operation.

BEV vehicles can have several recuperation modes that differ in deceleration and controllability. In some cases, the generator load is so high that the brake pedal hardly needs to be operated. However, if a pedal change occurs when cornering, a sudden strong deceleration due to the onset of recuperation can lead to an unstable driving situation such as understeer or oversteer.

An object of the present invention is to ensure the stability of an electrically powered vehicle in recuperation mode even when driving through a curve.

1. a) Abschätzen einer maximal erlaubten Beschleunigung des Kraftfahrzeugs;
2. b) Abschätzen einer aus dem Durchfahren einer Kurve resultierenden Transversalbeschleunigung;
3. c) Begrenzen der aus einem regenerativen Bremsen mit Hilfe einer als Generator betriebenen elektrischen Maschine beim Durchfahren der Kurve resultierenden Longitudinalverzögerung derart, dass die aus der Transversalbeschleunigung und der Longitudinalverzögerung resultierende Gesamtbeschleunigung die maximal erlaubte Beschleunigung nicht übersteigt.

According to one aspect of the invention, the object is achieved by a method for controlling regenerative braking operation in a motor vehicle, comprising the steps

1. (a) Estimating the maximum permissible acceleration of the motor vehicle;
2. b) estimating a transverse acceleration resulting from negotiating a curve;
3. (c) limiting the longitudinal deceleration resulting from regenerative braking using an electric machine operating as a generator when negotiating the curve in such a way that the total acceleration resulting from the transverse acceleration and the longitudinal deceleration does not exceed the maximum permitted acceleration.

An unstable driving situation occurs when the sum of the longitudinal and transverse forces, i.e. the deceleration and centrifugal forces, is greater than the force that can be transmitted between the wheel and the road. This latter force limits (possibly taking into account a safety margin) the maximum acceleration permitted for the vehicle. The forces acting on the vehicle (or accelerations proportional to them) can be represented by the force circle (Kamm circle). A driving situation in which a resulting force vector extends beyond the limits of the force circle is an unstable driving situation. The transverse acceleration resulting from driving through a curve is determined by the curve radius and the vehicle speed. It cannot therefore be adjusted faster than the vehicle speed if the curve radius is determined by the road surface. However, in order to avoid or end an unstable driving situation, rapid adjustment is necessary. Such rapid adjustment is possible with the deceleration caused by the excitation of the electric machine.

The maximum possible acceleration during stable driving (corresponding to the radius of the Kamm circle) depends on the characteristics of the vehicle such as load distribution on the wheels, chassis structure, type of tires and the road, such as type of road surface, wetness, ice/snow. These influencing factors should therefore be taken into account when estimating the maximum permissible acceleration.

The step of estimating the transverse acceleration can involve a direct measurement of the current acceleration using an acceleration sensor. However, it can also be carried out taking into account a current or impending curvature of the road. For this purpose, for example, the steering angle of a vehicle's steering wheel can be recorded, since it can be assumed that a driver of the vehicle will always adapt this to the course of the road. In addition to the steering angle, the curvature of the road can also be recorded using other variables, for example calculated from the difference in speed of the wheels.

An impending road curvature can also be detected based on data from a navigation system or a location-resolving sensor carried by the vehicle, such as a camera or radar system.

1. c1) eine erste Soll-Longitudinalverzögerung vorgegeben sein,
2. c2) geprüft werden, ob eine aus der ersten Soll-Longitudinalverzögerung und der Transversalbeschleunigung resultierende Gesamtbeschleunigung die maximal erlaubte Beschleunigung übersteigt, und, wenn ja,
3. c3) eine die maximal erlaubte Beschleunigung nicht übersteigende zweite Soll-Longitudinalverzögerung ermittelt werden und die elektrische Maschine angesteuert werden, um die zweite Soll-Longitudinalverzögerung zu erreichen.

In order to adequately limit the longitudinal delay in step c),

1. c1) a first target longitudinal deceleration is specified,
2. (c2) check whether a total acceleration resulting from the first target longitudinal deceleration and the transverse acceleration exceeds the maximum permitted acceleration and, if so,
3. c3) a second target longitudinal deceleration not exceeding the maximum permitted acceleration is determined and the electric machine is controlled to achieve the second target longitudinal deceleration.

Steps c2 and c3 should be repeated periodically to allow adaptation of the second target longitudinal deceleration to changing curve radii and/or vehicle speeds while negotiating a curve.

The invention further relates to a vehicle with a brake control unit which is designed to carry out the method as described above, as well as a computer program which, when executed by an on-board computer of a vehicle, causes the latter to carry out the method.

• 1 ein Blockdiagramm eines Kraftfahrzeugs;
• 2 einen Kammschen Kreis;
• 3 ein Flussdiagramm eines Arbeitsverfahrens der Steuereinheit des Kraftfahrzeugs aus 1; und
• 4 ein Flussdiagramm eines alternativen Arbeitsverfahrens.

Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying figures. They show:

• 1 a block diagram of a motor vehicle;
• 2 a Kamm circle;
• 3 a flow chart of an operating procedure of the control unit of the motor vehicle 1 ; and
• 4 a flow chart of an alternative working procedure.

1 shows schematically a motor vehicle with wheels 2 driven by an electric machine 1. The front wheels 2 are turned under the control of a steering wheel 3 so that the vehicle moves on a curved path.

An inverter 4 is connected to the electric machine 1 in order to supply it with electrical energy from a battery 5 during engine operation and to generate electrical energy during recuperation operation, with which the battery 5 is charged or other electrical consumers of the vehicle are supplied.

A control unit 6 is connected to a sensor 7, which is coupled to a pedal 8 in order to detect a driver's desire for acceleration or deceleration. Typically, the extent to which the driver operates the pedal 8, i.e. its deflection from a rest position, is interpreted by the control unit 6 as a measure of a desired acceleration, while non-operation or release of the pedal 8 by the driver is interpreted as a desire for deceleration. Alternatively, a neutral position of the pedal 8 that deviates from the rest position can also be defined, so that if the driver holds the pedal in the neutral position, this is interpreted as a desire for no acceleration, while a position between the rest and neutral positions is interpreted as a desire for deceleration. The extent of the desired deceleration can depend on the position of a selector element, which, like the selector lever of a conventional automatic transmission, can be switched between several modes of forward travel such as D, 1, 2 and at least one mode R of reverse travel. Mode 1 can be assigned a higher target deceleration than mode 2, which in turn can be assigned a higher target deceleration than mode D. Acceleration vectors a ₁ , a ₂ and a _D corresponding to the target decelerations are shown in the diagram of the 2 marked.

The control unit 6 is further connected to a speedometer 9 and a further sensor 10, which detects a steering angle of the steering wheel 3. Based on the data from the speedometer 9 and the sensor 10, the control unit 6 calculates the radius of the curve taken by the vehicle and a resulting centrifugal acceleration a _y .

Alternatively or additionally, a camera 11 or a radar sensor can be provided to detect the road ahead of the vehicle, and the control unit 6 is further configured to determine a radius of the road ahead from the captured image data and to use this as the basis for calculating the centrifugal acceleration a _y to be expected in the near future. A navigation system 12 can be provided to provide information about curve radii ahead or to check the plausibility of the results obtained from the image data.

In order to gain information about the properties of the road surface, the control unit can be connected to a rain sensor and a thermometer in order to differentiate between dry, wet and possibly icy surfaces and to be able to estimate the friction coefficient of the surface accordingly. It is also conceivable to derive corresponding information from the behavior of an anti-lock braking system, in the simplest case, for example, to temporarily assume a reduced friction coefficient when the anti-lock braking system has intervened in a braking process and/or to estimate the roughness of the surface based on a driving noise spectrum.

The friction coefficient estimated by the control unit in this way determines the radius of a Kamm circle K, as in 2 shown.

As in 2 As can be seen, the resulting accelerations from a _y and a _D or a ₂ lie within the Kamm circle K, but the resulting acceleration from a _y and a ₁ extends beyond it and would therefore lead to an unstable driving situation.

Thus, if the driver has selected mode 1 and causes the control unit 6 to enter recuperation mode by releasing the accelerator pedal 8, it is sufficient, for example, to keep the vehicle stable for the control unit 6 to control the machine 1 in the manner normally associated with mode 1, as is normally the case in mode 2, and to maintain this type of control until the curve has been negotiated.

3 shows, using a flow chart, an example of a method carried out by the control unit 6 for controlling recuperation in the electric machine 1 for the above-mentioned case in which a release of the pedal 8 is interpreted as a deceleration request by the driver. The method is repeated at short intervals as long as the vehicle is moving. In step S1, it is checked whether the accelerator pedal 8 is actuated or released.

When it is activated, the control unit 6 collects information about the environment of the vehicle in step S2 as outlined above, based on which it estimates a friction coefficient µ of the road. From this friction coefficient µ, possibly reduced by a safety margin ε, a maximum permissible acceleration a _K of the vehicle is obtained according to a _K =(µ-ε) g, where g denotes the acceleration due to gravity.

The speed v of the vehicle and the radius r of the roadway currently being traveled or ahead are determined in steps S3, S4. From this, the centrifugal acceleration a _y =v ² /r acting on the vehicle is obtained (S5).

For the currently set driving mode M=1, 2 or D, the total acceleration a _total = (a _y ² + a _M ² ) ^1/2 is calculated in S6, which would result from a vectorial addition of the centrifugal acceleration a _y and the target deceleration a _M assigned by default to the driving mode in the event that the accelerator pedal 8 is released by the driver.

If the total acceleration a _total remains below a _K , there is no risk of instability. The procedure therefore sets the deceleration a _M as a temporary target deceleration at and returns to output S1 to start again.

Otherwise, the control unit in S7 determines a value of the temporary target deceleration at such that (a _y ² + a _t ) ^1/2 <a _K is satisfied and then returns to the output.

If it is now determined in a subsequent iteration of the method in step S1 that the driver has released the pedal 8, it can be assumed that the parameters determined in steps S2-S4 have not changed significantly since the previous iteration and that the deceleration at determined in this iteration enables stable driving; consequently, when switching to recuperation mode, the control unit 6 controls the inverter 4 (S8) so that the machine 1 causes the deceleration at. This is followed by steps S2-S7, so that a current value of at is again available in a subsequent iteration of the method.

If the pedal 8 has a neutral position that differs from the rest position as described above, then the driver can quantitatively specify a desired deceleration a _x by bringing the pedal 8 into a position between the rest and neutral positions that is associated with this deceleration. The steps S2, S3, S4, S5 are described in this 4 The procedures described are the same as in the procedure of 3 . The total acceleration a _Ges =(a _y ² + a _x ) ^1/2 resulting from the desired deceleration a _x and the centrifugal acceleration a _y =v ² /r is compared with a _K (S6). If a _Ges <a _K , then stable driving is possible at the desired deceleration and the electric machine 1 is controlled (S8`) so that the desired deceleration a <sub>y</sub> is achieved. Otherwise, a deceleration a <sub>t</sub> is determined for which a <sub>Ges</sub> ≤(a <sub>y</sub> <sup>2</sup> +a <sub>t</sub> ) <sup>1/2</sup> applies (S7`), and the electric machine 1 is controlled in S8' with the deceleration a _t as the target deceleration.

Reference symbol

1

electric machine

2

wheel

3

steering wheel

4

Inverter

5

battery

6

Control unit

7

sensor

8

Accelerator pedal

9

sensor

10

sensor

11

camera

12

Navigation system

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• US 5915801 A [0004]

Claims (9)

Method for controlling regenerative braking operation in a motor vehicle, comprising the steps of a) estimating (S2) a maximum permitted acceleration (a _K ) of the motor vehicle; b) estimating (S5) a transverse acceleration (a _y ) resulting from driving through a curve; c) limiting (S7) the longitudinal deceleration (at) resulting from regenerative braking with the aid of an electrical machine (1) operated as a generator when driving through the curve in such a way that the total acceleration (a Ges ) resulting from the transverse acceleration (a _y ) and the longitudinal deceleration ( _at ) does not exceed the maximum permitted acceleration (a _K ). Procedure according to Claim 1 , in which the step (S2) of estimating the maximum permissible acceleration (a _K ) is carried out taking into account properties of the vehicle and/or the environment of the vehicle. Procedure according to Claim 2 , where the properties taken into account are selected from climatic properties such as the presence or absence of precipitation and the temperature of the environment, as well as road surface properties. Method according to one of the preceding claims, in which the step of estimating (S5) the transverse acceleration (a _y ) is carried out taking into account a current or impending road curvature. Procedure according to Claim 4 , in which the consideration of the impending road curvature is based on data from a navigation system (12) or a spatially resolving sensor (11) carried by the vehicle. Method according to one of the preceding claims, in which the step of limiting (S7, S8) comprises the steps of: c1) specifying a first target longitudinal deceleration (a _M ), c2) checking whether a total acceleration (a _Ges ) resulting from the first target longitudinal deceleration (a _M ) and the transverse acceleration (a _y ) exceeds the maximum permitted acceleration (a _K ), and, if so, c3) determining (S7) a second target longitudinal deceleration (at) which does not exceed the maximum permitted acceleration and controlling (S8) the electric machine in order to achieve the second target longitudinal deceleration (at). Procedure according to Claim 6 , in which steps c2 and c3 are repeated periodically. Vehicle with a brake control unit (6) which is designed to carry out the method according to one of the Claims 1 until 7 to execute. Computer program which, when executed by an on-board computer of a vehicle, causes the vehicle to carry out the method according to one of the Claims 1 until 7 to execute.

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