BE1031342B1 - Method for controlling a motor vehicle with a failed steer-by-wire steering system with drift and braking process - Google Patents

Abstract

The invention relates to a method for controlling a motor vehicle (1) with two axles, each with two wheels (RL, RR, FL, FR) and two-wheel steering, wherein the two front wheels (FL, FR) can be steered by means of a steer-by-wire steering system (2) and are connected to one another via a handlebar, and the motor vehicle (1) has a drive and braking system (5) with at least one wheel drive which drives the two rear wheels (RL, RR), and the method comprises the following steps if the steer-by-wire steering system (2) is not available: a. determining a target trajectory (4) of the motor vehicle (1), b. carrying out a drifting process (8) by controlling the drive and braking system (5) so that the motor vehicle turns towards the target trajectory (4), c. After the drifting process (8), carrying out a braking process (9) by controlling the drive and braking system (5) in such a way that all four wheels (RL, RR, FL, FR) are braked, i.e. after the braking process (9), if a deviation between the desired trajectory (4) and an actual trajectory (7) of the motor vehicle (1) exceeds a predetermined limit value, repeating steps b) and c).

Description

; BE2023/5108

Method for controlling a motor vehicle in the event of a steering failure

By-wire steering system with drift and braking

The present invention relates to a method for controlling a

Motor vehicle and a motor vehicle designed to carry out this method,

In steer-by-wire steering systems, the position of the steered wheels is not directly linked to the steering wheel. There is a connection between the steering wheel and the steered wheels via electrical signals. The driver's steering request is picked up by a steering angle sensor and the position of the steered wheels is controlled by a steering actuator depending on the driver's steering request. There is no mechanical connection to the wheels.

With such a steer-by-wire steering system, the driver is able to

Failure of the steering assistance is not possible by means of a mechanical

Continue to steer the vehicle by using force and muscle power.

However, in the event of a fault in the steer-by-wire system, it must be possible to

To be able to bring a motor vehicle to a stop safely at the side of the road,

The vehicle can then be recovered, for example by loading it onto a

trailer and taken to a workshop.

It is an object of the present invention to provide a method for controlling a

motor vehicle that allows a 'limp aside', i.e. steering/moving/driving the vehicle into a safe parking position,

This object is achieved by a method for controlling a motor vehicle having the features of claim 1 and a motor vehicle having the features of

Claim 6 is solved. The subclaims contain advantageous developments of the

called invention.

Accordingly, a method is provided for controlling a motor vehicle with two axles, each with two wheels and a two-wheel steering system, wherein the front two wheels can be steered by means of a steer-by-wire steering system and

Steering rod are connected to each other and the motor vehicle is a drive and

? BE2023/5108

Braking system with at least one wheel drive that drives both rear wheels, and the method comprises the following steps when the steer-by-wire

steering system is not available: a. Determining a SoH trajectory of the motor vehicle, b. Executing a drift process by controlling the drive and

braking system so that the motor vehicle moves towards the target trajectory, c. After the drifting process, carrying out a braking process by controlling the drive and braking system in such a way that all four wheels are braked (preferably as in a braking process with an anti-lock braking system), d. After the braking process, if a deviation between the target trajectory and an actual trajectory of the motor vehicle exceeds a predetermined limit value, repeat steps b} and c},

The drifting and braking processes allow the vehicle to safely stop in case of failure of the

Steering system to the roadside, The term “turning” means that the orientation of the motor vehicle changes in such a way that the actual trajectory is aligned with the target trajectory, The turning and the

Orientation of the vehicle refers to the yaw rate and the sideslip angle of the

Vehicle speed, yaw rate and sideslip angle clearly describe the vehicle condition and these values are preferentially controlled in order to realize the desired trajectory (in this case limp aside maneuver).

The at least one wheel drive may comprise two independent wheel drives of the rear wheels or a single wheel drive that drives the rear wheels via a differential.

Preferably, in step b} a differential drive torque between the two rear wheels is brought about by accelerating a rear wheel in the direction of travel and at least one of the front wheels is selectively braked.

The motor vehicle can be steered by braking a single front wheel and driving a rear wheel. Preferably, the front wheel of a first

Longitudinal side of the vehicle braked and the rear wheel of the other

Longitudinal side of the vehicle accelerates,

© BE2023/5108

It can be provided that the target trajectory is specified by an automatic, in particular autonomous or semi-autonomous driving mode. However, it is also conceivable that the target trajectory is determined by a driver in a

The steering torque introduced by the steering means is determined.

Preferably, steps b) and c) are repeated until the actual

Trajectory corresponds to the target trajectory and the vehicle is in a

Braking process until the vehicle comes to a standstill.

The Sofl trajectory preferably represents a 'limp-aside',

Furthermore, a motor vehicle is provided which is designed to carry out the aforementioned method.

Preferred embodiments of the invention are described below with reference to

Drawings explained in more detail, Similar or equivalent components are designated in the figures with the same reference numerals, They show:

Fig. 1: a schematic representation of a motor vehicle with a failed steer-by-wire steering system with a soil trajectory and an actual trajectory,

Fig. à: a schematic representation of a motor vehicle with a failed steer-by-wire steering system during a driving process, as well as

Fig. 3: a schematic representation of a motor vehicle with a failed steer-by-wire steering system during braking.

Figure 1 shows a motor vehicle 1 with a steer-by-wire steering system 2 and a rear axle drive 3. The vehicle can also alternatively have a

Rear-wheel drive, Based on a steering input from a driver or when the motor vehicle is in an automated driving mode, one

Signal from a control unit that implements automated driving, its soil

Trajectory 4 of the motor vehicle 1 is calculated. Automated driving is, for example, driving with automated lateral and

Longitudinal guidance, The term ‘automated driving’ includes an automated

Driving with any level of automation. Examples

4 BE2023/5108

Levels of automation are assisted, semi-automated, highly automated or fully automated driving,

The steer-by-wire steering system 2 is faulty and is not available.

Actuators of a drive and braking system 5 are controlled accordingly, so that by targeted braking and acceleration of the wheels 6 of the

motor vehicle 1, it can be kept on the soil trajectory 4. The target

Trajectory 4 preferably represents a “limp-aside”, the deviation between the

The difference between the target trajectory 4 and the actual trajectory 7 is minimized when the drive and brake system 5 is activated and the motor vehicle 1 is braked to a standstill. To do this, the drive and brake system alternately performs a

Drifting process 8 and braking process 9 until the motor vehicle 1 moves on the soil trajectory 4 and it is stopped by braking process 9 until the

Standstill can be braked.

Figure 2 shows a drift process. During a drift process, a

Slip angle a and a yaw moment w of the motor vehicle 1 by means of the

drive and braking system 5. In the example shown, the

Motor vehicles 1 turn anti-clockwise in the direction of travel to avoid

Target trajectory 4. A control unit calculates based on

Vehicle conditions and the determined target trajectory 4, a soliging moment and a target slip angle to calculate the difference between target trajectory 4 and actual

Trajectory to minimize, sideslip angle and yaw rate describe the

Vehicle condition clearly (together with the vehicle speed). The

Yaw moment is proportional to the derivative of the yaw rate. Based on the target values, SteligrôGen are determined for the front wheel brakes 50,51, for the rear axle drive 3 and the rear wheel brakes 52,53 and the drive and brake system 5 is controlled accordingly. In the example shown, the left front wheel

FL is braked, causing the vehicle to turn to the left. In addition, the right rear wheel RR is accelerated in the direction of travel by means of the rear axle drive 3.

The exemplary mini-axle drive 3 has a single actuator 2,

In particular, an electric motor that drives the rear wheels RL,RR via an open

Differential (without locking device) or a partially open differential.

The acceleration of the right rear wheel RR creates a drive torque difference between the left and right rear wheels on the rear axle,

S BE2023/5108 whereby the motor vehicle 1 rotates anti-clockwise about the vertical axis.

As shown in Figure 1, a drift process can cause the soil

Trajectory 4 is crossed by the actual trajectory 7 and the motor vehicle 1 "oversteers". After the time-limited drifting process 8, a braking process 9 is carried out in which all four wheels are braked evenly. The

Rear axle drive 3 does not drive the wheels,

If the motor vehicle 1 is not yet on the ground during the braking process 9,

Trajectory 4, the motor vehicle is only slightly braked and then a drift process 8 is carried out again, as shown in Figure 1. The next drift process 8 brings the actual trajectory 7 of the motor vehicle 1 closer to the soil trajectory 4. If the control error of the soil trajectory 4 is reduced in a control cycle, the vehicle is braked. If the

If the steering error is again too high, the drift function is applied again to reduce this error and to return the vehicle to the desired orientation.

direction. If there is an overlap of the actual

Trajectory 7 with the soil trajectory 4, a drift process 8 is carried out again after the subsequent braking process 9. This

The sequence continues until the actual trajectory 7 corresponds to the target trajectory 4.

Error tolerances can be provided here. After this, motor vehicle 1 is only braked.

This braking process is shown in Figure 3. During a braking process, all four wheels FL, FR, RL, RR are braked as in an emergency stop with an anti-lock braking system (ABS). Since the motor vehicle 1 in the example shown is already on the soil trajectory 4, the motor vehicle is braked to a standstill during the braking process.

Claims (5)

Patent claims 1. Method for controlling a motor vehicle (1) with two axles, each with two wheels (RL, RR, FL, FR) and a two-wheel steering system, wherein the front two wheels (FL, FR) can be steered by means of a steer-by-wire steering system (2) and are connected to one another via a steering rod and the motor vehicle {1} comprises a drive and braking system (5) with at least one wheel drive which drives the two rear wheels (RL, RR), and the method comprises the following steps if the steer-by-wire steering system {2) is not available: a. Determining a target trajectory (4) of the motor vehicle (1), b. Carrying out a drifting process (8) by controlling the drive and braking system (5) so that the motor vehicle turns towards the target trajectory (4), c., After the drifting process (8), carrying out a braking process (9) by controlling the drive and braking system (5) such that all four wheels (RLRR,FL,FR) are braked, d. After the braking process (9), if a deviation between the desired trajectory (4) and an actual trajectory (7) of the motor vehicle (1) exceeds a predetermined limit value, repeat steps b) and c). 2. Method according to claim 1, characterized in that in step b} a differential drive torque between the two rear wheels (RLRR} is brought about by accelerating a rear wheel (RR) in the direction of travel and at least one of the front wheels (FL) is selectively braked. 3. Method according to claim 1 or 2, characterized in that the target trajectory (4) is predetermined by an automatic driving mode, 4. Method according to one of claims 1 to 3, characterized in that the desired trajectory (4) is determined by means of a control input by a driver into a steering means ; BE2023/5108 introduced steering torque is determined, 5. Method according to one of the preceding claims, characterized in that steps b) and c) are repeated until the actual trajectory (7) corresponds to the desired trajectory (4) and the motor vehicle (1) is braked to a standstill in a braking process (9), ©. Method according to one of the preceding claims, characterized in that the target trajectory (4) depicts a "limp-aside", 7, Motor vehicle (1) which is set up to carry out the method according to one of claims 1 to 6,