WO2021058405A1

WO2021058405A1 - Method and device for a simultaneous lateral vehicle guidance by a driver and an assistance system using electric steering actuators

Info

Publication number: WO2021058405A1
Application number: PCT/EP2020/076208
Authority: WO
Inventors: Frank Sader
Original assignee: Continental Automotive Gmbh
Priority date: 2019-09-23
Filing date: 2020-09-21
Publication date: 2021-04-01
Also published as: DE102019214446A1

Abstract

The invention relates to a method for a simultaneous lateral vehicle guidance by a driver and an assistance system (10), wherein a steering torque generated by the driver and an assistance target angle calculated by an assistance system (10) are used to determine a resulting target steering angle, and a steering angle controller (24) implements the target steering angle using an EPS engine torque. When the assistance system (10) is active, the steering angle controller (24) is the sole source of the EPS engine torque.

Description

Method and device for simultaneous lateral vehicle guidance by the driver and assistance system with electric steering actuators

The invention relates to a method for simultaneous lateral vehicle guidance by the driver and the assistance system, with a steering torque generated by the driver and an assistance target angle calculated by an assistance system being used to determine a resulting target steering angle and a steering angle controller realizing this using an EPS engine torque.

Electric power steering systems (EPS) are used in addition to their actual function to support the driver's steering force by modern driver assistance systems for lateral control of the vehicle. This enables functions such as automated parking (in the low speed range) but also lane departure warning systems or vehicle follow-up control (even at high vehicle speeds, e.g. car) or even avoidance assistants (with correspondingly high dynamics). In order to maintain a vehicle trajectory (including a trajectory), the determination of which is not the subject of this, corresponding Stellbe commands are sent to the steering, i. A. via bus signals such as CAN or Flexray, transmitted, whereby angle or torque interfaces have established themselves. Depending on the interface, the steering generates the EPS motor torque required to implement the control command via additional interconnected controllers.

Both the assistance system and the driver act as trajectory and thus steering angle controllers. Both drivers as well as the assistance system, generate a moment as a manipulated variable such that the desired steering angle is set. If the driver would like to follow a different trajectory than the assistance system, this would, without suitable measures, result in the two controllers regulating against each other and, in doing so, always increasing their requested torque. In any case, the motor in an EPS is designed to be so powerful that it can bring forces into the steering that the driver can no longer control. The vehicle would follow the instructions of the assistance system and not that of the driver.

For safety reasons, however, it is necessary for the driver to be in control of his vehicle at all times and to be able to override the intervention by the driver assistance system if necessary. The feedback of the assistance system on the driver's steering torque must not exceed defined limits (e.g. 3 Nm). Usually this is realized by the fact that the moment from the assistance function, i. H. the assistance torque is superimposed on the normal steering function torque of the power steering and this superimposition torque of the driver assistance function (assistance torque) is limited in such a way that the driver can override the assistance system. Known embodiments of the overlay are described below be.

In principle, the two known embodiments described below are based on the superposition of the torque requested by the assistance function, ie the assistance torque, on signals that are already present from the actual steering assistance functions of an EPS. Embodiments are known for superposing the torque required by the assistance system either on the input or output side of the actual EPS steering functions.

In the first case, the assistance torque is superimposed on the measured steering torque. To ensure controllability, the steering torque and the assistance torque can be weighted differently in the addition, or the assistance torque is limited before the addition.

In the second case, the assistance torque is superimposed directly on the steering function torque. Here, too, it is possible to weight or limit the assistance torque before the addition.

In the first case, the reaction to the driver's hand torque can be set precisely, but due to the non-linear behavior of the EPS steering functions, the EPS engine torque and thus the vehicle reaction are dependent on the driving situation, especially the driving speed. Therefore, in this case, the higher-level angle or trajectory controller must be designed to be robust with regard to the non-linear behavior of the controlled system and can therefore not provide the optimal control quality in all driving situations.

In the second case, the requested assistance torque is applied directly to the EPS engine torque. The vehicle reaction can thus be precisely defined. In this case, however, the non-linearity of the steering functions means that the feedback on the steering torque is dependent on the driving situation, ie identical interventions by the assistance function lead to different degrees of feedback on the driver's hand torque. The design must be such that the driver does Can still control the vehicle in the most critical case, in all other cases, however, the permissible safety limit is not exhausted, so the intervention options of the assistance system are not fully exploited.

The necessary limitation of the intervention torque of the driver assistance function or the assistance torque generally leads to the fact that only limited curve radii or dynamics, i.e. in particular steering angle accelerations or speeds, can be represented, so that the desired assistance function may not meet the expectations gen can meet.

Another known embodiment is such that a switch is used to switch between vehicle guidance either by the assistance system or by the driver. A cooperative behavior of both in parallel is not intended in this case. So that the driver can override the assistance function if necessary, driver intervention monitoring is carried out, for. B. the steering torque is monitored so that if necessary a switching signal can be generated.

The assistance system is given sole control over the EPS engine torque by switching the torque path. The controllability is guaranteed tet that a driver intervention is recognized, z. B. by observing the steering torque. If a threshold value is exceeded, possibly with temporal debouncing, control is switched to the driver. This deactivates the assistance system. In this embodiment, the driver assistance function can use the full available engine torque, but the driver has no defined haptic feedback on the steering torque, and thus no information on how far he deviates from the target trajectory of the assistance system.

Ensuring vehicle controllability by superimposing a limited amount of assistance has several disadvantages. The EPS steering functions generate a non-linear ratio of driver steering torque to EPS engine torque that is dependent on the driving situation and the parameters. Depending on the selection of the superposition point, only either the driver steering torque generated by the superposition intervention (relevant for controllability) or the EPS engine torque can be defined, which is relevant for the vehicle reaction, but not both at the same time.

The invention is therefore based on the object of specifying a method and a corresponding device that provides the full engine torque for the assistance function, but allows corrective driver intervention and at the same time defines and limits the forces / torques to be provided by the driver.

In relation to the method according to the invention, this object is achieved in that, when the assistance system is active, the steering angle controller is the sole source of the EPS engine torque.

Advantageous refinements of the invention are the subject matter of the subclaims.

The invention is based on the consideration that with a lateral vehicle guidance, which is carried out simultaneously by the driver and assistant sistence system takes place, the controllability of the vehicle must be reliably fulfilled at all times.

As has now been recognized, this requirement can be met in that a driver intervention function detects the driver's request on the basis of the steering torque measured by the steering torque sensor and uses this to determine a correction angle desired by the driver. The steering angle requested by the assistance system, i. H. the assistance target angle is changed by this driver correction angle. The steering angle controller sets the steering angle modified in this way by means of a suitable EPS motor torque. The driver's sovereignty over the vehicle's course is guaranteed. The implementation of the assistance torque with the help of the EPS engine torque means preferably that the assistance torque is passed on to the EPS module 1: 1 in software. The assistance torque thus corresponds exactly to the EPS engine torque.

Advantageously, a driver correction angle is calculated from the steering torque in a driver intervention function, which is added to the assistance target angle calculated by the assistance system, and the sum of these angles represents the target steering angle and is an input variable for the steering angle controller.

The concept of the steering angle, i.e. the assistance target angle, the driver correction angle and the target steering angle, is to be understood broadly. It can be the steering angle in the narrower sense of the single-track model. In alternative embodiments, instead of the steering angle in the narrower sense, an equivalent variable that has a defined relationship to the steering angle is regulated, for example the curvature and / or wheel angle and / or rack position.

When the assistance system is activated, an EPS engine torque is preferably initialized which corresponds to the EPS steering function torque present immediately before activation. In this way, when the assistance function is activated, a steady and jerk-free torque curve can be achieved without any disruptive repercussions on the driver's hand torque.

When deactivating - as an alternative to the above-mentioned method also when activating - the assistance system is in a preferred embodiment gradually transferred from the assistance torque to the EPS steering function torque - reversed when activated. In this way, a steady and jerk-free torque curve can be generated without any disruptive repercussions on the driver's manual steering torque.

The steering torque is preferably measured by means of a steering torque sensor, the driver's hand torque, that is to say the torque directly transmitted by the driver to the steering, being determined from the measured steering torque by a correction method.

The steering torque sensor measures the torque between the output of the steering column (in the steering gear) and the steering wheel. With rapid steering accelerations, the steering wheel exerts a counter-torque due to its inertia, which is also measured by the sensor, but not initiated by the driver. The actual driver's hand torque cannot be measured, but can be approximately calculated using a compensation method. In addition to the mass inertia, there are other im Torque components visible to the sensor but not initiated by the driver: friction, off-center steering wheel center of gravity.

For this purpose, components from the steering wheel inertia and other factors influencing the measured value, in particular friction, are advantageously calculated in the correction method from the steering torque or its measured value.

With regard to the device, the above-mentioned object is achieved according to the invention with means for carrying out the method described above.

The means preferably include a steering angle controller for calculating the assistance torque and a driver intervention module for calculating a driver correction angle.

The means advantageously include a control unit of the steering in which the driver intervention function module and / or the steering angle controller are implemented in terms of hardware and / or software.

The advantages of the invention are, in particular, that since both the driver and the assistance system use the same angle controller, its output no longer has to be limited. The assistance system can utilize the full power and dynamics of the steering system / motor. By designing and parameterizing the driver intervention function, the haptic feedback to the driver can be designed and defined as a function of the correction angle.

The entire power that can be provided by an electric power steering to maintain the course is available through the assistance system, so that highly dynamic driving maneuvers can also be carried out using support systems are made possible. However, when interfering with the lane guidance, the driver retains full control of the vehicle and can override the assistance system.

An exemplary embodiment is explained in more detail with reference to a drawing. Therein, in a highly schematic representation, the single FIGURE shows a diagram to illustrate a method according to the invention.

First, the case is described in which the assistance function is deactivated. The steering torque measured by means of a sensor is the input variable for an EPS module 2 in which at least one EPS steering function is implemented. Typically, other variables such as the vehicle speed or the steering angle are taken into account as input variables for the EPS steering function (s) in EPS Model 2. The corresponding EPS steering function calculates an EPS steering function torque, which is then implemented as the EPS engine torque.

When the assistance function is activated, the EPS engine torque is calculated in a preferred embodiment of the method as follows.

In a laterally intervening assistance function of an assistance system 10, an assistance target angle is calculated. In a driver intervention function 14, a driver correction angle is calculated from a steering torque measured by means of a steering torque sensor of the EPS. The assistance target angle calculated by the assistance function and the driver correction angle calculated by the driver intervention function 14 are added to one another in an addition step 20. The resulting target steering angle serves as an input variable to a Steering angle controller 24. This calculates the necessary assistance torque at which the desired steering angle is set.

In normal power steering operation, a switching module 6 feeds the EPS steering function torque to the EPS engine torque; when the assistance function is activated, the assistance torque is passed on instead.

It is essential in this method that the steering torque is used as a correction variable by means of which the assistance target angle calculated or provided by the laterally intervening assistance function of assistance system 10 is corrected. The EPS engine torque is set exclusively via the assistance torque provided by the steering angle regulator 24. So there is no superposition of two moments, for example a steering function moment calculated as a function of the steering moment and possibly other variables and an assistance moment.

In the method proposed according to the invention, the steering torque is used earlier in the chain of calculations; it is already used to modify or correct the target steering angle. Instead of a superposition of moments, there is already a superposition of the angles. The steering angle controller thus has a corrected input variable available from which it can calculate the assistance torque. Since only this assistance torque is the source or basis of the EPS engine torque, the full range of values for the EPS engine torque is available to the steering angle controller.

Claims

1. A method for simultaneous lateral vehicle guidance by the driver and the assistance system (10), with a steering torque generated by the driver and an assistance target angle calculated by an assistance system (10) being used to determine a resulting target steering angle, and a steering angle controller (24) this using an EPS Realized engine torque, characterized in that when the assistance system (10) is active, the steering angle controller (24) is the sole source of the EPS engine torque.

2. The method according to claim 1, wherein a driver correction angle is calculated from the steering torque in a driver intervention function (14), which is added to the assistance target angle calculated by the assistance system (10), and the sum of these angles represents the target steering angle and an input variable for the steering angle regulator (24).

3. The method according to claim 1 or 2, wherein instead of the steering angle, at least one variable is used to determine the EPS torque, which is in a fixed relationship with the steering torque / steering angle, in particular curvature and / or wheel angle and / or rack position.

4. The method according to any one of claims 1 to 3, wherein when the assistance system (10) is activated, an EPS engine torque is initialized which corresponds to the EPS steering function torque present immediately before the activation.

5. The method according to claim 4, wherein when the assistance system (10) is deactivated gradually from the assistance torque to the EPS steering function torque and / or when activating the assistance system (10) is gradually faded from the EPS steering function torque to the assistance torque.

6. The method according to any one of the preceding claims, wherein the steering torque is measured by means of a steering torque sensor, and wherein the driver's hand torque is determined from the steering torque sensor signal by a correction method.

7. The method according to claim 6, wherein in the correction method Ren from the steering torque components of the steering wheel inertia and other factors influencing the measured value, in particular friction, are calculated.

8. Device for simultaneous lateral vehicle guidance by the driver and assistance system (10), comprising means for performing a method according to one of the preceding claims.

9. The device according to claim 8, the means comprising a steering angle controller (24) for calculating the Assistenzmomen tes and a driver intervention module (14) for calculating egg Nes driver correction angle.

10. The device according to claim 9, wherein the means comprise a STEU er device of the steering, in which the driver's handle function module (14) and / or the steering angle controller (24) are implemented in hardware and / or software.