GB2453024A

GB2453024A - A method for reducing the risk of tilting in vehicles

Info

Publication number: GB2453024A
Application number: GB0816078A
Authority: GB
Inventors: Manfred Gerdes; Frank Niewels; Sylvia Futterer; Peter Ziegler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2007-09-24
Filing date: 2008-09-03
Publication date: 2009-03-25
Anticipated expiration: 2028-09-03
Also published as: GB0816078D0; GB2453024B

Abstract

At least one state variable which characterises the transverse dynamics of the vehicle is established, on which variable a vehicle-stabilising intervention in the steering system and the brake system is based. A driver 1 determines a steering angle Ww and a brake pressure pf. A multivariable control is carried out by two control circuits. The first control circuit is based on control of the yaw rate C and the second control circuit is based on control of the lateral acceleration a<WC 1>y. Both the steering system and the brake system can be adjusted via the first and the second control circuit.

Description

Description Title

Method for reducing the risk of tilting in vehicles The invention relates to a method for reducing the risk of tilting in vehicles according to the preamble of Claim 1.

Prior art

DE 199 18 597 Al describes a method of this kind in which a tilting coefficient which represents the risk of tilting and is based on the ratio of the height of the centre of gravity to the track width of the vehicle is continuously calculated. The lateral acceleration and the roll angle are included in the calculation of the tilting coefficient. If the actual tilting coefficient exceeds a limit value, a steering intervention for stabilising the vehicle is automatically carried out. A brake pressure control can additionally be activated if a critical value is exceeded, so that active intervention in the longitudinal dynamics of the motor vehicle also takes place by activating the brake.

However DE 199 18 597 Al contains no details as to how the braking action is carried out with simultaneous steering intervention.

Disclosure of the invention

The object of the invention is to present a method for reducing the risk of tilting in vehicles which is to be carried out with simple measures and with which improved vehicle stabilisation can be achieved. Higher lateral acceleration values should advantageously be achieved without putting the vehicle stability at risk.

This object is achieved according to the invention with the features of Claim 1. The subclaims present expedient developments.

In order to reduce the risk of tilting in vehicles, in the method according to the invention at least one state variable which characterises the transverse dynamics of the vehicle is established, on which variable a vehicle-stabilising intervention in the steering system and in the brake system is based. The intervention for stabilising the vehicle is carried out via a multivariable control in which two control circuits are superimposed. The first control circuit is based on control of the yaw rate or of a state variable corresponding with the yaw rate and the second control circuit is based on control of the lateral acceleration or of a state variable corresponding with this. A further basic feature of the invention is that both the steering system and the brake system can be adjusted via the first and also the second control circuit.

The interventions which are carried out with this method result in the best possible driving safety with optimised travelling comfort and minimal impairment of the driving performance. Since, according to the invention, both the yaw rate and the lateral acceleration are taken as a basis in the two superimposed control circuits, oscillation of the control circuits with susceptibility to instability is prevented. The lateral acceleration control behaviour in each driving condition is stabilised via the multivariable control with the Concurrent variables yaw rate and lateral acceleration. Since, with the presented control, the vehicle avoids extreme slip angles, in the case of which the lateral forces of the tyres are greatly reduced, higher lateral acceleration values can be achieved without putting the vehicle stability at risk.

Steering angles inadvertently covered by the driver can in particular be neutralised or at least reduced with the interventions in the steering system and the brake system, while both optimal driving safety and optimal travelling comfort, which is synonymous with minimal interventions in the vehicle behaviour, can be achieved as the target function. If an active steering system with the possibility of predetermining a superimposition steering angle is present, it is possible, via the multjvarjable control, to undertake steering interventions in the active steering system which are optionally assisted by additional stabilising braking interventions. The active steering system can be designed as a front-axle steering system and/or as a rear-axle steering system.

As the braking interventions have a considerable influence on the travelling comfort, it may be of advantage primarily to carry out an improvement in directional stability via the steering interventions and to undertake the braking interventions only as an assisting measure if sufficient stabilisation cannot be achieved via the steering alone. In this way a hierarchy in the action on the steering and brake system is produced such that the steering system is acted upon permanently and the brake system only as required while the method is carried out, with the action on the brake system being decided upon in particular on the basis of a criterion which characterises the stability of the vehicle, for example of the slip angle. The brake system is acted upon if necessary for reasons of stability, otherwise the brake system remains uninfluenced.

The division of the control into a first control circuit which relates to the yaw rate and a second control circuit which relates to the lateral acceleration has the further advantage of enabling an additional, considerable gain in stability being achieved via the yaw rate control circuit on the basis of the quicker intervention. Moreover, there are additional degrees of freedom via which, given appropriate parametrisation of the controllers, the agility of the vehicle can also be increased in addition to the improved directional stability. The driving performance can be adapted to different requirements with regard to driving safety, travelling comfort and driving agility.

Generally speaking, the method can be applied to vehicles with any type of steering system. An actively adjustable steering system with the possibility of predetermining a superimposition steering angle permits steering interventions which have a particularly marked effect on the stability of the vehicle. However it is in principle also conceivable to use a steering system which is formed, for example, as electric power steering (EPS) and does not provide a superimposition steering angle for the method according to the invention. In this case the degree of torque assistance with which the steering system increases or reduces the steering torque exerted by the driver is influenced.

As the intervention according to the method for preventing the vehicle from tilting over has maximum priority, other interventions of other control systems which are implemented in the vehicle and likewise act on the steering system, the brake system and/or other active actuating devices in the vehicle are suppressed during the action on the steering system and optionally also the brake system in order to prevent a negative influence on the stabilising process. In the case of an active steering system, the parametrisatjon of the variable steering ratio is advantageously frozen during the stabilisation intervention. In the case of active steering systems, when the stabilisation method according to the invention commences the superimposition steering angles which are actually predetermined by other steering systems are again reset to neutral values and only the superimposition steering angles resulting on account of the execution of the method according to the invention are allowed.

After the end of the method the interventions of other control systems can be allowed again.

In a preferred design the two control Circuits of the multjvarj.able control are based on a common desired value command variable. This is a lateral acceleration limit value which is predetermined as the desired value for the control circuit relating to the lateral acceleration and from which a corresponding desired yaw rate value is established via a kinematic connection. This is obtained, for example, by dividing the yaw acceleration limit value by the vehicle speed. The lateral acceleration limit value is assumed for a stable and stationary circular trip, for example. This procedure prevents oscillation of each control circuit and therefore improves stability.

According to a further advantageous design, the state variables, established by a sensor system, of an electronic stability program (ESP) implemented in the vehicle are used. The actual yaw rate and the actual lateral acceleration are possibilities in this case. The data which are available in the ESP can be taken as a basis for the initial condition, in which case an inquiry is made as to whether there is a risk of the vehicle tilting over, which is a precondition for the start of the method according to the invention. This avoids the necessity of providing additional hardware components; it is instead sufficient to use existing hardware components which are integrated in the vehicle.

Provided that an active chassis with an adjustable actuator is present in the vehicle, this can also be used to carry out the method.

Further advantages and expedient designs can be found in the further claims, the description of the figures and the drawings, in which: Fig. 1 is a block diagram representing the controller architecture for carrying out the method, Fig. 2 is a block diagram which illustrates the control algorithm, Fig. 3 is a further block diagram with a representation of the condition for carrying out and for discontinuing the method for reducing the risk of tilting.

Fig. 1 represents the controller architecture for carrying out the multicircujt control method with a first control circuit which influences the yaw rate and a second control circuit which influences the lateral acceleration. Block 1 symbolises the driver, who predetermines a steering angle oF and a brake pressure PF. Superimposition values O for the steering angle and p for the brake pressure, which are effective in the vehicle symbolised in block 2, are in each case superimposed on the values predetermined by the driver. An actively adjustable steering system which enables a superimposition steering angle to be produced is a prerequisite. If this is not provided in the vehicle, the steering torque can also be influenced via the control instead of a superimposition steering angle.

Following the activation of the actuators in the steering system and in the brake system and optionally also of an actuator to be associated with an active chassis, the actual values of the yaw rate,l' and of the lateral acceleration a are available for further control circuits.

These actual values are in addition fed back in a closed circuit in the multivariable control in question for reducing the risk of the vehicle tilting. For this purpose desired values established in a block 3, which is a component part of the regulating or control device in which the method proceeds, are subtracted from the actual values of the yaw rate J' and the lateral acceleration ay, which are available at the output of the block 2. The control deviation for the yaw rate and for the lateral acceleration are obtained as a result, these being fed to a controller 4 which is likewise a component part of the regulating or control device. Actuating signals are generated via the controller 4 and a block 5, which is connected downstream of the controller and serves as a coordination unit, which signals are supplied to the actuators 6 and 7 of the steering system and of the brake system and optionally also of the active chassis.

Superimposition values and p are generated in these actuators and, as already described above, superimposed on the corresponding values and p predetermined by the driver.

The control algorithm for carrying out the multivariable control is represented schematically in Fig. 2. A coefficient calculation is carried out in a block 8 as a function of supplied actual values for the vehicle speed V, the lateral acceleration a, the yaw rate and optionally further vehicle state variables. These coefficients are subsequently delivered to the control algorithm for the lateral acceleration control (block 10) and the yaw rate control (block 11), in which the adjustment variables are established with regard to the control deviations and, these variables being supplied to the subsequent coordination block 12 for distributing the control interventions between the steering system and the brake system. The actual values predetermined by the driver are additionally fed to this coordination block 12 via the block 9.

On the output side the signals of the coordination block 12 are firstly converted in a subsequent block 13 and then supplied as superimposition values and Ap to the steering system or the brake system. For example, a further superimposition value x is also present at the output of the block 13, which value is to be supplied, for example, to an active chassis.

A simple block diagram with a block 14 which symbolises the condition for carrying out and discontinuing the method is represented in Fig. 3. A decision is taken, as a function of the slip angle o at the wheels of the front axle and ar at the wheels of the rear axle, as to whether the vehicle is in the stable or in the unstable state or one which approaches the unstable state. Depending on the value of the slip angles Qf, r the method for the stabilising multivariable control is either started or discontinued.

The conditions can also be formulated so that different systems in the vehicle are activated or remain uninfluenced in a hierarchically classified manner, with, for example, only the steering system being firstly acted upon when there is an increased risk of tilting and the brake system also being acted upon in addition only if the risk of tilting increases further.

Claims

Claims 1. Method for reducing the risk of tilting in vehicles, in which at least one state variable which characterises the transverse dynamics of the vehicle is established, on which variable a vehicle-stabilising intervention in the steering system and in the brake system is based, characterised in that, in order to stabilise the vehicle, a multivariable control is carried out in which two control circuits are superimposed, of which the first control circuit is based on control of the yaw rate () or of a corresponding state variable and the second control circuit is based on control of the lateral acceleration (ay) or of a corresponding state variable, and that both the steering system and the brake system can be adlusted via the first and the second control circuit.
2. Method according to Claim 1, characterised in that the two control circuits are based on a common desired value command variable.
3. Method according to Claim 2, characterised in that a lateral acceleration limit value is predetermined as the desired value for the lateral acceleration control circuit, and a desired yaw rate value for the yaw rate control circuit is established from the desired lateral acceleration value.
4. Method according to any one of Claims 1 to 3, characterised in that the state variables, established by a sensor system, of an electronic stability program (ESP) implemented in the vehicle are used, in particular the yaw rate (v') and the lateral acceleration (ay).
5. Method according to any one of Claims 1 to 4, characterised in that the inquiry as to whether there is a risk of the vehicle tilting over is carried out with the data which are available in the electronic stability program (ESP).
6. Method according to any one of Claims 1 to 5, characterised in that the steering system is acted upon permanently and the brake system as required while the method is carried out.
7. Method according to Claim 6, characterised in that a decision is taken on the basis of a criterion which characterises the stability of the vehicle, in particular of the slip angle (ar, Cr), as to whether the brake system is acted upon or remains uninfluenced.
8. Method according to any one of Claims 1 to 7, characterised in that a chassis actuator is acted upon if required.
9. Method according to any one of Claims 1 to 8, characterised in that an actively adjustable steering (AFS) is acted upon, with which system an additional steering angle () which is superimposed on the steering angle (CF) predetermined by the driver can be adjusted.
10. Method according to any one of Claims I to 9, characterised in that additional interventions of other control systems in the steering system are suppressed during the action on the steering system.
11. Method according to any one of Claims 1 to 10, characterised in that a steering system which can be electrically actuated (EPS) and with which an assisting torque can be generated is acted upon.
12. Regulating or control device for carrying out the method according to any one of Claimsitoll.
13. Vehicle with a regulating or control device according to Claim 12, a steering system and a brake system.
14. Vehicle according to Claim 13, with an actively adjustable chassis system.
15. Method for reducing the risk of tilting in vehicles, substantially as hereinbefore described, with reference to the accompanying drawings.
16. Regulating or control device substantially as hereinbefore described, with reference to the accompanying drawings.
17. Vehicle substantially as hereinbefore described, with reference to the accompanying drawings.