DE102006044425B4 - Method for rollover stabilization of motor vehicles - Google Patents

Abstract

Method for reducing the risk of a vehicle (1) tipping over by an automatic braking intervention on at least one wheel (2a-2d), the braking intervention being carried out on at least two wheels (2a-2d) arranged on different longitudinal sides of the vehicle (1), characterized in that characterized in that the braking intervention is carried out on a front wheel (2b) on the inside of the curve and on a rear wheel (2c) on the outside of the curve.

Description

State of the art

The invention relates to a method for reducing the risk of a vehicle tipping over according to the preamble of patent claim 1, and a corresponding device according to the preamble of patent claim 7.

Especially in vehicles with a high center of gravity and soft suspension, such as off-road vehicles, there is a risk of the vehicle tipping over at high cornering speeds or heavy steering manoeuvres. Various systems for rollover stabilization are known from the prior art, which are intended to prevent the vehicle from tipping over. The known systems usually use various sensors to analyze the risk of the vehicle tipping over and intervene in driving operation by means of the wheel brakes when a critical tipping situation has been identified. In the systems known from the prior art, the front wheel on the outside of the curve or the front and rear wheels on the outside of the curve are usually braked simultaneously. On the one hand, this reduces the driving speed, whereby the lateral acceleration decreases quadratically, but on the other hand, the braking intervention also leads to an additional yawing moment in the direction of the outside of the curve. Thus, the vehicle experiences an understeering momentum that causes the vehicle to spin out of the turn. This can cause the vehicle to quickly leave its lane and get into another critical situation.

A method according to the preamble of claim 1 is, for example, from the published application DE 10 2004 034 399 A1 known.

Disclosure of Invention

It is therefore the object of the present invention to provide a method for reducing the risk of a vehicle tipping over, which does not influence the direction of travel of the vehicle.

This object is achieved according to the invention by the features specified in patent claim 1 and in patent claim 7 . Further configurations of the invention are the subject matter of dependent claims.

An essential aspect of the invention consists in braking at least two wheels, which are arranged on different longitudinal sides of the vehicle, in the event of a rollover-critical driving state, and in doing so interpreting the braking forces on the wheels in such a way that the braking intervention overall is essentially yaw moment-neutral. This has the advantage that the driving speed and thus also the lateral acceleration of the vehicle can be reduced without influencing the yaw behavior of the vehicle at the same time.

According to the invention, the front wheel on the inside of the curve and the rear wheel on the outside of the curve are braked at the same time. When cornering, both the front wheel on the inside of the curve and the rear wheel on the outside of the curve have comparatively high contact forces, so that the automatic braking intervention can be implemented best on these wheels. The braking forces can therefore be selected to be relatively large. The vehicle speed and thus also the centrifugal force decrease rapidly as a result. When selecting the wheels to be braked, the rear wheel on the inside of the curve should be avoided in particular, as this is the first to lift off the ground in the event of high lateral acceleration.

The braking intervention on the selected wheels is preferably controlled; in particular, the wheel brake slip is regulated to a desired value. The target brake slip for the individual wheels is preferably calculated using an algorithm. The target brake slip values for the front wheel on the inside of the curve and the rear wheel on the outside of the curve result from the following calculation, for example: $${\text{f}}_{\text{B}}=\frac{\mathrm{<figure-callout\; id="2"\; label="\lambda \; \lambda "\; filenames="DE102006044425B4\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}{\sqrt{{\mathrm{\lambda }}^{}}}\cdot {\mathrm{\mu }}_{\text{res}}\cdot {\text{f}}_{\text{N}},{\text{f}}_{\text{S}}=\frac{\mathrm{a}}{\sqrt{{\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102006044425B4\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}^2+{\mathrm{a}}^2}}\cdot {\mathrm{\mu }}_{\text{res}}\cdot {\text{f}}_{\text{N}}$$

Here, F _B is the braking force and Fs is the lateral force, α is the slip angle, µ _res is the road surface friction coefficient and _FN is the vertical force on the respective wheel. In order for the braking interventions on both wheels to be yaw moment-neutral, the slip values for the front wheel on the inside of the curve λ _VR and the front wheel on the outside of the curve must be the same rear wheel λ _HL can be chosen so that the yaw moment does not change. The yaw moment balance is thus (ignoring the steering angle for the sake of simplicity): $$\begin{array}{c}-{\text{f}}_{\text{S,VR}}\left({\mathrm{a}}_{\text{VR}},{\mathrm{\lambda }}_{\text{VR}}=0\right)\cdot {\text{I}}_{\text{V}}+{\text{f}}_{\text{S,HL}}\left({\mathrm{a}}_{\text{HL}},{\mathrm{\lambda }}_{\text{HL}}=0\right)\cdot {\text{I}}_{\text{H}}=\\ -{\text{f}}_{\text{S,VR}}\left({\mathrm{a}}_{\text{VR}},{\mathrm{\lambda }}_{\text{VR}}\right)\cdot {\text{I}}_{\text{V}}+{\text{f}}_{\text{S,HL}}\left({\mathrm{a}}_{\text{HL}},{\mathrm{\lambda }}_{\text{HL}}\right)\cdot {\text{I}}_{\text{H}}-{\text{f}}_{\text{B, VR}}\left({\mathrm{a}}_{\text{VR}},{\mathrm{\lambda }}_{\text{VR}}\right)\cdot \frac{{\text{b}}_{\text{<figure-callout id="2" label="v" filenames="DE102006044425B4\_0005.png" state="{{state}}">v</figure-callout>}}}{2}+{\text{f}}_{\text{B,HL}}\left({\mathrm{a}}_{\text{HL}},{\mathrm{\lambda }}_{\text{HL}}\right)\cdot \frac{{\text{b}}_{\text{<figure-callout id="2" label="H" filenames="DE102006044425B4\_0005.png" state="{{state}}">H</figure-callout>}}}{2}\end{array}$$

The indices VR and HL designate the front wheel on the inside of the curve (here, front right) and the rear wheel on the outside of the curve (here, back left).

The wheel slip λ _VR and λ _HL can e.g. B. be calculated depending on a difference Δa _Y between the actual lateral acceleration and a maximum permissible lateral acceleration. In this case, Δa _Y is the excess transverse acceleration that needs to be compensated. For example, the following equation can be used for the desired change in lateral acceleration Δa _Y : $$\Delta {\text{a}}_{\text{Y}}=-\frac{1}{\text{m}}\cdot \left\{\left(1-\frac{{\mathrm{a}}_{\text{VR}}}{\sqrt{{\mathrm{\lambda }}_{\text{<figure-callout id="2" label="VR" filenames="DE102006044425B4\_0005.png" state="{{state}}">VR</figure-callout>}}^2+{\mathrm{a}}_{\text{VR}}^2}}\right)\cdot {\mathrm{\mu }}_{\text{res,VR}}\cdot {\text{f}}_{\text{N, VR}}+\left(1-\frac{{\mathrm{a}}_{\text{HL}}}{\sqrt{{\mathrm{\lambda }}_{\text{<figure-callout id="2" label="HL" filenames="DE102006044425B4\_0005.png" state="{{state}}">HL</figure-callout>}}^2+{\mathrm{a}}_{\text{HL}}^2}}\right)\cdot {\mathrm{\mu }}_{\text{res,HL}}\cdot {\text{f}}_{\text{N,HL}}\right\}$$

Equation (3) in conjunction with equation (2) and equation (4) form a system of equations consisting of two equations for two unknowns (λ _VR and λ _HL ), which can thus be calculated from the system of equations. The slip angle α, the road surface friction μ and the contact forces F _N are assumed to be known. Optionally, of course, characteristic curves for the setpoint slip or setpoint slip changes could also be stored, from which the respective value for the braked wheels could be read as a function of the desired transverse acceleration change Δa _Y .

wobei K_P, K_I und K_D die wählbaren P-, I- und D-Verstärkungsfaktoren sind.Instead of the desired reduction in lateral acceleration Δa _{Y ,} a PID control law could also be used, for example. In this case, the left-hand side of equation (4) would have to be replaced by: $${\text{K}}_{\text{P}}\cdot \Delta {\text{a}}_{\text{Y}}+{\text{K}}_{\text{D}}\cdot {\dot{\text{a}}}_{\text{Y}}+{\text{K}}_{\text{I}}\cdot {\displaystyle \int \Delta {\text{a}}_{\text{Y}}\cdot \text{German}}$$

where K _P , K _I and K _D are the selectable P, I and D gains.

character list

• 1 eine schematische Ansicht eines Fahrzeugs mit einem System zur Kippstabilisierung.

The invention is explained in more detail below by way of example with reference to the attached drawings. Show it:

• 1 a schematic view of a vehicle with a system for rollover stabilization.

Embodiments of the invention

1 shows a schematic view of a vehicle with a system for rollover stabilization, which intervenes in the driving operation in a critical driving situation by means of the wheel brakes 3a-3d. The system essentially comprises a control unit 4 with a rollover stabilization algorithm 5, which constantly monitors the current driving condition using sensors 6 with regard to a risk of rollover and intervenes in driving operation via the wheel brakes 3a-3d if certain limit values are exceeded.

The sensor system 6 preferably includes a lateral acceleration sensor and a steering wheel angle sensor. In addition, e.g. B. also be provided a roll rate sensor that measures the roll rate about a longitudinal axis of the vehicle. A risk of overturning can be recognized relatively well by evaluating the lateral acceleration and steering wheel angle signal and possibly also the roll rate signal. The algorithm 5 preferably defines an indicator (parameter) which is a measure of the risk of tipping. If this indicator, such as B. an effective lateral acceleration, a predetermined threshold value, an automatic braking intervention is activated on selected wheels 2a-2d of the vehicle.

In order to reduce the risk of the vehicle tipping over, the front wheel 2b on the inside of the curve and the rear wheel 2c on the outside of the curve are braked. In the example shown 1 the vehicle 1 drives a right turn, as can be seen from the position of the front wheels. The wheels 2b and 2c are therefore braked. The selection of precisely these wheels 2b, 2c is based in particular on the fact that comparatively high contact forces act on these wheels. Relatively high braking forces can thus be exerted on the wheels 2b, 2c, which brake the vehicle quickly and reduce the risk of tipping.

Algorithm 5 includes a slip controller that sets a predetermined target brake slip at selected wheels 2b, 2c. The setpoint brake slip to be set is calculated in such a way that overall a braking intervention is carried out that is neutral in terms of the yawing moment. Ie there is no additional yaw moment ΔM _z around the vertical axis of the vehicle.

The target braking slip values can be calculated, for example, from the equation system (2 to 4) described above.

Claims (7)

Method for reducing the risk of a vehicle (1) tipping over by an automatic braking intervention on at least one wheel (2a-2d), the braking intervention being carried out on at least two wheels (2a-2d) arranged on different longitudinal sides of the vehicle (1), characterized in that characterized in that the braking intervention is carried out on a front wheel (2b) on the inside of the curve and on a rear wheel (2c) on the outside of the curve. procedure after claim 1 , characterized in that the braking intervention is designed so that it is essentially yaw moment neutral. Method according to one of the preceding claims, characterized in that brake slip control is carried out. Method according to one of the preceding claims, characterized in that a setpoint brake slip (λ) is determined for the wheels (2a-2d) to be braked. Method according to one of the preceding claims, characterized in that the setpoint brake slip (λ) is calculated from a torque balance and from a specified change in transverse acceleration. Method according to one of the preceding claims, characterized in that the setpoint brake slip (λ) is read from a characteristic curve as a function of the transverse acceleration (Δa _Y ). Device for reducing the risk of tipping of a vehicle (1), comprising a control unit (4) in which a corresponding algorithm (5) is stored, which intervenes in driving operation by means of braking when a risk of tipping is detected, and a sensor system (6) for determining a risk of tipping over, the algorithm (5) carrying out a braking intervention on at least two wheels (2a-2d) arranged on different longitudinal sides of the vehicle (1) if a risk of tipping over has been detected, characterized in that the algorithm (5) carries out the braking intervention on one front wheel (2b) on the inside of the curve and a rear wheel (2c) on the outside of the curve.

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