DE102004056108A1 - Estimation method for the center of gravity of a vehicle for use with a vehicle ABS system, in which it is determined from longitudinal forces acting on the wheels, vehicle longitudinal acceleration, and wheel separation - Google Patents

Abstract

Method for approximate determination of the center of gravity of a motor vehicle, especially for use in a vehicle ABS system. According to the method the center of gravity in the longitudinal direction of the vehicle is estimated from the road gradient, the longitudinal forces acting on the wheels, the vehicle's longitudinal acceleration, and the wheel separation.

Description

The The invention relates to a method for the approximate determination of Center of gravity of a vehicle with respect to the longitudinal direction of the vehicle in particular for use in an anti-lock system of the vehicle.

In Modern control and safety systems for motor vehicles may be in addition to other information also the evaluation of the gravity of the Vehicle, usually related to the vehicle longitudinal direction, be significant. That is how it can be in electronic stability systems, for example during a braking process, the knowledge of the current vehicle center of gravity Benefits for have the control intervention. In particular, the knowledge about the current focus during braking with an anti-blockage system (ABS) relevant because the vehicle's center of gravity affects the control quality of the ABS can have. For example, the least possible braking distance be achieved. The center of gravity of the vehicle is used as a parameter for the Dosing of the braking force used.

For the investigation This center of gravity usually has a high technical complexity operate. So far only systems are known, in addition to be known in the vehicle system components of a more extensive require apparatus technical effort. All other preliminary investigations have proven to be too inaccurate or proved too slow.

Of the The invention is therefore based on the object of specifying a method with the in a comparatively simple way with little additional Effort the center of gravity in the longitudinal direction a vehicle can be determined comparatively accurate.

These The object is achieved according to the invention by to an approximation Determining the center of gravity of a vehicle in the longitudinal direction from the longitudinal forces of Bikes, the pitch angle of the road, the longitudinal acceleration of the vehicle and the wheelbase an estimate of the center of gravity of the vehicle longitudinal is determined.

The Invention is based on the consideration from that with the usual in a vehicle and in particular with those in the safety systems existing measured variables themselves the center of gravity and the change of the center of gravity of the vehicle are sufficient estimate exactly leaves. The invention thus assumes that no additional device technology Effort must be operated, as by a corresponding Combination of the mentioned variables estimated value for the Determining the center of gravity of a vehicle.

To leads in particular the fact that between the wheel contact forces, from which the center of gravity of the vehicle, and the longitudinal forces of Wheels of the Motor vehicle is an analogy. The wheels act on the Longitudinal forces are again reconstructable. Furthermore, in case of a delay process with the help of an anti-lock system assume that the coefficients of friction of all wheels are approximately identical, so the ratio the wheel-up force of the sum of the front to the rear wheels analog ratio the longitudinal force the wheels equivalent.

advantageously, the estimated value settles for the Center of gravity therefore composed of two summands. The first addendum is made up of half the wheelbase multiplied by a longitudinal force-dependent coefficient the wheels together. The second addend advantageously corresponds to that of the longitudinal acceleration and the slope angle of the road dependent height of the vehicle's center of gravity. Of the Longitudinal force-dependent coefficient expires expediently from the quotient of the difference of the longitudinal force of the front and rear wheels and the sum of the longitudinal force all wheels together. This corresponds to a shift of the center of gravity of the vehicle in the longitudinal direction the percentage longitudinal force shift in the vehicle longitudinal direction. Multiply this coefficient by half the wheelbase receives you get a distance-representing summand of the estimate. In this way it is considered that the center of gravity in a motor vehicle usually not exactly in the middle of the wheels is because the vehicle's center of gravity by the comparatively high weight of the engine moves accordingly.

In order to include the longitudinal acceleration of the vehicle in the determination of the estimated value, the height of the vehicle heavy point is preferably multiplied by the quotient of the longitudinal acceleration of the vehicle and the gravitational acceleration and with the reciprocal of the cosine of the road gradient angle to determine the second summand. Thus, the slope angle of the road flows into the Be bill. The reciprocal of the cosine of the road gradient angle, the height of the vehicle is converted into a running in the longitudinal direction of the vehicle distance component. The ratio of vehicle longitudinal acceleration to gravitational acceleration corresponds to the proportion of the acceleration of the vehicle, which acts in the direction of the longitudinal movement of the vehicle's center of gravity.

Around from the estimated values one for more reliable applications estimated Center of gravity of the vehicle to determine the no extreme values and whose course is comparatively smoothed, become a number of estimates expediently filtered. As a result, a continuous signal can be obtained which has no widely spaced measured values. measured Extreme values of the vehicle's center of gravity can thus be filtered out. For one Such filtering are various calculation methods such as an averaging or otherwise structured smoothing of the Measurements conceivable.

For a simple and good smoothing the estimates for determining the center of gravity is advantageously a moving average calculated from a number of estimates. This moving average can also be an average of the determined estimates be.

The particular advantages of the invention are that the values required to determine the center of gravity of the vehicle On the one hand are known and all other values with the help of in the Vehicle contained systems, in particular the security systems like ABS, are measurable. From these values can be with the described Calculation rule an estimate for the Center of gravity in the longitudinal direction of the vehicle. The calculation method described therefore provides a very simple method to estimate the location of the vehicle center of gravity in the longitudinal direction to calculate. Furthermore can the changeable Values like the longitudinal acceleration of the vehicle or the longitudinal force the wheels recorded very fast and with a high temporal frequency so that this also has a high dynamic in determining the Center of gravity allows.

One embodiment The invention will be explained in more detail with reference to two graphs. Show:

1 : the braking operation of a vehicle, wherein the speed of the vehicle and the speed of a wheel of the motor vehicle are shown as a function of time, and

2 : the braking action of a vehicle, wherein the center of gravity of the motor vehicle, an estimate of the center of gravity and the expected estimate of the center of gravity are respectively shown in the longitudinal direction of the vehicle as a function of time.

Of the attached below Reference numerals are the explanations to take to the formulas.

In 1 shows the braking of a motor vehicle from a speed of 100 km / h, the speed of the motor vehicle and the speed of a wheel of the motor vehicle are shown as a function of time. In order to prevent locking of the wheels when braking, the motor vehicle is equipped with an anti-lock braking system (ABS). The effect of the ABS can be out 1 remove. Thus it can be seen that the speed of the wheel is reduced by braking until it almost blocked. At this time, the brake is released, so that the wheel accelerates again. Then the brake is reset, so that the speed is reduced again. This results in the wave-shaped overall decreasing speed course of the wheel. The speed of the vehicle decreases, however, as well as from the 1 can be seen, approximately linear from. In addition, the deceleration time is comparatively low, because blocking of the wheels is prevented by the ABS. At the same time, this results in further advantages, since the vehicle remains steerable, for example because the wheels do not lock.

For the ABS and other safety systems of the motor vehicle is a knowledge the center of gravity in the longitudinal direction the vehicle advantageous because this value as a parameter in safety systems as the ABS come in. Therefore, this situation will be over estimated in the Motor vehicle determined.

näherungsweise berechnen.In principle, the position of the vehicle's center of gravity can be determined via the contact forces. For the front left wheel, this uprising power can be

approximate.

For the others Wheels apply the corresponding calculation rules:

Of the Quotient of the Aufstandskraft of the front wheels and rear wheels is in consideration above equations:

Around the rioting forces replaced by sizes to be able to which are measurable, becomes an analogy between the insurgents and the longitudinal forces of Wheels formed. This is calculated to

at An assumed deceleration with an anti-lock braking system may be approximate assume that the resulting coefficients of friction are identical for all wheels are. It follows:

Do you add the the latter two equations together follows from it

If now I _H and 1 / I _{V replaced} with the wheelbase I _ges and x results for the center of gravity in x direction of the motor vehicle depending on the sampling time k:

Out 2 the course of this estimated value x can be recognized during ABS deceleration. To smooth this course, the mean of these values is formed. As is also apparent 2 can be detected, corresponds to this average x _{KFZ, est,} which represents the expected position of the center of gravity, comparatively well the actual position of the center of gravity in the x-direction x _{motor vehicle} .

F

force at the wheel

I _V

distance Front axle to vehicle center of gravity

I _H

distance Rear axle to vehicle center of gravity

I _sat

wheelbase,

a

longitudinal acceleration of the vehicle

b

gauge

G

acceleration due to gravity,

H

Height of the center of gravity of the vehicle

k

sampling

x ^ (k)

Estimated value for the center of gravity in

longitudinal direction of the motor vehicle

x _{car, est}

expected Position of the center of gravity in the longitudinal direction

of motor vehicle

x _car

location the center of gravity in the longitudinal direction of

motor vehicle

x

along the vehicle

y

crosswise to the vehicle

z

perpendicular to the vehicle

α _Str , α _driving

lead angle the roadway

μ

adhesion coefficient

HL

behind Left

MR

behind right

VL

ahead Left

VR

ahead right

Claims (7)

Method for determining approximately the center of gravity of a vehicle, in particular for use in an anti-lock braking system of the vehicle, in which the longitudinal acceleration of the wheels (F _x ), the pitch angle of the road (α), the longitudinal acceleration of the vehicle (a _x ) and the wheel spacing (I _tot ) an estimated value for the longitudinal center of gravity of the vehicle (x ^ (k)) is determined. Method according to Claim 1, in which the estimated value (x ^ (k)) is the sum of the half wheel distance (I _ges ) multiplied by a longitudinal force-dependent coefficient of the wheels and by the longitudinal acceleration (a _x ) and the gradient angle of the road (α) dependent height of the vehicle's center of gravity (h) is determined. Method according to one of claims 1 or 2, wherein the longitudinal force-dependent coefficient from the quotient of the difference of the longitudinal force of the front and rear wheels and the sum of the longitudinal force all wheels determined. Method according to one of Claims 1 to 3, in which the height of the vehicle center of gravity (h) is multiplied by the quotient of the longitudinal acceleration of the vehicle (a _x ) and the gravitational acceleration (g) and by the reciprocal of the cosine of the road gradient angle (α). Method according to one of Claims 1 to 4, in which the estimated value (x ^ (k)) at the sampling instant (k) of Claim 2 is calculated according to the following procedure:

F, the longitudinal force on the wheel, I _ges the wheelbase, adie acceleration of the vehicle, GThe acceleration of gravity, α _Str road pitch angle HThe height of the center of gravity of the vehicle, k to the sampling time and x ^ an estimate of the center of gravity of the vehicle is, and the indices HL rear left , HR rear right, VL front left, front right VR and xlängs represent the vehicle. Method according to one of claims 1 to 5, wherein the or each estimated value (x ^ (k)) is filtered / who the. Method according to one of claims 1 to 6, wherein the estimated center of gravity of the vehicle in the longitudinal direction (x _{KFZ, est} ) from the moving average of a number of estimated values (x ^ (k)) is calculated.