GB2266957A

GB2266957A - Method of determining driving behaviour of a vehicle

Info

Publication number: GB2266957A
Application number: GB9308133A
Authority: GB
Inventors: Dieter Ammon
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1992-05-16
Filing date: 1993-04-20
Publication date: 1993-11-17
Anticipated expiration: 2013-04-20
Also published as: GB2266957B; GB9308133D0; DE4216301A1; DE4216301C2

Abstract

In a method for determining quantities which characterise the driving behaviour of a vehicle, signals which represent the steering angle ( delta ), the longitudinal speed of the vehicle (v) and transverse accelerations (aqv, aqh) at two points located one behind the other in the longitudinal direction of the vehicle, are fed to a computing device. Further quantities are derived in the computing device by the use of vehicle-specific quantities and of a vehicle model, and then at least yaw-angle velocity and preferably also sideslip angle is/are determined and outputted. <IMAGE>

Description

2266957 Method for.determining auantities which characterise driving

behaviour The invention relates to a method f or determining quantities which characterise the driving behaviour of a vehicle, with a computing device, to which are fed signals which represent measured quantities of the steering angle (6), of the longitudinal speed of the vehicle (v) and of two transverse accelerations (aclvr aqh) located (1v, 'h) one behind the other in the longitudinal direction of the vehicle.

A method of the relevant type, by which the Sagnac ef fect is used to determine the yaw-angle velocity, is already known. In this, monochromatic coherent light is split and is guided in opposite directions on a circular path by means of light-guide cables. As a result of a rotation (yawing movement) of the light-guide cables, a rotating reference system is thus obtained for the split light. Since the electromagnetic waves behave differently in this rotating reference system than in a stationary reference system in conformity with the relativistic transformation equations, the interference phenomena of the split light also change in dependence on the rotational acceleration (yaw- angle acceleration) and rotational speed (yaw-angle velocity). By evaluating these interference phenomena, conclusions can thus be drawn as to the corresponding quantities of rotational movement.

It could be considered a disadvantage of this method that a light source with light capable of interference first has to be provided. Moreover, with regard to vibrations, the arrangement of the light-guide cables must be mounted in such a way that the interferences can occur.

A linear single-track model of a vehicle is known, furthermore, and in this the height of the centre of gravity of the vehicle is ignored. Thus, in this approximation, the centre of gravity of the vehicle is shifted into the plane of the tread contact points of the wheels. Since rolling and 2 pitching movements are thus excluded, in this model the wheels of an axle can be combined to form one wheel in the middle of the axle. This model is described by way of example in German Book: Zomotor, Adam: Fahrwerktechnik, Fahrverhalten, [Chassis technology, driving behaviour], publisher J6rnsen Reimpell, WUrzburg: Vogel 1987, ISBN 38023-0774-7 on pages 99 to 116.

This illustration does not indicate how the yawangle velocity and the yawangle acceleration can be derived from measurable quantities.

A method for determining the sideslip angle by using the yaw-angle velocity as a measurement quantity is known from German Patent Specification 3,608,420. There, a sideslip angle of the vehicle is calculated by using a vehicle model and from the measurement quantities of the longitudinal speed of the vehicle, the steering-wheel angle, two transverse accelerations of the vehicle which are located one behind the other in the longitudinal direction of the vehicle, and the yaw-angle of velocity.

The present invention seeks to design a method for determining quantities which characterise the driving behaviour, in such a way that as high a measuring accuracy as possible, along with as low an outlay as possible in terms of the hardware required, can be achieved.

According to the present invention there is provided a method for determining quantities which characterise the driving behaviour of a vehicle, with a computing device, to which are fed signals which represent measured quantities of the steering angle (6), of the longitudinal speed of the vehicle (v) and of two transverse accelerations (a(IV1 aqh) located (1 v, 'h) one behind the other in the longitudinal direction of the vehicle, and in which computing device, as a result of these measured quantities, further quantities are derived by the use of vehicle-specific quantities and of a vehicle model, wherein at least the yaw-angle velocity (d)/dt) is determined and outputted in the computing device by means of the vehicle model by the use of the measured and 3 derived further quantities.

Preferably, the determination of the yaw-angle velocity (d4/dt) takes place independently of a particular driving state, and, furthermore, the sideslip angle (3) may be determined and outputted. Rolling movements of the vehicle may be taken into account in the vehicle model.

Preferably, the transverse acceleratIons (aqvr aq11) are measured by means of transverse- acce 1 eration sensors, the respective installation heights (hvi h h) of which are identical and correspond to the height (hs) of the centre of gravity. An adaptation of the vehicle-specific quantities may also take place, in which case, the adaptation may take place by means of a sliding average method. In a preferred embodiment, at least one further quantity of the quantities determined during the method is outputted.

Some equations, by means of which the quantities to be determined are represented in dependence on measurable quantities, are first to be derived. For this purpose, a table illustrating the meaning of the symbols used hereafter will be prepared first.

Symbol Meaning d#/dt First time derivation of a quantity #, which is one of the quantities contained in this table d2#/dt2 Second time derivation of a quantity # which is one of the quantities contained in this table a Longitudinal acceleration of the vehicle aq Transverse acceleration of the vehicle aqh Transverse acceleration of the vehicle, rear aqv Transverse acceleration of the vehicle, front ch Cornering stiffness, rear CV Cornering stiffness, front csh Transverse spring rigidity, rear csv Transverse spring rigidity, front 4 Symbol Meaning c X Torsion spring rigidity during rolling movement about longitudinal axis of vehicle h h Installation height of transverse- acceleration sensor, rear h p Rolling-pole height (distance between the point of fixed location and the ground during a rolling movement) hs Height of centre of gravity hv Installation height of transverse-acceleration sensor, front ix Moment of inertia about the longitudinal axis of the vehicle iz Moment of inertia about the vertical axis of the vehicle kx Rotational damping during a rolling movement along the longitudinal axis of the vehicle 1 Wheelbase 1h Distance between transverse-acceleration sensor, rear, and front axle 1V Distance between transverse-acceleration sensor, front, and front axle is Distance between centre of gravity and front axle Vehicle mass Sh Lateral force on the rear wheels sv Lateral force on the front wheels v Longitudinal speed of vehicle vq Transverse speed of vehicle ah Slip angle on rear axle av Slip angle on front axle 13 Sideslip angle Symbol Meaning 6 Wheel steering angle st Integration step size 53 Yaw angle 7 Roll angle The force balance in the transverse direction of the vehicle gives the equation:

maq = Svcos(s) + Sh The moment balance about the vertical axis of the vehicle gives the relation:

izd24/dt2 = 1 S S Vcos(S) - (1-1s)Sh (2).

Moreover, the dynamics of a rolling movement, modelled by the formulation of a differential equation of the second order, becomes:

ixd2r/dt2 + kxdr/dt + cxr = M(hs-h p)aq (3).

A modelling of the transverse-force build-up on the tyres is carried out according to the following equations:

dSv/dt v 1 - + -sv = -a v (4) csv CV COS(6) dSh/dt v - + _Sh = % (5) csh ch av = vsin(S) - lsd./dt - vq - (hs-h p)dr/dt (6) ah = (1-1s)dT5/dt - vq - (hs-h p)dT/dt (7).

These equations describing the transverse-force build-up have a high dependence on the longitudinal speed of the vehicle v.

The accelerations aq and a depend on the change in time in the amount of the respective speed and on the change in time in the direction of the respective speed. The following equations are thus obtained:

aq = dvq/dt + vd4/dt (8) 6 a = dv/dt - v q dl)/dt The steering angle 8, the longitudinal speed of the vehicle v and two transverse accelerations a qv and ac will now be used as measurement quantities. The two transverseacceleration sensors can each be described by the distance from the front axle and by the respective height. In view of the geometry, the following is obtained for these two acceleration sensors:

aqV = aq + (1 S-lv)d2)/dt2 + (hs-hv)d2T/dt2 (10) aqh = a q + (1 S-1h) d2q/dt2 + (hs-hh)d2r/dt2 (11).

Since the equations (10) and (11) relate to a system of two equations which are linearly independent in that 1 h is unequal to 1v, consequently, with a known or negligible rolling acceleration d2,r/dt2, the yaw-angle acceleration d2,15/dt2 and the transverse acceleration of the vehicle can be determined. Combining the two equations (10) and (11) produces:

aq= - (is-1h)(aqv-(hs-hv)d2T/dt2)_(1s_lv)(aqh-(hs-hh)d27/dt2) (1 V-1h) (12) d2,1,/dt2= a qv - aqh + (h,-hh)d2T/dt2 (13).

(1 V-1h) Advantageously, when the transverse-acceleration sensors are mounted, provision can be made for ensuring that hvhhh P This does away with the rolling-acceleration terms, irrespective of the order of magnitude of the rolling acceleration, with the result that the evaluation is simplified considerably.

Alternatively to this, the rolling dynamics can be 7 obtained by means of a numerical evaluation, known per se, of the differential equatio n (3), for example by means of the Runge-Kutta method or by means of the explicit Euler method with the integration step size 6t:

d27./dt2 -kxdT/dt - cxT + m(hs-h p)aq ix (14) Tnew: = T + dr/dt6t; dT/dtnew:= dT/dt + d2T/dt28t (15).

The yaw-angle and transverse accelerations and the rolling quantities can thus be determined by using the equations (12), (13), (14) and (15) or by estimations of state by means of the equations (3), (10) and (11).

The lateral forces can be obtained from the force balance according to equation. (1) and from the moment balance according to equation (2):

Sv - (1-1s)maq + iz d2q)/dt2 (16) 1COS(S) Sh ismaq - izd2(I)/dt2 (17).

1 Differentiation of the two equations (16) and (17) thus produces:

(1-1,)mdaq/dt + izd(d2,1/dt2)/dt dSv/dt lcos(6) - - (18) sin(S) ((1-1s)maq + izd2q)/dt2) d6/dt lcos2(6) dSh/dt ismdaq/dt - Jzd211,/dt2 (19).

1 Equations (4), (5), (6) and (7) thus produce two linear equations, by means of which the quantities vq and d>/dt can be determined from known quantities.

8 dS v /dt v 1 S dI,/dt+v q CS + c S v) cos (6) +vsin (6) - (h s_h p)dr/dt (20) v v dSh/dt V -(1-1 S)d,/dt + v q ±S h) - (hs-h p)dT/dt (21).

CS h c h The equations (16), (17), (18) and (19) contain only quantities which are measured directly (6, v, agh, aqv) orp as described above, can be determined by means of the measured quantities. Time derivations of known quantities can be derived by quotient formation. The quantities vq and dE)/dt can thus be calculated at any time. The sideslip angle B is finally obtained:

B = arctan (vq/v) (22).

It was previously described how quantities which characterise the driving behaviour are determined-from known parameters relating to the vehicle. These parameters experience some fluctuations. The vehicle mass and the position of the centre of gravity vary as a result of different loads. The tyre-dependent quantities vary with the tyre temperature and with different road surfaces. The most important fluctuation occurs in the cornering stiffness. A method by which an adaptation of the cornering stiffness is possible will be presented below. An adaptation of the other parameters can then likewise take place. First of all, for this adaptation, it is necessary to find system equations which contain only known or derivable quantities and which are linearly independent as the equations used to determine the known or derived quantities. Suitable equations are obtained, for example, by differentiating the equations (20) and (21).

CV = Cv(t) = (Sv cos(S) dv/dt + v cos(&) dSv/dt + v SV sin(6) d6/dt) fv(t) (23) 9 S d! /dt2 -a q +vdl/dt+sin(6)dv/dt-vcos(6)d6/dt- f V(t) cos(6)d 2S v /dt2+sin(6)dS v /dtd6/dt)d2 t2 CS (h s-h p T/d v (24) c c dv/dt + vdSh/dt) (25) h h(t) = (Sh fh(t) - = (1-1) d2 1,/dt2 -6 +vdI,/dt- d. S h /dt2 (h -h) d2 r/dt2 f h(t) S q CS h p (26) The yaw-angle velocity is obtained from the equations (20) and (21) by the elimination of v q The lateral f orces are calculated by means of the equations (16), (17), (18) and (19) and corresponding difference quotients. Actual estimated values are thus obtained for the cornering stiffness at the front and at the rear respectively. An updating of the values of the cornering stiffness which are used in the further calculations can be carried out by L2 approximation with sliding time averaging. The parameters to be used in the following calculations are designated by cv,act and ch,act The previous parameters are designated by cv and by ch. The actual estimated values are designated by Cv(t) and by Ch(t).

Cv,act (1-r)cv + rcv(t) (27) ch,act (1-r)ch + rCh(t) (28).

In these, r is a factor having a value of between 0 and 1. The larger r is, the more the actual estimated values are taken into account. At a small value of r, a slow adaptation takes place. If the adaptation is to take place, for example, at a critical frequency 2G, then r=nGSt is true.

An embodiment of the invention is illustrated diagrammatically in the drawing and is described in more detail below.

Representations showing the quantities according to the above table on a vehicle are to be taken from Figs. 1 and 2. Fig. 3 shows a possible flow of the method according to the invention. A f irst step 301 determines the values, on the basis of which the quantities characterising the driving behaviour are determined. These values afe the steering angle 6, the longitudinal speed of the vehicle v and the two transverse accelerations aqv and aqh. The steering angle is preferably measured directly, and the longitudinal speed of the vehicle can be determined, for example, from the signals of revolution sensors. The two transverse accelerations are preferably measured directly by means of suitably mounted transverse-acceleration sensors. If appropriate, it is also possible to measure the yaw-angle velocity directly. However, this is not absolutely necessary, since the yawangle velocity can also be determined from the said measurement quantities, for example by means of the method described. In the second step 302, the transverse acceleration aq and the yaw-angle acceleration d2)/dt2 are determined from these quantities, for example by means of the equations (12) and (13). Then, in a step 303, the roll angle r with its time derivations is determined, for example by means of the equations (14) and (15). The higher derivations of the state quantities, which are also required below, are then formed by means of difference quotients. The lateral forces and their derivations are then obtained in a step 304 by means of the equations (16), (17), (18) and (19). Then, in a step 305, the sideslip angle and the yawangle velocity, if this quantity has not already been measured directly, are obtained. by means of the equations (20), (21) and (22).

Furthermore, it can be seen from Fig. 4 that an adaptation of the parameters can take place. For this purpose, in a step 401 higher derivations of the lateral forces are first determined by means of difference quotients. Actual estimated values of the parameters are then determined in a step 402 by means of the equations (23), (24), (25) and (26). Then, in a step 403, values of the parameters which, in the calculations which then follow, are used to determine quantities characterising the driving behaviour are determined by means of the equations (27) and (28).

Fig. 5 shows a computing device 501, to which the said quantities are fed, according to the step 301 shown in Figure 3, as input signals 502, 503, 504, 505. After the corresponding quantities have 'been determined in the computing device according to the flow diagram of Fig. 3 by means of the said equations, output signals 506, 507, 508 representing the specific quantities are outputted. These specific quantities can be the sideslip angle, the yaw-angle velocity and/or a further quantity which was determined during the flow of the method. Furthermore, an adaptation of the parameters, by means of which the vehicle model is described, takes place according to the flow diagram of Fig. 4.

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Claims

Claims

A method for determining quantities which characterise the driving behaviour of a vehicle, with a computing device, to which are fed signals which represent measured quantities of the steering angle (6), of the longitudinal speed of the vehicle (v) and of two transverse accelerations (aqv, aqh) located (1v, 'h) one behind the other in the longitudinal direction of the vehicle, and in which computing device, as a result of these measured quantities, further quantities are derived by the use of vehicle-specific quantities and of a vehicle model, wherein at least the yaw-angle velocity (dg/dt) is determined and outputted in the computing device by means of the vehicle model by the use of the measured and derived further quantities.
2. A method according to Claim 1, wherein the determination of the yawangle velocity (dcl/dt) takes place independently of a particular driving state.
3. A method according to Claim 1, wherein, furthermore, the sideslip angle (8) is determined and outputted.
4. A method according to Claim 1, wherein rolling movements of the vehicle are taken into account in the vehicle model.
5. A method according to Claim 1, wherein the transverse accelerations (aqv, aqh) are measured by means of transverse- acceleration sensors, the respective installation heights (hv, hh) of which are identical and correspond to the height (hs) of the centre of gravity.
6. A method according to any one of Claims 1 to 5, wherein an adaptation of the vehicle-specific quantities takes place.

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7. A method according to Claim 6, wherein the adaptation takes place by means of a sliding average method.
8. A method according to any one of Claims 1 to 5, wherein at least one further quantity of the quantities determined during the method is outputted.
9. A method for determining quantities which characterise the driving behaviour of a vehicle, substantially as described herein with reference to and as illustrated in the accompanying drawings.