Procedure for on board determination of dynamic safety margins of utility vehicles

0001The invention relates to a method according to the preamble of claim 1.

0002A method of this type is known from DE 42 00 997 C2. The adhesion value in the longitudinal direction and in the transverse direction is determined separately from measured vehicle values. From these values, the current driving state is detected by vectorial combination and the actual safety reserve is determined by comparison with a limit curve. The limit curve is stored in a computer and is affinely enlarged or reduced, depending on whether a major change in the coefficient of friction has been determined or not. By separately determining the adhesion values ​​in the longitudinal and transverse directions, it is also possible to make a statement about driving safety in mixed driving conditions, e.g. B. braking in the curve. The process is suitable for passenger cars, including all-wheel drive vehicles. The loading condition of the passenger car was not taken into account.

0003In other known methods, such as. B. described in DE 43 00 481 A1, ASR and ABS determine the tendency to spin or lock at least one wheel, the coefficient of friction between the wheel and the road in the longitudinal direction. The possible lateral acceleration is derived from this. The values ​​are usually not sufficiently precise, and often cannot be used, especially when cornering. The state of loading regarding mass and its center of gravity is not discussed.

0004Methods such as B. described in DE 40 10 507 C1 and EP 0 345 817 B1, which determine a speed difference between a driven and a non-driven wheel, use the approximately linear range of the slip characteristic. A prediction of the adhesion potential in the no longer linear limit range is therefore not possible or inaccurate. In addition, only the coefficient of friction in the circumferential direction of the wheel is determined in this method; coefficients of friction transverse to the circumferential direction are not taken into account.

0005The invention has for its object to provide a method of the type mentioned that detects the most accurate vehicle dynamic values ​​and other parameters so that the driver can be offered effective support through information about the current safety reserves of his vehicle.

0006The object is achieved by the features of claim 1.

0007In the method according to the invention, the mass of the load and its position must first be determined, since both are important prerequisites for the determination of safety reserves for commercial vehicles.

0008In commercial vehicles, lateral accelerations lead to pronounced roll movements. It is irrelevant whether these lateral accelerations from centrifugal accelerations from cornering or as a result of inclined lanes come from the proportion of gravity. In order to take advantage of this knowledge, it is necessary to know the roll stiffness for a particular vehicle. The roll stiffness is among others depending on the type and rigidity of the frame, the suspension, the number of axles and tires and the load. The roll stiffness is preferably determined on a circular test track, on which the corresponding commercial vehicle is driven at a certain circle radius at several speeds. This process is carried out with different loads from unloaded to full loading at different loading heights. As the roll angle, the relative roll angle between the vehicle frame and at least one axis, for. B. the jth axis. The lateral acceleration is measured. The family of curves of roll stiffness determined, which are valid for exactly this vehicle type, are stored in a computer and are available for further calculations. The determination of the loading state is preferably carried out at the start of a journey and is determined in the case of the commercial vehicle known in a vehicle-specific manner by determining the roll stiffness, for example when driving in a curve, and by comparing it with stored data.

0009The present frictional connection is understood to be the quotient between the maximum possible contact force F_Max and the riot F_e.g..

0010Knowledge of the behavior typical of a commercial vehicle is important for calculating the adhesion and the safety reserves in the linear and non-linear adhesion area of ​​the tires. So differs z. B. a three-axle vehicle with a steered axle of a two-axle by greater directional stability in the vehicle longitudinal direction and thereby when cornering through the need for a larger steering angle of the three-axle commercial vehicle.

0011If a vehicle is traveling through an arc in a stationary manner, the steering angle requirement is made up of the kinematic Ackermann steering angle and the dynamic correction steering angle: The Ackermann steering angle is a fixed, vehicle-specific steering angle for driving a circular arc with a fixed radius without lateral force, i.e. when Driving at a very low speed. The dynamic correction steering angle characterizes the control tendency of the vehicle with increasing lateral acceleration.

0012In the beginning, non-linear area, a smaller steering angle is required for oversteering vehicles and a larger steering angle for understeering vehicles to maintain the course. This behavior is described with the steering rigidity.

0013Based on these behaviors, the relative steering roll stiffness is used in the method according to the invention to determine the vehicle-specific relationship between the roll angle and the correction steering angle for a specific load, depending on the coefficient of friction between the wheel and the road. For this purpose, the relative roll angle and the correction steering angle are determined in driving tests with a specific load and with a specific roadway. These measurements are repeated with different loads and different road surfaces. The determined curves of the relative steering roll stiffness are also stored for the further calculations.

0014The adhesion map is approximated and initially applies to a specific load. For this, the adhesion map is three-dimensional with the axes, roll angle, correction steering angle and adhesion. In the following, the loading is added as a further parameter. The adhesion map is hereby vehicle-specific and stored in the on-board computer of the vehicle.

0015To determine the current adhesion value during operation, proceed as follows: First, at the start of a journey, e.g. B. caused by the driver or automatically determines the loading condition and pass on to the computer as known. For the ON-BOARD determination of the instantaneous adhesion value, the instantaneous adhesion value is directly calculated with the roll angle occurring, the correction steering angle occurring and the load as an input variable from the adhesion map. Z. B. the existing frictional connection between the tire and the road surface, this manifests itself - while maintaining the curve radius and driving speed - in an increase in the steering angle requirement with understeering vehicle. If the steering angle is maintained, the vehicle will make a further turn, ie the roll angle will decrease.

0016Since the swaying of a commercial vehicle, depending on the vehicle type and the load, takes place in the seconds range, the detection of the current force-locking value is also possible in this range. If the adhesion value changes very quickly, the roll angle of the vehicle cannot change so quickly. In such a driving state, the existing correction steering angle, whether corrected by the vehicle driver or not, and the roll angle do not reflect the correct behavior of the vehicle. In order to take this process into account and not to trigger false alarms, the specification of the change in the desired roll angle is corrected dynamically by applying a dynamic delay element to the correction steering angle that occurs, so that the desired, time-delayed and the real process change in the computational change Roll angle results. This enables the expected process to be adapted to the real process. A jump function of the correction steering angle is entered in order to set and possibly check the function later. The driver will not achieve this step function of the correction steering angle, but reflex movements of the driver to a suddenly different adhesion value can be very fast. The actual conditions are also taken into account on the part of the possible correction steering angle change. The degree of dynamic correction of the roll angle must be determined and saved for each vehicle type.

0017By knowing the instantaneous adhesion value determined, it is possible according to the invention to compare the instantaneous adhesion value with an experimentally determined adhesion value using further variable parameters, such as road inclination, incline / slope and driving condition, such as wheel speeds, vehicle longitudinal and lateral accelerations. to calculate and / or display the braking potential or the steerability of the vehicle depending on the road geometry. There is a risk of tipping if the current adhesion value is greater than the saved adhesion value.

0018This procedure applies to solo vehicles and towing vehicles for articulated and semi-trailers. With articulated lorries the articulation angle between the semitrailer and the tractor and with articulated trains the angle between the towing vehicle and the trailer is advantageously to be included.

0019An example of the implementation of the method is shown in the drawings. Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>a traction map,</dd><dt>Fig. 2</dt><dd>a roll stiffness map,</dd><dt>Fig. 3</dt><dd>a diagram of the steering rigidity of vehicles,</dd><dt>Fig. 4</dt><dd>a drawing to indicate roll angles,</dd><dt>Fig. 5</dt><dd>a map of the relative steering roll stiffness,</dd><dt>Fig. 6</dt><dd>a diagram about the regulation of the time structure roll angle,</dd><dt>Fig. 7</dt><dd>a picture of the calculation process and</dd><dt>Fig. 8</dt><dd>a picture of the control process of the ON-BOARD determination.</dd></dl>

0020An example of the method for the ON-BOARD determination of safety reserves of commercial vehicles according to the present invention is described with reference to FIGS. 1 to 9.

0021Fig. 1 shows a adhesion map for a certain loading condition, for. B. unloaded B0. The adhesion map describes the relationship between the input variables, correction steering angle δ_K, the relative roll angle Δϕ_j and the resulting Kratschlusswert µ in the form<maths id="math0001" num=""><math display="block"><mrow><msub><mrow><mtext>µ = f (δ</mtext></mrow><mrow><mtext>K</mtext></mrow></msub><msub><mrow><mtext>, Δϕ</mtext></mrow><mrow><mtext>j</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP0758601A2_D0001.tif" /></maths>    for B = const.

0022Curves 11, 12, 13 indicate driving conditions for constant correction steering angles, namely δ_K01> δ_K02 > δ_K03. The map itself is approximated from the map of the relative steering roll stiffness determined by measurements, FIG. 5, with the<maths id="math0002" num=""><math display="block"><mrow><msub><mrow><mtext>Relationship δ</mtext></mrow><mrow><mtext>K</mtext></mrow></msub><msub><mrow><mtext>= g (µ, Δϕ</mtext></mrow><mrow><mtext>j</mtext></mrow></msub><mtext>).</mtext></mrow></math><img file="EP0758601A2_D0002.tif" /></maths>

0023This connection is particularly feasible in terms of measurement technology, e.g. B. by measuring runs on a circular test track, which has annularly different pads known friction.

0024From Fig. 1 can be read z. B. that in the presence of a certain roll angle with increasing correction steering angle there is obviously a loss of adhesion. This means that in curve 11 a large correction steering angle δ_K01 with a small adhesion value µ (ice), with curve 12 an average correction steering angle δ_K02 with a medium adhesion value µ (gravel road), with curve 13 a small correction steering angle δ_K03, with a high adhesion value µ (dry asphalt). The family of curves does not necessarily have to go through the zero point, since there is a permanent roll deviation Δϕ₀ can adjust through one-sided loading. The limit value area to the right of limit line 14 is in the range from 5 ° to 7 ° (degrees) and is mainly dependent on the type of commercial vehicle. If the limit line 14 is exceeded on a level road, the vehicle slips at low adhesion values ​​µ, curve 11, at high adhesion values ​​µ, curve 13, the vehicle tilts.

0025Fig. 2 shows a roll stiffness map, from which the loading state, depending on the lateral acceleration and the relative roll angle Δϕj, emerges. The map is determined in driving tests on circular orbit journeys and applies to a vehicle type. Curve 21 describes a vehicle that is not loaded, curve 22 a partially laden vehicle and curve 23 a fully loaded vehicle. The load state, which is made up of the vehicle's own mass with its center of gravity and the additional payloads with its centers of gravity that are loaded on the vehicle, can also be used<maths id="math0003" num=""><math display="block"><mrow><msub><mrow><mtext>m</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext>H</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msup><mrow><mtext> </mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> + m</mtext></mrow><mrow><mtext>N</mtext></mrow></msub><msup><mrow><mtext> H</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> </mtext></mrow><mrow><mtext>N</mtext></mrow></msub><msub><mrow><mtext> = m</mtext></mrow><mrow><mtext>total</mtext></mrow></msub><msup><mrow><mtext> H</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> </mtext></mrow><mrow><mtext>res</mtext></mrow></msub><mtext>,</mtext></mrow></math><img file="EP0758601A2_D0003.tif" /></maths> e.g. B. for a partially loaded vehicle, which expresses a relationship between the total load m_total and a resulting center of gravity h_res is made. For a specific vehicle, the dead weight is m₀ and its center of gravity h_0, e.g. B. to the street, always the same. The expression m₀H₀² saved as known and unchanged. Additional loads and their focal points can be determined by comparison with stored data. Thus, preferably in a curve, the measured lateral acceleration a_y and the measured relative roll angle Δϕj is compared with the stored data. This results in the loading condition, which consists of the mass and center of gravity of the entire vehicle. The vehicle driver can determine the time of the measurement, this is preferably done automatically. The measurement duration is in the range of seconds and is automatically ended after the values ​​have been recorded.

0026Fig. 3 shows a diagram of the known steering rigidity of vehicles in a curved path. The straight line 31 shows the Ackermann steering angle δ_A, which is required to maintain a certain curved path. However, this only applies close to the speed 0. The curve 32 shows the actually required steering angle δ (grd) in the linear adhesion range. The distance 33 is the dynamic correction steering angle. Curves 35 and 36 show the driving behavior of a vehicle in the non-linear adhesion area, curve 35 being for an understeering vehicle and curve 36 for an oversteering vehicle. The wheel speed differences resulting from cornering can be used for the approximate determination of the current curve radius R and subsequently with the geometry data of the vehicle, such as track width and wheelbase, for determining the Ackermann steering angle δ_A be used.

0027Fig. 4 shows a drawing to indicate roll angles. The roll tendency of the body or the vehicle frame 43 with respect to the roadway 44 is the absolute roll angle ϕ, 42, and the roll inclination of the vehicle frame 43 with respect to a vehicle axis 45 is the relative roll angle Δϕj, 41, to the j-th vehicle axis 45.

00285 shows a map of the relative steering roll stiffness. For the approximation of the non-positive map, the values ​​of relative roll angle Δϕj and dynamic correction steering angle δ are preferably based on the relative steering roll stiffness_K, determined and saved depending on the vehicle weight and the adhesion value. The curve 52 relates, for example, to an empty commercial vehicle with a low adhesion value μ_L, curve 51 the same empty commercial vehicle with a high adhesion value µ_H. Curve 54 relates to the same commercial vehicle with a specific load B1 and the same low adhesion value μ_L, as in curve 52 and curve 53 relates to the same vehicle with the same load B1 and the same high adhesion value µ_H, as in curve 51. The map can be determined on a circular test track with several ring-shaped lanes of different road surfaces. The family of curves does not necessarily have to go through the zero point, it can also cross the abscissa by an offset Δϕo amount 55.

0029Fig. 6 shows the time structure of the roll angle ϕ (t). While the adhesion µ can change suddenly, e.g. B. by different road surfaces, the roll angle ϕ of the commercial vehicle can follow only with delay due to inertia. So that the reactions of the vehicle driver are assessed realistically, it is necessary to specify a real roll behavior of the vehicle in order to take into account the temporal structure of the roll angle ϕ (t). The delayed build-up of the roll angle ϕ (t) of the vehicle is described by curve 62, which settles in time to the stationary roll angle 63. The necessary change in the steering angle δ_Spr., Curve 61 is the programmed steering angle change as an input variable, which is delayed so that curve 62, structure of the roll angle ϕ (t) results. In addition to the realistic reaction by the driver, the input of curve 61 into the computer in this form also has the advantage that the input is uniform and the control behavior can be checked at any time.

00307 shows an image of the calculation process for calculating safety reserves. Vehicle-specific data 71, variable parameters 72, the driving state 73, criteria 74 of the road adhesion and the road geometry are taken into account. The braking potential 76, the steerability 77 and the safety 78 against the overturning of the commercial vehicle are determined from these values.

0031FIG. 8 shows a picture of the ON-BOARD determination of the adhesion µ and its evaluation. The input variables are initially the steering angle δ and the wheel speeds ω_i and the relative roll angle. The Ackermann steering angle δ becomes the wheel speed difference Δωi_A calculated according to 82, the correction steering angle δ with the absolute steering angle δ_K results. In order to compensate for the delayed build-up of the roll angle Δϕj due to inertia, a delay element 81 is required for the steering angle δ. The previously identified load BX or m_total forms a further input variable in the process block 83 for determining the current adhesion value μ, in accordance with 84. Knowing the current adhesion value μ, suitable evaluation strategies can subsequently be derived. In process block 85 z. B. the current adhesion value µ compared with the limit adhesion value µ *, or the current roll angle ϕ with the defined limit roll angle ϕ *. The evaluation itself is based on the relationships shown in FIG. 7. In particular, the results obtained can either be in the form of visible, audible or perceptible information as a driver warning, according to 86 as<img file="EP0758601A2_D0004.tif" />Open Loop "- or directly for further active intervention in the vehicle system according to 87 as <img file="EP0758601A2_D0004.tif" />Implement a closed loop solution.