DE19904216A1 - Procedure for determining changes of centre of gravity of vehicle with at least two axles and at least three wheels has vehicle driven in curve and state parameters corresponding with respective wheel load detected at least at two wheels. - Google Patents

Abstract

A procedure for determining changes of the centre of gravity of a vehicle with at least two axles and at least three wheels has the vehicle driven in a curve. During the travel in the curve, first state parameters corresponding with the respective wheel load are detected at least at two wheels. The detected first state parameters are compared with reference values representing the respective wheel load and from the deviations between them, a corresponding change of center of gravity is calculated. As first state parameters corresponding with the wheel load, the spring displacement which can be measured on the wheel suspension and/or the spring pressure and/or the damper pressure which can be measured on the shock absorber and/or the tyre inner pressure or the side deformation of the tyre are used.

Description

The invention relates to a method and a corresponding device for detecting changes in the Center of mass of at least a biaxial and at least three-wheel vehicle, such as Changes caused by local shifts in loads or by changing the total vehicle mass e.g. B. as a result of Vehicle load are conditional. In particular, the Invention on a method and an apparatus for preventive detection of the risk of tipping over Vehicle in which the mentioned changes in focus Find consideration and where the risk of tipping through a critical state variable correlating with the risk of tipping is represented.

In T. D. Gillespie "Fundamentals of Vehicle Dynamics", Society of Automotive Engineers, Inc., Warrendale 1992, Chapter 9, Pages 309-333, different models for Rollover accidents described. Starting with a quasi stationary model for a rigid vehicle over a quasi stationary model for a sprung vehicle up to dynamic models taking into account Wankeigen frequencies become conditions for existing tipping risks specified.  

While it is for trucks, trucks, buses, minibuses and Off-road vehicle due to high-lying focal points and / or narrow track width already at publication of the above Book was known that when cornering with large Roll motion there is a risk of tipping, it has only turned in more recently shown that there are also passenger cars can swing sideways until it tips over. Such Risk of tipping is caused by improper loading, for example extremely one-sided or on the vehicle roof, significantly increased, because the position of the center of gravity of the vehicle is up or is shifted to one side.

As shown in FIGS. 1a and 1b, in the static case, the considerations of the forces and moments apply to the stable balance of a vehicle.

FIG. 1a shows the distribution of the vehicle weight force _G F to the wheel contact forces F _{A_xx.} In Fig. 1b the lateral displacement y _s of the center of gravity S of the vehicle center shown. The moment set related to a wheel shows the influence of the center of gravity shift in static and dynamic cases.

If a disturbing force now occurs during driving, e.g. B. the centrifugal force when cornering or a wheel load fluctuation due to an uneven ground, the vehicle can ever according to the size of the interference in the unstable or unstable Condition.

With an electronic stability program (ESP), at for example, that developed and ver driven system, a system is already available to critical driving conditions by comparing the driver's  given course with the actual trajectory of the Recognize vehicle and through targeted brake intervention prevent. For this purpose, the wheels are available as information speeds, the lateral acceleration, the steering angle and the Yaw rate available. Reaches from this information certain driving condition a critical area, so by a wheel-selective braking intervention by the vehicle model of the ESP controller defined self-steering behavior of the vehicle maintained. This control process can only be done by everyone influence two-dimensional processes and state variables, d. H. Processes that are caused by lateral acceleration and turning around have the vehicle vertical axis (yaw) described.

Now the position of the center of gravity changes in longitudinal and / or Transverse direction of the vehicle, e.g. B. as a result of loading with ESP, taking into account the changed curve limit speeds automatically in that in the vehicle model specified self-steering behavior should be maintained. The focus shifts z. B. to the rear, so increased tendency to oversteer when cornering under Controlling designed basic vote by reducing the permissible curve speed counteracted.

A change in the center of gravity now leads to a change in the inclination behavior of the vehicle in the longitudinal and transverse directions. If a lateral acceleration acts on the vehicle, then the torque consideration applies according to FIG. 1b

F _c × h _s + F _{n_r} × b = F _G × (b / 2 + y _s ) (1)

where F _{c is} the centrifugal force due to the transverse acceleration a _transverse , F _G the gravity, m the vehicle mass, F _{n_r, l} the wheel contact force (wheel load) for the right and left wheel, h _s , y _s the height of the center of gravity, y _s the lateral distance of the center of gravity from the center of the vehicle, and b denote the track width. From this follows directly the relationship for the lateral acceleration a _transverse

a _quer = 1 / h _s × [g (b / 2 + y _s ) - F _{n_r} × b / m] (2)

The vehicle tilts when a critical lateral acceleration is exceeded, for which the following relationship applies

a _{quer, crit.} = (b / 2 + y _s ) / h _s × g (3)

The critical lateral acceleration therefore depends directly on the Location of the center of gravity.

Furthermore, in known vehicle motion control systems in which the vehicle stability, especially at Cornering, should be increased, that is, in particular a lateral tipping should be avoided as the risk of tipping Descriptive critical state variables in general the Vehicle lateral acceleration or the roll angle of the vehicle based on.

DE-A 197 46 889 describes a system for increasing the Side stability described when cornering, which with an inclination detection device. This Tilt detector either measures the height below differentiated between the right and left side of the vehicle, or the Lateral acceleration of the vehicle to the roll angle between  the vehicle horizontal and the road horizontal to capture. If the inclination detection device If the danger of tipping is recognized, a counteracting yaw moment is created generated by braking the front wheel on the outside of the curve.

However, as previously described, the allowable Lateral acceleration and the permissible roll angle are sensitive depending on the location of the vehicle's center of gravity, in particular the center of gravity. In those known in the prior art Generic methods and devices are driving focus, in particular changes of focus, in Not related to preventive overturn prediction sufficiently taken into account.

The present invention is therefore based on the object to provide a method and an apparatus which enable a risk of tipping over as early as possible to be able to work. The primary aim of the invention is the most preventive possible prediction of an impending To allow a vehicle to tip over.

This object is achieved in that during cornering on at least two wheels with the respective Wheel load corresponding first state variables are detected, that the detected first state variables with the respective Reference values representing cornering are compared be, and that from the differences between the detected first state variables and the reference values corresponding change in center of gravity is calculated.

The invention is based on the knowledge that the best suitable influencing variable with a preventive as possible Detection of the risk of a vehicle tipping over the location of the Vehicle center of gravity and thus the current  Center of gravity as a starting point for the invention proposed method and the device essential be taken as a basis.

The influencing variable provides an immediate indication of that There is a critical state of tipping. As preventive countermeasures come either active Control interventions, e.g. B. on the part of ESP, or a passive warning of the driver.

In contrast to the prior art, the invention proposed preventive approach the advantage that the Vehicle during a necessary corrective intervention remains manageable and driving comfort during of an active control intervention is still retained. On Another advantage of the invention over the prior art is that the possible intervention strategies on a recognized critical driving situation are almost arbitrary, not least because of the extremely predictive detection. Therefore, the present invention can be made without particular Expenses as an extension or improvement of a existing driving stability control, e.g. B. the electronic Realize stability program (ESP) of the applicant.

As the first state variable corresponding to the wheel load can be measured on the suspension suspension, the Spring pressure, the damper pressure that can be measured on the shock absorber Tire pressure, or the side deformation of the tire be taken as a basis.

The invention is described below with reference to a preferred one Embodiment with reference to the accompanying Drawings explained in more detail, with the same reference numerals designate the same elements. Show in detail  

Figure 1a is a schematic side view of a four-wheeled vehicle when driving through a curve.

Figure 1b is a schematic rear view of a four-wheeled vehicle also when passing through a right curve.

FIG. 2 shows a rear view corresponding to FIG. 1 of a vehicle in a left-hand curve to show the physical state variables for describing a tilted state;

Figure 3 on the basis of a flow chart a preferred operational sequence of the inventive method and apparatus.

Fig. 4 is a schematic representation of a preferred embodiment of the device according to the invention with a spring travel switch on a wheel and a characteristic curve illustrating the switching time of the spring travel switch.

The embodiment described below Modifications in an electronic stability control (ESP). In contrast to that used in the prior art two-dimensional model, is used in the present invention is based on a three-dimensional vehicle model in which in addition to the lateral acceleration and yaw, the nod and roll of the vehicle can be taken into account and hence the tendency to tilt as a value of the critical condition size comes into question. A fundamental adaptation of the Vehicle model taking into account the current Static center of gravity shows the success of the rule favor. But also a reaction only to the inclination  holding the vehicle already gives a clear Improve stability control.

The information required to determine the center of gravity and the vehicle inclination can preferably be obtained from the changes in travel. The center of gravity can be determined by measuring the static spring deflection for axles without level control or by measuring the pressure in the level control. With known spring stiffness C of the suspension suspension spring, the wheel contact force F _{_xx} ( Fig. 1a) can be determined from the known force F _{n_xx_o} in the construction position with spring travel S _{_xx_o} as follows:

F _{n_xx} = F _{n_xx_o} + K.ΔS

where ΔS is the measured change in travel directional sign (positive for deflection, negative for rebound).

A level control device compensates for deflection, so that ΔS = 0. The system pressure change Δp required for this compensation is proportional to the change in force, so the following applies

F _{n_xx} = F _{n_xx_o} + K.Δp

where k is the proportionality factor.

The roll angle is based on the different spring travel the left and right side of the vehicle and the Pitch angle accordingly via the spring travel at the front and rear.  

The center of gravity can then be calculated from the angle of inclination and the associated acceleration. The position of the center of gravity in the longitudinal and transverse directions (l _v , l _h , y _s ) is known from the static consideration. The height of the center of gravity can thus be derived from the previously described relationship with known lateral acceleration

h _s = ¹ / _aquer . [g ( ^b / ₂ + y _s ) - F _{n_r} . ^b / _m ]

or with known longitudinal acceleration

A center of gravity shifted laterally from the center of the vehicle can be differentiated by the directional Roll angle at a given lateral acceleration determine. Thus, for example, for a vehicle a level control on the rear axle four sensors to determine the travel and, in the case of a wheel-specific axle control, one or two sensors for Determination of the pressure in the level control device of the Rear axle required.

The flowchart shown in FIG. 3 illustrates an exemplary functional sequence of a modified ESP control in which - in accordance with the aforementioned simplified embodiment of the invention - a limit switch is used. The limit switch responds when a predefined suspension travel threshold value is exceeded in one or more of the vehicle wheels, that is to say in relation to the forces present when a predefined wheel load is exceeded. Since the mode of operation of the end position switch thus depends on the direction of cornering, it is first necessary to find out which one (preferably the wheel on the front axle) or which wheels are on the outside of the vehicle on the curve. Because only the wheels on the outside of the curve can respond at all in accordance with the curve inclination of the vehicle in the manner mentioned. The selection of the wheels on the outside of the curve can be done by means of vehicle dynamics sensors already available at the ESP, e.g. B. a steering angle sensor and / or a yaw rate sensor. In general, other sensors with which the direction of cornering can be determined can also be considered.

Now speak one or more of those on the outside of the curve the limit switch located on the vehicle, the Change in ESP driving already described in detail above test model made. In advance, however, it is required to receive the switch signals check or filter that such signals "Filtered out" where one or more Limit switches due to the nature of the road, e.g. B. due to bumps, but none Cornering was present and therefore there was no risk of tipping.

Taking into account other driving dynamics, for example, the steering angle and the vehicle speed, are now based on those already mentioned mathematical relationships a corresponding Change of center of gravity of the vehicle and from the changed Focus on a changed or corrected Boundary lateral acceleration calculated. Based on the corrected The ESP vehicle model is then used to limit the lateral acceleration change the way that the vehicle temporarily to "Understeer" and thus the changed Center of gravity conditions is better adapted.  

After the end of cornering, the limit switch in Normally no longer respond. The filtered accordingly Signal makes the temporary change in ESP driving undo the test model and thus represents the one before Restoration of the current state of the ESP.

In the aforementioned embodiment, the ESP vehicle model only temporarily d. H. modified while cornering. However, it can also be provided that from the above Signals of the limit switch to changed center of gravity due to permanent changes in the ESP Vehicle model is reacted. The above Comments apply in in this case analog.

On the basis of the knowledge of a changed center of gravity, the vehicle model present in an electronic stability program (ESP), for example that of the applicant, can be adapted to the changed center of gravity conditions. First of all, when adapting the ESP control, it is necessary to specify a critical state variable, for example a _limit lateral acceleration aq _limit , taking into account the current size and position of the vehicle's center of gravity. This limit acceleration can take the form of a parameter change within the vehicle model

Change = basic change + k × f (a _transverse - a _{transverse, border} ) (4)

be taken into account in the ESP regulation, where a _transverse denotes the current value of the vehicle lateral acceleration and a _{transverse, limit} the corresponding critical limit value. Furthermore, "K" is a proportional factor and f (x) is a function with predetermined upper and lower limits, the lower limit being that the change must not be less than zero. The functional relationship specified above can preferably be implemented as a P or PI controller, the second summand on the right-hand side of equation (4) either acting proportionally as a P controller, ie according to the relationship

k × [abs (a _transverse) - abs (a _{transverse, cross-)]} (5)

or acting proportionally-integrally as a PI controller, ie according to the following context

k × [abs (a _cross ) - abs (a _{cross, border} )] + k × integral [abs (a _cross ) - abs (a _{cross, border} )] (6)

is designed. Change to "understeer" can be done via the Lateral stiffness can be defined.

In the vehicle model from ESP (single track model)

mv (-) F _{lateral force in} front + F _{lateral force in} rear
Θ. = F _sv .l _v -F _sh .l _n

With

With

tire side stiffness C _sv , C _sh , front and rear are included.

You can now _understand this C _{sv, sh} as C _sv , C _sh for normal operation and C _1sv , C _1sh as a variable component.

C _sv = C _0sv + C _1vs
C _sh = C _0sh + C _1sh .

These C _1sv , C _1sh can now be changed depending on the lateral acceleration, as described on page 12 (P, PI controller)

C _1sv smaller
C _1sh larger

so that an ESP brake intervention on the outside wheel that Vehicle stabilized.

When exceeding the one modified by the Center of gravity or center of gravity given Curve limit acceleration or speed can be a anti-tipping intervention, for example in the form of a Brake intervention. Appropriate intervention strategies are, for example, from 19821593.2 and 19816430.0 known to the full extent in the present context Reference is made. So the critical state variable, e.g. B. the lateral acceleration, by deliberately understeering the Vehicle, in particular by corresponding detuning or Setting the vehicle model that the ESP regulation pres underlying, will be undercut again and thus prevent tipping.  

In a simplified embodiment, only the rolling behavior of the vehicle is taken into account. If one also assumes that the center of gravity is only slightly shifted from the vehicle's longitudinal axis, then travel information per axis is sufficient. If the center of gravity is largely the same, a critical situation can also be recognized by only one travel information. The vehicle model is adapted to the roll behavior and the permissible lateral acceleration is reduced while maintaining the defined self-steering behavior. This adjustment can be both analog, e.g. B. by means of information by sensor signal (s), as well as digital, z. B. by means of information through switches. The simplest embodiment is thus a suspension travel switch on a wheel described below with reference to FIG. 4.

A preferred embodiment of a limit switch relating to a simplified control approach is shown schematically in FIG. 4a. This control approach can advantageously be implemented as an ESP with a limit switch arranged on the shock absorber or on the spring of the wheel suspension. In the case of a limit switch designed as a spring travel switch, proceed as follows in accordance with the time profile shown in FIG. 4b. If the switch responds to at least one wheel on the outside of the curve, preferably the outer front wheel, then the critical lateral acceleration a _{transverse, limit is} exceeded in accordance with the assumed characteristic curve and a targeted _{countermeasure is initiated} to prevent further build-up or to reduce the lateral acceleration. Understeering of the vehicle is preferred, for. B. via a corresponding "detuning" of the ESP vehicle model to the "understeer", ie caused by a change in the driving trajectory, for example by a control approach according to equations (4) to (6).

The change can be about the lateral stiffness of the tires are defined, where "understeering" means that the Lateral stiffness on the front axle of the vehicle is smaller becomes.

The intervention in the vehicle model leads to braking and thus reducing the cornering force on the outside of the curve Rad. Regarding the physical relationship between Cornering force and brake slip (longitudinal force) is in this connection fully to the German Publication DE-A 196 32 943 "Operation method a motor vehicle with brake stabilizing grab ", Daimler-Benz AG.

If the switch closes again, these changes reversed over time or unlearned. This ends the control process.

Monitoring the switch is also on the way Plausibility assessment possible. For example be provided that the switch only when driving straight ahead closed a minimum period of, for example, 200 ms may be before countermeasures to reduce the Lateral acceleration can be activated. Alternatively, you can be provided that the triggering of countermeasures - in addition the switch position - is subject to further conditions, e.g. B. a threshold value for lateral acceleration, for example <0.5-0.7 g.

Claims (10)

1. A method for determining changes in the center of mass of an at least two-axle and at least three-wheel vehicle, characterized in that
that the vehicle is operated when cornering,
that first state variables corresponding to the respective wheel load are recorded on at least two wheels during cornering,
that the detected first state variables are compared with reference values representing the respective cornering, and
that a corresponding change in the center of gravity is calculated from the deviations between the detected first state variables and the reference values. 2. The method according to claim 1, characterized in that as the first state variable corresponding to the wheel load the travel that can be measured on the wheel suspension and / or the Spring pressure and / or the measurable on the shock absorber Damper pressure and / or the tire pressure or the Side deformation of the tire can be used as a basis. 3. Procedure for recognizing the risk of tipping over at least one biaxial and at least three-wheel vehicle under Using a method for determining Changes in the center of mass after one or several of the preceding claims, characterized  characterized that from the calculated Change of focus a correspondingly changed critical second representing the risk of tipping State variable is determined. 4. The method according to claim 3, characterized in that as the second state variable representing the risk of tipping the lateral acceleration applied at the center of gravity and / or the roll angle of the vehicle and / or the Pitch angle of the vehicle and / or the Vehicle speed and / or the steering angle and / or the yaw rate that is used. 5. Device for determining changes in the center of mass of an at least two-axle and at least three-wheel vehicle, characterized by
Means for detecting the driving state of cornering, means for detecting first state variables corresponding to the respective wheel load on at least two wheels,
Means for comparing the detected first state variables with reference values representing the respective cornering,
Means for calculating the change in the center of gravity from the deviations between the detected first state variables and the reference values. 6. The device according to claim 5, characterized in that as the first state variable corresponding to the wheel load the travel that can be measured on the wheel suspension and / or the Spring pressure and / or the measurable on the shock absorber Damper pressure and / or the tire pressure and / or the Side deformation of the tire can be used as a basis. 7. Device for detecting the risk of tipping over at least biaxial and at least three-wheel vehicle under Use of a device for determining Changes in the center of mass after one or several of claims 5 or 6, characterized by Means to determine the risk of tipping representing the second state variable from the calculated change in center of gravity. 8. The device according to claim 7, characterized in that as the second state variable representing the risk of tipping the lateral acceleration applied at the center of gravity and / or the roll angle of the vehicle and / or the Pitch angle of the vehicle and / or the Vehicle speed and / or the steering angle and / or the yaw rate are taken as a basis. 9. The device according to claim 7 or 8, characterized characterized in that the shock absorber or the spring element the wheel suspension is provided with a limit switch, its switching point over a temporal relationship with the second representing the risk of tipping State variable is linked.   10. The device according to claim 9, characterized in that the switching time of the limit switch to others Driving condition conditions is tied.