EP1929241A1

EP1929241A1 - System for determining an absolute tilt angle in relation to the horizontal

Info

Publication number: EP1929241A1
Application number: EP06806875A
Authority: EP
Inventors: Thomas Brandmeier; Christian Lauerer; Michael Feser; Jens Paggel
Original assignee: Continental Automotive GmbH
Current assignee: Continental Automotive GmbH
Priority date: 2005-09-30
Filing date: 2006-09-28
Publication date: 2008-06-11
Also published as: DE102005047021B3; US20090025998A1; WO2007036556A1; JP2009510424A

Abstract

The invention relates to a system for determining an absolute tilt angle (a) in relation to the horizontal, especially for use in a motor vehicle (1). Said system comprises at least one sensor element having a main axis of sensitivity (H1, H2), the at least one sensor element being arranged in such a manner that its main axis of sensitivity (H1, H2) lies in the plane of the tilt angle to be detected (plane of tilt) and the at least one sensor element produces a sensor signal depending on the tilt angle (a) in relation to the horizontal (2). The sensor signal produced by the sensor element is a measured acceleration (A1,m, A2,m) of the system. The system further comprises a device (14) for detecting an acceleration component (ay,dyn) of the measured acceleration (A1,m, A2,m) and a processing unit (16) to which the measured acceleration (A1,m, A2,m) and the acceleration component (ay,dyn) are supplied in order to determine an acceleration component-corrected acceleration (A1, A2) from which the absolute tilt angle (a) of the system in relation to the horizontal can be determined.

Description

description

Arrangement for determining an absolute angle of inclination with respect to the horizontal

The invention relates to an arrangement for determining an absolute angle of inclination relative to the horizontal with at least one sensor element having a main axis of sensitivity, wherein the at least one sensor element is arranged such that its main axis of sensitivity is in the plane defined by the angle of inclination to be detected (inclination plane) and at least one sensor element generates a sensor signal as a function of the angle of inclination relative to the horizontal.

The detection of the absolute inclination angle is for example for the reliable detection of a rollover of a motor vehicle of great importance. The fundamental problem in detecting a vehicle smash - next to the long time scale on which the event occurs - is the angle of the vehicle relative to the horizontal.

This angle, which is also referred to as the vehicle or roll angle, has hitherto been determined by integration over a measured angular velocity (so-called roll rate or yaw rate) over the vehicle's longitudinal axis (so-called roll axis). The precision of the result for this integration is determined by two unknowns: the start value of the integral and the sensor zero point of a rotation rate sensor used to determine the rotation rate. To make matters worse, in practice that all real rotation rate sensors have a zero point drift.

The zero-point drift of the sensor is usually determined by a very slow low-pass filter. This is based on the assumption that the motor vehicle is normal

Use does not rotate permanently in one direction around the roll axis. This procedure provides correct results for as long as possible However, if the motor vehicle moves in the room due to ascent and descent with simultaneous steering movement in space, then using a single yaw rate sensor basically creates an error in the measurement of the roll angle can be eliminated only by using three rotation rate sensors, whereby the costs for the sensor arrangement are very high.Although the zero point of the rotation rate sensor is well known, the starting value of the integral remains as unknown.

Known solutions to the problem rely on the fact that the vehicle is usually horizontal in normal operation, which is why the vehicle angle on average over a longer period, e.g. several seconds, should be zero. Reversal events do not only take place in normal traffic, but also in the terrain. For off-road driving, it can not be assumed that the vehicle is on average over the longer period in the horizontal. A slow low pass as Integralruckfuhrung can therefore lead to misjudgments of the situation, so that the activation of an occupant protection means under circumstances not or at the wrong time. As an example, a longer trip with bank is called. This can not be ruled out, that after a sufficiently long time a correspondingly large bank angle is 'forgotten'.

FIG. 1 shows the roll rate necessary for the rollover of a motor vehicle as a function of the bank angle and thus of the vehicle angle relative to the horizontal. With increasing

Vehicle angle decreases the roll rate necessary for the rollover. If the vehicle angle of the vehicle relative to the horizontal is unknown, a safe decision for the draw of an occupant protection system or a system for stabilizing the motor vehicle can not be made. DE 44 36 379 A1 discloses a sensor arrangement for detecting a specific angle of inclination. The sensor arrangement consists of at least two sensor elements, these being arranged such that their main sensitivity axes lie in the plane defined by the tilt angles to be detected and form an angle with respect to a reference plane of the arrangement corresponding to the tilt angles to be detected. The sensor elements each generate a sensor signal as a function of the angle of inclination of the reference plane relative to the horizontal direction. The sensor elements are arranged with their Hauptempfindlichkeitsachse at an angle to the horizontal, which corresponds to the tilt angle of, for example, integrated in a vehicle arrangement. This means that the main axis of sensitivity of a sensor element lies exactly level when the vehicle is in the right or left tilt position. Due to the principle of the structure of the sensor elements, a sensor signal is emitted exactly when the vehicle has reached this tilting position.

Although the sensor arrangement described in DE 44 36 379 A1 is thus able to detect an absolute angle of the vehicle relative to the horizontal, the detection is restricted to a single angle, which is determined by the arrangement of the main sensitivity axes of the sensor elements.

It is therefore an object of the present invention to provide an arrangement for determining an absolute angle of inclination relative to the horizontal, which does not have the abovementioned disadvantages.

This object is achieved by an arrangement for determining an absolute inclination angle with the features of patent claim 1. Advantageous embodiments emerge from the dependent claims. An inventive arrangement for determining an absolute inclination angle, which is also referred to below as the absolute angle, has at least one sensor element which has a main axis of sensitivity. The at least one sensor element is arranged such that its main sensitivity axis lies in the plane defined by the inclination angle to be detected (inclination plane) and the at least one sensor element generates a sensor signal as a function of the inclination angle relative to the horizontal. The sensor signal provided by the sensor element is a measured acceleration of the device. There is further provided a device for determining an acceleration component of the measured acceleration and a processing unit to which the measured acceleration and the acceleration component can be supplied in order to determine an acceleration adjusted by the acceleration component, from which the absolute angle of inclination of the arrangement relative to the horizontal can be determined is.

The invention is used inter alia in a means of transport, in particular in a motor vehicle in conjunction with an occupant protection system, wherein the absolute angle of inclination is used for the decision whether a protective device of the occupant protection system is triggered and / or the vehicle stabilizing measures are taken.

The tilt plane formed or defined by the at least one sensor element is perpendicular to a vehicle longitudinal axis of the vehicle. Accordingly, the tilting axis of the vehicle to be monitored runs parallel to the direction of travel of the vehicle.

The arrangement according to the invention makes it possible to determine the actual angle of inclination relative to the horizontal, that is to say independent of the criticality of the angle of inclination with regard to an unstable driving situation or an threatened rollover. It can thus not only a single angle, such as the tilt angle in DE 44 36 379 Al, are recognized, but it is possible at any time of movement, but also during the stoppage of the arrangement, the indication of the angle to the horizontal.

According to a preferred embodiment, the acceleration component is determined in a direction which deviates from a direction of movement of the arrangement. The direction of movement corresponds, for example, to the direction of travel of the vehicle.

According to a further preferred embodiment, the acceleration component is a transverse acceleration of the, moved in the direction of movement, arrangement. The lateral acceleration corresponds to that during a dynamic driving situation of the vehicle

Vehicle occurring centrifugal acceleration by what proportion of the measured by the at least one sensor device acceleration is adjusted. The measured acceleration is attributed to the proportion of the vertical dynamics and the gravitational acceleration, from which the absolute angle of the arrangement or of the vehicle can be determined with high accuracy.

The acceleration component can be determined in different ways, eg measured or calculated. In this case, sensory determined measured values can be used in particular in a vehicle elsewhere, as a result of which the realization of the invention is possible in a cost-effective manner without further components. For this purpose, the device for determining the acceleration component according to a further preferred embodiment is designed to determine these from at least one of the following parameters: the speed of the arrangement; a curve radius on which the arrangement is located; a yaw rate; a steering angle. This information is provided, for example, by an ABS (antilock braking system) and / or an ESP (Electronic Stability Program) sensor system. Wheel speed information and possibly speed information can be used by the ABS sensor system to calculate the lateral acceleration. The ESP sensor can be used to interrogate the yaw angle change and the longitudinal speed and possibly also the steering angle and to calculate the lateral acceleration.

According to a further preferred embodiment, the at least one sensor element is arranged with its main sensitivity axis at an angle in the inclination plane to the horizontal, whereby an improved measurement accuracy of the measured acceleration and thus the absolute angle determined therefrom can be achieved.

In accordance with a further preferred embodiment, a first sensor element with a first main sensitivity axis and a second sensor element with a second main sensitivity axis are provided. With two sensor elements, one obtains an intrinsic correction of the sensor drift if it has the same sign for both sensors. In the worst case of an opposite sensor drift, the error is as great as that of the measured value determined with a single sensor.

According to a further preferred embodiment, the absolute inclination angle α of the arrangement with respect to the horizonals according to the formula

CC _ 4 -A: D

A + A ₂

calculated, where

1

A = A, _m (2: 1

A - A, m ^{+ "} TTlf ^' ay, dyn (3)

and

Ai, m is the acceleration measured by the first sensor element;

A ₂ , m are the acceleration measured by the second sensor element; a _y , dyn the acceleration component;

AAii the adjusted acceleration of the first sensor element;

A _{2 is} the adjusted acceleration of the second sensor element; α is the absolute inclination angle.

The vehicle angle α to the horizontal can be determined by the measured gravitational accelerations Al and A2 of the two sensor elements according to (1), where (1) applies in this general form at rest and straight ahead of the arrangement or the vehicle. In dynamic driving situations the centrifugal acceleration of the vehicle must be considered. The centrifugal acceleration can be determined from the measurement signals described above, for example the ABS or ESP sensor technology. If the acceleration component a _y , _d y _n caused by the driving dynamics _is known, the measured lateral acceleration (Ai, _{m of} the first sensor element and A ₂ , _{m of} the second sensor element) can be in a dynamic driving situation (eg fast cornering) around the "dynamic" component The remaining static acceleration (Ai or A ₂ ) can be used to calculate the angle, which determines the absolute angle of the vehicle.

According to a further preferred embodiment, the first main sensitivity axis of the first sensor element and the second main sensitivity axis of the second sensor element are arranged at an angle of 90 ° to one another. WEI Preferably, the first main axis of sensitivity of the first sensor element and the second main axis of sensitivity of the second sensor element each occupy an angle of 45 ° to the vertical of the arrangement when the absolute inclination angle to the horizontal is 0 °. The two sensor elements determine - when the vehicle is at rest and in the horizontal - the same measured value. The change in the measured value is linear in the angular variation of the vehicle relative to horizontal. This achieves two advantages: On the one hand, the sensor signal is linear in the measured variable and, on the other hand, two signals are compared in order to determine a parameter. This redundancy increases the accuracy in measuring the acceleration of the vehicle. However, an angle-linear measured value is already available with a sensor element.

In driving-dynamic borderline situations, these must be recognized as those in which the inventive approach reaches its limits. If necessary, the absolute angle calculation must be discarded and a conventional angle calculation made using the yaw rate. According to a further preferred embodiment, this therefore also has a further device for tilt angle calculation, which is designed to carry out an integration via a rotation rate determined by a rotation rate sensor. Since dynamic driving limit situations are generally only of short duration and the method of calculating the angle for short time intervals is quite precise, the faulty integration does not represent a disadvantage.

As a starting value for the integration of the yaw rate, the last determined absolute angle is used according to a further preferred embodiment, which is determined as described above. This ensures a higher accuracy in determining the angle compared to conventional methods. According to a further preferred embodiment, a switching device is provided, which determines according to predetermined criteria, whether the inclination angle of the arrangement relative to the horizontal by the further device using rotation rate signals or not to be determined, and the second device is activated accordingly or not.

The invention will be explained in more detail with reference to the exemplary embodiments indicated in the drawings. Show it:

1 shows the rolling rate necessary for the rollover of a vehicle as a function of the vehicle angle relative to the horizontal;

2 shows a vehicle in a schematic representation from the rear with a sensor element pair in a position inclined relative to the horizontal;

FIG. 3 shows the course of determined vehicle inclinations over time, which contrasts uncompensated inclination angle determination with a reference method; FIG.

4a shows a representation of a first vehicle model, according to which a driving dynamics-induced acceleration component a _y , _d yn can be determined;

4b a representation of further vehicle models, according to which an acceleration component a _y , _d yn caused by driving dynamics can be determined;

FIG. 5 shows the comparison of time profiles of the acceleration-dynamically induced acceleration component ay, dyn r determined with different vehicle models 6 is a schematic representation of the arrangement according to the invention, which is extended by a further device for tilt angle calculation, which is designed to perform an integration via a rotation rate determined by a rotation rate sensor;

FIG. 7 shows the comparison of time profiles of the determined bank angle; FIG.

8 shows the comparison of time profiles of the determined roll rate, which contrasts a reference method with the procedure according to the invention.

With reference to FIG. 2, in which a vehicle 1 is shown in a schematic representation from behind with a sensor element pair (not shown in detail in the figure) in a position inclined by the angle α relative to the horizontal, the determination according to the invention of the actual inclination angle becomes α is best.

The sensor elements designed as acceleration sensors have a main sensitivity axis H1 or H2. The tilt plane spanned by the sensor elements or by their main sensitivity axes is perpendicular to a vehicle longitudinal axis (perpendicular to the plane of the page) of the vehicle 1. Accordingly, the tilting axis of the vehicle to be monitored runs parallel to the direction of travel of the vehicle.

In the main sensitivity axes Hl and H2 respectively an acceleration Ai, _m or A ₂ , _{m is} measured, each of a component a _y , _d y _n in the y-direction (transverse to the direction of travel and parallel to a reference plane 3) and a component of a _z, _dyn Reassemble the in z-direction (perpendicular to the reference plane 3). The reference plane 3 is inclined relative to a horizontal plane 2 by the inclination angle α to be determined. The component acting in the direction of travel (x-direction), which is influenced by ascending and descending, can be neglected in the context of the present invention, since its influence is low.

The main sensitivity axes Hl, H2 of the two acceleration sensors form an angle of 90 ° to each other. Both acceleration sensors preferably assume an angle Oi, O ₂ of 45 ° to the vehicle vertical or to the reference plane 3. Thus, both accelerometers measure gravity and inertial acceleration in dynamic driving situations.

Deviating from the arrangement of the acceleration sensors shown and described here, other angles can also be selected. In addition, the determination of the inclination angle α is possible even with only one sensor element.

The measuring range of the acceleration sensors should be chosen such that, taking into account the digitization errors or the possible signal resolution (determined by a signal background noise), the proportion of gravity delivers a sufficiently large signal in the measurement of the acceleration Ai, _m or A ₂ , _m ,

In order to determine the angle α, the determination of the force acting on the vehicle centrifugal acceleration is required, which is caused by a driving dynamics situation. The centrifugal acceleration can be e.g. determine measurement signals provided by an ABS or ESP sensor. In addition, other methods can be used.

The driving dynamics caused acceleration component a _y , _d yn, as can be seen from Figure 4a, from the

Speeds v _VL , V _VR , V _HL and V _{HR of} the four wheels or their wheel speeds of the vehicle are determined from which the speed v of the vehicle and a driven by this radius of curvature can be determined. The arrangement is typical for an ABS sensor. Using a in the figure as a vehicle model 1 designated and familiar to those skilled algorithm then a _y , _d y _n can be determined.

The driving-dynamically induced acceleration component a _y , _d yn can also, as can be seen from FIG. 4b, be calculated from the vehicle speed v and the yaw rate ψ (in the figure above) or the vehicle speed v, the yaw rate ψ and the steering angle δ _L (in FIG the figure below) are determined. This arrangement is typical for an ESP sensor. Using an algorithm designated in the figure as vehicle model 2 or 3 and familiar to the person skilled in the art, it is then also possible to determine a _y , _d yn.

If the acceleration-dynamically induced acceleration component a _y , _d yn is known, the measured lateral acceleration (Ai, _{m of} the first sensor element and A ₂ , _{m of} the second sensor element) can be reduced by the "dynamic" component in a dynamic driving situation (eg fast cornering) ( equations (2) and (3)) and the remaining static acceleration (Ai or A ₂ ) are used for the angle calculation (see equation (I)), whereby the absolute angle α of the vehicle can be determined.

The measured acceleration is thus attributed to the vertical dynamics and the gravitational acceleration. With this remaining acceleration, the absolute angle α of the vehicle is determined with high accuracy.

By differentiation can be determined from the absolute angle, the rollout rate of rotation of the vehicle, which in principle a replacement of conventional yaw rate sensors can be created. The dynamic vertical acceleration can be determined by the fact that the gravitational acceleration is constant. If the vehicle is traveling on a gradient (in the x-direction), errors of the order of magnitude (1-cosΦ) occur, where Φ represents the inclination angle of the gradient. In most everyday situations, the error is negligible.

The influence that the adjustment of the measured acceleration has on the lateral acceleration can be seen with reference to FIG. 3, in which the time profile of the bank is compared with a reference measurement made with a sensor and a determination according to the invention (referred to as the V2g method) are, with a compensation to a _y , dyn did not occur.

FIG. 5 shows different time profiles of centrifugal accelerations which were determined with different vehicle models and thus with different input values, as described in conjunction with FIGS. 4a and 4b by way of example.

In driving-dynamic borderline situations, these must be recognized as those in which the approach according to the invention reaches its limits. The absolute angle calculation using the measured acceleration 10, the determination of the driving dynamics information 12 and the application of a vehicle model for calculating a _y, _dyn to the inclination calculation 16 is discarded in such a limiting situation and it is a conventional angle calculation over a sensorially determined rotation rate 20 and an integration 22 is performed (FIG. 6). The control of when one or the other method is applied is via a switching logic 18. Criteria for a changeover could be one or more of the following: wheel speeds of the wheels, drift angle of the vehicle, lateral acceleration (centrifugal acceleration), steering angle, etc. Starting value for the Integration of the angle is the last absolute angle calculated by 16. As driving dynamics border situations usually only of short Duration and the method of the angle calculation for short time intervals is quite accurate, the error-prone integration is not a disadvantage.

FIG. 7 shows the result of the two different calculation methods on the basis of the chronological progression of the bank angle, wherein a switchover takes place at the time 9 sec. As can be clearly seen, the absolute angle detection in boundary situations by 16 leads to useless results.

The high precision of the absolute angle detection makes it possible to use the determined absolute angle to determine the roll rate. Fig. 8 shows the result of differentiation of the absolute angle compared to a reference sensor.

The arrangement according to the invention allows a simple and cost-effective variant for absolute angle detection. There are no more sensor elements needed than are necessary in conventional arrangements.

It is possible to replace the roll rate sensor by the combination of two acceleration sensors, which can also realize significant cost savings.

Claims

claims

1. Arrangement for determining an absolute inclination angle (α) relative to the horizontal, in particular for use düng in a motor vehicle (1), with at least one sensor element having a main axis of sensitivity (Hl, H2), wherein the arranged at least one sensor element is that the main axis of sensitivity (Hl, H2) is in the plane defined by the angle of inclination to be detected and the at least one sensor element generates a sensor signal as a function of the angle of inclination (α) relative to the horizontal (2), characterized in that that of the sensor signal supplied to the sensor element is a measured acceleration (A _x , _m , A ₂ , _m ) of the arrangement; a device (14) for determining an acceleration component (a _y , _d yn) of the measured acceleration (Ai, _m , A ₂ , _m ) is provided; a processing unit (16) is provided, to which the measured acceleration (A _x , _m , A ₂ , _m ) and the acceleration component (a _y , _d yn) can be fed in order to accelerated by the acceleration component acceleration (Ai, A ₂ ) determine from which the absolute inclination angle (α) of the arrangement relative to the horizontal can be determined.

2. Arrangement according to claim 1, characterized in that the acceleration component (a _y , _d y _n ) is determined in a direction which deviates from a direction of movement of the vehicle.

3. Arrangement according to claim 1 or 2, characterized in that the acceleration component (a _y , _d y _n ) is a lateral acceleration or the centrifugal acceleration of the moving in the direction of movement, arrangement.

4. Arrangement according to one of the preceding claims, characterized in that the means (14) for determining the acceleration component is adapted to determine these from at least one of the following parameters: the speed of the arrangement; a curve radius on which the arrangement is located; a yaw rate; - a steering angle.

5. Arrangement according to one of the preceding claims, characterized in that the at least one sensor element is arranged with its Hauptempfindlichkeitsachse (Hl, H2) at an angle in the plane of inclination to the horizontal (2).

6. Arrangement according to one of the preceding claims, characterized in that a first sensor element with a first main axis of sensitivity (Hl) and a second sensor element with a second main axis of sensitivity (H2) are provided.

7. Arrangement according to claim 6, characterized in that the absolute inclination angle α of the arrangement relative to the horizontal (2) according to the formula

A ₁ -A ₂ CC = ^■ ' ²

A ₁ + A ₂

is calculated, and

A = A _{2 m} + -j = ^■ a _ydyn is, where

Ai, _{m is} the acceleration measured by the first sensor element; A2, _{m is} the acceleration measured by the second sensor element; a _y , dyn the acceleration component;

Ai is the adjusted acceleration of the first sensor element; A _{2 is} the adjusted acceleration of the second sensor element; α is the absolute inclination angle.

8. Arrangement according to claim 6 or 7, characterized in that the first main axis of sensitivity (Hl) of the first sensor element and the second main axis of sensitivity (H2) of the second sensor element are arranged at an angle of 90 ° to each other.

9. Arrangement according to one of claims 6 to 8, characterized in that the first main axis of sensitivity (Hl) of the first sensor element and the second main axis of sensitivity (H2) of the second sensor element each occupy an angle of 45 ° to the vertical of the arrangement, when the absolute inclination angle to Horizontal is 0 °.

10. Arrangement according to one of the preceding claims, characterized in that it further comprises a further means (20,22) for the inclination angle calculation, which is adapted to perform an integration over a rotational rate of rotation detected by a rotation rate sensor.

11. Arrangement according to claim 10, characterized in that is used as the starting value for the integration of the rotation rate of the last determined absolute angle.

12. Arrangement according to claim 10 or 11, characterized in that a switching device (18) is provided which determines according to predetermined criteria, whether the inclination angle of the arrangement relative to the horizontal by the further device using rotation rate signals or not to be determined, and second device accordingly activated or not.

13. Use of the arrangement according to one of the preceding claims in a means of transport, in particular in a motor vehicle in conjunction with an occupant protection system, wherein the absolute angle of inclination is used for the decision whether a protective device of the occupant protection system is triggered and / or the motor vehicle stabilizing measures to be hit.