Method for improving the gradient calculation of motor vehicles when cornering

Abstract

Method for improving the gradient calculation of motor vehicles (1) when cornering, characterized in that the influence of the measured transverse acceleration (AY) on the measured longitudinal acceleration is mathematically determined as a correction value from the known vehicle speed (v) and the mechanical installation position of the longitudinal acceleration sensor (3) of the motor vehicle (1), and the measured longitudinal acceleration is corrected accordingly, wherein the road gradient is determined from the difference between the measured longitudinal acceleration minus the correction value and the vehicle acceleration determined from the wheel or output speeds of the motor vehicle (1), characterized in that the correction value (AX) for the longitudinal acceleration value is determined from the measured transverse acceleration (AY), the vehicle speed (v), and the distance (d) of the longitudinal acceleration sensor (3) to the pivot point,at which the tangential acceleration hits the vehicle's centerline at a right angle, is determined by the following formula for a small ratio of distance d to curve radius r: AX= AY, 2 * d / v 2 .

Description

[0001] The present invention relates to a method for improving the gradient calculation of motor vehicles when cornering according to the preamble of patent claim 1.

[0002] It is known from the prior art that motor vehicles are generally equipped with driving dynamics control systems (also known as ESP). Such systems use acceleration sensors to determine vehicle dynamics, which measure the vehicle's acceleration in the longitudinal and lateral directions. The gradient the vehicle is traveling on can be calculated from the longitudinal acceleration measured by the acceleration sensors. This is made possible by the fact that, on uphill and downhill gradients, the acceleration due to gravity also acts on the longitudinal acceleration sensor.

[0003] Accelerations due to a change in vehicle speed would distort the gradient calculation and must therefore be determined in order to compensate for the measured acceleration accordingly. The vehicle's acceleration over ground can be calculated in a conventional manner from the vehicle's wheel or output speeds. The current road gradient can therefore be determined from the difference between the vehicle's longitudinal acceleration measured with the acceleration sensor and the vehicle acceleration determined from the vehicle's wheel or output speeds.

[0004] When the vehicle corners, the calculation of the road gradient is adversely affected by the difference between the vehicle's longitudinal acceleration measured by the acceleration sensor and the vehicle acceleration determined from the vehicle's wheel or output speeds. When the vehicle corners, a centripetal acceleration acts on the vehicle. Since the longitudinal acceleration sensor is not positioned tangentially to the center of the curve, the centripetal acceleration also acts on the longitudinal acceleration sensor, thus distorting the longitudinal acceleration measurement and consequently the gradient calculation.

[0005] DE 197 43 059 A1 discloses a method for determining a value representing the driving resistance of a motor vehicle, wherein rotatable elements such as a vehicle engine, engine auxiliary units, a clutch, a torque converter, a gear ratio-variable transmission, a differential gear and / or vehicle wheels are arranged in the drive train of the vehicle, within the framework of which an acceleration value representing the instantaneous acceleration of the vehicle is detected and a reference value for the acceleration of the vehicle is determined,wherein a variable representing the driving resistance in a motor vehicle is detected as a function of a comparison of the detected acceleration variable with the determined reference variable for the acceleration of the vehicle, and wherein a rotational variable representing the rotational torque of at least one element arranged in the drive train is determined, and the determination of the reference variable is dependent on the determined rotational variable.

[0006] Furthermore, DE 197 28 867 A1 discloses a method for determining a mass value of a motor vehicle, in particular a commercial vehicle with a drive unit, which represents the vehicle mass, in the context of which at least a first and a second acceleration value are recorded, which represent the vehicle acceleration at a first and a second time, and at least a first and a second drive value are recorded, which represent the drive force or the drive torque of the drive unit at the first and the second time.Furthermore, at least a first and a second driving resistance or mass estimate are determined at least as a function of the detected acceleration values ​​and the detected drive values, wherein the mass value is subsequently determined at least as a function of a comparison of at least the determined first driving resistance or mass estimate with the determined second driving resistance or mass estimate.

[0007] From the applicant's DE 102 35 969 A1, a method for controlling a transmission for a motor vehicle with an electronic control unit for setting a gear ratio adapted to the current driving situation is known. In this method, a driving resistance is determined using a current excess torque and a prevailing vehicle acceleration as a function of a signal supplied by an inclination sensor and representing a road gradient variable. A current vehicle mass is determined by comparing a current excess torque-vehicle acceleration relationship with a torque-excess vehicle acceleration characteristic curve defined for a specific vehicle mass and stored as a map or mathematical formula in an electronic control unit.

[0008] From the applicant's generic document DE 10 2010 041 967 A1, a method for determining the vehicle inclination in the direction of travel from data from a yaw angle sensor and an acceleration sensor is known.

[0009] The present invention is based on the object of specifying a method for improving the gradient calculation of motor vehicles when cornering, by the implementation of which the influence of the centripetal acceleration is compensated in a simple manner.

[0010] This object is achieved by the features of patent claim 1. Further embodiments and advantages according to the invention emerge from the subclaims.

[0011] Accordingly, a method for improving the gradient calculation of motor vehicles when cornering is proposed, in which the influence of the measured lateral acceleration on the measured longitudinal acceleration is mathematically determined as a correction value from the known vehicle speed of the motor vehicle and the mechanical installation position of the longitudinal acceleration sensor and the measured longitudinal acceleration is corrected accordingly.

[0012] The invention will be explained in more detail below using the attached figure, which illustrates the acceleration vectors of a motor vehicle 1 cornering at a speed v, comprising a lateral and a longitudinal acceleration sensor 2, 3. It can be provided that the lateral and longitudinal acceleration sensors 2, 3 are integrated into one component.

[0013] The ratio of the correction value AX for the longitudinal acceleration value to the actual lateral acceleration AQ is equal to the ratio of the distance d of the longitudinal acceleration sensor 3 to the pivot point and the curve radius r. AX / AQ=d / r

[0014] The pivot point is the point at which the tangential acceleration impinges on the vehicle's centerline at a right angle. For vehicles with a non-steered rear axle, the pivot point on the rear axle is at the intersection point between the rear axle and the vehicle's longitudinal centerline. The curve radius r is the distance between the curve center and the longitudinal acceleration sensor 3.

[0015] In the equation AX / AQ = d / r, the curve radius r is calculated from the vehicle speed v and the lateral acceleration AQ according to the formula AQ = v 2 / r and assuming that the lateral acceleration AQ is approximately equal to the measured lateral acceleration AY, the correction value AX for the longitudinal acceleration value can be determined with this formula using known quantities as follows. AX=AY2*d / v2

[0016] The simplification that the measured lateral acceleration AY corresponds to the actual lateral acceleration AQ is possible because the ratio of distance d to radius r is small.

[0017] The road gradient can be determined from the difference between the longitudinal acceleration measured with the acceleration sensor minus the correction value AX and the vehicle acceleration determined from the wheel or output speeds of the vehicle.

[0018] In order to correctly compensate for the influence of the lateral acceleration on the longitudinal acceleration sensor 3 when cornering, the installation position, ie the distance d between the longitudinal acceleration sensor 3 and the pivot point of the motor vehicle 1 in the curve, is a crucial factor.

[0019] For vehicles with a steered front axle and an unsteered rear axle, the pivot point corresponds to the intersection point between the rear axle and the vehicle's longitudinal centerline, so that the distance between the longitudinal acceleration sensor 3 and the intersection point between the rear axle and the vehicle's longitudinal centerline can be easily determined. For vehicles 1 with a steered rear axle, the ratio of the steering angle of the front axle to the steering angle of the rear axle must be taken into account to determine the pivot point. If this relationship is dynamic, for example, if it depends on the vehicle speed, the pivot point and thus the distance d of the longitudinal acceleration sensor 3 from the pivot point must also be taken into account with this dependency, i.e., in this example, as a function of the vehicle speed.

[0020] Alternatively, the distance d of the longitudinal acceleration sensor 3 to the pivot point can be easily determined as follows: When driving in a circle at constant speed and constant steering angle on the plane, the lateral acceleration AY, the vehicle speed v and the longitudinal acceleration AX are measured, whereby the distance d can be calculated using the following formula: d = AY 2 * AX / v 2 The measured longitudinal acceleration corresponds to the correction value, since the circular movement on the plane takes place at a constant speed.

[0021] If no lateral acceleration measurement value is available in vehicle 1, it is suggested to calculate the correction value AX for the longitudinal acceleration value using the equation AX = v 2 * d / r 2 to determine.

[0022] The curve radius r can be determined from the steering angle of the motor vehicle 1 or from the difference in speed between the inside and outside wheel of an axle. Reference symbol 1 motor vehicle 2 lateral acceleration sensor 3 Longitudinal acceleration sensor AX Correction value for the longitudinal acceleration value AY measured lateral acceleration AQ actual lateral acceleration d Distance d of the longitudinal acceleration sensor 3 to the pivot point r curve radius v Vehicle speed

Claims

[1] Method for improving the gradient calculation of motor vehicles (1) when cornering, characterized by that the influence of the measured transverse acceleration (AY) on the measured longitudinal acceleration is mathematically determined as a correction value from the known vehicle speed (v) and the mechanical installation position of the longitudinal acceleration sensor (3) of the motor vehicle (1), and the measured longitudinal acceleration is corrected accordingly, the road gradient being determined from the difference between the measured longitudinal acceleration minus the correction value and the vehicle acceleration determined from the wheel or output speeds of the motor vehicle (1), characterized bythat the correction value (AX) for the longitudinal acceleration value is determined from the measured lateral acceleration (AY), the vehicle speed (v) and the distance (d) of the longitudinal acceleration sensor (3) to the pivot point at which the tangential acceleration strikes the vehicle centerline at a right angle, with a small ratio of distance d to curve radius r by the following formula: AX = AY 2 * d / v 2 . [2] Method for improving the gradient calculation of motor vehicles (1) when cornering according to claim 1, characterized by that in vehicles with a steered front axle and an unsteered rear axle, the pivot point corresponds to the intersection point between the rear axle and the vehicle's longitudinal centerline and that in vehicles with a steered rear axle, the ratio of the steering angle of the front axle to the steering angle of the rear axle must be taken into account to determine the pivot point. [3] Method for improving the gradient calculation of motor vehicles (1) when cornering according to claim 2, characterized by that if the ratio of the steering angle of the front axle to the steering angle of the rear axle is dynamic, the pivot point is determined as a function of this dynamic. [4] Method for improving the gradient calculation of motor vehicles (1) when cornering according to claim 1, characterized by that the distance (d) of the longitudinal acceleration sensor (3) to the pivot point is determined by measuring the lateral acceleration (AY), the vehicle speed (v) and the longitudinal acceleration (AX) during circular travel at constant speed and constant steering angle on the plane, the distance d being calculated using the following formula: d = AY 2 * AX / v 2 . [5] Method for improving the gradient calculation of motor vehicles (1) when cornering according to the preamble of claim 1, characterized bythat the correction value (AX) for the longitudinal acceleration value is calculated from the vehicle speed (v), the distance (d) of the longitudinal acceleration sensor (3) to the pivot point at which the tangential acceleration strikes the vehicle centerline at a right angle, and the curve radius (r) using the equation AX = v 2 * d / r 2 is determined, whereby the curve radius (r) can be determined from the steering angle of the motor vehicle (1) or from the difference in speed between the inside and outside wheel of an axle.

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