Method and device for calculating the axle load of non-load-sensed axles of a vehicle

Abstract

Method for calculating the axle load of non-load-sensed axles of a vehicle, wherein the axle load of the non-load-sensed axle is calculated on the basis of a function f(µ) which describes the dependence of the longitudinal friction coefficient µ of a wheel of a non-load-sensed axle on the longitudinal slip value S, characterized in that the load of the non-load-sensed axle is determined while driving during suitable braking, wherein suitable braking is defined as follows: 1.2 bar ≤ brake pressure ≤ 3.5 bar, curve radius ≥ 60 m, vehicle speed ≥ 20 km / h.

Description

[0001] The invention relates to a method and a device for calculating the axle load of non-load-sensed axles of a vehicle.

[0002] Electronic stability control systems for commercial vehicles require axle load, especially that of the rear axle, as input variables. Axle loads are measured using axle load sensors, for example, an air spring pressure sensor for measuring the spring pressure in an air suspension or a travel sensor for measuring the compression travel of a steel suspension.

[0003] Alternatively, axle loads can also be determined or estimated indirectly from other variables. For example, DE 197 07 210 B4 describes a braking system with a 4S / 3M system for drawbar trailers. In this system, the differential slip between the axles is calculated and an initially assumed load is incremented or decremented accordingly. The changed load results in a redistribution of the brake pressure on the axles. This, in turn, influences the differential slip. The calibration is terminated when the differential slip falls below a specified value. This known method is only suitable for vehicles with separate brake pressure circuits for the load-sensing and non-load-sensing axles.

[0004] DE 103 07 510 A1 discloses a method for computer-aided calculation of the axle loads of a vehicle. The axle loads are calculated based on a function f(λ), which is a function of a ratio of a longitudinal force Fx to an insurgent force F z at one wheel of the vehicle by a longitudinal slip λ. The axle loads are calculated during normal driving, without the need for prior braking maneuvers.

[0005] DE 10 2005 060 857 A1 discloses a method for detecting the load condition of a motor vehicle. The load condition is detected during driving, depending on whether the vehicle is cornering. For this purpose, individual wheel loads are determined from a friction coefficient-slip curve.

[0006] The object of the present invention is to develop a method and a device of the type mentioned at the outset such that the load of non-load-sensed axles can be determined with sufficient accuracy.

[0007] According to the invention, this object is achieved by the features of patent claims 1 and 7.

[0008] Advantageous and expedient embodiments of the solution are specified in the subclaims.

[0009] The invention will be explained in more detail with reference to an embodiment shown in the attached drawing, in which the graphical course of a function f(µ) = S is shown, which forms the basis of the invention and which describes the relationship between the longitudinal friction coefficient µ and the longitudinal slip S on a wheel.

[0010] When braking force is applied, the tires slip. This can be represented as a function of the coefficient of friction µ between the tire and the road surface. This is shown in the attached figure. The relationship between these variables is almost linear in the lower range of the function f(µ)= S. A best-fit straight line G provides a good approximation of the curve in this section. The axle load is inversely proportional to the coefficient of friction. The difference in slip between two axles is therefore a parameter for load distribution in the approximate range of the curve. The load on the non-load-sensing axle is calculated while driving under suitable braking conditions. Suitable braking is defined as follows: 1.2 bar ≤ brake pressure ≤ 3.5 bar, curve radius ≥ 60 m, vehicle speed ≥ 20 km / h.

[0011] The basic idea of the invention is to calculate the axle load of the axle without an axle load sensor from the measured slip difference during braking. For this purpose, an average u-slip curve with a gradient of µ0 / S0 is assumed. The deceleration µ or the friction coefficient µ corresponds to the quotient of brake pressure / normal force of the respective axle. The unknown axle load can be calculated. The following mathematical relationship results from the graph shown in the drawing: S0μ0=SAxes1μAxes1=SAxes2μAxes2=const. S0μ0=SAxes1μAxes1 SAxis1μAxis1=SAxis2μAxis2

[0012] From the physical contexts Si=v0−viv0,μi=FBFNiand FNi=Mi⋅g with v0 vehicle speed v i average wheel speed on axle i S i Slip on axle i F B Braking force on axle i (calculated from the brake pressure) F Ni Normal force on axis i M Ni Load on axle i g acceleration due to gravity Axle 1 load-sensing axle Axle 2 non-load-sensed axle and equation 1, the vehicle speed v0 can be calculated according to v0=vAxis1⋅MAxis1MAxis1−FBg⋅S0μ0 determine.

[0013] Using the vehicle speed and equation 2, the load of the non-load-sensing axle can be calculated as follows MAxis2=(v0−vAxis1)(v0−vAxis2)⋅MAxis1

[0014] The quotient S0μ0 is a constant and is determined experimentally. This can be done with a measured reference of the vehicle speed v 0,Ref after S0μ0=v0,Ref−vAxis1v0,RefFBMAxis1⋅g and / or by determining the load M Achse2,Ref the non-load-sensing axle S0μ0=gFB⋅(MAxis1+vAxis1⋅MAxis1⋅(MAxis1−MAxis2,Ref)vAxis2⋅MAxis2,Ref−vAxis⋅MAxis1)

[0015] The function f(µ) = S describes the relationship between the longitudinal friction coefficient µ, which corresponds to the quotient of braking force / normal force of the respective axle, and the longitudinal slip S. As can be seen from the graph in the drawing, the curve is linear for longitudinal slip values up to S0. Consequently, the gradient S0 / µ0 or µ0 / S0, which is determined experimentally, is constant, as already mentioned above. This constant is used as a predefined input variable when calculating the axle load.

[0016] The inventive solution enables the load calculation of a non-load-sensing axle in vehicles by generating identical decelerations or braking forces on two or more axles. The invention eliminates the need for brake components. Only one load sensor is required. Nevertheless, it can be ensured that the vehicle is braked according to the load.

Claims

[1] Method for calculating the axle load of non-load-sensed axles of a vehicle, wherein the axle load of the non-load-sensed axle is calculated on the basis of a function f(µ) which describes the dependence of the longitudinal friction coefficient µ of a wheel of a non-load-sensed axle on the longitudinal slip value S, characterized by that the load of the non-load-sensing axle is determined during travel under suitable braking conditions, where suitable braking is defined as follows: 1.2 bar ≤ brake pressure ≤ 3.5 bar, curve radius ≥ 60 m, vehicle speed ≥ 20 km / h. [2] Method according to claim 1, characterized by that the axle load is calculated in the range of the function f(µ) in which the function f(µ) is approximately linear, whereby the gradient µ0 / S0 of the function is given. [3] Method according to claim 2, characterized by that the course of the function f(µ) is taken for values of the longitudinal slip smaller than S0. [4] Method according to claim 1 or 3, characterized by that the longitudinal slip S is determined as the differential slip between the wheels of a load-sensing axle and the wheels of a non-load-sensing axle. [5] Method according to one of the preceding claims, characterized by that the axle load of the non-load-sensing axle is determined based on the MAxis2=(v0−vAxis1)(v0−vAxis2)⋅MAxis1 is calculated, where M Achse2 the load on the non-load-sensing axle, M Achse1 the load on the load-sensing axle, v0 the vehicle speed, v Achse1 the average speed of the wheels on the load-sensing axle and v achse2 the average speed of the wheels on the non-load-sensing axle. [6] Method according to claim 2, characterized by that the approximately constant slope µ0 / S0 of the function f(µ) is determined experimentally. [7] Device for carrying out the method according to one or more of the preceding claims, which has a computing device which is designed in such a way that it calculates the axle load of the non-load-sensing axle on the basis of a function f(µ) which describes the dependence of the longitudinal friction coefficient µ of a wheel of a non-load-sensing axle on the longitudinal slip S, characterized by that the computing unit calculates the load of the non-load-sensing axle during travel under suitable braking conditions, where suitable braking is defined by: 1.2 bar ≤ brake pressure ≤ 3.5 bar, curve radius ≥ 60 m, vehicle speed ≥ 20 km / h. [8] Device according to claim 7, characterized by that the computing unit is designed in such a way that it calculates the axle load of the non-load-sensing axle in a range of the function f(µ) in which the function f(µ) is approximately linear, the gradient µ0 / S0 of the function being predetermined in this range. [9] Device according to claim 7 or 8, characterized by that it has sensors for directly or indirectly measuring the wheel speeds and / or the forces or moments acting on the wheel. [10] Device according to one of the preceding claims, characterized by that the computing unit calculates the axle load of the non-load-sensing axle based on the MAxis2=(v0−vAxis1)(v0−vAxis2)⋅MAxis1 calculated, where M Achse2 the load on the non-load-sensing axle, M Achse1 the load on the load-sensing axle, v0 the vehicle speed, v Achse1 the average speed of the wheels on the load-sensing axle and v Achse2 the average speed of the wheels on the non-load-sensing axle.

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