Method for operating an electronic brake system

Abstract

A method for operating an electronic brake system in a vehicle having at least two tires on an axle, wherein the vehicle has a center of gravity (SP) with a height (hSP), is disclosed. According to the method, the height (hSP) of the center of gravity (SP) is calculated and used as a parameter by the electronic brake system. An electronic control unit, an electronic brake system, and a vehicle including the same for carrying out the method are also disclosed.

Claims

1. A method for operating an electronic brake system in a vehicle having at least two tires on one axle, wherein the vehicle has a center of gravity (SP) with a height (h.sub.SP), said method comprising: providing a transverse acceleration sensor adapted to measure a transverse acceleration (a.sub.SP) of the vehicle; iteratively calculating the height (h.sub.SP) of the center of gravity (SP) as a parameter by the electronic brake system to determine whether a critical driving state is present, wherein iteratively calculating the height (h.sub.SP) of the center of gravity (SP) is performed by an electronic control unit and includes: estimating the height of the center of gravity of the vehicle, calculating a transverse acceleration based on the estimated height of the center of gravity of the vehicle, and comparing the calculated transverse acceleration with the measured transverse acceleration (a.sub.SP) from the transverse acceleration sensor, wherein, if the calculated transverse acceleration does not approximately correspond to the measured transverse acceleration (a.sub.SP), repeating the iterative calculation by estimating a different height of the center of gravity of the vehicle; and operating a brake control unit of the vehicle while the vehicle is cornering based on the iteratively calculated height (h.sub.SP) of the center of gravity (SP) of the vehicle to prevent the vehicle from overturning.

2. The method as claimed in claim 1, wherein the height (h.sub.SP) of the center of gravity (SP) is further determined as a function of a difference between wheel speeds at a wheel on an inside of a bend and a wheel on an outside of the bend when cornering.

3. The method as claimed in claim 1, wherein the height (h.sub.SP) of the center of gravity (SP) is iteratively calculated as a function of track width (s) and axle load (m).

4. The method as claimed in claim 1, wherein the height (h.sub.SP) of the center of gravity (SP) is further determined as a function of data from sensors for monitoring the state of the tires.

5. The method as claimed in claim 1, wherein the calculation of the height (h.sub.SP) of the center of gravity (SP) is further carried out as a function of measured values occurring during straight-ahead travel of the vehicle using a systematic error or a constant offset of the calculation is determined in advance.

6. The method as claimed in claim 5, wherein in the case of straight-ahead travel of the vehicle the systematic error or the constant offset of the calculation is determined in advance by defining a reference signal as zero or other known value.

7. An electronic control unit for a vehicle having a transverse acceleration sensor and a center of gravity (SP) with a height (h.sub.SP), the electronic control unit being adapted to perform the following method steps: iteratively calculate a height (h.sub.SP) of the center of gravity (SP) to determine whether a critical driving state is present by estimating the height (h.sub.SP) of the center of gravity (SP), calculating a transverse acceleration based on the estimated height of the center of gravity (SP) and comparing the calculated transverse acceleration with a measured transverse acceleration (a.sub.SP) from the transverse acceleration sensor, wherein, if the calculated transverse acceleration does not approximately correspond to the measured transverse acceleration (a.sub.SP), repeating the iterative calculation by estimating a different height (h.sub.SP) of the center of gravity (SP); and cause operation of a brake control unit of the vehicle while the vehicle is cornering based on the iteratively calculated height (h.sub.SP) of the center of gravity (SP) of the vehicle to prevent the vehicle from overturning.

8. A vehicle having a center of gravity (SP) with a height (h.sub.SP), the vehicle comprising: at least two tires on one axle; a transverse acceleration sensor to measure a transverse acceleration (a.sub.SP) of the vehicle; an electronic control unit adapted to perform the following method steps: iteratively calculate the height (h.sub.SP) of the center of gravity (SP) to determine whether a critical driving state is present, wherein iteratively calculating the height (h.sub.SP) of the center of gravity (SP) includes: estimating the height (h.sub.SP) of the center of gravity of the vehicle (SP), calculating a transverse acceleration based on the estimated height of the center of gravity (SP) and comparing the calculated transverse acceleration with a measured transverse acceleration (a.sub.sp) from the transverse acceleration sensor, wherein, if the calculated transverse acceleration does not approximately correspond to the measured transverse acceleration (a.sub.SP), repeating the iterative calculation by estimating a different height (h.sub.SP) of the center of gravity (SP); and operate a brake control unit of the vehicle while the vehicle is cornering based on the iteratively calculated height (h.sub.SP) of the center of gravity (SP) of the vehicle to prevent the vehicle from overturning.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in greater detail below with reference to the accompanying drawing FIGURES, in which:

(2) FIG. 1 shows a simplified rear view of a vehicle 10 with two rear wheels 11, 12 and a box-shaped body 13.

DETAILED DESCRIPTION

(3) Referring to FIG. 1, the vehicle 10 can be a traction vehicle or a trailer vehicle and is equipped in a manner known per se with compressed air brakes, wheel speed sensors, an electronic brake system, a brake control unit with a transverse acceleration sensor and with travel sensors or bellows pressure sensors for determining an axle load.

(4) Cornering is assumed, with the wheel 11 as a wheel on the inside of the bend and the wheel 12 as a wheel on the outside of the bend. In this context, a transverse acceleration a.sub.SP acts on a center of gravity SP of the vehicle 10. The center of gravity SP is at a height h.sub.SP.

(5) The center of gravity SP is assumed here to be a location of an axle load acting on the wheels 11, 12. The axle load results in tire deformation at the wheels 11, 12, which tire deformation depends on the transverse acceleration a.sub.SP which is occurring. The effective tire radius r.sub.a of the wheel 12 on the outside of the bend decreases, while the effective tire radius r.sub.i of the wheel 11 on the inside of the bend increases somewhat. This effect is used for the calculation of the height h.sub.SP of the center of gravity SP.

(6) An exemplary calculation example for the determination of the height h.sub.SP from the tire deformation and the resulting difference in the wheel speeds during cornering is represented below: The height h.sub.SP of the center of gravity of the vehicle is to be calculated by way of example on the basis of the data of one axle Measured speed of the vehicle at the center of gravity is

(7) $v_{\mathrm{SP}}=11\frac{m}{s}$ (can be determined from an average value of the wheel speeds, derived from the values of wheel speed sensors of the respective axle or of all of the wheel speed sensors) Measured transverse acceleration during constant cornering is a.sub.SP=0.15 g=1.47 m/s.sup.2 (from the signals of a transverse acceleration sensor) Measured axle load is m=7000 kg, determined via a travel sensor in the chassis or by means of bellows pressure and travel sensor in the case of air suspension, or determined via evaluation of the slip behavior of the wheels Track width is s=2.0 m (vehicle constant or obtained from vehicle parameterization) Tire radius is r.sub.0=0.517 m (measurement in a stationary state or constant dependent on the type of tire or basic value obtained from vehicle parameterization, fine adjustment and determination in the case of straight-ahead travel via internal functions) Tire rigidity is

(8) $C_R=1\text{/}\left(2.1*{10}^6\right)\frac{m}{N}$ (constant dependent on the type of tire) Wheel differential speed V.sub.M (outer/inner) measured during cornering=0.37 m/s.

(9) The vehicle drives at 11 m/s. During cornering with a transverse acceleration of 0.15 g, a difference V.sub.M between the wheel speeds of 0.37 m/s is measured between the wheel on the inside of the bend and the wheel on the outside of the bend.

(10) The theoretical difference between the wheel speeds calculated from the track width and the transverse acceleration is V.sub.A:

(11) $\begin{array}{cc}{V}_A=v_{\mathrm{Aa}}-v_{\mathrm{Ai}}=\frac{a_{\mathrm{SP}}}{v_{\mathrm{SP}}}s=0.26m\text{/}s& \left(\mathrm{Equation}1\right)\end{array}$

(12) The difference V.sub.R between the theoretical difference V.sub.A between the wheel speeds and the measured difference V.sub.M between the wheel speeds is here:
V.sub.R=0.37 m/s0.26 m/s=0.11 m/s(Equation 2)

(13) The reason for the difference V.sub.R is the tire deformation during cornering, which deformation brings about a change in the tire radius. The tire deformation is caused by the outwardly directed centrifugal force owing to mass inertia. A reduction in the tire radius occurs at the wheels on the inside of the bend and an increase in the tire radius on the outside. The higher the axle load and the center of gravity, the greater the tire deformation. The tire deformation and axle load can be calculated and measured, and the height of the center of gravity can then be calculated.

(14) The difference V.sub.R also results from the speeds of the wheel speeds v.sub.Ra and v.sub.Ri measured on the outside of the bend and the inside of the bend, caused by tire deformation:
v.sub.Rav.sub.Ri=V.sub.R(Equation 3)

(15) The speed (translatory wheel speed), tire radius and rotational speed are dependent on one another:

(16) $\begin{array}{cc}{V}_R=*r& \left(\mathrm{Equation}4\right)\\ =\frac{v_{\mathrm{SP}}}{r_0}& \left(\mathrm{Equation}5\right)\end{array}$

(17) Equation 4 with equation 5 yields:

(18) $\begin{array}{cc}\frac{1}{2}*V_R=\left(\frac{v_{\mathrm{SP}}}{r_0}*r\right)*\frac{1}{2}\mathrm{and}& \left(\mathrm{Equation}6\right)\\ r=V_R*\frac{r_0}{v_{\mathrm{SP}}}=0.11\frac{m}{s}*\frac{0.517m}{11\frac{m}{s}}0.005m& \left(\mathrm{Equation}7\right)\end{array}$

(19) The change r in radius is obtained from the change F in the wheel load and the tire rigidity C.sub.R:

(20) $\begin{array}{cc}r=\frac{F}{C_R}\mathrm{with}{C}_R=1\text{/}\left(2.1*{10}^6\right)\frac{m}{N}& \left(\mathrm{Equation}8\right)\end{array}$

(21) And also yields:

(22) $\begin{array}{cc}F=\frac{r}{C_R}=0.005m*2.1*{10}^6\frac{N}{m}=10500N& \left(\mathrm{Equation}9\right)\end{array}$

(23) The change F in wheel load per wheel at an axle is obtained from:

(24) $\begin{array}{cc}F=\frac{a_{\mathrm{SP}}*m*h_{\mathrm{SP}}}{s}& \left(\mathrm{Equation}10\right)\end{array}$

(25) The calculated height of the center of gravity follows from this:

(26) $\begin{array}{cc}{h}_{\mathrm{SP}}=\frac{F*s}{a_{\mathrm{SP}}*m}=\frac{10500N*2m}{1.47m\text{/}{s}^2*7000\mathrm{kg}}2.04m& \left(\mathrm{Equation}11\right)\end{array}$

(27) It is possible to assume a height of the center of gravity in the region of approximately 2 m. The method serves to estimate the vehicle properties. It is sufficient here to differentiate, for example, between a fully loaded vehicle with a very low center of gravity (steel plates loaded), a vehicle with a very high center of gravity. This information can be made available to e.g. stability regulating functions which can adjust their method of functioning (e.g. activation limits or intervention intensity) in this way to the individual vehicle with a load.

(28) In a second exemplary embodiment, the height h.sub.SP of the center of gravity SP is determined by iteration. It is possible to use for this the transverse acceleration a.sub.SP. The equation 10 is resolved according to the transverse acceleration a.sub.SP. An estimated value is assumed for the height h.sub.SP, e.g. a relatively improbable high value of 3.5 m for the vehicle. The other values for F, m and s are as in the first exemplary embodiment. This results in a calculated transverse acceleration a.sub.SP of 0.857 m/s.sup.2 and therefore a significant difference from the transverse acceleration of 1.47 m/s.sup.2 measured in the first exemplary embodiment.

(29) In a subsequent step, a relatively low estimated value of the height h.sub.SP is used, e.g. 3 m. With this estimated value a calculated transverse acceleration a.sub.SP of 1 m/s.sup.2 is obtained. There is still a significant difference from the measured transverse acceleration a.sub.SP of 1.47 m/s.sup.2. The iteration is therefore carried out until the calculated transverse acceleration and the measured transverse acceleration correspond approximately. The estimated value last used for the height h.sub.SP then corresponds approximately to the actual height of the center of gravity.

(30) In addition, a calibration process can be carried out before the calculation of the height of the center of gravity. In the case of straight-ahead travel of the vehicle, no transverse acceleration occurs. If, nevertheless, a transverse acceleration which is different from zero is measured, this deviation can be included as a systematic error in the further calculations. The straight-ahead travel can be determined, for example, by comparing the measured values of wheel speed sensors on both sides of the vehicle, even in conjunction with measured values of tire pressure sensors.