Fluid-pressure and analogous brake systems – Speed-controlled – And traction control
Reexamination Certificate
2002-01-09
2003-09-09
Schwartz, Christopher P. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
And traction control
Reexamination Certificate
active
06616250
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method of controlling the performance of a vehicle in which the forces acting upon wheels and tires are detected by wheel force and tire sensors and are used as controlled variable(s) for an automotive servo-system, such as ABS, TCS, EHB, EMB etc. The variables are referred to in order to determine and/or modulate the brake pressure in the wheel brakes of the wheels and/or the driving torque.
A lot of similar methods controlling the performance of a motor vehicle are known which use the tire sensors for detecting the forces and moments acting upon the tires. While in EP 04 441 09 B1 the deformation of the tread area of the tire—the tread contact area—is monitored, in WO 96/10505 the deformation of the side wall—the torsion deformations—of a tire is detected by measuring a space of time between the passing of at least two marks on the rotating wheel which are located on different radii to the rotation axis. WO 97/44673 describes a tire sensor detecting a change of the phase position between measuring signals emitted by measuring elements due to forces acting upon the wheel in case of deformation and evaluating said change of the phase position as dimension for the moments and/or the actual coefficient of friction. In automotive servo-systems the forces acting upon the tire in such a way and detected by the tire sensor are referred to so as to determine and/or modulate the brake pressure in the wheel brakes of the wheels.
Apart from these automotive servo-systems which control the determination and/or modulation of the brake pressure in the wheel brakes of the wheel on the basis of forces detected with tire sensors and/or moments between the tire and the roadway, automotive servo-systems, such as ABS and/or TCS are referenced which are equipped with conventional sensor devices for detecting the four wheel speeds of a motor vehicle. If a wheel during braking or accelerating exceeds the optimal slippage area leading to the risk that the wheels block or spin, the ABS or TCS control automatically intervenes.
With said referenced automotive servo-systems, such as ABS or TCS, the information needed for the control is obtained by determining the rotational performance of the single wheels, where a vehicle reference speed is determined by logical linkage of the wheel rotation signals which approximately reflects a motor vehicle speed. Said vehicle reference speed is then referred to determine the wheel slippage and other controlled variables and finally to control the brake pressure in the wheel brakes of the wheels. Known ABS or TCS servo-systems determine the wheel slippage up to a slip limit value, i.e. the critical slip value, up to which the transmittable brake force or the drive torque only increases, by braking or driving the vehicle in excess of said critical slip, whereupon the circumferential wheel speed changes with regard to the vehicle reference speed in such a way that the tendency of the wheels to block or spin is detected. The control cycles consisting of the phases which appear in any sequence: maintain pressure, build up pressure, reduce pressure, can be repeated several times per wheel in presence of an ABS or TCS servo-system.
Since the critical slip has to be exceeded in order to recognize the slip limit value, the braking or driving performance in each ABS or TCS control cycle is reduced. At the same time the stopping distance is increased. By exceeding the critical slip the lateral forces on the wheel are reduced. The vehicle stability and the maneuverability of the vehicle is reduced.
SUMMARY OF THE INVENTION
It is therefore desirable to have a method of controlling the performance of a motor vehicle in which sensors detect or determine the slip limit value or a slip value on the wheel suitable for ABS or TCS control without having to exceed the slip limit value or critical slip value for detecting or determining it.
Tire sensors detecting the forces transmitted by the wheel onto the roadway and acting upon the tire may in principle be used as controlled variables in an ABS or TCS servo-system since they detect the forces immediately at the point where they develop. But since there are &mgr;-slip curves in which the coefficient of friction (&mgr;) increases in proportion to the slippage thus increasing the force between tires and roadway in case of blocking wheels, the slip values suitable for ABS or TCS control cannot be determined clearly by means of the forces detected with the tire sensors.
It is an object of the present invention to create a method of controlling the performance of a vehicle which allows to optimize the influence on the movement of the vehicle.
The particularity of the method consists in that the working point and/or operative range of forces detected by means of wheel force or tire sensors is adjusted by the detected wheel slippage at the beginning of an ABS or TCS control action. The wheel slippage is determined subject to values measured and/or calculated with conventional sensors, e.g. wheel speeds and motor vehicle reference speeds, and the evaluation of the dynamic rotational performance of the wheel. The working point and/or the operative range of the controlled variables detected with wheel force or tire sensors is adjusted by the simultaneous determination of the forces at the critical wheel slippage and/or at least one wheel slippage and at the wheel reversing point of the speed or its derivation in the first ABS or TCS control cycle. The maximum force is determined when the brake or drive slip or the negative (ABS) or positive (TCS) acceleration begins to increase, i.e. within the range of the critical slip value during the first ABS or TCS control cycle. Furthermore the minimum force is determined in case of a positive acceleration from the brake slip or a negative acceleration from the propulsive slip and re-acceleration from the wheel slippage. The working point and/or operative range of the controlled value “force” is adjusted by balancing the evaluated rotational performance of the single wheels and the vehicle reference speed during the critical slip with the forces determined by the wheel force or tire sensors, especially the longitudinal forces. Thus the present invention is based on the finding that the working point and/or operative range of the forces detected by means of wheel force or tire sensors is recognized at the beginning of the first control cycle by detecting the wheel slippage, i.e. the critical slippage, by means of the speed performance and the vehicle reference speed in order to determine definitely the frictional connection between tire and roadway and exclude errors of the controlled variables basing on &mgr;-slip curves in which the coefficient of friction (&mgr;) and thus the force between the tires and the roadway increases in proportion to the slip in case of blocking or spinning wheels.
The method according to the present invention allows that the working point and/or operative range of the forces acting upon the vehicle wheel is adjusted within the ABS or TCS control range of the wheel slippage. Therefore the rotational performance of the wheels in the unstable area is detected for the first time at the beginning of the control process and evaluated, if necessary, by including further variables. Afterwards the subsequent ABS or TCS control cycles, i.e. the control of the wheel slippage, are adjusted below the critical slip value up to the critical slip (slip limit value) by means of the forces detected with wheel force or tire sensors, as long as no external influences, as for example, changes of the coefficient of friction, shift the working point and/or the operative range and the slip limit value is exceeded.
According to a particularly advantageous embodiment of the present invention, the determination of the working point and/or operative range described above begins from the start so that the working point and/or operative range is adjusted according to the new parameters of condition variables.
It is a further advant
Batistic Ivica
Fennel Helmut
Continental Teves, AG & Co.oHG
Nguyen Xuan Lan
Schwartz Christopher P.
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