Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Reexamination Certificate
1998-10-28
2001-03-06
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
C303S186000, C303S123000
Reexamination Certificate
active
06196640
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for coordinating braking forces between two connected units forming a vehicle train.
A method for providing coordination of braking forces in connected units of a vehicle train is disclosed for example in EP 0 532 863 B1 (U.S. Pat. No. 5,333,940). The method disclosed therein is directed to use with a towing vehicle and a trailer which together constitute two connected units in a vehicle train subjectable to independent braking forces. The known method attempts to obtain even distribution of braking force through adaptive influence exerted upon the trailer braking pressure which generates the braking force in the trailer controlled from the towing vehicle.
Control of the trailer braking pressure is based upon slip-encumbered wheel speed signals which are obtained from wheels on both units of the vehicle train and transmitted for central evaluation within the towing vehicle as speed signals corresponding to a particular unit of the vehicle train.
The different braking forces on the slipping wheels, analysis of which provides a basis for adaptively influencing the trailer braking pressure, are assumed by applying a physical law relating braking force and a difference between the various measured slip-encumbered wheel signals. In accordance with the known method, the braking pressure of the trailer is adaptively influenced when a difference is detected between the speed signals of the various wheels of a unit or between the speed signals of the towing vehicle and the trailer calculated from same, in such manner that the difference between the speed signals is minimized, and braking forces are thereby divided nearly equally between the towing vehicle and the trailer.
The above described method requires that at least one speed signal from each unit of the vehicle train, i.e. the towing vehicle and the trailer, be transmitted to an electronic control device which centrally evaluates the speed signals and effects adaptive influence of the trailer braking pressure to properly coordinate the braking forces.
Since the vehicle train may at times be very large, a substantial time offset may occur between the speed signals, caused for example by running times during signal transmission from the trailer to the towing vehicle, or due to different filtering processes of the wheel speed signals in the units of the vehicle train.
As a consequence, practice of the known method may at times result in insufficient coordination of the braking forces between the towing vehicle and the trailer, resulting in unequal brake lining wear for different wheels, extended braking distance and, under certain conditions, hazardous braking.
It is therefore an object of the invention to provide a method for the coordination of braking forces between two connected units which comprise a vehicle train, in which precise control is made possible even when speed signals of different kinds are used.
SUMMARY OF THE INVENTION
In accordance with these and other objects of the invention, there is provided a method for the coordination of braking forces between two units connected to one another in a vehicle train, for example a towing vehicle and a trailer attached thereto. Each of the two units includes a braking system which produces a braking force when imparted a braking control value. The inventive method imparts the braking system of each of the two units with a braking control value having a value based upon a starting value upon start-up of the towing vehicle. An additional braking control value for transmission between units of the vehicle train is also imparted a value. Slip-encumbered wheel signals are obtained from wheels located on each of the two units, and a unit speed for each of the two units is derived from the slip-encumbered wheel signals corresponding to a respective one of the two units. For each of the two units a derivative with respect to time of the unit speed is determined. A differential value is then calculated during at least a time segment of a brake application, the differential value being a difference between the derivatives over time of each of the units. The braking control value for each unit is then altered on the condition that a calculated value of the differential value lies in a range defined by a predetermined lower limit and a predetermined upper limit.
In addition to finding application in coordination of braking forces between a towing vehicle and a trailer, the invention is also useful in coordinating braking forces within each of the individual units, i.e. the towing vehicle and/or the trailer itself. Depending on the particular application of the invention, the units of the vehicle train are therefore understood to be the combination of the towing vehicle and the trailer, or alternatively the different axle groups within each of the towing vehicle and/or the trailer. Multiple application of the invention within the vehicle train is furthermore deemed advantageous.
The invention provides the advantage that any combination of vehicle units can be coupled together to form a vehicle train, even units produced by different manufacturers and equipped with components, such as for example braking systems and/or wheel speed detection means, which operate differently from one another.
By utilizing a control program which involves very few computing steps and which can be executed by a microprocessor, the method in accordance with the invention may be practiced in a simple manner. Furthermore, the invention advantageously permits use of the wheel speed sensing means already present in vehicle trains of newer construction for the detection of the slip-encumbered wheel speed signals. By obviating installation of additional sensing means, the method in accordance with the invention may be practiced economically.
When a significant difference occurs between the braking forces of the units of the vehicle train, coordination of the braking forces is implemented by alteration of braking control values which are normally provided to produce the braking forces. Such braking control values include, for example, pneumatic or hydraulic braking pressures, or alternatively electrical signals.
In order to coordinate the braking forces it is possible, in principle, to modify the braking control values corresponding to the two units of the vehicle train, such that one braking control value is reduced while the value of the remaining unit is increased to an equal extent. In an advantageous embodiment in accordance with the invention, however, only one of the two control values is changed relative to the other braking control value, the latter being set for a chosen unit of the vehicle train designated as a reference unit. As a result, the computations required to carry out the method in accordance with the invention are minimized.
In accordance with an embodiment of the invention, a magnitude is used as a measure of the difference between braking forces present on the two units of the vehicle train, referred to herein as a “differential value”. The differential value represents a computation magnitude which has no immediate relationship with physical force measured in Newtons.
In a particularly advantageous embodiment, the differential value is determined either as an absolute difference, i.e., a difference between the derivatives over time of the vehicle unit speeds, or alternatively as a relative difference, i.e., as a quotient of the derivatives over time of the vehicle unit speeds. This feature permits the method to be compatible with a wide range of different type control devices, for example, various microprocessors. Through selection of a calculating step specifically suited to the particular microprocessor being used for determination of the differential value, i.e., a step involving either subtraction or division, the method can be optimally adapted to the individual performance capabilities of the microprocessor, thereby maximizing efficiency by shortening computing time.
In a further advantageous embodiment in accordance w
Oberleitner Robert J.
Proskauer Rose LLP
Siconolfi Robert A.
WABCO GmbH
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