Land vehicles – Suspension modification enacted during travel – Riding or suspension height
Reexamination Certificate
2000-03-24
2001-07-24
Dickson, Paul N. (Department: 3618)
Land vehicles
Suspension modification enacted during travel
Riding or suspension height
C280S006157
Reexamination Certificate
active
06264213
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Priority is claimed under 35 U.S.C. §119 with respect to German Patent Application No. 199 14 647.0-21 filed on Mar. 31,1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a suspension system for land vehicles, in particular non-track-bound motor vehicles, with a sensor system which detects the actual values of the positions of the vehicle wheels relative to the vehicle body or chassis and longitudinal and/or transverse accelerations of the vehicle, and with a ride-height control system which controls control elements or assemblies so as to change the actual position of the wheels as a function of a set/actual value comparison between variably specifiable set values for the positions of the wheels and averages over time of the actual values of the abovementioned positions.
2. Description of the Related Art
A suspension system of this kind forms the subject-matter of DE 41 38 831 A1. Here, the signals representing the longitudinal and transverse accelerations of the vehicle are processed in such a way that the pitching or rolling angle of the body during longitudinal or transverse acceleration is reduced.
Suspension systems of the abovementioned type can be of numerous different design configurations.
For example, a vehicle can have any passive suspension system, for example one with mechanical springs and, in parallel with this, a controllable additional suspension system, by means of which additional forces dependent on the vehicle loading can be produced in order to keep the vehicle body at a specified level relative to the vehicle wheels, to a very large extent independently of disturbing forces.
The prior art also includes pneumatic spring systems whose pneumatic spring units, generally pneumatic bellows, can be connected to a pneumatic pressure source and/or to atmosphere by a corresponding control system, making it possible to establish a specified level by supplying or discharging air to or from the pneumatic spring unit.
In hydropneumatic suspension systems, hydraulic displacer units are arranged between the vehicle body and the vehicle wheels, their displacer working space communicating with a, generally pneumatic, spring energy store. The vehicle body can be raised or lowered relative to the wheels or to individual wheels by supplying or discharging hydraulic medium to or from the hydraulic displacer unit, thus once again allowing a specified level to be established.
Finally, it is possible on fundamentally any suspension systems, particularly those with mechanical spring elements, to arrange in series with each or with specified spring elements a hydraulic displacer unit which forms an adjustable body-side or wheel-side abutment for the respective spring element. Here, it is possible, by supplying or discharging hydraulic medium, to perform adjustment of the height of the body relative to the respective vehicle wheels and hence to achieve ride-height control.
To keep down the control outlay required and, in particular, the power requirement for the control elements or assemblies for changing the actual position of the wheels relative to the body, DE
35
25
367
Al discloses subjecting the actual-value signals for the position of the vehicle wheels relative to the body to low-pass filtering. This ensures that only correspondingly slow or prolonged level changes are eliminated and that the control system does not respond to normal suspension travel. Here, use is made of the fact that low-pass filtering of a signal leads to averaging of the signal over time, the period of time over which the averaging is carried out being determined by the limit frequency of the low-pass filter.
The present invention is directed towards one or more of the problems set forth above.
BRIEF SUMMARY OF THE INVENTION
It is then the object of the invention to ensure optimum operating behaviour in suspension systems with slow-acting ride-height control.
According to the invention, this object is achieved by virtue of the fact that movements of the body to be expected on the basis of longitudinal and/or transverse accelerations of the vehicle are not eliminated since the set values are changed in accordance with the movement of the body to be expected.
The invention is based on the general idea of not eliminating level changes initiated by accelerations of the vehicle.
This takes account of the fact that a slow-operating ride-height control system is capable of only delayed elimination of the pitching movements which occur during braking or acceleration maneuvers of the vehicle and of the rolling movements of the vehicle body which occur during cornering. This can lead to very undesirable phenomena. If, for example, a ride-height control system responds during braking of the vehicle and counteracts the tendency of the front of the vehicle to dip and the tendency of the rear of the vehicle to rise, this results temporarily in a state in which the level of the front of the vehicle is significantly above, and the level of the rear of the vehicle is significantly below, a desired set value upon completion of the braking maneuver, with the result that the ride-height control system has to intervene again.
The invention furthermore takes account of the fact that, in modern vehicle designs, predetermined changes in the camber and track of the wheels generally occur during pitching and/or rolling movements of the vehicle body in order to effect appropriate support for the respective driving state of the vehicle on the roadway. Here, a ride-height control system could lead in certain circumstances to unwanted impairment of the road-holding of the vehicle.
Finally, it is advantageous that, by virtue of the measures according to the invention, the power requirement for the ride-height control system can be further significantly reduced. This makes it possible to make available suspension systems with ride-height control even for vehicles which should or must operate in a particularly energy-saving manner.
Otherwise, attention is drawn as regards preferred features of the invention to the claims and to the following explanation of the drawing, with reference to which particularly preferred variant embodiments of the invention are described.
REFERENCES:
patent: 5684698 (1997-11-01), Fujii et al.
patent: 35 25 367 A1 (1985-07-01), None
patent: 41 38 831 A1 (1991-11-01), None
patent: 530755-A1 (1993-03-01), None
patent: 60-255514 (1985-12-01), None
Calcaterra Mark P.
Daimler-Chrysler AG
Dickson Paul N.
Fleming Faye M.
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