Spring devices – Vehicle – Comprising compressible fluid
Reexamination Certificate
2000-01-20
2001-05-01
Oberleitner, Robert J. (Department: 3613)
Spring devices
Vehicle
Comprising compressible fluid
C188S322500, C303S015000, C303S003000, C280S735000
Reexamination Certificate
active
06224044
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a level control system for a motor vehicle wherein the level control system includes air springs and each air spring is provided with a switchable valve for filling or venting (discharging) the corresponding air spring. A further switchable valve is provided by which each air spring can be connected to the atmosphere for venting. A first control unit controls the switchable valves for filling or venting the air spring.
BACKGROUND OF THE INVENTION
In recent times, modern motor vehicles have often been equipped with level control systems of the kind described above. These level control systems afford the advantage that the spacing of the vehicle chassis relative to a fixed reference point can be held constant independently of the state of loading of the vehicle. However, it is noted that modern level control systems are also burdened with a safety risk. For example, the situation can occur that a vehicle, which is equipped with a level control system, is heavily loaded. In this situation, the air pressure in the air springs must be increased by filling the latter in order to maintain the spacing of the vehicle chassis relative to the reference point constant. Correspondingly, after unloading the motor vehicle, the air pressure in the air spring must again be reduced by discharging the air spring. The filling and discharging of the air spring is controlled by the above-mentioned control unit in that this control unit transfers the switchable valves into a corresponding switching state. If a fault occurs in the first control unit during the loaded condition of the motor vehicle, then a discharge of the air springs is no longer possible, so that, after unloading the motor vehicle, the air pressure in the air springs can no longer be reduced. This has the consequence that the vehicle chassis is lifted relative to the reference point after the vehicle is unloaded. This can lead to the condition that the center of gravity of the motor vehicle after unloading lies very high so that the motor vehicle is in a dynamically unsafe driving condition.
A further safety risk can occur in an off-road vehicle equipped with a level control system. Accordingly, and to provide a large ground clearance of the off-road vehicle, the center of gravity of the vehicle can be brought to a very high level with the aid of the level control system. This takes place by filling the air springs with pressurized air. If the ground clearance of the off-road vehicle is no longer needed, then the air springs must be vented. The filling operation as well as the discharging operation are controlled by the above-mentioned control unit which transfers the switchable valves into a corresponding switching condition. A situation can occur wherein the off-road vehicle has a high ground clearance and a fault occurs in the first control unit which leads to a situation that the air springs can no longer be discharged. In such a situation, dropping the chassis of the off-road vehicle is no longer possible. The off-road vehicle is then in a dynamically unsafe driving condition because of the high center of gravity.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a level control system which ensures the safety of the motor vehicle even when the first control unit functions defectively or not at all.
The level control system of the invention is for a motor vehicle and includes: a plurality of air springs; a plurality of controllable first valves connected to corresponding ones of the air springs for filling and venting the respective air springs; a controllable second valve switchable to connect the air springs to the atmosphere for venting the air springs; a first control unit for controlling the controllable first and second valves to fill or vent the air springs; a second control unit for controlling the controllable first and second valves to fill or vent the air springs; the first control unit having means for transmitting check signals to the second control unit at respective time intervals; and, the second control unit having checking means for checking whether the second control unit receives each of the check signals from the first control unit and, when one of the signals expected from the first control unit is not received, the second control unit functioning to assume control of the controllable first and second valves so as to drive the first and second valves to bring the motor vehicle into a dynamically safe driving condition.
The time intervals at which the first control unit transmits signals to the second control unit can, for example, be regular time intervals. As an alternative, it is also possible that time intervals are defined in the second control unit and that the second control unit checks with a test device as to whether a signal is transmitted from the first control unit to the second control unit in each time interval.
The basic idea of the invention is that the first control unit of the level control system is provided with a second control unit which concludes that a fault is present when an expected signal from the first control unit is not received and the second control unit assumes control of the switchable valves of the level control system in such a manner that the motor vehicle can be transferred at any time into a dynamically safe driving condition.
The advantages achieved with the invention are especially that the safety of the motor vehicle is ensured even when the first control unit malfunctions because, in this case, no signals are transmitted by the first control unit to the second control unit and the second control unit then assumes the control of the switchable valves. A further advantage of the invention is that the additional costs which arise are low notwithstanding the increase in safety in the level control system because only a second control unit must be made available which assumes only a simple control function, namely, the transfer of the motor vehicle into a dynamically safe driving condition.
According to a first embodiment of the invention, the second control unit opens the switchable valves when it does not receive a signal expected from the first control unit so that each air spring of the level control system is connected to the atmosphere. In this embodiment, it is possible that the switchable valves of the level control system are not driven again by the second control unit and remain open. In this case, the air pressure in the air springs drops down to atmospheric pressure. The air springs can then no longer support the chassis independently of the loaded state so that the chassis sets down on the bumpers of the shock absorbers and therefore assumes the lowest possible center of gravity. The motor vehicle is in a dynamically safe driving condition because of this lowest possible center of gravity of the vehicle body. The advantage of this first embodiment of the invention is that the second control unit can be configured very simply because it needs to drive the switchable valves only once to open and the valves thereafter remain in the open condition. A further advantage of the embodiment is that the level control system requires no elevation sensors for control and therefore is cost effective.
According to another feature of the first embodiment, the second control unit maintains, by opening the switchable valves, the condition in which each air spring of the level control system is connected to the atmosphere and this condition is maintained over a pregiven time span. After the elapse of this pregiven time span, the second control unit closes the switchable valves. The pregiven time span is so dimensioned that the air springs discharge within this time span to the extent that the motor vehicle assumes the lowest possible level condition. In this feature too, the lowest possible level condition is characterized in that the air springs have been controlled down so far that the vehicle body of the motor vehicle sets down on the bumpers of the shock absorbers and the center of gravity of the vehicl
Heilenkötter Carsten
Matthies Thomas
Sommer Stefan
Continental Aktiengesellschaft
Nguyen Xuan Lan
Oberleitner Robert J.
Ottesen Walter
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