Spring devices – Vehicle – Comprising compressible fluid
Reexamination Certificate
2000-12-08
2002-10-29
Rodriguez, Pam (Department: 3683)
Spring devices
Vehicle
Comprising compressible fluid
C267S064280, C280S006157, C280SDIG001, C701S037000
Reexamination Certificate
active
06471196
ABSTRACT:
FIELD OF THE INVENTION
The invention relates a method for controlling (open loop or closed loop) the level of a vehicle body of a motor vehicle by means of a level control system having actuators with which the level of the vehicle body can be lowered by discharging an actuating means from the actuating elements. The level control system also includes a control unit which carries out the following method steps: determining the level of the vehicle body relative to a reference point; and, initiating a discharge operation of the vehicle body when the determined level lies above a pregiven level.
BACKGROUND OF THE INVENTION
Modern motor vehicles often have a level control system, for example, in the form of an air-spring system which has actuators in the form of air springs. A pregiven level is stored in the control unit of the level control system. The vehicle body is intended to assume this level compared to a fixed reference point. The pregiven level can, if required, be adapted by the driver of the motor vehicle to the actual driving situation. If, for example, an especially large ground clearance of the motor vehicle is needed offroad, then the driver can, for example, pregive a correspondingly high level in the control unit via a switch on the dashboard.
Level control systems afford the advantage that the pregiven level can be maintained independently of the loading condition of the motor vehicle by lowering or lifting the vehicle body. Furthermore, the vehicle body can also be lowered to a low level, for example, in order to facilitate a simple loading of the vehicle.
However, in a motor vehicle having a level control system, the following problems can occur. The vehicle body of the motor vehicle can seat on the ground, for example, on snow or on the ground when the vehicle is offroad. The wheels of the motor vehicle then drop away relative to the vehicle body. As a consequence of this situation, the actual level of the vehicle body can lie higher than the level, which is pregiven by the control unit, so that the control unit initiates a discharge operation of the vehicle (for example, by evacuating pressurized air out of the air springs of an air-spring system) in order to compensate the actual level to the pregiven level. This process increases the seating of the vehicle on the ground so that an unhindered further travel of the vehicle is not possible.
Another problem results when the motor vehicle is raised by means of a lift. In this case, the wheels of the vehicle deflect completely downwardly so that the vehicle body assumes a maximum level clearly above the level pregiven by the control unit. The control unit then initiates a discharge operation via which the actual level of the vehicle body is intended to adapt to the pregiven level. This takes place in that an actuating means (hydraulic liquid is evacuated in a hydraulic level control system and pressurized air is released from air springs in a pneumatic level control system) is released from the actuators of the level control system. Since the vehicle body is not lowered, the actuators are substantially emptied until only a minimum of the actuating means is held in the actuators. When reaching the minimum, a further discharge of the actuating means is prevented by a valve. When the motor vehicle is taken from the lift, the vehicle body lowers below the pregiven level because of the low level of actuating means in the actuators so that the actuators must again be filled with the actuating means in order to lift the vehicle body to the pregiven level. This is time-intensive and furthermore loads the components of the level control system with which the actuating means is conducted into the actuators.
The same problem results for a single actuator of the level control system when the wheel, which is assigned to this actuator, is lifted with a jack.
In summary, it can be seen that in specific critical situations of the motor vehicle (namely, when the vehicle body is seated on the ground or is on a lift) a lowering of the vehicle body or an emptying of the actuators of the level control system is initiated by the control unit even though this is not wanted in these situations.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for controlling the level of a vehicle body of a motor vehicle by means of a level control system wherein a seating of the vehicle body on the ground or on a lift is detected as early as possible in order to avoid an unwanted lowering of the vehicle level.
The method of the invention is for controlling the level of a vehicle body of a motor vehicle with a level control system having a plurality of actuator elements with which the level of the vehicle body can be lowered by discharging an actuating means from the actuator elements. The level control system includes a control unit and the method includes the steps of: determining a first level of the vehicle body relative to a reference point directly before a discharge operation; initiating a discharge operation of the vehicle body when the first level lies above a pregiven level; after initiating a discharge operation, checking in the control unit as to whether the vehicle body has lowered from the first level in accordance with an input; and, interrupting the discharge operation when the vehicle body has not lowered from the first level in accordance with the input.
A discharge operation is understood to mean an operation wherein the current level of the vehicle body is intended to be adapted to a level, which is pregiven in the control unit, by discharging actuating means from the actuators of the level control system until this pregiven level is reached. Correspondingly, the interruption of a discharge operation is understood to be a prevention of a further discharge of actuating means from the actuators of the level control system even though the current level of the vehicle body is above the level pregiven in the control unit. The current level of the vehicle body is preferably determined by one or several elevation sensors.
The basic idea of the invention is that, after initiating a discharge operation via the control unit, a check is made after a short time span as to whether the vehicle body has lowered from a determined level in accordance with an input and that the control unit interrupts the discharge operation when this is not the case.
The advantages achieved with the invention are especially seen in that a discharge operation is interrupted early by the control unit when this control unit determines that the vehicle body of the motor vehicle has not lowered from the level, which was determined before the discharge operation, in accordance with an input, because, for example, the vehicle body of the motor vehicle is seated on the ground or is raised by a lift or a vehicle is on the lift with the wheels free. A vehicle body which is seated on the ground is therefore not lowered further or lowered further only minimally and a “more intense landing” of the vehicle body is thereby prevented.
A further advantage of the invention is seen in that a touchdown of the vehicle body on the ground or on the lift is automatically detected by the control unit and is interrupted. An active intervention of an operator is thereby not necessary. A further advantage of the invention is that, to execute the method of the invention, only components are necessary which are anyway present in level control systems so that the cost of the level control system is not increased notwithstanding the added comfort and safety provided.
According to another feature of the invention, the control unit interrupts the discharge operation even when the vehicle body is lowered in accordance with an input after initiation of the discharge operation but, after initiating the discharge operation, the actuating means pressure or at least a wheel contact force has been reduced beyond a pregiven amount. Based on the reduction of the actuating means pressure or the wheel standup force, the control unit determines that the vehicle has touched down, fo
Continental Aktiengesellschaft
Ottesen Walter
Rodriguez Pam
LandOfFree
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