Patent Publication Number: US-6220026-B1

Title: Active control system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an active control system of the type including a fluid-operated piston-cylinder unit for moving a movable member, wherein provision is made for opening a fluid connection to the unit in emergency conditions to permit axial displacement of the piston rod relative to the cylinder. 
     2. The Prior Art 
     FIG. 7 of DE 42 24 132 discloses an active door-locking system that has a piston-cylinder unit which is connected by connecting lines to a pump unit. An on-off valve permits regulation of the flow of pressure medium into a working chamber of the piston-cylinder unit. Such a system allows a door or tailgate motion in a motor vehicle, for example, to be performed very conveniently by operation of the piston-cylinder unit. 
     In the case of such active control systems, it should be considered that fingers or objects may possibly be pinched when, for example, a vehicle is being loaded. Physical harm to humans or damage to the goods loaded would be the unfortunate consequence. 
     In addition, the supply of energy may be interrupted, so that the control system is no longer capable of performing the control motion automatically. In such circumstances, the possibility that the door or tailgate cannot be opened must be avoided, because otherwise one could be trapped in the vehicle. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide measures by which the above-described problems in the prior art can be eliminated. 
     According to the invention, this object is accomplished in that the control system is provided with a pressure-limiting valve which, in emergency operation, opens to permit a displacement motion of the piston rod. The piston rod can be initially displaced by manual force, so as to release the pressure-limiting valve and permit free displacement of the piston rod. A condition in which the door cannot be opened or closed is thereby avoided. 
     An additional part of the object is accomplished in that the pressure-limiting valve is connected controlwise with the on-off valve, and the on-off valve, in the event of unduly increased pressure in the piston-cylinder unit resulting from a displacement motion of the piston rod, switches to the on position, at which the piston rod, preloaded by a spring force, carries out an opposite displacement motion. Thus, even without additional manual force or pump operation, the piston-cylinder unit is moved in the opposite direction, thereby providing protection not only against pinching, but also advantageously a release motion. Controlwise, this means that a limit switch for example recognizes the switch position of the pressure-limiting valve, and transmits this information to the on-off valve electrically, pneumatically or hydraulically as a control signal. 
     In order to reduce the manual force required in emergency operation to a minimum and at the same time ensure reliable normal operation, the pressure-limiting valve has two pressure threshold values at which it will be moved to and held in the open position. The two pressure threshold values result from the provision of two pressurized surfaces of unlike size on the pressure-limiting valve piston. 
     In order to obtain as simple as possible a control system, the piston-cylinder unit is preferably designed as a single-acting hydraulic cylinder. 
     In order to prevent a vacuum from occurring in the piston-cylinder unit under unfavorable operating conditions, the working chamber of the piston-cylinder unit is preferably connected via a check valve with a reservoir which releases a flow of fluid medium from the reservoir to the working chamber. 
     To obtain as low as possible an input of energy, a passive energy accumulator is connected in parallel with the active control system. Especially in emergency operation, the advantageous use of the energy accumulator results in distinctly reduced manual force being required. 
     It has been shown to be particularly advantageous if the passive energy accumulator is a pneumatic spring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention is described below by reference to the accompanying drawings, in which: 
     FIG. 1 shows the mounting of the active control system in connection with a vehicle tailgate, 
     FIG. 2 is a circuit diagram of the control system; and 
     FIG. 3 is a sectional view through a preferred embodiment of a pressure-limiting valve. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1 shows a partial view of a motor vehicle  1  with a tailgate  3 , which may be opened as desired through operation of an active control system indicated schematically at  5 . The active control system includes a piston-cylinder unit designed as a hydraulic operator  6 , which is connected by fluid connecting elements with a pump unit  7  (see FIG.  2 ). In addition, an accumulator  9  and an on-off valve  11  are included. The control system  5  may be controlled by an actuating means  13 . The actuating means has the switch positions “Up” and “Down” for motion and “Stop” for blocking of the hydraulic operator  6 . A pneumatic spring  15 , which may be conventional, is connected to operate in parallel with the active control system  5 . A suitable pneumatic spring is disclosed for example in DE 29 50 888. 
     Referring to FIG. 2, the hydraulic operator  6  and the pneumatic spring  15  act in tandem to provide a force F that lifts the tailgate from a closed position S 1  to an open position S 2  in one state of the control system, as described below. The pump  7  supplies fluid to the hydraulic operator  6  to close the tailgate against the force F in another state of the control system. 
     In addition to the components mentioned in relation to FIG. 1, the active control system includes a pressure-limiting valve  17 . The hydraulic operator  6  is divided into two working chambers  6   a / 6   b  by a piston  19  on a piston rod  21 . As shown in FIG. 1, the hydraulic operator is mounted on the vehicle in the rod-up position when the tailgate is closed. The chamber  6   b  is in active fluid communication with the accumulator  9 , and the chamber  6   a  is connected by the connecting line  23  to a cross connection  25  between the pump unit  7 , the on-off valve  11  and the pressure-limiting valve  17 . 
     In the “Up” position of the actuating means  13 , the pump unit  7  does not deliver, but stands still. At the same time, the on-off valve  11  is switched to the open position. Consequently, the accumulator  9 , under pressure, is capable of displacing the piston  19  in the direction of the diminishing working chamber  6   a , whereupon the medium in the chamber  6   a , as a rule an oily liquid, is able to escape through the connecting line  23 , the cross connection  25  and the on-off valve  11  into a reservoir  27 . At this point the piston rod  21  has come to rest with the tailgate of the vehicle at an opened position. 
     In the “stop” switch position of the control system, no medium is delivered by the pump unit  7  and the on-off valve  11  is in the closed position. Consequently, the two working chambers  6   a ,  6   b  are both closed off. The tailgate is then held fixed in the instantaneous position. 
     Upon a closing motion of the tailgate of the vehicle or the “Down” switch position of the actuating means  13 , medium is delivered from the pump  7  to the working chamber  6   a  of the hydraulic cylinder  6 . The on-off valve  11  is in the closed position. The quantity of medium delivered moves the piston in the direction of the working chamber  6   b.  The medium forced out of the working chamber  6   b  is received in the accumulator  9 . 
     With an active control system, it may happen that the energy supply, in this case the pump drive, fails. In order to ensure opening of the tailgate even in this operating condition, the pressure-limiting valve  17  permits piston motion in the direction of the working chamber  6   a.  A manual opening force applied to the tailgate provides the necessary pressure increase in the control pressure on the event of failure of the power supply. Then the on-off valve, owing to spring loading (as indicated at  26 ), assumes the closed position, as shown in FIG.  2 . 
     The possibility of closing the hydraulic operator  6  mechanically also exists. The piston  19  is forced into the working chamber  6   b,  and the medium found therein is forced into the accumulator  9 . To keep a vacuum from being produced in the working chamber  6   a,  medium flows from the reservoir  27  through a check valve  29  via the cross connection  25  into the working chamber  6   a.    
     The active control system additionally provides protection against pinching. Should it happen that, in the course of descent of the piston rod  21  as the tailgate closes, an object or fingers become pinched between the vehicle tailgate and the vehicle body, it must be presumed that the on-off valve  11  has assumed the closed position and the pump unit  7  is able to deliver fluid to the chamber  6   a.  A pinched object produces a restraining force on the piston, so that a pressure increase appears in the working chamber  6   a  due to the delivery of the pump unit  7  since, as already stated, the on-off valve  11  has assumed the closed position. An increased pressure likewise appears on the pressure-limiting valve  17 , which switches the pressure-limiting valve  17  over to the open position. The pressure-limiting valve  17  is connected controlwise with the on-off valve  11 , which is then switched over into the open position. The reference character S 3  designates a control linkage between the between the pressure-limiting valve  17  and the on off valve  11 , such as a limit switch, for example, that senses the switch position of the pressure-limiting valve and transmits this information to the on-off valve electrically, pneumatically or hydraulically as a control signal. 
     The preloaded medium in the accumulator  9  is capable of moving the piston rod  21  in the ascending direction, since the pump unit  7  easily pumps through the released on-off valve  11 . The volume present in the working chamber  6   a  is forced by the pressure into the reservoir  27 . In principle, the ascending motion of the tailgate is supported by the additional pneumatic spring  15 , owing to which the manual force necessary in an emergency is distinctly reduced. 
     A special feature of the pressure-limiting valve can be seen in FIG.  3 . The pressure-limiting valve piston  31  is designed stepped. A pin extension  31   a,  sealed by an O-ring  33 , represents a first small pressurized surface  35 , which is constantly loaded by a combined control and operating pressure connection  17   a.  An adjustable preloading spring  37  represents a counterforce to the operating pressure or control pressure on the pressurized surface  35 . If a greater opening pressure becomes effective, the pin extension  31   a  is displaced out of the O-ring  33 . Axially behind the O-ring an enlarged pressure chamber with a greater second pressurized surface  39  is available on the pressure-limiting valve piston  31 . The surface  39  is the annular surface that results from the difference between the areal content of the outside diameter of the piston and the areal content of the pressurized face  35  of the pin extension  31   a.    
     This structural measure results in two points of operation for the pressure-limiting valve  17 . If a first greater pressure threshold value is exceeded, the pressure-limiting valve opens by virtue of the pressure acting on the surface  35 . In the open position, a distinctly smaller control pressure is necessary to hold the pressure-limiting valve in the open position, since the greater ring-shaped surface  39  is available as the pressurized surface against which the pressure acts. Specifically, in emergency operation this results in a distinct reduction of the force that must be exerted to move the piston rod in the ascending direction. 
     Although the invention has been described herein by reference to the foregoing preferred embodiment, it will be understood that such embodiment is susceptible of variation and modification without departing from the spirit and scope of the appended claims. Also, it will be understood that the invention may be applied to applications other than vehicular doors or tailgates.