Patent Application
20050028763
The present invention is directed to an hydraulic valve actuator for activating a gas-exchange valve in a combustion cylinder of an internal combustion engine.
German Published Patent Application No. 198 26 047 describes a hydraulic valve actuator of this type, which is also referred to as an “actuator”. In this actuator, the lower pressure chamber, via which the operating piston is displaced in the direction of valve closing, is continually charged with pressurized fluid. The upper pressure chamber, provided with an intake line and a return line, via which a piston displacement in the direction of valve opening is effected, is selectively charged with pressurized fluid via the intake, using control valves, such as 2/2 solenoid valves, or it is relieved again to approximately ambient pressure via the return line. A regulated pressure-supply device supplies the pressurized fluid. Of the control valves, a first control valve connects the upper pressure chamber to a relief line discharging into a fluid reservoir, and a second control valve connects the upper pressure chamber to the pressure-supply device. In the closed state of the gas exchange valve, the upper pressure chamber is disconnected from the pressure supply device by the closed second control valve and connected to the relief line via the open first control valve, so that the actuating piston is retained in its closed position by the fluid pressure prevailing in the lower pressure chamber. To open the gas exchange valve, the control valves are switched over, so that the upper pressure chamber is cut off from the relief line and connected to the pressure supply device. The gas-exchange valve opens because the effective area of the operating piston delimiting the upper pressure chamber is larger than the effective area of the operating piston delimiting the lower pressure chamber, the magnitude of the opening stroke lift being a function of the generation of the electrical control signal applied to the second control valve, and the opening speed being a function of the fluid pressure applied by the pressure-supply device. To close the gas exchange valve, the control valves are switched over again, thereby connecting the upper pressure chamber, which is blocked off from the pressure supply device, to the relief line. The fluid pressure prevailing in the lower pressure chamber guides the operating piston back into its upper limit position, so that the gas exchange valve is closed by the operating piston.
Such a device requires rapid closing of the gas exchange valve and, at the same time, a low impact speed of the valve member of the gas-exchange valve on the valve seat formed in the cylinder head of the combustion cylinder. For reasons of noise and wear, this speed must not exceed certain limit values.
To this end, the use of a valve brake has been proposed in German Published Patent Application No. 102 01 167.2, which brake is connected to the valve member of the gas-exchange valve or to the valve actuator. The valve brake, which acts during a residual closing stroke of the valve member, includes an hydraulic damping member having a fluid displacement volume that discharges via a throttle opening. In one version, where the damping member is integrated in the valve actuator, the return line of the upper pressure chamber is split between two discharge orifices, which are connected to one another and arranged in the housing with axial clearance. A restrictor is assigned to the upper discharge orifice, and the lower discharge orifice is situated in the displacement path of the operating piston in such a way that it may be closed by the operating piston prior to reaching the upper limit position. The throttle opening is realized by a pressure-controlled restrictor whose control pressure is adjusted as a function of the viscosity of the displacement volume with the aid of an electrically controlled hydraulic pressure valve and an electronic control device that triggers it. This has the advantage that the valve member is decelerated during the closing stroke before it reaches its closed position, the braking effect being independent of the temperature and the resulting viscosity of the fluid volume displaced via the throttle opening. Since the opening cross section of the throttle opening is reduced with increasing temperature and attendant decreasing viscosity, the flow velocity of the displaced fluid volume through the throttle opening is reduced to the same extent, so that the magnitude of the braking of the operating piston via the damping member remains approximately constant.
The valve actuator according to the present invention for actuating a gas-exchange valve in a combustion cylinder of an internal combustion engine has the advantage that during the closing stroke of the operating piston, that is, with an operating piston moving into its upper limit position, the lower discharge orifice is closed by the operating piston following a certain displacement travel. Thus, the fluid from the upper pressure chamber may only be expelled via the restrictor. This lowers the displacement velocity of the operating piston, so that the gas-exchange valve connected to the operating piston has a reduced closing speed and the valve member subsequently sets down on the valve seat with considerably reduced striking speed. Since the lower discharge opening is situated at a distance from the upper limit position of the operating piston, the braking operation sets in when the valve member of the gas-exchange valve is at a certain distance from the valve seat. The magnitude of the speed reduction may be influenced by adjusting the opening-cross section of the restrictor. If, however, due to manufacturing tolerances of the gas-exchange valve or as a result of different thermal expansions of the valve parts, the lift of the valve member of the gas-exchange valve has changed slightly by the time it sets down on the valve seat of the gas-exchange valve, the displaceable design of the lower discharge opening allows an automatic tolerance compensation. By a corresponding slight shifting of the lower discharge opening, the braking, which is triggered by the closing of the lower discharge opening via the operating piston, sets in with a closing stroke of the operating piston, adapted to the modified valve-member lift, in such a way that in all closing operations of the gas-exchange valve the braking of the valve member always sets in at the same point relative to the distance from the valve member. This means that the valve member is decelerated over a constant, tolerance-independent braking path until it sets down on the valve seat.
According to an embodiment of the present invention, the displaceable design of the lower discharge opening is realized in that the lower discharge opening is made up of a radial bore penetrating the housing and a radial bore, communicating therewith, in a compensation piston, which encloses the operating piston and is displaceable relative to the operating piston. On the one side, the compensation piston, which is designed such that it is carried along by the operating piston moving into the upper limit position, axially delimits the upper pressure chamber together with the operating piston. On the other side, it axially delimits a blockable compensation chamber via its annular end face, which faces away from the upper pressure chamber.
According to a particular embodiment of the present invention, the compensation chamber is blocked off over the displacement path of the operating piston. It is released again for a fluid exchange when the operating piston, moving into its upper limit position, begins to take the compensation piston along. In this way, when the lower discharge opening is closed, the compensation piston is still able to move within certain limits and adjusts the position of the lower discharge opening with respect to the closed position of the gas-exchange valve, the lower discharge opening determining the onset of the braking operation. As a result, the braking always sets in when the valve member is at precisely the same distance in front of the valve seat, regardless of tolerances or thermal expansions occurring in the gas-exchange valve.
According to an alternative embodiment of the present invention, to ensure that an axial displacement of the compensation piston is possible once the operating piston has closed the lower discharge opening, the compensation chamber is connected to a fluid reservoir at least as soon as the compensation piston begins to be taken along by the operating piston moving into its upper limit position. The connection between the compensation chamber and the fluid reservoir may also be permanent; however, the restriction that the connection is established only when the compensation piston is taken along has the advantage that it prevents the compensation piston from being taken along prematurely, as a result of friction between the compensation piston and the operating piston.
Providing the fluid reservoir has the additional advantage that the movement of operating piston out of its upper limit position, which is accompanied by the opening of the gas-exchange valve, takes place with a relatively great displacement force. This force is reduced following a displacement travel determined by the fluid reservoir, namely when no further fluid volume is able to be expelled into the reservoir from the compensation chamber. Reducing the displacement force in the subsequent displacement path of the operating piston saves energy, since the actuating force required for the further opening of the gas-exchange valve following the initial opening of the gas-exchange valve is much lower than the actuating force that is generated during the initial opening of the gas-exchange valve against the high internal pressure in the combustion cylinder.
The hydraulic valve actuator schematically shown in longitudinal section in
The valve actuator, also called an actuator, for activating gas-exchange valve 10, which represents a double-acting working cylinder, has a hollow-cylindrical housing 15 and an operating piston 16 guided in housing 15 so as to be displaceable in an axial direction. Operating piston 16 is fixedly connected to valve shaft 11 and, in a displacement limit position shown in
In the exemplary embodiment of
Operating piston 16 is enclosed by a compensating piston 32, which is displaceable relative to operating piston 16. Operating piston 16 and compensating piston 32 are guided in a guide sleeve 33 so as to be axially displaceable, guide sleeve 33 being fixed in housing 15 in a non-displaceable manner. Compensating piston 32, together with the effective area of operating piston 16, axially delimits upper pressure chamber 17, and by its annular end face facing away from upper pressure chamber 17 it delimits a compensating chamber 34 in guide sleeve 33. Compensating piston 32 carries a stop 321 near its end facing upper pressure chamber 17, and operating piston 16 carries a counter stop 161 on its end forming the effective area, counter stop 161 cooperating with stop 321 in taking along compensating piston 32 by operating piston 16 moving into the upper limit position.
As a result of compensating piston 32 and guide sleeve 33, lower discharge opening 232 is made up of a first radial bore 35 in housing 15, a second radial bore 36 in guide sleeve 33 and a third radial bore 37 in compensating piston 32. Compensating chamber 34 is blocked off over the displacement path of operating piston 16; it is released for fluid discharge or fluid intake only at the point where operating piston 16, moving into its upper limit position, begins to take along compensating piston 32. To this end, a compensation channel 39, which connects second radial bore 36 with a radial bore 40 in guide sleeve 33, is worked into guide sleeve 33, radial bore 40 being set apart from second radial bore 36 and discharging toward operating piston 16. Operating piston 16 has an annular groove 41 having an axial groove width such that, in a certain relative position of operating piston 16 and compensating piston 32, it establishes a connection between the mouth of radial bore 40 and compensating chamber 34. To this end, annular groove 41 is placed on operating piston 16 in such a way that the connection is established as soon as compensating piston 32 begins to be carried along by operating piston 16, i.e., with the stop of counter stop 161 striking stop 321; the connection is severed again only when operating piston 16 has moved slightly out of its upper limit position. In the upper limit position of operating piston 16, the connection between compensating chamber 34 and radial bore 40 is maintained via annular groove 41, as can be seen in
Inside upper pressure chamber 17, a spacer sleeve 42, which forms a stop for compensating piston 32, is inserted in housing 15. Compensating piston 32 can thus move between the floor of compensating chamber 34, which is formed by guide sleeve 33, and spacer sleeve 42. Since spacer sleeve 42 is located in the region of upper discharge opening 231 and intake opening 31, spacer sleeve 42 is provided with a radial bore 43, as shown in
The operation of the hydraulic valve actuator is as follows:
In
In the further course of the closing movement of gas-exchange valve 10, operating piston 16 passes over radial bore 37 in compensating piston 32, thereby closing off lower discharge opening 232. Now, the fluid can discharge into return line 24 solely via upper discharge opening 231 and via restrictor 29. Only a small fluid quantity per time unit is able to flow off through restrictor 29, so that operating piston 16 and gas-exchange valve 10 are decelerated. Operating piston 16 continues a displacement movement into its upper limit position—now at reduced speed—until gas-exchange valve 10 is closed, that is to say, until valve member 12 sets down on valve seat 13.
The displacement stroke in which the deceleration of operating piston 16 begins depends on the relative position of operating piston 16 with respect to compensating piston 32. Compensating piston 32 is able to move between the base of compensating chamber 34 and spacer sleeve 42. When the internal combustion engine is started up, or during a starting procedure after the internal combustion engine has been at a standstill for a longer period of time, compensating piston 32 assumes an arbitrary position between chamber base and spacer sleeve 42. If compensating piston 32 is located too far to the left in the representation in
To open gas-exchange valve 10, first control valve 25 is closed and second control valve 27 opened. Upper pressure chamber 17 is now under the fluid pressure supplied by pressure-supply device 20. Since the effective area of operating piston 16 delimiting upper pressure chamber 17 is larger than the effective area of operating piston 16 delimiting lower pressure chamber 18, operating piston 16 moves to the left in the graphical representation, and gas-exchange valve 10 is opened. Via annular groove 41, compensating chamber 34 is connected to lower discharge opening 232 and the latter is connected to upper pressure chamber 17 via restrictor 29, so that compensating chamber 34 has the same pressure as upper pressure chamber 17. Since the two effective areas of compensating piston 32 that delimit compensating chamber 34 and upper pressure chamber 17 are of the same size, compensating piston 32 is pressure-equalized, so that no resulting displacement force is generated at compensating piston 32. However, the pressure in compensating chamber 34 is generated somewhat later because of restrictor 29, so that compensating piston 32 makes a slight movement to the left. As soon as operating piston 16 has moved to such an extent that annular groove 41 breaks off the connection to compensating chamber 34, compensating chamber 34 is blocked off, so that compensating piston 32 remains in the attained position. In this way, compensating piston 32 is aligned, and radial bore 37 in compensating piston 32, which is part of lower discharge opening 232, has a fixed position with respect to the closed state of gas-exchange valve 10. As a result, operating piston 16 always closes radial bore 37 at a fixed distance prior to reaching its limit position, and the braking operation at gas-exchange vale 10 thus always begins when valve member 12 is at a fixed distance from valve seat 13. If compensating piston 32 is too far to the right in the closing operation shown in the representation of FIGS. 1 to 3, compensating piston 32 is adjusted as described during the subsequent closing and opening operation of gas-exchange valve 10 in that compensating piston 32 executes a slight movement to the left.
The valve actuator for a gas-exchange valve 10 shown in,
Fluid reservoir 44 has a control chamber 48 provided with two chamber openings 481, 482 lying axially opposite one another, and a control member 49, which is axially displaceable in control chamber 48 for the alternate closing of the two chamber openings 481, 482. Connected to one chamber opening, 481, is connecting line 47 leading to radial bore 45 in housing 15, whereas the other chamber opening, 482, is connected to relief line 28 via a connecting line. The connection to relief line 28 is provided in a line section between the output of first control valve 25 and a pressure-modulation valve 51 disposed in relief line 28. Pressure-modulation valve 51 ensures that a slight fluid pressure of approximately 0.1 Mpa is always present at chamber opening 481. In the exemplary embodiment of fluid reservoir 44 shown in
The manner of operation of the valve actuator is as follows:
During closing of the gas-exchange valves, control valves 25, 27 assume the position shown in
To open gas-exchange valve 10, the two control valves 25, 27 are switched over, so that first control valve 25 closes and second control valve 27 opens. Fluid pressure builds up in upper pressure chamber 17, which acts on the effective area of operating piston 16 and on the end face of compensating piston 32. The sum of the effective areas of operating piston 16 and compensating piston 32 results in a high displacement force in the opening direction of gas-exchange valve 10. Compensating chamber 34 is reduced in size by the displacement movement of compensating piston 32. The fluid is expelled into control chamber 48, which causes spherical control member 49 to move to the right in control chamber 48. The fluid present in control chamber 48 is expelled into relief line 28 via chamber opening 482. Via radial bore 52, fluid may also briefly flow from compensation chamber 32 directly into relief line 28, but throttle 53 ensures that this is only a very small fluid quantity. With the aid of a non-return valve assigned to throttle 53, this slight flow of fluid may be cut off completely. As soon as control member 49 closes other chamber opening 482, no further fluid is able to be expelled from compensating chamber 34 and compensating piston 32 is unable to execute any further displacement movement. Via the volume in control chamber 48, the displacement travel of compensating piston 32 may thus be adjusted.
As soon as compensating piston 32 is in a fixed position, operating piston 16, which continues to move, lifts off from compensating piston 32. The displacement force acting on operating piston 16 is substantially reduced, since it is only the effective area of operating piston 16 delimiting upper pressure chamber 17 that generates the displacement force.
Since compensating piston 32 is taken along by operating piston 16 during closing of gas-exchange valve 10 until valve member 12 comes to rest against valve seat 13, and since compensating piston 32 may travel only a certain displacement path during opening with the aid of control chamber 48, it is ensured that lower discharge opening 232, which controls the braking onset during closing of gas-exchange valve 10, is always in the same position, regardless of thermal expansions and manufacturing tolerances. As a result, the braking onset does not vary.
Shoulder 322 on compensating piston 32, which can still be seen in
The constructive design of the valve actuator illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 39 747.3 | Aug 2002 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE03/00699 | 3/5/2003 | WO |
