EP1440225B1 - Hydraulic actuator for an engine valve - Google Patents

Abstract

A hydraulic actuator for gas exchange valves of internal combustion engines is disclosed, in which the lifting of the gas exchange valve from the valve seat is effected with great force. The opening motion of the gas exchange valve then ensues at reduced force. Upon closure of the gas exchange valve, the gas exchange valve is braked before striking the valve seat, so that operation of the gas exchange valve with little wear and little noise can be achieved.

Description

State of the art

The invention relates to a hydraulic actuator for a Gas exchange valve for internal combustion engines (see, for example, SE-B-353575).

The opening and closing of the gas exchange valve should as possible done quickly to the flow losses of the Gas exchange valve when sucking the combustion air or to minimize when pushing out the exhaust gases from the combustion chamber.

The ruling temporarily in the combustion chamber of the internal combustion engine Overpressure presses the gas exchange valve in the valve seat. Because of This overpressure requires the opening of the gas exchange valves an increased power requirement for lifting the gas exchange valve, in particular the exhaust valve, from the valve seat. After that Gas valve has lifted from the valve seat, the sinks Pressure in the combustion chamber from strong, so that the power requirement for Opening the gas exchange valve is correspondingly lower.

When closing the gas exchange valve is also on it Make sure that the speed at which the valve plate of the Gas exchange valve on the valve seat does not hit too large is. If this speed is too high, a result unwanted noise and increased wear when Impingement of the valve disk on the valve seat.

The invention is based on the object, a hydraulic Actuator for a gas exchange valve to provide a great force at the beginning of the opening movement on the Gas exchange valve can exercise, the fast control movements allows the gas exchange valve and in which the Gas exchange valve with low speed on the Valve seat impinges.

This object is achieved by a hydraulic actuator for a gas exchange valve one Internal combustion engine with a cylinder bore, with a Piston and an annular piston, the piston and the Ring piston are guided in the cylinder bore, wherein the Piston, the ring piston and the cylinder bore in axial Limit a first chamber whose volume increases, when the actuator opens the gas exchange valve, wherein the Ring piston and the cylinder bore in the axial direction a second chamber limit, whose volume decreases when the Actuator opens the gas exchange valve, the piston and the Cylinder bore limit a third chamber whose volume decreases when the actuator opens the gas exchange valve, wherein a device for limiting the volume decrease of second chamber is provided and the first chamber and the second chamber via a throttle communicate with each other.

Advantages of the invention

In the hydraulic actuator according to the invention is at the beginning the opening movement of the gas exchange valve a large hydraulic force from the actuator to the gas exchange valve transferred so that despite the back pressure from the combustion chamber on the valve plate of the gas exchange valve the Gas exchange valve safely and quickly lifted off the valve seat can be. As soon as the power required to operate the Gas exchange valve has decreased, for example, because no Back pressure in the combustion chamber is more present, the Ring piston stops moving and it works As a result, only a lower hydraulic force the piston of the actuator, in turn, on the gas exchange valve is transmitted. With reduction of hydraulic power reduces the adjustment of the actuator piston required energy, so that the total energy demand for the valve control of the internal combustion engine decreases. Simultaneously with the reduction of this force changes also the positioning speed of the gas exchange valve. Finally, when closing the gas exchange valve with the A hydraulic actuator according to the invention a braking of the Gas exchange valve can be achieved before the gas exchange valve impinges on the valve seat of the internal combustion engine. Thereby be the wear of valve seat and gas exchange valve as well as the noise development of the valve control Internal combustion engine reduced.

Moreover, the beginning of the deceleration process of Gas exchange valve when closing the same regardless of the Manufacturing tolerances of the gas exchange valve and at Internal combustion engines always present temperature-related Length changes due to thermal expansion. That's why with the actuator of the invention is a very stable Operating behavior of the internal combustion engine feasible, the neither by thermal expansions nor by Manufacturing tolerances is affected.

In a variant of the invention it is provided that the Piston has a puncture that the annular piston a Outer surface and a stepped center hole with a larger diameter and a smaller diameter has, and that the annular piston with the larger diameter the center hole on the piston can be pushed, so that on simple way the ratio of the operating forces of the Actuator when opening the gas exchange valve and during the remaining adjusting movement is adjustable.

This effect can be further increased by the fact that the Diameter of the piston on both sides of the groove are different and that the ring piston on the larger Diameter is pushed.

In a further feature of the invention, it is provided that the means for limiting the decrease in volume of the second chamber is hydraulically connected to the second chamber pressure accumulator with a piston and that the path of the piston can be limited, so that in a simple manner by hydraulic means of Ring piston can be locked. Since the accumulator does not reach the high temperatures of the gas exchange valve and the cylinder head of the internal combustion engine, the position in which the annular piston is locked after the opening of the gas exchange valve, regardless of the thermal expansion of the gas exchange valve and the cylinder head.
Further embodiments of the invention provide that the pressure accumulator is a spring accumulator or a gas storage and / or that the way of the piston by a stop, in particular an adjustable stop, can be limited, so that the actuator according to the invention can be easily adjusted.

Further additions of the invention provide that the first Chamber via a first switching valve with a pump is connectable, that the second chamber via a second Switching valve with an oil sump is connectable and that the third chamber with the delivery pressure of the pump acted upon is, so that by operating two switching valves the Gas exchange valve with the hydraulic according to the invention Actuator can either be opened or closed, with the increased force when lifting the gas exchange valve from Valve seat and the delay of the gas exchange valve before the Impact on the valve seat automatically from the be realized according to the invention hydraulic actuator.

A separate control of the same is not required. This relieves that for driving the actuator required control unit and makes the inventive hydraulic actuator robust and insensitive to external influences.

The inventive effect of the actuator is further characterized supports that the first chamber and the second chamber via an adjustable throttle, hydraulically communicate with each other and / or that one Check valve between the second chamber and the first chamber is provided, which is the hydraulic connection of the first chamber to the second chamber locks. The throttle has decisive influence on the deceleration of the gas exchange valve before hitting the valve seat.

According to an advantageous embodiment of the invention the device for limiting the volume decrease in the second chamber with an opening in the second chamber in Connection standing on shut-off valve, the opening in its one switching position closes and in its other Switching position releases fluid outflow. With closing the Shut-off valve, the ring piston is fixed so that the Closing time of the shut-off valve the stroke of the Determines annular piston. From the stroke of the ring piston is turn the time of onset of braking effect Closing the gas exchange valve dependent, the at a larger stroke of the ring piston earlier and a smaller one Hub starts later. By the shut-off valve can thus the Brake start regardless of manufacturing tolerances or Material expansion due to temperature fluctuations be set.

According to an advantageous embodiment of the invention is the shut-off valve not as an additional unit but its function anyway for the Initiation of the closing process of the gas exchange valve assigned required second switching valve. By omission the shut-off valve and by dispensing with the above described pressure accumulator for the device for Limit the volume decrease in the second chamber reduces the construction costs for the valve control.

According to an advantageous embodiment of the invention between the first chamber and the one between the two Chambers arranged throttle to influence the Abbremsverhaltens the actuator piston and thus the Gas exchange valve arranged a flow-controlled valve, which is designed to be that of the first chamber inflowing fluid is closable. This has the advantage that in the initial phase of the stroke of the actuator piston, in which both Switch valves are open, fluid from the first Switching valve is not directly above the throttle in the hydraulic discharge space or oil sump can drain. At a high throttle effect, the throttle can indeed on this flow-controlled valve can be dispensed with, since only small amounts of fluid flow through the throttle, but at larger throttle opening to achieve only a small Braking effect on the gas exchange valve is the flow-controlled Valve to shut off the throttle to avoid larger Leakage essential.

Further advantages and advantageous embodiments of Invention are the following drawings, whose Description and claims removed.

drawing

Fig. 1

einen Längsschnitt eines erfindungsgemäßen hydraulischen Aktors mit dessen hydraulischer Anbindung,

Fig. 2

einen Längsschnitt des Aktors gemäß Fig. 1 in drei verschiedenen Stellungen,

Fig. 3 und 4

jeweils ausschnittweise einen Längsschnitt des Aktors gemäß Fig. 1 mit unterschiedlich modifizierter hydraulischer Anbindung,

Fig. 5 und 6

jeweils einen Längsschnitt eines strömungsgesteuerten Ventils in Fig. 4 im geöffneten (Fig. 5) und geschlossenem (Fig. 6) Zustand.

The invention is explained in more detail with reference to embodiments illustrated in the drawings in the following description. In a schematic representation:

Fig. 1

a longitudinal section of a hydraulic actuator according to the invention with its hydraulic connection,

Fig. 2

3 shows a longitudinal section of the actuator according to FIG. 1 in three different positions,

3 and 4

in each case a detail of a longitudinal section of the actuator according to FIG. 1 with differently modified hydraulic connection,

FIGS. 5 and 6

in each case a longitudinal section of a flow-controlled valve in FIG. 4 in the opened (FIG. 5) and closed (FIG. 6) state.

Description of the embodiment

The embodiment of FIG. 1 represents a hydraulic actuator with a housing 1 in longitudinal section. The housing 1 has a stepped cylinder bore 3. to Simplification of the production is in the housing 1 a sleeve 5 pressed, the inner bore part of the stepped Cylinder bore 3 is. In the area of the sleeve 5 is in the Cylinder bore 3 an annular piston 7 and a piston 9 out. In the position of the piston 9 shown in Fig. 1 is the not shown gas exchange valve closed.

The cylinder bore 3, the piston 9 and the annular piston 7 limit in the direction of a longitudinal axis 11 of the piston 9 a first chamber 13. So between cylinder bore 3 and piston 9 no fluid or fluid can escape, is a first Sealing ring 15 at the left in Fig. 1 end of the first chamber thirteenth arranged.

The piston 9 has a recess 17. The diameter of the piston 9 on both sides of the groove 17 are of different sizes. At the side facing the sealing ring 15, the piston 9 has a smaller diameter d ₁ , and at the other end of the recess 17, the piston 9 has a larger diameter d ₂ .

Between the sleeve 5 and the piston 9, the annular piston 7 is arranged. The annular piston 7 is fitted in the cylinder bore 3 so that it is displaceable on the one hand in the axial direction and that on the other hand, a good sealing effect between the cylinder bore 3 and the annular piston 7 is achieved. The annular piston 7 has a stepped center hole 19 with a smaller diameter d ₃ and a larger diameter, which is as large as d ₂ , on. The fit between the annular piston 7 and the larger diameter d _{2 of} the piston 9 is also chosen so that the annular piston 7 and piston 9 are movable relative to each other in the axial direction and still a good sealing effect is achieved.

On the right in Fig. 1 side of the annular piston 7, the cylinder bore 3 and the annular piston 7 define a second chamber 27. The cylinder bore 3 has a diameter d ₄ in this area, which corresponds to the outer diameter of the annular piston 7. At the right in Fig. 1 end of the piston 9, this has a shoulder with the diameter d ₅ .

At the right in Fig. 1 end of the cylinder bore 3 is the Annular gap between the cylinder bore 3 and piston 9 by a Second sealing ring 21 Bridged and against the environment sealed. At this end of the piston 9, the shaft 23rd a partially shown gas exchange valve with the Piston 9 positively connected.

Between the shoulder of the piston 9 with the diameter d ₅ and the cylinder bore 3 with the diameter d ₂ is a third chamber 25 which is sealed by the sealing ring 21 from the environment. The annular piston 7, the part of the cylinder bore 3 with the diameter d ₄ and the piston define a second chamber 27. The first chamber 13 is hydraulically connectable via a first switching valve 29 to a pump 31. The first switching valve 29 may be formed, for example, as an electrically operated solenoid valve.

The pump 31 acts on the third chamber 25 permanently the delivery pressure generated by it.

By a second, for example. As electrically operated Solenoid valve formed switching valve 33 may be a hydraulic connection between the second chamber 27 and a relief space or oil sump 35 are made. In a conduit 37, which second chamber 27 and second Switching valve 33 connects, is a check valve 39th arranged. Between check valve 39 and second chamber 27, a hydraulic accumulator 41 is connected. Of the Hydraulic reservoir 41 has a piston 43 which extends against the force of a spring 45 moves when the on the Spring 45 facing away from the end face of the piston 43 acting pressure is sufficiently high. This print is the same size as the Pressure in the line 37. The path of the piston 43 against the Force of the spring 45 is by a stop 47, which also can be made adjustable, limited. Between the first chamber 13 and the second chamber 27 is a provided hydraulic connection in which an adjustable Throttle 49 is arranged.

• Der Durchmesser d₄ der Zylinderbohrung 3, der Ringkolben 7 und die in Fig. 1 rechte Seite des Einstichs 17 bilden eine erste Ringfläche A₁ mit einem Außendurchmesser d₄ und einem Innendurchmesser d₆, welcher dem Innendurchmesser des Einstichs 17 entspricht. Der auf die erste Ringfläche A₁ wirkende Druck des in der ersten Kammer 13 befindlichen hydraulischen Fluids versucht den Kolben 9 nach rechts zu bewegen. Die daraus resultierende Kraft ist für das Öffnen des nicht dargestellten Gaswechselventils verantwortlich.
• Der Absatz auf der in Fig. 1 rechten Seite des Einstichs 17, der durch die Durchmesser d₂ und d₆ begrenzt wird, wird nachfolgend auch als zweite Ringfläche A₂ bezeichnet.

When the first chamber 13 and the third chamber 25 are subjected to the delivery pressure of the pump 31, which is the case when the first switching valve 29 is open, different hydraulic forces act on the piston 9, which are explained below:

• The diameter d _{4 of} the cylinder bore 3, the annular piston 7 and the right in FIG. 1 side of the groove 17 form a first annular surface A ₁ with an outer diameter d ₄ and an inner diameter d ₆ , which corresponds to the inner diameter of the recess 17. The pressure acting on the first annular surface A _{1 of the} hydraulic fluid in the first chamber 13 attempts to move the piston 9 to the right. The resulting force is responsible for opening the gas exchange valve, not shown.
• The paragraph on the right in Fig. 1 side of the groove 17, which is bounded by the diameter d ₂ and d ₆ , hereinafter referred to as the second annular surface A ₂ .

The hydraulic force acting on the first annular surface A _{1 is} reduced by the hydraulic forces acting on a third annular surface A ₃ and a fourth annular surface A ₄ .

The third annular surface A ₃ is limited by the shoulder in the piston 9, which is formed by the diameter d _{1 of} the piston 9 and the diameter d _{6 of} the recess 17. On the third annular surface A ₃ , the hydraulic fluid in the first chamber 13 exerts a force acting in FIG. 1 to the left.

The fourth annular surface A ₄ is bounded by a shoulder 51 of the piston 9 in the region of the third chamber 25. The heel 51 is formed by the diameter d ₂ and the diameter d _{5 of} the piston 9. The fourth annular surface A ₄ always exerts a force acting counter to the opening direction on the piston 9, since, as already mentioned, the third chamber 25 is always acted upon by the pre-pressure of the pump 31.

Since the first annular surface A _{1 is} larger than the third annular surface A ₃ and the fourth annular surface A ₃ , the piston 9 moves to the right when the first chamber 13 is acted upon by the delivery pressure of the pump 31. The annular piston 7 transmits the hydraulic force acting on it via the shoulder of its stepped center hole 19 on the piston 9. The movement of the piston 9 in Fig. 1 to the right has the opening of the gas exchange valve, not shown result.

When the annular piston 7 and the piston 9 in Fig. 1 after move right, the volume of the second chamber 27 decreases. Since the second switching valve 33 is closed, this can the movement of the annular piston 7 and the piston 9 to the right from the second chamber 25 displaced fluid only in the hydraulic accumulator 41 flow. The hydraulic fluid, which flows into the hydraulic accumulator 41, moves the Piston 43 against the spring 45 until the piston 43 on the Stop 47 rests.

When the piston 43 rests against the stop 47, hydraulic fluid can no longer flow out of the second chamber 27 into the hydraulic reservoir 41, with the result that the volume of the second chamber 27 remains constant. This means nothing else than that the annular piston 7 can not move further to the right. As a result, reduces the hydraulic force, which moves the piston 9 to the right, since now only the force acting on the second annular surface A ₂ hydraulic force for the opening of the gas exchange valve, not shown, is available.

The above-described, on the third annular surface A ₃ and the fourth annular surface A ₄ acting hydraulic forces, which want to push the piston to the left, ie contrary to the opening movement, remain unchanged. As a result, the force acting on the gas exchange valve, not shown opening force is reduced after lifting the gas exchange valve from the valve seat, not shown.

In the figures 2a, 2b and 2c are various stages of Opening movement and the closing movement shown by which the above should be clarified. To the Not to overload drawing in Fig. 2 are not all Reference number of Fig. 1 has been repeated.

2a, the actuator is shown in a position, in which the gas exchange valve is closed and the full Opening force is available.

In Fig. 2b, the state is shown in which the volume of the second chamber 27 is no longer decreasing, since the pressure accumulator 41, not shown in Fig. 2 no longer receives fluid. As a result, the annular piston 7 no longer moves. If the gas exchange valve is opened further, leaves the piston 9 with its diameter d _2, the stepped center hole 19 of the annular piston 7. From this position, a direct hydraulic connection between the first chamber 13 and second chamber 27 is present. At the opening force, this does not change anything.

In Fig. 2c, the hydraulic actuator in a position shown, in which the gas exchange valve is fully open and the piston 9 from the annular piston 7 to the right moved out.

To close the gas exchange valve, the piston 9 in the Fig. 1 and 2 are moved to the left. this happens in that the first switching valve 29 is closed and the second switching valve 33 is opened. This position of Switching valves 29 and 33 is shown in Fig. 1. The on the paragraph 49 of the piston 9 from that in the third chamber 25th and under the delivery pressure of the pump 31 standing fluid applied hydraulic force moves the piston 9 to the left. In this case, hydraulic fluid from the first chamber 13 and the second chamber 27 via the check valve 39 and the second Switching valve 33 is conveyed into the oil sump 35. In addition, can the spring 45 of the hydraulic accumulator 41 the piston 43 from Lift stop 47 and the piston 43 back into his Move starting position.

As soon as the piston 9 with its diameter d ₂ dips into the stepped bore 19 of the annular piston 7, the hydraulic fluid contained in the first chamber 13 can no longer pass directly through the second chamber 27 and the line 37 into the oil sump 35, but must via the throttle 49 drain into the oil sump 35. As a result, a certain overpressure builds up in the first chamber 13. As a result, the movement of the piston 9 is decelerated. As soon as the annular piston 7 rests on the piston 9 with its stepped inner bore 19, the annular piston 7 and the piston 9 move together. As a result, a larger volume of oil is conveyed through the throttle 49, which leads to an increase in the braking effect.

The position at which the desired deceleration of the gas exchange valve begins before impinging on the valve seat, not shown, is dependent on the stroke of the accumulator piston 43 and thus not on the thermal expansion to which the hydraulic actuator is exposed. Even manufacturing tolerances of the actuator do not influence this position. By the appropriate choice of the diameter d ₁ to d ₆ , the ratios of the opening force when lifting the gas exchange valve from the valve seat and the reduced opening force upon further opening of the gas exchange valve and the closing force when closing the gas exchange valve can be matched to an optimum performance of the hydraulic actuator to reach.

In Fig. 3 is a detail of the actuator according to FIG. 1. only in the scope of interest with housing 1, the first Chamber 13, second chamber 27 and third chamber 25 and its hydraulic connection to the hydraulic pump 31 with the example. as a 2/2-way solenoid valve formed first switching valve 29th and the hydraulic connection between the first chamber 13 and second chamber 27 via the throttle 49 shown. Of the hydraulic discharge chamber or oil sump is still with 35 and the second chamber 27 with the example. As a 2/2-way solenoid valve formed second switching valve 33rd connecting line designated 37. The hydraulic actuator is modified insofar as the device for limiting the decrease in volume of the second chamber 27, the in Fig. 1 as hydraulic spring accumulator 41 is executed, now by a Shutoff valve 50 is replaced with an opening in the second chamber 27 is in communication, for example. To the line 37 is connected, and the opening in the second chamber 27 and the line connection to the line 37 in his one switching position closes and in its other Switching position to the fluid drain towards the oil sump 35 releases. The function of this in Fig. 3 only symbolically drawn Shut-off valve 50 is, however, the second switching valve 33rd assigned to release the fluid drain from the second chamber 27 in the basic position shown in Fig. 3 stands and shut off the second chamber 27 in its other Switched position is switched. In addition, that retains Changeover valve 33 its already described to Fig. 1 Function for closing the gas exchange valve unchanged at.

As described above, to open the Gas exchange valve, the first switching valve 29 are opened. Fluid now flows under the delivery pressure into the chamber 13, so that the piston 9 of the actuator together with the annular piston. 7 is shifted as shown in Fig. 2b. Becomes a any time during the displacement of the annular piston 7, the second switching valve 33 in its blocking position switched, so no fluid from the second chamber 27th flow out and the annular piston 7 is blocked. The hub of the Ring piston 7 is thus by the time of switching of the open at the beginning of the opening movement of the actuator second Changeover valve 33 set.

As described above, closing of the Gas exchange valve of the annular piston 7 by the pressure in the third valve chamber 25 pushed back as soon as the first Switching valve 29 locked again and the second switching valve 33 is reopened. This builds the pressure in the first chamber 13 via the throttle 49 from. After a stroke the piston 9 abuts against the annular piston 7 and takes this on his further stroke with. This will be a high Volume flow and a strong pressure increase in the first Chamber 13 triggered so that the piston 9 is braked strong. The braking effect starts from the time at which the Ring piston 7 moves with the piston 9, so that the time the onset of braking by the at Opening process of the gas exchange valve set stroke of the annular piston 7 is fixed. This can be done by the Time of switching of the second switching valve 33 in its blocking position when opening the gas exchange valve Time of onset of braking when closing the Gas exchange valve are set.

The fragmentary shown in Fig. 4 Embodiment of the actuator with hydraulic connection is compared to Fig. 3 only insofar modified as between the first chamber 13 in the housing 1 and the throttle 49 in the Connecting line to the second chamber 27 in the housing 1 a flow-controlled valve 51 is turned on, the like is formed so that it from the first chamber 13th inflowing fluid is closable. This flow-controlled Valve 51 prevents being in the initial phase to Aufsteuern the gas exchange valve in which both the first switching valve 29 and the second switching valve 33 is opened, fluid directly from the first switching valve 29 via the second Switching valve 33 flows to the oil sump 35; because of the Throttle 49 flowing leakage increases the energy demand for the valve control when it rises unacceptably. This is especially the case when the braking effect at Closing process of the gas exchange valve by a larger Control of the throttle 49 should be moderately lowered. is the first switching valve 29 is opened, then by the Hydraulic pump 31 flowing into the first chamber 13 Fluid flow closes the valve 51 and thus the connection shut off to the throttle 49. Will the first switching valve 29th closed, that is in the illustrated in Fig. 4 Returned switching position, so opens the valve 51, and the necessary connection for pushing out the fluid from the first chamber 13 via the throttle 49 during the closing of the Gas exchange valve is restored.

The structure of the flow-controlled valve 51 is shown in FIG. 5 and FIG. 6 shows schematically, FIG. 5 showing the opened one Valve and Fig. 6 shows the closed valve. The flow-controlled valve 51 has a housing 52 with a associated with the chamber 13 of the actuator first Valve terminal 53, with a throttle 49th connected second valve port 54 and one with the Output of the first switching valve 29 connected third Valve connection 55 on. The first valve port 53 is available a lower valve chamber 56, the third valve port 55 with an upper valve space 57 and the second valve port 54th with a between the lower and upper valve chamber 56, 57 itself located annular space 58 in conjunction. Between the bottom Valve chamber 56 and the annular space 58 is in the housing 52 one of a valve seat 59 surrounded valve opening 60 is formed. In the upper valve space 57 is a guide sleeve 61 used in a trained as a sliding piston Valve member 62 is slidably guided. The valve member 62nd acts with the valve seat 59 to close and release the Valve opening 60 together, so that the annular space 58 at on the Valve seat 59 seated valve member 62 (Fig. 6) of the lower valve chamber 56 is shut off and at by the Valve seat 59 lifted valve member 62 (Fig. 5) with the lower valve space 56 is connected. In the lower valve chamber 56 is a valve opening spring 63 inserted, acting as a compression spring is formed and on the one hand at one in the bottom Valve chamber 56 trained shoulder 64 and on the other hand on Valve member 62 is supported. The valve opening spring 63 applies this Valve member 62 against a in the guide sleeve 61st trained stop 65 at.

The valve member 62 is provided with a central passage opening 66 provided permanently the upper valve chamber 57 with the lower valve chamber 56 connects. The passage opening 66 is designed as a throttle, including its inner contour 67 a having such an embodiment that that of the upper Valve chamber 57 to the lower valve chamber 56 flowing fluid causes a pressure drop in the passage opening 66. in the Exemplary embodiment of FIGS. 5 and 6 has the Through opening 66 in the form of a double truncated cone, at the two truncated cones with their smaller bases are juxtaposed.

Is to open the gas exchange valve, the first switching valve 29, fluid flows from the outlet of the pump 31 the passage opening 66 in the valve member 62, due to the inner contour 67, a pressure drop between the upper and lower valve space 57, 56 is formed. Thus, the pressure is in upper valve space 57 larger than in the lower valve chamber 56, and it arises on the valve member 62 a resultant Displacement force, contrary to the spring force of the Valve opening spring 63, the valve member 62 on the valve seat 59 touches and thus closes the valve opening 60, whereby the connection to the throttle 49 is blocked.

If the first switching valve 29 is closed again, then flows no more fluid through the passage opening 66. It arises no pressure drop at the inner contour 67, so that the pressures in lower valve chamber 56 and 57 in the upper valve chamber the same size are. The force acting on the valve member 60 is zero, and by the spring force of the valve opening spring 63 is the Valve member 62 to the stop 65 in the guide sleeve 61st created. The valve member 62 is thus from the valve seat 59th lifted and the first chamber 13 of the actuator with the throttle 49 connected. When closing the gas exchange valve can now that by the sliding movement of the pistons 9 and 7th from the first chamber 13 displaced fluid volume over the Throttle 49 and the opened second switching valve 33 in the Drain off oil sump 35.

Claims (16)

1. Hydraulic actuator for a gas exchange valve of an internal combustion engine, with a cylinder bore (3), with a piston (9) and with an annular piston (7), the piston (9) and the annular piston (7),being guided in the cylinder bore (3), the piston (9), the annular piston (7) and the cylinder bore (3) delimiting in the axial direction a first chamber (13), the volume of which increases when the actuator (1) opens the gas exchange valve (23), the annular piston (7) and the cylinder bore (3) delimiting in the axial direction a second chamber (27), the volume of which decreases when the actuator (1) opens the gas exchange valve (23), the piston (9) and the cylinder bore (3) delimiting a third chamber (25), the volume of which decreases when the actuator (1) opens the gas exchange valve (23), characterized in that a device for limiting the decrease in volume of the second chamber (27) is provided, and the first chamber (13) and the second chamber (27) are connected to one another via a throttle (49).
2. Actuator according to Claim 1, characterized in that the piston (9) has an indentation (17), in that the annular piston (7) has a stepped central bore (19) with a larger diameter (d₂) and with a smaller diameter (d₃), and in that the annular piston (7) can be pushed with the larger diameter (d₂) of the central bore (19) onto the piston (9).
3. Actuator according to Claim 2, characterized in that the diameters (d₁, d₂) of the piston (9) are different on both sides of the indentation (17), and in that the annular piston (7) can be pushed onto the larger diameter (d₂).
4. Actuator according to one of Claims 1-3, characterized in that the third chamber (25) is connected directly and the first chamber (13) is connected via a first switching valve (29) to the outlet of a pump (31) generating a conveying pressure, and the second chamber (27) is connected via a second switching valve (33) to a fluid-receiving relief space (35).
5. Actuator according to one of Claims 1-4, characterized in that the device for limiting the decrease in volume of the second chamber (27) is a pressure accumulator (41) connected to the second chamber (27) and having a piston (43), and in that the travel of the piston (43) can be limited.
6. Actuator according to Claim 5, characterized in that the pressure accumulator (41) is a spring accumulator (45) or a gas accumulator.
7. Actuator according to Claim 5 or 6, characterized in that the travel of the piston (43) can be limited by a stop, in particular an adjustable stop (47).
8. Actuator according to one of Claims 1-4, characterized in that the device for limiting the decrease in volume in the second chamber (27) has a shut-off valve (50) which is connected to an orifice in the second chamber (27) and which, in one of its switching positions, closes the orifice and, in its other switching position, releases the orifice for the outflow of fluid.
9. Actuator according to Claims 4 and 8, characterized in that the shut-off valve is formed by the second switching valve (33).
10. Actuator according to one of Claims 1-9, characterized in that the first chamber (13) and the second chamber (27) are connected to one another via an adjustable throttle (49).
11. Actuator according to one of Claims 1-9, characterized in that a non-return valve (39) is provided between the second chamber (27) and the first chamber (13), and in that the non-return valve (39) shuts off the connection from the first chamber (13) to the second chamber (27).
12. Actuator according to Claim 10, characterized in that between the first chamber (13) and the throttle (49) is arranged a flow-controlled valve (51) which is designed in such a way that it is normally open and can be closed by the fluid flowing to the first chamber (13).
13. Actuator according to Claim 12, characterized in that the flow-controlled valve (51) has a housing (52) with a first valve space (56) connected to the chamber (13), with a second valve space (57) connected to the throttle (49), with a third valve space (57) connected to the first switching valve (29) and with a valve orifice (60) arranged between the first and the second valve space (56, 58) and surrounded by a valve seat (59), and also has a valve member (62) which delimits the third valve space (57) and is displaceable axially in the housing and which cooperates with the valve seat (59) for the closing and opening of the valve orifice (60), and a throttle orifice (66) which is formed in the valve member (62) and which connects the first and the third valve space (56, 57) to one another.
14. Actuator according to Claim 13, characterized in that the throttle (49) is formed by the inner contour (67) of a central passage orifice (66) which is introduced into the valve member (62) and which has an inner contour (67) configured such that the fluid flowing from the third valve space (57) into the first valve space (56) brings about a pressure drop at the valve member (62).
15. Actuator according to Claim 14, characterized in that the inner contour (67) of the passage orifice (66) and the valve-opening spring (63) are coordinated with one another in such a way that the displacement force acting on the valve member (62) on account of the pressure difference is greater than the counteracting force of the valve-opening spring (63).
16. Actuator according to one of Claims 13-15, characterized in that the passage orifice (66) is in the form of a double cone frustum in which two coaxial cone frusta stand with their smaller bases one on the other.

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