Valve drive
Valve drive with a first actuator (1) for opening and/or closing a gas-exchange valve (2), in particular of an internal combustion engine, and a separate second actuator (3) for the valve-play compensation of the gas-exchange valve (2), the second actuator (3) being developed as a double-action, preferably hydraulic, piston cylinder arrangement with at least two working surfaces (A1, A2) that can be subjected to pressure.
The present invention relates to a valve drive with a first actuator for opening and/or closing a gas-exchange valve, in particular of an internal combustion engine, and a separate second actuator for the valve-play compensation of the gas-exchange valve.
Valve drives with a device for valve-play compensation are known in principle from the state of the art. There are many reasons for valve-clearance. Thus, during the overall life cycle of a gas-exchange valve, mechanical wear occurs at the valve seat. Above all in large engines, because of the long valve stems of the gas-exchange valves used there, considerable thermal expansions occur which also require a valve-play compensation. Thus it is the rule in large engines to compensate for a valve-clearance of up to 4 mm over the life cycle of a gas-exchange valve.
It is known in the state of the art to provide a hydraulically operated plunger cylinder with a ram as a second actuator for the valve-play compensation of the gas-exchange valve, while the opening and closing of the gas-exchange valve is carried out by a first actuator e.g. in the form of a cam, acting on the cylinder, of a camshaft. In principle it is preferable that the second actuator for the valve-play compensation remains as rigid or firm as possible in terms of length during the actuation which means opening and/or closing of the gas-exchange valve, in order to guarantee a relatively rigid transfer of the lifting movement caused by the first actuator and thus a slight sinking of the second actuator. On the other hand the valve-clearance is to be compensated in enclosed engine valves. In the valve drives known in the state of the art the rigidity of the second actuator during the opening and closing of the gas-exchange valve leaves something to be desired. This is frequently attributable to problems with a very high air content in the hydraulic fluid.
It is thus the object of the invention to improve a valve drive according to the preamble such that these problems are avoided.
This is achieved according to the invention by developing the second actuator as a double-action, preferably hydraulic, piston cylinder arrangement with at least two working surfaces that can be subjected to pressure.
Thus according to the invention it is provided, in a system with a first actuator for opening and closing the gas-exchange valve and a separate second actuator for valve-play compensation, to develop the second actuator as a double-action cylinder. This has at least two, preferably opposed, working surfaces to which pressure can be applied. It is now possible, through the measure according to the invention, to operate with higher system pressures for valve-play compensation. Thus valve drives according to the invention provide, in favourable variants, impaction with a pressure of at least 100 bar, preferably at least 200 bar. Overall a valve drive is thereby created, the second actuator or which is very rigid for valve-play compensation upon the lifting movement for the opening and closing of the gas valve. Additionally, problems with air bubbles in hydraulic fluids at correspondingly high pressures are avoided. Moreover, air bubbles initially present are quickly displaced at high pressures in the cylinder space. Operational readiness can therefore be quickly reached with high pressures.
In order to guarantee a compact design it is preferably provided that the first actuator is arranged essentially in the piston of the piston cylinder arrangement of the second actuator. The first actuator can be able to be actuated hydraulically or pneumatically or electrically. Alternatively a compact design is also achieved if the first actuator has a bush, preferably a bush-shaped piston, the piston cylinder arrangement of the second actuator being arranged essentially in the bush, preferably in the bush-shaped piston. Here the first actuator can be actuated hydraulically or pneumatically or electrically or by means of a cam or a camshaft.
Valve drives according to the invention can be used for both small and large engines. They generally have a high dynamic during adjustment. The sinking of the second actuator during a period is very well settable.
Further advantages and details of the present invention arise from the following description of figures. There are shown in:
In the state of the art it is customary, as shown in
A first variant according to the invention of a valve drive is represented in
In a further variant, not explicitly represented here, the spring 16 can also be omitted in the embodiment according to
In both variants the piston 25 is drawn back down by the actuator force upon closing of the gas-exchange valve. A corresponding valve-play compensation takes place through the described alternating play upon each opening and closing stroke of the first actuator 1. This movement is damped by the throttle action of the inlet throttles 14 and l5. The first actuator 1 is thus housed floating essentially inside the second actuator 3. The cylinder of the second actuator 3 is made up, for ease of dismantling and assembly, of two e.g. cylinder elements 9 and 10 which can be screwed to each other. In order to make possible an assembly and dismantling of the first actuator 1, a double-shell structure, not shown in detail here, is also recommended for the piston 25 in all variant versions with the first actuator 1 located in the piston 25.
Another version of the invention is represented in
A further embodiment is shown in
In order on the one hand to be able to set, uncoupled from each other, the slight sinking of the valve-play compensation upon the lifting movement of the gas-exchange valve 2 and on the other hand a low power requirement of the system, it is provided to use the outlet throttles 12 and 13 in order to set the total consumption of the system. For this purpose, they preferably have a much greater throttle coefficient than the inlet throttles 14 and 15. Thus something approaching the system pressure pS is established in the compensation chambers 4 and 5. The influence of the two inlet throttles 14 and 15, which advantageously have the smaller throttle coefficient, ensure sinking during the lifting phase. As a result, the two described requirements are uncoupled from each other, an overall low output and fluid consumption respectively of the second actuator being able to be ensured by the outlet throttles 12 and 13. In further versions, not explicitly shown here in more detail, the throttles 12, 13, 14 and 15 can also be realized as separate throttles. The second actuator is preferably developed hydraulically and is operated with hydraulic fluid. In the case of the shown embodiments, however, it is also possible to operate the second actuator 3 pneumatically. In this case the driving fluid is a gas, preferably air.
Claims
1. Valve drive with a first actuator for opening or closing a gas-exchange valve and a separate second actuator for the valve-play compensation of the gas-exchange valve, wherein the second actuator is developed as a double-action piston cylinder arrangement with at least two working surfaces that can be subjected to pressure.
2. Valve drive according to claim 1, wherein the double-action piston cylinder arrangement has at least two equal-sized working surfaces and the second actuator has an additional elastic element.
3. Valve drive according to claim 1, wherein the additional elastic element is a helical spring.
4. Valve drive according to claim 1, wherein the double-action piston cylinder arrangement is developed as a differential piston cylinder arrangement with at least two different-sized working surfaces.
5. Valve drive according to claim 1, wherein the first actuator is essentially located in the piston of the piston cylinder arrangement of the second actuator.
6. Valve drive according to claim 5, wherein the first actuator can be actuated hydraulically or pneumatically or electrically.
7. Valve drive according to claim 1, wherein the first actuator has a bush, the piston cylinder arrangement of the second actuator being essentially arranged in the bush.
8. Valve drive according to claim 7, wherein the bush is a bush-shaped piston.
9. Valve drive according to claim 7, wherein the first actuator can be actuated hydraulically or pneumatically or electrically or by means of a cam or a camshaft.
10. Valve drive according to claim 1, wherein the working surfaces each at least partially border a compensation chamber, and an inlet throttle is arranged in each case between each compensation chamber and a feed line for pressurized fluid.
11. Valve drive according to claim 10, wherein the feed line is located essentially centrally between the inlet throttles.
12. Valve drive according to claim 10, wherein a pressure of at least 100 bar can he applied at the feed line.
13. Valve drive according to claim 10, wherein a pressure of at least 200 bar can be applied at the feed line.
14. Valve drive according to claim 10, wherein the inlet throttles have different throttle coefficients.
15. Valve drive according to claim 10, wherein an outlet throttle is located in each case between each compensation chamber and at least one drain line for draining off the fluid.
16. Valve drive according to claim 15, wherein the throttle coefficient of the outlet throttles is greater than the throttle coefficient of the inlet throttles.
17. Valve drive according to claim 10, wherein the fluid is a hydraulic fluid or a gas.
18. Valve drive according to claim 1, wherein the first actuator opens or closes a gas-exchange valve of an internal combustion engine.
19. Valve drive according to claim 1, wherein the second actuator is developed as a double action hydraulic piston cylinder arrangement.
Type: Application
Filed: Jun 16, 2005
Publication Date: Dec 22, 2005
Inventors: Rudolf Scheidl (Plaika), Andreas Plockinger (Wels)
Application Number: 11/154,862