Patent Application
20110277712
The invention relates to an electrohydraulic valve controller for the variable actuation of a gas-exchange valve of an internal combustion engine. The valve controller comprises:
a master piston driven by a camshaft,
a slave piston driving the gas-exchange valve,
a pressure space defined by the master piston and the slave piston and having variable volume,
a pressure-relief space connected to a hydraulic medium supply of the internal combustion engine,
a control line connecting the pressure space to the pressure-relief space and an electrically controllable hydraulic valve that is arranged in this control line and releases or blocks a hydraulic medium flow through the control line,
a bypass line connecting the pressure space to the pressure-relief space and a non-return valve that is arranged in this bypass line and releases a hydraulic medium flow through the bypass line into the pressure space and blocks a hydraulic medium flow into the pressure-relief space.
Such a valve controller emerges from EP 0 931 912 A2 that is considered a class-forming patent. The variability of the control times and the maximum stroke of the gas-exchange valve is achieved in that a sub-volume of the pressure space acting as a so-called hydraulic linkage can be stepped-down continuously into the pressure-relief space for an opened hydraulic valve and accordingly the cam stroke specified by the camshaft is transmitted completely, partially, or not at all to the gas-exchange valve. Consequently, the hydraulic valve whose switching function must be guaranteed in a precise and reproducible way under all operating conditions of the internal combustion engine takes over a significant amount of responsibility for the functional reliability of the valve control.
However, because a no longer closing hydraulic valve is accompanied with a closure of the gas-exchange valve or the associated gas-exchange valves and incorrect functioning of the hydraulic valve can never be completely ruled out, the valve control proposed in the cited publication lacks emergency running properties that allow at least a limited further operation of the internal combustion engine.
The present invention is therefore based on the objective of refining a valve control of the type named above so that this also has, in the case of incorrect functioning of the hydraulic valve, adequate emergency running properties. Below it is understood that a valve stroke that is adequate for a successful gas-exchange cycle in the internal combustion engine can be generated also in the emergency running mode.
The objective is met by the features of the invention, while advantageous refinements and constructions of the invention are described below and in the claims. Consequently, the valve control should comprise an additional hydraulic valve that is arranged in the control line between the hydraulic valve and the pressure-relief space and blocks, in the case of an incorrectly open hydraulic valve, the hydraulic medium flow through the control line into the pressure-relief space. Through these measures, also for a permanently open hydraulic valve—for example, due to an electrical current interruption or a mechanical defect in the hydraulic valve—a pressure buildup adequate for the stroke transfer to the gas-exchange valve is made possible in the pressure space in that the additional hydraulic valve is closed during the emergency running operation and thus prevents a pressure relief of the pressure space.
For the case that is preferred in the sense of the invention such that the hydraulic valve has a non-energized open construction, it can be provided that the additional hydraulic valve likewise can be controlled electrically and has a non-energized open construction. One essential advantage of this design is the favorable energy balance of the valve control, because the additional hydraulic valve would then be energized only during the emergency running operation. Regardless of this arrangement, the possibility nevertheless also arises to provide the additional hydraulic valve as a non-energized closed construction and/or to select, instead of an electrical control, a hydraulic, pneumatic, or mechanical control.
In addition, the hydraulic valve should have a construction that switches significantly more quickly than the additional hydraulic valve. Because the normal functionality of the valve control can be eliminated during the time-limited emergency running operation, the additional hydraulic valve can remain permanently closed and consequently can be constructed as an economical valve that switches comparatively more slowly.
Additional features of the invention emerge from the following description and from the drawing in which one embodiment of the invention is shown simplified. The sole FIGURE shows a hydraulic switching diagram of an electrohydraulic valve controller according to the invention.
In the FIGURE, the essential components of an electrohydraulic valve controller 1 according to the invention for variable actuation of a gas-exchange valve 2 of an internal combustion engine are disclosed with reference to a hydraulic switching diagram. Shown are a master piston 3 that is driven via a lever-like cam follower 4 by a cam 5 of a camshaft 6 and a slave piston 7 that drives, through the use of a valve bridge 8, a pair of identically acting gas-exchange valves 2, i.e., intake or exhaust valves, against the force of valve springs 9 acting in the closing direction. The master piston 3 and the slave piston 7 define a hydraulic pressure space 10 that is connected by a control line 11 to a hydraulic pressure-relief space 12. A hydraulic valve 13 that is arranged in the control line 11 and has an electrically controllable and non-energized open construction according to the drawn switching symbol provides that a hydraulic medium flow through the control line 11 is opened up or blocked and accordingly the pressure space 10 has a variable volume during the actuation of the master piston 3. The continuous variability of the valve actuation generated in this way extends within the limits of the maximum opening stroke of the gas-exchange valve 2 on one hand, when the hydraulic valve 13 is located in the closed position during the entire stroke phase of the master piston 3, and complete shutdown of the gas-exchange valve 2 on the other hand, when the hydraulic valve 13 is located in the open position at least up to the maximum height of the master piston 3.
The pressure-relief space 12 connected to a hydraulic medium supply 14 of the internal combustion engine and, in the present case, to its lubricant supply via a non-return valve 15 that has a spring-loaded pressure storage device 16 of known construction and is connected via a bypass line 17 to the pressure space 10 for the purpose of balancing out hydraulic medium losses caused by leakage from the pressure space 10. In this way, a non-return valve 18 arranged in the bypass line 17 has the effect that a hydraulic medium flow through the bypass line 17 is opened up into the pressure space 10 and blocked into the pressure-relief space 12.
In case that the hydraulic valve 13 incorrectly remains open during the operation of the internal combustion engine—as mentioned above, a cause for this could be, in particular, an interrupted power supply to the hydraulic valve 13—and this would lead to the complete closure of the gas-exchange valve 2 for a correspondingly unacceptable operating behavior of the internal combustion engine, the valve controller 1 comprises, according to the invention, an additional hydraulic valve 19 that is arranged in the control line 11 between hydraulic valve 13 and pressure-relief space 12 and is opened during the normal, i.e., error-free operation of the valve controller 1. The additional hydraulic valve 19, however, allows emergency running operation of the internal combustion engine. This is initiated in that the additional hydraulic valve 19 closes after detection of the incorrectly open hydraulic valve 13, so that the hydraulic medium pressure building up in the pressure space 10 can no longer be discharged into the pressure-relief space 12 and the gas-exchange valves 2 open sufficiently wide. In the theoretical case of a completely incompressible and leak-tight pressure space 10, the stroke specified by the master piston 3 could be transmitted to the gas-exchange valves 2 and would correspond to the maximum opening stroke mentioned above.
Compared with requirements for the hydraulic valve 13, significantly lower requirements can be placed on the switching rate of the additional hydraulic valve 19 that likewise has an electrically controllable and non-energized open construction according to its switching symbol. This is based in that the additional hydraulic valve 19 must switch only once at the beginning of the emergency running operation from the open position into the closed position. Accordingly, the additional hydraulic valve 19 could be constructed significantly more economically than the significantly more quickly switching hydraulic valve 13.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 049 181.0 | Sep 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/061895 | 9/15/2009 | WO | 00 | 6/3/2011 |
