Device for controlling gas exchange valves

Abstract

A device is described for controlling gas exchange valves of an internal combustion engine, which has hydraulic valve positioners (17, 18), each having a positioning piston (26) acting on the gas exchange valve (12, 13) and two hydraulic working chambers (27, 28), delimited by the positioning piston (26), of which the first working chamber (27), for closing the gas exchange valve (12, 13), is continuously under fluid pressure and the second working chamber (28), for opening the gas exchange valve (10), may be alternately filled and emptied with pressurized fluid via a first and second electrical control valve (34, 35). To reduce the number of control valves necessary, for a valve pair, the filling of the second working chamber (28) of the second valve positioner (18) is performed via the second working chamber (28) of the first valve positioner (17), which is connected to the first control valve (34), after a predetermined stroke of the positioning piston (26) of the first valve positioner (17) to open the assigned gas exchange valve (12).

Description

BACKGROUND INFORMATION

[0001] The present invention is directed to a device for controlling gas exchange valves in combustion cylinders of an internal combustion engine as recited in the preamble of claim 1.

[0002] In a known device of this type (German Patent Application 198 26 047 A1) each valve positioner, whose positioning piston is connected in one piece with the valve tappet of the assigned gas exchange valve, has its first working chamber continuously connected to a high-pressure source and has its second working chamber connected to a first electrical control valve, which alternately closes or releases a supply line to the high-pressure source, and to a second control valve, which alternately closes or releases a relief line. The electrical control valves are implemented as 2/2 directional-control solenoid valves having spring return. In the event the control valves are without current, the first working chamber is still under high pressure, while the second working chamber is disconnected from the high-pressure source and is connected to the relief line. The gas exchange valve is closed. To open the gas exchange valve, both control valves have current applied to them. Through the changeover of the control valves, the second working chamber of the valve positioner is shut off in relation to the relief line by the second control valve and connected to the high-pressure source by the first control valve using the supply line. The gas exchange valve opens, the size of the opening stroke being a function of the implementation of the electrical control signal applied to the first electrical control valve and the opening speed being a function of the pressure introduced from the high-pressure source. In order to keep the gas exchange valve in a specific open position, the first control valve is subsequently deenergized, so that it shuts off the supply line to the second working chamber of the valve positioner. In this way, all of the valve opening positions of the gas exchange valve may be set using an electrical control unit for producing control signals. Two electrical control valves, which apply hydraulic pressure to the assigned valve positioner appropriately, are necessary for controlling each gas exchange valve.

ADVANTAGES OF THE INVENTION

[0003] The device according to the present invention for controlling gas exchange valves, having the features of claim 1, has the advantage that through the direct hydraulic coupling of the second working chambers of two valve positioners of a pair of valve positioners to convert the hydraulic energy into a linear movement of the gas exchange valves, the number of control valves required for controlling two valve positioners may be reduced from the four previously necessary to only two. Since in this way the number of output stages required in the electronic control unit for activating the control valves is halved, and therefore the wiring cost is also reduced, the manufacturing costs for the control device may be significantly reduced overall. In addition, the installation space required is reduced by dispensing with components and wiring, the probability of breakdown of the control valves is reduced through the lower number of valves, and both the hydraulic and the electrical energy required are reduced.

[0004] Advantageous refinements and improvements of the device for controlling gas exchange valves specified in claim 1 are possible through the measures listed in the further claims.

[0005] According to a preferred embodiment of the present invention, the two gas exchange valves actuated by the first and second valve positioners are situated in the same combustion cylinder of the internal combustion engine. This has the advantage that the power surplus of the second valve positioner for opening the assigned gas exchange valve does not have to be dimensioned as high as that of the first valve positioner, which must open the assigned gas exchange valve against the maximum counterpressure occurring in the combustion cylinder, but may be dimensioned lower, since the counterforce for opening the second gas exchange valve of the same combustion cylinder may have already been partially reduced via the open first gas exchange valve.

[0006] According to an advantageous embodiment of the present invention, at least the first valve positioner has a mechanical stroke limiter, which is dimensioned in such a way that it blocks further stroke movement of the positioning piston in the valve opening direction after release by the positioning piston of the outlet on the first valve positioner connected to the second working chamber of the second valve positioner. Such a stroke limiter in the first valve positioner is energetically advantageous if the maximum opening cross-section of both gas exchange valves is still sufficient for the full-load range; if the positioning piston in the first valve positioner is blocked, the entire power surplus may be used to displace the positioning piston in the second valve positioner and to open the second gas exchange valve. The stroke speed of both gas exchange valves is a function of pressure and is influenced by the overlap of the strokes in connection with the release of the outlet in the second working chamber of the first valve positioner to the second working chamber of the second valve positioner. In this way, a speed characteristic of the gas exchange valves which is a function of pressure and stroke results.

DRAWING

[0007] The present invention is described in the following in greater detail on the basis of an exemplary embodiment illustrated in the drawing. In this case, the drawing shows a circuit diagram of a device for controlling two gas exchange valves in a combustion cylinder of an internal combustion engine.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0008] Using the device for controlling gas exchange valves which is illustrated in the circuit diagram in FIG. 1, a pair of gas exchange valves 12, 13, which are positioned in a combustion cylinder 10 of an internal combustion engine (only shown as a section), is controlled to optimize energy as a function of an operating map of the internal combustion engine. Gas exchange valves 12, 13 may be intake valves or exhaust valves which seal a combustion chamber 11, implemented in combustion cylinder 10, gas-tight. Each gas exchange valve 12, 13 has, in a known way, a valve seat 15 which encloses an opening cross-section 14 in the combustion cylinder and a valve element 16 having a valve closing body 162, seated on an axially displaceable valve shaft 161, which works together with valve seat 15 to close and release opening cross-section 14. By displacing valve shaft 161 in one axial direction or the other, valve closing body 162 lifts off of valve seat 15 or presses against valve seat 15.

[0009] The device for controlling both gas exchange valves 12, 13, which is illustrated in the drawing in a block diagram, has a first valve positioner 17, which actuates gas exchange valve 12, and a second valve positioner 18, which actuates gas exchange valve 13. Each of the two hydraulic valve positioners 17, 18, also called actuators, engages on valve shaft 161 of one of the two gas exchange valves 12, 13. The valve control device also includes a pressure supply device 19, which includes a preferably regulatable high-pressure pump 20 that conveys fluid, hydraulic oil, for example, from a fluid reservoir 21, a non-return valve 22, and a pressure accumulator 23. A continuous, regulatable high pressure acts on output 191 of pressure supply device 19, tapped between non-return valve 22 and pressure accumulator 23, which a second non-return valve 24, having a passage direction pointing toward output 191, may also be connected upstream from.

[0010] Both hydraulic valve positioners 17, 18 are implemented identically and are each implemented as a double-acting working cylinder having a cylinder housing 25 and a positioning piston 26 guided axially displaceably therein, which divides the inside of cylinder housing 25 into a first working chamber 27 and a second working chamber 28. Both first working chambers 27 of both valve positioners 17, 18 are permanently connected to output 191 of pressure supply device 19. Second working chamber 28 of first valve positioner 17 has an inlet 29 and two outlets 30, 31, second outlet 31 being positioned at a stroke distance from first outlet 30 such that in the closed position of positioning piston 26 illustrated in FIG. 1, in which it has caused closing of gas exchange valve 12, second outlet 31 is sealed by positioning piston 26 and is only released to second working chamber 28 after a predetermined opening stroke of positioning piston 26 for opening gas exchange valve 12. Second working chamber 28 of second valve positioner 18 has an inlet 32 and an outlet 33. Inlet 29 on first valve positioner 17 is connected via a first control valve 34 to output 191 of pressure supply device 19. First outlet 30 of first valve positioner 17 is connected to the valve input of a second control valve 35, whose valve output is connected to a return line 36 to fluid reservoir 21. Inlet 32 on second valve positioner 18 is connected, using second outlet 31 on first valve positioner 17 and outlet 33 on second valve positioner 18, to the valve inlet of second control valve 35 via a non-return valve 37. The passage direction of non-return valve 37 points from outlet 33 to second control valve 35. Both control valves 34, 35 are implemented as 2/2 directional-control solenoid valves having spring return.

[0011] The mode of operation of the valve control device is as follows:

[0012] If, as shown in the drawing, first control valve 34 is closed and second control valve 35 is open, both second working chambers 28 of valve positioners 17, 18 are unpressurized and the high pressure of pressure supply device 19 existing in first working chambers 27 of valve positioners 17, 18 ensures that positioning pistons 26 are located in their upper final stroke position and thus keep gas exchange valves 12, 13 in their closed position. In this upper final stroke position or closed position, positioning piston 26 in first valve positioner 17 seals second outlet 31, connected to inlet 32 on second valve positioner 18.

[0013] If control valves 34, 35 are switched over, second working chambers 28 of both valve positioners 17, 18 are shut off from return line 36 and second working chamber 28 of first valve positioner 17 is connected to output 191 of pressure supply device 19. Since the area of positioning piston 26 delimiting second working chamber 28 is greater than the working area of positioning piston 26 in first working chamber 27, the high pressure existing in second working chamber 28 causes positioning piston 26 to move downward and lift valve closing body 162 off of valve seat 15 via valve shaft 161, so that gas exchange valve 12 opens.

[0014] Depending on the operating point of the internal combustion engine, different opening cross-sections 14 must be provided in combustion cylinder 10, i.e., only one gas exchange valve 12 or both gas exchange valves 12, 13 must be activated using a larger or smaller stroke. If a larger opening cross-section is required, outlet 31 is released by positioning piston 28 after a defined stroke of positioning piston 26 in first valve positioner 17, so that high pressure now also builds up in second working chamber 28 of second valve positioner 18. The power excess in second working chamber 28 thus acting on positioning piston 26 in second valve positioner 18 now displaces positioning piston 26, so that valve element 13 also opens.

[0015] Both outlets 30, 31 are spaced optimally on first valve positioner 17 with regard to energy as a function of the operating characteristics map of the internal combustion engine. It is also possible to make the stroke distance of both outlets 30, 31 controllable, in that, for example, second outlet 31 is placed in a positioning ring, displaceable on cylinder housing 25, which is connected liquid-tight to second working chamber 28. A lifting drive, controlled by an electronic control unit which also controls both control valves 34 and 35, engages on the positioning ring. The axial displaceability of second outlet 31 in relation to first outlet 30 is symbolized in the drawing by a double arrow 39 assigned to second outlet 31. Alternatively, multiple second outlets 31, which are sealable in sequence by the positioning ring, may be positioned one behind another in the stroke direction of positioning piston 26.

[0016] The stroke height of particular gas exchange valve 12 or 13 upon opening is primarily a function of the activation duration of first control valve 34. In the event of longer activation, a mechanical stroke limiter engages, which is at least provided in first valve positioner 17. The stroke limiter, which is only schematically indicated in the drawing as stop 38, is dimensioned, for example, so that positioning piston 26 in first valve positioner 17 is prevented from further stroke movement in the valve opening direction shortly after releasing outlet 31 to second working chamber 28 of second valve positioner 18. Such a stroke limiter is energetically advisable, since then only hydraulic energy is still necessary for displacing positioning piston 26 in second valve positioner 18. A requirement for such a stroke limiter is that the sum of opening cross-sections 14 in both gas exchange valves 12, 13 still achievable through the stroke limiter is sufficient for the full-load range of the internal combustion engine.

[0017] The stroke speed of both gas exchange valves 12, 13 is primarily a function of pressure and is influenced by the overlap of the strokes and the release of the connection between first working chambers 28 of both valve positioners 17, 18.

Claims

1. A device for controlling gas exchange valves (12, 13) in combustion cylinders (10) of an internal combustion engine, having hydraulic valve positioners (17, 18), assigned to each gas exchange valve (12, 13), which each have a positioning piston (26) acting on the gas exchange valve (12, 13) and two hydraulic working chambers (27, 28), delimited by the positioning piston (26), of which the first working chamber (27), which acts on the gas exchange valve (12, 13) in the closing direction, is continuously filled by a pressurized fluid and the second working chamber (28), which acts on the gas exchange valve (12, 13) in the opening direction, can be alternately filled and emptied by a pressurized fluid via a first and second electrical control valve (34, 35), wherein the second working chamber (28) of the second valve positioner (18) of a pair of valve positioners is filled via the second working chamber (28) of the first valve positioner (17), the second working chamber communicating with the first control valve (34), following a predetermined stroke of the positioning piston (26) of the first valve positioner (17) in the opening direction of the assigned gas exchange valve (12).

2. The device as recited in claim 1, wherein the second working chamber (28) of the first valve positioner (17) has an inlet (29) connected to the first control valve (34) and two outlets (30, 31), of which a first outlet (30) is connected to the second control valve (35) and a second outlet (31) is connected to the second working chamber (28) of the second valve positioner (18), which, in turn, is connected via a non-return valve (37), whose shutoff direction is towards the second working chamber (28), to the second control valve (35); and the second outlet (31) is positioned in the second working chamber (28) of the first valve positioner (17) at a stroke distance from the first outlet (30) such that it is sealed by the positioning piston (26) of the first valve positioner (17) in the closed position, thereby causing the assigned gas exchange valve (12) to close, and it is released after a predetermined stroke of the positioning piston (26) in an opening direction, thereby causing the assigned gas exchange valve (12) to open.

3. The device as recited in claim 2, wherein the mutual stroke distance of the two outlets (30, 31) on the first valve positioner (17) is variable in a controlled way.

4. The device as recited in claim 2 or 3, wherein the second working chamber (28) of the second valve positioner (18) has an inlet (32) connected to the second outlet (31) on the first valve positioner (17) and an outlet (33) connected to the non-return valve (37).

5. The device as recited in one of claims 2 through 4, wherein the first valve positioner (17) has a mechanical stroke limiter (38), which is dimensioned in such a way that, after release of the second outlet (31) by the positioning piston (26), it blocks further stroke movement of the positioning piston (26) in the opening direction the assigned gas exchange valve (12).

6. The device as recited in one of claims 1 through 5, wherein the two gas exchange valves (12, 13) actuated by the first and second valve positioners (17, 18) are situated in the same combustion cylinder (10).

7. The device as recited in one of claims 1 through 8, wherein the gas exchange valves (12, 13) assigned to the first and second valve positioners (17, 18) are used as intake or exhaust valves.