Device for controlling charge exchange valves

Abstract

A device is proposed for controlling gas-exchange valves, at least one of which is assigned as intake valve (11) and at least one of which as discharge valve (12) to a combustion chamber of an internal combustion engine. The internal combustion engine includes electrohydraulic valve actuators (18) assigned in each case to a gas-exchange valve for its actuation, and a pressure-supply reservoir (26) having a high-pressure pump and a pressure-storage unit, which supplies the valve-actuators (18) with a fluid at high pressure. To reduce the energy consumed by the control device, the pressure-storage unit has two separate high-pressure reservoirs (31, 32), one of which is connected to the valve actuator (18) for the at least one intake valve (11) and the other to the valve actuator (18) for the at least one discharge valve (12). With the aid of a switching member (30), the high-pressure pump (27) is alternatively able to be connected to one or the other high-pressure reservoir (31, 32) and to a return line (37) leading to a fluid reservoir (29).

Description

BACKGROUND INFORMATION

[0001] The present invention is based on a device for controlling gas exchange valves according to the definition of the species in claim 1.

[0002] In a known device of this type (DE 198 26 047 A1), each electrohydraulic valve actuator has an operating piston that acts on a gas-exchange valve, and two hydraulic working chambers that are delimited by the operating piston. The first working chamber, which acts on the gas-exchange valve in the closing direction, is constantly filled with a fluid under high pressure, and the second working chamber, which acts on the gas-exchange valve in the opening direction, is alternately able to be filled with, or relieved of, a working medium or fluid under high pressure via a first and a second electrical control valve. For this purpose, a pressure-supply device delivers a fluid under high pressure, which is conveyed via the first electrical control valve to first working chamber, on the one hand, and to the second working chamber, on the other hand. The second working chamber is connected to a return line leading back to the fluid reservoir by way of the second electrical control valve. The pressure-supply device includes a working-pressure accumulator and a controlled variable displacement pump, which conveys fluid from a fluid reservoir to the working-pressure accumulator via a check valve. In the closed state of the gas exchange valve, the second working chamber is separated from the pressure supply device by the closed first control valve, and connected to the return line through the open second control valve, so that the operating piston is displaced into its closed position by the fluid pressure prevailing in the first working chamber. To open the gas exchange valve, the control valves are switched over, so that the second working chamber is cut off from the return line and connected to the pressure supply device. While opening the gas exchange valve, the operating piston is displaced toward the first working chamber since the piston area of the operating piston is larger in the second working chamber than the effective area of the operating piston in the first working chamber, the length of the opening stroke depending on the formation of the electric control signal applied to the first control valve and the opening velocity depending on the fluid pressure controlled by the pressure supply device. To close the gas exchange valve, the control valves switch over again, thereby connecting the second working chamber, which is blocked off from the pressure supply device, to the return line, and the fluid pressure prevailing in the first working chamber guiding the operating piston back into its valve-closed position, so that the gas exchange valve is closed by the operating piston.

SUMMARY 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 by dividing the pressure accumulator unit into two high-pressure accumulators for separately supplying of fluid to the valve actuators for the at least one intake valve, on the one hand, and for the at least one discharge valve, on the other hand, the fluid pressure in the two high-pressure circuits can be adapted for the intake and the discharge valve depending on the requirement for the degree of freedom allowed in the valve control by the electrohydraulic valve control, such as instant of valve actuation, lift, lift velocity and valve opening duration; and different pressure levels can be implemented. This makes it possible, for instance, to set a lower fluid pressure in the high-pressure circuit for the intake valves than the fluid pressure in the high-pressure accumulator for the discharge valves, which is predefined by the force required at the discharge valve, as specified by the combustion-chamber pressure. Because of this pressure drop in the one high-pressure circuit, it is possible to reduce the required energy. As a result, the hydraulic valve actuators for the intake and discharge valves may be standardized, since the higher forces required for activating the discharge valves against the combustion-chamber pressure are realized via the higher fluid pressure in the associated high-pressure circuit. Furthermore, appropriate control of the switching element for the alternate supply of the two high-pressure accumulators allows a torque compensation in the energy intake. In this way, a more homogeneous torque pick-up with a reduced effect on the driving comfort is attained.

[0004] The measures specified in the further claims permit advantageous further developments and improvements of the device for controlling gas-exchange valves indicated in claim 1.

[0005] Dividing the pressure-supply device into two separate high-pressure circuits for the intake valves and for the discharge valves as proposed by the present invention also allows the use of a constant displacement pump, which has a simple design, instead of the variable delivery pump, which has generally been used heretofore and has a technically more complicated design, thereby achieving a considerable savings effect in the production cost of the control device. The known constant displacement pump is distinguished in that it generates a delivery or volumetric rate that is a function of only its driving speed, regardless of the delivery pressure. The constant displacement pump may either be operated by an upstream delivery pump, for instance by the oil pump of the internal combustion engine, or it may be configured as a self-priming pump.

[0006] According to an advantageous specific embodiment of the present invention, the switching member is provided for the alternate connecting of the two high-pressure accumulators to the constant displacement pump and is configured as a 4/3 directional solenoid control valve having spring resetting. One of the three valve outlets of the solenoid valve is connected to one of the high-pressure accumulators and one is connected to the other high-pressure accumulator, and the third to the return line, while the valve inlet of the solenoid valve is connected to the pump outlet of the constant displacement pump.

BRIEF DESCRIPTION OF THE DRAWING

[0007] The present invention is elucidated in the following on the basis of an exemplary embodiment depicted in the drawing.

[0008] The figures show:

[0009] FIG. 1 a circuit diagram of a device for controlling gas exchange valves for an internal combustion engine;

[0010] FIG. 2 a detailed circuit diagram of an electrohydraulic valve actuator for actuating a gas-exchange valve in the control device according to FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0011] In the chosen exemplary embodiment, the device for controlling gas-exchange valves, shown as a circuit diagram in FIG. 1, controls a total of four intake valves 11 and a total of four discharge valves 12 of an internal combustion engine via an electronic control device 13. The number of intake valves 11 and discharge valves 12 may vary, however. Each intake valve 11 and discharge valve 12 is arranged in a cylinder head 14, shown in a cutaway view in FIG. 2, of a combustion cylinder and seals a combustion chamber formed in the combustion cylinder in a gastight manner. In a known manner, each gas exchange valve has a valve seat 16, which encloses an opening cross section 15 in cylinder head 14, and a valve element 17, which has a valve closure element 172 sitting on a valve shaft 171 that is guided so as to be axially displacable and cooperates with valve seat 16 to close and release opening cross section 15. By displacing valve shaft 171 in one axial direction or the other, valve closure element 172 lifts off from valve seat 16 or sets down on valve seat 16.

[0012] In the control device for the gas-exchange valves, each gas-exchange valve, that is each intake valve 11 and each discharge valve 12, is assigned an electrohydraulic valve actuator 18 for its actuation. Electrohydraulic valve actuator 18, which is known per se, is illustrated in detail in FIG. 2. It includes a double-acting hydraulic working cylinder 19 and two electrical control valves 20, 21, which are preferably configured as 2/2 directional solenoid control valves having spring resetting. Electrical control valves 20, 21 are controlled by electronic control device 13. In a manner known per se, hydraulic working cylinder 19 has a cylinder housing 22 and an operating piston 23, which is connected to valve shaft 171 of a gas-exchange valve and guided in cylinder housing 22 so as to be axially displacable, the operating piston dividing the interior of cylinder housing 25 into a first working chamber 24 and a second working chamber 25. First working chamber 24 is connected directly, and second working chamber 25 via first electrical control valve 20, to an hydraulic inlet 181 of valve actuator 18. Second working chamber 25 is connected to an hydraulic outlet 182 of valve actuator 18 via second electrical control valve 21. The mode of action of valve actuators 18 for opening and closing the associated gas-exchange valve is known and described in the introduction in the section “Background Information”.

[0013] To provide electrohydraulic valve actuator 18 with a working medium or a fluid under high pressure, the control device has a pressure-supply device 26. Pressure-supply device 26 includes a constant displacement pump 27 for generating high pressure, which is supplied from a fluid reservoir 29 by a presupply pump 28; a switching member 30 connected to the pump outlet of constant displacement pump 27; and two high-pressure accumulators 31, 32 which, depending on the switching position of switching member 30, are alternately able to be connected to the pump outlet of constant displacement pump 27 via a check valve 33 and 34, respectively. First high-pressure accumulator 31 is connected to a first outlet 261 of the pressure-supply device, and the second high-pressure accumulator to a second outlet 262 of pressure-supply device 26. Via outlet 261 and 262 of pressure-supply device 26, each high-pressure accumulator 31, 32 is connected to a pressure-relief valve 35 and 36, respectively, whose valve outlet is connected to a return line 37 discharging into fluid reservoir 29. In the exemplary embodiment shown, switching member 30 is configured as a 4/3 directional solenoid control valve 41 having spring resetting, which is triggered by electronic control device 13. Of the altogether three valve outlets of solenoid valve 41, a first valve outlet 412, having a check valve 33 interposed, is connected to first high-pressure accumulator 31, a second valve outlet 413, having check valve 34 interposed, to second high-pressure accumulator 32, and a third valve outlet 414 is connected to return line 37 or directly to fluid reservoir 29 via a connecting line 42; valve inlet 411 is connected to the pump outlet of constant displacement pump 27.

[0014] All electrohydraulic valve actuators 18 activating an intake valve 11 are connected to first output 261 of pressure-supply device 26 by way of their hydraulic input 181 and thus are connected to first high-pressure accumulator 31. All hydraulic outlets 182 of these valve actuators 18 are connected to return line 37 via a shared connecting line 38. All electrohydraulic valve actuators 18 for activating discharge valves 12 are connected to second input 262 of pressure-supply device 26 by way of their hydraulic inlets 181 and thus are connected to second high-pressure accumulator 32. Hydraulic outlets 182 of these valve actuators 18 are in turn connected to return line 37 via a shared connecting line 39. A check valve 43 and 44 may also be arranged in both connecting lines 38 and 39, respectively, the check valves opening toward return line 37.

[0015] Electrohydraulic valve actuators 18 for all gas-exchange valves, i.e., for all intake valves 11 and all discharge valves 12, have a uniform design. However, the actuating force that must be generated by valve actuators 18 for discharge valves 12, which is predefined by the combustion-chamber pressure, is considerably higher than the actuating force that valve actuators 18 must generate to actuate intake valves 11. These different forces are realized by different pressure levels in high-pressure accumulators 31, 32. The different pressure levels are realized by an appropriate adjustment of pressure-relief valves 35, 36. Depending on the switching position of 4/3 directional solenoid control valve 41, high-pressure accumulators 31 or high-pressure accumulator 32 are then tensioned by constant displacement pump 37 to the pressure level specified by respective pressure-relief valve 35 and 36. Since high-pressure accumulator 31 is set to a lower pressure level, the energy required for pressure generation is reduced. If no fluid is drawn off from the two high-pressure circuits via valve actuators 18, 4/3 directional solenoid control valve 41 is controlled to its intermediate position shown in FIG. 1, in which the fluid circulates without pressure via fluid reservoir 29.

[0016] Constant displacement pump 27 may alternatively be configured as a self-priming pump. In this case, presupply pump 28 is omitted, and constant displacement pump 27 draws in fluid directly from fluid reservoir 29.

[0017] The present invention is not limited to the described exemplary embodiment. For instance, the number of intake valves 11 and discharge valves 12 operated by the control device may vary. A so-called 3-valve operation is possible as well, in which each combustion chamber formed in a combustion cylinder of the internal combustion engine is assigned two intake valves 11 and one discharge valve 12.

Claims

1. A device for controlling gas-exchange valves, at least one of which is assigned as an inlet valve (11) and at least one as a discharge valve (12) to a combustion chamber of the internal combustion engine, each having an electrohydraulic valve actuator (18) assigned to a gas-exchange valve (11, 12) for its actuation, and having a pressure-supply device (26) supplying the valve actuators (18) with a fluid at high pressure, the pressure-supply device (26) having a high-pressure pump and a pressure-storage unit, wherein the pressure accumulator unit has two separate high-pressure accumulators (31, 32), one of which is connected to the valve actuator (18) for the at least one intake valve (11) and the other to the valve actuator (18) for the at least one discharge valve (12), and the high-pressure pump is optionally connectable by way of a switching member (30) to the one or to the other high-pressure accumulator (31, 32) and to a return line (37) leading to a fluid reservoir (29).

2. The device as recited in claim 1, wherein the high-pressure pump is configured as constant displacement pump (27) whose pump outlet is connected to the inlet of the switching member (30).

3. The device as recited in claim 1 or 2, wherein the switching member (30) is configured as a 4/3 directional solenoid control valve (41) having one valve inlet (411) and three valve outlets (412, 413, 414) having spring setting, whose valve inlet (411) is connected to the pump outlet and one of whose three valve outlets (412, 413, 414) is connected to the one and the other to the other high-pressure accumulator (31, 32) and the third is connected to the return line (37).

4. The device as recited in claim 3, wherein the 4/3 directional solenoid control valve (41) is controlled by an electronic control device (13).

5. The device as recited in one of claims 1 through 4, wherein the two high-pressure reservoirs (31, 32) are set to different pressure levels.

6. The device as recited in claim 5, wherein the high-pressure reservoirs (31, 32) are in each case connected via a pressure relief valve (35, 36) to the return line (37).

7. The device as recited in one of claims 1 through 6, wherein in a plurality of gas-exchange valves (11, 12) the valve actuators (18) of all intake valves (11) are connected to one, and the valve actuators (18) of all outlet valves (12) are connected to the other high-pressure reservoir (31, 32).

8. The device as recited in one of claims 2 through 7, wherein a presupply pump (28) delivering from the fluid reservoir (29) is arranged upstream from the constant displacement pump (27).

9. The device as recited in one of claims 2 through 7, wherein the constant displacement pump (27) is implemented as self-priming pump whose pump intake is directly connected to the fluid reservoir (29).

10. The device as recited in one of claims 1 through 9, wherein each electrohydraulic valve actuator (18) has a double-acting hydraulic working cylinder (19) for valve actuation and electric control valves (20, 21) controlling the operating pressure in the working cylinder (19).