GB2410063A - An electro-hydraulic device for controlling a gas exchange valve for an internal combustion engine - Google Patents

Abstract

A device 1 for controlling a gas exchange valve 2 for an internal combustion engine comprises: an electro-hydraulic valve actuator 36, means 13, 14 for influencing the valve actuator 36 in the opening direction of the gas exchange valve 2 by means of a fluid which is subjected to actuation pressure, and means 20 for the controlled discharge of the fluid out of the valve actuator 36. In order to be able to reliably and precisely adjust the closing speed of the gas exchange valve 2 and thus the speed at which a valve disc 5 of the gas exchange valve 2 impinges upon the valve seat ring 6, there is included a means 20 for the controlled discharge of the fluid comprising a pressure-controlled restrictor clement 22 which can be influenced by a control pressure and the device 1 further comprises means 24, 25, 26 to regulate the control pressure to a predeterminable pressure value.

Description

N 1, j 24 1 0063 j

DESCRIPTION

DEVICE FOR CONTROLLING A GAS EXCHANGE VALVE FOR AN INTERNAL

COMBUSTION ENGINE

The present invention relates to devices for controlling gas exchange valves for internal combustion engines, of the type comprising an electrohydraulic valve actuator, means for influencing the valve actuator in the opening direction of the gas exchange valve by means of a fluid which is subjected to actuation pressure, and means for the controlled discharge of the fluid out of the valve actuator, when the gas exchange valve moves in the closing direction.

Gas exchange valves are provided in the form of inlet valves of combustion chambers of an internal combustion engine for admitting a fuel- air mixture or only air into the combustion chambers and are provided in the form of outlet valves for discharging combustion exhaust gases from the combustion chambers. In the case of an electro hydraulic control of the gas exchange valves, force is introduced hydraulically for the actuation of the gas exchange valves, however the flow of force is controlled electrically, e.g. by means of solenoid valves. The ob Active of controlling the gas exchange valves of an internal combustion engine electro-hydraulically is to increase the efficiency of the internal combustion engine e.g. by dethrottling and to optimise the exchange of gas. This gives rise to a reduced consumption, lower exhaust gas emissions and lower noise development in the internal combustion engine.

The structure and mode of operation of a device for controlling a gas exchange valve of the type stated in the introduction is described in detail e.g. in DE 198 26 047 A 1. In the case of the known control device, a piston-shaped valve member is guided in an axially displaceable manner in a housing, wherein the valve member comprises on its end proximal to the combustion chamber a disc-shaped valve sealing surface, with which it cooperates with a valve seat fixed to the housing for controlling an inlet/outlet cross section at the combustion chamber of the internal combustion chamber to be supplied. At its shaft end remote from the combustion chamber, the valve member comprises a hydraulic piston which in the axial direction separates two hydraulic working chambers from one another, of which a lower working chamber which is proximal to the combustion chamber influences the valve member of the gas exchange valve in the closing direction, and an upper working chamber which is remote from the combustion chamber influences the valve member in the opening direction. In so doing, the lower working chamber is connected via a high pressure supply line in a continuous manner to a high pressure source (hydraulic pump) and is thus influenced with high pressure. The upper working chamber can be alternately filled with and relieved of high pressure via a high pressure supply line, which contains an electrical control valve, and via a relief line which contains means for the controlled discharge of the fluid from the valve actuator, e.g. a further electrical control valve.

The gas exchange valve is actuated by the controlled filling of the upper working chamber, wherein when the control valve is open in the high pressure supply line, a high pressure fluid flows into the upper working chamber, whose force application surface on the piston of the valve member of the gas exchange valve is larger than the force application surface in the lower working chamber, so that the piston and with it the valve member are displaced in the opening direction downwards and thus control the opening cross-section on the valve member seat to open. During this time, the relief line of the upper working chamber is closed by the means for the controlled discharge of the fluid (the further control valve). Then, by virtue of the controlled actuation of the control valves in the high pressure supply line and the relief line on the upper working chamber of the gas exchange valve member, it is possible to achieve various opening positions and to move the gas exchange valve back on to its valve seat by controlling the control valve in the relief line to open.

In addition to the approach of a single circuit system as disclosed in DE 198 26 047 A I, i.e. the engine oil used to lubricate the internal combustion engine is also used to actuate the electro-hydraulic valve control, it is also possible to operate the electro-hydraulic valve control by a separate hydraulic circuit. As a consequence, this prevents the electro hydraulic valve control system from exerting a serious influence both as a result of the expected contamination of the oil and also by the ageing of the oil. The closed fluid circuit for the electrohydraulic valve control is described in detail in the subsequently published DE 103 12 108 which relates back to the same Applicant as the present patent application.

Finally, in the likewise subsequently published DE 103 10 298 which also relates back to the same Applicant as the present patent application, an electro-hydraulic valve control system is described, in which upon closure of the gas exchange valves the speed at which the valve disc impinges upon the valve seat ring is controlled in dependence upon the engine speed. It is proposed to adjust the discharge of the fluid from the valve actuator by means of a pressure-controlled restrictor, in order in a controlled manner to be able to reduce the actuation pressure prevailing in the upper working chamber and to control the speed at which the valve disc impinges upon the valve seat ring.

It is an object of the present invention to provide a simple and reliable way of adjusting the speed at which the valve actuator impinges upon the valve seat ring as a gas exchange valve closes.

In accordance with the present invention the means for the controlled discharge of the fluid comprise a pressure-controlled restrictor element which can be influenced by a control pressure and the device comprises means for regulating the control pressure to a predeterminable pressure value.

By regulating the control pressure, the pressure-controlled restrictor can be actuated in a particularly precise and reliable manner and the gas exchange valves can be actuated in such a manner as to generate very little noise, to protect the material and above all with an extremely high degree of precision. In particular, it is possible in a controlled manner to reduce the speed of the gas exchange valves during the closing movement and to control with high-precision the speed at which the valve disc impinges upon the valve seat ring which is fixed to the housing.

In accordance with an advantageous development of the present invention, it is proposed that the predeterminable pressure value, to which the control pressure is regulated, is variable. The current pressure value, to which the control pressure is regulated, can be determined e.g. by time-controlled or event-controlled descent of a pressure characteristic curve. Moreover, it is feasible that the current pressure value is determined with reference to operating variables of the internal combustion engine and/or of a motor vehicle, into which the internal combustion engine is installed.

In accordance with a preferred embodiment of the invention, it is proposed that the means for regulating the control pressure comprise control means to vary the control pressure in a control path of the device. The control pressure which is to be regulated is thus present in a control path of the device, wherein the control path is provided with control means to vary the control pressure. The control path can branch off e.g. from a high pressure I S circuit. The control means are actuated by the means for regulating the control pressure for the purpose of regulating the control pressure to the predeterminable pressure value.

The number and configuration of the control means can be individually tailored in dependence upon the respective requirements. During usage of the internal combustion engine and the device in accordance with the invention for controlling gas exchange valves in a motor vehicle, it is necessary to ensure that the control means are particularly costeffective, reliable and robust.

In an advantageous manner, the control means in a non-return control path comprise at least one 2-way pressure reducing valve at the beginning of the control path. In the case of this embodiment, the control means are thus formed as a straightforward pressure reducing valve which cannot be used, however, to discharge pressure. It is also feasible to use a 3-way pressure reducing valve which can be used to build up and also reduce pressure. It is also proposed that the control means comprise two 2-way pressure reducing valves at the beginning of the control path. The first pressure reducing valve can be used to reduce an applied high pressure to a constant pressure. The second pressure reducing valve can be adjusted in such a manner that it uses the reduced constant pressure to generate the control pressure desired for the control path. This approach has

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the advantage that the pulsations, which are present in the high pressure circuit of the electro-hydraulic valve control, in the reduced pressure are considerably reduced downstream of the first pressure reducing valve and are scarcely still able to have an effect upon the control pressure prevailing in the control path. A further advantage is that the pressure difference from the reduced pressure to the desired control pressure is lower and the system is thus less sensitive and the accuracy of the control pressure is increased.

Preferably, between the at least one 2-way pressure reducing valve and the pressure- controlled restrictor a return line branches off from the control path, said return line having a restrictor. The restrictor has a fixed or variable restrictor cross-section. In the case of the exemplified embodiment having only one 2-way pressure reducing valve at the beginning of the control path, the pressure is built up in the control path by the restricted volume flow which is not leaked out via the restrictor. In the stationary case, when the control pressure is to be kept constant, precisely as much fluid as is discharged via the restrictor in the return line flows subsequently via the pressure reducing valve. In order to build up and reduce pressure, more or less fluid respectively is discharged via the pressure reducing valve than via the restrictor, as a result of which the pressure in the control path is increased or reduced. The advantage of this is that it is possible to obviate the hysteresis- encumbered switching procedure between the build-up of pressure and reduction in pressure in the pressure reducing valve.

In accordance with another advantageous development of the present invention, it is proposed that the control means comprise a 3-way pressure reducing valve at the beginning of the control path, wherein the control path is formed without any return line.

The control pressure can thus be built up and reduced via the pressure reducing valve.

When the pressure reducing valve opens, fluid flows into the control path and the control pressure is increased. In order to reduce the pressure in the control path, the 3-way pressure reducing valve opens a cross-section which issues via a return line into a fluid storage container.

In accordance with yet a further preferred embodiment of the present invention, it is proposed that the control means comprise a restrictor having a fixedly adjusted cross- section at the beginning of the control path and comprise a 2-way solenoid valve at the end of the control path, wherein the control path comprises a return line. The return line issues into a fluid storage container. The desired control pressure in the control path is thus adjusted by means of a fixedly adjusted restrictor point and a rapid switching solenoid valve. The control pressure is built up in the control path as a result of the difference in a volume flow from a high pressure circuit via the restrictor at the beginning of the control path and a leakage volume flow from the pressure-controlled throttling of the valve actuators. In order to be able to adjust the control pressure to the desired value, the solenoid valve is actuated at the end of the control path by a suitable actuation signal.

The volume now being discharged via the solenoid valve reduces the control pressure in the control path accordingly. By actuation of the solenoid valve in the closed loop the control pressure can be adjusted within predetermined limits. The cross-sectional area of the restrictor having the fixedly adjusted cross-section, the cross- sectional area of the 2way solenoid valve and the functional clearances on the pressurecontrolled restrictors, which produce the leakage volume flow, must be tailored to suit one another.

in accordance with yet another advantageous development of the present invention, it is proposed that the control means comprise a 2-way pressure reducing valve at the beginning of the control path and comprise a 2-way solenoid valve at the end of the control path, wherein the control path comprises a return line. The required control pressure in the control path is generated with the aid of a 2-way pressure reducing valve and the 2-way solenoid valve from the high pressure circuit. The pressure reducing valve is a 2-way valve, i.e. the control pressure in the control path can only be increased by the pressure reducing valve, in that corresponding actuation of the valve allows fluid to pass from the high pressure circuit into the control path. it is not possible to reduce the control pressure in the control path with the aid of the pressure reducing valve. For this purpose, a 3-way pressure reducing valve would be required. However, by reason of the design, this valve has either a relatively high leakage rate or else a point of discontinuity which would make it more difficult to regulate the control pressure in an exact manner. The control pressure is reduced with the aid of the 2-way solenoid valve. This is preferably closed when no current is supplied and is opened briefly for the purpose of reducing the control pressure. In order to be able to prevent the reduction in pressure occurring too rapidly, the solenoid valve has a relatively small opening cross- sectional area. The S leakages in the pressure-controlled restrictors of the valve actuators can lead to a steady increase in pressure in the control path which can also be reduced with the aid of the 2- way solenoid valve. The control pressure can be regulated even more conveniently if a proportional valve is used instead of the 2-way solenoid valve.

Moreover, a further embodiment is proposed, in which the control means comprise a 2- way solenoid valve at the beginning of the control path and comprise a 2- way solenoid valve at the end of the control path, wherein the control path comprises a return line. The required control pressure in the control path is thus generated with the aid of second switching valves directly from the high pressure circuit. In order to build up pressure in the control path, the first switching valve is opened. In order to reduce pressure in the control circuit, the second switching valve is opened. The second control valve is closed when no current is supplied and is only briefly actuated and thus opened for the purpose of reducing pressure. A suitable actuation of the two 2-way solenoid valves in the closed loop allows the control pressure to be adjusted in a convenient manner precisely and reliably within predetermined limits. In order to ensure that the electro-hydraulic valve control system can be regulated in an effective manner, the two solenoid valves have a relatively small opening cross-sectional area. The leakages in the pressure-controlled restrictors of the valve actuators can lead to a steady increase in pressure in the control path which can also be reduced with the aid of the second solenoid valve. Preferably, a restrictor having a fixedly adjusted cross-sectional area is connected in the direction of flow upstream of the 2-way solenoid valve at the beginning of the control path.

It is possible to improve the way in which the control pressure is regulated by using proportional valves instead of the switching valves. Accordingly, it is proposed that the control means comprise a proportional valve at the beginning of the control path and comprise a proportional valve at the end of the control path, wherein the control path comprises a return line.

Further features, possible applications and advantages of the invention are evident in the description hereinunder of exemplified embodiments of the invention which are illustrated in the drawing by way of example only. All of the described or illustrated features apply in their own right or in any combination, irrespective of their combination in the claims or their reference to previous claims and irrespective of their wording or depiction in the description and drawing respectively. In the drawings, Figure 1 shows a device in accordance with the invention for controlling a gas exchange valve for an internal combustion engine according to a first preferred embodiment; Figure 2 shows a device in accordance with the invention according to a second preferred embodiment; Figure 3 shows a device in accordance with the invention according to a third preferred embodiment; Figure 4 shows a device in accordance with the invention according to a fourth preferred embodiment; Figure 5 shows a device in accordance with the invention according to a fifth preferred embodiment; Figure 6 shows a device in accordance with the invention according to a sixth preferred embodiment; Figure 7 shows a device in accordance with the invention according to a seventh preferred embodiment; r Figure 8 shows a device in accordance with the invention according to an eighth preferred embodiment; Figure 9 shows a device in accordance with the invention according to a ninth preferred embodiment; Figure 10 shows an embodiment of a pressure-controlled restrictor element.

A device in accordance with the invention for controlling a gas exchange valve for an internal combustion engine is designated in Figure I in its entirety by the reference numeral 1. The device I serves to actuate gas exchange valves 2 for an internal combustion engine, not illustrated. By way of example only two of the gas exchange valves 2 which can be actuated by the device I are illustrated in Figure I and the subsequent I; igures. Of course, the device I in accordance with the invention can also be used to actuate more than two gas exchange valves 2. It would also be feasible to use it to actuate just one gas exchange valve 2.

A gas exchange valve 2 comprises a valve member 4 which can be displaced axially in a housing 3 and comprises on a lower disc-shaped end on the combustion chamber side a valve sealing surface 5 with which, in order to control an opening cross-section, it cooperates with a valve seat surface 6 on a housing 7 of the internal combustion engine, preferably a region of a cylinder head of the internal combustion engine. The opening provides access to a combustion chamber, not illustrated, of the internal combustion engine. The gas exchange valve 2 can be formed as an inlet valve, via which a fuel-air mixture (intake pipe injection) or merely air (direct injection) can pass into the combustion chamber. The gas exchange valve 2 can also be formed as an outlet valve, via which the combusted exhaust gases and other combustion residues can pass from the combustion chamber into an outlet pipe of the internal combustion engine. The valve member 4 comprises on its upper end remote from the combustion chamber a cross- sectional widening which forms a piston and with which the valve member 4 axially separates from each other two hydraulic working chambers 9, 11 in the housing 3. A bottom hydraulic working chamber 9 proximal to the combustion chamber influences the valve member 4 on a lower piston ring end surface 10 in the closing direction of the gas exchange valve 2. A top working chamber 1 I remote from the combustion chamber influences the downwardly opening valve member 4 in the opening direction, wherein the pressure in the upper working chamber 11 acts upon the entire upper piston end surface 12.

In order to supply pressure to the control device I by means of a fluid which is subjected to high actuation pressure, a pressure supply device is also provided which in the illustrated exemplified embodiment is formed by a pre-delivery pump 13 and a regulated high pressure pump 14 which deliver the fluid, preferably oil, from a fluid supply container 15 into a high pressure supply line 16. The pre-delivery pump 13 and the high pressure pump 14 are preferably driven mechanically. However, it is certainly feasible to drive one of the two pumps 13, 14 or even both pumps 13, 14 electrically. The high pressure pump 14 can be regulated on the intake side or on the pressure side. As an alternative, it is also possible to use a pressure reservoir chamber as a fluid source, *om which a large number of high pressure supply lines then lead off to the individual control devices of the individual gas exchange valves 2.

Branching off from the high pressure supply line 16 is a branch line 17 which issues via an opening I into the lower hydraulic working chamber 9. The original part of the high pressure supply line 16 issues via an opening IV into the upper hydraulic working chamber I 1, wherein between the branch into the branch line 17 and the opening IV into the upper working chamber I I there is disposed an electrical control valve l 8 into the high pressure supply line 16.

Furthermore, leading away from an opening III in the upper working chamber 11 is a relief line l 9 which issues into the fluid storage container 15 and in which there is disposed a second electrical control valve 20 which serves to close the relief line 19. Just upstream of the second control valve 20, a return line 21 branches off from the relief line 19 and issues via an opening 11 into the upper working chamber 11 of the gas exchange valve 2. A pressure-controlled restrictor element 22 is disposed between the branching point of the return line 21 from the relief line 19 and the opening 111 in the upper working chamber 11. The restrictor element 22 comprises a restrictor 22a which is influenced by a control pressure p which is present in a control path 23. The restrictor is illustrated in detail in Figure 9. In the case of the exemplified embodiment illustrated in Figure 1, the control path 23 terminates in the restrictor 22a of the second illustrated gas exchange valve 2. Therefore, this is a non-return control path 23. With the aid of the restrictor element 22, the discharge of the fluid from the upper working chamber 11 of the gas exchange valve 2 can be controlled, in order to be able to reduce the speed of the gas exchange valve 2 in a controlled manner during a movement in the closing direction.

The control pressure p prevailing in the control path 23 is regulated to a predeterminable pressure value which in certain circumstances can also be variable. For this purpose, the control path 23 is provided with a 3- way pressure reducing valve 24 upstream of the gas exchange valve 2 and upstream of the pressure-controlled restrictor elements 22 as seen in the direction of flow and is provided with a pressure sensor 25 downstream thereof as seen in the direction of flow. A measurement signal which corresponds to the control pressure p is transmitted by the sensor 25 to means 26 for regulating the control pressure p to a predeterminable pressure value. The means 26 are formed e.g. as microcontrollers or as a microprocessor. In dependence upon the detected actual value of the control pressure p, an actuation signal 27 for the purpose of actuating the 3-way pressure reducing valve 24 is determined in the means 26 and is transmitted to said 3-way pressure reducing valve. For example, by running a suitable control and/or regulation program in the means 26, the actuation signal 27 is determined by the actual values p ist, which are detected by means of the sensor 25, and by the predetermined desired pressure values p_soll.

By means of the actuation signal 27, an opening pressure, at which the 3way pressure reducing valve 24 opens, can be adjusted. Alternatively, the opening pressure could also be adjusted manually. The pressure reducing valve 24 can be used both to build up and reduce the control pressure p. If the pressure reducing valve 24 opens, fluid flows into the control path 23 and the control pressure p increases. In order to reduce the control pressure p in the direction of flow downstream of the pressure reducing valve 24, the valve 24 opens a cross-section which is connected via a line 28 to the fluid storage container 15.

The device 1, as illustrated in Figure 1, for controlling a gas exchange valve 2 for an internal combustion engine is a so-called open system, in which the required preliminary pressure is generated with the aid ofthe pre-delivery pump 13. The embodiments illustrated in Figures 5 to 8 are also open systems. In contrast thereto, the embodiments as shown in Figures 2 to 4 are closed systems, in which the level of the preliminary pressure is influenced with the aid of a fluid quantity located in the fluid circuit and is dependent upon the compressibility of the fluid and the design of the reservoir elements.

The mode of operation of the closed systems will be explained in detail hereinunder with reference to Figure 2. However, the mode of operation of the open system shall be explained in detail first. The device I in accordance with the invention for controlling a gas exchange valve 2 of an internal combustion engine operates as follows: As operation of the internal combustion engine commences, the high pressure pump 14 which is driven preferably thereby delivers a fluid, preferably oil, under high pressure into the high pressure supply line 16. This high pressure passes via the continuously open branch line 17 into the lower hydraulic working chamber 9 which by way of the lower piston ring end surface 10 holds the valve member 4 in its upwardly directly closed position. In the nonoperative or closed position of the gas exchange valve 2, the electrical control valves 18 and 20 are switched to a currentless state, wherein the first control valve 18 closes the high pressure supply line 16 into the upper working chamber 11. The second control valve 20 is switched to an open position in the currentless state, so that the relief line 19 leading off from the upper working chamber I I and into the fluid supply container 15 is open. In this manner, the valve member 4 is pressed against its valve seat 6 by the pressure in the lower working chamber 9. There is only ambient pressure in the upper working chamber 11.

In order then to open the gas exchange valve 2, the first control valve 18 in the high pressure supply line 16 is supplied with current and thus opened, whereas the second control valve 20 is closed by the supply of current thereto. As a consequence, fluid then flows into the upper working chamber I l. Since the upper pressure surface l 2 of the piston 4 is larger than the lower pressure surface 10 and the pressure in both working chambers 9, I I is approximately equal, the resultant compressive force then displaces the valve member 4 of the gas exchange valve 2 downwards to its opening position. The opening cross-section of the gas exchange valve 2 is controlled to open as a result of the valve sealing surface 5 being lifted from the valve seat 6 on the housing 7. In order to fix the gas exchange valve member 4 in a specific opening position, the control valve l 8 is closed and therefore the supply of fluid in the upper working chamber l l is interrupted.

As a result, the gas exchange valve 4 comes to a standstill, if the resultant force of the compressive forces in the working chambers 9 and 11 in cooperation with the restoring forces on the valve member 4 is zero. Thus, by the controlled actuation of the electrical control valves 18 and 20, which are preferably formed as a solenoid valve, all of the valveopening positions can be adjusted in dependence upon operating parameters of the internal combustion engine by means of the electrical control device 26.

In order then to close the gas exchange valve 2, the second control valve 20 in the relief line 19 is opened whilst the first control valve 18 remains closed. As a result, the pressure in the upper working chamber I I falls virtually to the level of ambient pressure, whereas the high system pressure still remains in the lower working chamber 9. Since the product of the pressure and the pressure surface in the lower working chamber 9 is then greater than in the upper working chamber 11, the piston 8 and thus the valve member 4 of the gas exchange valve 2 are displaced once again to the closed position by virtue of the resulting force and are pressed with the valve sealing surface 6 against the valve seat 7. The non-operative state is then achieved and a new operating cycle can take place. The high fluid pressure remains in the pressure line system, which is connected downstream to the high pressure pump 14, and in the lower working chamber 9. a

The pressure-controlled restrictor element 22 which is disposed in the return line 19 is illustrated in detail in Figure l O. The restrictor element 22 is influenced by the control pressure p prevailing in the control path 23. The restrictor element 22 comprises a housing 29 which is provided with a bore 30, in which a control piston 3 l is guided in an axial direction so as to be able to move in a reciprocating manner. The control pressure p acts upon a circular surface A of the control piston 31 and causes a force F = p A upon the control piston 31. This force F is counteracted by the force of a spring 32 which is supported on the one hand on the housing 29 and on the other hand on the control piston 3 l. If the control pressure p is increased, the spring 32 will be compressed until the l O resilient force is equal to the compressive force F. If the control pressure p is reduced, the spring 32 extends until the resilient force is equal to the compressive force F. As a result, the position of the control edge 33 of the control piston 31 changes with respect to the fluid openings 34 in the housing 29 and the degree of throttling of the fluid flow thus also changes, as the restrictor cross-section, through which fluid flows, of the openings l 5 34 is changed. By virtue of a corresponding formation of the control edge 33 and the spring 32, it is possible to produce a specific restrictor characteristic curve in dependence upon the position of the control piston 31 and thus upon the control pressure p. Since, during a closing movement of the valve member 4 of the gas exchange valve 2, the fluid escaping from the upper working chamber l l through the opening III is discharged through the pressure controlled restrictor element 22, more specifically through the openings 34 in the restrictor element 22, it is possible to use the control pressure p or the position of the control piston 31 and thus the control edge 33 to control the discharge of the fluid from the upper working chamber l l. This will give a suitable progression of the control pressure p over time, in order to be able to reduce the speed of the closing movement of the valve member 4 of the gas exchange valve 2 in a controlled manner. In addition to a temperature compensation of the speed at which the valve disc 5 impinges upon the valve seat ring 7, it is also possible to achieve rotational speed dependence of the contact speed by the restrictor element 22. l

Figure 2 illustrates a second preferred embodiment ofthe device I in accordance with the invention, wherein the device I which is illustrated in Figure 2 does not comprise an open fluid circuit but rather comprises a closed fluid circuit. This is a so-called closed system.

In a closed system, the level of the preliminary pressure is not influenced by a pre delivery pump but rather with the aid of the fluid quantity located in the fluid circuit and is dependent upon the compressibility of the fluid and upon the design of the reservoirs present in the fluid circuit. The fluid quantity located in the system is determined by a recirculating pump 35 which delivers the fluid from a fluid storage container 15 (compensation container) into the preliminary pressure circuit. In the closed fluid circuit an approximately constant fluid volume is circulated which is supplied and kept constant by means of the recirculating pump 35, in that any leakage losses occurring in the valve actuators 36 are compensated for by the recirculating pump 35. For this purpose, the recirculating pump 35 draws corresponding fluid volumes from the fluid storage container 15 and supplies them to the fluid circuit. The leakage losses or leakages occurring in the valve actuators 36 are fed back via a leakage line 37 into the fluid storage container 15.

The switching on and off of the recirculating pump 35 or the rotational speed of the recirculating pump 35 is controlled by a control device 38 in dependence upon the fluid pressure prevailing in the preliminary pressure circuit. For this purpose, the fluid pressure in the preliminary pressure circuit is measured by means of a pressure sensor 39.

If the fluid pressure falls below a predeterminable pressure value, the recirculating pump is switched on or its rotational speed increased. If the predeterminable pressure value is then achieved, the recirculating pump 35 is then switched off or its rotational speed reduced. The control device 38 and the means 26 for regulating the control pressure p to a predeterminable pressure value can be formed either as two separate units or as one joint unit. However, since in the case of the embodiment in Figure 2 the control means 24 are controlled by pressure and are not actuated electrically, the means 26 are not provided.

In the case of the exemplified embodiment which is illustrated in Figure 2, the control means to vary the control pressure p in the control path 23 ofthe device 1 are likewise formed as a 3-way pressure reducing valve 24, in which the opening pressure is adjusted by means of the actuation signal 27.

The exemplified embodiment illustrated in Figure 3 is also a device I in accordance with the invention having a closed fluid circuit. However, the control means to vary the control pressure p in the control path 23 of the device I comprise a 2-way pressure reducing valve 40 and a restrictor 41 having a fixedly adjusted cross-sectional area. The restrictor 41 is disposed in a bypass line 42 which in the direction of flow downstream of the pressure reducing valve 40 branches off from the control path 23 and issues via the leakage line 37 into the fluid storage container 15. The pressure reducing valve 40 alone is not able to discharge any pressure. In the case of this exemplified embodiment, the pressure is built up in the control path 23 by means of a volume flow which is discharged via the restrictor 41 into the leakage line 37. In the stationary case, when the control pressure p is to be kept constant, precisely as much fluid as is discharged via the restrictor 41 flows subsequently via the restrictor element 40. In order to build up and reduce pressure, more or less fluid respectively is discharged via the pressure reducing valve 40 than via the restrictor 41, as a result of which the control pressure p in the control path 23 is increased or reduced. The advantage of this embodiment is that the switching procedure, which is encumbered by hysteresis, between the build-up of pressure and the reduction in pressure of a 3-way pressure reducing valve 40 is obviated. This embodiment can also be utilised both in a closed fluid circuit (cf. Figure 3) and in an open system.

Figure 4 illustrates another preferred embodiment of the device 1 in accordance with the invention. The control means to vary the control pressure p in the control path 23 are provided in the form of two 2-way pressure reducing valves 40a, 40b which are disposed in series. The first 2-way pressure reducing valve 40a reduces the high pressure prevailing in the high pressure supply line 16 to a constant pressure, e.g to 25 bar. The second 2-way pressure reducing valve 40b is adjustable and uses the reduced pressure to generate the control pressure p desired for the control path 23. This approach has the advantage that the pulsations, which are present in the high pressure circuit of the electro hydraulic valve control 1, in the reduced pressure are considerably smaller downstream of the constant pressure reducing valve 40a and are thus no longer able to have such a significant effect upon the control pressure p in the direction of flow downstream of the adjustable pressure reducing valve 40b. A further advantage is that the pressure difference from the reduced high pressure to the desired control pressure p is smaller and thus the entire system I becomes less sensitive and the control pressure p can be regulated with a greater degree of accuracy.

Figure 5 illustrates a fifth preferred embodiment of the present invention. The required control pressure p in the control path 23 is adjusted by a restrictor 43 and by a rapid switching solenoid valve 44 (control valve). The restrictor 43 preferably has a constant opening cross-sectional area. The control pressure p is built up in the control path 23 by means of a volume flow Q6 from the high pressure circuit and a volume flow Q37 as a leakage volume flow from valve actuators 36 of the pressure-controlled restrictor elements 22 via the leakage line 37. In order to be able to adjust the control pressure p to a desired pressure value, the solenoid valve 44 is actuated by means of a suitable actuation signal 27. In the currentless state, the control valve 44 is closed. By actuation of the valve 44, it is opened for the duration of the actuation. The volume flow Q44 thus being discharged reduces the control pressure p in the control path 23 accordingly. By actuation of the valve 44 in the closed loop, the control pressure p can be adjusted with high precision within the predetermined limits. The restrictor 43, the solenoid valve 44 and the functional clearances on the brake slides 22b of the pressurecontrolled restrictor elements 22 must be tailored to suit one another.

Figure 6 illustrates a sixth preferred embodiment of the device I in accordance with the invention. The required control pressure p in the control path 23 is generated from the high pressure circuit 16 with the aid of a pressure reducing valve 45 and a rapid switching solenoid valve 44 which can be formed as a 2-way valve. The pressure reducing valve 45 is a 2-way valve, i.e. it can only increase the control pressure p in the control path 23, in that fluid passes from the high pressure circuit l 6 into the control path 23. It is not possible to reduce the control pressure p in the control path 23 with the aid of the pressure reducing valve 45. For this purpose, a 3-way valve would be required. However, by reason of the design, this valve has either a relatively high leakage rate or a point ol discontinuity which makes it more difficult to regulate the control pressure p in an exact manner. rl he control pressure p is reduced with the aid of the 2-way switching valve 44.

This is closed when no current is supplied and is actuated briefly and thus opened for the purpose of reducing the reservoir pressure p. In order to prevent the pressure from being reduced too quickly, the solenoid valve 44 has a relatively small opening cross-sectional l O area. Leakages in the pressure-controlled restrictor element 22 can lead to a steady increase in pressure in the control path 23 which can also be reduced with the aid of the solenoid valve 44.

It is possible to simplify the ability to regulate the control pressure p by using a proportional valve 46 instead of the 2-way valve 44. A corresponding embodiment of the device l in accordance with the invention is illustrated in Figure 7.

In Figure 7, the pressure reducing valve 45 is controlled by pressure, i. e. it is controlled in dependence upon the applied controlled pressure p or upon the pressure applied in the direction of flow downstream of the valve 45, depending upon whether they exceed or are less than a predeterminable desired pressure value (so-called opening pressure). The size of the opening pressure can be predetermined by means of the control device 26 via a corresponding actuation signal 27a. The actuation signal 27b can be used to vary the opening characteristic of the proportional valve 46, so that it opens by a corresponding value when a specific pressure value is applied. This means that the valve characteristic curves can be predetermined by the control device 26.

Figure 8 illustrates a further preferred exemplified embodiment of the device l in accordance with the invention. The required control pressure p in the control path 23 is generated with the aid of two switching valves 47 and 48 directly from the high pressure applied in the high pressure circuit. In the direction of flow upstream of the first switching valve 47, a restrictor 49 is disposed in the control path 23, which restrictor preferably comprises a fixed cross-sectional area. In order to build up the pressure in the control path 23, the first switching valve 47 is opened, wherein the second switching valve 48 remains in its closed position with no current being supplied thereto. In order to reduce the control pressure p in the control path 23, the second switching valve 48 is opened briefly. This is closed when no current is supplied and is only opened briefly for the purpose of reducing pressure. By suitable actuation of the two valves 47 and 48 by means of the actuation signals 27a and 27b in the closed loop, the control pressure p can be regulated quickly and reliably within the predetermined limits. In order to ensure that the entire system can be regulated effectively, the two solenoid valves 47 and 48 have a relatively small opening cross- section. Leakages in the pressure-controlled restrictors 22 lead to a steady increase in pressure in the control path 23 which can also be reduced with the aid of the solenoid valve 48. It is possible to improve the ability to regulate the control pressure p by using proportional valves instead of the switching valves 47 and 48.

In the case of the last exemplified embodiment of the present invention as illustrated in Figure 9, a restrictor 50 which has a constant crosssectional area is disposed at the beginning of the control path 23. Disposed adjacent thereto is a pressure reducing valve 45, preferably a 2-way valve, of which the opening pressure is adjusted by means of the actuation signal 27a. Disposed at the end of the control path 23 is a control valve 44 which as required is actuated and thus opened via the actuation signal 27b in order to reduce the control pressure p in the control path 23.

As a departure from the exemplified embodiments which have been described with reference to Figures I to 9, it is naturally possible to combine, on the one hand, a non return control path 23 or a control path 23 with a return line with, on the other hand, the various control means (pressure reducing valves, control valves or proportional valves, 2 way or 3-way valves, mechanically or electrically actuated valves, restrictors etc.) as required, in order to regulate the control pressure p to influence the pressure-controlled restrictor element 22 depending upon the requirements of the respective application.

Claims (14)

1. Device for controlling a gas exchange valve for an internal combustion engine, comprising - an electro-hydraulic valve actuator, - means for influencing the valve actuator in the opening direction of the gas exchange valve by means of a fluid which is subjected to actuation pressure, and - means for the controlled discharge of the fluid out of the valve actuator, if the gas exchange valve moves in the closing direction, wherein the means for the controlled discharge of the fluid comprise a pressure controlled restrictor element which can be influenced by a control pressure and the device further comprises means to regulate the control pressure to a predeterminable pressure 1 5 value.

2. Device as claimed in claim I, wherein the predeterminable pressure value is variable.

3. Device as claimed in claim 1 or 2, wherein the means to regulate the control pressure comprise control means to vary the control pressure in a control path of the device.

4. Device as claimed in claim 3, wherein the control means comprise at least one 2-way pressure reducing valve at the beginning of the control path, wherein the control path is formed without any return line.

5. Device as claimed in claim 4, wherein the control means comprise two 2way pressure reducing valves at the beginning of the control path.

6. Device as claimed in claim 4 or 5, wherein between the at least one 2way pressure reducing valve and the pressure-controlled restrictor element a return line branches off from the control path, said return line being provided with a restrictor.

7. Device as claimed in claim 3, wherein the control means comprise a 3-way pressure reducing valve at the beginning of the control path, wherein the control path is formed without any return line.

8. Device as claimed in claim 3, wherein the control means comprise a restrictor having a fixedly adjusted cross-section at the beginning of the control path and comprise a 2-way solenoid valve at the end of the control path, wherein the control path comprises a return line.

9. Device as claimed in claim 3, wherein the control means comprise a 2way pressure reducing valve at the beginning of the control path and a 2way solenoid valve at the end of the control path, wherein the control path comprises a return line.

10. Device as claimed in claim 3, wherein the control means comprise a 2way pressure reducing valve at the beginning of the control path and comprise a proportional valve at the end of the control path, wherein the control path comprises a return line.

I 1. Device as claimed in claim 3, wherein the control means comprise a 2way solenoid valve at the beginning of the control path and a 2-way solenoid valve at the end of the control path, wherein the control path comprises a return line.

12. Device as claimed in claim 11, wherein a restrictor having a fixedly adjusted cross- sectional area is connected upstream of the 2-way solenoid valve in the direction of flow at the beginning of the control path.

13. Device as claimed in claim 3, wherein the control means comprise a proportional valve at the beginning of the control path and comprise a proportional valve at the end of the control path, the control path comprising a return line.

14. A device for controlling a gas exchange valve for an internal combustion engine, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.