US20040074456A1

US20040074456A1 - Device for controlling gas exchange valves

Info

Publication number: US20040074456A1
Application number: US10/399,290
Authority: US
Inventors: Hermann Gaessler; Hubert Schweiggart; Bernd Rosenau; Ralph Engelberg
Original assignee: Individual
Current assignee: Robert Bosch GmbH
Priority date: 2001-08-17
Filing date: 2002-06-08
Publication date: 2004-04-22
Also published as: KR20040030072A; EP1432891A1; JP2005500463A; WO2003018968A1; DE10140528A1; RU2286468C2; KR100928405B1

Abstract

An apparatus for controlling gas exchange valves of an internal combustion engine is disclosed, which have hydraulic valve actuators (11) each assigned to one gas exchange valve, with one adjusting piston (13) acting on the gas exchange valve and two hydraulic work chambers (121, 122) defined by the adjusting piston (13), of which chambers the first work chamber (121), acting on the gas exchange valve (10) in the closing direction, is constantly filled with fluid that is under pressure, and the second work chamber (122), acting on the gas exchange valve (10) in the opening direction, can be filled with and relieved of fluid that is under pressure in alternation via a first and second electrical control valve (24, 25; 26, 27). To reduce the cost, the second control valves, which are preferably combined into a valve unit (40), for one pair of valve actuators (11), which actuate two gas exchange valves used as inlet or outlet valves of a combustion cylinder, are triggered by a common electrical control signal

Description

PRIOR ART

The invention is based on an apparatus for controlling gas exchange valves in combustion cylinders of an internal combustion engine as generically defined by the preamble to claim 1.

In a known apparatus of this type (German Patent Disclosure DE 198 26 047 A1), each valve actuator, whose adjusting piston is connected integrally to the valve tappet of the associated gas exchange valve, communicates constantly by its first work chamber with a high-pressure source and with its second work chamber on the one hand is connected to a first electrical control valve that in alternation closes or opens a supply line to the high-pressure source and on the other to a second control valve that alternately opens or closes a relief line. The electrical control valves are embodied as 2/2-way magnet valves with spring restoration. When the control valves are without current, the first work chamber is at high pressure as before, while the second work chamber is disconnected from the high-pressure source and is connected to the relief line. The gas exchange valve is closed. For opening the gas exchange valve, both control valves are supplied with current. Because of the switchover of the control valves, the second work chamber of the valve actuator is blocked on the one hand from the relief line by the second control valve and on the other is made to communicate, by the first control valve, with the supply line to the high-pressure source. The gas exchange valve opens; the length of the opening stroke and the opening speed depend on the embodiment of the electrical control signal applied to the first electrical control valve. To keep the gas exchange valve in a defined open position, the first control valve is then switched to be without current, so that it blocks off the supply line to the second work chamber of the valve actuator. In this way, by means of an electrical control unit for generating control signals, all the valve opening positions of the gas exchange valve can be set. For controlling each gas exchange valve, two electrical control valves are required, which correspondingly subject the associated valve actuator to hydraulic pressure.

ADVANTAGES OF THE INVENTION

The apparatus according to the invention for controlling gas exchange valves as defined by claim 1 has the advantage that by means of the linkage of the two second control valves of a pair of valve actuators for common closure of the two gas exchange valves used as inlet or outlet valves in a combustion cylinder of the internal combustion engine, the expense for calculation for generating the control signals for the valve control is reduced, and in the control unit, there is a savings of one control signal output with an associated end stage or amplifier stage. Moreover, by keeping the separately triggered first control valves, the opening stroke of the inlet or outlet valves can be performed with a variable length and at staggered times.

By the provisions recited in the other claims, advantageous refinements of and improvements to the apparatus for controlling gas exchange valves as disclosed in claim 1 are possible.

In a preferred embodiment of the invention, the two second control valves for one pair of valve actuators are embodied as a structural valve unit with a common electrical control input. As a result, there is a saving of one complete control valve, and only one signal line from the control unit to the control input of the valve unit is required.

In the simplest case, in an advantageous embodiment of the invention, the valve unit is a 2/2-way magnet valve with two switching positions and two controlled valve connections, of which one valve connection is connected to a relief line and the other valve connection is connected, each via a respective connecting line, to the second work chambers of the pair of valve actuators. In that case, one check valve with a flow direction toward the 2/2-way magnet valve must be inserted into each of the connecting lines, so that at different strokes of the gas exchange valves, an inflow of fluid from the valve actuator of the more widely opened gas exchange valve to the valve actuator of the less widely opened gas exchange valve will be avoided. If the same gas exchange valve is always opened earlier or more widely, then it suffices to provide only a single check valve for the valve actuator associated with the other gas exchange valve that does not open as widely or as early. In designing the control signal, a distinction should still be made between a one-and two-valve mode, or in other words whether one or both of the gas exchange valves have to be closed, since this has an effect on the closing speed of the gas exchange valves. Because of the faster diversion of fluid from the valve actuator, a faster closing motion can be attained in the one-valve mode.

In an advantageous embodiment of the invention, the valve unit is a 3/2-way magnet valve with two switching positions and three controlled valve connections, of which a first valve connection communicates with a relief line, and the two further valve connections, which can be connected simultaneously to the first valve connection, each communicate with a respective second work chamber of the pair of valve actuators. Here the check valves in the connecting lines between the valve unit and the two valve actuators can be dispensed with, if the valve connection that forms the valve outlet and that communicates with the relief line is dimensioned as large enough in the open state that a reverse flow of fluid from one of the further valve connections to the other of the further valve connections is avoided. Once again, however, in designing the control signals a distinction must be made between a one-and two-valve mode.

In an advantageous embodiment of the invention, the valve unit is a 4/2-way magnet valve with two switching positions and four controlled valve connections, of which a first valve connection and a second valve connection each communicate with one relief line, and the third valve connection, which can be connected to the first valve connection, and the fourth valve connection, which can be connected to the second valve connection, can each communicate with a respective second work chamber of the pair of valve actuators. Preferably, the first and second valve connections are connected to relief lines that lead separately to a fluid reservoir. In this embodiment of the valve unit, the same closing speeds of the gas exchange valves always result, regardless of whether one gas exchange valve is open, or both gas exchange valves are open. This greatly simplifies the calculation of the control signals.

In an advantageous embodiment of the invention, the valve unit is a 4/3-way magnet valve ( 46), with three switching positions and four controlled valve connections, of which two valve connections each communicate with a respective relief line and two valve connections each communicate with a respective second work chamber of the pair of valve actuators. The 4/3-way magnet valve is embodied such that in one switching position, both second work chambers of the pair of valve actuators each communicate with a respective relief line, while in a further switching position, both second work chambers of the pair of valve actuators are blocked, and in a further switching position, one of the two second work chambers of the pair of valve actuators is blocked while the other communicates with a relief line.

In an alternative embodiment of the invention, the valve unit is a 4/4-way magnet valve with four switching positions and four controlled valve connections, of which two each communicate with a respective relief line and two each communicate with a respective second work chamber of the pair of valve actuators. The 4/4-way magnet valve is embodied such that in one switching position, the second work chambers of the pair of valve actuators communicate with the relief lines, in a further switching position the second work chambers are blocked off, and in the two further switching positions, in alternation, one of the two second work chambers of the pair of valve actuators communicates with a respective relief line, and the other one is blocked. In both above variants of the embodiment of the valve unit, an expansion of the function can be achieved because in addition to the joint closure of the gas exchange valves, now the two gas exchange valves can also be closed at staggered times.

DRAWING

The invention is described below in further detail in terms of an exemplary embodiment shown in the drawing. Shown are: [0011]
FIG. 1, a circuit diagram of an apparatus for controlling two gas exchange valves, disposed in different combustion cylinders of an internal combustion engine; [0012]
FIG. 2, a schematic illustration of a gas exchange valve in a combustion cylinder of the engine; [0013]
FIGS. [0014] 3-5, each, a circuit diagram of a modified apparatus for controlling two gas exchange valves, disposed in a combustion cylinder of an internal combustion engine, in three further exemplary embodiments;
FIGS. 6 and 7, each one alternative exemplary embodiment of the valve unit in the apparatus of FIG. 5.[0015]

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The apparatus shown in a circuit diagram in FIG. 1 is used to control two gas exchange valves in one combustion cylinder of an internal combustion engine; typically this cylinder is equipped with two inlet valves and two outlet valves. The two [0016] gas exchange valves 10 form the inlet valves or the outlet valves of the combustion cylinder. In FIG. 1, the control is shown for only the two inlet valves of the combustion cylinder. An identical circuit diagram applies to the two outlet valves of the combustion cylinder. In a 4-cylinder engine with a total of sixteen gas exchange valves, there are eight inlet valve and eight outlet valves, whose triggering in the correct order is performed by a common electronic control unit 30. In a 4-cylinder engine with twelve gas exchange valves, there are two inlet valves and one outlet valve in each of the four individual cylinders. Below, the triggering of two inlet valves of one combustion cylinder will be described as an example. The same remarks apply correspondingly to the other gas exchange valves.
For each [0017] gas exchange valve 10 in the system, one valve actuator 11 is provided, which has an adjusting piston 13 that is guided axially displaceably in a work cylinder 12. The adjusting piston 13 divides the work cylinder 12 into two hydraulic work chambers 121 and 122, defined by the work cylinder, and is solidly connected to the valve tappet 14 of the gas exchange valve 10. FIG. 2, in an enlarged illustration, schematically shows a valve actuator 11 in conjunction with the associated gas exchange valve 10. The valve tappet 14, on its end remote from the adjusting piston 13, has a platelike valve sealing face 15, which to control an opening cross section cooperates with a valve seat face 17 embodied on the housing 16 of the combustion cylinder of the engine. The work cylinder 12 has a total of three hydraulic connections, of which one hydraulic connection 121a discharges into the first work chamber 121, and two hydraulic connections 122 a and 122 b discharge into the second work chamber 122.
The apparatus also has a [0018] pressure supply system 22, which comprises a fluid reservoir 18, a high-pressure pump 19, a check valve 20, and a reservoir 21 for pulsation damping and energy storage. The outlet 221 of the pressure supply system 22 that is tapped between the check valve 20 and the reservoir 21 communicates via a line 23 with the hydraulic connections 121 a of the two valve actuators 11, so that the first work chambers 121 of the valve actuators 11 are acted upon constantly by the approximately constant hydraulic pressure prevailing at the outlet 221 of the pressure supply system 22, which can be regulated to various set-point values.
The [0019] second work chambers 122 of the work cylinders 12 can be connected on the one hand, by means of the hydraulic connections 122 a and 122 b of the work cylinder 12 and via first electrical control valves 24 and 26, to the outlet 221 of the pressure supply system 22 and on the other, via hydraulic connecting lines 35, 36 and second electrical control valves 25 and 27, to a relief line 28 and 29, respectively, which in turn discharge into the fluid reservoir 18. All the control valves 24-27 are embodied as switching valves, specifically as 2/2-way magnet valves with spring restoration. However, proportional valves can also be used as the control valves. The electrical control inputs are connected to the electronic control unit 30 via electrical signal lines 31, 32, 33, 34; the electrical signal lines 31 and 32 lead away to the two first control valves 24, 26 from separate signal outputs 301, 303 with separate end stages of the control unit 30, while the two electrical signal lines 32 and 34, which lead to the two second control valves 25, 27, lead away from a common signal output 302 with an end stage or amplifier stage.
Each [0020] valve actuator 11 is integrated with the associated first control valve 24 and second control valve 25, or the associated first control valve 26 and second control valve 27, respectively, in a respective actuator housing 35 and 36, which is indicated by dashed lines in FIG. 1. For joint triggering of the two second control valves 25 and 27 in the two actuator housings 35, 36 via the signal output 302 of the electronic control unit 30, the end stage of the control unit must be dimensioned accordingly.
The mode of operation of the apparatus for controlling the two inlet valves or [0021] gas exchange valves 10 is as follows:
In the basic position or position of repose shown in FIG. 1, all the control valves [0022] 24-27 are without current, and the first control valves 24 and 26 assume their blocking position and block off the respective second work chamber 122 of the associated valve actuator 11 from the outlet 221 of the pressure supply system 22, while the second control valves 25 and 27 assume their open position and connect the second work chamber 122 with the respective relief line 28 or 29. As a result of the system pressure prevailing in the first work chamber 121 of each valve actuator 11, the adjusting piston 13 is displaced upward in terms of FIG. 2, until the valve sealing face 15 of the gas exchange valve 10 rests on the valve seat face 17 on the housing 16 of the combustion cylinder of the engine. The adjusting piston 13 assumes the position inside the work cylinder 12 of the valve actuator 11 as shown in FIG. 1, and the gas exchange valves 10 are closed.
For opening the two [0023] gas exchange valves 10, a control signal for reversing the second control valves 25, 27 is generated by the electronic control unit 30, and after amplification in the end stage via the signal output 302, this signal reaches both the electrical control input of the second control valve 25 and the electrical control input of the second control valve 27. As a result, the second control valves 25, 27 are simultaneously transferred to their blocking position, in which they block off the second work chamber 122 from the respective relief line 28 and 29. At a certain instant, an amplified control signal is applied to the electrical control input of the first control valve 24 by the electronic control unit 30, via its signal output 301. This first control valve switches over and connects the second work chamber 122 with the outlet 221 of the pressure supply system 22, so that now the system pressure prevails in the second work chamber 122 of the valve actuator 11 as well. Since the piston face of the adjusting piston 13 that defines the first work chamber 121 is smaller than the face of the adjusting piston 13 that defines the second work chamber 122, the result is a displacement force that moves the adjusting piston 13 downward in FIGS. 1 and 2, as a result of which the gas exchange valve 10 is opened. The length of the opening stroke of the gas exchange valve 10 is dependent on the opening duration and opening speed of the first control valve 24 and 26, respectively. Once the desired stroke of the gas exchange valve 10 is reached, the current supply to the first control valve 24 is discontinued, and the first control valve 24 returns to its blocking position. The pressure in the second work chamber 122 is maintained, so that the gas exchange valve 10 maintains its assumed opening stroke unchanged.
The [0024] electronic control unit 30, either simultaneously or at staggered times depending on requirements, generates a control signal for the first control valve 26; via the signal output 303, this signal reaches the electrical control input of the first control valve 26. This valve switches over in the same way into its work position, and via the adjusting piston 13 that is being displaced, the other gas exchange valve 10 is opened. The length of the opening stroke can be dimensioned to be the same as or different from the opening stroke of the other gas exchange valve 10. Once again, when the desired opening stroke is reached, the control signal at the signal output 303 of the control unit 30 disappears, causing the first control valve 26 to return to its blocking position and to block off the second work chamber 122 that is under pressure.
For closing the two [0025] gas exchange valves 10, which takes place at the same instant, the control signal at the signal output 302 of the electronic control unit 30 disappears, and the two second control valves 25, 27 are transferred, by the restoring force of the restoring springs, to their position of repose, in which they cause the second work chamber 122 of the two gas exchange valves 11 with the respective relief line 28 and 29. The pressure in the second work chamber 122 disappears, and as a result of the system pressure prevailing in the first work chamber 121 of the two valve actuators 11, the piston 13 in the work cylinder 12 moves upward in terms of FIGS. 1 and 2, until the two gas exchange valves 10 are closed.
The control apparatuses, shown in FIGS. [0026] 3-5 in modified form, for a pair of identical gas exchange valves, such as inlet or outlet valves, in a combustion cylinder of an internal combustion engine differ from the control apparatus described in conjunction with FIG. 1 in that the two second control valves 25, 27 for controlling the pair of valve actuators 11 in FIG. 1 are combined into a valve unit 40, and the pair of valve actuators is integrated with the valve unit 40 and the two first control valves 24, 26, each associated with one valve actuator 11, in a common actuator housing 39. Depending on how the valve unit 40 is embodied, there is either—as in FIGS. 3 and 4—now only one common relief line 28, or—as in FIG. 5—once again two relief lines 28, 29 are carried separately to the fluid reservoir 18. With regard to the other components, the control apparatuses of FIGS. 3-5 match the apparatus of FIG. 1, and thus identical components are identified by the same reference numerals.
In the control apparatus of FIG. 3, the [0027] valve unit 40 is a 2/2-way magnet valve 41 with spring restoration. It has two switching positions with two controlled valve connections 411 and 412, of which the valve connection 411 is connected to the relief line 28. The two connecting lines 35 and 36, leading from the two work chambers 122 of the valve actuators 11 of the pair of valve actuators to the valve unit 40 are connected to the other valve connection 412. In each connecting line 35, 36, there is a respective check valve 42 and 43, with a flow direction pointing to the 2/2-way magnet valve 41.
These [0028] check valves 42, 43 prevent a fluid flow from the valve actuator 11 of the more widely open gas exchange valve 10 to the valve actuator 11 of the less widely open gas exchange valve 10 in the event that the strokes of the gas exchange valves 10 are of different lengths. If one gas exchange valve 10 is always opened earlier or more widely, then in the associated valve actuator 11, the check valve 42 or 43 in the connecting line 35 or 36 leading to the relief line 28 can be dispensed with, although at the cost of a certain limitation in function.
The control apparatus of FIG. 4 differs from that in FIG. 3 only in having a different embodiment of the [0029] valve unit 40. Here the valve unit 40 is a 3/2-way magnet valve 44, with two switching positions and three controlled valve connections 441, 442 and 443, of which a first valve connection 441 communicates with the relief line 28, and the two further valve connections 442 and 443, which can be connected simultaneously to the first valve connection 441, each communicate via a respective one of the connecting lines 35 and 36 with a second work chamber 122 of the two valve actuators 11. The valve connection 441, which forms the valve outlet and communicates with the relief line 28, is dimensioned as large enough, in the open state of the 3/2-way magnet valve 44, that a reverse flow of fluid from one valve connection 442 to the other valve connection 443, or vice versa, is avoided. It is understood that in the closing state of the 3/2-way magnet valve 44, there is no communication between the valve connections 442 and 443. The check valves required in the connecting lines 35, 36 in the exemplary embodiment of FIG. 3 can be omitted here.
In the exemplary embodiment of the control apparatus of FIG. 5, the [0030] valve unit 40 is a 4/2-way magnet valve 45, with two switching positions and four controlled valve connections 451-454, of which a first valve connection 451 is connected to the relief line 28, and a second valve connection 452 is connected to the relief line 29; a third valve connection 453 that can be connected to the first valve connection 451 is connected to the connecting line 35, and a fourth valve connection 454, which can be connected to the second valve connection 452, is connected to the connecting line 36. The two connecting lines 35, 36 in turn lead to the second work chambers 122 of the valve actuators 11 of the pair of valve actuators.
With this version of the [0031] valve unit 40—unlike the versions of the valve units 40 in FIGS. 3 and 4—the resultant closing speeds of the gas exchange valves 10 are always identical, regardless of whether only one gas exchange valve 10 is open or both gas exchange valves 10 are open. In the versions of the valve unit 40 of FIGS. 3 and 4, conversely, a distinction must be made between a one-valve mode and a two-valve mode, since the fact whether only one gas exchange valve 10 is open or both gas exchange valves 10 are open has an effect on the closing speed of the gas exchange valves 10. If the same closing instant is to be attained in both the one-and the two-valve mode, then the control signals applied via the signal output 302 of the electronic control unit 30 must be designed accordingly.
An expansion of the function of the control apparatus of FIG. 5 can be attained if the [0032] valve unit 40 is embodied as a 4/3-way magnet valve 46 or as a 4/4-way magnet valve 47. The 4/3-way magnet valve is shown in FIG. 6, and the 4/4-way magnet valve 47 in FIG. 7, both in the form of a circuit diagram. The 4/3-way magnet valve 46 has three switching positions and four controlled valve connections 461-464, and the 4/4-way magnet valve 47 has four switching positions and four controlled valve connections 471-474. Compared to the 4/2-way magnet valve 45 described in conjunction with FIG. 5, the 4/3-way magnet valve 46, in one additional switching position, connects the second work chamber 122 of the one valve actuator 11 to the relief line 28 via the connecting line 35, and blocks off the second work chamber 122 of the other valve actuator 11 by closing the connecting line 36. It is accordingly not only possible, as in the other valve units 40 of FIGS. 3 and 4, to close the two gas exchange valves 10 at the same instant jointly, but also to trigger one gas exchange valve 10 at a staggered time relative to the other.
In the 4/4-[0033] way magnet valve 47 shown in FIG. 7, in comparison to the 4/3-way magnet valve 46 in FIG. 6, in the fourth switching position the second work chamber 122 of the one valve actuator 11 communicates via the connecting line 36 with the relief line 29, while the second work chamber 122 of the other valve actuator 11 is blocked via the connecting line 35. It is thus possible to trigger one or the other gas exchange valve 10 selectively at a staggered time relative to the other gas exchange valve 10.
The invention is not limited to the exemplary embodiment described. For instance, instead of the [0034] multi-position magnet valves 25, 27, 41, 44, 45, 47 described in the various exemplary embodiments, which are open when without current, such valves that are blocked when without current can also be used.

Claims

1. An apparatus for controlling gas exchange valves in combustion cylinders of an internal combustion engine, having hydraulic valve actuators (11), each of which is assigned to one gas exchange valve (10) and which each have one adjusting piston (13), acting on the gas exchange valve (10), and two hydraulic work chambers (121, 122) defined by the adjusting piston (13), of which chambers the first work chamber (121), acting on the gas exchange valve (10) in the closing direction, is constantly filled with a fluid that is under pressure, and the second work chamber (122), acting on the gas exchange valve (10) in the opening direction, can be filled with and relieved of a fluid that is under pressure via a first and second electrical control valve (24, 25; 26, 27), characterized in that the second control valves (25, 27) for one pair of valve actuators (11), which actuate two gas exchange valves (10) used as inlet or outlet valves in one combustion cylinder, are triggered by a common electrical control signal.

2. The apparatus of claim 1, characterized in that the electrical control inputs of the two second control valves (25, 27) are connected to the same signal output (302) of an electronic control unit (30).

3. The apparatus of claim 1 or 2, characterized in that the two second control valves (25, 27), associated with one pair of valve actuators, are embodied as a valve unit (40), with one common electrical control input.

4. The apparatus of claim 3, characterized in that the valve unit (40) is a 4/2-way magnet valve (45), with two switching positions and four controlled valve connections (451-454), of which a first and a second valve connection (451, 452) each communicate with a respective relief line (28, 29), and a third valve connection (453), which can be connected to the first valve connection (451), and a fourth valve connection (454), which can be connected to the second valve connection (452), can each communicate with a respective second work chamber (122) of the pair of valve actuators.

5. The apparatus of claim 3, characterized in that the valve unit (40) is a 3/2-way magnet valve (44), with two switching positions and three controlled valve connections (441-443), of which a first valve connection (441) communicates with a relief line (28), and the two further valve connections (442, 443), which can be connected simultaneously to the first valve connection (441), each communicate with a respective second work chamber (122) of the pair of valve actuators.

6. The apparatus of claim 3, characterized in that the valve unit (40) is a 2/2-way magnet valve (41), with two switching positions and two controlled valve connections (411, 412), of which one valve connection (411) is connected to a relief line (28), and the other valve connection (412) is connected, each via a respective connecting line (35, 36), to the second work chambers (122) of the pair of valve actuators; and that in at least one connecting line (35, 36), there is a check valve (42, 43), with a flow direction pointing toward the 2/2-way magnet valve (41).

7. The apparatus of claim 3, characterized in that the valve unit (40) is a 4/3-way magnet valve (46), with three switching positions and four controlled valve connections (461-464), of which two valve connections (461, 462) each communicate with a respective relief line (28, 29), and two valve connections (463, 464) each communicate with a respective work chamber (122) of the pair of valve actuators; and that the 4/3-way magnet valve (46) is embodied such that in one switching position, both second work chambers (122) each communicate with a respective relief line (28, 29), while in a further switching position, both second work chambers (122) are blocked, and in a third switching position, one of the two second work chambers (122) is blocked while the other communicates with a relief line (28).

8. The apparatus of claim 3, characterized in that the valve unit (40) is a 4/4-way magnet valve (47), with four switching positions and four controlled valve connections (471-474), of which two valve connections (471, 472) each communicate with a respective relief line (28, 29), and two valve connections (473, 474) each communicate with a respective second work chamber (122) of the pair of valve actuators; and that the 4/4-way magnet valve (47) is embodied such that in one switching position, the second work chambers (122) of the pair of valve actuators communicate with the relief lines (28, 29), in a further switching position the second work chambers (122) are blocked off, and in the two further switching positions, in alternation, one of the two second work chambers (122) communicates with a respective relief line (28 or 29), and the other of the second work chambers (122) is blocked.

9. The apparatus of claim 1 or 2, characterized in that each valve actuator (11), with associated first and second control valves (24, 25; 26, 27), which are preferably embodied as 2/2-way magnet valves, is integrated into a respective actuator housing (37; 38).

10. The apparatus of one of claims 3-8, characterized in that the two valve actuators (11) of a pair of valve actuators and the associated control valves (24, 26, 40) are integrated into a common actuator housing (39).