Apparatus for adjusting turbine guide vanes and the like

Abstract

Apparatus for adjusting a movable member, for example a guide vane for a gas turbine engine, including an actuating cylinder, and an actuating piston slidably disposed in said cylinder, with one of the cylinder and piston connected in a direct drive linkage for moving the guide vane. A control valve is provided for controlling the opening and closing of respective inlet and exhaust ports leading to a control chamber which effects movement of the actuating piston. This control valve includes a control valve member having one end face acted upon by a fluid control pressure and one arm of a two armed elastically loaded lever contacting the control valve member to force the same against the fluid control pressure. The other arm of the lever includes a roller and is in contact with a predetermined generating line provided in a cavity of the actuating piston such that movement of the actuating piston changes the resistance to movement of the control valve member exerted by way of the lever, whereby a precise and accurate positioning of the actuating piston, irrespective of the reactive forces acting on the actuating piston is obtained.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to appratus for adjusting a movable member, for example turbine guide vanes and the like. The present invention is more specifically related to an improved actuator which has an actuating piston slidable in an actuating cylinder in accordance with a predetermined characteristic in response to fluid pressure acting on said piston.

Previously contemplated fluid pressure responsive actuators of the just-mentioned category utilize a cam disk for maintaining and giving the predetermined characteristic. (See British Pat. No. 1,055,319). A disadvantage of such previously contemplated actuator is that additional means are required to operate the cam disk by means of a hydraulic or electrical input signal in an automatically occurring process. A further disadvantage of such actuators is seen in that an actuating rod extending through a control chamber between the actuating piston and a control valve for fluid supply to said actuating piston, in parallel with the control valve for endwise movement imparted to it by the cam disk against the force of a spring and carrying a rotatably mounted two-armed lever leads through the housing of the hydraulic actuator. Such a lead-in of the lever through the housing is difficult to seal off, causes friction, and poses further design problems related to hydraulic thrust imposed on the actuating rod.

The present invention overcomes the above-mentioned disadvantages by providing a pressure medium operated piston-cylinder actuator which achieves respective intended positions of the actuating piston with great precision and relatively moderate complexity of the actuating means. According to the invention, the previously contemplated actuating rod, the lead-in through the actuator housing, and the cam disk bearing the characteristic are all eliminated and a hydraulic input signal is supplied to the hydraulic actuator directly and in the absence of intervening mechanical links. In this way, the characteristic curve for changing the control force on the control valve in dependence upon the relative position of the actuator piston and cylinder can be constructed in a simple manner to be linear, nonlinear, or not uniformly linear.

More specifically, the present invention contemplates apparatus for imparting adjusting movements to a movable member, such as a linkage member in an actuating train for a guide vane on a vehicular gas turbine engine, which apparatus includes an actuating cylinder, an actuating piston slidably disposed in the cylinder, means for connecting one of the actuating cylinder and actuating piston to a movable member for movement therewith, a control chamber communicating with a first face of the actuating piston such that supply of fluid under pressure to the control chamber effects movement of the actuating piston in a first direction and drainage of fluid from the control chamber permits movement of said actuating piston in a second direction opposite the first direction, control chamber inlet means for communicating fluid under pressure to the control chamber, control chamber exhaust means for exhausting fluid from the control chamber, a control valve for controlling the opening and closing of the control chamber inlet and exhaust means, said control valve including a control valve member acted upon in one direction by a fluid control pressure and in the other opposite direction by a control biasing force, the actuating piston including a cavity bounded in part by a generating surface which is spaced from the centerline of said actuating piston by varying amounts along the length of said actuating piston, and interconnecting means in contact with both the control valve member and the generating surface for effecting changes in the control biasing force as a function of the position of the actuating piston along the travel path thereof in the actuating cylinder. According to a further aspect of the invention, the apparatus just described is constructed such that the cavity forms part of the control chamber, wherein a second face of the actuating piston which faces oppositely of and is smaller than the first face is continuously communicated with the fluid under pressure supplied to the control chamber inlet means, wherein the fluid under pressure is a hydraulic fluid, wherein the interconnecting means is a two-armed lever having one arm thereof in contact with the control valve member and the other arm thereof in contact with the generating surface, and wherein the two-armed lever is supported intermediate the arms thereof at a part fixed with said actuator cylinder.

In preferred embodiments of the invention, the actuating piston, which is constructed as a differential area piston, will not move so long as the force of control pressure acting on said end face of said control valve member is equal to the force of flexural preload of the lever acting on the control valve member in the axially opposite direction. Said preload of the lever varies with the position of the actuating piston as a result of the form of the generating line. When a change occurs in control pressure the resulting discrepancy between said two forces causes the control valve member to move away from its shut-off position in one or the other axial direction. This movement of the control valve member either pressurizes the larger face of the actuating piston in the control chamber and the actuating piston is moved in its one axial direction, or exhausts the control chamber and the actuating piston is moved in the opposite direction while the control chamber is being emptied accordingly. Movement of the actuating piston, due to the form of the generating line, causes the force of lever preload to change until equibrium is achieved with the new force of control pressure, which returns the control valve to its shut-off position. The actuating piston comes to rest in very precisely the intended position.

With the apparatus of the present invention, the actuating piston travels, as a function of control pressure, an intended distance which is independent of the magnitude, direction and change in load resistance acting on the actuating piston. In use for adjusting turbine engine guide vanes, the load resistance has its origin especially in the gas forces acting on the guide vanes. The actuating means of the present invention is relatively simple and free from complexity. Forces are balanced one against the other and a lead-in in the housing is eliminated together with its above-mentioned disadvantages. Due to the simplicity of design, the actuating means of the present invention can be a robust construction. The actuating means of the present invention is also practically insensitive to vibrations, which prevents wear on its parts and noise.

The actuating accuracy of the hydraulic actuator of the present invention can be improved by increasing the inclination of the generating line relative to the centerline of the actuating piston. Depending upon the desired characteristic acceleration and deceleration of the member being adjusted (e.g. turbine guide vane), the generating line may be curved over part of all of its length or it may angleoff in a straight line, according to the present invention. In the case of non-uniform linearity between the pressure signal and the stroke of the actuating piston, a preferred embodiment varies the inclination of the generating line relative to the centerline of the actuating piston to effect drive, neutral and deceleration ranges respectively, where more particularly the inclination is relatively great at first (drive range), then relatively small, and finally relatively great again (deceleration range). The actuating accuracy is thus made relatively great in the drive range and in the deceleration range, as it would indeed be desireable in use. In between the accuracy of actuation, and with it the inclination, may well be less. The gradient of the generating line is preferably steeper in the drive range than in the deceleration range according to the present invention.

In a preferred embodiment of the present invention a control cylinder inlet, with a pressure line connecting to it, communicates with that portion of the control cylinder chamber adjacent to the control pressure end face of the control valve member through a restrictor duct. This last-mentioned portion of the control cylinder chamber communicates with a control nozzle, for controlling the magnitude of the control pressure arranged ahead of which is a control member loaded by a variable electromagnetic force for controlling the control nozzle. The restrictor duct is preferably located in the control valve member but may optionally be provided also in the valve body. The control valve thus likewise functions also as a pilot restrictor for the pressurization of the control oil or for the control pressure circuit. For pressurization of the control oil, hydraulic medium flows from the inlet of the control cylinder, through the restrictor duct, into said portion of the control cylinder chamber and into a control pressure chamber surrounding the area of the control nozzle inlet, in which spaces the hydraulic medium backs up until it attains the control pressure at which the force of control pressure acting on the control member and the electromagnetic force are in equilibrium. In this balanced condition the control nozzle is in a somewhat open position and allows control pressure medium to escape from it continuously. When a change occurs in the electromagnetic force, a new control pressure results, the force of which on the control valve is equal to the new electromagnetic force. The continuous flow of medium through the restrictor duct and the control nozzle also serves to cool the actuating means of the hydraulic actuator.

The actuating means of the present invention can be used, e.g., for varying the blade angle of the guide vanes of an inlet stator of a power turbine of a two-spool gas turbine engine.

These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 of the accompanying drawings are longitudinal sections illustrating an embodiment of the actuating means assembled in accordance with the present invention for varying the blade angle of gas turbine guide vanes of a vehicular gas turbine engine, where FIG. 1 shows the hydraulic actuator with its actuating piston and control valve in a section taken at their centerlines (longitudinal section) and FIG. 2 shows in longitudinal section the transducer furnishing the control pressure;

FIG. 3 of the drawings illustrates an alternative preferred embodiment of the control valve and body in a section taken at the centerline of the control valve and at right angles to the centerline of the actuating piston; and

FIG. 4 of the drawings illustrates a further alternative preferred embodiment of a control valve body and valve as seen in partial longitudinal section from FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

The actuating means of FIGS. 1 and 2 essentially comprise an actuator (FIG. 1) exhibiting a cylindrical actuating piston 10 and a cylindrical control valve 11, and a transducer (FIG. 2) in the form of an electromagnetic device for motivating a control member 46 for a control nozzle 21, where the member 46 is under a magnetic force which varies proportionally to the variation in input voltage -- arrowheads 88 -- to a solenoid 47.

The centerline 30 of the actuating piston and the centerline 36 of the control valve 11 are at right angles to one another and in the plane of projection. The actuator housing essentially consists of a cylinder 12 accommodating the actuating piston 10, and a cylinder head 13 accommodating the control valve 11. The cylinder 12 and its head 13 are fixedly connected, more particularly screwed, one to the other, or they may alternatively be a solid construction. The cylinder head 13 is essentially about centerline 30. The cylinder head 13 and the actuating piston 10 are each fitted with a lug 63 and 64, respectively. Lug 63, which stiffens the cylinder head 13 to resist distortion constitutes a fixed point of the actuator, while lug 64 connects - this is not shown - to a guide vane actuating ring gear via further connecting members and absorbs the load. See the above-mentioned British Pat. No. 1,055,319 for a showing of a system with guide vanes and mechanism for adjusting same.

One face 14, of the actuating piston 10 is half the size of another face 15, part of which face 14 is formed by an axially arranged central cavity 16. An oil pump, details omitted on the drawing, supplies oil pressure p to face 14 through a pressure line 60 (arrowhead 89) extending from the pump. Installed in pressure line 60 is a pressure limiter valve 44 set at the maximum allowable oil pressure. The cavity 16 and the adjacent members in the interior of the actuator form a chamber which is filled with oil and closed off by control valve 11. The actuating piston 10 is at rest in the position illustrated in FIG. 1.

In this control chamber a double-armed lever 20 is carried on knife-edge on a bearing member 19 of a cylindrical cover fixedly connected to head 13. The lever 20 extends through an opening in the cover and can be loaded flexurally in that its upper arm as seen in the drawing consists of a relatively short and relatively stiff portion. Attached to said upper arm, by riveting or otherwise, is a relatively long leaf spring 23 with a ball and socket 25 or alternatively a sliding member or a roller at its extreme end. This leaf spring 23 is disposed fully within cavity 16 as illustrated. Ball 25 rests against the generating line of the cavity 16, whereas the end of the other arm of lever 20 forks around a centrally arranged cylinder control valve member 51 flattened on both sides at that point. The one visible (FIG. 1) of the two flattened lands, which are arranged symmetrically with respect to the plane of projection, is indicated with the numeral 35. The two parts of the fork, which approximately takes up the outer half of said arm, contact with their rounded ends with the two equidirectional faces 39 of the two lands 35 in the longitudinal plane 40 of the control valve 11 at right angles to the plane of projection. In this manner a balance undisturbed by tilting moment is achieved between the spring force of lever 20 and a force acting axially on control valve 11 of a control pressure p' of the oil.

The lever 20 or its leaf spring 23 are preloaded by this force of control pressure. The control pressure p' comes to bear in a portion 41 of the control cylinder chamber, in a hole of an adjacent member, in a connecting line 43 -- for which see FIG. 1, and FIG. 2 for its connecting portion -- and in a control pressure chamber 45 of the transducer. Control pressure p' acts on a control pressure end face 48 of the control valve 11. With the respective force of control pressure being equal to the preload on the lever; the control valve 11 is at rest.

The generating line or surface of the cavity 16 is formed to suit an intended or given characteristic, i.e., to suit the intended travels of the actuating piston, ultimately the desired change in blade angle of the guide vanes, as a function of said input voltage, or the control pressure p' proportional to it or the magnetic force. The characteristic schematically depicted to the right of the actuating cylinder 12 in FIG. 1, includes two relatively flat and short straight lines, line 26 for drive range .DELTA. s.sub.F and line 28 for deceleration range .DELTA. s.sub.B of the guide vanes, and a relatively steep and long straight intermediate line 27 for an intermediate range with a neutral position s.sub.N of the actuating piston 10 or of the guide vanes. The full travel of the actuating piston is indicated with the symbol .DELTA. s.sub.G. Accordingly, the generating line consists of two short, straight and, with respect to centerline 30, relatively steep runs 31, for drive range .DELTA. s.sub.F, and 33, for deceleration range .DELTA. s.sub.B, and of a relatively flat and long straight intermediate run 32. The ball 25 rests against the straight run 33 in the illustrated rest position.

The control valve 11 and the cylinder head 13 are simple constructions. The control valve 11 exhibits, at each end of valve member part 51, a cylindrical member part 49 and 50, respectively, having a diameter larger than that of valve member 51 and, at the level of the respective said end, an inlet control edge 52 and an outlet control edge 53, respectively. The control cylinder 54 and the cylinder head 13 respectively exhibit an annular inlet slot 55 controlled by inlet edge 52 and an annular outlet slot 56 controlled by outlet edge 53. This inlet connects to a pressure line 61 diverted from pressure line 60. The annulus 57 surrounding the valve memmber 51 forms part of the control chamber. The distance of the edge 52 and 53 from one another is equal to that between the two inner controlling edges of annular slots 55 and 56.

The pressure line 61 connects to an inlet duct 62 which in turn connects to annular inlet slot 55. The annular inlet slot 55 communicates with portion 41 of the cylinder chamber via an annular slot, an axially arranged central hole and an axially arranged central restrictor port 42 of the control valve 11 or the valve member 49, causing pressure oil to flow from the annular inlet slot 55 into portion 41 of the cylinder chamber for duty as control pressure oil. The force of control pressure of the oil acting on control member 46 (FIG. 2) is in balance with the magnetic force applied by solenoid 47, solenoid 47 being of known construction. Control nozzle 21 is always in a somewhat open position and allows oil to drain continuously into an oil reservoir not shown on the drawings, as indicated by arrowhead 90. The extent of opening of control nozzle 21, and hence the value of control pressure p' is controlled by voltage input 88. The control pressure p' is therefore always smaller than the oil pressure p prevailing in the annular inlet slot 55.

With reference now to FIG. 2, it is noted that the control pressure p' acts, in control pressure chamber 45, on a diaphragm 17 and, via a connecting duct 38 in a control pressure chamber 22, on a diaphragm 18 the effective portion of which is somewhat smaller than that of diaphragm 17, so that the resulting force of oil pressure on control member 46, which is in fixed and oil-tight connection with diaphragms 17 and 18, is very modest and therefore requires not more than an equally modest magnetic force and, thus, only a relatively small-sized electromagnetic means.

Annular outlet slot 56 communicates with an outlet duct 29 from which a drain line 37 leads to an oil reservoir not shown on the drawings, as indicated by arrowhead 91. A gland leakage line (dashed line at right side of FIG. 1) likewise discharges into this reservoir. In order to attenuate axial vibrations of control valve 11, this outlet of the control cylinder and a portion 59 of the control cylinder chamber adjacent to the end face 58 of control valve 11 are in communication through a damping duct formed in valve body 13 by a slot 24 extending in parallel with centerline 36.

When the input voltage 88 falls off, the magnetic force is reduced, the control nozzle 21 is opened wider and the control pressure p' is thus reduced until balance is established between the associated force of control pressure on control member 46 and the reduced magnetic force. When the input voltage is raised, the process is reversed. The oil pressure p in the annular inlet slot 55 is the maximally attainable control pressure p' for the reasons noted above. Any reduction or rise in control pressure p' causes the control valve 11 to move from its shut-off position in its one axial direction, or opposite it, to establish communication between the annular inlet slot 55 and the cavity 16 or between it and the annular outlet slot 56. This causes face 15 to come under oil pressure p and the actuating piston 10 to be moved away from control valve 11, or actuating piston 10 to be moved in the opposite direction as the control chamber is being emptied accordingly. In the process of movement of actuating piston 10, the form of the generating line causes the ball and socket 25 to travel farther apart from centerline 30 or closer to it, or the preload on the lever to fall or rise until balance is established with the new force of control pressure, thus pushing control valve 11 back to its shut-off position. The actuating piston 10 therefore comes to rest very accurately in the position that relates to control pressure p' or the input voltage producing it.

The control valve 79 and the cylinder head 78 shown in FIG. 3 are equally simple constructions. This cylindrical control valve 79, here shown in its shut-off position, exhibits a centrally arranged cylindrical valve member 70 having an inlet control edge 71 at its one end and an outlet control edge 72 at its other. The control chamber (cavity 16 and portion opening to the control valve are described in FIG. 1 above) leads, with a cylindrical duct or opening 73, to the valve member 70 where it is as wide as the distance 74 between control edge 71 and control edge 72. The diameter of the duct 73 is equal to this distance 74. The two fixed edges are formed by the wall of duct 73 and the wall of a control cylinder 75. The control cylinder 75 exhibits, outside the valve member 75 axially, an uncontrolled inlet duct 76 on the one axial side and an uncontrolled outlet duct 77 on the other. This FIG. 3 control valve operates in the FIG. 1 system in a manner as described above for control valve 11.

In accordance with the arrangement in FIG. 4 a control valve 11 is seated for sliding movement in a bushing 80 having a controlled inlet slot 81 and a controlled outlet slot 82 and being seated in a cavity 84 of the actuator housing, here of cylinder head 83. The bushing 80 is connected, at the seating port of cavity 84, with cylinder head 83 for a fixed position axially but at a distance radially from the cavity 84. When a load is applied at a lug 64 (see FIG. 1) with the actuator housing secured in an abutment lug 63 (see FIG. 1) of cylinder head 83, the forces occurring in the cylinder head 83 will not affect the control valve 11 if use is made of this bushed design. This FIG. 4 arrangement otherwise operates as described in connection with FIG. 1.

Sealing rings, here represented by O-rings, arranged between the bushing 80 and the cavity 84 serve to seal differently pressurized chambers one from the other. So that bushing 80 may readily permit insertion axially in cylinder head 83 the outer diameter of the bushing and the inner diameter of the cavity are widened counter the direction of insertion in several steps. As a result the O-rings will be seated, as shown, between the respective bushing sections and cavity sections.

While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

Claims

We claim:

1. Apparatus for imparting adjusting movements to a movable member, comprising:

an actuating cylinder,

an actuating piston slidably disposed in said cylinder,

one of said actuating cylinder and actuating piston including means for connecting same to said movable member for movement therewith,

a control chamber communicating with a first face of said actuating piston such that supply of fluid under pressure to said control chamber effects movement of said actuating piston in a first direction and drainage of fluid from said control chamber perm its movement of said actuating piston in a second direction opposite said first direction,

control chamber inlet means for communicating fluid under pressure to said control chamber,

control chamber exhaust means for exhausting fluid from said control chamber,

a control valve for controlling the opening and closing of said control chamber inlet and exhaust means, said control valve including a control valve member acted upon in one direction by a fluid control pressure and in the other opposite direction by a control biasing force,

said actuating piston including a cavity bounded in part by a generating surface which is spaced from a centerline of said actuating piston by varying amounts along the length of said actuating piston, and interconnecting means in contact with both said control valve member and said generating surface for effecting changes in said control biasing force as a function of the position of said actuating piston along the travel path thereof in said actuating cylinder.

2. Apparatus according to claim 1, wherein said cavity forms part of said control chamber, wherein a second face of said actuating piston which faces oppositely of and is smaller than said first face is continuously communicated with the fluid under pressure supplied to said control chamber inlet means, wherein said fluid under pressure is a hydraulic fluid,

wherein said interconnecting means is an elastically bendable two-armed lever having one arm thereof in contact with said control valve member and the other arm thereof in contact with said generating surface, and wherein said two-armed lever is supported intermediate the ends thereof at a part fixed with said actuating cylinder so as to apply an elastic stressing force as said control biasing force.

3. Apparatus according to claim 2, wherein said control valve member is constrained to move transversely to the direction of movement of said actuating piston.

4. Apparatus according to claim 3, wherein said control valve means includes means for opening one of said control chamber inlet and exhaust means upon minimal movement of said control valve member from a central position thereof.

5. Apparatus according to claim 4, wherein said movable member is a guide vane of a gas turbine engine or the like.

6. Apparatus according to claim 1, wherein the inclination of the generating surface relative to the centerline of the actuating piston: is relatively great near one end of the cavity to define a drive range, is relatively small along an intermediate portion of the cavity, and is relatively great at the end of the cavity opposite said one end to define a deceleration range.

7. Apparatus according to claim 5, wherein the inclination of the generating surface relative to the centerline of the actuating piston: is relatively great near one end of the cavity to define a drive range, is relatively small along an intermediate portion of the cavity, and is relatively great at the end of the cavity opposite said one end to define a deceleration range.

8. Apparatus according to claim 2, wherein the inclination of the generating surface relative to the centerline of the actuating piston: is relatively great near one end of the cavity to define a drive range, is relatively small along an intermediate portion of the cavity, and is relatively great at the end of the cavity opposite said one end to define a deceleration range.

9. Apparatus according to claim 2, wherein said control valve member is constructed with cylindrical valve member end portions at the ends thereof having control edges for controlling openings of said control chamber inlet and exhaust means, said control edges being located at the juncture of said end portions with a central portion of said control valve member which has a smaller diameter than either of said end portions such that the annulus formed around said central portion forms part of the control chamber.

10. Apparatus according to claim 8, wherein said control valve member is constructed with cylindrical valve member end portions at the ends thereof having control edges for controlling openings of said control chamber inlet and exhaust means, said control edges being located at the juncture of said end portions with a central portion of said control valve member which has a smaller diameter than either of said end portions such that the annulus formed around said central portion forms part of the control chamber.

11. Apparatus according to claim 2, wherein said control valve member has an inlet control edge at one end and an exhaust control edge at the other end, wherein said control chamber communicates with said control valve member by an opening having a width in the direction of movement of said control valve member which is the same as the distance between said inlet and exhaust control edges, and wherein a control cylinder within which said control valve member is slidably guided exhibits an uncontrolled inlet duct and an uncontrolled exhaust duct at respective opposite axial sides of said opening with respect to movement of said control valve member.

12. Apparatus according to claim 11, wherein said uncontrolled inlet duct communicates with a pressure line and said uncontrolled exhaust duct communicates with a drain line.

13. Apparatus according to claim 8, wherein said control valve member has an inlet control edge at one end and an exhaust control edge at the other end, wherein said control chamber communicates with said control valve member by an opening having a width in the direction of movement of said control valve member which is the same as the distance between said inlet and exhaust control edges, and wherein a control cylinder within which said control valve member is slidably guided exhibits an uncontrolled inlet duct and an uncontrolled exhaust duct at respective opposite axial sides of said opening with respect to movement of said control valve member.

14. Apparatus according to claim 2, wherein the one arm of said lever is of forked configuration with two spaced fork parts, wherein said control valve member is flattened on two opposite sides to accommodate said contact of said fork parts in said flattened sides in a longitudinal center plane of the control valve member.

15. Apparatus according to claim 8, wherein the one arm of said lever is of forked configuration with two spaced fork parts, and wherein said control valve member is flattened on two opposite sides to accommodate said contact of said fork parts in said flattened sides in a longitudinal center plane of the control valve member.

16. Apparatus according to claim 9, wherein the one arm of said lever is of forked configuration with two spaced fork parts, and wherein said control valve member is flattened on two opposite sides to accommodate said contact of said fork parts in said flattened sides in a longitudinal center plane of the control valve member.

17. Apparatus according to claim 11, wherein the one arm of said lever is of forked configuration with two spaced fork parts, and wherein said control valve member is flattened on two opposite sides to accommodate said contact of said fork parts in said flattened sides in a longitudinal center plane of the control valve member.

18. Apparatus according to claim 2, wherein a restrictor duct communicates said control chamber inlet means with a face of said control valve member acted upon by said fluid control pressure, and wherein said last-mentioned face of said control valve member is arranged in direct fluid communication with a mechanism for controlling the magnitude of said fluid control pressure, said mechanism including means operable by a variable electromagnetic force to vary said magnitude of said fluid control pressure.

19. Apparatus according to claim 8, wherein a restrictor duct communicates said control chamber inlet means with a face of said control valve member acted upon by said fluid control pressure, and wherein said last-mentioned face of said control valve member is arranged in direct fluid communication with a mechanism for controlling the magnitude of said fluid control pressure, said mechanism including means operable by a variable electromagnetic force to vary said magnitude of said fluid control pressure.

20. Apparatus according to claim 9, wherein a restrictor duct communicates said control chamber inlet means with a face of said control valve member acted upon by said fluid control pressure, and wherein said last-mentioned face of said control valve member is arranged in direct fluid communication with a mechanism for controlling the magnitude of said fluid control pressure, said mechanism including means operable by a variable electromagnetic force to vary said magnitude of said fluid control pressure.

21. Apparatus according to claim 11, wherein a restrictor duct communicates said control chamber inlet means with a face of said control valve member acted upon by said fluid control pressure, and wherein said last-mentioned face of said control valve member is arranged in direct fluid communication with a mechanism for controlling the magnitude of said fluid control pressure, said mechanism including means operable by a variable electromagnetic force to vary said magnitude of said fluid control pressure.

22. Apparatus according to claim 18, wherein said mechanism controls a drain for varying the back pressure build up from the fluid communicated by said restrictor duct to said face of said control valve member.

23. Apparatus according to claim 2, wherein said control valve includes a control valve cylinder for accommodating sliding movement of said control valve member, and wherein a damping duct communicates said control chamber exhaust means with a face of said control valve member which faces oppositely to the face of said control valve member which is acted upon by said fluid control pressure.

24. Appararatus according to claim 8, wherein said control valve includes a control valve cylinder for accommodating sliding movement of said control valve member, and wherein a damping duct communicates said control chamber exhaust means with a face of said control valve member which faces oppositely to the face of said control valve member which is acted upon by said fluid control pressure.

25. Apparatus according to claim 9, wherein said control valve includes a control valve cylinder for accommodating sliding movement of said control valve member, and wherein a damping duct communicates said control chamber exhaust means with a face of said control valve member which faces oppositely to the face of said control valve member which is acted upon by said fluid control pressure.

26. Apparatus according to claim 11, wherein said control valve includes a control valve cylinder for accommodating sliding movement of said control valve member, and wherein a damping duct communicates said control chamber exhaust means with a face of said control valve member which faces oppositely to the face of said control valve member which is acted upon by said fluid control pressure.

27. Apparatus according to claim 18, wherein said control valve includes a control valve cylinder for accommodating sliding movement of said control valve member, and wherein a damping duct communicates said control chamber exhaust means with a face of said control valve member which faces oppositely to the face of said control valve member which is acted upon by said fluid control pressure.

28. Apparatus according to claim 2, wherein said control valve includes a bushing inserted into a hollow portion of an actuator housing fixed with said actuating cylinder, said control valve member being slidable inside of said bushing, said bushing being radially spaced from internal walls of said hollow portion by sealing rings.

29. Apparatus according to claim 28, wherein said bushing is of stepped diameter with the maximum diameter at an end thereof which is axially fixed to said actuator housing, whereby axial insertion of said bushing and sealing rings is accommodated.

30. Apparatus according to claim 8, wherein said control valve includes a bushing inserted into a hollow portion of an actuator housing fixed with said actuating cylinder, said control valve member being slidable inside of said bushing, said bushing being radially spaced from internal walls of said hollow portion by sealing rings.

31. Apparatus according to claim 9, wherein said control valve includes a bushing inserted into a hollow portion of an actuator housing fixed with said actuating cylinder, said control valve member being slidable inside of said bushing, said bushing being radially spaced from internal walls of said hollow portion by sealing rings.

32. Apparatus according to claim 11, wherein said control valve includes a bushing inserted into a hollow portion of an actuator housing fixed with said actuating cylinder, said control valve member being slidable inside of said bushing, said bushing being radially spaced from internal walls of said hollow portion by sealing rings.

33. Apparatus according to claim 18, wherein said control valve includes a bushing inserted into a hollow portion of an actuator housing fixed with said actuating cylinder, said control valve member being slidable inside of said bushing, said bushing radially spaced from internal walls of said hollow portion by sealing rings.

34. Apparatus according to claim 23, wherein said control valve includes a bushing inserted into a hollow portion of an actuator housing fixed with said actuating cylinder, said control valve member being slidable inside of said bushing, said bushing being radially spaced from internal walls of said hollow portion by sealing rings.

35. Apparatus according to claim 8, wherein the inclination of the generating surface relative to the centerline of the actuating piston is greater in said deceleration range than in said drive range.