Device For Adjusting The Stroke Volume Of Hydraulic Units

Abstract

A control cylinder is operative for adjusting the stroke volume of a hydraulic unit, and restoring means is provided for restoring a piston in the control cylinder from a displaced control position to a normal starting position. Servo-control means is associated with the control cylinder and comprises fluid supply means for supplying pressure fluid to the cylinder, control valve means controlling the flow of such pressure fluid to the cylinder, and throttling-gap regulating means operatively associated with the control valve means and with the cylinder via the restoring means for controlling the operation of the cylinder.

Parent Case Text

This is a continuation, of application Ser. No. 58,031, filed July 24, 1970, now abandoned.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a device for adjusting the stroke volume of hydraulic units, and more particularly to a device for continuously regulating the stroke volume of hydraulic pumps and hydraulic motors via the use of a servo-control adjusting cylinder with restoring means.

It is already known to effect continuous displacement of the adjusting cylinder by positional changes of the restoring member from the adjusting cylinder to the control valve. The positional changes of the restoring member for the purpose of continuous adjustment of the hydraulic pump or the hydraulic motor is usually carried out manually and with these known devices a regulating of the adjustment which can be programmed is not possible, because the necessary short adjusting times and the accuracy of adjustment cannot be obtained. This is particularly true when other values which influence the stroke volume must be considered during the adjustment, such as the pressure and the temperature of the system or the rotational speed, for instance of a hydraulic motor.

SUMMARY OF THE INVENTION

It is, accordingly, an object of the present invention to provide a device for the continuous adjustment of the stroke volume of hydraulic pumps and hydraulic motors which constitutes an improvement over what is known from the art.

More particularly it is an object of the invention to provide such a device which, utilizing commercially available regulating units, guarantees a high accuracy of adjustment and short adjusting times such as they are especially required for programming of the regulating function.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides briefly stated in a device for adjusting the stroke volume of hydraulic units which comprises a hydraulic unit, a control cylinder operative for adjusting the stroke volume of the unit, and restoring means for restoring a piston in the control cylinder from a displaced control position to a normal starting position. Servo-control means is provided for the control cylinder and comprises fluid supply means for supplying pressure fluid to the cylinder, control valve means controlling the flow of such pressure fluid to the cylinder, and throttling-gap regulating means operatively associated with the control valve means and, via the restoring means, with the cylinder for controlling operation of the latter.

Through the use of a known and commercially available throttling-gap regulating device which is operated by electrical signals, as a part of the servo-control unit it is possible to obtain quite readily --in a simple manner and with the least possible technical expenditure--the provision of a regulating function for the stroke volume of the hydraulic pump or motor, which can be programmed. The magnitude of the electrical signal for actuating of the throttling-gap regulating device is simultaneously a measure for the adjustment of the adjusting or control cylinder.

According to a further embodiment of the invention the restoring device is constituted by an elastic member which is known per se and secured to the impingement plate of the throttling-gap regulating device, and by a cam track which is coupled with the adjusting cylinder, with the elastic member and the cam track being operatively associated. Advantageously, the cam track is provided on a lever arm which is coupled with the adjusting cylinder and in a simple manner the elastic member is maintained in tracking abutment with the cam track by engagement with a pressure member which is spring-biassed.

According to a further concept of the invention, permitting a still further simplification of the restoring device, the cam track lever coupled with the adjusting cylinder is provided in the region of one end with a blind bore and a coupling portion on the piston rod of the piston in the adjusting cylinder is matingly received in this blind bore and has a generally ball-shaped configuration. For setting the starting or center position of the adjusting cylinder at an electrical signal of zero magnitude for the adjusting drive of the throttling-gap regulating device, the member which mounts the lever arm and constitutes the pivot axis for the same is itself displaceable. To permit the construction of a compact control unit the control valve which is operatively associated with the throttling-gap regulating device and which is hydraulically operated, is configurated as a cylindrical unit which is mounted in a corresponding recess of a housing section which in turn is secured to the adjusting cylinder and provided with bores for the hydraulic fluid. At the same time this housing section carries the throttling-gap regulating device with the electrically activatable drive therefor.

According to still another embodiment of the invention the electrical singals which activate the throttling-gap regulating device are the output signals of a function generator to which the rotational speed of the hydraulic motor or the hydraulic pump, the temperature and the pressure in the hydraulic system are supplied in form of electrical signals as variable dependent on the stroke volume to be regulated, whereby a resulting signal is formed which operates upon and controls the operation of the throttling-gap regulating device.

The novel features which are considered as characteristic for the invention are set forth in the following claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a section through the housing of an adjustable axial-piston pump in the region of the adjustable disc member;

FIG. 2 is a section through the adjusting cylinder and associated components;

FIG. 3 is a section through the control valve of the embodiment of FIGS. 1 and 2;

FIG. 4 is a section through the throttling-gap regulating device of the illustrated embodiment;

FIG. 5 is a diagrammatic showing illustrating the construction of the regulating device;

FIG. 6 illustrates in diagrammatic form the hydraulic system of the disclosed embodiment;

FIG. 7 is a block diagram of the system shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be realized that FIGS. 1-7 illustrate a single exemplary embodiment, but that this embodiment is indeed nothing more than exemplary and that changes and modifications are possible and will offer themselves readily to those skilled in the art. The illustrated embodiment should therefore be considered nothing but an exemplary vehicle for explanation of the invention.

Discussing now the drawing in detail, it will be seen that in FIG. 1 reference numeral 1 identifies the housing of a hydraulic pump or a hydraulic motor, that is of a hydraulic unit in general. Mounting pins or bolts 2 are provided at opposite sides of the housing 1 and mount a disc member 3 for turning movement about an axis of rotation 79. The disc member 3 constitutes the adjusting member for the hydraulic pump or hydraulic motor, that is for the hereafter referred-to hydraulic unit.

The disc member is provided with a bifurcated extension 4 to which there is mounted by means of a bolt or pin 5 an extension 6 of the piston rod 7 of an adjusting cylinder 8 which is more clearly shown in FIG. 2. The mounting is such that the extension 4 and the extension 6 are pivotable with reference to one another. The cylinder body 9 of the cylinder unit 8 is accommodated in a bore 10 of the housing 1 as shown in FIG. 2, and the cylinder space 11 is closed to the ambient atmosphere via a cover 12. A housing section 14 is secured to the portion 13 of the housing 1, and is intended for accommodating the control valve 5 and the throttling-gap regulating device 16 as well as the mount 17 for a lever 18.

As seen in FIGS. 1 and 2, the mount 17 includes a bolt member 19 with a bifurcated portion 20 in the recess 21 of which the lever 18 is pivotably mounted via a bolt 22. Two roller bearings 23 and 24 are mounted on the bolt 19 with a spacer sleeve 25 keeping them axially spaced; a nut 26 prevents the bearings 23, 24 and the spacer sleeve 25 from withdrawal from the bolt 19. The two outer rings 23a, 24a--that is axially outer rings as seen with reference to the axial elongation of the bolt 19--are axially guided in the recesses 27 and 28 of the portion or section 14. A ring 30 abuts against the shoulder 29 between the recesses 27 and 28 and in turn dished springs 31 bear upon the ring 30 and constitute abutment surfaces for the bearing 23. Through the provision of a threaded sleeve 32, in conjunction with the springs 31, the bolt 19 with its extension 20 is axially adjustable. The cap 33 protects the threaded sleeve 32 against damage or unintentional or undesired tampering.

FIG. 3 shows that the control valve 15 constitutes a unitary construction and is provided with a cylindrical housing 34 which is mounted in the bore 36 (see FIG. 2) of the housing section 14 by means of a screw 35 or analogous means. Sealing rings 37 provide for a fluid-tight seal with respect to the ambient surroundings. At the end face 38 of the cover 39 of the valve a pressure spring 40 forming part of cam-follower means, abuts as shown in FIG. 2, and urges a pressure member 41, forming another part of the cam-follower means; in the direction of the cam track 42 provided on the lever 18 and thus maintains the elastic member or extension 43a of the abutment plate 43 (see FIG. 4) of the throttling-gap regulating device 16 in tracking engagement with the cam track 42. The abutment or impingement plate 43 is located between the two nozzles 44 and 45; at its upper end 46 it is connected to a tubular body 47 which is fluid-tightly secured to the flange 48 at the nozzle housing 49, a seal 50 providing for such fluid-tight connection. The armature 51 of an electromagnet 52 is connected to the tubular body 47, and the armature windings 53 surround the armature 51. The tubular body 47 has a cross-sectional restriction in its portion 47a of its axial extension, so that in effect it acts in the manner of bourden tube. The nozzle spaces 54 and 55 are connected with the spring-accommodating spaces 62 and 63 of the control valve via bores 56, 57 provided in the nozzle housing, bores 58 and 59 provided in the housing section 14, as well as transverse bores 60, 61 in the housing 34 of the control valve 15. The control space 64 of the control valve is connected via transverse bores 65 in the housing 34 as well as via a circumferential groove 66 and control bores 67 and 68 provided in the housing section 14 and the portion 13 of the housing 1, with the cylinder space 11. The cylinder space 69 of the adjusting or control cylinder is connected directly via bores 70, 71 in the housing portion 13 and the housing section 14 with the non-illustrated source of pressure medium.

FIG. 5 shows the adjusting cylinder 8 in its starting position in which its piston 72 is located midway between the ends of the adjusting cylinder 8, so that it can be moved in either axial direction by the same distance. In operation of the device, the member 3 is positioned vertically in the housing 1 when the piston 72 is in the aforementioned position. This corresponds to a zero stroke volume.

When an electrical signal is passed into the windings 53 of the armature 51 of the magnet 52, the armature 51 is displaced by a corresponding distance. This causes the abutment plate 43--which is connected with the armature 51--to be similarly displaced in such a manner that the distance between one of the nozzles and the plate 43 may for instance increase while the distance between the other nozzle and the plate 43 is decreased by the corresponding distance. Because the nozzle spaces are connected to a common source of pressure medium P.sub.s =l via the filter 73 and the constant throttles 74, a reduction in the distance between the nozzle and the plate 43 results in an increase in the associated nozzle space of the prevailing pressure, whereas the pressure decreases if the distance increases.

If for instance the armature 51 is displaced in such a manner that the distance between nozzle 44 and plate 43 decreases with a corresponding increase in the distance between nozzle 45 and plate 43, then a higher pressure will prevail in the nozzle space 44 and in the spring chamber 62 of the valve 15 which is connected with the nozzle space 54 via the conduit portions L.sub.1, L.sub.11 than in the nozzle space 55 and the pressure chamber of the control valve 15 which is connected with the nozzle space 55 via the conduit portion L.sub.2, L.sub.22. Because of the differential pressure acting in the two spring chambers 62 and 63 the control piston 75 of the control valve 15--which is in corresponding connection with its opposite ends with these spaces 62 and 63--overcomes the spring 76 and moves in the direction of the chamber 63, connecting via the edges 73 and the control space 64 which is in connection with the cylinder space 11, with the control space 78 which in turn is in connection with the tank T. Because the cylinder space 69 is subject to the pressure of the pressure medium source P.sub.s, the piston 72 with piston rod 7 is displaced in the direction of the cylinder space 11 and in so doing displaces the member 3 about its pivot axis 79 through a corresponding amount.

The displacement of the piston 72 continues until the restoring arrangement--constituted by the lever 18 coupled with the piston rod 7 and cooperating with the cam track 42 and the elastic member 43a of the plate 43--have restored the plate 43 in direction oppositely the magnetic attraction of the throttling-gap regulating device back to its zero position; this causes identity of pressure in the nozzle spaces 54 and 55 and their associated spring chambers 62 and 63 of the valve 15, whereupon the control piston 75 is returned to the illustrated zero position by the action of the springs 82 and 76 and hydraulically blocks the cylinder space 11 of the cylinder 8. Coupling of the lever 18 with the piston rod 7 takes place via a ball-shaped portion 81 of the bolt 5 which is connected with the extension 6 of the piston rod 7, which portion 81 is matingly received in a blind bore 80 of the lever 18. The cam track which causes the positional displacement of the elastic member 43a of the plate 3, has such a configuration that its distance to the pivot axis S of the lever 18 continuously decreases from its one end 41a to its other end 41b.

The armature 51 is so magnetized--by a requisite electrical signal centering into its windings 53--that a displacement of the plate 43 takes place in the direction of the nozzle 45 and thus causes an increase of the pressure in the nozzle space 55 and the spring chamber 63, then the piston 75 moves in the direction of the spring chamber 62 and provides a connection between the pressure medium source P.sub.s via the circumferential groove 84, the control space 64 as well as the control conduit 85, with the cylinder space 11 of the adjusting cylinder 8. In view of the fact that the surface of the piston 72 which is exposed in the cylinder space 11 and on which pressure can be applied, is larger than the surface exposed in the cylinder space 69, the piston 72 with its piston rod 7 in this control position of the valve 15 affects movement in the direction of the cylinder space 69. The piston 72 stops such movement as soon as the plate member 43 is returned to its starting position via the restoring device. The displacement distance of the cylinder 8 depends, in addition to the magnitude of the electrical signal for the adjusting drive of the throttling-gap regulating device--which drive consists of the magnet and the armature with its electrical windings--upon the elasticity of the elastic member 43a which cooperates with the blade 43, a lever ratio of the lever 18, and the configuration of the cam track 42. The starting or center position of the cylinder 8 is adjusted--with an electrical signal zero, that is with the drive of the throttling-gap regulating device 16 de-energized--by corresponding displacement of the lever axis S with the lever 18 via the threaded sleeve 32.

The hydraulic system illustrated in FIG. 6 consists essentially of a regulating pump P which is driven at constant rotational speed, and a hydraulic motor M. The setting of the stroke volume of the pump P takes place via the adjusting cylinder Z which is activated by the servo-valve V. The latter in turn is influenced by the electrical adjusting drive E.

Conduits A and B connect the pump P with the motor M, and supply conduits F with one-way valves R communicate with the conduits A and B for maintaining the filling pressure. In the conduit F.sub.1 there is provided a flush valve SV, and in the conduits A and B there are provided pressure-limiting valves DV. A filter Fi is placed upstream of the servo-valve V.

There is further interposed an electrical temperature measuring device Te and two electrical pressure measuring devices Dr.sub.1 and Dr.sub.2 in the conduits A and B connecting the pump P with the motor M. The two devices Dr.sub.1 and Dr.sub.2 are provided upstream and downstream of the motor M to determine the torque of the latter. In addition a tachometer generater TG is coupled with the shaft W of the motor M. to measure the actual number of rotations of the motor. The thus-determined actual values of the number of rotations n, as well as the torque DM determined from the pressure differential upstream and downstream of the motor M, and of the temperature Te of the pressure medium, are supplied to a function generator FG shown in FIG. 7, whereinto the individual nominal values and the relative dependencies of the same are programmed. The control signal SE entering the function generator FG is modified with these values before it is passed on to the servo valve V, whereby in a very simple manner a predetermined regulating program of the hydraulic system can be provided.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a device for adjusting the stroke volume of hydraulic units, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

Claims

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended

1. A device for adjusting the stroke volume of hydraulic units, comprising a hydraulic unit; a control cylinder operative for adjusting the stroke volume of said unit; servo-control means for said control cylinder, comprising fluid supply means for supplying pressure fluid to said cylinder, and control valve means controlling the flow of such pressure fluid to said cylinder; throttling-gap regulating means operatively associated with said control valve means and with said cylinder for controlling operation of the latter, said throttling-gap regulating means comprising a plate element mounted for displacement in response to impingement of pressure fluid from one of two opposite directions; and feedback detector means for detecting the displacement from a normal starting position of a piston in said control cylinder, said feedback detector means comprising an elastic member carried by said plate element for displacement therewith, a lever pivotally coupled with and displaceable by said piston and having a portion provided with cam means, and cam-follower means cooperating with said cam means and said elastic member for elastically deflecting said elastic member in response to relative displacement of said piston and plate element.

2. A device as defined in claim 1, said cam-follower means comprising spring-biased pressure means urging and maintaining said elastic member in tracking engagement with said cam means.

3. A device as defined in claim 1, said lever having an end portion provided with a blind bore, and said piston having a piston rod provided with a ball-shaped coupling portion which is matingly received in said blind bore.

4. A device as defined in claim 1; further comprising an elongated mounting member mounting said lever for pivotal movement about an axis transversely to the elongation of said mounting member; and displacing means for displacing said mounting member longitudinally of itself.

5. A device as defined in claim 1, said control valve means being hydraulically operated and in form of a cylindrical valve unit; further comprising a housing section provided with a recess accommodating said cylindrical valve unit, passage means for passage of hydraulic fluid to and from said valve unit, said throttling-gap regulating means being carried by said housing section.

6. A device as defined in claim 5; and further comprising electrically operated settling means for said throttling-gap regulating means cooperating with the latter and also mounted on said housing section.