GB2076183A - Hydraulic apparatus for controlling a flow of pressure medium - Google Patents

Abstract

An apparatus (10) is proposed with which a closed circuit (13) for a braking function is supplied with a priority constant flow and an open circuit (16) for an additional load (18) is supplied with the residual flow or a total flow. A control valve (21) switching the flow from the pump (12) is coupled to a stepped piston (47) and influences a flow of control oil branched from the pump flow and which can be conveyed to the tank (69) through a throttle (32) and a pilot valve (23) controlled by the pressure in the accumulator (14) wherein the pressure drop across the throttle (32) can be effective at the stepped piston (47) to move the piston (47) and attached control valve to the switched position. The pilot controlled control valve (21) switches accurately and always moves into stable end positions in which it operates in addition as a flow regulator. A modified valve arrangement is described with respect to Fig. 2 (not shown). <IMAGE>

Description

SPECIFICATION Hydraulic apparatus for controlling a flow of pressure medium STATE OF THE ART The invention originates from an hydraulic apparatus for controlling the flow of pressure medium from a pressure medium source in a closed circuit comprising an accumulator and a load and/or in an open circuit comprising an additional load according to the preamble to the main claim. Such an apparatus is already known from United States Specification 3 142 962 in which an hydraulic brake valve is connected in the closed circuit and a steering valve is connected in the open circuit. Both circuits can be provided with pressure medium from a pump wherein a flow regulator supplies the closed circuit comprising the accumulator with a constant priority flow through a pressure control valve and conducts the residual flow into the steering circuit.When the accumulator is charged, the pressure control valve switches over whereupon the flow regulator valve member operates as a changeover valve and conducts the entire flow from the pump into the steering circuit. The disadvantage with this solution is that the function of an accumulator charging valve is undertaken in this case by a directly controlled valve since the valve member of the pressure control valve actuated by the accumulator pressure directly controls the constant flow to the accumulator. Thus, the valve member of the pressure control valve has a relatively large outer diameter which leads to high friction and thus to an inaccurate switching characteristic of the apparatus.In addition, the valve member of the pressure control valve operates with a mechanical ball detent which is of relatively expensive construction and with which no accurate switching pressures for the accumulator charging function are possible.

Moreover, with this apparatus, there is also the danger that the valve member of the pressure control valve sticks in an intermediate position so that the flow regulator valve member cannot switch completely whereby a situation known under the name "fixed throttling" exists in which the pump delivers against a relatively high pressure which can rapidly lead to its breakdown.

Furthermore, with the known apparatus, there is the danger that, when the accumulator is charged and a pressure exists in the open circuit which is higher than the accumulator pressure, leakage oil arrives at the accumulator through the valve member of the pressure control valve and charges the accumulator still further.

ADVANTAGES OF THE INVENTION As opposed to this, the hydraulic apparatus in accordance with the invention comprising the characterising features of the main claim has the advantage that, by using a pilot controlled valve, it permits an accurate switching characteristic of the apparatus in relationship to the accumulator charging function and also prevents the danger of a fixed throttling during switching over into both directions. The real changeover valve influenced by the accumulator pressure then operates as a pure pilot valve which only influences a flow of control oil. Thus, the changeover valve can be made small which leads to lower friction and to accurate switching characteristics. Moreover, in spite of using a pilot control, the control oil losses are maintained low.

Advantageous further developments and improvements of the apparatus set forth in the main claim are made possible by the measures set forth in the sub-claims. A particularly simple construction of the apparatus is achieved when the control valve member is formed as a hollow valve member in accordance with claim 14.

Furthermore, a construction according to claim 1 5 is of special advantage whereby, with a pressure in the open circuit, which exceeds the pressure in the charged accumulator, an additional charging of the accumulator by leakage oil is avoided.

Furthermore, a construction according to claims 1 7 and 18 favours an especially rapid switching over for charging the accumulator circuit. Further advantageous constructions will become apparent from the remaining claims, the description and the drawing.

DRAWING Two embodiments of the invention are illustrated in the drawing and are described in detail in the following specification. Figure 1 shows a first apparatus in simplified representation and Figure 2 shows a portion of a second apparatus in which-the function of the control valve member in Figure 1 is undertaken by a hollow valve member.

DESCRIPTION OF THE EMBODIMENTS Figure 1 shows an apparatus 10 in which an accumulator charging valve 11 distributes the pressure medium delivered by a pump 12 into a closed circuit 13 comprising an accumulator 14 and a brake valve 1 5 and/or into an open circuit 16 comprising a multiway valve 17 and an additional load 18. The accumulator charging valve 11 consists essentially of a flow regulating valve 1 9 provided with a control valve member 21, a non-return valve 22 protecting the accumulator 14 and a changeover valve 23 influenced by the pressure in the accumulator 14 and pilot-controlling the control valve 21.

The control valve 21 is mounted in a slide bore 24 which has a supply chamber 25, an accumulator chamber 26 and an overflow chamber 27 formed as annular grooves. When the supply chamber 25 is in communication with the pump 12 a duct 28 leads from the accumulator chamber 26 through a first throttle 29 and the non-return valve 22 to the accumulator 14. The open circuit 1 6 is connected to the overflow chamber 27. An annular control groove 31 is machined in the slide bore 24 spaced from the overflow chamber 27 and which is in communication with a control bore 33 through a second throttle 32. A control line 34 which branches from the duct 28 downstream of the first throttle 29 in the closed circuit, issues into the slide bore 24 in the region of the control groove 31.In the region of its entry into the slide bore 24, the control line 34 is divided into a first branch line 35, in which a third throttle 36 is arranged, and a second branch line 37. Whereas the latter (37) issues into the slide bore 24 in the region between the control groove 31 and the overflow chamber 27, the first branch line 35 leads into the slide bore 24 on the other side of the control groove 31.

At its end remote from the accumulator chamber 26, the slide bore 24 proceeds by way of a shoulder forming an abutment 38 and an annular groove 39 into a piston space 41 which is in communication with the slide bore 33 through a bore 42. By means of a first piston section 43, the control valve 21 controls the communication from the supply chamber 25 to the accumulator chamber 26. By means of a second piston section 44, it controls the communication from the supply chamber 25 to the overflow chamber 27. Control grooves 45 which, in the illustrated first end position of the control valve 21 open the communication from the pump 12 to the closed circuit 13, are formed on the first section 43.

Furthermore, the first section 43 has a throttle bore through which the supply chamber 25 is permanently connected to the accumulator chamber 26. In the illustrated left-hand end position of the control valve 21 with the connection from the pump 12 to the accumulator circuit 13 open, the second section 44 closes the connection from the pump 12 to the open circuit 16. A pin 48 directed towards a stepped piston 47 is fixed to the second section 44. A pretensioned spring 52 is supported on the pin 48 by a spring plate 49 and a snap ring 51. An inner first piston section 53 of smaller diameter of the stepped piston 47 engages the spring plate 49. A second section 54 provided with a larger diameter of the stepped piston 47 is supported by the abutment 38 under the action of a second spring and the pressure in the piston space 41.The sections of the stepped piston 47 and of the control valve 41 facing one another have the same outer diameter and between them bound a first pressure space 56 into which the control line 34 issues and in which the control groove 31 is also located. The control valve 44 is coupled non-positively to the stepped piston 47 by the first spring 52 located in the pressure space 56. In addition, the pin 48 is made-long enough that, after exceeding a limited stroke, its end abuts the smaller section 53 of the stepped piston 47.

The changeover valve 23 serving for the pilot control, has an inlet chamber 57 which is in communication with the control bore 33. The inlet chamber 57 is in communication with a return chamber 58 through a valve seat 59 onto which a spring 61 urges a spherical closure member 62. A piston 63 provided with a pin 64 is associated with the closure member 62 and can be influenced at its end carrying the pin 64 by the pressure in the inlet chamber 57 and at its opposite end of the same size can be influenced through a duct 65 by the pressure in the accumulator 14. The effective area of the piston 63 is chosen to be greater by about 20% than the effective area of the valve seat 59 so as to achieve a certain switching hysteresis. Furthermore, a duct 66 connects the annular groove 39 to the outlet chamber 58 of the changeover valve 23.

By means of the brake valve 13, which is controlled by a- tractor brake system 67, the pressure in the trailer brake 68 may be controlled.

The method of operation of the apparatus 10 according to Figure 1 will be explained as follows: Since the power actuated trailer brake 68 must always be ready to operate it is connected in a closed circuit comprising the accumulator 14 which is supplied with pressure medium by the pump 12 through the accumulator charging valve 11 as a matter of priority. A completely constant flow of oil is sufficient for the additional load 1 8 for some kind of working hydraulic system when the motor for the vehicle provided with the apparatus 10 is running. Thus, the entire quantity delivered by the constant pump 1 2 with the accumulator 14 charged, flows through the accumulator charging valve 11 into the open circuit 16 and then to the tank 69.On the other hand, when the accumulator 14 is not charged, the accumulator charging valve 11 diverts a constant amount of pressure medium delivered by the pump 12 into the closed circuit 13 whilst the excess pressure medium arrives in the open circuit 16.

Some operating conditions will be described in the following wherein the individual pressures in the apparatus 10 are referenced as follows: the instantaneous pressure in the accumulator 14 is referenced p; the charging pressure at which the accumulator charging begins is p1; the switching off pressure at which the accumulator charging terminates is p2; p3 is the brake pressure which acts in the brake cylinder of the trailer brake 68; p4 is the control pressure which prevails in the tractor brake equipment 67; p5 is the instantaneous pressure in the additional load 18.

First of all, the operating condition of charging the accumulator 14 will be described when the pressure p is less than the pressure p2. This operating condition corresponds to the illustrated position of the control elements in the accumulator charging valve 11. In so doing, the control valve 21 takes up the illustrated first epd position so that the pressure medium delivered by the pump 12 into the supply chamber 25 flows through the control grooves 45, the duct 28 comprising the first throttle 29 and the non-return valve 22 into the accumulator and charges the latter. The pressure in the duct 28 downstream of the first throttle 29 also builds up in the first pressure space 56 through the control line 34. In this manner, the pressure drop generated by the first throttle 29 acts on the control valve 21 against the force of the first spring 52 whereby the control valve provides an upper limit for the flow of pressure medium flowing to the accumulator 14 and maintains it constant. If the delivery from the pump 12 exceeds the constant flow to the accumulator 14, then the second section 44 on the- control valve 21 opens the connection from the supply chamber 25 to the overflow chamber 27 whereupon a residual flow arrives in the open circuit 1 6. With the multi-way valve 1 7 not operated, this residual flow flows unthrottled to the tank 69. During this flow regulation, the first spring 52 is supported by the first section 53 of the stepped piston 47.The pressure effective in the first pressure space 26 can also build up in the piston space 41 through the second throttle 32, the control bore 33 and the bore 42. There it acts on the larger effective area of the second section 54 of the stepped piston 47 whereupon the latter engages the abutment 38. The pressure in the first pressure space 56 also arrives in the inlet chamber 57 of the changeover valve 23 and there acts on the effective seat area of the closure member 62 and also on the end surface of the piston 63. The opposite end surface of the piston 63 is directly influenced by the pressure in the accumulator 14 through the duct 65 so that the piston 63 is almost completely hydraulically balanced.

In the following, the operating condition will be described when the pressure p in the accumulator 14 reaches the switching off pressure p2* In this case, the spherical closure member 62 in the changeover valve 23 then opens. Then, a flow of control oil branches off from the duct 28 and flows through the control line 34, the first and second branch lines 35 and 37, the first pressure space 56, control box 33, the inlet chamber 57 and past the closure member 62 into the outlet chamber 58 and to the tank 69. In so doing, the second throttle 32 causes a pressure drop in the flow of control oil which becomes effective in the piston space 41.If, for example, the effective area of the second section 54 of the stepped piston 47 is greater than the effective area of the first section 53 by 30%, then the stepped piston 47 is only released from the abutment 38 after a pressure drop of about 30% with respect to the opening pressure of the closure member 62 and is pushed by the first piston section 53 towards the right against the force of the second spring 55.

The pressure drop in the control bore 33 produced by the second throttle 32 also acts in the inlet chamber 57 of the pressure control valve 23 whilst the pressure p from the accumulator 14 acts on the opposite end surface of the piston 63.

Furthermore, since the effective end surface of the piston 63 is about 20% larger than the effective surface of the valve seat 59, an additional force exists directed against the force of the spring 61 due to the pressure drop at the second throttle 32 and which assists the opening of the closure member 62. This automatically increasing force after overcoming the friction, leads to the complete opening of the closure member 62 due to the collapse of the pressure in the inlet chamber 57. Thus, a fixed throttling of the accumulator charging valve 11 is prevented so that switching over of the control valve 21 only takes place after a drop in pressure at the second throttle 32 by about 30% and at this instant the automatically increasing force has already increased to such an extent that the formation of a balanced condition is excluded.

As a result of the described pressure drop in the inlet chamber 57 and the pressure drop in the piston space 41 associated with it, the stepped piston 47 takes up its second right-hand end position wherein the end of the second section 54 abuts against the base of the piston space 41. The stepped piston 47 is retained in this position by the first section 53 on the end surface of which facing the first pressure chamber 56 the pressure in the control oil circuit upstream of the second throttle 32 acts. During this movement of the stepped piston 47, an expansion of the second spring 52 serving as a control spring is prevented since it is supported by a spring plate 49 and a snap ring 51 on the pin 48 of the control valve 21.

As a result, the control valve 21 is moved to the right towards its second end position by the same amount as the piston 47. In so doing, the second section 44 of the control valve 21 closes the second branch line 37 so that control oil can then only flow through the first branch line 35 provided with the third throttle 36. During this movement of the control valve 21 towards the right, its second section 44 provided-with a control edge 50 also enters the control groove 31 and thus forms a fourth adjustable throttle 71. Thus, together with the second spring 52, the control valve 21 forms a pressure maintaining valve associated with the third throttle 36 whereupon the control oil flowing away through the changeover valve 23 is maintained constant at a lower level even during high pressure loading of the open circuit 1 6.

As the next operating condition, the case will be considered when the loading of the accumulator 14 is terminated and the pressure p is higher than the switching on pressure p1 but on the other hand is equal to or lower than the switching off pressure p2. Moreover, the piston 47 is located in its right-hand second end position. The pressure medium delivered by the pump 12 flows for the greater-part through the accumulator charging valve 11 into the open circuit 16. The control grooves 45 on the control valve 21 are closed, A flow of control oil flows from the supply chamber 25 through the throttle bore 46 in the first section 43, the duct 28, the control line 34, the first branch line 35 provided with the third throttle 36, the fourth throttle 71, the second throttle 72, the control bore 33 and the open closure member 62 to the tank 69.Due to the pressure drop in the fourth throttle 71 and in the second throttle 32, the stepped piston 47 is retained in its right-hand second end position. In a corresponding manner, the control valve 21 is retained in its second end position by the pressure drop at the third throttle 36 whereby it is so adjusted by the pressure in the open circuit 1 6 that the flow of control oil is maintained constant. Thus, the flow of pressure medium delivered by the pump 12 less the quantity of control oil flowing through the control valve 23 to the tank 69, flows into the open circuit 1 6 where the additional load 1 8 can be controlled with the aid of the multiway valve 1 7. This takes place as long as the pressure p5 in the open circuit 1 6 is lower than the pressure p in the accumulator 14.On the other hand, if the pressure p5 in the open circuit 1 6 is higher than the pressure p in the accumulator 14, then an additional partial flow flows through the throttle bore 46 and the nonreturn valve 22 to the accumulator 14 and charges it until its pressure p is equal to or higher than the pressure p5.

As the next operating condition, the case will be considered where the pressure p in the accumulator 14 has fallen to a value which is lower than the switching on pressures q 1 so that the accumulator charging valve 11 switches to the accumulator charging, function. At the end of the accumulator charging, the pressure in the inlet chamber 57 of the control 23 has dropped and the spherical closure member 62 is still fuily open. The position of the open closure member 62 is dependent on the instantaneous pressure p in the accumulator 14 which influences the area of the piston 63 larger by 20% through the duct 65.

Thus, when the pressure in the accumulator 14 drops by about 20% then the closure member 62 begins to close. The pressure in the inlet chamber 57 then increases and acts in the piston space 41 through the bore 42. Thus, the stepped piston 47 is pushed from its right-hand second end position towards the left towards its first end position whereby it strongly pretensions the first spring 52.

Simultaneously however, a higher spring pretensioning leads to an increasing amount of control oil and this leads once again to an additional increase in pressure in the inlet chamber 57. As a result of the different pressure influenced areas of the piston 63 and the closure member 62 the increasing pressure rise in the inlet chamber 57 generates an automatically increasing force which supports the closing operation at the closure member 62. In this manner, the control valve 23 changes over and the closure member 62 blocks the return to the tank 69.During movement towards the left of the stepped piston 47 out of its right-hand end position towards its first left-hand end position, the first section 53 finally comes to rest against the pin 48 after increasing the pretensioning of the first spring 52 and entrains the control valve 21 towards the left in the direction of its first end position. In so doing, the control groove 31 is fully opened and the fourth throttle 71 is therefore ineffective. Finally, during further movement towards the left, the second branch line 37 is opened which leads to an avalanche type of increase in the amount of control oil and as a result to a corresponding pressure rise in the inlet chamber 57 in the changeover valve 23.This increase in the amount of control oil during the movement to the left of the control valve 21 and the stepped piston 47 assist the changing over operation of the changeover valve 23. This is of particular advantage since the closing force resulting from the different pressure influenced areas on the piston 63 and the valve seat 59 is relatively small. If the spherical closure member 62 finally blocks the discharge to the tank 69 completely so that control oil can no longer flow, then the stepped piston 47 and the control valve 21 can move into their left-hand first end position.

A charging of the accumulator 14 can then begin as has already been described.

As a further operating condition, the braking operation will be considered. On actuation of the tractor braking system 67 the brake pressure built up in it is conveyed to the control connection for the brake valve 1 5. The brake valve 1 5 regulates the pressure in the brake cylinders of the trailer brakes 68 in proportion to the said control pressure. As long as a balance prevails between the control pressure p4 and the brake pressure p3 the brake valve 1 5 blocks the communications from the trailer brake 68 to the accumulator 14 and to the tank 69. If, due to an increase in braking pressure, the balance is upset, then the brake valve 1 5 opens the communication fromlhe accumulator 14 to the trailer brake 68 whereby the discharge to the tank 69 is blocked.With a drop in braking pressure, the connection from the trailer brake 6 & o the accumulator 14 is blocked and the trailer brake 68 is relieved to the tank 69 in a correspondingly reverse manner.

Thus, with the present apparatus 10, a closed circuit 13 may be supplied in a preferred manner with a constant flow with the aid of the accumulator charging valve 11 and an open circuit 1 6 may be supplied largely continuously with pressure medium wherein the open circuit can be loaded. In this case, the control valve 21 can take up two initial positions in an especially advantageous manner as a result of its coupling to a stepped piston 47 since the stepped piston 47 is fixed in two positions by mechanical abutments. In one of its initial positions, the control valve 21 can operate with the aid of the first throttle 29 as a flow regulator for the flow of charging pressure medium flowing to the accumulator 14.

Furthermore, in its other initial position the control valve 21 can operate in association with the third throttle 36 as a flow regulator for the flow of control oil since the free through flow crosssection of the third throttle 36 is substantially smaller than that of the first throttle 29.

Furthermore, due to the coupling between the control valve 21 and the stepped piston 47 in association with the kind and manner in which the flow of control oil takes place and is throttled, the accumulator charging valve 11 always moves into one of two stabie end positions. This applies during changing over of the accumulator valve 11 both to the beginning and to the end of a charging operation of the accumulator 14. In that way, the reliable switching over of the accumulator charging valve 11 is achieved although it operates as a pilot controlled valve and accurate switching pressures can be produced by it. As a result, the control oil losses can be maintained relatively low despite the pilot control. Moreover, this effect may be achieved with elements of relatively simple construction.Although it is preferable to make the stepped piston from two piston sections separate from one another, it can, if necessary, also be made in one piece. A further advantage is that if necessary, a second closed circuit can be connected to the accumulator charging valve 11 instead of the illustrated open circuit 1 6.

Figure 2 shows an accumulator charging valve 81 partially in longitudinal section as a portion of a second apparatus. Moreover, components with corresponding functions as in Figure 1 are given the same references but provided with a '. An essential difference exists in the fact that in this case the control valve arranged coaxially with respect to the stepped piston is formed as a hollow slide valve 21'. As a result of the hollow slide valve construction, first of all the supply chamber 25' then the overflow chamber 27', the accumulator chamber 26', a first intermediate chamber 27', the accumulator chamber 26', a first intermediate chamber 82, the first control groove 31', finally a second intermediate chamber 33 and the second control groove 39' are arranged in the housing of the accumulator charging valve 81.In its interior, the first section 43' of the hollow valve 21' accommodates the first throttle 29' and apart from a ring of through-flow bores 84 carries the control grooves 45' on the outside the through bores 84 are located in the region of a first annular groove 85 which separates a second section 86 from the first section 85'. A second annular groove 87 and a third section 88 are connected to the section 45'. In the region of the second section 86 there is a third annular groove 89 from which radial bores 91 lead into the interior of the hollow valve 21'. A threaded plug 92 which accommodates within it the third throttle 36', is located in the interior of the hollow valve 21' in the region between the through bores 84 and the radial bores 91. The control edge 50' is arranged on the second section 86 further out than the annular groove 87.In this case, the second throttle 32' is formed as a radial bore in the region of the second annular groove 87. In the region between the second throttle 32' and the radial bores 91 the hollow valve 21' has in its interior a flange 93 against which engages the head of a screw 94 serving as a coupling member. The screw 94 is rigidly screwed into the first section 53' of the stepped piston 47'. The pretensioned first spring 52' is supported on the first section 47' of the stepped piston and on the flange 93 in the hollow valve 21'. Control pressure medium can arrive unhindered in the first pressure space 56' through bores 95 in the screw 94. A fourth annular groove 96 which, in the illustrated first left-hand end position of the stepped piston, is in communication with the second intermediate chamber 83, is arranged on the first section 47' of the stepped piston.The intermediate chamber 83 is in communication through a transverse bore 97 with the duct 28' in the region between the accumulator chamber 26' and the non-return valve 22'. Furthermore, the accumulator charging valve 81 differs from that according to Figure 1 chiefly by the fact that the changeover valve 23' together with the non-return valve 22' is arranged on one and the same valve axis 97 which extends parallel to the axis of the hollow valve 21'.

Furthermore, the brake valve 1 5 is accommodated in the housing of the accumulator charging valve 81 on a third valve axis 91.

The method of operation of the apparatus 80 comprising the accumulator charging valve 81 corresponds in principle completely to the method of operation of the apparatus 10 according to Figure 1. Thus, in the following, largely the differences will be contrasted. Due to the construction of the hollow valve 21', the tapping for the quantity of control oil no longer takes place downstream of the control grooves 45' but upstream thereof in the supply chamber 25'. Thus, when the first section 43' completely closes the connection to the non-return valve 22' during charging of the accumulator 1 4, the first section 53' of the stepped piston 47' is also located in a second end position (not shown).In this second end position, the fourth annular groove 96 connects the second intermediate chamber 83 to the annular groove 39' which is relieved to the outlet chamber 58' in the changeover valve 23' and thus to the tank 69. Even if the pressure p5 in the open circuit 1 6 should rise above the pressure p in the accumulator 14, pressure medium leaking through the piston section 43' into the duct 28' can only arrive in the outlet chamber 58' and thus at the tank through the transverse bore 99, the second intermediate chamber 83, the fourth annular groove 96, the annular groove 39', the duct 66, but not charge the accumulator 1 4 still further through the non-return valve 22'. Thus, the accumulator circuit 14 is better protected against over-charging.Furthermore, there is the advantage that the flow of control oil branched off from the pump delivery and conveyed to the tank through the changeover valve 23' is only conveyed in the region of the supply chamber 25' up to the second throttle 32' through the hollow spaces in the hollow valve 21' or through external annular grooves 85, 89. Thus, expensive and complicated ducting for the control line system in the housing of the accumulator charging valve 81 is not required. Thus, the second throttle 32' and the third throttle 36' can be arranged in a simple manner in the hollow valve 21'. Also, the second branch line 37' maybe provided in a substantially simple manner by the radial bores 91 and the annular groove 89 in the hollow valve 21'.

Moreover, the function of the fourth throttle 71' can be undertaken by the control edge 50' which, in the case of a throttling, can cooperate with the right-hand edge of the control groove 31' in the housing. Then, in contrast to Figure 1, the fourth throttle 71' is connected in series with the throttle 32' in respect of the flow of control oil in the accumulator charging valve 81. Due to the particular kind of coupling with the aid of the screw 94, both elements are non-positively coupled to one another during changing of the hollow valve 21' with the stepped piston 47' from a left-hand first end position towards the right into a second end position, whilst in the reverse switching direction the hollow valve 21' is positively coupled to the first section 53'. Apart from its construction which is advantageous from the manufacturing point of view, the accumulator charging valve 81 also has the advantages on the valve 11 according to Figure 1.

Claims (23)

1. Hydraulic apparatus for controlling the flow of pressure medium from a pressure medium source into a closed circuit provided with an accumulator and a load and/or into an additional circuit provided with a further load, comprising a control valve loaded by at least one spring and influencing the said connections, which control valve is controllable in accordance with pressure and with which is associated a changeover valve influenced by the pressure in the accumulator and through which is conveyed a flow of control oil branched from the pressure medium source and in which at least one throttle is provided and comprising a non-return valve in series with the control valve protecting the accumulator, characterised in that, the control valve is coupled by the spring to a stepped piston which is retained by a second spring in a first end position and that, in the flow of control oil, a second throttle is connected through the pressure difference across which the stepped piston can be displaced into a second end position against the force of the second spring.

2. Apparatus according to claim 1, characterised in that, the stepped piston has a first piston section of smaller diameter and a second piston section of larger diameter and the first piston section together with the coupled control valve bounds a first pressure space through which the flow of control oil is conveyed to a region between the first throttle and the second throttle.

3. Apparatus according to claim 2, characterised in that, the first pressure space can be relieved to the tank through the second throttle and the changeover valve.

4. Apparatus according to claim 1 or 2, characterised in that, the effective areas of the control valve bounding the first pressure space and of the first piston section are equal.

5. Apparatus according to one of claims 1 to 4, characterised in that the changeover valve has a closure member and a piston associated with the latter and which has an effective area of a different size with respect to the valve seat and determining the switching time.

6. Apparatus according to claim 5, characterised in that, the effective cross-sectional area of the piston influenced by the accumulator pressure is greater than the area of the valve seat associated with the closure member.

7. Apparatus according to one of claims 2 to 6, characterised in that, the line carrying the control flow is branched in the region between the first throtttle and the first pressure space into a first branch line, in which a third throttle is connected, and into a second branch line.

8. Apparatus according to claim 7, characterised in that, the through flow crosssection of the third throttle is substantially smaller than that of the first throttle.

9. Apparatus according to one of claims 7 and 8, characterised in that, with the control valve located in a first end position, the second branch line is opened and with the stepped piston located in a second end position, is closed and that the first branch line is opened independently of the position of the control valve.

10. Apparatus according to one of claims 1 to 9, characterised in that, the control valve and the stepped piston are arranged coaxially.

11. Apparatus according to one of claims 1 to 10, characterised in that, the spring connected between the control valve and the stepped piston is pretensioned with the aid of the coupling member and the control valve forms a mechanical abutment for the stepped piston.

12. Apparatus according to one of claims 1 to 11, characterised in that, together with the control valve, the first throttle forms a flow regulator which limits the flow into the closed circuit to a constant value.

13. Apparatus according to one of claims 2 to 12, characterised in that, an abutment fixed to the housing is associated with the second piston section and a relief duct conducting leakage oil away arriving through the stepped piston is provided in the region of the said abutment.

14. Apparatus according to one of claims 2 to 13, characterised in that, a fourth throttle which is formed by a control edge or control notch in the control valve, is connected in series with the third throttle and the second throttle.

1 5. Apparatus according to one of claims 2 to 14, characterised in that the control vlave has a first section which, in a first end position, connects a supply chamber to an accumulator chamber, in a second end position separates them from one another and in intermediate positions throttles the said communication, and has a second section which, in the first end position, blocks the connection to the overflow chamber.

1 6. Apparatus according to claim 1 5, characterised-in that, a throttle bore connecting the supply chamber to the accumulator chamber is arranged in particular in the first section.

1 7. Apparatus according to one of claims 1 to 4 and 7 to 14, characterised in that, the control valve is formed as a hollow valve which accommodates the first throttle in its interior.

1 8. Apparatus according to claim 17, characterised in that, with the connection from the pump to the open circuit open the hollow valve closes the connection from the pump to the accumulator and that a section of the closed circuit in the region between the non-return valve and the hollow valve is relieved to the tank, especially through the stepped piston in its second end position.

19. Apparatus according to claim 17 or 18, characterised in that, the second throttle and the third throttle are arranged in the hollow valve.

20. Apparatus according to one of claims 1 7 to 19, characterised in that, the coupling between the hollow valve and the stepped piston is so designed that, during closing of the connection from the pump to the closed circuit, the hollow valve entrains the first section through a nonpositive connection and during opening in the reverse direction entrains it through a positive connection.

21. Apparatus according to claim 20, characterised in that, the coupling member is a screw fixed in the stepped piston and the head of which abuts against a flange in the hollow valve and against which also abuts the pretensioned spring arranged between the hollow valve and the stepped piston.

22. Apparatus according to claim 19, characterised in that, the third throttle is arranged in the hollow valve in the region between through flow bores andradial bores.

23. Hydraulic apparatus substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.