WO1991019923A1

WO1991019923A1 - Valve arrangement

Info

Publication number: WO1991019923A1
Application number: PCT/SE1991/000419
Authority: WO
Inventors: Gunnar Lindmark
Original assignee: Hiab Ab
Priority date: 1990-06-11
Filing date: 1991-06-11
Publication date: 1991-12-26
Also published as: AU8072191A; SE9002069D0; EP0592416A1; SE9002069L; SE466273B

Abstract

A valve arrangement used for connecting one side of a hydraulic device to a pump for supplying hydraulic fluid comprises a stationary valve housing and a slide member (21) rotatably mounted therein. The slide member is in the form of a cylinder having a cavity (30) with closed end walls. The slide member is mounted only hydraulically in the valve housing. Thus, the valve arrangement has no mechanical bearings. The circumferential surface of the cylinder has openings (32-34) through which the cavity is connectible to the pump and an optional side of the hydraulic device. At each of the end walls of the slide member, there are provided spaces (28) communicating with the low-pressure side of the hydraulic system. The pressure in the spaces at the two end walls is equal. The slide member is statically hydraulically balanced in both the radial and the axial direction.

Description

VALVE ARRANGEMENT

The present invention relates to a valve arrangemen adapted to connect a source for supplying hydraulic flui to one or the other side of a hydraulic device, comprisi a stationary valve housing with at least one connection the source of hydraulic fluid, at least two symmetricall disposed connections to one side of the hydraulic device and at least two symmetrically disposed connections to th other side of the hydraulic device, and a slide member rotatably mounted in the valve housing and .substantially being in the form of a cylinder having at least one cavit and at least two openings which are symmetrically dispose in the circumferential surface of the cylinder and adapte to connect the cavity to the connections to one side of t hydraulic device, and at least two openings symmetrically disposed in the circumferential surface of the cylinder a adapted to connect the cavity to the connections to the other side of the hydraulic device, the source of hydraul fluid being connected to one or the other side of the hy¬ draulic device by rotation of the slide member.

Directional valves are used for controlling the flow of hydraulic fluid to piston and cylinder assemblies and hydraulic motors, e.g. in hydraulic cranes and other working machines.

One known type of directional valve comprises a valv housing having an axially movable slide member which, whe displaced from the neutral position, connects^•one side of the piston and cylinder assembly or hydraulic motor to a pump, and the other side to a tank. The valve can be oper ated hydraulically, electrically or mechanically.

One problem encountered in directional valves with axial slide members is that substantial forces are requir for operating the slide member because of the considerabl impulse forces and the friction prevailing between the slide member and the valve housing. Another problem is that high accuracy is required i the manufacture of the valve. The valve housing has conn tions to the pump and the tank, and to each side of the hydraulic device. Each of these connections is connected a circumferential channel provided in the valve housing around the slide member. The slide member has recesses b means of which the channels in the valve housing can be connected to each other. When the slide member of the va is shifted, the passages between the channels in the val housing and the recesses in the slide member are opened. these passages are not symmetrically disposed relative t the slide member, an impulse force affecting the slide m ber will occur when liquid flows through the passages, whereby the slide member is unbalanced in the valve housing, thus increasing the friction.

One way of reducing the operating forces is to repl the axial slide member with a rotary slide member. Valve with rotary slide members are known in the patent litera ture. US 2,907,349, for example, describes a rotary four- valve having a valve housing with a connection to a pump, connection to the tank, a connection to the first side o piston and cylinder assembly, a connection to the other side of the piston and cylinder assembly, and a rotary slide member defining four spaces between the valve hous and the slide member. By rotating the slide member, the connections to the piston and cylinder assembly can be connected to either the tank or the pump. The connection to the pump and the tank are in the same axial plane in housing, whereas the connections to the piston and cylin assembly are located at each of the ends of the slide me ber and are directed at a 90° angle to the slide member.

US 2,946,348 describes a similar valve arrangement. this case, the valve housing has two connections to the pump, the tank and the two sides of the piston and cylin assembly. All the connections are in one and the same plane. This means a bulky design with a valve slide memb of large diameter. Such a valve arrangement permits but limited flow and, besides, entails substantial operatin forces.

Another example of a similar design is described i 3,363,651.

US 3,454,049 discloses a rotary servo valve having rotary slide member mounted in a sleeve, in turn rotatab mounted in a valve housing having connections to the pu the tank and a hydraulic device. The slide member is in form of a spool with a plurality of recesses. These rece ses are distributed axially and circumferentially on the slide member, and by rotating the slide member the conne tions to the hydraulic device can be connected to the pu or the tank through the recesses. In all the above patents, communications between th different connections in the valve housing are achieved means of recesses, grooves or the like provided in the surface of the slide member of the valve. This calls for high manufacturing accuracy. In the case where there are two diametrically opposed connections in the valve housi for connecting one side of the hydraulic device, e.g. to the pump, these connections must in fact be accurately positioned and designed, or else unbalance will occur in the same way as in the case of the axial slide member. From a brochure from Modular Controls, a directiona valve with a rotary slide member is known. The basic des of this valve is shown in Fig. 1. The valve has a valve housing 1 with a connection 2 to a pump for supplying hy draulic fluid, two diametrically opposed connections 3 t one side of a hydraulic device and two diametrically opposed connections 4 to the other side of the hydraulic device. The rotary slide member 5 is in the form of cyli der in which a cavity is provided and whose circumferent surface is formed with openings 6 for selectively connec ing the cavity to the valve housing connections to the hydraulic device. The inlet for hydraulic fluid from the pump to the cavity of the slide member of the valve is provided in one side wall of the valve housing and the slide member. The slide member is operated by a rod 7 fi to the slide member. At the end of the slide member oppo site to the inlet, there is provided a thrust bearing 8, beyond which a seal 9 is mounted on the rod 7.

The cavity slide member offers manufacturing advan¬ tages over slide members with recesses in the circumfere tial surface, since it is easier to make a number of sma bores in the slide member with high accuracy than a numb of large recesses in its circumferential surface.

The valve now described from Modular Control howeve suffers from a number of drawbacks. Thus, as a result of the inflow of hydraulic fluid taking place in one side w of the slide member, an axial force will be produced whi is equal to the working pressure of the hydraulic fluid multiplied by the area of the rod 7. This axial force is taken up in the thrust bearing 8. Since it is impossible mount the thrust bearing 8 in a plane exactly perpendicu to the longitudinal axis of the slide member, the slide member will be subjected to radial forces, leading to un balance, friction and, hence, the need of increased oper ating forces.

Since the working pressure acts on one side of the ^' seal 9 and the atmospheric pressure on the other side, there will also be a substantial pressure drop across th seal 9, which entails increased friction and, hence, the need of increased operating forces.

US 4,199,007 describes a servo valve having a rota and axially displaceable slide member and a housing wit connection to the pump, a connection to each side of a piston and cylinder assembly, and two connections to th tank. The slide member has two cavities, and its circum¬ ferential surface has openings which can be aligned wit the connections in the housing. The size of the flow to piston and cylinder assembly is controlled by axial dis¬ placement of the slide member, while the direction of t flow is controlled by rotation of the slide member. Thi valve necessitates considerable operating forces, sinc unsymmetrical flow pattern is obtained in the radial d tion during steady-state flow.

One object of the present invention is to provide valve having a rotary valve member which is better bal than known rotary valve members and which thus require smaller operating forces.

This object is achieved by means of a valve arran ment having the features stated in the accompanying cl The slide member of the valve arrangement accordi the invention is balanced both radially and axially, a affected only by an external turning moment. Thus, the operating forces required for the rotation will, become small. The present invention will now be desribed in som bodiments with reference to the accompanying drawings, which

Fig. 1, as mentioned, is a longitudinal section of a kn valve; Fig. 2 is a longitudinal section of a first embodiment the invention; and Fig. 3 is a longitudinal section of a second embodimen the invention. Fig. 2 shows an embodiment of a valve arrangement cording to the invention in what is known as a cartridg design. The arrangement, which has a "semi"-directional valve function, comprises a sleeve 20 to be mounted det ably, but stationarily in a housing (not shown) with co nections to a pump for supplying hydraulic fluid and to both sides of a hydraulic device, a slide member 21 rot ably mounted in the sleeve 20, a step motor 22 for rota the slide member 21, and a coupling 23 between the moto and the slide member 21.

The sleeve 20 has two diametrically opposed openin 24 to the connection to one side of the hydraulic devic and two similarly disposed openings 25 to the connectio the other side of the hydraulic device. The sleeve 20 f ther has three symmetrically disposed openings 26 to the connection to the pump. The sleeve 20 also has a plurali of seals 27 against the housing. On the outer side of t two end walls of the slide member 21, between the valve housing and the slide member and also between the sleev and the slide member, there are spaces 28 communicating with the tank for hydraulic fluid. The spaces 28 need however not communicate directly with the tank, the ess tial thing being that they communicate with the low- pressure side of the hydraulic system, such that the pressure is low, and that the pressure is equal in the spaces 28, such that the axial forces acting in opposit directions on the end walls of the slide member are equ and thus counterbalance each other. Drains 29 are provi between the connections 24, 25 and the spaces 28.

The slide member 21 is in the form of a cylinder having an axial bore or an axial cavity 30. The end wal of the cylinder are closed, one with a plug 31. The cir ferential surface of the cylinder has two openings 32 w can be aligned with the openings 24 to one side of the hydraulic device, two openings 33 which can be aligned the openings 25 to the other side of the hydraulic devi and which are angularly offset with respect to the open 32, and three symmectrically disposed openings 34 which the openings 26 can connect the cavity to the pump port The outer side of the slide member is further formed wi relief grooves 35 extending circumferentially and servi to equalise the pressure in the gap between the slide member 21 and the sleeve 20 for improved balancing. The step motor 22 is guided in a block 36 and has output shaft 37 which is fixed in a cylindrical element rotatably mounted in the space 28. A seal 39 is provide between the space 28 and the motor 22.

The coupling 23 includes the cylindrical element 3 having a milled portion 40 in which a torsion spring 41 fixed, which serves to return the slide member to its n tral position and extends around the sleeve. The coupli 23 further includes a plate 42 which is mounted with on end in a chisel groove 43 in the slide member and with other end in a chisel groove 44 in the cylindrical elem 38. The plate 42 serves to take up displacements betwee the centre of the output shaft 37 of the motor and the slide member 21. The coupling 23 further ensures that o a turning moment is transmitted from the motor shaft to slide member and that the forces exerted by the torsion spring 41 acts only on the motor shaft. The torsion spr 41 may be replaced by a detector sensing the neutral po tion.

In the valve according to the invention, both the rection and the size of the hydraulic flow to the hydra device are controlled by rotation of the slide member through a limited angle.

In the arrangement according to the invention, exe plified in Fig. 2, the hydraulic fluid is fed from the into and out of the cavity in the slide member in the r dial direction and, thus, does not give rise to any axi force on the slide member. Moreover, the supply and dis charge of hydraulic fluid takes place through symmetric disposed openings, which means that the jet impulse for counterbalance each other in the radial direction.

The spaces 28 will contain hydraulic fluid of tank pressure. This means that the^' pressure drop over the se 39 becomes small, which keeps friction down and, thus, operating forces. The axial force exerted on the motor shaft is small and is taken up in the bearing of the st motor 22. Since the pressure is equal on both ends of t slide member, no axial force will be exerted on the slid member. The slide member 21 is mounted only hydraulicall in the sleeve 20. Thus, there are no mechanical thrust o radial bearings that may produce undesired forces on the slide member. The slide member 21 will "float" in the sleeve 20 and be completely statically hydraulically balanced in both the axial and the radial direction, whi means that the operating forces become small. Upon rotat of the slide member, the coupling 23 ensures that only a torque is exerted on it.

Fig. 3 shows an embodiment of a valve arrangement according to the invention having a "full" directional valve function. In this case, the slide member of the va is mounted directly in a valve housing. If so desired, t valve arrangement may of course also be of cartridge design.

The valve arrangement in Fig. 3 comprises a valve housing 50, a slide member 51 rotatably mounted therein a coupling 52 indicated by a dash-dot line in the right- hand portion of the Figure and connected to a drive unit (not shown) for rotating the slide member 51. The valve housing 50 has a bore 53. From this bore extends a conne tion 54 to a pump for supplying hydraulic fluid under pressure. The connection 54 partly is in the form of a recess or a groove extending circumferentially in the bo From the bore 53 further extend two pairs of connections one side of a hydraulic device. Each pair includes two d ametrically opposed connections 55 and 56, respectively. From the bore 53 also extend two further pairs of connec tions to the other side of the hydraulic unit. Like the above-mentioned two pairs, each of these pairs includes diametrically opposed connections 57 and 58, respectivel As in the embodiment in Fig. 2, there are provided^' between the valve housing and the end walls of the slide member spaces 70 which via connections 71, 72 in the val housing communicate with the low-pressure side of the system, such that the same pressure acts on both end wal The slide member 51, which is mounted in the bore 5 is in the form of a cylinder. The central portion of the cylinder has a cavity 59 with closed end walls. One end wall is provided by a plug 60. In the central portion of the slide member 51, there are three symetrically dispos openings 61 for connecting the cavity 59 to the connecti 54 to the pump. Further, this central portion has two si larly disposed openings 62 which, by rotation of the sli member 51, can be aligned with the connections 55 for supplying hydraulic fluid to one side of the hydraulic device. Also, the central portion has two similarly dis¬ posed openings 63 which are angularly offset in relation the openings 62 and which, by rotation of the slide memb can be aligned with the connections 57 for supplying hy¬ draulic fluid from the pump to the other side of the hy- draulic device. The left-hand portion of the slide member in Fig. 3 thus accommodates the above-mentioned plug 60 which has a recess 64 extending circumferentially, and tw channels 65 extending axially. In this portion, the sleev 51 has two openings 66 which, by rotation of the slide me ber, can be aligned with the connections 56 for- connectin one side of the hydraulic device to the tank. In the righ hand portion of the slide member in Fig. 3 are provided a bore 67 and two openings 68 which, by rotation of the sli member, can be aligned with the connections 58 for connec ing the other side of the hydraulic device to the tank.

As in the embodiment shown in Fig. 2, hydraulic flui is fed into and out of the cavity in the slide member in the radial direction through symetrically disposed openin in the circumferential surface of the slide member. This, in combination with the fact that the same pressure acts the end walls of the slide member, entails that the slide member becomes very well-balanced and, thus, requires onl small operating forces for its rotation. The coupling and the step motor may be arranged in the same way as in Fig. 2. The pressure drop over the seal between the space 70 a the motor then becomes small, and the operating forces ar kept down. The axial force acting on the motor shaft be¬ cause of the tank pressure becomes small and is taken up the motor bearing. Further, the valve arrangement has no mechanical bearings. Instead, the slide member is mounted in the valve housing only hydraulically, and it is com- pletely statically hydraulically balanced in the radial a axial directions, resulting in very small operating force The embodiments described above may be modified in many different ways within the scope of the present inve tion. For example, the slide member may have two cavitie instead of one, in which case both cavities communicate with the pump for supplying hydraulic fluid, each cavity communicating with one side of the hydraulic device. The hydraulic flow can be throttled either on the inlet side on the outlet side. The outlets to the hydraulic device be arranged on one side of the inlet from the pump in th axial direction of the slide member. In the above embodi ments, the slide member has two diametrically opposed openings to one side of the hydraulic device and two sim larly disposed openings to the other side^'of the hydraul device, and similarly disposed connections are provided the valve housing. Other numbers and locations of the openings and connections are also conceivable. It should however be ensured that, in respect of force distributio the flow pattern is symmetrical for the outflow of hydra lic fluid from the slide member, such that the jet impul forces are kept down. It is however not necessary that t feed of hydraulic fluid from the pump to the cavity of t slide member is symmetrical, since the pressure drop is here small, resulting in small jet impulse forces. It is' however preferable that the feed be symmetrical. Finally, it should be pointed out that there is no basic difference between implementing the invention as a slide member arranged in a sleeve mounted in a valve housing (Fig. 2), or as a slide member mounted directly a valve housing (Fig. 3). In the former case, the sleeve plus housing performs the same function as the housing i the latter case.

Claims

1. Valve arrangement adapted to connect a source for supplying hydraulic fluid to one or the other side of a hydraulic device, comprising a stationary valve housing (20; 50) with at least one connection (26; 54) to the source of hydraulic fluid, at least two symmetrically disposed connections (24; 55) to one side of the hydrauli device and at least two symmetrically disposed connection (25; 57) to the other side of the hydraulic device, and a slide member (21; 51) rotatably mounted in the valve housing and substantially being in the form o ^•a cylinder- having at least one cavity (30; 59) and at least two open ings (32; 62) which are symmetrically disposed in the cir cumferential surface of the cylinder and adapted to conne the cavity (30; 59) to the connections (24; 55) to one si of the hydraulic device, and at least two openings (33; 6 symmetrically disposed in the circumferential surface of the cylinder and adapted to connect the cavity (30; 59) t the connections (25; 57) to the other side of the hydraul device, the source of hydraulic fluid being connected to one or the other side of the hydraulic device by rotation of the slide member (21; 51), c h a r a c t e r i s - e d in that the valve arrangement comprises at least one opening (34; 61) disposed in the circumferential surface the cylinder and adapted to connect the cavity (30; 59) t the connection (26; 54) to the source of hydraulic fluid, that the cavity (30; 59) has closed end walls, and that t valve arrangement further has spaces (28; 70) between the end walls of the slide member (21; 52) and the valve housing (20; 50), said spaces communicating with the low- pressure side of the hydraulic system, and the pressure acting on said two end walls being equal.

2. Arrangement as claimed in claim 1, c h a r a c ¬ t e r i s e d in that it comprises at least two openings (34; 61) symmetrically disposed in the circumferential surface of the cylinder and adapted to connect the cavity (30; 59) to the connection (26; 54) to the source of hy¬ draulic fluid.

3. Arrangement as claimed in claim 1 or 2, c h a r a c t e r i s e d by means (22) for rotating the slide member (21; 51), and a coupling element (42) between the slide member and said means for rotating the slide member, said element being adapted to take up displacements betwe the centre of said means (22) for rotating the slide memb and the centre of the slide member (29; 51).

4. Arrangement as claimed in claim 3, c h a r a c ¬ t e r i s e d by a seal (39) arranged between o e of sai spaces (28; 70) communicating with the low-pressure side - the hydraulic system, and said means (22) for rotating th slide member.