GB2240835A

GB2240835A - Valve structure

Info

Publication number: GB2240835A
Application number: GB9105412A
Authority: GB
Inventors: Paul F Hayner
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 1987-05-18
Filing date: 1991-03-14
Publication date: 1991-08-14
Anticipated expiration: 2008-05-18
Also published as: GB9105412D0; GB9105411D0; GB2240857A; GB2240835B; GB2240857B

Abstract

A valve structure for use in the pilot valve of a servo-controlled hydraulic valve assembly comprises a nozzle (136), a flapper (144) movable toward and away from the nozzle (136), and a buffer (196) integral with the nozzle (136) and disposed so as to prevent the nozzle (136) and the flapper (144) from being pressed against each other. The nozzle is screw-threaded into a valve housing so as to be adjustable towards and away from the flapper. <IMAGE>

Description

VALVE STRUCTURE This invention pertains to a valve structure suitable for use in the pilot valve of an improved, servocontrolled, hydraulic valve assembly and particularly to a valve assembly of a type comprising a directional valve, such as a spool valve, and a pilot valve controlling the directional valve. Such an assembly is described and claimed in the parent application no. 8811711.4 entitled Hydraulic Valve Assembly from which the present application is divided out and in our co-pending divisional application no. , (Agent's Ref. 80/4007/01) entitled Flow Restrictor and also filed this day.

An example of a valve assembly of the type noted above, wherein a directional, four-way, spool valve is controlled by a pilot valve, is disclosed in U.S. patent No. 3,943,957.

Prior valve assemblies in which such a directional valve is controlled by a pilot valve have a number of shortcomings, most of which are attributable to the pilot valve. Prior pilot valves employing feedback pressures (see, for example, U.S. Patent No. 3,943,957) tend to react erroneously to feedback pressures which are due to leakage of hydraulic fluid in the directional valve or to hysteresis in the motor used to operate the pilot valve.

Furthermore, such pilot valves tend to be highly sensitive to any temperature or viscosity changes in hydraulic fluid.

Consequently, in a valve assembly employing such a pilot valve to control a directional valve, the directional valve tends undesirably to drift out of its centre or null condition.

According to this invention a valve structure comprises a nozzle, a flapper moveable toward and away from the nozzle, and a buffer integral with the nozzle and disposed so as to prevent the nozzle and the flapper from being pressed against each other.

Preferably, the buffer is an annular bluffer formed in one piece with the nozzle. If the nozzle is mounted to the body of the pilot valve for threaded adjustment of the nozzle relative to the body, the buffer prevents the nozzle and the flapper means associated with the nozzle from being crushed by being pressed against each other in the event that the nozzle is threaded too far toward the flapper means.

A particular example of a nozzle in accordance with this invention will now be described with reference to the accompanying drawings, in which: FIGURE 1 is a schematic diagram of a valve assembly constituting a preferred embodiment of this invention.

FIGURE 2 is a greatly enlarged, fragmentary detail of one of a pair of nozzles included in the valve assembly of FIGURE 1, as taken in axial cross-section, a juxtaposed flapper being shown also; and FIGURE 3 is a simplified schematic diagram of the valve assembly of FIGURE 1, together with associated elements including a pump providing hydraulic fluid at primary pressure, a pump providing hydraulic fluid at pilot pressure, a reservoir, and a load.

As disclosed in Figure 1 and also in Figure 3, this invention may be embodied in a valve assembly 10, which comprises a directional valve 12 and a pilot valve 14 of a unique design. The pilot valve 14 controls the directional valve 12. Broadly, in keeping with conventional nomenclature, the directional valve may be described as a four-way, spring-centred, hydraulically positioned, spool valve.

As illustrated in Figure 3, a pump 16, which is driven by a motor 18, delivers hydraulic fluid at pilot pressure to the directional valve 12. Also, a pump 20, which is driven by a motor 22, delivers hydraulic fluid at primary pressure to the directional valve 12. The pumps 16, 20, draw hydraulic fluid from a common reservoir 24. A single pump (not shown) may replace the pumps 16, 20, in some applications. Typically, primary pressure required is far greater than pilot pressure. Hence, if a single pump is used, pressure-reducing means of a conventional type may be provided between the single pump and those connection where pilot pressure is required. Conventional filters and other conventional components of hydraulic systems may be provided.

In accordance with this invention, the pilot valve 14 has a body 120, in which an elongated chamber 122 is provided. A pair of nozzles 124, 126, are mounted so as to extend through the body 120, into the chamber 122, in spaced relation to each other. The nozzle 124 is connected via the hydraulic line 78 to the chamber 70 serving as one of the pilot connections of the directional valve 12. The nozzle 126 is connected via the hydraulic line 80 to the chamber 74 serving as the other pilot connection of the directional valve 12. Each nozzle is mounted to the valve body 120 for threaded adjustment with respect to the valve body 120. Specifically, the nozzle 124 has a threaded end 128, which cooperates with a threaded socket 130 in the valve body 120, and the nozzle 126 has a threaded end 132, which cooperates with the threaded socket 134 in the valve body 120.The nozzle 124 has a small precisely formed orifice, which may be best seen in Figure 2. The nozzle 126 has a similar orifice 138.

The pilot valve 14 also comprises a rocker arm 140, which is pivotally mounted within the chamber 122 by means of a spring restraint hinge 142, which is made of a resilient material resistant to hydraulic fluid. The hinge 142 provides a pivot point approximating the midpoint of the rocker arm 140.

A flapper 144 is carried by the rocker arm at its left end. The flapper 144 is juxtaposed to the orifice 136 of the nozzle 124 with a small gap remaining between the flapper 144 and the nozzle 124. A flapper 146 is carried by the rocker arm 140 at its right end. The flapper 146 is juxtaposed to the orifice 138 of the nozzle 126 with a similar gap remaining between the flapper 146 and the nozzle 126. Each flapper impedes the flow of hydraulic fluid through the juxtaposed nozzle. Each flapper allows hydraulic fluid to flow less freely through the juxtaposed nozzle when such flapper is moved by the rocker arm further toward the juxtaposed nozzle. Each nozzle allows hydraulic fluid to flow more freely through the juxtaposed nozzle when such flapper is moved by the rocker arm 140 further away from the juxtaposed nozzle.Accordingly, the rocker arm 140 and the flappers 144, 146, may be controllably moved so as to cause differential pressures to be controllably provided in either direction in the chambers 70, 74 of the directional valve 12. When the flapper 144 is moved closer to the nozzle 124, the flapper 146 is moved farther from the nozzle 126, back pressure in the chamber 70 is higher than back pressure in the chamber 74, and vice versa.

The chamber 22 of the pilot valve 14 is connected to the reservoir 24 via a hydraulic line 148 so as to return hydraulic fluid to the reservoir 24.

Moreover, the pilot valve 14 comprises motor means, which includes a pair of permanent magnet field, linear force motors. One such motor 150 is located at the left end of the chamber 122. The armature coil 152 of the force motor 150 is mounted on the rocker arm 140 at its left end.

The other motor 154 is located at the right end of the chamber 122. The armature coil 156 of the force motor 154 is mounted on the rocker arm 40 at its right end. Thus, each of the motors 150, 154, is coupled electromagnetically to the rocker arm 140. When actuated, each of the motors 150, 154, imparts a torque to the rocker arm 140. One of the motors can be actuated while the other motor remains deactuated. Preferably, both motors can be simultaneously actuated but provided with armature currents in opposite directions, the permanent magnet fields of the respective motors being similar, whereupon the torque imparted by the motor means is a net torque. Electrical connections (not shown) are made to the respective coils 152, 156, in a conventional manner.As shown in Figure 1, if a counterclockwise torque is imparted by the motor means, the flapper 144 is moved closer to the nozzle 124 and the flapper 146 is moved farther from the nozzle 126.

If a clockwise torque is imparted by the motor means, the flapper 146 is moved closer to the nozzle 126 and the flapper 144 is moved farther from the nozzle 124.

Preferably, neither of the flappers 144, 146 contacts the juxtaposed nozzle. Moreover, the pilot valve 14 comprises a pair of transducers, which serve as feedback devices.

Specifically, a transducer 60 has a cavity 162, which is connected to the annular chamber 60 of the directional valve 12 via the hydraulic line 62. As a component of the transducer 160, a plug 164 is fitted loosely in the cavity 162. The plug 164 has a relatively sharper circumferential edge 166 at its lower end. The cavity 162 has a relatively sharper peripheral edge at its upper end. A pair of leaf springs 170, 172, couple the plug 164 mechanically to the rocker arm 140, between the flapper 144 and the pivot hinge 142. Similarly, a transducer 180 has a cavity 182, which is connected to the annular chamber 64 of the directional valve 12 via the hydraulic line 66. As a component of the transducer 180, a plug 184 is fitted loosely in the cavity 182. The plug has a relatively sharp circumferential edge 186 at its lower end.The cavity 172 has a relatively sharp peripheral edge 188 at its upper end. A pair. of leaf springs 190, 192, couple the plug 184 mechanically to the rocker arm 140 between the flapper 146 and the pivot hinge 142.

When the directional valve 12 has been operated so as to allow hydraulic fluid to return to the reservoir 24 through the pilot valve 14, the cavity 162 receives hydraulic fluid from the annular chamber 60 of the directional valve 12 via the hydraulic line 62. The plug 164 senses the pressure of hydraulic fluid received by the cavity 162 and imparts a torque to the rocker arm 140 in response to the sensed pressure and in opposition to the torque imparted by the motor means. When the directional valve 12 is operated so as to allow hydraulic fluid to be returned from the annular chamber 64 of the directional valve 12 to the reservoir 26 through the pilot valve 14, the cavity 182 receives hydraulic fluid from the annular chamber 64 via the hydraulic line 66.The plug 184 senses the pressure of hydraulic fluid received by the cavity 182 and imparts a torque to the rocker arm 140 in response to the sensed pressure and in opposition th the torque imparted by the motor means. In either instance, equilibrium is achieved when the torque imparted by the motor means and the torque imparted by whichever of the transducers 160, 180 receives hydraulic fluid in its cavity balance each other. Advantageously, the force imparted by hydraulic fluid to either of the plugs 164, 184, is multiplied, which greatly improves the feedback response of the pilot valve 14 in contrast with known pilot valves which do not multiply feedback forces (see, for example, U.S. Patent No. 3,943,957).

As may be best seen in Fig. 2, the nozzle 124 is provided with an integral, annular baffle 196, which surrounds the nozzle 24 near the orifice 136, and which is disposed to prevent the nozzle 124 at its orifice 136 and the flapper 144 from being pressed against each other. If the nozzle 124 and the flapper 144 were to be somehow pressed against each other, as in an instance when the nozzle 124 was threaded too far into the chamber 122, the nozzle 124 at its orifice 126 could be easily crushed. The nozzle 126 is provided with a similar baffle 198 serving a similar purpose, which is to prevent the nozzle 126 at its orifice 138 and the flapper 146 from being pressed against each other.

Claims

1. A valve structure comprising a nozzle, a flapper movable toward and away from the nozzle, and a buffer integral with the nozzle and disposed so as to prevent the nozzle and the flapper from being pressed against each other.

2. The valve structure according to claim 1, further comprising a body, the nozzle being mounted to the body for threaded adjustment of the nozzle relative to the body so as to move the nozzle toward and away from the flapper.

3. The valve structure according to claim 1 or 2, wherein the buffer is annular and surrounds the nozzle.

4. The valve structure according to claim 1, 2 or 3, wherein the nozzle and the buffer are made in one piece.

5. A valve structure substantially as described with reference to the accompanying drawings.