GB1583699A - Solenoid valve - Google Patents

Description

(54) A SOLENOID VALVE (71) We, ROBERT BOSCH GmbH, a German company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a solenoid valve for use in controlling the passage of a pressure medium.

In particular the present invention relates to a solenoid valve of the type having an armature which is axially movable within a valve housing relative to a fixed sleeve surrounded by an excitation winding. A valve of this type is known (German Offenlegungsschrift 2,403,770). In this known valve the armature is slidingly guided in a sleeve. The magnet is energizable in two stages. The valve closure bodies thereby have three stable positions in the valve, thus resulting in three different combinations of position. The valve is a three port, three position solenoid valve.

When the magnet is non-energized, the force of a spring causes the armature to assume a stable end position in which a load is connected to a pump and a return line is closed. At approximately half the rated current, the closure bodies are in a further stable position in which all the connections are shut off. At the rated current, and thus when the magnet is fully magnetized, the armature assumes the other end position, the pump being shut off, and the load being connected to the return line. The idle switching time from the fully energized to the semi-energized state is very important with respect to the ability of this valve to function. This time should be very short.

Since a specific magnetic force potential is retained when switch back from the fully energized to the semi-energized state, the differential between a total spring force and the magnetic force, and thus the restoring force for the magnetic armature, is very small. Since the armature is in the form of a sliding armature, the friction between magnetic the armature and the valve housing is imperceptible.

According to the present invention there is provided a solenoid valve for controlling the passage of a pressure medium, which valve comprises an armature which is axially movable within a valve housing relative to a fixed sleeve surrounded by an excitation winding, the armature being centrally guided in the valve housing by two bearings secured in the valve, each bearing comprising a plastics material cage within which ball bearings are retained, the ball bearings projecting radially outwardly from the cage and engaging a cylindrical bearing sleeve.

A valve constructed according to the present invention has the advantage that the friction is negligible in an axial direction, and that the bearing is stable and free from play in a radial direction. Furthermore, the bearing is wear-resistant and resistant to temperatures of up to 18()0C.

Furthermore, it is ensured that the bearing does not cause a magnetic shunt. Furthermore, the bearing is simple and inexpensive to manufacture, particularly since the tubular extensions of the valve seats, in any case required in the valve, at the same time act as carriers for the bearing. To prevent the passage for the pressure medium from being obstructed, the ball bearings have a large, free flow-through cross-section.

Finally, the special armature bearing can also be used to advantage in electromagnetically operated pressure regulators, since it permits very accurate regulation of the pressure with a low power consumption.

The present invention will now be further described. by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the armature bearing in a three port, three position solenoid valve constructed according to the present inven tion; Figure 2 shows the armature bearing in a pressure-regulating valve constructed according to the present invention; Figure 3 shows a bearing for use in the present invention; Figure 4 is an elevation and a plan view of the main body of the ball bearing cage of Figure 3; and Figure 5 shows a cage cover plate for the bearing of Figures 3 and 4.

In Figure 1 an electro-magnetic three position valve 1 is arranged between a pressure-responsive device 2 and a pressure source 3 and a relief point 4. A coil 5 is mounted on a coil carrier 6 and the latter is in turn mounted on a guide tube 7 which has a non-ferrous portion 8.

Two receiving members 9 and 10 are secured in the guide tube 7 and each carry a tubular member 9' and 10' respectively. The tubular member 10' facing the pressure source 3 has an inlet valve seat 11, and the tubular member 9' facing the relief point 4 has an outlet valve seat 12. A relatively large region of each of the tubular members (9' and 10') extends into an armature 13 which is movable in the guide tube 7 and which is supported by means of a main spring 14 located in a cavity in the receiving member 10 the cavity being offset from the central axis of the receiving member 10. A shoulder 15 of the receiving member 10 carries a spacer ring 16 by means of which both the stroke of the armature is reduced in the end region thereof and the armature is prevented from sticking.

The armature 13 incorporates a recess 17 which forms a shoulder 17' at the end thereof facing the inlet and in which two annular members 18 and 19 are fitted. The distance between the annular members 18 and 19 is determined by a sleeve 20 and several rings. Two holders 25 and 26, each carrying a closure member 27 and 28 respectively, are located in a gap 21 between the rings and a shoulder 22 formed by the rings.

The holders 25 and 26, and thus the closure members 27 and 28, are pressed outwardly by means of a spreader spring 29. The closure member 27 and the valve seat 11 together form an inlet valve 11/27. and the closure member 28 and the valve seat 12 together constitute an outlet valve 12/28.

Each tubular member 9' and 10' carrying the valve seats 11 and 12 respectively has a turned portion onto which is pressed an inner race of a ball bearing 30 and 31 respectively. The inner race of each ball bearing is hardened and non-magnetic. The balls of each bearing 30 and 31 are arranged between the inner race of the bearing and the annular members 18 and 19, and the surfaces acting as contact surfaces for the balls are hardened. The balls 40 are simple mass-produced balls and are chosen to be as large as possible in order to minimize the surface pressure.Each ball bearing 30 and 31 has a cage which is illustrated again in Figures 3 to 5 in which it will be seen that each ball cage 32 essentially comprises a cylindrical member which is injectionmoulded from plastics material and which acts as a basic body 32' having a wall thickness which is somewhat smaller than the diameter of the balls. The member injection-moulded from plastics material is reinforced with glass fibre. The cylindrical wall 33 of the basic body 32' incorporates cylindrical blind bores 34 which are equal in number to the number of balls in the bearing and which have a diameter which is somewhat larger than the diameter of the balls. An internal slot 35 and an external slot 35 are thus formed in each blind bore 34.The widths of the slots 35 are sufficient to allow the balls 40 to roll in a frictionless manner, although the slots are smaller than the diameter of the balls.

After the balls 40 have been fitted, the open ends of the blind bores 30 are closed by means of a disc 36 shown detached in Figure 5. The disc 36 is centered by means of studs 37 which are injection-moulded onto the basic body 32' of the ball cage. The disc 36 is connected to the basic body 32' by glueing or by ultrasonic welding. Thus, during final assembly, the ball cage 32 and the balls 40 are available in the form of a prefabricated component (Figure 3). As already stated, the cage 32 is rigidly mounted in the annular member 18 or 19.

Since the pressure medium in this valve 1 flows through the ball bearings 30 and 31, the internal diameter of the ball cage 32 is as large as possible in order to leave a sufficiently large annular gap for the flowthrough of pressure medium.

Figure 1 shows the valve 1 in its nonenergized starting position. The outlet valve 12/28 is closed. The inlet valve 11/27 is open to a relatively great extent by virtue of the fact that the main spring 14 has pressed the armature 13 upwardly to the fullest extent.

The pressure-responsive device 2 is connected to the pressure source 3.

The coil 5 is fed with a first partial current in order to attain a first stage of energization. The armature 13 covers a first portion of its travel.

When the armature is in this central position, both the inlet valve 11/27 and the outlet valve 12/28 are closed. A force transient now occurs and has to be overcome in order to assume the energized end position from the central position. The central position is rendered absolutely stable by virtue of this force transient.

If the valve arrangement 1 has to be fully changed over, the current for the coil 5 is increased, and the armature 13 is displaced downwardly to its fullest extent. The spring 14 is greatly compressed. In this position, the holder 26 carrying the closure member 28 is pulled downwardly such that the closure member 28 can no longer cover its seat 12. The outlet valve 12/28 is opened, and pressure medium from the pressureresponsive device 2 can flow off to the relief point 4.

The armature 13 can no longer effect the last portion of is stroke, since it is prevented from doing so by means of the spacer ring 16. The steep region of the magnetic force characteristics is thereby cut off, so that a flatter region of the force characteristics of the magnet is available for the operation of the armature 13.

A certain magnetic force potential is retained upon switching back from the fully energized magnet into the semi-energized state, and the difference between the total spring force and the magnetic force is very small. Nevertheless, a very short switching time is obtained by virtue of the special ball bearing.

Figure 2 shows the use of a valve arrangement 41, in accordance with the invention, in a pressure-regulating valve. In this instance, an armature 42 is secured to a rod 43 which is made from a hardened, nonmagnetic material. The armature 42 and a coil 55 form a magnet having a linear characteristic over approximately 15 mm. A closure body or throttle body 44 is secured to the rod 43 in addition to the armature and is adjustable relative to a conical valve seat 45 such that the flow-througli cross section in the seat 45 varies over a wide range. The magnet is energized in a stepless manner up to full magnetization, wherein its closure body 44 opens a constantly increasing flowthrough cross section. A return spring 46 causes the armature 42 to assume a stable end position when the magnet is nonenergized.The adjusted pressure of the pressure-regulating valve is thereby at a minimum. The armature 42 assumes its other end position under full magnetization, and the pressure then established is at a maximum. The pressure is continuously variable between these two end positions, and a pressure once set can be maintained accurately irrespective of the quantity offered by a pump. Thus, there are very high demands on the linearity of the magnetic force and on the hysteresis.

These requirements are met by mounting the armature in a low-friction manner in accordance with the invention. Two ball bearings 47 and 48 are secured to the rod 43, one bearing 47 being arranged in a fixed core 49, and the other bearing 48 being arranged in a cylindrical housing extension 50. Pressure medium flows only through the inner bearing 47. The two bearings 47 and 48 are rigidly mounted on the rod 43 between a respective shoulder 51 and 52 on the rod and a respective spring ring 53 and 54. The two ball bearings 47 and 48 are bearings of the type or of substantially the same caged construction as those illustrated in Figures 3 to 5.

WHAT WE CLAIM IS: 1. A solenoid valve for controlling the passage of a pressure medium, which valve comprises an armature which is axially movable within a valve housing relative to a fixed sleeve surrounded by an excitation winding, the armature being centrally guided in the valve housing by two bearings secured in the valve, each bearing comprising a plastics material cage within which ball bearings are retained, the ball bearings projecting radially outwardly from the cage and engaging a cylindrical bearing sleeve.

2. A valve as claimed in claim 1, which is in the form of a three port, three position solenoid valve and which has two valve seats each provided at the end of a respective tubular member, the tubular members acting as bearing surfaces for the ball bearings.

3. A valve as claimed in claim 2, in which each ball bearing has a hardened inner race which is pressed onto an outer wall of the tubular member and each cage is held on an annular member in the armature.

4. A valve as claimed in claim 2 or 3, in which the pressure medium flows through the two ball bearings.

5. A valve as claimed in claim 1, which is in the form of a pressure-regulating valve, wherein the armature carries a closure body, and is secured to a rod which extends coaxially through the valve, the rod being centered in the valve housing by means of the two ball bearings.

6. A valve as claimed in one of the claims 1 to 5, in which a basic body of the ball bearing cage has blind bores for the balls which blind bores open at one end onto an end face of the cage, the bores being closed at the said end face by means of a disc.

7. A valve as claimed in claim 6, in which the disc is also made from a plastics material and is glued or welded to the basic body of the cage to form a prefabricated unit retaining the balls.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. stable by virtue of this force transient. If the valve arrangement 1 has to be fully changed over, the current for the coil 5 is increased, and the armature 13 is displaced downwardly to its fullest extent. The spring 14 is greatly compressed. In this position, the holder 26 carrying the closure member 28 is pulled downwardly such that the closure member 28 can no longer cover its seat 12. The outlet valve 12/28 is opened, and pressure medium from the pressureresponsive device 2 can flow off to the relief point 4. The armature 13 can no longer effect the last portion of is stroke, since it is prevented from doing so by means of the spacer ring 16. The steep region of the magnetic force characteristics is thereby cut off, so that a flatter region of the force characteristics of the magnet is available for the operation of the armature 13. A certain magnetic force potential is retained upon switching back from the fully energized magnet into the semi-energized state, and the difference between the total spring force and the magnetic force is very small. Nevertheless, a very short switching time is obtained by virtue of the special ball bearing. Figure 2 shows the use of a valve arrangement 41, in accordance with the invention, in a pressure-regulating valve. In this instance, an armature 42 is secured to a rod 43 which is made from a hardened, nonmagnetic material. The armature 42 and a coil 55 form a magnet having a linear characteristic over approximately 15 mm. A closure body or throttle body 44 is secured to the rod 43 in addition to the armature and is adjustable relative to a conical valve seat 45 such that the flow-througli cross section in the seat 45 varies over a wide range. The magnet is energized in a stepless manner up to full magnetization, wherein its closure body 44 opens a constantly increasing flowthrough cross section. A return spring 46 causes the armature 42 to assume a stable end position when the magnet is nonenergized.The adjusted pressure of the pressure-regulating valve is thereby at a minimum. The armature 42 assumes its other end position under full magnetization, and the pressure then established is at a maximum. The pressure is continuously variable between these two end positions, and a pressure once set can be maintained accurately irrespective of the quantity offered by a pump. Thus, there are very high demands on the linearity of the magnetic force and on the hysteresis. These requirements are met by mounting the armature in a low-friction manner in accordance with the invention. Two ball bearings 47 and 48 are secured to the rod 43, one bearing 47 being arranged in a fixed core 49, and the other bearing 48 being arranged in a cylindrical housing extension 50. Pressure medium flows only through the inner bearing 47. The two bearings 47 and 48 are rigidly mounted on the rod 43 between a respective shoulder 51 and 52 on the rod and a respective spring ring 53 and 54. The two ball bearings 47 and 48 are bearings of the type or of substantially the same caged construction as those illustrated in Figures 3 to 5. WHAT WE CLAIM IS:

1. A solenoid valve for controlling the passage of a pressure medium, which valve comprises an armature which is axially movable within a valve housing relative to a fixed sleeve surrounded by an excitation winding, the armature being centrally guided in the valve housing by two bearings secured in the valve, each bearing comprising a plastics material cage within which ball bearings are retained, the ball bearings projecting radially outwardly from the cage and engaging a cylindrical bearing sleeve.

2. A valve as claimed in claim 1, which is in the form of a three port, three position solenoid valve and which has two valve seats each provided at the end of a respective tubular member, the tubular members acting as bearing surfaces for the ball bearings.

3. A valve as claimed in claim 2, in which each ball bearing has a hardened inner race which is pressed onto an outer wall of the tubular member and each cage is held on an annular member in the armature.

4. A valve as claimed in claim 2 or 3, in which the pressure medium flows through the two ball bearings.

5. A valve as claimed in claim 1, which is in the form of a pressure-regulating valve, wherein the armature carries a closure body, and is secured to a rod which extends coaxially through the valve, the rod being centered in the valve housing by means of the two ball bearings.

6. A valve as claimed in one of the claims 1 to 5, in which a basic body of the ball bearing cage has blind bores for the balls which blind bores open at one end onto an end face of the cage, the bores being closed at the said end face by means of a disc.

7. A valve as claimed in claim 6, in which the disc is also made from a plastics material and is glued or welded to the basic body of the cage to form a prefabricated unit retaining the balls.

8. A solenoid valve for controlling the

passage of a pressure medium, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.