GB2253721A

GB2253721A - Pressure control valve

Info

Publication number: GB2253721A
Application number: GB9205558A
Authority: GB
Inventors: Wilhelm Blumendeller; Volkmar Leutner; Berthold Pfuhl; Roland Schempp
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-03-13
Filing date: 1992-03-12
Publication date: 1992-09-16
Anticipated expiration: 2012-03-12
Also published as: DE4108080A1; GB2253721B; GB9205558D0; DE4108080C2

Abstract

In a pressure control valve (10) which controls a hydraulic pressure in proportion to a continuously adjustable electrical setpoint signal, the pressure-dependent position changes of a valve cone (19) supported against a measuring spring (21) are detected by a displacement pickup (13) and are used, via a position control loop (42) with control amplifier (39), for driving a proportional magnet (12) which controls the setting of the valve, either by adjustment of a piston (16) which defines a valve seat (18) or by adjusting the closing force of the spring (21) (Fig 2, not shown). The displacement of the valve cone (19) is transmitted via a rod (43) through the magnet (12) to the displacement pickup (13) so that a precise displacement measurement of the measuring spring (21) and thus an accurate and wear-independent pressure control is possible. In the embodiment of Fig. 2, the position of the armature of the magnet (12) may also be detected by the displacement pickup. <IMAGE>

Description

2253721 - 1 Pressure control valve

Prior art

The invention is based on a pressure control valve for controlling the fluidic pressure in proportion to an electric setpoint signal of the generic type specified in the precharacterising clause of Claim 1.

Such a pressure control valve is already known from EP 0 047 848 B1, in which the magnetic armature of the electromagnet is connected in a forcelocked manner to a valve body carrying the valve seat f or the valve cone. The position of the valve cone is picked up by means of an inductive displacement pickup. From the displacement-proportional output signal of this pickup, a control signal is generated for the proportional magnet after comparison with an electric setpoint signal in the differential amplifier. The magnetic armature, and with it the valve body, is displaced in accordance with the excitation of the solenoid winding against the force of the measuring spring until the actual stroke measured via the displacement of the valve cone and the change in length of the measuring spring with the aid of the displacement pickup corresponds to the nominal stroke. Such a pressure control valve operates with a high control accuracy since the controlled variable spring travel and the pressure produced proportionally to the spring force is set in a closed control loop. This pressure control valve can also be used for achieving a pressure/setpoint characteristic of high linearity since this also takes into consideration the influence of the pre s sure -dependent closing member travel. In addition, this pressure control valve exhibits a good long-time stability since wear in the valve seat and in the valve cone are compensated f or. In some applications, it is disadvantageous that the electromagnet and the displacement pickup are located at mutually opposite sides of the fluidic pressure valve. It is difficult to build up integrated valve electronics for electromagnet and displacement pickup since the interposed valve housing must be bridged.

Advantages of the invention By comparison, the pressure control valve according to the invention, having the characterising features of the main claim, has the advantage that, maintaining the previous good characteristics, more advantageous installation conditions can be achieved since the magnet and the displacement pickup are arranged on the same valve side. Integrated valve electronics can therefore be produced with relatively little expenditure.

Due to the measures listed in the subclaims, advantageous further developments and improvements of the pressure control valve specified in the main claim are possible. it is particularly advantageous if the transfer element is mechanically constructed in accordance with Claim 2, as a result of which a rugged, compact and relatively inexpensive construction can be achieved. An embodiment according to Claim 3 is particularly suitable, a displacement pickup of simple construction with only one coil system being sufficient for accurate detection of the displacement of the measuring spring. It is also particularly advantageous if the pressure control valve is constructed in accordance with Claim 6 and the displacement pickup determines the precise displacement of the measuring spring by means of two coil systems; this makes it possible to achieve a construction with particularly low hysteresis. According to Claim 9, it is also suitable to construct the displacement pickup in the pressure control valve in accordance with the principle of a differential transformer in order to provide a possibility for direct measurement of a displacement difference by this means. Further advantageous embodiments are obtained from the remaining claims as well as the description and the drawing.

Drawing Three illustrative embodiments of the invention are shown in the drawing and explained in greater detail in the description following. Figure 1 shows a longitudinal section through a first illustrative embodiment of the pressure control valve in a simplified representation, Figure 2 shows a longitudinal section through a second illustrative embodiment of the invention and Figure 3 shows a part of a third illustrative embodiment in section.

Description of the illustrative embodiments

Figure 1 shows a longitudinal section through a pressure control valve 10 which essentially consists of an hydraulic valve 11, a proportionally operating magnet 12 and an inductively operating electromechanical displacement pickup 13.

The hydraulic valve 11 exhibits a valve housing 14 with a longitudinal hole 15 in which a valve body 16, constructed as slider piston, is sealingly and slidingly carried. The valve body 16 exhibits at its end opposite to a bottom part 17 a valve seat 18 which operates in conjunction with an associated valve cone 19. The valve cone 19 is pressed onto the valve seat 18 by a measuring spring 21 and, in doing so, blocks off a pressure space 22 formed in the valve body 16 which is continuously connected via radial holes 23 formed in the valve body 16 to a first connection 24 for the inflow and thus for the controlied pressure. Valve cone 19 and measuring spring 21 are located in a return chamber 25 which is formed as an extension of the longitudinal hole 15 in the valve housing 14. This return chamber 25 is closed by a cover 26 on which the measuring spring 21 is also supported in a housing-fixed manner. Furthermore, the return chamber 25 is connected to a second connection 27 for the return flow. Furthermore, a cross duct 28 leads from the return chamber 25 to a relief chamber 29 which is open towards the other end face 31 of the valve housing 14 and which is blocked off by the flanged-on magnet 12. The pistonshaped valve body 16 is thus only exposed to the return flow pressure at its two end faces. Furthermore, a relatively weak compression spring 32 is arranged on the side of the valve seat 18 between the valve body 16 and the valve cone 19 in a manner known per se.

The proportionally operating magnet 12 installed at the front end 31 of the valve housing 14 exhibits an armature 33 which protrudes with a sleeve-shaped plunger 34 into the relief chamber 29 and the end of which rests against the bottom part 17 of the valve body 16 in a force-locked manner. A pressure tube 35 is installed at the magnet 12 on the side opposite to the plunger 34.

The pressure tube 35 forms a part of the inductively operating displacement pickup 13 which, in turn, is installed at the magnet 12. The pressure tube 35 accommodates in its interior a ferrite core 36, the travel of which is converted into a displacementproportional electrical output signal at the connection 38 via an electrical coil system 37. The actual-value signal at the connection 38 is supplied to a control amplifier 39 which is supplied with an electrical setpoint signal 41 for the pressure and the output signal of which drives the proportional magnet 12. The magnet 12 is thus a part of a position control loop 42 in which the travel of the measuring spring 21 is controlled as controlled variable. To make this possible, the valve cone 19 is mechanically connected to the ferrite core 36 in the pressure tube 35 via a rod 43 acting as transmission element. This rod 43 extends coaxially with respect to the valve cone 19, the valve body 16, the armature 33 with its sleeve-shaped plunger 34 and passes through the magnet 12 in this arrangement. In the area of the bottom part 17 at the valve body 16, this rod 43 exhibits a piston-shaped thickening 44 by means of which it is carried sealingly and slidingly in a cylindrical hole 45 in the bottom part 17. Together with the hole 45, the thickening 44 thus forms a sealing point 46 blocking off the pressure space 22 from the relief chamber 29. The diameter of the hole 45 is selected to be smaller compared with the diameter of the valve seat 18 so that an effective ring area remains for the valve cone 19 on which it is loaded by the pressure in the pressure space 22 or at the first connection 24 against the force of the measuring spring 21.

The operation of the pressure control valve 10 is explained as follows: in this pressure control valve 10, the measuring spring 21 is supported in a housing-fixed manner so that only the travel of the valve cone 19 needs to be detected for an accurate detection of the measuring spring displacement and thus the pretensioning force. The valve body 16 with valve seat 18 is movably carried in the valve housing 14 and is pressed against the valve cone 19 by the proportional magnet 12. The pressure occurring in the first connection 24 and thus in the pressure space, referred to the effective ring crosssection at the valve body 19, generates a force which is in equilibrium with the force of the measuring spring 21. If therefore the position signal of the valve cone 19 is compared with the setpoint signal 41 and the magnet 12 is activated via the control amplifier 39, the valve body 16 with the valve seat 18 is displaced by the proportional magnet 12 in dependence on the pressure until the predetermined measuring spring displacement and thus the force at the measuring spring 21 has been produced.

If the friction forces acting on the valve body 16 remain unconsidered, a proportional relationship is obtained between setpoint signal 41 and the controlled pressur6 in the first connection 24.

In the present pressure control valve 10, the advantages of the previously known pressure control valve can be retained particularly with respect to its accurate pressure control, its linear pressure characteristic, good long-time stability and so forth. In addition, the magnet 12 and the displacement pickup 13 can be adjacently arranged in this pressure control valve 10 which is advantageous for the construction of integrated electronics on the valve. The pressure control valve 10 must be adapted to the installation conditions at the customer in a much more advantageous manner.

Figure 2 shows a longitudinal section through a second pressure control valve 50 which differs from the first pressure control valve 10 as follows, the same reference symbols being used for the same components. Above all, the second pressure control valve 50 has a differently constructed hydraulic valve 51 and a changed displacement pickup 52. The valve body 53, exhibiting the valve seat 18, is now arranged in a housingfixed manner and constructed as threaded bolt, which can be adjusted from the outside, for this purpose. The first connection 24 for the controlled pressure and the second connection 27 for the return flow are now arranged exchanged in their position relative to the magnet 12. Thus, the return chamber 25 connected to the return flow connection 27, in which the measuring spring 21 and the valve cone 19 are arranged, is open towards the other end f ace 31 and blocked off from the flanged-on magnet 12. The measuring spring 21 resting against the valve cone 19 is supported with its other end on a spring cup 54 located in the return chamber 25, which is now effectively connected to the plunger 34 of the armature 33 and is thus positionally adjustable by it.

In the displacement pickup 52, the first coil system 37 operates in conjunction with the first ferrite core 36 arranged in the pressure tube 35 in order to detect the travel or displacement of the valve cone 19 with the aid of the rod 43 carried through the proportional magnet 12. In addition, the displacement pickup 52 exhibits a second coil system 55 which operates in conjunction with a second ferrite core 56 in the pressure tube 35. This second ferrite core 56 is coupled to the armature 33 via a sleeve-shaped transmission member 57.

7 - The second coil system 55 can thus be used for determining the travel of the armature 33 and thus of the spring cup 54. With the aid of electronic means, not drawn in greater detail, a difference signal is formed from the signals of the two coil systems 37 and 55, which difference signal is forwarded via the connection 38 to the control amplifier 39 and the magnitude of which is directly proportional to the precise displacement of the measuring spring 21 and thus also to its actual pretensioning force. The displacement pickup 52 operates in accordance with the principle of a differential transformer and exhibits, for the determination of the travels of valve cone 19 and spring cup 54, two coil systems 37, 55 which are completely isolated from one another and which are arranged in the axial direction at a distance from one another and behind one another.

In principle, the operation of the second pressure control valve 50 corresponds to that of the first pressure control valve 10 in as much as here, too, the precise travel of the measuring spring 21 and thus the accurate pretensioning force is compensated for via the position control loop 42, the respective pretensioning force of the measuring spring 21 being in equilibrium with the pressure on the valve cone 19 acting in the valve seat 18. Transmitting the travel of the valve cone 19 in a particularly low-friction manner to the displacement pickup 52 provides for a type of construction which operates with a particularly low hysteresis. The quality of the linear relationship in the setpoint /pressure characteristic is essentially determined by the linearity of the control spring 21 and of the displacement pickup 52 in this arrangement.

Figure 3 shows a part of a third pressure control valve 60 which mainly differs from the second pressure control valve 50 according to Figure 2 due to a different displacement pickup 61. In this displacement pickup 61, the ferrite cores connected to the rod 43 and to the sleeve-shaped transmission membeir 57 are constructed as sleeves 62 and 63 which can be pushed onto one another.

Instead of two coil systems, a single coil system 64 which consists of a primary coil 65, a secondary coil 66 and an exciter coil 67, is suf f icient in the displacement pickup 61. This displacement pickup 61 also operates in accordance with the principle of a differential transf ormer and, due to its design and arrangement of the coils, enables the displacement of the measuring spring 21 to be measured directly and accurately. For the rest, the third pressure control valve 60 operates in a corresponding manner to the second pressure control valve 50 according to Figure 2.

Naturally, changes are possible in the embodiments shown without deviating f rom the concept of the invention. Thus, the rod 43 constructed of one piece can also be replaced by the transmission member being constructed of several members.

Claims

Claims

Pressure control valve for controlling the fluidic pressure in proportion to an electric setpoint signal, comprising a valve cone loaded by a measuring spring in opposition to the fluidic pressure, which valve cone is arranged in a valve housing exhibiting at least two connections for the controlled pressure and the return flow and which is associated with a valve body exhibiting a valve seat, and comprising a proportionally operating magnet, the armature of which is used for adjusting the pretension of the measuring spring and comprisirig an electromagnetic displacement pickup, the output signal of which is influenced by the travel of the measuring spring, magnet and displacement pickup being located in a position control loop which is supplied with a setpoint signal for the pressure, characterised in that the magnet (12) with its armature (33) is arranged between valve housing (14) and displacement pickup (13; 52; 61), and in that a transmission element (43) transmitting the travel of the valve cone (19) through the magnet (12) to the displacement pickup (13; 52; 61) is provided.
2. Pressure control valve according to Claim 1, characterised in that the transmission element is a centrally arranged rod (43) which effectively connects the valve cone (19) to a core (36) of the displacement pickup (13; 52; 61) and which extends coaxially with respect to the valve cone (19), to the armature (33) and to the pressure tube (35) of the displacement pickup (13; 52; 61).
3. Pressure control valve according to Claim 1 or 2, characterised in that the measuring spring (21) resting against the valve cone (19) is supported, on the other hand, against the housing (14, 26) and the valve body (16) exhibiting the valve seat (18) is movably carried in the housing (14) and can be adjusted by the armature (33) of the magnet (12) in opposition to the f orce of the measuring spring (21), in that the armature (33) exhibits a sleeve-shaped plunger (34) which rests against a bottom part (17) of the valve body (16), and in that the transmission element (43) is sealingly and slidingly passed through at a sealing point (46) in the valve body (16).
4. Pressure control valve according to Claim 3, characterised in that in the valve body (16), a pressure space (22) is formed which is connected to the first connection for the inflow (24) via radial holes (23) in the valve body (16), and in that the cross-section of the valve seat (18) is larger than the cross-section (44) of the transmission element (43) at the sealing point (46) in order to form an effective ring cross-section at the valve cone (19).
5. Pressure control valve according to one or more of Claims 1 to 4. characterised in that the valve body (16) is constructed as a cylindrical piston with end faces having the same sized diameter which in each case adjoin spaces (25, 29) relieved with respect to the return flow connection (27).
6. Pressure control valve according to Claim 1 or 2, characterised in that the.measuring spring (21) resting against the valve cone (19) is supported, on the other hand, on a spring cup (54) which can be adjusted by the armature (33) of the magnet (12) in opposition to the force of the measuring spring (21), in that the displacement pickup (52) exhibits, in addition to the first coil system (37) detecting the travel of the valve cone (19), a second coil system (55) for determining the travel of the armature (33), and in that the valve seat (18) andlor the valve body (53) are arranged in a housing-fixed manner..
7. Pressure control valve according to Claim 6y characterised in that the two coil systems (37r 55) with their associated pickup cores (36,. 56) located in a pressure tube (35) are arranged behind one another in the 11 longitudinal direction of the pressure tube (35) and the displacement pickup (52) outputs a signal, which is proportional to the precise displacement of the measuring spring (21), to the position control loop (42).
8. Pressure control valve according to one of Claims 6 or 7. characterised in that the armature (33) is supported with a sleeve-shaped plunger (34) on the spring cup (54) loaded by the measuring spring (21) and is effectively connected on its side opposite the plunger (34) via a transmission member (57) to a second core (56) which is associated with the second coil system (55).
9. Pressure control valve according to one of Claims 6 to 8, characterised in that the displacement pickup (61) is constructed as differential transformer with primary, secondary and exciter coil (65, 66, 67) and the two pickup cores are constructed as sleeves (62, 63) which can be pushed onto one another.
10. A pressure control valve substantially as herein described with reference to Figure 1, or Figure 2, or Figure 3, of the accompanying drawing.