MULTIPIECE SPOOL AND SPOOL VALVE

Abstract: A multipiece control spool (20,22) of a control valve is hooked together by hooks (38,52) extending from the end surface (36,34) of each spool member. At least one hook (38) is provided with central plateaus on the axially inner and outer surfaces (46,44) of a radially inwardly extending hook arm (42). These surfaces are bevelled away from the plateaus to allow for axial misalignment between hooked spool members. The end surface (34) of one of the spool members (20) is also provided with a central plateau (58) and a recessed surface extending from the plateau, to further aid in allowing for axial misalignment.

Description: The invention relates to a multipiece spool for a spool valve in which spool members are coupled together by hooks and also relates to a spool valve with a multipiece spool and to a spool member for a multipiece spool. Spool valves are widely used in hydraulic control systems to control the flow of hydraulic fluid. The elongated control spool is positioned inside a valve body having an elongated cavity for accepting the spool. The valve body is provided with ports through which hydraulic fluid can communicate with the elongated cavity. The control spool is provided with control surfaces which control the flow of hydraulic fluid into and out of the cavity. The hydraulic fluid flow pattern is varied by adjusting the axial insertion distance of the spool into the cavity. The spool may also be provided with detents which cooperate with a spring biased ball mounted in the valve body for defining specific axial locations of the spool. As hydraulic control systems become more sophisticated, the system designer increasingly wants to include more hydraulic control functions in each valve. As the number of hydraulic functions increase, the length of the spool and the valve housing must also increase. However, practically, because of the close tolerances involved, there is an upper limit as to the length of a spool and the length of the housing a manufacturer can properly produce. One way to lengthen spools has been to make multipiece spools that are provided with hooks which couple adjoining spool members together to form a longer control spool. Such a spool configuration is disclosed in US-A 4 418 711 and US-A 4 576 203. Although longer spools can be fabricated in the manner suggested above, the spool manufacturer must still make the valve body cavity to very close tolerances to accept the extended spool. Typically, to maintain these close tolerances, the valve body cavity is bored from only one end so that the cavity is coaxial throughout. Therefore, the longer the cavity must be bored, the more complicated the machining. As such, it is desirable to bore the valve cavity from both ends to minimise the length of the boring operations. However, such an operation, unless it is very carefully monitored, can result in a non-coaxial cavity. The present invention accordingly provides a control spool as defined in claim 1. The means for providing limited axial misalignment between the spool members permit larger allowable tolerances in the valve body, thereby reducing manufacturing costs. The invention further provides a control valve as defined in claim 8 and a spool member as defined in claim 9. Axial misalignment includes both the centre axes of the spool members being offset or displaced and also the centre axes of the spool members being non-parallel. Preferably one end of each spool member is provided with a hook having an axially extending portion that is provided with a radially inwardly extending portion. The radially inward extending portion of at least one spool is provided with an axial outer surface and an axial inner surface, both of which are provided with a central plateau that lies along the central axis of the spool member. Outwardly from the central plateaus, the inner and outer surfaces are bevelled to allow for axial misalignment. In addition, the end of the spool member is provided with another plateau having a recess area extending therefrom which further provides for axial misalignment. Brief Description of the Drawings Fig. 1 is a side cross sectional view of a control valve. Fig. 2 is a side cross sectional view of the hooks of the spool members. Fig. 3 is an end view of the second spool member. Fig. 4 is a top view of the spool member illustrated in Fig. 3, taken along line 4--4. Fig. 1 illustrates a hydraulic control valve 10 having a valve body 12 and a control spool 14. The valve body is provided with a plurality of test ports 16 and control ports 17 which communicate with cavity 18 formed in the interior of the valve body. The control spool comprises a first spool member 20 and a second spool member 22 that are joined together by a hook assembly 24. The first spool member 20 is provided with control surfaces 26 and forms a control spool member, whereas the second control spool member 22 is provided with detents 28 and forms a detent spool member. The detents of the detent spool member cooperate with a spring biased pin 30 having conical surface 32, the detents and the pin defining axial positions of the control spool in the valve body cavity. It should be noted that the spool member 22 could also be provided with control surfaces in addition to the detents. Similarly, the spool member 20 could be provided with detents for controlling the axial position of the spool member. As illustrated in Fig. 2, the first and second spool members are each provided with an end surface 34 and 36 respectively. The second spool member is provided with a second hook 38 that comprises an axially extending portion 40 extending from the end surface 36 and a radially inwardly extending portion 42 that extends from the axial portion 40. The radial portion 42 is provided with an axially outer surface 44 and an axially inner surface 46. The axially inner surface 46 is provided with a first, central rectangular plateau 48. The inner surface 46 is bevelled away from the first plateau 48, as illustrated in Fig. 4. Similarly, the axially outer surface 44 is provided with a second, circular plateau 50 and the surface 44 is bevelled away from the second plateau, as illustrated in Figs. 3 and 4, the surface 44 having an essentially truncated conical shape. The first spool member is provided with a first hook 52 having an axially extending portion 54 and radially inwardly extending portion 56. The hook 52 may be straight milled to simplify the manufacturing process. The end surface 34 of the spool member 20 is provided with a third central plateau 58 that together with the inner surface 60 of the radial portion 56 defines a hooking space for receiving the radial portion 42 of the second hook 38. The end surface 34 is recessed away from the central plateau 58 to better accommodate axial misalignment. It should be noted that the central plateau 58 and inner surface 60 may be bevelled in the way used in the second hook 38 but, in the preferred embodiment, such additional machining is unnecessary because the second hook 38 adequately accounts for the required axial misalignment. The backlash of the valve is the difference between the axial distance defined by the central plateau 58 and the inner surface 60 and the axial distance defined by the first plateau 48 and second plateau 50. As illustrated in Fig. 4, the total degree of axial misalignment allowed in hooking structure 24 is controlled by the amount of backlash designed into the hook structure. More specifically, by increasing backlash, the spool members become more free to axially misalign in a non-parallel configuration as illustrated by the divergent central axes CA₁ and CA₂. The degree of non-parallelism may also be limited by the slope of the bevelled surfaces 44 and 46. Therefore, as greater axial misalignment is required, backlash must be increased and the bevelled surfaces sloped to a greater degree. Therefore, by controlling the backlash, the designer controls the amount of axial misalignment the spool members will accept; however it should be noted that a certain amount of backlash is required to allow for non-parallel axial misalignment.

Claims: 1. A spool for a control valve comprising a first elongated spool member (20) having a first central axis (CA₂) and terminating in an end surface (34) that is provided with a first hook (52), a second elongated spool member (22) having a second central axis (CA₁) and terminating in an end surface (36) that is provided with a second hook (38), characterised in that the hooks (52,38) are together shaped to allow for limited axial misalignment between the first and second spool members (20,22) when the spool members are joined together by the first and second hooks (52,38). 2. A spool according to claim 1, characterised in that the first and second hooks (52,38) each comprise an axially extending portion (54,40) that extends outwardly from the end surface (34,36) of the spool member and which is provided with a radially inwardly extending portion (56,42), whereby a hooking space is formed between the inwardly extending portion (56,42) of each hook and the end surface (34,36) of the corresponding spool member (20,22). 3. A spool according to claim 2, characterised in that the radially inwardly extending portion (42) of the second hook (38) has an axially inner surface (46) bevelled away from a first central plateau (48) and an axially outer surface (44) bevelled away from a second central plateau (50), the bevelled surfaces allowing the limited axial misalignment. 4. A spool according to claim 3, characterised in that the first plateau (48) is rectangular and the second plateau (50) is circular, both plateaus having centres located along the second central axis (CA₁) of the second spool member (22). 5. A spool according to claim 4, characterised in that the end surface (34) of the first spool member (20) is provided with a third central plateau (58) having a centre located along the first central axis (CA₂), the third plateau (58) abutting the second plateau (50) of the second spool member (22) when the first and second spool members (20,22) are hooked together. 6. A spool according to claim 5, characterised in that the end surface (34) of the first spool member (20) is provided with an inwardly recessed surface that extends from the third plateau (58) and cooperates with the bevelled axially outer surface (44) of the hook (38) of the second spool member (22) further for allowing for limited axial misalignment. 7. A spool according to claim 6, characterised in that the first spool member (22) is a control spool member having fluid control surfaces and the second spool member (22) is a detent spool member and is provided with spool position controlling detent recesses (28). 8. A control valve for controlling the flow of fluid between a plurality of conduits, the control valved comprising a valve body (12) having an elongated cavity with a substantially longitudinal axis and in fluid communication with a plurality of ports located in the valve body; and an elongated, axially movable control spool (14) extending along the longitudinal axis of the cavity, the spool having a plurality of control surfaces for controlling the flow of fluid into and out of the cavity through the ports, the spool being in accordance with any of claims 1 to 7. 9. A spool member which is adapted and constructed to be hooked on to another spool member to form a spool of a spool valve, the spool member comprising an elongated shaft (22) having a central axis (CA₁) and terminating in an end surface (36) and a hook (38) comprising an axially extending portion (40) extending from the end surface (36) and a radially inwardly extending portion (42) projecting from the axially extending portion (40), the radially inwardly extending portion (42) and the end surface (36) defining a hooking space, characterised in that the axially inner surface (46) of the radially inwardly extending portion (42) is bevelled away from a first central plateau (48) and the axially outer surface (44) is bevelled away from a second central plateau (50), the bevelled surfaces forming a means for allowing for limited axial misalignment between the spool member and the said other spool member when they are hooked together to form a control spool. 10. A spool member according to claim 9, characterised in that the first plateau (48) is rectangular and the second plateau (50) is circular, both plateaus having a centre located along the central axis of the elongated shaft (CA₂, CA₁). 11. A spool member according to claim 9 or 10, characterised in that the elongated shaft is provided with control surfaces for controlling fluid flow. 12. A spool member according to claim 9, 10, or 11 characterised in that the elongated shaft is provided with spool position controlling detent recesses.

Inventors: CHMELAR, MARK ALAN
Applicants: DEERE & COMPANY
Application year: 1988
Main classification: F15B13
IPC codes: F16K11