Temperature sensitive valve mechanism

A pump housing has a main oil passage, a return oil passage provided substantially in parallel with the main oil passage, and a valve insertion hole extending across the main oil passage such that a closed fore end of the valve insertion hole reaches in the vicinity of the return oil passage. The valve insertion hole has a female screw formed at an open end thereof, and a through-hole is formed in the pump housing, having one end connected to the valve insertion hole at a portion adjacent to the closed fore end thereof and an opposite end opened to the outside of the pump housing. With the valve insertion hole thus provided, a temperature sensitive valve mechanism can be readily inserted in the valve insertion hole at any time.

FIELD OF THE INVENTION

The present invention relates to a temperature sensitive valve mechanism mounted in a structural member (such as a pump housing or a cylinder block) having an oil passage so as to release a lubricating oil to the outside of the oil passage in response to a temperature of the lubricating oil flowing in the oil passage.

BACKGROUND OF THE INVENTION

Temperature sensitive valves mounted in a cylinder block of an internal combustion engine for releasing a lubricating oil to the outside of an oil passage in response to a temperature of the lubricating oil flowing in the oil passage are known as disclosed, for example, in Japanese Patent Application Laid-open Publication (JP-A) No. H08-93430.

As shown in FIG. 7 of JP H08-93430A, a cylinder block includes a lubrication oil supply passage, a bypass hole, a through-hole, and a temperature sensitive valve.

The bypass hole is closed by a top surface of the temperature sensitive valve. As the temperature of a lubricating oil goes down, the temperature sensitive valve contracts, causing the top surface of the temperature sensitive valve to separate from the bypass hole. Thus, the lubricating oil in the supply passage is allowed to bypass the temperature sensitive valve and discharged from the through-hole. By thus releasing the lubricating oil at a low temperature, it is possible to lower the engine loads to thereby reduce fuel consumption of the internal combustion engine.

In general, a valve mechanism is constituted by a valve and a valve casing in which the valve is housed. In case of JP H08-93430A, the cylinder block corresponds to the valve casing, and the temperature sensitive valve corresponds to the valve. A distance between the bypass hole and the temperature sensitive valve provides a valve opening. Thermal performance of the valve mechanism can be determined by a correlation between the lubricating oil temperature and the valve opening.

In the structure shown in JP H08-93430A, the temperature sensitive valve and the cylinder block are immersed in a liquid tank or placed in a thermostatic tank when determining thermal performance of the valve mechanism. The temperature sensitive valve is a small-sized component, however, the cylinder block is a medium-sized or large-sized component, so that performance determination of the valve mechanism necessarily involves high cost.

A demand for a reduction in cost of the cylinder block or the like structural member also causes a need for a technique which is capable of reducing cost for performance determination of the temperature sensitive valve.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a temperature sensitive valve mechanism which is capable of determining thermal performance thereof at a low cost.

According to the present invention, there is provided a temperature sensitive valve mechanism mounted in a structural member having an oil passage so as to release a lubricating oil to the outside of the oil passage in response to a temperature of the lubricating oil flowing in the oil passage, the temperature sensitive valve mechanism comprising: a fixing part fixed to the structural member; a thermoelement disposed in the oil passage and having a first end supported by or made in contact with the fixed part; a valve element fixed to a second opposite end of the thermoelement; a valve casing surrounding the valve element; and a connecting part extending from the fixing member in such a manner as to surround the valve element and supporting the valve casing, the connecting part having oil passage through-holes for allowing the lubricating oil to pass therethrough and hit on the thermoelement, wherein the valve casing has a discharge port adapted to be opened and closed by the valve element for releasing the lubricating oil therefrom to the outside of the oil passage.

Since the valve element and the valve casing are attached to the fixing part, the temperature sensitive valve mechanism including the fixing part, the valve element and the valve casing can be solely subjected to determination of valve characteristics such as valve opening. With this arrangement, installation of a cylinder block or the like structural member in a water tank or a thermostatic tank as required in a conventional thermal performance determination is no longer necessary. According to the invention, the temperature sensitive valve mechanism which is small in size and light in weight is solely installed in the water tank or the thermostatic tank. As a result, performance determination of the temperature sensitive valve mechanism can be achieved with reduced cost.

In one preferred form of the present invention, the connecting part and the valve casing are formed integrally with each other. Integration of the valve casing and the connecting part provides a reduction in the number of component parts and a reduction of assembling man-hours.

In another preferred form of the present invention, the connecting part and the valve casing are separate members structurally independent from one another, and the valve casing is joined to the connecting part via a clenched portion or a screw-connected portion. With this arrangement, the connecting part and the valve casing can be joined together while dimensional adjustment is performed after a relative position between the discharge port and valve element is fixedly determined. Manufacturing tolerances which are inevitably involved in the component parts can thus be taken out or cancelled, and valve characteristics can be determined with increased accuracy.

Preferably, the connecting part is joined to the fixing part via a clenched portion or a screw-connected portion. This arrangement ensures that the connecting part and the valve casing can be joined together while dimensional adjustment is performed after a relative position between the discharge port and valve element is fixedly determined. Manufacturing tolerances which are inevitably involved in the component parts can thus be taken out or cancelled, and valve characteristics can be determined with increased accuracy.

It is preferable that the connecting part is joined to the fixing part via a clenched portion, and the clenched portion is a portion joined by clenching performed to cause deformation over the entire periphery thereof. By virtue of the clenched portion formed by clenching performed to cause deformation over the entire periphery of the connecting part, a tilt and a center offset can be suppressed and smooth sliding movement of the valve element as well of highly accurate hydraulic control of the valve element can be attained.

In one preferred form of the invention, the connecting part is joined to the fixing part via a circlip. The circlip is received in clip reception grooves and allowed to move within the clip reception grooves. The connecting part is movable relative to the structural part within a slight extent. The fixing part and the connecting part are both attached to the structural member, however, it may occur that a center axis of a hole in which the connecting part is attached and a center axis of another hole in which the fixing part is attached are offset or tilt relatively to each other due to, for example, manufacturing errors during machining processes, temperature differences during operation, or aging after prolonged use. The center offset and the tilt can be taken out or cancelled via relative movement of the circlip within the clip reception grooves. This arrangement facilitates easy attachment of the temperature sensitive valve mechanism and insures a long service life of the temperature sensitive valve mechanism.

Preferably, the groove width of a clip reception groove in which the circlip is received is set to be larger than a thickness of the circlip, and the circlip is in the form of a spring washer. In an arrangement in which the circlip is fitted in the clip reception grooves, the circlip or the clip reception grooves are slightly movable in a longitudinal or axial direction of the fixing part. According to the invention, however, since the circlip is formed by the spring washer, movement of the circlip or the clip reception grooves can be suppressed by the effect of a spring force of the spring washer.

Preferably, the connecting part has a plurality of through-holes provided along the clip reception groove. By virtue of the through-holes provided along the clip reception groove of the connecting part, it is possible to confirm a condition of the circlip by, for example, visual inspection performed through the through-holes. In case where a defect is detected, suitable jigs are inserted into the through-holes to thereby contract the diameter of the circlip. While keeping this condition, the connecting part is detached from the fixing part and thereafter reassembling can be performed.

It is preferable that the structural member, the valve casing and the connecting part are formed of aluminum alloys. With this arrangement, thermal expansion coefficients of the respective component part are nearly equal to one another so that a clearance between the structural member and the valve casing and a clearance between the structural member and the connecting part can be reduced to a minimum. By thus minimizing the clearances, a leakage of the lubricating oil from the clearances can be minimized. Even when a seal member provided on an outer periphery of the valve casing or the connecting part is omitted, a remarkable oil leakage does never take place and highly accurate control can be performed.

Preferably, the structural member is a cylinder block of an engine, and the cylinder block has a wall or a plate disposed such that the lubricating oil discharged from the discharge port hits on the wall or the plate before dropping into an oil reservoir of the cylinder block. In an arrangement in which the lubricating oil discharged from the discharge port is allowed to fall directly into an oil reservoir, splashes are produced and air is entrained in the splashes. As a consequence, an increased amount of undesirable bubbles is contained in the lubricating oil. According to the invention, however, by virtue of the wall or the plate provided on the cylinder block, the lubricating oil discharged from the discharge port hits on the wall or the plate before dropping into the oil reservoir. With this arrangement, since the lubricating oil flows downward along the wall or the plate, splashes are unlikely to produce and an amount of air entrained in the splashes can be reduced to an allowable extent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which the drawings should be viewed in the direction of reference characters.

Referring now toFIG. 1, a description will be made about an embodiment in which a temperature sensitive valve mechanism20of the present invention is detachably mounted in a structural member10comprised of an oil pump11. As shown inFIG. 1, the oil pump11as the structural member10comprises an inner gear12, an outer gear13, and a pump housing14containing the inner gear12and the outer gear13. When the inner gear12is rotated by a part of engine power, the outer gear13is rotated with rotation of the inner gear12. During this rotation, a gap G between the inner gear12and the outer gear13changes in volume to thereby cause a lubricating oil to be sucked in as indicated by the arrow (1), then compressed, and finally discharged therefrom as indicated by the arrow (2).

The pump housing14has a main oil passage15as an oil passage, and a return oil passage16provided substantially in parallel with the main oil passage15. When the main oil passage15is at a high oil pressure, the lubricating oil is returned to the return oil passage16by a general return valve (not shown). The pump housing14further has a valve insertion hole17extending across the main oil passage15such that a closed fore end of the valve insertion hole17reaches in the vicinity of the return oil passage16. The valve insertion hole17has a female screw18formed at an open end thereof, and a through-hole19is formed in the pump housing14, having one end connected to the valve insertion hole17at a portion adjacent to the closed fore end thereof and an opposite end opened to the outside of the pump housing14. With the valve insertion hole17thus provided, the temperature sensitive valve mechanism20can be readily inserted in the valve insertion hole17at any time.

A structure of the temperature sensitive valve mechanism20will be described below with reference toFIG. 2. As shown inFIG. 2, the20generally comprises a flanged plug22as a fixing part21, a thermoelement24having one end (more particularly a piston23in the illustrated embodiment) supported by the flanged plug22, a valve element25fixed to an opposite end of the thermoelement24, a valve casing26surrounding the valve element25, and a connecting part27extending from flanged plug22and supporting the valve casing26.

The flanged plug22has an upper portion provided with a flange31and a hexagonal hole32, and an axially intermediate portion provided with a mail screw33. A lower portion of flanged plug22has a central recess34for receiving one end of the piston23, an annular groove35for insertion of an upper portion of the connecting part27, and a first cylindrical portion36surrounding the annular groove35for clenching. The flanged plug22can be rotated by turning a hexagonal wrench with an end of the wrench being inserted in hexagonal hole32. The hexagonal hole32can be omitted in which instance the flange31is formed into a polygonal shape.

The thermoelement24is provided with a return spring37. An internal structure of the thermoelement24will be described below with reference toFIG. 4. The thermoelement24also includes a second cylindrical portion39at a lower part thereof, the second cylindrical portion39surrounding a small-diameter extension part38extending from the valve element25.

The valve element25comprises a valve cylindrical portion41, a lid portion42closing an upper end of the valve cylindrical portion41, and the small-diameter extension part38extending upwardly from the lid portion42and having a smaller diameter than the valve cylindrical portion41. The lid portion42has a plurality of through-holes43extending vertically therethrough. The small-diameter extension part38is of a hollow shape so that the small-diameter extension part38can be easily inserted in the second cylindrical portion39while releasing air to the outside of the small-diameter extension part38.

In the illustrated embodiment, the valve casing26and the connecting part27are formed integrally with each other. This structure is advantageous in that the number of component parts is small and assembling man-hours can be reduced. The valve casing26and the connecting part27may be separate members structurally independent from one another, as will be described later.

The connecting part27comprises a cylindrical body having a pair of diametrically opposed oil passage through-holes44,44for allowing passage therethrough of the lubricating oil. The connecting part27includes a spring retaining portion45provided at a lower portion thereof for retaining the return spring37. The valve casing26comprises a cylindrical body configured such that the valve element25is axially slidably received in the valve casing26. The valve casing26has an annular groove46and a discharge port47formed in an axially intermediate portion thereof, and a circumferential groove49formed in a lower portion thereof for receiving a seal member48. In the valve casing26, a part of the periphery of the discharge port47is made thin so as to have a smaller diameter than other parts over the entire periphery of the valve casing26. With this arrangement, the lubrication oil can be smoothly discharged irrespective of the phase or position of the discharge port47.

It is desirable that the aperture width of the oil passage through-holes44is made larger than an outside diameter of the thermoelement24. With this arrangement, the passage resistance of the oil passage through-holes44can be reduced. To achieve a further reduction of the passage resistance, the oil passage through-holes44are aligned in phase with the main oil passage15. The number of the oil passage through-holes44is not limited to two as in the illustrated embodiment, but three or more oil passage through-holes44can be used. The valve casing26and the connecting part27are manufactured by casing, forging, cutting (cut machining), or a combination thereof. The discharge port47is preferably cut-machined as it requires a precise opening area.

As shown inFIG. 3, the male screw33is threaded into the female screw18so that the temperature sensitive valve mechanism20is mounted in the pump housing14. In this instance, the flanged plug22can be viewed from the main oil passage15through oil passage through-holes44. The lubricating oil is allowed to flow through the oil passage through-holes44, the lubricating oil flowing in the main oil passage15is always in contact with the thermoelement24.

As shown inFIG. 4(a), the thermoelement24comprises the piston23, an elastic film51surrounding or covering the piston23, a case52housing the elastic film51, and a thermo-wax53filled between the case52and the elastic film51. When the temperature of the lubricating oil is low, the thermo-wax53is in a contracted state so that the valve element25does not interfere with (or overlap) the discharge port47of the valve casing26. As a result, the lubricating oil is allowed to flow in a direction of the arrow (3). In other words, the lubricating oil flows successively through the through-holes43, the discharge port47, and the through-hole19of the pump housing14and eventually it is discharged into an oil reservoir67described later on.

An increase in temperature of the lubricating oil causes the thermo-wax53to expand and increase its volume whereupon a projecting length of the piston23increases, as shown inFIG. 4(b). Since the piston23is in abutment with the flanged plug22, the case52and the valve element25are displaced toward the discharge port47. As a consequence, about a half of the opening area of the discharge port47is closed by the valve element25, for example. As the temperature of the lubricating oil rises further, the thermo-wax expands further and the volume of the thermo-wax increases further. As a result, the discharge port47is fully closed by the valve element25. When the temperature of the lubricating oil is lowered, the thermo-wax53contracts and the valve element25is retuned from the position ofFIG. 4(b)to the position ofFIG. 4(a)by virtue of the action of the return spring37.

The discharge port47and the through-hole19are important elements from a viewpoint of the flow ability of the lubricating oil. The discharge port47is preferably a cut-machined hole formed by cut-machining, as previously described, whereas the through-hole19may be a cut-machined hole or a hole as cast (as-cast hole).

The as-cast hole will be described in detail. In case where the pump housing14is a cast article, the through-hole19may be an as-cast hole. To form an as-cast hole, a core is set in a cast mold, and while keeping this condition, a molten metal is filled in the mold. In case of a die-cast molding method, the core is removed from the cast mold. In case of a sand mold casting method, the core is removed by breaking. In either case, an as-cast hole can be formed by the core at the same time the cast article is formed, and a subsequent cut-machining is therefore not necessary and a corresponding cost reduction can be attained.

It may occur however that the core is slightly displaced by the effect of a pressure of the molten metal during casting, and the center of the as-cast hole is slightly offset from the center of the through-hole16. To deal with this problem, following measures will be taken when the through-hole19is formed by an as-cast hole. Given that the diameter of the discharge port47is represented by d1and the diameter of the as-cast hole (through-hole19) is represented by d2, the diameter d2of the through-hole19is set to be larger than the diameter d1of the discharge port47(d2>d1). An amount of offset (difference between d2and d1) is allowable up to (d2−d1)/2. When a larger offset amount is assumed, a possible counter-measurement would be setting the diameter d2of the through-hole19to a larger value. In case of a through-hole19formed by cut-machining, the diameter d2of the through-hole19can be made closer to the diameter d1of the discharge port49provided that d1<d2. Reduction in diameter of the through-hole19can thus be achieved.

Next, a modified embodiment of the present invention will be described. As shown inFIG. 5, the connecting part27and the valve casing26can be formed by separate members structurally independent from one another. Other parts are identical to those shown inFIG. 2and, hence, the same reference characters are used and a detailed description thereof can be omitted. The valve casing26has a female screw54formed in an upper part thereof, and a male screw55is formed on the connecting part27. The male screw55is threaded into the female screw54to thereby complete a screw-connected portion56. Alternatively, the valve casing26may be provided with a male screw and the connecting part27may be provided with a female screw. By turning the male and female screws55,54relatively to one another, an axial position of the discharge port47of the valve casing26can be accurately adjusted.

Assembling procedures of the temperature sensitive valve mechanism20will be described. As shown inFIG. 6(a), the thermoelement24is brought into abutment with the flanged plug22in a predetermined procedure. The small-diameter extension part38of the valve element25is fitted in the second cylindrical portion39of the thermoelement24. In this instance, a fitting length between the small-diameter extension part38and the second cylindrical portion39is fixed after adjustment such that a distance H1between a lower surface of the flange31and a lower end (fore end) of the valve element25becomes equal to a predetermined distance. Preferably, press-fitting is employed as a fixing method because adjustment of the fitting length can be easily achieved.

Next, as shown inFIG. 6(b), the27is fitted in the36. Preferably, a positioning jig57is fitted in the discharge port47. As an alternative, a non-illustrated positioning jig may be inserted in the valve casing26from below in this figure in such a manner as to assume the same axial position as the positioning jig57.

While the first cylindrical portion36for clenching is kept in an unclenched state, the temperature sensitive valve mechanism20is immersed in an oil bath having a temperature of 80° C., for example. The temperature sensitive valve mechanism20may be immersed in a water bath, but immersion into the oil bath is preferable because it can provide a rust preventive effect and lubrication during initial operation of the temperature sensitive valve mechanism20. Oil bath immersion causes the valve element25to move toward the positioning jig57, as shown inFIG. 6(c). After a predetermined time has passed (in which instance, the thermo-wax53has already reached a temperature of 80° C.), an axial position of the connecting part27is adjusted such that the valve element25is in contact with the positioning jig57. Position adjustment performed at a service temperature of the lubricating oil (at which the lubricating oil is used frequently) makes it possible to reduce variation in hydraulic characteristics.

After the position adjustment, a distance H2between the lower surface of the flange31and a center of the discharge port47has a predetermined length. While keeping this condition, a clenching force F is applied to reduce or contract the diameter of the first cylindrical portion36. In this instance, clenching is performed such that the clenching force F will cause the first cylindrical portion36to undergo deformation over the entire periphery thereof. With this clenching, tilting and center shift of the connecting part27, which may occur during clenching, can be suppressed with the result that smooth sliding of the valve element25and highly precise hydraulic control can be achieved. By virtue of the diameter contraction, the first cylindrical portion36is clench-connected to an upper end portion of the connecting portion27. A first clenched portion59is thus formed by and between the first cylindrical portion36and the upper end portion of the connecting part27.

Description will be next made about modifications of the fixing part21. As shown inFIG. 7(a), the fixing part21may be in the form of a flangeless plug61. Alternatively, the fixing part21may be formed by a polygonal shank62and a flange31, as shown inFIG. 7(b). The polygonal shank62is deficient in airtightness and an O-ring63is therefore provided on an underside of the flange31. In addition, a presser plate64and bolts65are used to prevent the fixing part21from floating upward. In the arrangement shown inFIG. 7(b), the structural member10does not require a female screw. The shape and configuration of the fixing part21can be changed in various ways.

Next, description will be made about an embodiment in which the structural member10is in the form of a cylinder block66.FIG. 8(a)shows a comparative example in which an oil reservoir67is always formed by an oil pan attached to the bottom of a cylinder block66of the ordinal engine. In the comparative example, a lubricating oil68discharged from the discharge port47drops directly into the oil reservoir67. As a height difference h1between an oil surface and the discharge port47becomes large, larger splashes69will be produced. The splashes69entrain surrounding air, which will increase air bubbles contained in the lubricating oil. The air bubbles are undesirable because they affect lubrication at lubricating surfaces.

FIG. 8(b)shows an embodiment of the present invention in which the cylinder block66has a wall71located at a position opposed to the discharge port47. In the case where provision of the wall71is hardly possible, a plate72may be provided on the cylinder block66. Partly because the wall71and the plate72provide a reduced height difference h2between themselves and a surface of the lubricating oil, and partly because kinetic energy of the lubricating oil68is reduced when the lubricating oil68hits on the wall71or the plate72, generation of splashes from the oil surface almost does never take place. It is therefore possible to prevent air bubbles from mixing in the lubricating oil68.

The structural member10should by no means be limited to the oil pump and the cylinder block as in the illustrated embodiments, but other types of structural members such as a reduction gear may be used provided that they have an oil passage.

In the illustrated embodiments, the connecting part27is fastened to the fixing part21by applying the clenching force F to the first cylindrical portion36to thereby reduce the diameter of the first cylindrical portion36, as explained above with reference toFIG. 6(c). Such fastening structure may be realized by using a circlip or a spring pin in place of the clenching, as will be described later on.

As shown inFIG. 9, a clip reception groove74is formed in a distal end portion (lower end portion in this figure) of the fixing part21, and another clip reception groove75is formed on an upper end portion of the connecting part27which illustrated at a position below the fixing part21. A circlip76is provided to act between the fixing part21and the connecting part27. Other structural parts are the same as those shown inFIG. 5orFIG. 2, the same reference characters as those shown inFIG. 5orFIG. 2are used and a detailed description thereof can be omitted.

The circlip76is a machine element formally called a “C-shaped stop ring” as specified by JIS-B2804 where JIS is the abbreviation of Japanese Industrial Standards. The circlip76may be called as a stop ring or a retaining ring. Throughout the specification, the term “circlip” is used as it is widely spread.

FIG. 10(b)is provided as a supplementary explanation of the circlip76shown inFIG. 10(a). As shown inFIG. 10(b), the circlip76is in the form of a spring washer. Given that the circlip76has a first thickness t1corresponding to a solid length of the spring washer (which is equal to a thickness of a wire material forming the spring washer) and a second thickness t2corresponding to a free length of the spring washer, and the clip reception groove74has a groove width t3, these dimensions t1, t2and t3are set to satisfy a correlation indicated by inequalities t1<t3and t1<t2.

More specifically, the groove width t3of the clip reception groove74is preferably 1.05 to 1.40 times as much as the first thickness (solid length) t1of the circlip76, and the second thickness (free length) t2of the circlip76is larger than the first thickness (solid length) t1of the circlip76although it can vary depending on the process used for producing the circlip76.

As shown inFIG. 10(a), the fixing part21has a male taper portion77formed on a distal end side (lower side) of the clip reception groove74in such a manner as to taper or converge in a direction away from the clip reception groove74. When the circlip76is forced to move on and along the male taper portion77in a direction indicated by the arrow (4), the diameter of the circlip76is gradually enlarged by the male taper portion77. As the forced movement of the circlip76further continues, the circlip76moves into fitting engagement with the clip reception groove74.

The connecting part27has a female taper portion78formed on a fore end side (upper side) of the clip reception groove75in such a manner as to taper or converge toward the clip reception groove75. When the fixing part21is forcibly inserted into the connecting part27as indicated by the arrow (5), the diameter of the circlip76is gradually contracted by the female taper portion78. As the forced movement of the fixing part21further continues, the circlip76moves into fitting engagement with the clip reception groove75.

As shown inFIG. 11, by virtue of the fitting engagement of the circlip76relative to the clip reception groove74of the fixing part21and the clip reception groove75of the connecting part7, the fixing part21and the connecting part27are fastened together. In this instance, a small annular gap or clearance t4is formed between the fixing part21and the connecting part27. The circlip76is resiliently deformable in a radial direction thereof, and there is a gap defined between the clip reception groove74and the circlip76. With this arrangement, the connecting part27is allowed to slightly move relatively to the fixing part21in a direction perpendicular to a longitudinal axis (axial centerline)79of the fixing part21.

As shown inFIG. 12(a), the pump housing14has a first hole81for attachment (by screwing) of the fixing part21, and a second hole82for attachment (by insertion) of the connecting part27. The first hole81and the second hole82are separated by the main oil passage15, and it may occur that a central axis81aof the first hole81and a central axis82aof the second hole82are slightly offset to such an extent as denoted by δ1. It may also occur that the central axis82aof the second hole82slightly tilts relative to the central axis81aof the first hole81to such an extent as denoted by δ2. The center offset and the tilting of the central axis may be caused, for example, by manufacturing errors during machining processes, temperature differences while the structural member10is in use, or aging after prolonged use of the structural member10.

The center offset δ1shown inFIG. 12(a)and the tilt δ2shown inFIG. 12(b)can be taken out or canceled because the connecting part27is slightly movable relative to the fixing part21in the perpendicular direction of the longitudinal axis79of the fixing part21, as previously described with reference toFIG. 11. This arrangement facilitates easy attachment of the temperature sensitive valve mechanism20relative to the pump housing14and insures a long service life of the temperature sensitive valve mechanism20.

As shown inFIG. 11, a relatively large axial space is present between the circlip76and the clip reception groove74. The axial space can be obtained by calculation from (t3−t1)/2. As previously described with reference toFIG. 10(b), the circlip76takes the form of a spring washer. By the effect of a spring force of the spring washer, an amount of axial movement of the connecting part27relative to the fixing part21shown inFIG. 11is resiliently limited. The circlip76may be formed by a flat washer in place of the spring washer. A typical example of the circlip formed by the flat washer will be described below with reference toFIG. 13.

As shown inFIG. 13, the circlip76formed by the flat washer (still in the form of a C-shaped stop ring) is used with a clip reception groove74having a groove width t5which is about 1.15 times as much as a thickness t1of the circlip76. The circlip76can exhibit no spring action and hence allows slight axial movement of the connecting part27relative to the fixing part21. The circlip76formed by a flat washer is inexpensive to obtain.

In the case where the cost is regarded as important, the structure shown inFIG. 13is employed. Alternatively, when the performance is regarded as important, the structure ofFIG. 11is employed. Various shapes and configurations have been proposed for the circlip76(regardless of whether they are standardized by JIS or not) and any of these shapes and configuration can be used without limiting to those shown in the illustrated embodiments.

Description will be next made about an embodiment in which a spring pin86is used. As shown inFIG. 14, the fixing part21has a pin hole84formed therein, and the connecting part27has another pin hole85formed therein. While the pin holes84,85are axially aligned with each other, the spring pin86is press-fitted in the pin holes84,85. The spring pin86is a machine element formally called a “grooved spring pin” as specified by JIS B 2808 and having a single groove or slit and a C-shaped cross section. By virtue of its C-shaped cross section, the spring pin86is resiliently deformable to reduce its diameter when subject to an external force. When the external force is released, the spring pin86will restore its original shape and diameter. The spring pin86is resiliently deformable in this manner.

As shown inFIG. 15, the fixing part21and the connecting part27are fastened together by the spring pin86. By virtue of the resiliency of the spring pin86and the presence of a small annular space or clearance t4between the fixing part21and the connecting part27, the structure may involve a center offset and tilting of the connecting part27relative to the fixing part21.

When the spring pin86is to be replaced, a metal rod having a smaller diameter than the pin holes84,85(FIG. 14) and a hummer for striking the metal rod are provided. While one end of the metal rod is in contact with an end of the spring pin86shown inFIG. 15, an opposite end of the metal rod is hit by the hummer. This will cause the spring pin86to partly project outwardly from the connecting part27. A projecting part of the spring pin86is gripped and pulled outward by a nipper or a pair of pliers until the spring pin86is removed from the pin holes84,85. The removed spring pin86is damaged and hence destroyed. A new spring pin86is press-fitted in the pin holes84,85to thereby join the fixing part21and the connecting part27.

The spring pin86can be attached and detached more easily than the circlip76. The circlip76is, in many cases, comprised of a tailor-made product, whereas the spring pin86is readily available on the market. The spring pin86is therefore advantageous over the circlip76in terms of the cost.

Net, a modified form of the connecting part27shown inFIG. 10will be described with reference toFIGS. 16(a) and 16(b). As shown inFIG. 16(a), the connecting part27has a plurality of through-holes88formed therein at regular intervals along the clip reception groove75. The through-holes88are holes extending between an outer peripheral surface and an inner peripheral surface of the cylindrical connecting part27. Other parts are the same as those shown inFIG. 10(a)and the same reference characters as those shown inFIG. 10(a)are used and a further description thereof can be omitted.

The through-holes88may be formed by horizontally elongated rectangular holes, square holes, vertically elongated rectangular holes, elliptical holes, oblong holes, or accurate circular holes. The through-holes88are preferably comprised of four holes formed at a pitch of 90 degrees, or of three holes formed at a pitch of 120 degrees. The number and pitch of the through-holes are not limited to those in the specific examples stated above. The connecting part27is joined to the fixing part21by the circlip76. A cross section taken along line b-b ofFIG. 16(a)is shown inFIG. 16(b).

As shown inFIG. 16(b), the connecting part27and the fixing part21are fastened or joined together by the circlip76. In this instance, a condition (such as an attachment posture) of the circlip76can be confirmed by visual inspection through the through-holes88. In place of the visual inspection by a human operator, an analysis of images captured by a CCD camera may be used. When a defect on the condition of the circlip76is found, jigs89,89are inserted into the through-holes88so as to reduce the diameter of the circlip76. While the circlip76is kept in a radially contracted state, the connecting part27is detached or separated from the fixing part21. Then, the circlip76is detached from the fixing part21. With this arrangement, when a defect, such as inaccurate positioning of the valve element25at a predetermined working temperature, occurs after assembly, reassembling of the temperature sensitive valve mechanism20is possible to perform.

The through-holes88may be formed by notched holes which open upward, as shown inFIG. 16(c). Machining of the notched holes is easier than that of the notch-free holes and, hence, a corresponding reduction in machining time can be attained.

It is preferable that the structural member10, the valve casing26and the connecting part27shown, for example, inFIG. 7are formed of the same kind of materials such as aluminum alloys. By thus using the same kind of materials, thermal expansion coefficients of the above-identified parts are nearly equal to one another. It is therefore possible to minimize a clearance between the structural member10and the valve casing26and a clearance between the structural member10and the connecting part27. As a result, a leakage of the lubricating oil from these clearance can be limited to a minimum.

In the illustrated embodiments shown, for example, inFIG. 7, the seal member48is provided between an outer periphery of the valve casing26and the structural member10. The seal member48can be omitted when the oil leakage is minimized. Even when the seal member48is omitted, a remarkable amount of oil leakage does never take place and, hence, control can be performed with increased accuracy.

The present invention is particularly advantageous when embodied in a temperature sensitive valve mechanism assembled in an oil pump.