COVER WITH VOLUMETRIC COMPENSATING DEVICE FOR HYDRAULIC PRESSURE ACTUATING CYLINDERS

Abstract: The disclosed cover comprises a substantially cylindrical hollow body (2), an elastic compensating membrane (3) and a compensating spring (16). The hollow body (2) has at one of its ends ( C ) an inlet to which is coupled the functional extremity (5) of a hydraulic cylinder ( C ), and at the other end a closure face (10). The membrane (3) has a retaining extension (9) for its secured positioning and prevents the liquid ( F ) contained in the cylinder ( C ) to leak to the outside. The helical spring (16) actuates permanently in a compression mode and one of its ends bears against the inside of the closure face (10) while its other end bears against the internal face (9) of the membrane (3). The membrane (3) and the hollow body (2) define a compensation chamber (15) whose volume ( VC ) varies as a function of the pressure exerted by the fluid ( F ) on the external face (8) of the membrane (3). Application to the motor vehicle industry.

Description: Field of the Invention This invention relates to a hydraulic pressurised piston-cylinder device having an internal volume variation compensating device. This invention has been developed within a research programme of wider general scope relating to the manufacture of hydraulic self-regulating devices for regulating, by way of permanent adjustment, the length of the cable, or linking member, connecting a mechanism with the corresponding control member. An example of such self-regulating devices are the devices for regulating the length of the control cable linking the clutch mechanism with the clutch pedal. The purpose of this regulation of the control cable length is to compensate for the wear of the clutch plate lining during use. Background of the Invention A known embodiment of the hydraulic self-regulating devices for the clutch control cable length is disclosed in Spanish patent P 9002014 (equivalent to EP-A-0 494 276) which describes a device which, in essence, comprises a main body member, or cylinder, housing therein a piston which comprises a check valve, a regulating rod which is connected at one end thereof to the said piston and at the other end, which extends out from the main body member, it is connected to the control cable linking it with the clutch pedal and a liquid completely filling the interior space of the cylinder. Among its many possible applications, the device according to Spanish patent P 9002014 (equivalent to EP-A-0 494 276) has proved to be highly efficient when used in the regulation of the length of the control cable extending from the clutch pedal to the pressure plate fork of the clutch mechanism, by automatically varying the length of the portion of the regulating rod housed within the cylinder appropriately to compensate for the wear of the clutch. In other words, the length of the outwardly extending portion of the rod increases, which is equivalent to increasing the operative length of the control cable, whereby, whenever there is a physically noticeable wear, the length of the cable increases, adjusting itself to the new situation arising from such wear. The self-regulating device according to Spanish patent P 9002014 (equilvalent to EP-A- 0 494 276) is provided with volumetric compensation means designed permanently and automatically to absorb the variations of volume affecting both the cylinder and the liquid contained therein owing to changes in the ambient temperature of the place where the device is installed. The compensation means are also designed to absorb the variations of volume caused inside the cylinder by the variations of the length of the rod portion contained in the cylinder. Hereinafter, with a view to achieving adequate clarity of disclosure in the description, the useful internal volume of the cylinder is defined to be the same as the volume occupied by liquid plus the volume occupied by the volumetric compensation means housed in the cylinder, as measured under the original manufacturing conditions, i.e. with the piston, other mechanical members and a particular portion of the rod housed in the cylinder, at the temperature of manufacture. In the hydraulic self-regulating devices such as the one described above, the useful internal volume of the cylinder does not remain constant, but quite otherwise. The said useful internal volume varies, basically, depending on the variation of the rod portion contained in the cylinder and depending on the variation of the operating temperature of the cylinder. In the former case, an increase of the length of the rod portion contained in the cylinder, caused when the piston moves inwardly, implies a reduction of the useful internal volume while, on the contrary, a shortening of the length of said rod portion contained in the cylinder, caused when the piston moves outwardly, implies an increase in the useful internal volume. In the latter case, an increase of the cylinder operating temperature causes the cylinder and the liquid contained therein to expand, increasing the useful internal volume while, on the contrary, a drop in the operating temperature causes the cylinder and the liquid contained therein to contract, reducing the useful internal volume. In this respect, it should be noted that the coefficients of expansion of the cylinder and of the liquid are substantially different, with the coefficient of expansion of the liquid being notably higher than that of the cylinder so that an increase of the cylinder temperature will cause an increase of the liquid pressure against the inner surface of the cylinder and on the volumetric compensation means. On the contrary, a lowering of the cylinder temperature will cause a lowering of the liquid pressure against the inner surface of the cylinder and on the volumetric compensation means. It will be gathered from the above that the volumetric compensation means included in the hydraulic self-regulating devices as described above absorb the variations of volume and, consequently, the variations in the pressure exerted by the liquid on the inside of the cylinder which affect both the cylinder and the liquid contained therein while the device is operating or even during the storage of the device prior to its assembly. In fact, at a constant temperature, a shortening of the length of the rod portion housed in the cylinder generates a depression causing a corresponding increase in the volume occupied by the volumetric compensation means, i.e., there is an increase in the useful internal volume while, on the contrary, an increase of the length of said rod portion causes a corresponding reduction of the volume occupied by the volumetric compensation means, i.e. there is a reduction of the useful internal volume. And, for a given position of the piston in the cylinder, i.e. for a given length of the rod portion housed in the cylinder, an increase of the cylinder temperature causes an expansion of the liquid greater than the expansion of the cylinder, which generates a pressure causing in turn a corresponding reduction of the volume occupied by the volumetric compensation means while, on the contrary, a lowering of the cylinder temperature causes a contraction of the liquid also greater than the contraction of the cylinder which, in turn, causes a corresponding increase in the volume occupied by the volumetric compensation means. Simultaneous changes of the length of the rod portion contained in the cylinder and of the cylinder temperature have a corresponding result, depression or pressure, which acts on the volumetric compensation means, increasing or reducing the compensation volume, as described above. FR-A- 2055597 discloses a hydraulic reservoir having a flexible diaphragm or membrane with a spring urging the diaphragm into the reservoir. This prior art device relates to a hydraulic reservoir, particularly for a master cylinder into a vehicle, but not a volumetric compensating device for pressurized hydraulic piston-cylinders. The objective of the device according to the invention is precisely to compensate said volumetric variations occuring during the operation of pressurized hydraulic piston-cylinders such as the one described above. It will, consequently, be understood that the device of the invention may be used where it is desired automatically to correct both the volumetric variations of the cylinder inner space due to its very functioning and those volumetric variations due to changes in the cylinder temperature. The device of the invention is distinguished from other known compensating devices by its structure and by the way it performs. Summary of the Invention The hydraulic pressurised piston-cylinder device comprises a cap in which it is installed the internal volume variation compensating device. This cap is applicable to a wide range of pressurized hydraulic piston-cylinders. The cap according to the invention has been tested with very good results in the piston-cylinders of hydraulic self-regulating devices used in the automobile industry, of the type where a piston with an operating rod is movable in a hydraulic pressure cylinder, a piston with an operating rod is movable therein and a liquid is contained inside. According to a first constructional mode, the invention is characterized in that the cap, which closes a functional end of the hydraulic pressure cylinder, comprises an essentially cylindrical hollow body member and a resilient compensating diaphragm, in which: the hollow body member is relatively short and is provided at one end thereof with an open end dimensioned snugly to receive the corresponding functional end of a hydraulic pressure cylinder and connecting means allowing firm engagement of said hollow body member and cylinder and at the other end thereof with an end wall, the hollow body member having means for retaining the resilient compensating diaphragm and means for sealing the engagement between said hollow body member and said cylinder end; the resilient compensating diaphragm is made from highly resilient material and the outer surface thereof, facing the cylinder, being convex and the inner surface, facing the hollow body member end wall, concave, the perimetral edge of the diaphragm being formed with a retaining extension which is coaxial with the longitudinal axis, or axis of revolution, of the diaphragm; the arrangement being such that when the corresponding functional end of the cylinder is engaged with the hollow body member, the resilient compensating diaphragm defines, between it and the hollow body member end wall, a variable volume compensating chamber, the volume variation of which depends on the pressure of the liquid contained in said cylinder and acting on the outer surface of the diaphragm. According to a further constructional mode of the invention, it is characterized in that the cap comprises the above described operative elements and in that: there is housed in the compensation chamber a compensating coil spring which is permanently under compression, with one end bearing against the inner concave surface of the resilient compensating diaphragm and the other end thereof bearing against the inner surface of the hollow body member end wall, said inner concave surface and said inner surface of the end wall comprising respective means for positionally retaining the compensating coil spring. In accordance with the feature described in the immediately foregoing paragraph, the compensating coil spring positioning means comprise, on the inner concave surface of the compensating diaphragm, a relatively short axial cylindrical extension snugly housed in one of the ends of the compensating coil spring and on the inner surface of the hollow body member end wall a relatively shallow recess in which the other end of the compensating coil spring is housed. In both of the above described constructions of the cap of the invention, the means for retaining the resilient compensating diaphragm and for sealing the engagement of the hydraulic cylinder with the hollow body member comprise, on the inner surface of the hollow body end wall, a coaxial slot of basically U-shaped section, dimensioned snugly to receive the corresponding portion of the resilient compensating diaphragm retaining extension, so that said retaining extension is compressively held between the cylinder and the hollow body member. Also in both above described constructions of the cap according to the invention, whenever required, the inner surface of the hollow body member end wall is provided with an axial concavity dimensioned to house the resilient compensating diaphragm. The operation of the cap, the features of which have been described above, is extremely simple and efficient and in no way alters the operation of the hydraulic cylinder on which it is mounted. In fact, once the hydraulic cylinder and the cap of the invention have been suitably coupled together, there is established an initial state, predetermined by the manufacturer, in which there is set the useful internal volume which, as defined above, is the volume occupied by the liquid plus the volume occupied by the volumetric compensating means. With regard to the volume occupied by the compensating chamber, it is thus understood to be the volume corresponding to the space defined by the resilient compensating diaphragm and by the hollow body member end wall of the cap of the invention. When, as a result of the operation of the cylinder and/or by a variation of the temperature of the latter, it is required to compensate for an increase of the useful internal volume of the cylinder by causing it to be reduced, the resilient compensating diaphragm, pressed on the outside by the liquid, is resiliently deformed so that the volume of the compensating chamber is progressively reduced until the pressures on the inner and outer sides of the compensating diaphragm become equalled. On the contrary, when it is required to compensate for a reduction of the useful internal volume of the cylinder by causing it to increase, the resilient compensating diaphragm is resiliently deformed so that the volume of the compensating chamber increases until once again the pressures on both sides of the compensating diaphragm are equal. The operation of the cap according to the invention is essentially the same in either of the two possible constructional modes described above. In fact, in accordance with the first constructional mode of the cap of the invention, the cap comprises the hollow body member and the resilient compensating diaphragm. In this case, the pressure of the liquid on the outer surface of the diaphragm is offset by the resilient reaction of the diaphragm itself. In accordance with the second constructional mode of the cap of the invention, the cap comprises the hollow body member, the resilient compensating diaphragm and, furthermore, a compensating coil spring. In this second case, the pressure of the liquid on the outer surface of the diaphragm is offset by the resilient reaction of the diaphragm itself and, furthermore, by the resilient reaction of the spring which, as said above, is permanently under compression. Obviously, whether one or the other characteristic constructional mode of the invention is used will depend on the technological requirements of each particular application. Brief Description of the Drawings The invention is illustrated in the drawing sheets accompanying this description. In the drawings: Figure 1 is a cross section view showing one constructional mode T1 of the cap according to the invention in which the compensating chamber occupies an intermediate volume. Figure 2 is a cross section view of the constructional mode T1 of the cap according to the invention in which, in comparison with Figure 1, the compensating chamber occupies a larger volume. Figure 3 is a cross section view of a second constructional mode T2 of the cap according to the invention in which the compensating chamber occupies an intermediate volume. Figure 4 is a cross section view of the constructional mode T2 of the cap according to the invention in which, in comparison with Figure 3, the compensating chamber occupies a larger volume. Figure 5 is a cross section view also showing a further embodiment of the constructional mode T2 of the cap. Detailed Description of the Embodiments For adequate clarity of disclosure, the constituent members of the three examples drawn of the cap which are mutually equivalent shall have the same reference symbols in both the description and in the drawing figures. In the drawing figures, both constructional modes T1 (Figures 1 and 2) and T2 (Figures 3 to 5) of the cap according to the invention are attached to a hydraulic cylinder C , which for the same reasons as given above, has been shown only in part. The hydraulic cylinder C can form part of any type of device, machine or apparatus such as, for example, the devices for permanently regulating the length of the control cable linking the clutch mechanism with the corresponding pedal. It is in the hydraulic cylinder C where the variations of the internal volume thereof caused by movements of the piston 1 as a result of the larger or smaller portion of the operating rod (not shown in the drawings) housed in the inside of the cylinder C have to be permanently and automatically compensated and the expansion of the cylinder C itself and of the liquid F contained therein caused by variations in the temperature of the environment in which the cylinder is working has also to be compensated. The embodiment corresponding to the constructional mode T1 of the cap is shown in Figures 1 and 2. The cap comprises the hollow body member 2 and the resilient compensating diaphragm 3. The hollow body member 2 is essentially elongate and cylindrical and at the front end A thereof there is the open end 4 snugly receiving the functional end 5 of the hydraulic cylinder C . The firm attachment of the functional end 5 of the hydraulic cylinder C to the hollow body member 2 is achieved by mutual coupling means comprising a plurality of equidistantly spaced apart perimetral retaining projections 6 on the end 5 of the hydraulic cylinder C and retaining grooves 7 on the hollow body member 2. There is the same number of retaining grooves 7 as retaining projections 6 and they are dimensioned such that the projections 6 are housed snugly therein. The resilient compensating diaphragm 3 is provided with an outer surface 8 and an inner surface 9. The outer surface 8 faces the piston 1 of the cylinder C and the inner surface 9 faces the end wall 10 of the hollow body member 2, the perimetral edge of the diaphragm 3 being provided with the retaining extension 11 which is coaxial it the axis of revolution of the diaphragm 3. The means for retaining the resilient compensating diaphragm 3 and at the same time for sealing the connexion between the hollow body member 2 and the end 5 of the cylinder C are formed by the curved section recess 12 provided all around the front surface of the said end 5 of the cylinder C and by the coaxial U-shaped groove 13 provided on the inner surface of the end wall 10 of the hollow body member 2. The recess 12 and the coaxial groove 13 of the cylinder C and of the hollow body member 2, respectively, are dimensioned to mate with the retaining extension 11 of the resilient compensating diaphragm 3. In this way, the connexion of the end 5 of the cylinder C to the hollow body member 2 of the cap of the invention, by way of the retaining projections 6 and slots 7 with which they are respectively provided, compresses the retaining extension 11 of the resilient compensating diaphragm 3, thereby preventing leaks of the liquid F to the outside. In this embodiment of the constructional mode T1 of the cap, the end wall 10 of the hollow body member 2 is provided internally with the concavity 14 which, as shown in Figure 1, is for housing the resilient compensating diaphragm 3. Between the resilient compensating diaphragm 3 and the hollow body member 2 there is defined the compensating chamber 15 which, in this embodiment, is bounded by the inner surface 9 of the resilient compensating diaphragm 3 and the end wall 10 of the hollow body member 2. Said compensating chamber 15 has a volume VC which, when the cylinder C is operating, may vary, having different values. Figures 3 and 4 show the embodiment of the constructional mode T2 of the cap, which comprises the hollow body member 2 and the resilient compensating diaphragm 3 as in the constructional mode T1 and, furthermore, the compensating coil spring 16 which is housed in the compensating chamber 15. The presence of the compensating coil spring 16 in the constructional mode T2 allows the internal concavity 14, which is more desirable for the above described constructional mode T1 , to be dispensed with. Therefore, the embodiments of Figures 3 and 4 have been drawn without the internal concavity 14. In the embodiments of Figures 3 and 4, there is drawn the central recess 18, to be explained hereinafter, situated approximately in the same place as the internal concavity 14. The compensating coil spring 16 is permanently under compression and bears at one end on the inner surface 9 of the resilient compensating diaphragm 3 and at the other end thereof on end wall 10 of the hollow body member 2. The positioning means for the spring 16 comprise the cylindrical axial extension 17 on the inner surface 9 of the diaphragm 3 and the central recess 18 on the inner surface of the end wall 10 of the hollow body member 2. The axial extension 17 is dimensioned so that it is snugly housed in the corresponding end of the compensating coil spring 16. On the other hand, the central recess 18 is dimensioned snugly to receive the other end of the spring 16. In this way, the axial extension 17 and the central recess 18 prevent the compensating coil spring 16 from coming out of its working position as a result of the operating conditions of the cap of the invention and of the cylinder C . Figure 5 shows a further embodiment of the constructional mode T2 of the cap according to the invention. The embodiment of Figure 5 comprises all the items described above for the embodiment T2 as well as the concavity 14 provided in the end wall 10 of the hollow body member 2 described for the constructional mode T1 . It will be understood that the centering function of the central recess 18 (Figures 3 and 4) may be performed by the internal concavity 14. In this way, by comparing the constructional mode T1 shown in Figures 1 and 2 with the constructional mode T2 shown in the embodiment of Figure 5, it is clearly seen that the characteristic difference of substance is to be found in the fact that the construction mode T2 (Figure 5) is provided, further, with the compensating coil spring 16. The fundamental operation of the embodiments of Figures 1 to 5 of the cap according to the invention is described below. Originally, in the ensemble formed by the cylinder C , the piston 1, the operating rod, and the cap of the invention, there is established, as said before, an initial state in which there is determined a useful internal volume of the cylinder which is the volume occupied by the liquid F plus the volume VC of the compensating chamber 15. Hereinafter, the operation of the embodiments of the invention shown in Figures 1 to 5 is essentially the same. In fact, when it is for any reason required to reduce the useful internal volume of the cylinder C , i.e. when the pressure of the liquid F on the inner surface 8 of the resilient compensating diaphragm 3 increases, the latter is progressively resiliently deformed, as shown in Figure 1, reducing the volume VC of the compensating chamber 15 until the pressure levels on the inner surface 8 and outer surface 9 of the diaphragm are balanced. On the contrary, when it for any reason required to increase the useful internal volume of the cylinder C , i.e. when the pressure of the liquid F on the outer surface 8 of the diaphragm 3 drops, the latter is progressively resiliently deformed, as shown in Figure 2, increasing the volume VC of the compensating chamber 15 until once again the pressure on the outer surface 8 and inner surface 9 of the diaphragm 3 are balanced. In the operation of the constructional mode T1 shown in Figures 1 and 2, the pressure of the liquid F on the outer surface 8 of the diaphragm 3 is opposed by the resilient reaction of the diaphragm 3 itself. And, in the operation of the constructional mode T2 shown in Figures 3 to 5, the pressure exerted by the liquid F on the outer surface 8 of the diaphragm 3 is opposed by the resilient reaction of the diaphragm 3 itself and, furthermore, by the resilient reaction of the compensating coil spring 16 which, as stated above, is permanently under compression. It will be understood that the adoption of the constructional mode T1 or T2 of the cap of the invention will depend on the requirements of the cylinder C in each particular application.

Claims: A hydraulic pressurised piston-cylinder device having an internal volume variation compensating device, in which a cap closes a functional end (5) of a hydraulic pressure cylinder ( C ), a piston (1) with an operating rod is movable in said hydraulic pressure cylinder ( C ), and a liquid ( F ) is contained therein, characterized in that said cap includes a substantially cylindrical hollow body member (2) and a resilient compensating diaphragm (3), in which: the hollow body member (2) is relatively short and is provided at one end thereof with an open end (4) dimensioned snugly to receive the corresponding functional end (5) of the hydraulic pressure cylinder ( C ) and connecting means (6) allowing firm engagement of said hollow body member (2) and cylinder ( C ) and at the other end thereof with an end wall (10), the hollow body member (2) having means (13) for retaining the resilient compensating diaphragm (3) and means (13) for sealing the engagement between said hollow body member (2) and said cylinder ( C ) end (5); the resilient compensating diaphragm (3) is made from highly resilient material and the outer surface (8) thereof, facing the cylinder ( C ), being convex and the inner surface (9), facing the hollow body member (2) end wall (10), being concave, the perimetral edge of the diaphragm (3) being formed with a retaining extension (11) which is coaxial with the longitudinal axis, or axis of revolution, of the diaphragm (3); the arrangement being such that when the corresponding functional end (5) of the cylinder ( C ) is engaged with the hollow body member (2), the resilient compensating diaphragm (3) defines, between it and the hollow body member (2) end wall (10), a variable volume ( VC ) compensating chamber (15), the volume ( VC ) variation of which depends on the pressure of the liquid (F) contained in said cylinder ( C ) and acting on the outer surface (8) of the diaphragm (3). A hydraulic pressurised piston-cylinder device having an internal volume variation compensating device, in which a cap closes a functional end (5) of a hydraulic pressure cylinder ( C ), a piston (1) with an operating rod is movable in said hydraulic pressure cylinder ( C ), and a liquid ( F ) is contained therein, characterized in that said cap includes a substantially cylindrical hollow body member (2), a compensating coil spring (16) permanently under compression and a resilient compensating diaphragm (3), in which: the hollow body member (2) is relatively short and is provided at one end thereof with an open end (4) dimensioned snugly to receive the corresponding functional end (5) of the hydraulic pressure cylinder ( C ) and connecting means (6) allowing firm engagement of said hollow body member (2) and cylinder ( C ) and at the other end thereof with an end wall (10) provided internally with means (12) for the positioning of the compensating coil spring (16), the hollow body member (2) having means (13) for retaining the resilient compensating diaphragm (3) and means (13) for sealing the engagement between said hollow body member (2) and said cylinder ( C ) end (5); the resilient compensating diaphragm (3) is made from highly resilient material and the outer surface (8) thereof, facing the cylinder ( C ), is convex and the inner surface (9), facing the hollow body member (2) end wall (10), is concave, having means (17) for positioning the compensating coil spring (16), the perimetral edge of the diaphragm (3) being formed with a retaining extension (11) which is coaxial with the longitudinal axis, or axis of revolution, of the diaphragm (3); one of the ends of the compensating coil spring (16) bears against the inner surface (9) of the resilient compensating diaphragm (3); and the other end bears against the inside of the hollow body member (2) end wall (10), such that when the corresponding functional end (5) of the cylinder ( C ) is engaged with the hollow body member (2), the resilient compensating diaphragm (3) defines, between it and the hollow body member (2) end wall (10), a variable volume ( VC ) compensating chamber (15), the volume ( VC ) variation of which depends on the pressure of the liquid ( F ) contained in said cylinder (C) and acting on the outer surface (8) of the diaphragm (3). A hydraulic pressurised piston-cylinder device having an internal volume variation compensating device according to claim 1 or claim 2, characterized in that in said cap the resilient compensating diaphragm (3) retaining means and the means sealing the engagement of the hydraulic cylinder ( C ) with the hollow body member (2) comprise, on the inner surface of the hollow body (2) end wall (10), a coaxial slot (13) of basically U-shaped section, dimensioned snugly to receive the corresponding portion of the resilient compensating diaphragm (3) retaining extension (11), so that said retaining extension (11) is compressively held between the cylinder ( C ) and the hollow body member (2). A hydraulic pressurised piston-cylinder device having an internal volume variation compensating device according to claims 2 and 3, characterized in that in said cap the compensating coil spring (16) positioning means comprise, on the inner surface (9) of the compensating diaphragm (3), a relatively short axial cylindrical extension (17) snugly housed in one of the ends of the compensating coil spring (16); and, on the inner surface of the hollow body member (2) end wall (10) a relatively shallow recess (18) in which the other end of the compensating coil spring (16) is snugly housed. A hydraulic pressurised piston-cylinder device having an internal volume variation compensating device according to any one of the foregoing claims, characterized in that in said cap the hollow body member (2) is formed at the end wall (10) thereof with an internal concavity (14) for housing the resilient compensating diaphragm (3).

Inventors: GABAS CEBOLLERO CARLOS, GABAS CEBOLLERO, CARLOS
Applicants: FICO CABLES SA, FICO CABLES, S.A.
Application year: 1993
Main classification: F16D13
IPC codes: F16J10, F16D25, F16D13, B60T11, F16D23