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A hydraulic control valve having a piezoelectric actuator comprises an expansible sleeve loosely received within a bore of the valve housing, with one end thereof being fixedly or stationarily mounted relative to the housing and the other end thereof being expansibly mounted within the bore. A slida

A hydraulic control valve having a piezoelectric actuator comprises an expansible sleeve loosely received within a bore of the valve housing, with one end thereof being fixedly or stationarily mounted relative to the housing and the other end thereof being expansibly mounted within the bore. A slidable first piston is mounted within the bore of the valve housing and is urged against the other end of the expansible sleeve. This first piston floatingly supports one end of the piezoelectric actuator, the other end of which is supported by a second piston which is slidably mounted within the sleeve and is coupled to a valve member operable to cooperate with a valve seat to open and close an inside fuel passage communicating an inlet port with an outlet port. The linear expansion of the sleeve due to a change in the ambient temperature causes the first piston to displace in one direction together with the piezoelectric actuator supported thereby so that the linear expansion of the piezoelectric actuator occurring in the opposite direction due to a similar ambient temperature change is counterbalanced whereby the second piston, serving as an output member of the piezoelectric actuator, is maintained at a constant distance with respect to the valve member regardless of change in the ambient temperature. Such a temperature compensation structure enabling precise positioning of the second piston ensures improved injection timing and injection quantity control of a fuel injection system for an internal combustion engine.

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1. A piezoelectric hydraulic control valve, comprising: (a) a housing having an axially-extending, closed-end central bore and having an inlet port for receiving pressurized fluid and an outlet port for delivering said pressurized fluid and a fluid passage communicating said inlet and said outlet

1. A piezoelectric hydraulic control valve, comprising: (a) a housing having an axially-extending, closed-end central bore and having an inlet port for receiving pressurized fluid and an outlet port for delivering said pressurized fluid and a fluid passage communicating said inlet and said outlet port; (b) a valve seat in said housing and extending across said passage; (c) a movable valve member cooperating with said valve seat; (d) a column of piezoelectric material received coaxially within said bore and having an upper and a lower end; (e) means for applying a voltage to said piezoelectric column to induce axial expansion of said column; (f) connecting means provided between said lower end of said column and said valve member for transmitting axial expansion of said column to said valve member to thereby open and close said fluid passage; (g) a thermal expansible sleeve received within said bore concentrically with said column, having a coefficient of linear expansion equal to that of said piezoelectric column and having an upper and a lower end, said lower end of said sleeve being fixedly supported by said housing but other portions of said sleeve being loosely fitted within said bore to permit said upper end of said sleeve to displace axially in response to thermal expansion of said sleeve due to a variation in the ambient temperature; and (h) movable supporting means, received movably within said bore and attached to the upper end of said sleeve, for maintaining said lower end of said column at a constant distance from said valve member regardless of ambient temperature variations by supporting said upper end of said piezoelectric column such that is displaces together with said upper end of said sleeve, whereby expansion and contraction in one direction of said sleeve compensates for the expansion and contraction, due to ambient temperature variation, in the opposite direction of said piezoelectric column, thereby maintaining said constant distance. 2. A piezoelectric hydraulic control valve according to claim 1, wherein said expansible sleeve has an axial length equal to that of said piezoelectric column. 3. A piezoelectric hydraulic control valve according to claim 1, wherein said expansible sleeve is made from the same material as that of said piezoelectric column. 4. A piezoelectric hydraulic control valve according to claim 1, wherein said housing comprises an upper and lower housing member threadingly connected to each other, said lower housing member having a stepped bore open at the top and closed at the bottom, said stepped bore including an upper large-diameter bore portion, a lower small-diameter bore portion, and a shoulder portion interconnecting said upper and said lower bore portion, said upper housing member having a bore forming said axially-extending central bore of said housing, said bore of said upper housing member having a diameter smaller than that of said upper bore portion of said lower housing member, said valve seat having a disc-like shape and being sandwiched between said shoulder portion of said lower housing member and the lower end of said upper housing member, said disc-like valve seat having a central aperture through which said connecting means extends fluid-tightly to engage with said movable valve member, said lower small-diameter bore portion in said lower housing member cooperating with the lower surface of said valve seat to define a valve chamber receiving said valve body, said valve chamber forming part of said fluid passage. 5. A piezoelectric hydraulic control valve according to claim 4, wherein said disc-like valve seat is provided at the lower surface thereof with an annular groove forming part of said fluid passage and wherein said movable valve member has a disc-like shape and is provided at the upper surface thereof with an annular projection cooperating with said annular groove to open and close said fluid passage. 6. A piezoelectric hydraulic control valve according to claim 5, wherein said disc-like valve member comprises a rounded central projection which is in point contact with said connecting means. 7. A piezoelectric hydraulic control valve according to claim 6, wherein the inner wall of said valve chamber in said lower housing member is provided with a plurality of spaced, axially-extending ribs to guide said valve member therealong. 8. A piezoelectric hydraulic control valve according to claim 1, further comprising means for relieving the pressurized fluid in said fluid passage downstream of said valve member at a relief rate which is less than the flow rate of the incoming fluid flowing into said inlet port so as to develop a rapid pressure drop at said outlet port as said valve member shuts off said fluid passage, and wherein said relieving means comprises a relief passage provided in said housing and communicating said fluid passage downstream of said valve member with the outside of said housing, and further comprises a relief valve provided in said relief passage. 9. A piezoelectric hydraulic control valve according to claim 8, wherein said relief valve is set to operate at a fluid pressure which is less than the fluid pressure at said inlet port. 10. A piezoelectric hydraulic control valve according to claim 9, wherein said relief valve comprises a relief valve member which is spring-biased toward the upstream of said relief passage to increase the relief rate as it is displaced downstream of said relief passage and stopper means to limit the maximum displacement of said relief valve member to restrict the maximum relief rate through said relief valve. 11. A piezoelectric hydraulic control valve according to claim 9, wherein said relief valve comprises a relief valve member which is spring-biased toward a neutral position thereof and which is adapted to decrease the relief rate as it is displaced downstream of said relief passage, whereby the relief rate is reduced in response to an increasing fluid pressure in said relief passage. 12. A piezoelectric hydraulic control valve according to claim 1, wherein said connecting means comprises a pumping piston received fluid-tightly and slidably within said expansible sleeve and defining a pumping chamber in said axially extending central bore of said housing at the side of said piston opposite to said piezoelectric column, said pumping chamber forming part of said fluid passage, said pumping piston being operable to be displaced in response to the piezoelectric deformation of said column as said column is activated and deactivated to pressurize and de-pressurize the fluid in said pumping chamber thereby to accelerate the pressure build-up and collapse at said outlet port. 13. A piezoelectric hydraulic control valve for controlling a high-pressure fluid, comprising: (a) a housing having an axially extending central bore and having an inlet port for receiving a high-pressure fluid and an outlet port for delivering said fluid and a fluid passage communicating said inlet and outlet ports; (b) a valve seat in said housing provided across said fluid passage and having an inside passage forming part of said fluid passage; (c) a movable valve member disposed upstream of said valve seat and cooperating with said valve seat to make and break communication between said inlet and outlet ports; (d) means for biasing said valve member against said valve seat; (e) a piezoelectric actuator received coaxially within said bore of said housing and having one end supported by said housing and the other end displaceable in response to energization of said actuator; (f) connecting means for transmitting the displacement of said other end of said piezoelectric actuator to said valve member; (g) a relief passage for connecting said fluid passage downstream of said valve member to the outside of said housing; and (h) a relief valve disposed in said relief passage for relieving the fluid in said fluid passage downstream of said valve member at a relief rate which is less than the incoming flow rate at said inlet port so that a substantial fluid pressure is built up at said outlet port as said valve member makes an open communication between said inlet and outlet ports but said fluid pressure at said outlet port is rapidly diminished due to fluid escaping through said relief passage as said valve member breaks said communication. 14. A piezoelectric hydraulic control valve according to claim 13, wherein said relief valve is adjusted to open at a fluid pressure which is less than the fluid pressure at said inlet port. 15. A piezoelectric hydraulic control valve according to claim 14, wherein said relief valve comprises a relief valve member spring-biased toward the upstream of said relief passage to increase the relief rate as said valve member is displaced downstream of said relief passage, said relief valve further comprising stopper means for limiting the maximum displacement of said relief valve member to restrict the maximum relief rate through said relief valve. 16. A piezoelectric hydraulic control valve according to claim 14, wherein said relief valve comprises a relief valve member which is spring-biased toward a neutral position thereof and which is adapted to reduce the relief rate as said valve member is displaced downstream of said relief passage under the action of fluid pressure so that the relief rate is reduced in reverse proportion to the fluid pressure in said fluid passage. 17. A piezoelectric hydraulic control valve comprising: (a) a housing having an axially-extending, closed-ended central bore and having an inlet and an outlet port; (b) a disc-like valve seat closely and fixedly fitted within said bore of said housing to divide said bore into an upper cavity and a lower cavity, said valve seat having at the lower surface thereof an annular groove open into said lower cavity, said valve seat having a central through-aperture; (c) a pumping piston slidably and fluid-tightly received in said upper cavity of said bore, said pumping piston having a cylindrical central projection extending fluid-tightly through said central aperture in said valve seat; (d) a pumping chamber defined in said upper cavity between said pumping piston and said valve seat; (e) a disc-like valve member in contact with said central projection of said pumping piston and received movably within said lower cavity of said bore of said housing for opening and closing said annular groove in said valve seat in response to the displacement of said pumping piston; (f) means disposed in said lower cavity of said bore for biasing said valve member into contact with said valve seat and said central projection; (g) a first passage in said housing for transmitting pressurized fluid at said inlet port into said lower cavity; (h) a second passage in said housing and said valve seat for transmitting pressurized fluid at said annular groove into said outlet port; (i) a third passage in said valve seat for communicating said annular groove with said pumping chamber; and (j) a piezoelectric actuator received coaxially within said upper cavity of said bore of said housing, said actuator being supported at the top thereof by said housing and at the bottom thereof by said pumping piston so that upon energization, said actuator expands axially causing said pumping piston to move downward to lift said valve member off of the associating valve seat against the action of said biasing means as well as to pressurize the fluid in said pumping chamber thereby accelerating the pressure rise at said outlet port, and, upon de-energization, said actuator contracts axially allowing said pumping piston to move upward under the action of said biasing means and the fluid pressure in said pumping chamber thereby allowing the valve member to close said annular groove and accelerating the collapse of fluid pressure at said outlet port. 18. A piezoelectric transducer for converting electric pulse into linear displacement, comprising: a housing having an axially-extending central bore; a column of piezoelectric elements received coaxially within said bore; means for applying a voltage to said piezoelectric column to induce piezoelectric deformation of said column in response to said voltage; output means connected to the lower end of said piezoelectric column for transmitting linear displacement due to piezoelectric deformation to the outside of said transducer; a thermally expansible sleeve, mounted within said bore concentrically around said piezoelectric column, having a coefficient of linear expansion equal to that of said piezoelectric column with the lower end of said sleeve beign fixedly supported by said housing and with the other portions thereof being loosely fitted within said bore to permit the upper end of said sleeve to displace axially in response to thermal expansion and contraction of said sleeve due to a variation in the ambient temperature; and movable supporting means, received movably within said bore of said housing and connected to the upper ends of said sleeve and said column, for compensating for expansion and contraction of said column due to ambient temperature variations by supporting said upper end of said column to displace conjointly with said upper end of said sleeve, whereby the expansion and contraction in one direction of said column due to ambient temperature variation compensates for the expansion and contraction in the opposite direction of said sleeve so that the relative position of said lower end of said column with respect to said housing is kept constant regardless of ambient temperature variations. 19. A piezoelectric hydraulic control valve, comprising: (a) a housing having an axially-extending, closed-ended central bore and having an inlet port for receiving pressurized fluid and an outlet port for delivering said pressurized fluid and a fluid passage communicating said inlet and said outlet port; (b) a valve seat in said housing and extending across said passage; (c) a movable valve member cooperating with said valve seat; (d) a column of piezoelectric material received coaxially within said bore and having an upper and a lower end; (e) means for applying a voltage to said piezoelectric column to induce axial expansion of said column; (f) connecting means provided between said lower end of said column and said valve member for transmitting axial expansion of said column to said valve member to thereby open and close said fluid passage; (g) a thermal expansible sleeve received within said bore and having an upper and a lower end, said lower end of said sleeve being fixedly supported by said housing but other portions of said sleeve being loosely fitted within said bore to permit said upper end of said sleeve to displace axially in response to thermal expansion of said sleeve due to a variation in the ambient temperature; and (h) movable supporting means received movably within said bore and attached to the upper end of said sleeve for supporting the upper end of said piezoelectric column in such a manner that is displaces together with the upper end of said sleeve, whereby the expansion and contraction in one direction of said sleeve compensates for the expansion and contraction, due to ambient temperature variation, in the opposite direction of said piezoelectric column so that the lower end of said column is maintained at a constant distance with respect to said valve member regardless of the temperature variation, said movable supporting means comprising a piston received fluid-tightly and slidably in said bore of said housing and defining a pressurizing chamber in said bore and wherein said housing is provided with a second fluid passage therein for transmitting the pressurized fluid in said first-mentioned fluid passage to said pressurizing chamber to pressurize said piston against said sleeve and said piezoelectric column to support said sleeve and said column together. 20. A piezoelectric hydraulic control valve according to claim 19, further comprising means for biasing said piston against said piezoelectric column. 21. A piezoelectric hydraulic control valve according to claim 20, wherein said biasing means comprises a Belleville washer disposed in said pressurizing chamber between said piston and an inner wall of said housing. 22. A piezoelectric hydraulic control valve according to claim 19, wherein said connecting means comprises a second piston received fluid-tightly and slidably within said sleeve and defining a second pressurizing chamber in said bore opposite said first-mentioned pressurizing chamber, said second pressurizing chamber being communicated with said first fluid passage via a third fluid passage to transmit the pressurized fluid into said second pressurizing chamber causing said second piston to pressurize said piezoelectric column in a direction opposite to the direction of action of said first piston thereby causing the elastic deformation which said sleeve undergoes due to said first piston under the action of fluid pressure in said first-mentioned pressurizing chamber to be counterbalanced by the elastic deformation which said piezoelectric column undergoes due to said second piston under the action of fluid pressure in said second pressurizing chamber so that the lower end of said column is maintained at a constant distance with respect to said valve member regardless of a variation in the fluid pressure. 23. A piezoelectric hydraulic control valve according to claim 22, wherein said expansible sleeve has an axial length equal to that of said piezoelectric column and wherein said sleeve has a coefficient of linear expansion and a modulus of longitudinal elasticity equal to those of said column. 24. A piezoelectric hydraulic control valve according to claim 23, wherein the transversal cross-sectional areas of said column, said second piston, said sleeve, and said first piston have a correlation expressed by the equation ##EQU##S 2 /S 1 =(S 4 -S 2 )/S 3 wherein S 1 is the transversal cross-sectional area of said column, S 2 is the transversal cross-sectional area of said second piston, S 3 is the transversal cross-sectional area of said sleeve, and S 4 is the transversal cross-sectional area of said first piston.