Abstract: The linear compressor for compressing and expanding working fluid contained in a regenerative refrigerator is composed of a compressor casing in which a pair of pistons are disposed and a plurality of electromagnets for driving the pair of pistons. A pair of rods for driving the pair of pistons are also disposed in the compressor casing, and permanent magnets are mounted on the driving rods. The plurality of electromagnets are disposed outside of the compressor casing along the axis of the driving rods so that the electromagnets face the permanent magnets. The pair of driving rods are driven by magnetic force between the permanent magnets and the electromagnets which are excited by alternating current. The linear compressor can be made small in size and heat generated in the electromagnets can be easily dissipated, because the electromagnets are disposed outside of the compressor casing.

Abstract: To improve cooling efficiency of a pulse tube refrigerator, it is found that creating two conditions in the refrigerator, particularly in a regenerator is effective. In a first condition, working fluid in the regenerator should be compressed or expanded without having any displacement thereof, while it should be displaced without compression or expansion in a second condition. In order to realize this idea, a fluid displacement control valve assembly including two relief valves is disposed between a pulse tube and a buffer tank. Each of the relief valves is a normally closed one-way valve, and the valves open in opposite directions to one another when a pressure difference between the pulse tube and the buffer tank reaches a predetermined value, thus allowing the working fluid to be displaced after its compression from the pulse tube to the buffer tank and after its expansion from the buffer tank to the pulse tube.

Abstract: To improve refrigerating efficiency by preventing working fluid flowing into a pulse tube from a high-temperature end side thereof from reaching a cooling part in a cryogenic refrigerator, a ball-shaped travel member which has almost the same cross-section as the cross section of the pulse tube is inserted into the pulse tube and moves together with the working fluid therein. In this arrangement, when the working fluid begins to flow into the pulse tube from a flow rate regulation part on the high-temperature end side of the pulse tube, the travel member located within the pulse tube moves toward a cooling part together with the working fluid flowing in the pulse tube. Since the travel member has almost the same cross-section as the cross-section of the pulse tube, there is no possibility that the working fluid flows through between the inner wall of the pulse tube and the travel member.

Abstract: A variable-damping-force shock absorber includes a piezoelectric actuator for producing a displacement, a hydraulic pressure chamber filled with a working oil and having a volume variable in response to the displacement produced by said piezoelectric actuator, and a plunger slidably disposed in a sleeve and reciprocally movable in response to a change in the volume of said hydraulic pressure chamber. The sleeve and said plunger define therebetween a gap communicating with said hydraulic pressure chamber. A supply passage for supplying a working oil from an external working oil source into said hydraulic pressure chamber extends through the gap. A leakage of the working oil from the hydraulic pressure chamber through the gap can automatically be compensated for by working oil supplied through the supply passage. Since the working oil leaks from and is supplied into the hydraulic pressure chamber through the gap, the leakage and supply of the working oil are kept in equilibrium.

Abstract: A damping force detecting apparatus for detecting a damping force of a variable damping force type shock absorber including a cylinder and a piston slidably inserted thereinto. The damping force detecting apparatus comprises a piezoelectric element assembly for generating a charge corresponding to a pressure applied thereto and a pressurizing device for pressurizing the piezoelectric element assembly. The piezoelectric element assembly has a diameter smaller than a cylindrical piston rod fixedly secured to the piston and is housed therein. The pressurizing device is screwed into the piston rod so as to be in contact relation to the piezoelectric element assembly for pressurizing the piezoelectric element assembly in correspondance with a distortion of the piston rod generated in the sliding directions of the piston with respect to the cylinder due to expanding and contracting action of the shock absorber.

Abstract: A shock absorber which selectively produces different magnitudes of damping forces includes a cylinder and a piston slidably disposed in the cylinder and dividing an interior space of the cylinder into first and second fluid chambers filled with a fluid. A housing assembly coupled to the piston has a main fluid passage providing fluid communication between the first and second fluid chambers at all times and an auxiliary fluid passage providing selective fluid communication between the first and second fluid chambers. The auxiliary fluid passage can be opened to provide fluid communication between the first and second fluid chamber in response to an external control signal. The auxiliary fluid passage can be closed to cut off fluid communication between the first and second fluid chambers when the speed of relative movement of the cylinder and the piston is substantially zero, i.e., when the speed of expansion and contraction of the shock absorber is substantially zero.