Patent Description:
Conventionally, pressure booster devices have been known which consecutively increase the pressure of pressurized fluid by means of reciprocating motion of pistons and then output the pressurized fluid.

For example, <CIT> discloses a pressure booster in which a pair of boosting cylinders having their respective pistons directly connected to a piston rod are arranged so as to face each other, and an energy collecting cylinder is provided between the pair of boosting cylinders. In this pressure booster, compressed air is supplied into the compressing chamber and operating chamber of one of the boosting cylinders and into the compressing chamber of the other boosting cylinder, and then the air supplied into the compressing chamber of that one boosting cylinder is boosted and outputted. Switching operation of air-supply between the boosting cylinders and of flow channels connected to the collecting cylinder is performed by reed switches detecting the positions of the pistons in the boosting cylinders to thereby turn on and off solenoids of a switching valve accordingly.

In the pressure booster of <CIT>, the pair of boosting cylinders each have the operating chamber for driving the piston and the compressing chamber for compressing the fluid. This may limit flexibility in design. In addition, since the reed switches and the solenoids are used to perform the switching operation, electrical means including electrical wiring is required.

Accordingly, the applicant of the present invention has filed a patent application of an invention relating to a pressure booster in which cylinders for driving the pistons and a cylinder for compressing pressurized fluid are separately arranged in an organized manner, and which is capable of performing switching operations without using electrical means (<CIT>).

The pressure booster of the above patent application includes driving cylinders provided respectively on both sides of a boosting cylinder, a pair of pilot valves each having a push rod with which the piston of the corresponding driving cylinder comes in contact at its travel end, and a pair of operating valves for switching the state of supply of the pressurized fluid from a pressurized fluid supply source to the pressurizing chambers of the individual driving cylinders.

<CIT> discloses a pressure booster in which drive cylinders are respectively disposed on one end side and the other side of a pressure boosting cylinder. The pressure booster includes sensors that detect a position of a drive piston, and knock pins are rendered unnecessary.

<CIT> discloses a device that comprises a low pressure cylinder, a pair of high pressure cylinders, a piston, a pair of control valves and a switching valve, in which a low pressure fluid supplied from a input port is boosted and outputted.

<CIT> Yl discloses a pressure booster that comprises a booster valve, pilot valves and a directional control valve, in which in the load stroke of a plunger, the plunger is operated by boosting a normal pressure of a pump.

With the pressure booster of the above patent application, force with which the piston of each driving cylinder pushes the push rod becomes weak, for example, when the output of the pressure booster has become close to saturation, and then the push rod may be disadvantageously returned by spring force without the pilot valve being sufficiently switched. The pressure booster was thus not completely satisfactory. The present invention has been devised considering such a situation, and an object of the present invention is to provide a pressure booster capable of reliably switching the pilot valves even when the pistons of the driving cylinders push the pilot valves with a weak force.

This problem is solved by the pressure booster according to claim <NUM>. Preferred embodiments of the invention are evident from the dependent claims.

According to the pressure booster above, a knock pin that has come in contact with the driving cylinder's piston can be pushed completely to the end by the certain fluid pressure, and the pilot valve can be kept in a fully switched position.

According to the pressure booster of the invention, the certain fluid pressure acts on the knock pins so as to keep the pilot valves in the fully switched positions. Accordingly, even if a driving cylinder's piston pushes the knock pin with a weak force, the knock pin can be pushed completely to the end and the pilot valve can be switched reliably.

pressure booster has changed from the state of <FIG> to another state.

The pressure booster of the present invention will be described below in detail in connection with preferred embodiments while referring to the accompanying drawings. A pressure booster <NUM> according to an embodiment of the invention is installed between a pressurized fluid supply source (compressor; not shown) and an actuator (not shown) that operates with the pressurized fluid whose pressure has been boosted.

As shown in <FIG> and <FIG>, the pressure booster <NUM> has a triple cylinder structure including a boosting cylinder <NUM>, a first driving cylinder <NUM> disposed at one end of the boosting cylinder <NUM> (an end on an A1 direction side), and a second driving cylinder <NUM> disposed at the other end of the boosting cylinder <NUM> (an end on an A2 direction side), which are connected in a row. That is, in the pressure booster <NUM>, the first driving cylinder <NUM>, the boosting cylinder <NUM>, and the second driving cylinder <NUM> are arranged in this order from the A1 direction to the A2 direction.

A first cover member <NUM> in the form of a block is interposed between the first driving cylinder <NUM> and the boosting cylinder <NUM>, and a second cover member <NUM> in the form of a block is interposed between the boosting cylinder <NUM> and the second driving cylinder <NUM>.

The boosting cylinder <NUM> includes a boosting chamber <NUM> therein, and the first driving cylinder <NUM> and the second driving cylinder <NUM> include a first driving chamber <NUM> and a second driving chamber <NUM> therein, respectively. In this case, a third cover member <NUM> is fixed at an end of the first driving cylinder <NUM> on the A1 side, and the first cover member <NUM> is disposed at an end thereof on the A2 side, thus forming the first driving chamber <NUM>. Also, the second cover member <NUM> is disposed at an end of the second driving cylinder <NUM> on the A1 side, and an end thereof on the A2 side is closed by a wall <NUM>, thus forming the second driving chamber <NUM>.

As shown in <FIG>, a piston rod <NUM> is provided to pass through the first cover member <NUM>, the boosting cylinder <NUM>, and the second cover member <NUM>. One end of the piston rod <NUM> extends into the first driving chamber <NUM>, and the other end of the piston rod <NUM> extends into the second driving chamber <NUM>.

In the boosting chamber <NUM>, a boosting piston <NUM> is coupled to a middle portion of the piston rod <NUM>. The boosting chamber <NUM> is thus partitioned into a first boosting chamber 22a on the A1 side and a second boosting chamber 22b on the A2 side (see <FIG>). In the first driving chamber <NUM>, a first driving piston <NUM> is coupled at one end of the piston rod <NUM>. The first driving chamber <NUM> is thus partitioned into a pressurizing chamber 24a on the A1 side and a back pressure chamber 24b on the A2 side (see <FIG>). Further, in the second driving chamber <NUM>, a second driving piston <NUM> is coupled to the other end of the piston rod <NUM>. The second driving chamber <NUM> is thus partitioned into a pressurizing chamber 26a on the A2 side and a back pressure chamber 26b on the A1 side (see <FIG>). The boosting piston <NUM>, the first driving piston <NUM>, and the second driving piston <NUM> are integrally connected through the piston rod <NUM>.

As shown in <FIG>, the boosting cylinder <NUM> includes, at an upper portion of the front surface, a supply port <NUM> to which a pressurized fluid is supplied from a pressurized fluid supply source (not shown). As shown in <FIG> and <FIG>, a fluid supply mechanism is provided in the interiors of the boosting cylinder <NUM>, the first cover member <NUM>, and the second cover member <NUM>. The fluid supply mechanism communicates with the supply port <NUM> and supplies the supplied pressurized fluid into the first boosting chamber 22a and the second boosting chamber 22b. The fluid supply mechanism includes a first supply passage 42a that allows the supply port <NUM> and the first boosting chamber 22a to communicate with each other, and a second supply passage 42b that allows the supply port <NUM> and the second boosting chamber 22b to communicate with each other.

The first supply passage 42a is provided with a first supply check valve 42c that permits the flow of fluid from the supply port <NUM> to the first boosting chamber 22a and blocks the flow of fluid from the first boosting chamber 22a to the supply port <NUM>. The second supply passage 42b is provided with a second supply check valve 42d that permits the flow of fluid from the supply port <NUM> to the second boosting chamber 22b and blocks the flow of fluid from the second boosting chamber 22b to the supply port <NUM>.

As shown in <FIG>, the boosting cylinder <NUM> includes an output port <NUM> formed in a lower portion of the front surface. Fluid whose pressure is boosted by boosting operation, which will be described later, is outputted from the output port <NUM> to the outside. As shown in <FIG> and <FIG>, a fluid output mechanism is provided in the interiors of the boosting cylinder <NUM>, the first cover member <NUM>, and the second cover member <NUM>. The fluid output mechanism communicates with the output port <NUM>, and outputs, from the output port <NUM>, fluid whose pressure has been boosted in the first boosting chamber 22a or the second boosting chamber 22b. The fluid output mechanism includes a first output passage 46a that allows the first boosting chamber 22a and the output port <NUM> to communicate with each other, and a second output passage 46b that allows the second boosting chamber 22b and the output port <NUM> to communicate with each other.

The first output passage 46a is provided with a first output check valve 46c that permits the flow of fluid from the first boosting chamber 22a to the output port <NUM> and blocks flow of fluid from the output port <NUM> to the first boosting chamber 22a. The second output passage 46b is provided with a second output check valve 46d that permits the flow of fluid from the second boosting chamber 22b to the output port <NUM> and blocks flow of fluid from the output port <NUM> to the second boosting chamber 22b.

Next, a configuration of the operating valves will be described. As shown in <FIG>, the first driving cylinder <NUM> includes, on an upper part thereof, a first housing <NUM> having a first operating valve <NUM>, and the second driving cylinder <NUM> includes, on an upper part thereof, a second housing <NUM> having a second operating valve <NUM>.

As shown in <FIG>, the first operating valve <NUM> has first to fifth ports 56A to 56E as points of connection and switching of passages. The first operating valve <NUM> is configured so as to be capable of switching between a first position for driving the first driving piston <NUM> and a second position for allowing the first driving piston <NUM> to follow movement of the second driving piston <NUM> being driven.

The first port 56A is connected to the pressurizing chamber 24a in the first driving cylinder <NUM> through a passage 58a. The second port 56B is connected to the back pressure chamber 24b in the first driving cylinder <NUM> through a passage 58b. The third port 56C is connected to the first supply passage 42a through a passage 58c. The fourth port 56D is connected through a passage 58d to a first silencer <NUM> having a discharge port. The fifth port 56E is connected to a midway point of the passage 58a through a passage 58e. The passage 58d has a first fixed orifice <NUM> interposed therein.

When the first operating valve <NUM> is in the first position, the first port 56A and the third port 56C communicate with each other, and the second port 56B and the fourth port 56D communicate with each other. Then, the pressurized fluid from the supply port <NUM> is supplied into the pressurizing chamber 24a through the passage 58c and passage 58a, and the fluid in the back pressure chamber 24b is discharged through the passage 58b and passage 58d and through the first fixed orifice <NUM> and the first silencer <NUM>.

When the first operating valve <NUM> is in the second position, the first port 56A and the fourth port 56D communicate with each other, and the second port 56B and the fifth port 56E communicate with each other. Then, part of the fluid in the pressurizing chamber 24a is collected into the back pressure chamber 24b through the passage 58a, passage 58e, and passage 58b, and the remaining part is discharged through the passage 58d and through the first fixed orifice <NUM> and the first silencer <NUM>.

The first operating valve <NUM> further includes a pilot port 56F for introducing a pilot pressure from a second pilot valve <NUM> which will be described later. The first operating valve <NUM> is in the first position when pressurized fluid (pilot pressure) is being supplied to the pilot port 56F, and it is in the second position when the pressurized fluid (pilot pressure) is not being supplied to the pilot port 56F.

The second operating valve <NUM> has first to fifth ports 64A to 64E as points of connection and switching of passages. The second operating valve <NUM> is configured so as to be capable of switching between a first position for driving the second driving piston <NUM> and a second position for allowing the second driving piston <NUM> to follow movement of the first driving piston <NUM> being driven.

The first port 64A is connected to the pressurizing chamber 26a in the second driving cylinder <NUM> through a passage 66a. The second port 64B is connected to the back pressure chamber 26b in the second driving cylinder <NUM> through a passage 66b. The third port 64C is connected to the second supply passage 42b through a passage 66c. The fourth port 64D is connected through a passage 66d to a second silencer <NUM> having a discharge port. The fifth port 64E is connected to a midway point of the passage 66a through a passage 66e. The passage 66d has a second fixed orifice <NUM> interposed therein.

When the second operating valve <NUM> is in the first position, the first port 64A and the third port 64C communicate with each other, and the second port 64B and the fourth port 64D communicate with each other. Then, the pressurized fluid from the supply port <NUM> is supplied into the pressurizing chamber 26a through the passage 66c and passage 66a, and the fluid in the back pressure chamber 26b is discharged through the passage 66b and passage 66d and through the second fixed orifice <NUM> and the second silencer <NUM>.

When the second operating valve <NUM> is in the second position, the first port 64A and the fourth port 64D communicate with each other, and the second port 64B and the fifth port 64E communicate with each other. Then, part of the fluid in the pressurizing chamber 26a is collected into the back pressure chamber 26b through the passage 66a, passage 66e, and passage 66b, and the remaining part is discharged through the passage 66d and through the second fixed orifice <NUM> and the second silencer <NUM>.

The second operating valve <NUM> further includes a pilot port 64F for introducing a pilot pressure from a first pilot valve <NUM> which will be described later. The second operating valve <NUM> is in the first position when pressurized fluid (pilot pressure) is being supplied to the pilot port 64F, and it is in the second position when the pressurized fluid (pilot pressure) is not being supplied to the pilot port 64F.

Next, a configuration of the pilot valves will be described. The first pilot valve <NUM> is provided inside the first cover member <NUM>, and the second pilot valve <NUM> is provided inside the second cover member <NUM>.

The first pilot valve <NUM> has first to fourth ports 76A to 76D. The first pilot valve <NUM> is configured to be capable of switching between a first position for generating the pilot pressure for the second operating valve <NUM> and a second position for eliminating the pilot pressure.

The first port 76A is connected to the pilot port 64F of the second operating valve <NUM> through a first pilot passage 78b. The second port (supply port) 76B is connected to the first supply passage 42a through a passage 78a. The third port 76C constitutes a discharge port. The fourth port (cooperation port) 76D is connected to a first port 80A of the second pilot valve <NUM>, which will be described later, through a branch passage 82c and a second pilot passage 82b described later. Further, a branch passage 78c connecting to a fourth port 80D of the second pilot valve <NUM>, which will be described later, branches off from the first pilot passage 78b.

When the first pilot valve <NUM> is in the first position, the first port 76A and the second port 76B communicate with each other. Then, the pressurized fluid from the supply port <NUM> is supplied to the pilot port 64F of the second operating valve <NUM> through the passage 78a and the first pilot passage 78b, and the pressurized fluid is also supplied to the fourth port 80D of the second pilot valve <NUM> (described later) through the branch passage 78c branching off from the first pilot passage 78b.

When the first pilot valve <NUM> is in the second position, the first port 76A and the third port 76C communicate with each other. Then, the pressurized fluid that has been being supplied to the pilot port 64F of the second operating valve <NUM> is discharged through the first pilot passage 78b, and the pressurized fluid supplied to the fourth port 80D of the second pilot valve <NUM> is discharged through the branch passage 78c and first pilot passage 78b.

The second pilot valve <NUM> has first to fourth ports 80A to 80D. The second pilot valve <NUM> is configured to be capable of switching between a first position for generating the pilot pressure for the first operating valve <NUM> and a second position for eliminating the pilot pressure.

The first port 80A is connected to the pilot port 56F of the first operating valve <NUM> through the second pilot passage 82b. The second port (supply port) 80B is connected to the second supply passage 42b through a passage 82a. The third port 80C constitutes a discharge port. The fourth port 80D (cooperation port) is connected to the first port 76A of the first pilot valve <NUM> through the branch passage 78c and the first pilot passage 78b. Further, the branch passage 82c connecting to the fourth port 76D of the first pilot valve <NUM> branches off from the second pilot passage 82b.

When the second pilot valve <NUM> is in the first position, the first port 80A and the second port 80B communicate with each other. Then, the pressurized fluid from the supply port <NUM> is supplied to the pilot port 56F of the first operating valve <NUM> through the passage 82a and second pilot passage 82b, and the pressurized fluid is also supplied to the fourth port 76D of the first pilot valve <NUM> through the branch passage 82c branching off from the second pilot passage 82b.

When the second pilot valve <NUM> is in the second position, the first port 80A and the third port 80C communicate with each other. Then, the pressurized fluid that has been being supplied to the pilot port 56F of the first operating valve <NUM> is discharged through the second pilot passage 82b, and the pressurized fluid supplied to the fourth port 76D of the first pilot valve <NUM> is discharged through the branch passage 82c and second pilot passage 82b.

Now, referring to <FIG>, a specific structure of the first pilot valve <NUM> will be described. The second pilot valve <NUM> has the same structure as the first pilot valve <NUM>, and so it will not be described herein.

The first pilot valve <NUM> includes a valve seat <NUM> accommodated in a valve container hole <NUM> formed in the first cover member <NUM>, a valve seat retainer <NUM>, and a knock pin <NUM>. The valve container hole <NUM> is closed on the side of the boosting cylinder <NUM> and opens on the side of the first driving cylinder <NUM>. The valve container hole <NUM> includes, at the closed end, a large-diameter hole portion 84a, and the fourth port 76D communicates with this large-diameter hole portion 84a.

The valve container hole <NUM> further has a small-diameter hole portion 84b connecting to the large-diameter hole portion 84a, and a medium-diameter hole portion 84c disposed on the opening side of the valve container hole and connecting to the small-diameter hole portion 84b. The first port 76A, the second port 76B, and the third port 76C communicate with the small-diameter hole portion 84b of the valve container hole <NUM>. Of these three ports, the second port 76B is located closest to the fourth port 76D, and the third port 76C is located farthest from the fourth port 76D.

The valve seat <NUM> having a thin-walled cylindrical shape, and the valve seat retainer <NUM> having a thick-walled cylindrical shape, are inserted and fitted into the small-diameter hole portion 84b of the valve container hole <NUM>. The valve seat retainer <NUM> includes one end surface located at one end in the axial direction and another end surface located at the other end in the axial direction, the one end surface facing toward the back pressure chamber 24b of the first driving cylinder <NUM>, the other end surface abutting against the valve seat <NUM>. A snap ring <NUM> abutting on the valve seat retainer <NUM> is fixed to the medium-diameter hole portion 84c of the valve container hole <NUM>. The valve seat <NUM> and the valve seat retainer <NUM> are thus positioned and fixed in the axial direction inside the valve container hole <NUM>. The valve seat <NUM> is engaged and locked with a step formed at a middle position of the small-diameter hole portion 84b.

An annular groove 86a facing the first port 76A is formed in the outer periphery of a middle portion of the valve seat <NUM> in the axial direction, and an annular recess 86b facing the third port 76C is formed in the outer periphery of an end of the valve seat <NUM> in the axial direction on a side that abuts on the valve seat retainer <NUM>. The annular groove 86a of the valve seat <NUM> communicates with the inner peripheral side of the valve seat <NUM> through a first through hole 86c that penetrates through the valve seat <NUM> in the radial direction, and the annular recess 86b of the valve seat <NUM> communicates with the inner peripheral side of the valve seat <NUM> through a second through hole 86d that penetrates through the valve seat <NUM> in the radial direction.

A first seal member 94a and a second seal member 94b that abut against the small-diameter hole portion 84b of the valve container hole <NUM> are fitted into grooves formed in the outer peripheral surface of the valve seat <NUM>. The first seal member 94a prevents the first port 76A and the second port 76B from communicating with each other through the gap between the valve seat <NUM> and the valve container hole <NUM>, and the second seal member 94b prevents the first port 76A and the third port 76C from communicating with each other through the gap between the valve seat <NUM> and the valve container hole <NUM>.

A third seal member 96a abutting against the small-diameter hole portion 84b of the valve container hole <NUM> is fitted into a groove formed in the outer peripheral surface of the valve seat retainer <NUM>, and a fourth seal member 96b in sliding contact with the knock pin <NUM> is fitted into a groove formed in the inner peripheral surface of the valve seat retainer <NUM>. The third seal member 96a and the fourth seal member 96b provide a seal between the third port 76C and the back pressure chamber 24b of the first driving cylinder <NUM>.

The knock pin <NUM> has a large-diameter shaft portion 90a, a medium-diameter shaft portion 90b, and a small-diameter shaft portion 90c. The large-diameter shaft portion 90a is inserted and fitted into the small-diameter hole portion 84b of the valve container hole <NUM>. The medium-diameter shaft portion 90b is inserted and fitted into the inside of the valve seat <NUM> in such a manner that part of the shaft portion 90b protrudes from the valve seat <NUM>, and the part protruding from the valve seat <NUM> faces the small-diameter hole portion 84b of the valve container hole <NUM> at a certain interval in the radial direction. The small-diameter shaft portion 90c is inserted and fitted into the inside of the valve seat retainer <NUM>.

A first packing 98a in sliding contact with the small-diameter hole portion 84b of the valve container hole <NUM> is fitted into a groove formed in the large-diameter shaft portion 90a of the knock pin <NUM>. The first packing 98a provides a seal between the second port 76B and the fourth port 76D. A second packing 98b and a third packing 98c that can be in sliding contact with the inner peripheral surface of the valve seat <NUM> are fitted into grooves formed in the medium-diameter shaft portion 90b of the knock pin <NUM>. The outer periphery of the medium-diameter shaft portion 90b of the knock pin <NUM> has, formed therein, an annular groove 90d between the portion where the second packing 98b is fitted and the portion where the third packing 98c is fitted.

The knock pin <NUM> can slide between a position where its end on the large-diameter shaft portion 90a side contacts the bottom surface (closed end surface) of the valve container hole <NUM> and a position where a step surface 90e between the medium-diameter shaft portion 90b and the small-diameter shaft portion 90c contacts the end surface of the valve seat retainer <NUM>. When the knock pin <NUM> contacts the end surface of the valve seat retainer <NUM>, the length that the small-diameter shaft portion 90c of the knock pin <NUM> projects into the back pressure chamber 24b of the first driving cylinder <NUM> (hereinafter referred to as "projecting length of the knock pin") becomes the maximum. The first driving piston <NUM> comes in contact with the end of the knock pin <NUM> on its small-diameter shaft portion 90c side and presses the knock pin <NUM> in the direction toward the bottom surface of the valve container hole <NUM>.

The annular groove 90d of the knock pin <NUM> communicates with the annular groove 86a through the first through hole 86c in the valve seat <NUM>, irrespective of the projecting length of the knock pin <NUM>. In other words, the annular groove 90d of the knock pin <NUM> always communicates with the first port 76A irrespective of the position of the knock pin <NUM>. Further, the second port 76B always communicates with the gap formed between the medium-diameter shaft portion 90b of the knock pin <NUM> and the small-diameter hole portion 84b of the valve container hole <NUM>.

When the projecting length of the knock pin <NUM> is large, the second packing 98b contacts the inner surface of the valve seat <NUM>, and the third packing 98c separates away from the inner surface of the valve seat <NUM> (see <FIG>). Accordingly, the first port 76A communicates with the third port 76C through the gap between the inner surface of the valve seat <NUM> and the knock pin <NUM> including the annular groove 90d of the knock pin <NUM>, and through the second through hole 86d and the annular recess 86b of the valve seat <NUM>.

When the first driving piston <NUM> comes in contact with the knock pin <NUM> and the projecting length of the knock pin <NUM> becomes somewhat shorter than in the state described above, then both the second packing 98b and the third packing 98c contact the inner surface of the valve seat <NUM> (see <FIG>). Accordingly, the first port 76A does not communicate with either of the second port 76B and the third port 76C.

When the projecting length of the knock pin <NUM> is small, the second packing 98b separates away from the inner surface of the valve seat <NUM> and the third packing 98c contacts the inner surface of the valve seat <NUM> (see <FIG>). Accordingly, the first port 76A communicates with the second port 76B through the gap between the inner surface of the valve seat <NUM> and the knock pin <NUM> including the annular groove 90d of the knock pin <NUM> and through the gap formed between the medium-diameter shaft portion 90b of the knock pin <NUM> and the small-diameter hole portion 84b of the valve container hole <NUM>.

When the pressurized fluid is supplied into the fourth port 76D, then the knock pin <NUM> is pushed in such a direction that its projecting length increases. This is because the area (pressure receiving area) on which the fluid pressure at the fourth port 76D acts in the direction to increase the projecting length of the knock pin <NUM> is larger than the area (pressure receiving area) on which the fluid pressure at the second port 76B acts in the direction to reduce the projecting length of the knock pin <NUM>.

On the other hand, when the pressurized fluid is not supplied into the fourth port 76D, then the knock pin <NUM> is pressed in such a direction that its projecting length decreases. This is because the fluid pressure at the fourth port 76D acting in the direction to increase the projecting length of the knock pin <NUM> disappears, while the fluid pressure at the second port 76B acting in the direction to reduce the projecting length of the knock pin <NUM> is maintained.

The pressure booster <NUM> of the first embodiment of the present invention is configured basically as described above. Next, its operations, and functions and effects will be described. As shown in <FIG>, it is assumed that, in the initial position, the first operating valve <NUM> has switched to the second position, the second operating valve <NUM> has switched to the first position, and the boosting piston <NUM> is positioned close to the center in the boosting chamber <NUM>. In the description below, in order to distinguish the knock pin of the first pilot valve <NUM> and the knock pin of the second pilot valve <NUM>, the former will be referred to as "knock pin <NUM>-<NUM>" and the latter will be referred to as "knock pin <NUM>-<NUM>". Further, in order to distinguish the valve container hole of the first pilot valve <NUM> and the valve container hole of the second pilot valve <NUM>, the former will be referred to as "valve container hole <NUM>-<NUM>" and the latter will be referred to as "valve container hole <NUM>-<NUM>".

In this initial position, the pressurized fluid is supplied from the pressurized fluid supply source to the supply port <NUM>, and then the pressurized fluid flows into the first supply passage 42a and the second supply passage 42b. Then, the pressurized fluid is introduced into the first boosting chamber 22a and the second boosting chamber 22b of the boosting cylinder <NUM> through the first supply check valve 42c and the second supply check valve 42d.

Part of the pressurized fluid supplied from the supply port <NUM> is supplied into the pressurizing chamber 26a in the second driving cylinder <NUM> through the passage 66c, the second operating valve <NUM> being in the first position, and the passage 66a. The pressurized fluid supplied into the pressurizing chamber 26a drives the second driving piston <NUM> in the A1 direction. Then, the boosting piston <NUM>, which is integrally coupled to the second driving piston <NUM>, slides to boost the pressure of the pressurized fluid in the first boosting chamber 22a of the boosting cylinder <NUM>. The boosted pressurized fluid is guided through the first output passage 46a and the first output check valve 46c to the output port <NUM> and is outputted therefrom.

On the other hand, the first driving piston <NUM>, which is integrally coupled to the second driving piston <NUM>, slides, and then the volume of the pressurizing chamber 24a in the first driving cylinder <NUM> becomes small. Since the first operating valve <NUM> is in the second position, part of the pressurized fluid in the pressurizing chamber 24a is collected into the back pressure chamber 24b through the passage 58a, passage 58e, and passage 58b, and the remaining part thereof is discharged through the passage 58d.

As explained earlier, in the process in which the boosting piston <NUM> moves from the initial position to a certain distance in the A1 direction, the first pilot valve <NUM> is in the first position and so the pressurized fluid from the supply port <NUM> is being supplied to the fourth port 80D of the second pilot valve <NUM> through the first pilot valve <NUM>. On the other hand, the second pilot valve <NUM> is in the second position, and so the pressurized fluid is not supplied to the fourth port 76D of the first pilot valve <NUM>. Accordingly, in the first pilot valve <NUM>, the knock pin <NUM>-<NUM> is urged in the direction to reduce the projecting length of the knock pin <NUM>-<NUM>, and therefore the first pilot valve <NUM> is stably kept in the first position. On the other hand, in the second pilot valve <NUM>, the knock pin <NUM>-<NUM> is urged in the direction to increase the projecting length of the knock pin <NUM>-<NUM>, and therefore the second pilot valve <NUM> is stably kept in the second position.

Then, as shown in <FIG>, in the vicinity of the stroke end of the displacement of the boosting piston <NUM> in the A1 direction, the second driving piston <NUM> comes in contact with the knock pin <NUM>-<NUM> of the second pilot valve <NUM>. The knock pin <NUM>-<NUM> is pushed and displaced by the second driving piston <NUM>, causing the first port 80A and the second port 80B of the second pilot valve <NUM> to communicate with each other. Then, the pressurized fluid from the supply port <NUM> is supplied to the pilot port 56F of the first operating valve <NUM> through the second pilot passage 82b, and also supplied to the fourth port 76D of the first pilot valve <NUM> through the branch passage 82c. This causes the first operating valve <NUM> to switch to the first position and the first pilot valve <NUM> to switch to the second position.

When the first pilot valve <NUM> has switched to the second position, the pressurized fluid that was being supplied to the pilot port 64F of the second operating valve <NUM> flows through the first pilot passage 78b and is then discharged from the third port 76C of the first pilot valve <NUM>. This causes the second operating valve <NUM> to switch to the second position.

Further, when the first pilot valve <NUM> has switched to the second position, the pressurized fluid that was being supplied to the fourth port 80D of the second pilot valve <NUM> is discharged from the third port 76C of the first pilot valve <NUM> through the branch passage 78c and the first pilot passage 78b. Accordingly, in the second pilot valve <NUM>, the fluid pressure acts in the direction to reduce the projecting length of the knock pin <NUM>-<NUM>. Then, the knock pin <NUM>-<NUM>, which has been pushed by the second driving piston <NUM> and displaced to a position at which the first port 80A and the second port 80B of the second pilot valve <NUM> communicate with each other, is further subjected to the fluid pressure, and is kept in the position in which the knock pin <NUM>-<NUM> abuts against the bottom surface of the valve container hole <NUM>-<NUM>. That is, the second pilot valve <NUM> is stably kept in the first position. The state in which the second pilot valve <NUM> is kept in the first position is maintained until the first driving piston <NUM> is driven in the A2 direction and displaces the knock pin <NUM>-<NUM>, as will be described later.

This time, part of the pressurized fluid supplied from the supply port <NUM> is supplied into the pressurizing chamber 24a in the first driving cylinder <NUM> through the passage 58c, the first operating valve <NUM> being in the first position, and the passage 58a. The pressurized fluid supplied into the pressurizing chamber 24a drives the first driving piston <NUM> in the A2 direction. This causes the boosting piston <NUM>, which is integrally coupled to the first driving piston <NUM>, to slide to boost the pressure of the pressurized fluid in the second boosting chamber 22b of the boosting cylinder <NUM>. The boosted pressurized fluid is guided through the second output passage 46b and the second output check valve 46d to the output port <NUM> and is outputted therefrom.

On the other hand, the second driving piston <NUM>, which is integrally coupled to the first driving piston <NUM>, slides, and then the volume of the pressurizing chamber 26a in the second driving cylinder <NUM> becomes small. Since the second operating valve <NUM> is in the second position, part of the pressurized fluid in the pressurizing chamber 26a is collected into the back pressure chamber 26b through the passage 66a, passage 66e, and passage 66b, and the remaining part thereof is discharged through the passage 66d.

Then, in the vicinity of the stroke end of the displacement of the boosting piston <NUM> in the A2 direction, the first driving piston <NUM> comes in contact with the knock pin <NUM>-<NUM> of the first pilot valve <NUM>. The knock pin <NUM>-<NUM> is pressed and displaced by the first driving piston <NUM>, causing the first port 76A and the second port 76B of the first pilot valve <NUM> to communicate with each other. Then, the pressurized fluid from the supply port <NUM> is supplied to the pilot port 64F of the second operating valve <NUM> through the first pilot passage 78b, and also supplied to the fourth port 80D of the second pilot valve <NUM> through the branch passage 78c. This causes the second operating valve <NUM> to switch to the first position and the second pilot valve <NUM> to switch to the second position.

When the second pilot valve <NUM> has switched to the second position, the pressurized fluid that was being supplied to the pilot port 56F of the first operating valve <NUM> is discharged from the third port 80C of the second pilot valve <NUM> through the second pilot passage 82b. This causes the first operating valve <NUM> to switch to the second position.

Further, when the second pilot valve <NUM> has switched to the second position, the pressurized fluid that was being supplied to the fourth port 76D of the first pilot valve <NUM> is discharged from the third port 80C of the second pilot valve <NUM> through the branch passage 82c and the second pilot passage 82b. Accordingly, in the first pilot valve <NUM>, the fluid pressure acts in the direction to reduce the projecting length of the knock pin <NUM>-<NUM>. Then, the knock pin <NUM>-<NUM>, which was pushed by the first driving piston <NUM> and displaced to a position at which the first port 76A and the second port 76B of the first pilot valve <NUM> communicate with each other, is further subjected to the fluid pressure, and is kept in the position in which the knock pin <NUM>-<NUM> abuts on the bottom surface of the valve container hole <NUM>-<NUM>. That is, the first pilot valve <NUM> is stably kept in the first position. The state in which the first pilot valve <NUM> is kept in the first position is maintained until the second driving piston <NUM> is driven again in the A1 direction and displaces the knock pin <NUM>-<NUM>. After this, in the same way, the boosting piston <NUM> repeats the reciprocating movement and the boosted pressurized fluid is continuously outputted from the output port <NUM>.

According to the pressure booster <NUM> of the embodiment, the knock pin <NUM>-<NUM> is pushed by the first driving piston <NUM> and displaced to such a position as to cause the first port 76A and the second port 76B of the first pilot valve <NUM> to communicate with each other, then the knock pin <NUM>-<NUM> is further pushed by a certain fluid pressure to a position where the knock pin <NUM>-<NUM> abuts on the bottom surface of the valve container hole <NUM>-<NUM>, and as a result, the knock pin <NUM>-<NUM> can be kept in this position. In the same way, after the knock pin <NUM>-<NUM> is pushed by the second driving piston <NUM> and displaced to such a position as to cause the first port 80A and the second port 80B of the second pilot valve <NUM> to communicate with each other, the knock pin <NUM>-<NUM> is further pushed by a certain fluid pressure to a position where the knock pin <NUM>-<NUM> abuts on the bottom surface of the valve container hole <NUM>-<NUM>, and as a result, the knock pin <NUM>-<NUM> can be kept in this position.

Further, the first operating valve <NUM> switches to the first position when the pilot pressure is supplied from the second pilot valve <NUM> configured to switch its position in cooperation with the first pilot valve <NUM>, and the first operating valve <NUM> switches to the second position when the supply of the pilot pressure from the second pilot valve <NUM> disappears. In the same way, the second operating valve <NUM> switches to the first position when the pilot pressure is supplied from the first pilot valve <NUM> configured to switch its position in cooperation with the second pilot valve <NUM>, and the second operating valve <NUM> switches to the second position when the supply of the pilot pressure from the first pilot valve <NUM> disappears. Thus, the first operating valve <NUM> and the second operating valve <NUM> operate stably and switch at the same time.

Further, part of the fluid that was supplied into the pressurizing chamber 24a in order to drive the first driving piston <NUM> is collected into the back pressure chamber 24b when the first driving piston <NUM> is driven in conjunction with movement of the second driving piston <NUM>, and thus it is possible to reduce the consumption of the pressurized fluid. In the same way, part of the fluid that was supplied into the pressurizing chamber 26a in order to drive the second driving piston <NUM> is collected into the back pressure chamber 26b when the second driving piston <NUM> is driven in conjunction with movement of the first driving piston <NUM>, and thus it is possible to reduce the consumption of the pressurized fluid.

Claim 1:
A pressure booster in which driving cylinders (<NUM>, <NUM>) are provided respectively on both sides of a boosting cylinder (<NUM>), comprising a pair of operating valves (<NUM>, <NUM>) each configured to switch a state of supply of a pressurized fluid from a pressurized fluid supply source into a pressurizing chamber (24a, 26a) of a corresponding one of the driving cylinders, characterized in that the pressure booster comprises a pair of pilot valves (<NUM>, <NUM>) each including a knock pin (<NUM>) with which a piston (<NUM>, <NUM>) of a corresponding one of the driving cylinders comes in contact at a travel end of the piston,
wherein, when one or another of the pilot valves switches to a first position by the knock pin of the pilot valve being pushed by the corresponding piston, then a state of supply of the pressurized fluid to the pair of operating valves is switched and a certain fluid pressure acts on the knock pin so as to hold the pilot valve in the first position.