JPH06286986A - Hydraulic jack - Google Patents

Abstract

PURPOSE:To perform the decrease of a force required for operation of an operation handle when a high load is exerted on a ram and to perform the increase of a rise amount of the ram per one action of an operation handle when a low load is exerted on the ram. CONSTITUTION:A hydraulic jack comprises first and second oil passages 32 and 35 through which an oil tank 2 and a ram cylinder 3 are intercommunicated; a third oil passage through which a first oil passage 32 is communicated with the small inside diameter part 7b of a pump cylinder 7; a fourth oil passage 48 through which the second oil passage 35 is communicated with the large inside diameter part 7a of the pump cylinder 7; a fifth oil passage 69 through which the first oil passage 32 is communicated with the second oil passage 35; and a sixth oil passage 76 through which the second oil passage 35 is communicated with the oil tank 2. A pressure control valve 78 is provided for being opened when a pressure in the first oil passage 32 exceeds a given value and returning oil in the second oil passage 35 to the oil tank 2 through the sixth oil passage 76.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic jack used in, for example, a hand pallet truck.

[0002]

2. Description of the Related Art As a manual hydraulic jack that is manually operated to lift and lower a luggage loading fork of a hand pallet truck, a ram is provided by switching a hydraulic jack switching operation lever to a ram raised position, a ram neutral position and a ram lowered position. It is known that it is possible to switch among three stages of rising, neutral, and falling (for example, actual Kaihei 4-
105090). With this hydraulic jack, the operating lever is switched to the raised position, and in this state the ram is raised by operating the hydraulic jack operating handle to raise the luggage loading fork, and the ram is switched by switching the operating lever to the lowered position. It is lowered and the fork for loading luggage is lowered. Further, when the operation lever is switched to the neutral position, the ram does not move up and down even if the operation handle is operated, and the luggage loading fork can be held at the fixed position.

[0003]

However, in the conventional hydraulic jack, when the amount of rise of the ram per operation of the operation handle is increased, the fork can be raised with a small number of operations. When a heavy object is loaded on the, an extremely large force is required to operate the operation handle. On the other hand, in order to reduce the force required to operate the operation handle, it is necessary to reduce the amount of rise of the ram per operation of the operation handle, and even when a lightweight object is loaded on the fork, There is a problem that the number of operations of the operation handle is increased and it takes time to raise the required amount of the ram.

An object of the present invention is to provide a hydraulic jack that solves the above problems.

[0005]

A hydraulic jack according to the present invention comprises an oil tank, a pump cylinder having two large and small inner diameters, and a large diameter slidably and closely fitted in the large inner diameter of the pump cylinder. Section and a plunger having a small diameter portion slidably and closely fitted in the small inner diameter portion of the pump cylinder, a ram cylinder, a ram slidably fitted in the ram cylinder, an oil tank and a ram cylinder The first and second oil passages communicating with each other are communicated with the intermediate portion of the first oil passage and the small inner diameter portion of the pump cylinder, and the opening on the first oil passage side serves as the high-pressure side pump port. An oil passage, and a fourth oil passage that communicates the intermediate portion of the second oil passage and the large inner diameter portion of the pump cylinder and has a second oil passage-side opening that serves as a low-pressure side pump port. 1 A suction neutral valve is provided in a portion of the oil passage between the oil tank and the high pressure side pump port, and a discharge lowering valve is provided in a portion between the high pressure side pump port and the ram cylinder. A valve switching member is movably arranged in the part on the oil tank side of the suction neutral dual-purpose valve so that the valve switching member does not interfere with the suction neutral dual-purpose valve and the discharge lower-purpose dual-purpose valve. Is forcibly opened to a ram neutral position, and the suction neutral valve and the discharge descending / combining valve are forcibly opened to a ram lower position. The oil tank and the low pressure side pump port in the second oil passage are connected to each other. A suction valve is provided in a portion between the first low pressure side pump port and the ram cylinder, and a first spring-loaded check valve that opens only to the ram cylinder side is provided in the first portion. A fifth oil passage that connects the intermediate portion of the two valves in the passage and the intermediate portion of the two valves in the second oil passage is provided, and the fifth oil passage opens only on the first oil passage side. The second spring-loaded check valve is provided, and the spring force of the second spring-loaded check valve is smaller than the spring force of the first spring-loaded check valve.
A part of the oil passage between the low-pressure side pump port and the first spring-loaded check valve for communicating with the oil tank
Is provided, and when the pressure in the first oil passage exceeds a predetermined value, a pressure control valve that opens to return the oil in the second oil passage to the oil tank via the sixth oil passage is provided. It is equipped.

[0006]

[Operation] With the valve switching member switched to the ram rising position,
When the plunger of the plunger pump is raised, the oil in the oil tank passes through the suction neutral valve of the first oil passage, flows into the third oil passage through the high pressure side pump port, and passes through this oil passage. It is sucked into the small inner diameter part of the pump cylinder, passes through the suction valve of the second oil passage, flows into the fourth oil passage through the low pressure side pump port, and passes through this oil passage into the large inner diameter portion of the pump cylinder. Be sucked. Then, when the plunger is lowered, the oil in the small inner diameter part of the pump cylinder is
It passes through the third oil passage and returns to the first oil passage through the high-pressure side pump port, and is sent into the ram cylinder through the discharge descending / combining valve. Further, the oil in the large inner diameter portion of the pump cylinder returns to the second oil passage through the fourth oil passage and the low pressure side pump port, and then passes through the first spring loaded check valve into the ram cylinder. Sent in. When a small load is applied to the ram, the oil inside the large and small inner diameters of the pump cylinder is fed into the ram cylinder as described above.
When the plunger descends once, the amount of rise of the ram increases. When a large load is applied to the ram, the pressure in the first oil passage exceeds a predetermined value, so the pressure control valve opens and the oil sent from the large inner diameter part of the pump cylinder is
It is returned to the oil tank through the oil passage. Therefore, the ram is raised only by the oil delivered from the small inner diameter portion of the pump cylinder.

When the plunger of the plunger pump is raised with the valve switching member switched to the ram neutral position and only the suction neutral valve is forcibly opened, as described above,
The oil in the oil tank is sucked into the large and small inner diameter portions of the pump cylinder. Then, when the plunger is lowered, the oil in the small inner diameter portion of the pump cylinder returns to the first oil passage through the third oil passage and the high pressure side pump port, and returns to the oil tank through this oil passage. Be done. Further, since the spring force of the second spring-loaded check valve is smaller than that of the first spring-loaded check valve, the oil in the large inner diameter portion of the pump cylinder passes through the fourth oil passage. And returns to the second oil passage via the low pressure side pump port, flows into the fifth oil passage, then flows into the first oil passage through the second spring-loaded check valve, and further flows through this oil passage. Passed back to the oil tank. In this way the ram is held in place.

When the valve switching member is switched to the ram lowering position to forcibly open the suction neutral valve and the discharge lowering valve, the oil in the ram cylinder returns to the first oil passage and passes through this oil passage. Returned to the oil tank. Thus the ram descends.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show a manual hydraulic jack which is manually operated to raise and lower a luggage loading fork of a hand pallet truck, FIGS. 3 to 11 show the main parts thereof, and FIG. 12 shows an oil. The arrangement of the channels and the various valves is shown, and FIG. 13 shows the hydraulic circuit. In the following description, the right side of FIG. 1 is referred to as the front, the left side of FIG. 1 is referred to as the rear, and the left and right of FIG. 2 are referred to as the left and right.

The external appearance of the hydraulic jack is a horizontal block-shaped main body (1), an oil tank (2) hermetically fixed to the upper side of the main body (1), and a vertical and sealed front lower side of the main body (1). Fixed to the ram cylinder (3), the ram (4) fitted in the ram cylinder (3) so that it can move up and down, and passing through the body (1) and the oil tank (2), and the body (1). It consists of a plunger pump (5) that is vertically and hermetically fixed to the upper rear part. Although not shown, the upper end of the ram (4) is rotatably attached to the upper rear part of the vehicle body equipped with a fork, and the middle part of the ram cylinder (3) is attached to the vehicle body via a link. The ram cylinder (3) is rotatably attached to the center of the connected horizontal members, and the lower end of the ram cylinder (3) is fixed to the axle of the rear steering wheel.

A circular vertical stepped hole (6) is formed in the front portion of the main body (1) so as to vertically pass therethrough. The upper end of the ram cylinder (3) is fitted into the lower part of the stepped hole (6). The lower part of the ram (4) fits inside the ram cylinder (3) with a small radial gap. The oil chamber of the ram cylinder (3) is formed by the space inside the ram cylinder (3) and the space inside the intermediate portion of the stepped hole (6).

On the upper rear surface of the main body (1), a plunger pump
The lower end of the vertical pump cylinder (7) of (5) is fixed. The pump cylinder (7) is located in the oil tank (2). The plunger (8) is fitted in the pump cylinder (7) tightly from above and vertically slidably.
The plunger (8) always projects upwards from the pump cylinder (7) and penetrates the oil tank (2), and the spring (9)
Is biased upward by. Pump cylinder (7)
Has a large inner diameter portion (7a) at its upper portion and a small inner diameter portion (7b) at its lower portion. The plunger (8) has a large diameter part (8a) that is tightly fitted in the large inner diameter part (7a) and slidable up and down in the upper part, and a small inner diameter part (7b) on the lower side. In addition, each has a small-diameter portion (8b) that can be vertically slidably fitted. And the pump cylinder by the large inner diameter (7a)
The low pressure side oil chamber of (7) is formed, and the high pressure side oil chamber of the pump cylinder (7) is formed by the small inner diameter portion (7b).

A pair of right and left rising walls (11) are integrally formed on the rear portion of the top wall of the oil tank (2). A bifurcated movable bracket for handle mounting (12) between the ascending walls (11)
The bifurcated portion is attached between the ascending wall (11) and is rotatably attached via a horizontal pin (13) extending in the left-right direction. The upper parts of the left and right central portions of the pin (13) are cut off, and a semicircular portion (13a) of a cross section is formed here.
A horizontal roller (14) parallel to the pin (13) is rotatably mounted on the movable bracket (12) slightly behind and above the pin (13), and this roller (14) always keeps the plunger.
It is pressed against the upper end surface of (8). An elongated tube (15) is fixed to the rotating end of the movable bracket (12). Although not shown, a steering / hydraulic jack operation handle is attached to the rotating end of the pipe (15), and a hydraulic jack switching operation lever is provided on this handle. The upper end of a further elongated operating rod (16) inserted in the pipe (15) so as to be movable in the axial direction is connected to the operating lever, and the lower end of the operating rod (16) is connected to the movable bracket (12). It is located in the through hole (12a) formed in the connecting portion of the rotating end. Further, a horizontal pin (17) extending in the left-right direction parallel to the pin (13) is rotatably attached to a portion slightly forward and below the pin (13) between the right and left rising walls (11). .
The lower part of the center part on the left and right of the pin (17) is cut off and is a semicircular part
(17a) is formed. On the lower surface of the semicircular part (17a),
The front part of the valve switching rod actuating plate (18) extending to the front and rear is fixed. A screw member (19) is attached so as to penetrate the rear portion of the valve switching rod actuating plate (18), and the upper end of the male screw member (19) and the lower end of the operating rod (16) are connected to the chain (21). Are connected by. An adjusting nut (22) is screwed into the male screw member (19) from below the valve switching rod actuating plate (18) to adjust the tension of the chain (21). In addition, the connecting chain (21) is
It is passed through a through hole (13b) formed in the semicircular portion (13a) of 3).

A vertical circular through hole is formed in the front and rear central portions of the main body (1).
(23) is formed, and the columnar body (24) is tightly screwed into the through hole (23). The cylindrical body (24) has a vertical circular stepped bottomed hole (25) extending from the upper end surface to the lower portion. Stepped holes (26a) (27
Two upper and lower cylindrical bodies (26) and (27) having a) are tightly fitted and stopped.

In the cylindrical body (24), a horizontal through hole (28) extending forward from the inner peripheral surface of the lower small diameter portion of the stepped bottomed hole (25) and opening to the outer peripheral surface of the cylindrical body (24). Are formed. Horizontal through hole
At the height position corresponding to the radially outer end of (28),
An annular groove (29) is formed on the inner peripheral surface of the through hole (23). In the body (1), one end opens to the bottom surface of the annular groove (29) and the other end opens to the inner peripheral surface of the intermediate portion of the stepped hole (6).
(31) is formed, the stepped holes (26a) (27) of the cylindrical body (26) (27)
a), the lower small diameter part of the stepped bottomed hole (25), the horizontal through hole (28), and the communication passage (31) make the oil chamber of the oil tank (2) and the ram cylinder (3) communicate with each other. The oil passage (32) is formed.

A horizontal through hole (2) is formed from the upper surface of the main body (1) at a portion slightly rearward and left of the circular through hole (23) of the main body (1).
A vertical stepped bottomed hole (33) is formed reaching almost the same height as 8). Also, the body (1) has a stepped bottomed hole (33) at one end.
A communication passageway (34) is formed which opens at the lower end of the oil passageway and the other end of which opens into the communication passageway (31) of the first oil passageway (32), which forms the oil tank (2) and the ram cylinder (3). A second oil passage (35) communicating with the oil chamber is formed. First and second oil passages
(32) and (35) share a part of the communication passage (31).

An annular groove (36) is formed at the upper end of the inner peripheral surface of the small inner diameter portion (7b) of the pump cylinder (7), and the pump cylinder (7)
At the same height as the annular groove (36) on the outer peripheral surface of the
(37) is formed. Further, a horizontal through hole (38) is formed in the peripheral wall of the small inner diameter portion (7b) of the pump cylinder (7) so that the annular grooves (36) and (37) communicate with each other. Further, at the height position corresponding to the lower cylindrical body (27), the cylindrical body (24)
A horizontal through hole (39) is formed in the rear portion of the peripheral wall of the cylindrical body (27) so as to extend over both sides. At the height position corresponding to the radially outer end of the horizontal through hole (39), the through hole
An annular groove (41) is formed on the inner peripheral surface of (23). Body (1)
A communication path (42) having one end opened to the bottom surface of the annular groove (37) and the other end opened to the bottom surface of the annular groove (41) is formed. And the annular groove (37), two horizontal through holes (38) (39)
And the communication passage (42), an intermediate portion of the first oil passage (32),
Third for communicating with the small inner diameter part (7b) of the pump cylinder (7)
The oil passage (43) is formed. The opening of the third oil passage (43) on the first oil passage (32) side forms the high-pressure side pump port (43a).

An annular groove (44) is formed at the lower end of the inner peripheral surface of the large inner diameter portion (7a) of the pump cylinder (7), and the pump cylinder (7)
An annular groove is formed on the outer peripheral surface of the
(45) is formed. Further, at the rear side portion of the peripheral wall of the pump cylinder (7), one end is opened to the lower side surface of the upper annular groove (44) and the other end is opened to the bottom surface of the lower annular groove (45). A passage (46) is formed. The main body (1) has a communication passage (47), one end of which opens at the lower end of the vertical stepped bottomed hole (33) and the other end of which opens at the left side of the annular groove (45). . The communication passage (46), the annular groove (45) and the communication passage (47) allow the middle portion of the second oil passage (35) and the large inner diameter portion (7a) of the pump cylinder (7) to communicate with each other. 4 oilways (4
8) has been formed. The opening of the fourth oil passage (48) on the second oil passage (35) side forms the low pressure side pump port (48a).

Upper cylindrical body in the first oil passage (32)
A valve seat facing downward between (26) and the lower cylindrical body (27).
A suction neutral / combined valve (52) having (49) and a ball valve body (51) is provided. In addition, the lower cylindrical body (27) and circular stepped bottomed hole
A discharge descending / combining valve (55) having a valve seat (53) facing downward and a ball valve body (54) is provided between the lower small diameter portion of (25). The ball valve bodies (50) and (54) are respectively placed in the upper large diameter part of the stepped hole (27a) of the lower cylindrical body (27) and the lower small diameter part of the circular stepped bottomed hole (25). Valve (52) pressed against seats (49) (53)
Compression coil springs (56) and (57) are arranged to urge the (55) in a closing direction.

In the upper cylindrical body (26), the valve switching rod (58)
The lower part of the (valve switching member) is arranged so as to be vertically movable. The lower portion of the valve switching rod (58) is formed elongated, and the lower end thereof is fitted in the lower small diameter portion of the stepped hole (26a) of the cylindrical body (26) with a gap. The valve switching rod (58) extends upward and penetrates the oil tank (2). The valve switching rod (58) is
It is urged upward by 9), whereby the upper end of the valve switching rod (58) is in pressure contact with the lower surface of the front portion of the valve switching rod actuating plate (18). Then, by raising the operation rod (16), the rear part of the valve switching rod actuating plate (18) pivots upwards about the pin (17), whereby the front part of the valve switching rod actuating plate (18) is moved. It rotates downward, and as a result, the valve switching rod (58) moves downward against the biasing force of the spring (59). When the operating rod (16) is lowered, the valve switching rod (58) moves upward due to the biasing force of the spring (59).

A valve operating member (61) is arranged in the lower cylindrical body (27). The valve operating member (61) is composed of a shaft portion (61a) and a head portion (61b) formed on the upper end thereof, and the shaft portion (61a)
A compression coil spring (56) is arranged in a portion between the head (61b) and the stepped portion of the stepped hole (27a) around the. Head (6
The upper surface of 1b) is in pressure contact with the ball valve body (51). The distance between the lower end of the shaft part (61a) and the ball valve element (54) of the discharge lowering valve (55) is larger than the distance between the lower end of the valve switching rod (58) and the suction neutral functioning valve (52). ing.

Vertical stepped bottomed hole in the second oil passage (35)
A suction valve (64) having a step-like valve seat (62) facing downward and a ball valve body (63) is provided in the (33). Vertical stepped bottomed hole (3
A compression coil spring (65) that presses the ball valve body (63) against the valve seat (62) and urges the valve (64) in a direction below the ball valve body (63) in the inside of the 3). Are arranged. In addition, the second oil passage (3
Low pressure side pump port (48a) and ram cylinder in 5)
A first spring-loaded check valve (66) which can be opened only on the side of the ram cylinder (3) is provided in a portion between and (3).

The cylindrical body (24) and the cylindrical body (27) straddle both sides of the third oil passage (43) so as to be on the same straight line as the horizontal through hole (39). A horizontal through hole (67) is formed. At the front side of the through hole (23) of the main body (1), one end is opened to the bottom surface of the annular groove (41) and the other end is the two valves (64) () in the second oil passage (35). A communication path (68) is formed in the middle of 66). Then, the horizontal through hole (67) and the communication passage (68) make it possible to form an intermediate portion between the two valves (52) and (55) in the first oil passage (32) and two in the second oil passage (35). A fifth oil passage (69) is provided that communicates with the intermediate portions of the valves (64) (66). A second spring-loaded check valve (71) that can open in the fifth oil passage (69) only on the first oil passage (32) side.
Is provided. The spring force of the second spring-loaded check valve (71) is set to be smaller than the spring force of the first spring-loaded check valve (66).

A straight line penetrating left and right at the same height as the horizontal through hole (28) of the first oil passage (32) at a portion slightly rearward of the circular through hole (23) of the main body (1). A circular horizontal stepped hole (72) is formed. From the right end of the circular horizontal stepped hole (72) to the part to the left of the through hole (23), there is a large diameter part (72a) with a relatively large diameter, and the right end has a screw plug (73). Is hermetically screwed. From the left end of the stepped hole (72) to the part immediately to the right of the second oil passage (35), the middle diameter part (7
2b), and a screw plug (74) is hermetically screwed into the left end portion thereof. A small diameter portion (72c) is provided between the large diameter portion (72a) and the medium diameter portion (72b). Also, in the body (1), the upper end opens to the oil tank (2) and the lower end (7)
The vertical through hole (75) opened in 2c) is formed, and the vertical through hole (75), small diameter part (72c) and middle diameter part (72b)
An intermediate portion between the low pressure side pump port (48a) and the first spring loaded check valve (66) in the second oil passage (35), and an oil tank.
A sixth oil passage (76) communicating with (2) is provided.

Straddling the main body (1) and the cylindrical body (24), the lower small diameter portion of the stepped hole (25) of the cylindrical body (24) and the large diameter portion of the circular horizontal stepped hole (72) ( 72a) seventh oil passage communicating with
(77) is formed.

In the circular horizontal stepped hole (72), the first oil passage (32)
Open the second oil passage when the internal pressure exceeds a specified value.
A pressure control valve (78) for returning the oil in (35) to the oil tank (2) via the sixth oil passage (76) is provided. A valve seat (79) facing the left side is formed between the medium diameter part (72b) and the small diameter part (72c), and the ball valve body (81) is housed in the middle diameter part (72b). . In addition, a compression coil spring (82) for pressing the ball valve element (81) against the valve seat (79) and biasing the valve (78) in the middle diameter portion (72b) is attached to the ball valve element (72). It is arranged with the pressing member (83) between it and 81. The spool (84) is hermetically and slidably fitted in the large diameter portion (72a). An elongated rod-shaped portion (84a) extending leftward is integrally formed at the left end portion of the spool (84), and the rod-shaped portion (84a) is fitted in the small diameter portion (72c) with a gap. Also, the spool (84) in the large diameter part (72a)
A compression coil spring (85) for urging the spool (84) to the left is arranged on the right side of the drawing. The biasing force of the compression coil spring (85) is smaller than the biasing force of the compression coil spring (82).

An escape passageway (86) is formed in the front portion of the main body (1) for communicating the portion of the communication passageway (31) in the first oil passageway (32) with the oil tank (2). 1st and 2nd oilways (32) (3
5) A safety valve (87) is provided in the oil tank (2) to allow oil to escape when the inside pressure becomes abnormally high.

When raising the fork of the hand pallet truck, the hydraulic jack switching operation lever of the operating handle is switched to the raised position. Then, in this state, by swinging the operation handle back and forth, the plunger pump (5) operates and the ram (4) gradually rises. When the operating lever is switched to the raised position, the operating rod (16) stops at the lower end, so that the valve switching rod (58) is moved upward by the spring (59) as shown in FIG. , Its lower end moves above the ball valve body (51) and stops at the raised position. At this time, even if the two ball valve bodies (51) (54) are in pressure contact with the valve seats (49) (53), the valve switching rod (58) and the valve operating member (61) are respectively in contact with the ball valve body (51) ( The two valves (52) and (55) can be opened and closed independently of the valve switching rod (58) and the valve operating member (61) without contacting the valve. When the plunger (8) of the pump (5) rises in this state, the suction neutral valve (52) opens and the oil tank (2)
The oil inside flows into the third oil passage (43) through the high-pressure side pump port (43a) opening in the first oil passage (32), and this oil passage (43)
And is sucked into the small inner diameter portion (7b) of the pump cylinder (7). Further, the suction valve (64) of the second oil passage (35) is opened, and the oil in the oil tank (2) passes through the low pressure side pump port (48a) opened to the second oil passage (35) to the first position. 4 into the oil passage (48) and is sucked into the large inner diameter portion (7a) of the pump cylinder (7) through the oil passage (48). And when the plunger (8) descends,
The suction neutral valve (52) closes and the discharge downward valve also
(55) opens, and the oil in the small inner diameter portion (7b) of the pump cylinder (7) passes through the third oil passage (43) and the high pressure side pump port (43
It returns to the 1st oil path (32) via a), and is sent in the oil chamber of a ram cylinder (3) through this oil path (32). In addition, the oil in the large inner diameter portion (7a) of the pump cylinder (7) flows through the fourth oil passage.
(48) and through the low pressure side pump port (48a) to the second oil passage (35), and through the first spring loaded check valve (66) into the oil chamber of the ram cylinder (3). Sent in.

When a lightweight object is loaded on the fork,
That is, when a small load is applied to the ram (4), as described above, the large and small inner diameter parts (7) of the pump cylinder (7) are
Since the oil in a) and (7b) is fed into the oil chamber of the ram cylinder (3), the amount of rise of the ram (4) per one operation of the operating handle increases, and the forks can be moved to the specified height with a small number of operations. It can be raised. At this time, the oil in the first oil passage (32) passes through the seventh oil passage (77) and the circular horizontal stepped hole.
Although it flows into the part of the large diameter part (72a) of (72) to the right of the spool (84), this pressure is less than a predetermined value and smaller than the biasing force of the compression coil spring (82), so the spool (84)
Does not move, the ball valve body (81) is pressed against the valve seat (79), the pressure control valve (78) is closed, and the second oil passage (35) and the sixth oil passage (76) are closed. Has been cut off.

When a heavy load is loaded on the fork,
That is, when a large load is applied to the ram (4), the oil in the first oil passage (32) passes through the seventh oil passage (77) and the large diameter portion (of the circular horizontal stepped hole (72) ( 72a) flows into the part to the right of the spool (84), but since this pressure exceeds a specified value and exceeds the biasing force of the compression coil spring (82), the spool (84) Move to the right and the ball valve body (81) is seated
The pressure control valve (78) opens away from (79) and the second oil passage (35)
And the sixth oil passage (76) are in communication with each other, and the second oil passage is sent out from the large inner diameter portion (7a) of the pump cylinder (7).
The oil in (35) is returned to the oil tank (2) through the sixth oil passage (76). Therefore, the ram (4) is connected to the pump cylinder (7).
It will be lifted only by the oil sent from the small inner diameter part (7b) of the ram, and as a result, the amount of lift of the ram (4) per one operation of the operating handle will be small, but it will not be possible to operate the operating handle. It does not require much power.

When lowering the fork of the hand pallet truck, the hydraulic jack switching operation lever is switched to the lowered position. As a result, the operating rod (16) moves to the upper end position and stops, and this movement is transmitted to the valve switching rod (58) via the chain (21) and the valve switching rod operating plate (18). As a result, as shown in FIG. 10, the valve switching rod (58) moves to the lower end and stops in the lowered position, and is pushed by the valve switching rod (58) so that the ball valve body (51) moves to the valve seat. (49) and away from the ball valve (5
The valve operating member (61) moves downward by being pressed by 1) and the ball valve body (54) is separated from the valve seat (53) by being pressed by the valve operating member (61), so that the two valves (52) (55) is forcibly opened. Therefore, the oil in the ram cylinder (3) flows through the first oil passage (32) due to the weight of the vehicle body and the fork, and the oil tank (2)
Return to and the ram (4) descends.

When moving the hand pallet truck, the hydraulic jack switching operation lever is switched to the neutral position. As a result, the operating rod (16) stops at the upper and lower intermediate positions, and as a result, the valve switching rod (58) stops at the neutral position intermediate between the ascending position and the descending position, as shown in FIG. To do. At this time, since the ball valve body (51) is pushed by the valve switching rod (58) and is separated from the valve seat (49), the suction neutral valve (52) is forcedly opened, but the valve operating member (61) is opened. The ball valve body (54) is not pushed, the ball valve body (54) is in pressure contact with the valve seat (53), and the discharge lowering / combining valve (55) is closed. If the plunger (8) of the pump (5) rises in this condition, the oil in the oil tank (2) will be removed in the same manner as when raising the fork.
It is sucked into both the large and small inner diameter parts (7a) and (7b) of (7). And even if the plunger (8) is lowered, the pump cylinder (7)
The oil in the small inner diameter part (7b) of the oil passes through the third oil passage (43) and the high pressure side pump port (43a) and returns to the first oil passage (32),
Return to the oil tank (2) through this oil passage (32). Also, the first
The spring force of the spring-loaded check valve (66) is larger than the spring force of the second spring-loaded check valve (71).
The oil in the large inner diameter part (7a) of (7) returns to the second oil passage (35) through the fourth oil passage (48) and the low pressure side pump port (48a), and then the fifth oil passage. After flowing into the passage (69), it flows into the first oil passage (32) through the second spring-loaded check valve (71), and this oil passage (32)
Return to the oil tank (2). Therefore, the plunger
Oil is not supplied to the oil chamber of the ram cylinder (3) even if the (8) is repeatedly moved up and down, and as a result, when moving the hand pallet truck, the operating handle is swung to move the plunger of the pump (5). Even if (8) is raised or lowered, the ram
(4) does not rise and can hold the fork or load in place.

[0034]

As described above, according to the hydraulic jack of the present invention, when a large load is applied to the ram,
Since the ram is raised only by the oil delivered from the small inner diameter portion of the pump cylinder, the force required to operate the operating handle is reduced. On the other hand, when a small load is applied to the ram, the amount of rise of the ram per operation of the operation handle increases, so the number of times of operation of the operation handle is small to raise the required amount of ram. , Work time is reduced.

[Brief description of drawings]

FIG. 1 is a cutaway side view of a hydraulic jack showing an embodiment of the present invention.

FIG. 2 is a rear view of the hydraulic jack of FIG.

3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a vertical sectional view showing a part of FIG. 1 in an enlarged manner.

5 is a sectional view taken along line VV of FIG.

6 is a sectional view taken along line VI-VI of FIG.

7 is a sectional view taken along line VII-VII of FIG.

8 is a sectional view taken along line VIII-VIII of FIG.

9 is a vertical cross-sectional view showing a part of FIG. 4 in an enlarged manner.

10 is a view corresponding to FIG. 9 and showing a state different from FIG.

FIG. 11 is a view corresponding to FIG. 9 and showing a state different from that of FIG. 9;

FIG. 12 is a diagram showing an arrangement of various oil passages and various valves.

FIG. 13 is a diagram showing a hydraulic circuit of a hydraulic jack.

[Explanation of symbols]

 2 Oil tank 3 Ram cylinder 4 Ram 7 Pump cylinder 7a Large inner diameter portion 7b Small inner diameter portion 8 Plunger 8a Large diameter portion 8b Small diameter portion 32 First oil passage 35 Second oil passage 43 Third oil passage 43a High pressure side pump Port 48 Fourth oil passage 48a Low pressure side pump port 52 Suction neutral dual purpose valve 55 Discharge lowering dual purpose valve 58 Valve switching rod (valve switching member) 64 Suction valve 66 First spring loaded check valve 69 Fifth oil passage 71 Second Spring Loaded Check Valve 76 Sixth Oil Path 78 Pressure Control Valve

Claims (1)

[Claims] 1. An oil tank (2) and two large and small inner diameter parts (7a)
Pump cylinder (7) with (7b), and pump cylinder
(7) Large diameter part (7a) is slidably and tightly fitted into the large diameter part (8a) and pump cylinder (7) Small inside diameter part (7b) is slidably and closely fitted. Plunger (8) with small diameter part (8b) inserted, ram cylinder (3), ram cylinder
The ram (4) slidably fitted in the (3), the first and second oil passages (32) and (35) for communicating the oil tank (2) and the ram cylinder (3), and the The intermediate portion of the first oil passage (32) and the small inner diameter portion (7b) of the pump cylinder (7) communicate with each other, and the opening on the first oil passage (32) side has a high-pressure side pump port (43a).
The third oil passage (43) made to communicate with the intermediate portion of the second oil passage (35) and the large inner diameter portion (7a) of the pump cylinder (7) communicate with each other, and the second oil passage (35) side Is the low-pressure side pump port
(48a) and the fourth oil passage (48),
Oil tank (2) and high pressure side pump port in oil passage (32) of
A suction neutral valve (52) is provided between the high pressure side pump port (43a) and the ram cylinder.
A discharge descending / combining valve (55) is provided between the oil tank (2) and the suction neutral valve (52) in the first oil passage (32).
The valve switching member (58) is movably arranged in the side part, and the valve switching member (58) does not interfere with the suction neutral / combined valve (52) and the discharge descending / combining valve (55). Valve (52)
The ram neutral position forcibly opening only the ram and the ram lower position forcibly opening the intake neutral / combined valve (52) and the discharge descending / combining valve (55) are arranged so that the second oil passage (35 ) Oil tank (2) and low pressure side pump port (48
A suction valve (64) is provided in the part between a) and
A first spring-loaded check valve (66) that opens only on the ram cylinder (3) side is provided between the low pressure side pump port (48a) and the ram cylinder (3), and the first oil passage ( A fifth oil passage (69) that connects the middle portion of the two valves (52) (55) in 32) and the middle portion of the two valves (64) (66) in the second oil passage (35).
And a second spring-loaded check valve (71) is provided in the fifth oil passage (69) that opens only on the first oil passage (32) side, and a second spring-loaded check valve is provided. The spring force of (71) is smaller than that of the first spring-loaded check valve (66), and the second oil passage
A sixth oil passage (76) is provided for communicating the oil tank (2) with the portion between the low pressure side pump port (48a) and the first spring loaded check valve (66) in (35). , When the pressure in the first oil passage (32) exceeds a predetermined value, the second oil passage (3
A hydraulic jack provided with a pressure control valve (78) for returning the oil in 5) to the oil tank (2) via the sixth oil passage (76).