A hydraulic circuit system for actuating a hydraulic jack

The present invention relates to a hydraulic circuit system for actuating a hydraulic jack, particularly a hydraulic circuit system for a jack having a piston to raise a raising arm and a support plate to a loading position to support and raise a load in "one step" by a single operation of a manual pump at no load or light load conditions.

Conventionally a hydraulic jack comprises a manual pump, a hydraulic cylinder with inner and outer reservoirs, a piston rod, a relief valve, a safety valve and a related hydraulic circuit. The outer end of the piston rod is linked to a raising arm and a support plate.

However, in such a conventional structure, a rocker or handle is usually pulled and pushed repeatedly to pump hydraulic fluid to drive the piston rod to raise upward gradually and consequently support a load.

In the conventional jack structure, the rocker or handle can be operated repeatedly either under no load or under light load conditions to pump sufficient hydraulic fluid to operate the hydraulic cylinder and to raise the piston rod for raising the raising arm and support plate accordingly at a very slow speed. The same speed occurs even if there is no load on the jack, or even if the load is very light. It is a time and labour consuming process, and the rising arm and support plate cannot be raised immediately in order to respond to urgency wherever there is an emergency, such as for rescue purposes in some accident where a heavy weight is involved.

GB 2164 630 discloses a hydraulic jack with a manual pump, a hydraulic cylinder with inner and outer reservoirs, a piston rod linked to a rising arm and an associated hydraulic circuit. It is however necessary to actuate the handle of the manual pump repeatedly to raise the arm to a working position under no load or under light load conditions.

Reference is also made to US 5090 296 which discloses a piston cylinder assembly that is more efficient and economical to operate than conventional systems.

It would be desirable to be able to provide a hydraulic circuit system for actuating a hydraulic jack whereby the jack can reach a desired loading position by a single stroke of the associated pump under no load or light load conditions.

According to the present invention, there is provided a hydraulic circuit system for actuating a hydraulic jack by means of a pump having a chamber therein for hydraulic fluid, the jack including a piston-cylinder assembly and an internal reservoir for hydraulic fluid, the system comprising an external reservoir, an inlet circuit for supplying fluid from the external reservoir via the pump to the piston-cylinder assembly, and a return circuit for returning fluid from the assembly to the external reservoir, characterised in that the system includes an inner oil chamber in the assembly, the inlet circuit extending from the external reservoir via a first check valve to the pump chamber and from the pump chamber via a second check valve to the inner oil chamber, and via a sequence valve to the internal reservoir, the external reservoir being connected to the internal reservoir via a third check valve, whereby, at no load or under light load conditions, the inlet circuit can provide hydraulic fluid in sequence via the pump chamber to the inner oil chamber to actuate the piston cylinder assembly immediately, the return circuit extending from the internal reservoir via a fourth check valve to the inner oil chamber and then through a relief valve to the external reservoir, whereby, after unloading and to resume a rest condition, the relief valve can be regulated to open the return circuit, the maximum effective capacity of the pump chamber being equal to or greater than that of the inner oil chamber whereby the piston of the assembly can be extended to a required loading position by a single stroke of the pump under no load or light load conditions.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which:

• Fig. 1 illustrates a hydraulic circuit system according to the present invention;
• Fig. 2 is a cross sectional view of structure of a jack according to the present invention;
• Fig. 3 illustrates displacement of the piston rod to its loading position in one step;
• Fig. 4 illustrates further raising of the piston rod to support a load;
• Fig. 5 illustrates displacement of the raising arm and support plate by action of the piston rod from a standstill position to a full raising position;
• Fig. 6 is a sectional view of the sequence valve according to the present invention;
• Fig. 7 is a perspective developed view of the safety valve according to the present invention; and
• Fig. 8 is a perspective developed view of the reilef valve according to the present invention.

As shown in Fig. 1, the hydraulic circuit system for one-touch jack according to the present invention comprises mainly an inlet circuit, a return circuit and an overload protection circuit together with a hydraulic cylinder 10 with an inner reservoir 1, an outer reservoir 2, a pump oil chamber 3, and piston rod 4 with an inner oil chamber 41 as well as other components in a configuration shown in Fig. 2.

The inlet circuit extends from the outer reservoir 2 of the hydraulic cylinder 10 via a check valve A1 to the pump oil chamber 3, and then via another check valve A2 to an inner oil chamber 41 of the piston rod 4. The said pump oil chamber 3 is connecting to the inner reservoir 1 of the hydraulic cylinder 10 via a sequence valve B. The said outer reservoir 2 is connecting to the inner reservoir 1 of the hydraulic cylinder 10 via a check valve A3. Therefore, at no load or light load condition, the inlet circuit can provide hydraulic fluid in sequence via the pump oil chamber 3 to the inner oil chamber 41 of the piston rod 4 to drive the piston rod 4 immediately.

The return circuit extends from the inner reservoir 1 of the hydraulic cylinder 10 to the inner oil chamber 41 of the piston rod 4 via a check valve A4, and then passes through a relief valve C to connect to the outer reservoir 2. After unloading, the relief valve C can be regulated to relief condition to make the return circuit in open condition so as to resume its original position.

The overload protection circuit extends from the outer reservoir 2 of the hydraulic cylinder 10 via a safety valve D to connect to the pump oil chamber 3. Whenever the pressure of the hydraulic cylinder 10 is greater than the rated pressure, the safety valve D is open to start the overload protection circuit automatically.

With the aforesaid hydraulic circuit, particularly when the ratio of the maximum effective capacity of the pump oil chamber 3 to the maximum effective capacity of the inner oil chamber 41 of the piston rod 4 is greater than or equal to one, the hydraulic jack can be raised to the required loading condition by one-touch at no load or light load condition.

As shown in Fig. 2, an embodiment of the aforesaid hydraulic circuit design for jack comprises mainly a cylinder 10 and a piston rod 4.

The hydraulic cylinder 10 is composed of an external cylinder body 101 and an inner cylinder body 102. It has a front block 103 at the front end, and a rear `block 104 at the rear end. The hydraulic cylinder 10 has an inner reservoir 1 and an outer reservoir 2 which are separated from each other. At the rear block a pump 20, a sequence valve B, a relief valve C and a safety valve D are placed in compliance with the above described hydraulic circuit.

The piston rod 4 is placed within the inner reservoir 1 of the hydraulic cylinder 10. It can be displaced by hydraulic action to raise or lower a rising arm 30 and top plate 40 of the jack. It has further an inner oil chamber 41 within its rod body in a manner that a oil guide tube 50 can be inserted into the inner oil chamber 41 of the piston rod 4, while an end of the oil guide tube 50 is locked to the rear block 104 of the hydraulic cylinder 10, and connecting to an oil channel 31 of the pump oil chamber 3 so that the hydraulic fluid at the pump oil chamber 3 can enter the inner oil chamber 41 of the piston rod 4 via the oil guide tube 50 to rise the piston rod 4.

The aforesaid pump 20 comprises a traction block 201, a plunger 202 and a rocker 204 fixed by a fixing pin 203. By upward and downward movement of the rocker 204, the hydraulic fluid in the pump oil chamber 3 can be circulated. The pump oil chamber 3 has an oil channel 31 to connect to the said oil guide tube 50 via the check valve A2, and the oil channel 31 is passing through the safety valve D and the oil channels D1 and C1 of the relief valve in order. The safety valve D has an oil channel D1 with two branch oil channels D11 and D12 to connect to the inner reservoir 1 and the outer reservoir 2 of the hydraulic cylinder 10 respectively. Between the branch oil channels D1 and D12 there are check valves A3 and A1 to prevent from entry of hydraulic fluid from the pump oil chamber 3 into the inner and outer reservoirs 1 and 2. The inner reservoir 1 is incorporated with a sequence valve B to connect to the oil channel D1 of the safety valve D. The said relief valve C is connecting to the outer reservoir 2 and the inner reservoir 1 respectively and has an oil guide channel C1 to pass through the sequence valve B so that the hydraulic fluid from the inner reservoir 1 can be returned to the outer reservoir 2 directly through the oil guide channel C1 which has a check valve A4 to prevent from flowing of the hydraulic fluid from the pump oil chamber 3 to the inner reservoir 1.

With the aforesaid hydraulic circuit design, when the jack is in no load or light load condition, a single rotating of the rocker 204 can raise the plunger 202 of the pump 20 to the uppermost position to apply a pulling force so that the hydraulic fluid can flow through the oil channel 31 of the pump oil chamber 3, the oil guide tube 50 and the inner oil chamber 41 of the piston rod 4 in sequence to drive the piston rod 4, and, as the volume of hydraulic fluid in the pump oil chamber 3 is greater than or equal to the volume of hydraulic fluid in the inner oil chamber 41 of the piston rod 4, the piston rod 4 of the jack is raised to the loading position required in one step as shown in Fig. 3.

While the aforesaid hydraulic circuit is at no load or light load condition, whenever the piston rod 4 is displaced forward, as the pressure in the inner reservoir 1 of the hydraulic cylinder 10 drops suddenly, the hydraulic fluid flows from the outer reservoir 2 via the oil channel D12 to replenish the inner reservoir 1 automatically, and another flow of hydraulic fluid can goes into the pump oil chamber 3 via the oil channel D1 for another operation of the pump 20. Then, the hydraulic fluid can not enter from the fully filled inner oil chamber 41 of the piston rod 4, the pressure to open the sequence valve B is thus reached. Therefore, the hydraulic fluid flows into the inner reservoir 1 from the oil channel 31 of the pump oil chamber 3 and the oil channel of the sequence B so that the piston rod can continue to hold and raise the load W upwards as shown in Fig. 4. In this respect, the sequence valve B can be set with an opening pressure.

Similarly, the aforesaid safety valve D can be set with an opening pressure so that the safety valve D is open when the piston rod 4 reaches its upper load limit or an overload is applied. In that case, the hydraulic fluid flows into the outer reservoir 2 from the pump oil chamber 3 via the safety valve D directly, and then return to the pump oil chamber 3 via the oil channel D12 to form a safety circuit restricting flowing of the hydraulic fluid into the inner reservoir 1.

When it is locked, the aforesaid relief valve C is to prevent from return of the hydraulic fluid to the outer reservoir 2 when the jack is used to maintain a load. However, after using it must be adequately loosen so that the hydraulic fluid in the inner oil chamber 41 of the piston rod 4 and the inner reservoir 1 can return to the outer reservoir 2, and, simultaneously, the hydraulic fluid can only flow from the pump oil chamber 3 to the outer reservoir 2 via the relief valve C to repeat the same circulation without driving the piston rod 4.

Fig. 5 illustrates the displacement of the raising arm 30 and the support plate 40 of the jack from standstill position to reach the load W in one step and to raise the load W consequently.

As described above, the sequence valve B can be preset for an opening pressure during assembly of the jack according to the present invention. Therefore, it can be designed according to the enduser's actual need to assure that the opening pressure can meet different requirements. As shown in Fig. 6, the sequence valve comprises mainly a hollow spiral post B1, a retraction spring B2 and a conical valve B3 and it is designed so that it can be placed within an oil channel B4 connecting to the oil channel D1 of the safety valve D. The hollow spiral post B1 is fixed to the outlet of the oil channel B4, and the conical valve B3 is placed to block a conical valve hole with the retraction spring B2 fixed between the hollow spiral post B1 and the conical valve B3. The retraction spring B2 is compressed by the hollow spiral post B1 in different degree for different opening pressure setting.

Similarly, as shown in Fig. 7, the safety valve D according to the present invention has a structure substantially same with the sequence valve B. It comprises a spiral post D2, a retraction spring D3 and a conical valve D4. The safety valve D is placed at an oil channel D1. The retraction spring D3 is compressed by the spiral post D2 in different degree for different opening pressure setting. However, there is no hydraulic fluid to pass through the spiral post D2, therefore a solid spiral post D2 is used.

The relief valve C according to the present invention comprises mainly a return gear C2 and a return valve rod C3 as shown in Fig. 8.

The return gear C2 is designed with a fixing hole C21 at its center.

The return valve rod C3 is a stepped rod structure with a small annular rib C31 at its front end for fixing the fixing hole C21 at the center of the return gear C2, two stepped annular ribs C32 and C33 at its middle section and a threaded section C35 of appropriate length at the lower section. An annular groove C34 is formed between the steppe annular ribs C32 and C33 for holding of an oil seal. The threaded section C35 has a pin-end extension C36 where a declined passage C37 is formed.