United States Patent 3828650

A hydraulic or pneumatic device is provided with a cylinder and piston system for providing a rapid stroke and a power stroke. The piston part of said system comprises a piston-rod like plunger piston, which at its lower end slidingly surrounds a tube extending upwardly from, but not secured to the bottom of the cylinder. The cylinder is also provided with two working chambers, which at least partly peripherically surround said piston. Passages are formed in said piston and in said tube for connection of the two working chambers.

Bryntse, Anders Ivar (Mjolby, SW)
Berkestad, Karl Erik (Linkoping, SW)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
91/519, 92/152
International Classes:
B66F3/25; F15B15/14; F15B15/20; (IPC1-7): F15B11/16
Field of Search:
91/411A,412 92
View Patent Images:
US Patent References:
2284228Pressure multiplying mechanism1942-05-26Page
2049335Quick action hydraulic jack1936-07-28Stephens

Primary Examiner:
Geoghegan, Edgar W.
Attorney, Agent or Firm:
Alter, Weiss, Whitesel & Laff
We claim

1. A hydraulic or pneumatic lifting device comprising a piston and cylinder system for providing a rapid stroke and a power stroke, the piston of said system comprising a piston-rod like plunger having a lower end with a central co-axial bore surrounding a tube extending upwardly from the bottom of the cylinder of said system, said piston further being provided with two pressure areas located in two separate and axially aligned working chambers longitudinally spaced apart along the direction of the piston stroke, said cylinder being in communication with both of said pressure areas of said piston and having upper and mid wall sections in direct contact with the outer surface of said piston thereby forming two peripheral chambers around said piston, one of said peripheral chambers being a first working chamber and the other of said peripheral chambers being in communication with the other working chamber in said bore, each of said working chambers being provided with a supply line for a pressure transmission medium, one of said lines having therein valve means controlled by the medium transmission pressure, passage ways for said pressure transmission medium being formed in said piston and in said tube for interconnecting the two working chambers with each other, and spring biased control means inserted in said passage ways to enable the pressure transmission medium to flow between said working chambers in only one direction and preclude flow in an opposite direction.

2. A device according to claim 1, wherein said tube is floatingly resting on the bottom of said cylinder.

3. The device of claim 2 and means for normally directing all of said pressure transmission medium into the other of said peripheral chambers to act upon a first of the pressure areas in the communicating working chambers and on said flow control means for normally precluding said flow in said opposite direction.

4. The device of claim 3 and means for diverting at least a part of said pressure transmission medium from said other peripheral chamber and into the other combined one peripheral working chamber and where said pressure transmission medium acts upon said flow control means to enable said pressure transmission means to flow in said one direction.

5. The device of claim 4 and means whereby said diverting means is operated responsive to pressure in the first peripheral chamber exceeding said spring bias acting on said flow control means.

6. The device of claim 5 wherein the relative dimensions of the two pressure areas are such that said plunger piston has an initial rapid stroke before said flow control means enables said flow in said one direction, followed by a power stroke after said enabled flow begins in said one direction.

7. The device of claim 1 and spring biased flow enabling means associated with said tube, means responsive to the pressure in one of the working chambers exceeding said spring bias by at least a predetermined amount for diverting at least a part of said pressure transmission medium from a working chamber and into the other of said working chambers where it acts upon said flow enabling means and enters said tube to act upon another pressure area.

The present invention relates to a hydraulic or pneumatic device including a cylinder and piston system for providing a rapid stroke and a power stroke, in which system the piston slidingly surrounds a tube extending from the bottom of the cylinder. The device is especially although not exclusively intended for use in trucks for handling goods, e.g. pallet trucks.

Known pallet trucks have a fixed ratio between the movement of the pump piston and the movement of the lift piston. The ratio is so chosen that, with maximum load on the pallet truck, it is possible, via a lever system, manually to effect the movements of the pump piston. The ratio is therefore not so effective when lifting light loads or when the truck is unloaded. An unloaded conditions occurs before the pallet truck, inserted under the load, has been pumped up into engagement with the load. The height of this unloaded lift movement is dependent upon the shape and dimensions of the pallet and usually varies between 15 and 45 mm. A ratio often used in pallet trucks is so chosen that one pump stroke gives about 10 mm movement of the lift piston.

The main object of the present invention is to provide a movement of the lift piston, which movement is automatically dependent on load, thereby eliminating most of the disadvantage mentioned above.

In other connections, devices are known, in which a pressure transmission medium (such as a hydraulic or pneumatic fluid) is supplied to the cylinder through its bottom and through a tube fixed to this bottom. The lift piston has a central bore for sealingly and slidingly around the tube. In this way, a further working chamber is provided inside the piston, which mounting the piston working chamber is used to effect a rapid lift. However, in this case an extension of the cylinder downwards is necessary to enable the medium to be supplied there.

The basic conception of the present invention is to give the cylinder together with the lift piston such a form, that two outer working chambers are formed in relation to the piston. This gives an opportunity to supply the pressure transmission medium almost everywhere along the whole length of the cylinder. Furthermore the construction will be simple and economical with a minimum number of movable parts. The method is especially suitable for cylinders having a relatively short length of stroke, e.g. cylinders in pallet trucks. The inventive supply of the medium makes it possible for a cylinder according to the invention to have outer dimensions in full conformity with conventional well tested and well motivated constructions.

According to the invention, the piston comprises a piston-rod like plunger piston working in and being at least partly peripherically surrounded by two working chambers formed in the associated cylinder. These working chambers are connected by a passage formed in the plunger piston.

A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawing, which is a longitudinal cross section view showing the piston and cylinder constructed according to the invention.

In the drawing, a cylinder housing 1 includes a piston-rod like plunger piston 5 with uniform diameter. This piston is sealingly guided in relation to the cylinder housing 1 by means of upper and mid wall section guides 3 and 4 and is arranged to run easily therein. Mid wall section 4 divides the cylinder into two peripheral chambers 14 and 16. The piston 5 is further provided with a central bore forming a working chamber 7. In this bore is slidingly mounted a tube 2, which extends upwardly from the bottom of the cylinder housing 1, but is not secured thereto.

Flow control means are pivoted in the form of the piston bore 7, the inner passage through the tube 2, passages 8 and 10 in the piston 5, passages 6 and 13 in the tube 2, a ball 11 and a valve seat 12, which enables the pressure transmission medium to pass from a first working chamber 14 to another chamber 15, but precludes flow in the opposite direction, since the ball 11 then seals itself against the seat 12.

The cylinder housing 1 also contains a reservoir 16 for the pressure transmission medium and passages 17 and 18, which permit the pressure transmission medium to flow from the reservoir 16 into the working chamber 14, but not in the opposite direction, since a valve ball 19 then seals itself against a seat 20.

The cylinder housing contains a further passage 21, which can be connected through a valve system known per se, but not disclosed here, to the pump (not shown) during the pumping up and to the reservoir during the lowering.

Furthermore the cylinder housing 1 contains a valve in a bore 291 the valve includes a hole 22, a ball 23, a piston 24, an O-ring 25, a spring 26 and a screw plug 27, provided with a hole 28. The piston 24 with the O-ring 25 is easily movable in relation to bore 29. When the spring loaded valve is opened, the passage 21 is connected to the working chamber 14 via the hole 22, the ball 23 and a passage 30.

The operation of the parts here above described is as follows:

In order to extend the piston 5, the pressure transmission medium is pressed, via the valve system known per se, through the passage 21 into the working chamber 15 and through the passages 8 and 10 into the bore 7, the ball 11 thereby being sealingly pressed against the seat 12 and the tube 2 being pressed against the bottom of the cylinder housing 1. At this time, there is no communication between the passage 21 and the working chamber 14 because it is closed by the ball 23, which the spring 26 and the piston 24 are sealingly pressing by against the opening of the hole 22. Thus, the pressure of the medium acts only inside the bore 7. Therefore, the piston 5 will receive a large movement in relation to the quantity transmission medium supplied to the bore 7. The pressure transmission medium will also be drawn from the reservoir 16 through the passage 17, past the ball 19 and via the passage 18 into the working chamber 14. If the piston 5 is sufficiently loaded, the pressure of the medium arrives at a value such that the total power acting on the sectional area of the hole 22 exceeds the spring power 26. Then the ball 23 is pressed from its seat and the pressure transmission medium has free access to the chamber, which is formed by the bore 29 and the piston 24, and from this chamber via the passage 30 to the working chamber 14. The ball 19 is now forced against its seat 20 to prevent the pressure medium from flowing into the reservoir 16. The pressure of the medium is then immediately decreased to a value, which corresponds to the load on the piston 5 divided by the sectional area of that piston. The screw plug 27 is provided with the hole 28 in order to ensure that atmospheric pressure always exists on the surface of the piston 24 which faces the spring 26.

The above described change-over device can use other means than the described valve 23 - 29, (e.g. valving may be accomplished through a small slot or the like), the pressure equalizing being made at a certain piston-rod load and pump speed. Such a system, however, is dependent on the viscosity of the pressure medium and causes losses through the choke which the slot represents. The change-over valve 23 - 29 is non-sensitive to viscosity differences and can be substantially loss free.

In order to lower the piston 5, the passage 21 is connected to the reservoir 16 via the valve system, known per se, there is substantially atmospheric pressure in reservoir 16. This means that the pressure transmission medium in the working chamber 15, which is under over-pressure, can freely flow to the reservoir 16. The medium in the working chamber 14 is also able to flow to the reservoir 16 through the passages 6 and 13, past the ball 11, the inner passage through the tube 2, the bore 7, the passages 8 and 10, the working chamber 15 and the passage 21.

The cylinder can be driven with either a gas or liquid as the pressure transmission medium.