The invention relates to a hydraulic unit compri- sing a hydraulic cylinder with a piston and a first cylinder chamber located at one side of the piston, and a second cylinder chamber at the other side of the piston, to which piston a piston rod has been secured, and a hydraulic pump with a driving motor and a hydraulic accumulator of the pis- ton or diphragm type, and which hydraulic unit besides is adapted so that a hydraulic fluid in the accumulator and the cylinder always is subject to pressure above atmospheric irrespective of the piston position, whereby the hydraulic fluid is conducted from the accumulator and the first cylin- der chamber when the pump presses the hydraulic fluid to the largest pressure area of the piston, and simultaneously hydraulic fluid from the second cylinder chamber is conducted back to the pump, and whereby the hydraulic fluid is conduc- ted to the second cylinder chamber when the pump presses hydraulic fluid to the smallest pressure area of the piston, and simultaneously hydraulic fluid from the first cylinder chamber is conducted back to the accumulator and to the pump, and where all the fluid communications in the hydraulic unit are formed inside the structural elements of the hydraulic unit, such as inside covers, piston rod, cylinder tubes or similar elements.

Known hydraulic units of this kind have a given performance for a given unit as far as stroke length, power output and speeds are concerned.

Consequently, by a need for amended performances it is necessary to replace the whole unit.

It is the purpose of the present invention to eliminate this drawback.

The hydraulic unit according to the invention is characterized in that one of the structural elements is a distributing element with fluid communication ducts for flow of hydraulic fluid between the hydraulic pump, the hydraulic accumulator and the hydraulic cylinder and having respective side faces to which the pump, the accumulator and the

cylinder is removably secured.

Thus it is obtained that the parts being removably secured to the distributing element can be replaced by parts with different performances.

The hydraulic unit according to the invention may in a preferred embodiment be characteristic in that the hydraulic connection between the fluid communication ducts of the distributing element and the second cylinder chamber is formed by an annular chamber situated between the cylinder wall of the hydraulic cylinder and a cylindrical tube arranged at the outer surface thereof, that a top cover is removably secured to that end of the hydraulic cylinder which is opposite the distributing element, that the side faces of the top cover and the distributing element, respectively, facing the cylinder wall is provided with grooves, whereby the groove in the top cover forms a fluid communication duct between the annular chamber and the second cylinder chamber, that the groove of the distributing element is connected to channels in the distributing element and forms a fluid communication duct between the distributing element and the annular chamber for a flow of hydraulic fluid to or from the second cylinder chamber, and that the distributing element has a channel for a flow of hydraulic fluid to or from the first cylinder chamber.

The hydraulic cylinder with its top cover, cylinder wall and tube may then by means of screw threads, pin bolts or the like arranged at the ends of the cylinder wall and the tube be secured to the distributing element and to the top cover, whereby a replacement of the hydraulic cylinder with a new or with a hydraulic cylinder of a different stroke length or diameter will become a simple operation, where merely the old hydraulic cylinder is screwed off and the amended or new hydraulic cylinder is fitted on the distribu- ting element of the hydraulic unit.

A preferred embodiment of a hydraulic cylinder, particularly for use in a hydraulic unit according to the invention and having a cylinder wall, a top cover, a bottom

cover, a double acting piston and a piston rod extending through the top cover, may be characteristic in that its channels for a flow of hydraulic fluid to and from its first cylinder chamber between the piston and the bottom cover and from or to its second cylinder chamber between the piston and the top cover, consist of one or more channels in the bottom cover carrying the hydraulic fluid to or from the first cylinder chamber, one or more channels in the bottom cover carrying the hydraulic fluid from or to the second cylinder chamber through an annular chamber formed between the cylinder wall and a cylindrical tube arranged around the cylinder wall, and through one or more channels in the top cover connecting the annular chamber with the second cylinder chamber, and that the cylinder wall and the tube is mutually rigidly connected independently of the end covers and pre- ferably connected by welding.

The invention will now be described in more detail in connection with an embodiment of a hydraulic unit and with reference to Fig. 1 in the drawing which shows a lateral view of the driving motor and the hydraulic pump driven thereby, and in axial section secured to the pump the distributing element, to which the hydraulic driving motor, the hydraulic cylinder and the hydraulic accumulator, respectively, have been secured, Figs. 2 and 3 showing a section of the distributing element and an alternative hydraulic cylinder of a larger diameter and a smaller diameter, respectively.

The upper side of the distributing element 04 is forming the bottom cover 06 of the hydraulic cylinder with piston 02. The piston rod 03 of the piston is turned away from the distributing element 04 and extends out through a top cover 05 of the cylinder. Here the end of the piston rod 03 may perform a pressure force or a pulling force.

The lower surface of the distributing element 04 forms a cover for a hydraulic accumulator 07 with a cylinder chamber 08 and a spring loaded piston 09.

The first cylinder chamber 10 is visible between

the upper side of the distributing element 04 and the lower side of the cylinder piston 02.

The second cylinder chamber 11 is visible between the upper side of the piston and the lower side of the top cover 05 and between the inner side of the cylinder wall 13 and the outer side of the piston rod 03.

The cylinder wall 13 of the cylinder is surrounded by a tube 01. An annular channel 14 is thus formed between the tube 01 and the cylinder wall 13.

The second cylinder chamber 11 can be fluid connected with either the hydraulic pump 15 or the hydraulic accumulator 07 by means of channels in the distributing element 04, an annular groove 16 in the distributing element 04 (cf. Fig. 2), the annular channel 14 around the cylinder wall 13 and an annular groove 17 in the lower side of the top cover 05.

By one rotational direction of the pump 15 hydrau- lic fluid is conducted from the accumulator 07 to the first cylinder chamber 10 under pressure through channels in the distributing element 04. Thereby the piston is displaced upwardly and presses hydraulic fluid from the second cylinder chamber 11 to the accumulator 07 via the annular channel 14 around the cylinder wall 13 and channels in the distributing element 04.

By the opposite rotational direction of the pump 15 hydraulic fluid is conducted from the accumulator 07 to the second cylinder chamber 11 under pressure through channels in the distributing element 04 and the annular channel 14 around the cylinder wall 13. Thus, the piston is displaced downward- ly and presses hydraulic fluid from the first cylinder chamber 10 to the accumulator 07 via channels in the dis- tributing element 04.

In the distributing element 04 are-if necessary- control valves built in for redirecting its fluid flows. This may be particularly necessary if the pump 15 is replaced by a pump type only intended for one way rotation and which thus is only able to deliver hydraulic fluid at one port and

receive it at another port during rotation, the pressure and suction ports.

The tube 01 surrounding the hydraulic cylinder is rigidly connected to a sleeve 18 arranged on the outer surface of the tube 01. Via the sleeve 18 the hydraulic unit may be secured in a given position in which the sleeve 18 forms an abutment to the forces to which the hydraulic unit is exposed when in operation.

As shown in Fig. 2 a hydraulic cylinder with an amended performance may have an annular element 19 with an outer diameter being larger than the diameter of the connec- ting part of the distributing element 04, and which at its outer circumference is welded to the cylinder wall 13 of the hydraulic cylinder and to the tube 01 arranged around said cylinder wall, respectively. The ring 19 may be removably secured to the connecting part of the distributing element 04 and is provided with a number of channels 20 connecting the groove 16 in the distributing element 04 with the annular chamber 14 between the cylinder wall 13 and the tube 01.

Outlets in those channels of the distributing element 04 leading to the groove 16 of the element and to the first cylinder chamber 10, respectively, may each be provided with a check valve in the manner of a quick coupling connec- tion for shutting off the channels when the cylinder wall and tube part of the hydraulic cylinder has been removed.

Other details will appear from the drawing which a. o. shows that the cylinder wall 13 of the hydraulic cylinder is welded to the outer tube 01 for forming a double walled tube via spacer rings arranged at each end, said rings having a number of axial bores for the passage of the hydraulic fluid. The double walled tube may also be manufac- tured in another way, e. g. by extrusion with radially and axially extending ribs in the annular chamber 14 between the tubes.