The present invention relates to a power unit for controlling a pressure medium for load control, in connection with which power unit is arranged in use both a supply circuit for supplying pressure medium under pressure into the power unit and a drive circuit, in connection with which is arranged an actuator, into which the pres- sure medium is to be supplied for loading said actuator, the pressure being created by control means arranged to the power unit, and in connection with which power unit is arranged a discharge circuit for discharging pressure medium from the drive circuit.

Power units according to that presented above are used specifically for controlling actuators intended for moving working machines, such as forklift hoists, excavator scoops and their arms. While directing the pressure medium required for load con- trol, the energy required by such arrangements, in other words fuel consumption, is relatively high, and their placement, specifically the placement of the power units in connection with the actuators, is often challenging. Often, the apparatus related to operation of the power unit, such as the valves and the connections between them for supplying pressure medium, must be positioned scattered apart from each other, which, in turn, disadvantageously increases energy requirements and, consequently, fuel consumption in power units of this type.

Such hydraulic control devices are presented, for example, in EP 1253327, in which for each actuator is arranged one directional control valve and its adjustment char- acteristics are also not very precise.

A system more precise in its adjustment characteristics is presented in FI 125918, which includes a system connected directly to the actuator, into its many working chambers. Herein, the actuator generates the total force affecting the load. Herein, the structure of the actuator is, however, quite restricted, at least for achieving a precise total force affecting the load.

The object of the present invention is to obviate or at least substantially decrease above said disadvantages, which thus relate to the adjustability of the power unit and the energy efficiency of the structure. In order to achieve the above-stated object, the present invention is characterized by that, which is specified in the characterizing part of independent claim 1. Using the invention, in prior known arrangements is achieved the advantage that the pressure medium control means and the transfer channels required for load control can be integrated into a very small space in the module frame and such that there is no need for separate channels or pipes causing control means pressure losses. Further, the directional control valves, the cylinders and a pressure accumu- lator included in the control means can be fitted into the module frame in such a required amount that provides for loading the actuator an exceptionally precise and energy-saving control of the pressure medium between the control means arranged in connection with the actuator and the module frame. That which is presented above thus provides a plug-and-play type power unit between the supply circuit and the drive circuit, which is even more energy-efficient and more precise in its ad- justments than in prior known solutions.

The preferred embodiments of the invention are presented in the accompanying dependent claims.

In the following, the invention is described in more detail by referring to the accom- panying drawings, in which:

Fig. 1 shows a diagrammatic view of a power unit according to a preferred embodiment of the invention, as well as the supply and drive circuits arranged in connection with it,

Fig. 2 shows an axonometric projection of a power unit according to Fig. 1, and

Fig. 3 shows diagrammatically the application of a power unit according to

Fig. 2 for controlling the load of a hydraulic cylinder. Fig. 1 thus illustrates diagrammatically a power unit according to the present inven- tion, which is designated by reference numeral 10. The control means included in the power unit are inside the box designated by reference numeral 10a representing the module frame and shown by a dashed line.

In connection with the power unit 10 is arranged a supply circuit 50, through which the pressure medium is supplied under pressure into the power unit 10. Preferably, the supply circuit 50 includes a tank 51, from which the pressure medium is pumped by a pump 53 (motor 53a) along the flow path 52 into the power unit 10. In the presented embodiment, the pressure medium is a hydraulic pressure medium, but the pressure medium can also be, for example, air or other fluid pressure medium. The supply circuit 50 can also be formed in some other manner for supplying pres- sure medium under pressure into the power unit 10. In other words, the presented embodiment is just one of many preferred examples of supplying a pressure medi- urn.

Fig. 2 shows a power unit 10 according to the invention, which comprises a module frame designated by reference numeral 11, as well as control means arranged im- movably in relation to the module frame 11 and presented in more detail in the fol- lowing.

The control means include at least one pressure accumulator 12, which is, for ex- ample, a piston pressure accumulator. From the supply means 50 is arranged via a connection 12a into the module frame 11 a first flow path 20, which is directly con- nected to the pressure accumulator 12 for supplying pressure medium thereto.

From the first flow path 20 shown in Fig. 1 branches also a flow path 20a or flow paths 20a, which are in connection with the cylinders 14 included in the control means. Flerein, the cylinders 14 are four units, and they are designated by refer- ence numerals 14a, 14b, 14c and 14d. The number of cylinders can generally vary according to the application. Flowever, there must be at least two, preferably how- ever 3 - 5 units. In Fig. 2 they are encased within the space defined by the protec- tive casing 10a. The flow paths 20a leading to the cylinders lead into their spaces on the side of the piston shaft. Each cylinder is preferably of different size. In this case, the diameters of the piston shaft are different, wherein from each cylinder is obtained, through the directional control valves presented below, different pressures for the actuator 100.

The piston-side spaces of the cylinders 14a, 14b, 14c and 14d are, in turn, via other flow paths 21a, 21b, 21c and 21d, in connection with the directional control valves arranged immovably into the module frame 11. The group of directional control valves is designated by reference numerals 15 and 16, and their number can vary depending on the number of the cylinders and/or the size of the valves, preferably being 9 - 30 units. The first directional control valves 15, which in the case of four cylinders are sixteen units, are divided here into groups of four directional control valves, of which each valve group is in such a connection with a corresponding cyl- inder such that the pressure medium directed from the corresponding cylinder can be directed through each directional control valve of the group to the external drive circuit 60 of the power unit 10 and to the actuator 100 in connection with it. Corre- spondingly, the pressure medium can be directed through the first directional con- trol valves 15 from the actuator 100 back to the cylinders 14a 14b, 14c and 14d. Hence, at least a portion of the pressurized pressure medium to be discharged from the actuator 100 can still be used for charging the pressure accumulator 12. The transfer of the pressure medium occurs thus through the connections (channels) integrated into the power unit.

In addition to this, the control means include second directional control valves, i.e. auxiliary valves 16, through which the pressure medium can be directed from the supply circuit 50 directly though the power unit 10 to the drive circuit 60 and, fur- ther, to the actuator 100. Correspondingly, the auxiliary valves include directional control valves 16' between the drive circuit 60 and the first directional control valves 15, through which the pressure medium to be discharged from the actuator can be directed directly through the power unit 10 (12b) to the discharge circuit 70 in con- nection with the tank 51.

Shown in Fig. 2, as the actuator 100 is a double-acting piston cylinder. Preferably, the directional control valves 15 and 16 are further divided in two such groups that the pressure medium can be directed through the supply channels 61 and 62 of the drive circuit 60 onto both sides of the piston of the piston cylinder. Such an ar- rangement can be adapted, for example, in an arrangement according to Fig. 3, in which the actuator 100 is adapted for turning the bucket arm of a shovel loader or the arm parts 81 of the arm 80 of a crane. Another example of the many applica tions for a power unit according to the invention is, for example, the forks of devic- es intended for lifting things, such as forklifts.

The actuator 100 is preferably equipped with detection means 110, on the basis of the data detected by which the control means are to be controlled to create the pressure required by the actuator 100. Herein, the detection means 110 can be, for example, pressure sensors arranged into the pressure spaces of the actuator 100, the detections of which sensors can be sent electronically along the data transmis- sion means 111 and 112 to the control unit 17, which is an integral part of the con- trol means of the power unit. Depending on the application, the detection means can be used to detect directly or indirectly also other parameters required for the control, such as force, position and/or station. Hence, from the control unit 17 can be sent, on the basis of detections, electronic control commands for controlling the control means.

In relation to prior art for loading an actuator, such an arrangement combines ex- ceptionally precise control as well as compact structure, using which new kind of combination a significant energy savings is achieved. Using the control means, which preferably include, for example, the above-described pressure accumulator 12, four cylinders 14a, 14b, 14c and 14d and twenty-four units of grouped direc- tional control valves 15, 16, 16', is already achieved as such a very precise control of loading in the presented embodiments. However, let it be noted that the inven- tion is not limited to these numbers of cylinders and directional control valves, as has already been specified earlier. This also involves that the control means achiev- ing precise control are arranged immovably in connection with the module frame 11 of the power unit 10. As a result of this, a great number of the flow paths connect- ing the control means, also in terms of length, are obtained as a single compact module in connection with a mobile power unit. This structure significantly shortens the length of the flow paths connecting the control means. This, in combination with precise adjustment of loading, has a direct reductive influence on the energy re- quirement needed for loading the actuator, for example the fuel consumption of a working machine. This provides also the possibility of a plug-and-play type control unit, the installation and maintenance of which is significantly simpler than in the past. The present invention is not limited to only the presented embodiments, rather many various modifications are possible within the protective scope of the claims.