Technical field This invention relates to pneumatic-hydraulic pressure amplifiers of a type used together with hydraulic machines for pressing, riveting clinching etc.

Background art Thus, a typical set up with a machine comprises a pneumatic system for feeding pressurised air, a pressure amplifier or booster and a hydraulic machine operated by means of high pressure oil.

The pneumatic system is feeding compressed air with a pressure of typically 6-7 bars to the pressure amplifier or booster which raises the pressure considerably and changes the working medium from air to oil. From an outlet on the booster the high pressure oil is fed through tubes or conduits to the machine. The machine as such can typically generate forces in the order of a couple of tons.

The machine could be of stationary or hand held type or could e. g. be mounted on a robot arm.

The booster comprises an oil reservoir connected through a valve to the high pressure hydraulic cylinder in order to feed that cylinder with oil. When the communication between the oil reservoir and the hydraulic cylinder of the booster is open oil can flow to the cylinder under the influence of gravity and to

the reservoir in the opposite direction due to a higher pressure in the cylinder than the reservoir. If due to the physical orientation of the oil reservoir the outlet from the same, i. e. the inlet to the hydraulic system of the booster, is exposed to air, air could enter the hydraulic system which would be detrimental to the proper operation.

Especially when the booster is used together with hand held machines or machines mounted on movable robot arms at least part of the hydraulic feeding conduit for the machine will be flexible. With the very high pressures used in the hydraulic system these flexible parts Will to some extent expand during the working stroke. This expansion represents energy which is not transferred to useful mechanical work in the machine. It is thus of interest to keep the flexible parts as short as possible. This can be achieved by arranging the booster closer to the machine.

The problem with prior art devices of the present type is, however, that they are sensitive to the orientation in space, cf. above. The manufacturer typically specifies that the booster should be free hanging or gives space angle intervals for allowed movements. With known boosters the possibility to move the booster closer to the machine is therefore limited.

During transport and storing of oil filled boosters ready for use it is of course also difficult to satisfy these strict orientation specifications.

Brief description of the invention One object of the present invention is to provide a solution to these problems by means of a pressure amplifier or booster having the characterising features according to the enclosed claims.

An advantage with the booster according to the invention is that it can be transported and stored ready for use without care concerning the orientation.

Another advantage is that in applications in which the pressure amplifier is going to be used in combination with a robot it will be possible to arrange the booster very close to the machine. This means that the high pressure part of the system will be very short.

A further object of the present invention is to provide a booster which can be used for delivering a relatively large volume of low pressure oil e. g. at the beginning of a working cycle. This feature can be of interest for machines making use of an approach stroke in addition to a power stroke as described below.

A design of the booster according to the invention opens the possibility to make the power unit for e. g. a hand held machine especially mobile. The complete unit could be designed in the form of a small cart on wheels which could be transported on the building site without concern about the orientation of the unit.

Brief description of the figures Other objects, uses and advantages of this invention will be apparent from the reading of this description which proceeds with reference to the accompanying drawings forming part thereof and wherein : Figure 1 shows in section an embodiment of the booster according to the invention in the starting position.

Figure 2 shows in section the booster according figure 1 in a position after delivering oil for an approach stroke.

Figure 3 shows in section the booster according figure 1 in a position at the end of the power stroke.

Figure 4 shows in section the booster according figure 1 in a position at the end of the power stroke when no approaching stroke has been made.

Figure 5 shows in section the booster according figure 1 with a connected hydraulic machine for e. g. clinching.

Detailed description of the invention In the following description the designation booster is used as an equivalent to pressure amplifier.

Figure 1 shows in section an embodiment of the booster, generally designated 100, according to the invention in the starting position.

A pneumatic cylinder 2 has a co-operating piston 1. Air from a source of compressed air enters the inlet 10. A control system (not shown) with valves and logic is timing the feeding of the air to the booster.

The end portion of the piston rod 9 forms a piston 3 for the hydraulic system.

The co-operating hydraulic cylinder is designated 4. An oil reservoir 5 is communicating with the hydraulic cylinder 4 through an opening 8. A piston 6 is arranged in the oil reservoir 5 in contact with the oil in the volume 11. Pneumatic pressure from the system feeding the air cylinder through the inlet 10 can be used for pressurising the oil reservoir through the inlet 12. Advantageously the

oil reservoir is pressurised at the same time as the air cylinder in the working cycle.

As an alternative the piston 6 of the oil reservoir 5 could be biased by means of a spring or similar arranged in the cylinder below the piston 6 in the figure forcing the piston into contact with the oil in the volume 11.

When the larger piston 1 is activated by means of the increased gas pressure to the inlet 10 of the cylinder 2, cf. figure 4, this piston will move downwards in the drawing. The high pressure piston 3 will also work as a valve in the shown embodiment and first close the communication 8 between the high pressure cylinder 4 and the oil reservoir 5. After that the working stroke will increase the pressure in the closed volume of cylinder 4 and deliver oil with the higher pressure through the outlet 7 via a tube or conduit to the machine further downstream.

When the hydraulic machine connected to the booster 100 has carried out the working stroke oil is returned from the machine into the oil cylinder 4 of the booster. The force needed for this return stroke could be taken from e. g. a spring in the machine driving the piston in the working cylinder of the machine back to its starting position.

The return movement of the air piston 1 in the booster could be assisted by means of a spring, not shown, or air fed to the chamber under the piston through the inlet 13.

When the air piston 1 of the booster and consequently the associated oil piston 3 are in the upper starting position the feeding channel 8 from the oil reservoir 5 is open. Oil could thus according to the inventive idea enter the oil cylinder 4 and completely fill it up prior to the stroke.

Thus, irrespective of the physical orientation of the booster 100 air can not enter the hydraulic system.

In a particular embodiment the piston 6 arranged in the oil reservoir 5 can be activated before the air piston 1 in the pneumatic cylinder 2 of the booster as shown in figure 2. If additionally the reservoir 5 is containing a considerable amount of oil this oil could be fed out through the hydraulic cylinder of the booster and the outlet to the machine. Such a flow of a relatively large volume of low pressure oil to the machine could be used for achieving an approach stroke of e. g. a jaw on the machine under safe conditions. When subsequently the air piston 1 of the pneumatic cylinder 2 of the booster is activated, cf. figure 3, the feeding channel 8 for oil from the reservoir is first cut off and then a shorter high pressure stroke will be achieved in the machine.

The control system including valves and logic for the feeding of the compressed air has not been shown. It is assumed that a technician skilled in the art could easily design such a system given the operating conditions.

Figure 5 shows the outlet 7 from the booster 100 connected to a machine 14 of a type exemplified above by means of a conduit 15. On the inlet to the machine or integrated in the machine is arranged a valve 16 which opens at a certain pressure level. A first lower pneumatic pressure is applied to the inlet 12. This pressure keeps the piston 6 against the oil surface in the oil reservoir 5 but is not high enough to open the valve 16. No air can enter the system. This first pressure could be applied constantly thereby constituting the biasing. As an alternative a spring below the piston 6 could generate the pressure.

The pressure is now increased at the inlet 12, the valve 16 opens and the machine 14 will carry out its approach stroke. A pneumatic pressure is thereafter applied to the inlet 10 of the booster and the power stroke is activated. The timing of the sequence of different pneumatic pressures could be controlled by

the operator of the machine and/or be controlled by process parameters in the machine. As an example the power stroke could be activated by the position of a tool in relation to the workpiece.

In another embodiment of the sequence for a machine working without approach stroke the first pneumatic pressure is as before keeping the piston 6 against the oil surface in the cylinder 5. When the pressure is applied to the inlet 10 of the booster the valve 16 will open automatically and the power stroke will be activated. As an alternative the valve 16 could be designed to be triggered by the operator.

The hydraulic machine according to figure 5 could be provided with a first and a second trigger, one for the approach stroke and one for the power stroke. The first trigger operates, for example, a hydraulic valve 16'which opens when the operator activates this trigger. As the piston 6 in the oil reservoir 5 in contact with the oil in the volume 11 is biased against the oil surface by means of pneumatic pressure or a spring below the piston relatively low pressure oil can now flow from the oil reservoir 5, through the hydraulic cylinder 4 and the conduit to the machine. The approach stroke is thus carried out. The operator could subsequently activate the second trigger.