EP1232335A1

EP1232335A1 - Free-piston engine

Info

Publication number: EP1232335A1
Application number: EP00981162A
Authority: EP
Inventors: Rudolf SCHÄFFER; Jörg Dantlgraber
Original assignee: Mannesmann Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 1999-11-24
Filing date: 2000-11-06
Publication date: 2002-08-21
Anticipated expiration: 2020-11-06
Also published as: EP1232335B1; WO2001038706A1; JP2003524727A

Abstract

A free-piston engine is disclosed, whose engine piston may have a force applied, in the compression direction, by means of an hydraulic cylinder, which can, by means of a switching valve, be connected to the pressure in a high pressure storage device or a low pressure storage device. According to the invention, a valve arrangement, with a control piston, is arranged between the hydraulic cylinder and the switching valve, whose control surface controls a connection with the high pressure reservoir device.

Description

description

Free piston engine

The invention relates to a free piston otor according to the preamble of claim 1.

In principle, a free-piston engine is an internal combustion engine working according to the 2-stroke process, in which a hydraulic circuit with a piston pump is used as a drive train instead of a crank. For this purpose, the engine piston is connected to a hydraulic cylinder, via which the translatory energy generated during an engine work cycle is fed directly to the hydraulic working medium without the classic detour via the rotary movement of a crank mechanism. The downstream, storable hydraulic circuit is designed in such a way that it takes up the work that has been done, stores it temporarily and, depending on the power requirement, feeds it to a hydraulic output unit, for example an axial piston machine.

DE 40 24 591 AI describes a free-piston engine of the generic type, which is also known as a Brandl-free piston engine. In this concept, the compression movement of the engine piston takes place through interaction with a hydraulic piston, which can be connected to a high-pressure accumulator or a low-pressure accumulator via a 2/3-way switch valve 1. At the beginning of the compression stroke, the engine piston accelerates by pressurizing the hydraulic cylinder with the pressure in the high-pressure accumulator. When a predetermined engine piston speed is reached, the hydraulic cylinder is connected to the low-pressure accumulator via the changeover valve 1, so that the further compression stroke of the engine piston takes place against the effective force from the compression pressure of the working gas. After reaching the outer dead center (AT), the working gas is ignited and the engine piston is accelerated towards the inner dead center (IT). During this piston movement from AT to IT, the connection to the high-pressure accumulator is opened via the switch tventi 1 ert, so that the engine piston is braked and its kinetic energy is converted into potential hydraulic energy and the high-pressure accumulator is charged. Although the switching times of the changeover valve are in the millisecond range, when opening and closing the connection to the high-pressure accumulator in the changeover valve throttle losses occur which can be in the order of 10% of the engine output.

These disadvantages of the Brandl free piston engine can be eliminated with another type of free piston, the so-called INNAS engine, as disclosed for example in EP 0613521 B1. However, such a motor has an extremely complex structure, so that the expenditure on device technology is considerably greater than in the case of a Brandl motor.

In contrast, the invention has for its object to develop the generic free piston engine in such a way that the throttle losses are reduced with minimal device complexity.

This object is achieved by a free engine with the features of claim 1.

According to the invention, a valve arrangement with a control piston is connected between a hydraulic cylinder receiving a hydraulic piston and a changeover valve for selectively hydraulic connection of the hydraulic cylinder to a high-pressure accumulator device or a low-pressure accumulator, by means of which the hydraulic piston with one of the output pressure at the changeover valve or pressure force dependent on the pressure in the high-pressure accumulator can be applied.

Since only the pressure acting on the valve body of the transmission valve arrangement has to be built up or reduced to control the engine piston, the changeover valve can be designed for a much lower flow than in the prior art, so that short switching times with minimal throttle losses can be achieved.

According to the invention, the control piston is designed with a control edge, via which a connection to the high-pressure accumulator can be opened. The control piston thus draws its switching energy from the high-pressure storage device via its own control edge, so that the quantity of pressure medium flowing via the changeover valve is only required to initiate the upward movement of the control piston and is therefore minimal.

By interposing the valve arrangement according to the invention, the pressure medium quantities flowing through the changeover valve can be minimized, so that the pressure losses when opening and closing the connection to the high-pressure accumulator are minimal.

The Querschm ^'ttsflache of the control piston is advantageously greater than that of Hydraul ikkolbens formed, so that due to the selected gear ratio is sufficient, a comparatively small stroke of the control piston to cause a sufficient acceleration of the engine piston.

In an alternative embodiment, the opening movement of the control piston is limited by a stop. After the control piston has hit this stop, there is no further pressure build-up in the hydraulic cylinder, so that there is no further acceleration of the engine piston. That is, according to the invention, the closing of the changeover valve required in the prior art is replaced by the run-up of the control piston to the stop, so that the throttle occurring when the changeover valve closes can practically not occur. This stop can be made adjustable in order to be able to adjust the maximum speed of the engine piston.

The control piston is reset during the combustion stroke essentially by the force of the control spring, whereby sufficient time is available for this closing process and practically no throttle losses occur.

The high-pressure storage device is loaded during the combustion stroke of the engine piston via a high-pressure channel in which a check valve is provided. In one embodiment of the free-piston engine according to the invention, this high-pressure channel can be opened or closed via a further control edge of the control piston, so that the charging process is dependent on the position of the control piston.

According to an advantageous further development of the free-piston engine according to the invention, a directional valve can be provided in the high-pressure channel leading to the high-pressure storage device, via which a bypass line that bypasses the check valve provided therein can be opened or closed. By means of this directional control valve, the hydraulic piston can be subjected directly to the pressure in the high-pressure storage device during the compression stroke, while the control piston initially remains in its closed position. After the hydraulic piston has reached a predetermined acceleration or speed, the bypass line is then closed, so that the further movement of the hydraulic piston is determined in the manner described above by the control piston.

The directional control valve can optionally be provided with a switch position in which the high-pressure channel can be connected to the tank, so that the free piston can be moved towards its inner dead center practically without counter pressure.

In another advantageous variant of the free-piston engine, the control piston is designed as a stepped piston, the annular surface which is effective in the opening direction being connected to the low-pressure accumulator via a low-pressure channel with a check valve. In the closing direction, the larger annular end face of the control piston is acted upon by the pressure in the hydraulic cylinder of the hydraulic piston and by the force of the control spring. With this variant during the entire opening movement of the control piston, pressure medium is sucked out of the low-pressure accumulator. This uniform suction of pressure medium over practically the entire range of motion of the control piston prevents cavitation in the hydraulic cylinder, which can occur in the above-described solutions, since the suction takes place there essentially when the hydraulic or engine piston reaches its maximum speed when the control piston runs up has reached the stop.

The annular space of the stepped piston is connected to the high-pressure accumulator via a pressure channel, so that the high-pressure accumulator device is charged when the control piston jerks back.

The rear circumferential edge of the larger end face of the stepped control piston is preferably designed in such a way that it opens the high-pressure channel shortly before the control piston runs onto its valve seat, so that the kinetic energy of the engine or hydraulic piston for loading the high pressure pressure storage device is used.

Preliminary tests showed that the pressure in the high-pressure storage device can fluctuate relatively strongly due to other connected consumers, which can lead to discontinuities during the compression stroke of the free-piston engine. In order to eliminate this disadvantage, it is proposed in a further advantageous variant to design the high-pressure storage device with a medium pressure accumulator and a high pressure accumulator, the energy required for the compression stroke being taken from the medium pressure accumulator. This is connected to the high-pressure accumulator via a suitable ventilating device and is kept at a pressure level which is below the minimum level of the high-pressure accumulator. If a limit pressure is exceeded, the pressure in the medium pressure accumulator can be reduced towards the low pressure accumulator. When the engine piston moves back to the inner dead center, the high-pressure accumulator feeding the medium-pressure accumulator is then advantageously charged.

In a further variant of the free-piston engine according to the invention, the hydraulic piston is designed as a differential piston, an annular space delimited by the differential piston being able to be connected to the low-pressure accumulator during the expansion stroke and the annular space of a stepped control piston during the compression stroke.

The free piston engine according to the invention can be particularly compact if the transmission valve arrangement is designed coaxially with the engine piston axis.

The valve arrangement is preferably designed as a logic valve or slide valve.

Other advantageous developments of the invention are the subject of the further subclaims.

Preferred exemplary embodiments of the invention are explained in more detail below with the aid of schematic drawings. Show it:

Figure 1 is a schematic representation of a first embodiment of a free piston engine;

Figures 2 to 6 different working phases of the embodiment shown in Figure 1;

Figure 7 shows another embodiment of a free piston engine according to the invention;

FIG. 8 shows an exemplary embodiment of a free-piston engine with a directional valve for hydraulic limitation of the engine piston speed; Figure 9 shows an embodiment of a free piston engine with a control piston designed as a stepped piston

10 shows a variant of the free-piston engine according to FIG. 9 with a hydraulic piston and a hydraulic cylinder

Figure 11 shows an embodiment of a free-piston engine with a medium pressure accumulator.

FIG. 1 shows a highly simplified, schematic illustration of a free-piston engine 1 according to the invention. This has a motor housing 2, through which at least one combustion cylinder 4 (to the right of the dash-dotted line in FIG. 1) and a hydraulic cylinder 6 (to the left of the dash-dotted vertical line) ) are limited.

An engine piston 10 is guided in a cylinder bore 8 of the combustion cylinder 4, via which the cylinder bore 8 is divided into a combustion chamber 16 and an inlet chamber 18. In the illustrated waiting position of the free-piston engine 1, the engine piston 10 is at its inner dead center (IT), an outlet channel 14 being opened so that combustion gases can flow out of the combustion chamber 16. Fresh gas is supplied via an inlet channel 20 opening into the rear inlet space 18 with an inlet valve. The inlet chamber 18 and the combustion chamber 16 are connected to one another by means of an overflow channel 22.

The fuel is injected into the combustion chamber 16 via an injection valve 24 in the cylinder head of the combustion cylinder Indian 4. For cooling the free-piston engine 1, 4 cooling channels 27 are formed in the peripheral wall of the combustion cylinder. In this respect, the free piston engine 1 corresponds to a conventional two-stroke engine, so that further versions are unnecessary.

The engine piston 10 carries a hydraulic piston 26, the diameter of which is substantially smaller than that of the engine piston 10 is. This hydraulic piston 26 plunges into a stepped axial bore 28 of the hydraulic cylinder 6.

In the piston bore penetrated by the hydraulic piston 26 between the axial bore 28 and the inlet space 18 are suitable

Sealing devices are provided so that the media accommodated in the combustion cylinder 4 and in the hydraulic cylinder 6 are separated from one another.

In the axial bore 28 of the hydraulic cylinder opens a radially arranged high-pressure channel 30, which is connected to a high-pressure accumulator 34 via a check valve 32. In a corresponding manner, a low pressure accumulator 36, for example a pressure medium tank, is connected via a low pressure channel 38 and a check valve 40 to the space delimited by the axial bore 28. The check valve 40 prevents a backflow of the pressure medium received in the axial bore 28 to the low pressure accumulator 36, while the check valve 32 prevents a backflow of the pressure medium received in the high pressure accumulator 34 into the axial bore 28.

The hydraulic piston 26 passes through the axial bore 28 and dips into a control chamber 42 in which a control piston 44 designed as a piston is guided. This is biased against a valve seat 48 by means of a control spring 46.

In the area of the control chamber 42 adjoining the valve seat 48, a pressure channel 50 opens, which is connected on the one hand to the high-pressure accumulator 34 and on the other hand to an input port P of a changeover valve 52.

A pilot space 54 adjoining the end face of the control piston 44 is connected via a control channel 56 to an output or working port A of the switching valve 52. This is designed as an electrically or electrohydraulically controlled 3/2-way valve which can be controlled via the motor control (not shown). In addition to the above-described output and pressure connections A, P the switching valve 52 also has a tank connection T, which is connected to a tank or the low-pressure accumulator 36.

In the illustrated basic position of the changeover valve 52, the tank connection T and the working connection A are connected to one another, while the pressure connection P is shut off. In a Schaltstelluπg the switch valve 52, the pressure port P is connected to the working port A and the tank port T is shut off. According to Figure 1, the control piston 44 is seated in the basic position of the free piston engine 1 on the valve seat 48, so that the pilot chamber 54 and the control chamber 42 are shut off from each other. The control piston 44 of the logic valve is acted upon in the closing direction by the force of the control spring 46 and by the pressure in the axial bore 28 and thus in the rear control chamber 42, while it is acted upon in the opening direction by the pressure in the pilot control chamber 54.

When the pressure in the low-pressure accumulator 36 acts in the pilot control chamber 54 and in the control chamber 42, the control piston 44 is thus essentially pressed against the valve seat 48 by the force of the spring.

In the combustion chamber 16 there is fresh gas which has been displaced from the inlet chamber 18 through the overflow channel 22.

To compress the fresh gas, the changeover valve 52 is brought into a second switching position via the engine control, in which, according to FIG. 2, the pressure port P is connected to the working port A, so that pressure medium from the high-pressure accumulator 34 via the pressure channel 50 and the control channel 56 into the Pilot room 54 is fed. That is, the end face of the control piston 44 is subjected to high pressure, while low pressure is still effective in the control chamber 42. Due to the pressure difference, the control piston 44 is lifted from its valve seat 48 and the connection between the pilot chamber 54 and the pressure channel 50 is opened via the control edge 58 formed by the peripheral edge of the control piston 44. The control piston thus receives its acceleration energy as a function of the control edge opening, through which the end face of the control piston 44 is directly subjected to the pressure in the high-pressure accumulator 34. Due to the resulting axial movement of the control piston 44, the hydraulic piston 26 is also accelerated and moved to the right in accordance with the engine piston 10 in the illustration according to FIG. 2 - the outlet channel 14 and the overflow channel 22 are controlled by the engine piston 10 and this in the combustion chamber 16 existing fresh gas is compressed.

The check valve 40 prevents pressure medium from flowing out of the axial bore 28 into the low-pressure accumulator 36 during the control piston movement.

Due to the movement of the engine piston 10 toward the outer dead center AT, fresh gas is sucked in through the inlet duct 20 into the inlet chamber 18.

According to FIG. 3, the control piston 44 runs against a stop 60 in the control chamber 42 after a predetermined distance D. The accelerated to its maximum speed engine piston 10 moves due to its inertia towards AT, whereby pressure medium is drawn in from the low-pressure accumulator 36 via the check valve 40 and the low-pressure channel 38 by the vacuum created in the axial bore 28. The position of the stop 60 is selected such that the kinetic energy of the engine piston 10 at the time the control piston 44 hits the stop 60 is sufficient to move the engine piston 10 toward the AT against the polytropically increasing compression pressure of the fresh gas in the combustion chamber 16 , The engine piston 10 is braked by the compression pressure and comes to a standstill.

This phase is shown in Figure 4. As soon as the engine piston 10 is braked in its AT, fuel is injected into the combustion chamber 16 and ignited by the high temperature of the fresh gas, so that the engine piston is accelerated from the AT toward the IT by the built-up combustion pressure in the combustion chamber 16 (FIG 5). Due to the resulting movement supply of the hydraulic piston 26 towards the control piston 44 builds up in the axial bore 28 and thus in the control chamber 42 a pressure which is equal to the pressure in the accumulator 34 minus the pressure equivalent of the spring 46, so that the control piston is re through from this pressure - Sul tating force and the force of the control spring 46 is lifted from its stop 60, moved by the distance D and pressed against its valve seat 48. As a result, the direct connection to the high-pressure accumulator 34 is controlled, so that the control piston 44 is borrowed only with high pressure in the opening direction via the changeover valve in its illustrated switching position.

After the logic valve closes, the pressure in the axial bore 28 and in the control chamber 42 increases to the pressure in the accumulator 34.

The further movement of the engine piston 10 and the hydraulic piston 26 takes place against this pressure, so that the engine piston 10 reduces its kinetic energy against the accumulator pressure and is braked. As a result of the pressure increase when the logic valve is closed, the check valve 32 is opened and the high-pressure accumulator 34 is charged via the high-pressure channel 30. Almost all of the kinetic energy of the engine piston 10 is thus converted into potential hydraulic energy and fed directly into the high-pressure accumulator 34. During the movement of the engine piston 10 toward its IT, the outlet duct 14 and the overflow duct 22 are turned on, so that fresh gas enters the combustion duct 16 through the overflow duct 22 and exhaust gas is flushed out through the outlet duct 14.

When the IT is reached, the changeover valve 52 is switched to its basic position, so that the end face of the control piston 44 is acted on by low pressure. The piston positions and pressure conditions now correspond to the initial conditions as described with reference to FIG. 1. By switching the switching valve 52, a new work cycle can begin. The acceleration of the engine piston 10 and thus the compression ratio of the free piston engine 1 is significantly influenced in the cycle described above by the length of the distance D, which the control piston 44 travels in the acceleration phase. In order to always achieve the same compression ratio as a function of the pressure in the high-pressure accumulator 34 during engine operation, the stop 60 for the control piston 44 can be designed to be adjustable. This adjustment can take place, for example, via the engine control.

In the variant shown in FIG. 7, the high-pressure channel 30 opens into the control chamber 42. This has the effect that the high-pressure channel 30 is opened or closed by a further control edge 62 formed on the piston skirt of the control piston 44, so that the control movement of the control piston 44 is further optimized and a quick closing of the logic valve is guaranteed. Otherwise, the exemplary embodiment shown in FIG. 7 corresponds to the previously described exemplary embodiment, so that further explanations are unnecessary.

Instead of the logic valve (seat valve) used in the exemplary embodiments described above, a slide valve can of course also be used.

In the exemplary embodiments described above, the axis of the logic valve is designed coaxially with the axis of the combustion cylinder. Of course, other relative positions can also be realized in which the hydraulic connection to the hydraulic cylinder 6 is ensured.

FIG. 8 shows an exemplary embodiment of a free-piston engine in which the hydraulic or working piston 26 can be acted upon directly with the high pressure in the high-pressure accumulator 34 via a directional valve 70. The basic structure of the free-piston engine shown in FIG. 8 corresponds to that shown in FIG Embodiment, so that only the newly added components are described below. According to FIG. 8, the check valve 32 can be bypassed via a bypass line 72, into which the directional valve 70 is connected. In the exemplary embodiment shown, the directional control valve is designed with three switching positions, the bypass line 72 being open in switching position a and a connection to the tank being shut off. In the basic position 0, both the connection to the tank and the bypass line 72 are blocked. In the switching position identified by b, the area of the high-pressure duct 30 upstream of the check valve 32 can be connected to the tank, so that the pressure in the axial bore 28 can be reduced toward the tank.

To initiate the compression stroke, the changeover valve 52 is brought into the working position, as in the exemplary embodiments described above, so that the pressure in the high-pressure accumulator 34 is applied to the left end face of the control piston 44. The directional control valve 70 is brought into the switching position shown, in which the check valve 32 is bypassed, so that the pressure in the hydraulic accumulator 34 also acts in the axial bore 28 and thus on the rear of the control piston 44. Due to the hydraulic balance of forces, the control piston 44 is then biased into its closed position by the force of the control spring 46.

Due to the pressure in the axial bore 28, the hydraulic piston 26 is accelerated and the compression stroke of the engine piston 10 is initiated. After the hydraulic piston 26 and / or the engine piston 10 has reached a predetermined maximum speed, for example 5 / s, the directional control valve 70 is brought into its blocking position marked 0, so that the bypass line 72 is shut off and the pressure medium is supplied from the high-pressure accumulator 34 in the axial bore 28 is prevented. Thereupon the control piston 44 lifts off its valve seat 48, so that the further movement of the engine piston 10 is determined by the axial movement of the control piston 44. By interposing the directional control valve 70, a variable starting speed of the engine piston 10 can thus be set before the control piston 44 takes effect. This variable initial speed can be adapted as a function of the operating conditions and the opening stroke and the opening time by actuating the directional control valve 70.

In the case of long opening times of the bypass line 72, it is possible, for example, to make do with relatively small axial movements of the control piston 44, so that a more compact design is possible. For this purpose, however, the directional control valve 70 must be designed with a correspondingly large nominal size. If one is satisfied with the relatively low initial speeds of the engine piston 10, the directional control valve 70 can be made very small, so that, due to the low pressure medium flows, rapid switching and low losses occur in the area of the directional control valve 70. In switch position b, the axial bore 28 is relieved of pressure, so that the hydraulic piston 26 or the engine piston 10 can be moved further to the internal dead center (IT) in the event of a misfire after the switchover.

FIG. 9 shows an embodiment which corresponds to the embodiment shown in FIG. 7 with regard to the basic structure. That is to say, also in the variant shown in FIG. 9, the high-pressure channel 30 is opened or closed by a rear control edge 72 of the control piston 44.

The essential difference in the exemplary embodiment shown in FIG. 9 is that the control piston 44 is designed as a stepped piston, a radially widened annular collar 74 being formed in a correspondingly widened section 76 of the control chamber 78 receiving the control piston 44.

The high-pressure channel 30 opens in the closed position of the control piston 44 in the space 78 delimited by the larger end face of the control piston 44, while a further pressure channel 80 opens in the annular space 82 delimited by the annular end face of the stepped piston 44. This pressure channel 80 is connected to the high-pressure accumulator 84, a check valve 84 preventing a flow from the high-pressure accumulator 34 into the annular space 82 in a manner similar to the check valve 32 arranged in the high-pressure duct 30.

In the embodiment shown in Figure 9, this can

Check valve 32 are bypassed via a bypass line 72 into which a metering valve 86 is connected, the function of which corresponds in principle to the directional control valve 70 from the exemplary embodiment described above.

The low-pressure duct 38 which connects to the low-pressure accumulator 36 likewise opens into the annular space 32, so that the control piston 44 is acted upon by the pressure in the low-pressure accumulator 36 in the opening direction. The force of the control spring 46 must therefore be designed such that it presses the control piston 44 against the pressure in the low-pressure accumulator 36 against the valve seat 48 in the basic position.

To initiate the compression stroke, the changeover valve 52 is brought into the working position, so that the control piston 44 lifts off the valve seat 48 and the hydraulic piston 26 and the engine piston 10 are accelerated. During the movement of the control piston 44, pressure medium is drawn in from the low-pressure accumulator 36 via the low-pressure channel 38 from the start, so that the opening movement is supported by the pressure in the low-pressure accumulator 36.

If this is necessary to compensate for frictional losses, temperature changes, etc., the pressure in the hydraulic accumulator 26 can be applied directly to the hydraulic piston 26 via the metering valve 36, as in the exemplary embodiment described above.

In the illustrated embodiment, the stop 60 is formed at such an axial distance from the control piston 44 that it has no effect. Ie, when operating the free col benmotors 1, the control piston 44 is stopped in its end position seen in the opening direction by a balance of forces and not by running up to a stop. This end position of the control piston 44 is reached when the engine piston 10 reaches its outer dead center AT.

Due to the resulting equilibrium of forces, both the engine piston 10 and the control piston 34 come to a standstill at the outer dead center AT and the mixture is ignited by injecting the fuel via the injection valve 24 - the engine piston 10 and the control piston 44 move back into their basic position , Due to the return movement of the control piston 44, the pressure medium located in the annular space 82 is conveyed via the pressure channel 80 and the check valve 84 into the high-pressure accumulator 34 and the latter is thus charged. After a predetermined axial displacement of the control piston 44, the high-pressure channel 30 is opened via the control edge 62 of the control piston 44, so that shortly before the control piston 44 hits the valve seat 48, the kinetic energy of the engine piston 10 for charging the hydraulic accumulator 34 via the high-pressure channel 30 and the check valve 32 is used. After the control valve 44 has run onto the control seat 48, the changeover valve 52 is switched over so that the smaller end face of the control piston 44 is relieved of pressure toward the tank or low pressure - the cycle can begin again.

FIG. 10 shows a variant of the embodiment shown in FIG. 9, in which the working or hydraulic piston 26 is designed as a differential piston, the radially recessed part being oriented toward the engine piston 10. The radially recessed part of the hydraulic piston 26 forms with the axial bore 28 a further annular space 88, which via a low-pressure line 90 and a check valve 92 with the low-pressure accumulator 36 and via a connecting channel 94 and a check valve 96 with the larger end face of the control piston 44 limited space 78 is connected. During the compression stroke, the pressure medium located in the further annular space 88 is discharged via the connecting channel 94 and the like Check valve 96 displaced to room 78. When the engine piston 10 moves back to the inner dead center IT, pressure medium is drawn in from the low pressure accumulator 36 into the annular space 88 via the low pressure line 90 and the check valve 92. This means that pressure medium can flow into the piston 78 on the compression stroke during the compression stroke, while pressure medium can flow into the annular space 88 from the low-pressure accumulator 36 during the expansion stroke. The particular advantage over the previously described solution is thus that the pressure medium during the compression stroke from the low pressure accumulator 36 via the low pressure channel 38 and the check valve 40 into the annular space 82 and during the expansion stroke via the low pressure line 90, the check valve 92 in the others Annulus 88 can flow. The pressure medium column does not have to be stopped at the dead center of the engine piston 10 but can circulate practically, so that the efficiency of the free piston engine 1 is improved compared to the solution shown in FIG. 9.

Finally, FIG. 11 shows an embodiment which corresponds to the embodiment shown in FIG. 7 with regard to the basic structure. In the variant shown in FIG. 11, in addition to the high-pressure accumulator 34 and the low-pressure accumulator 36, a further medium-pressure accumulator 98 is provided, which is connected to the pressure channel 50, so that the left end face of the control piston 44 in FIG. 11 is acted upon by the pressure in the medium-pressure accumulator 98 is when the holding valve 52 is brought into its working position. The medium-pressure accumulator 98 is connected via a line 100 to a control valve 102 with the part of the high-pressure duct 30 located downstream of the check valve 32. In a corresponding manner, the medium pressure accumulator 98 is connected to the low pressure accumulator 36 by means of a further line 104 and a further control valve 106.

In the solution shown in FIG. 11, the high-pressure accumulator 34 is connected to the high-pressure duct 30 via the check valve 32. This is opened when the control piston 44 moves back from its stop position via the control edge 62. The pressure level of the medium pressure accumulator 98 lies between that of the high-pressure accumulator 34 and the low-pressure accumulator 36. In the basic position, the two control valves 102 and 106 are closed, so that when the changeover valve 52 is switched into its working position, the end face of the control piston 44 with the pressure is acted upon in the medium pressure accumulator 98. That is, the acceleration of the engine piston 10 is essentially dependent on the pressure in the medium-pressure accumulator 98. This pressure can be kept at a constant level by suitable control of the control valves 102, 106.

When the pressure in the medium-pressure accumulator 98 drops below a predetermined level, the control valve 102 is opened, so that the medium-pressure accumulator 98 is charged via the high-pressure accumulator 34. If the predetermined pressure level is exceeded, the other control valve 106 is opened, so that pressure can be reduced towards the low-pressure accumulator 36.

During the expansion stroke, the high-pressure accumulator 34 is charged after opening the high-pressure channel 30. With this solution, the pressure supply to the free piston engine is essentially independent of external influences and pressure fluctuations in the high-pressure accumulator 34, which can occur, for example, when driving other consumers connected to this high-pressure accumulator 34.

The above-described variants with the directional control valve 70 for direct pressurization of the hydraulic piston 26, the medium pressure accumulator 98, the control piston 44 designed as a stepped piston and the hydraulic piston 20 designed as a differential piston can be combined with one another practically in any way, so that the invention is in no way limited to above-described embodiments is limited. A free piston engine is disclosed, the engine piston of which can be acted upon by a force in the compression direction via a hydraulic cylinder. This can be connected to the pressure in a high-pressure accumulator device or in a low-pressure accumulator via a changeover valve. According to the invention, a valve arrangement with a control piston is provided between the hydraulic cylinder and the changeover valve, through the control edge of which a connection to the high-pressure storage device can be opened.

Claims

Aπsprüche

1. Free-piston engine with an engine piston (10) and with a hydraulic piston (26) interacting with it, which can be acted upon by the pressure in a high-pressure accumulator device (34) or in a low-pressure accumulator (36) via a changeover valve (52), characterized in that a valve arrangement (44, 46, 48) with a control piston (44) is arranged between the hydraulic piston (26) and the changeover valve (52), a connection to the control piston (44) being connected via a control edge (58) High-pressure storage device (34) is openable and the control piston (44) in the closing direction is acted upon by the pressure in the hydraulic cylinder (6) and the force of a control spring (46) and in the opening direction by the output pressure of the changeover valve (52) or by the pressure in the high-pressure storage device (34) is.

2. Free piston engine according to claim 1, wherein the piston area of the control piston (44) is larger than the hydraulically effective cross-sectional area of the hydraulic piston (26).

3. Free piston engine according to claim 1 or 2, wherein the stroke of the control piston in the opening direction before the stroke end of the hydraulic piston (26) is limited by a stop (60).

4. Free piston engine according to claim 1, 2 or 3, wherein the stop (60) is adjustable.

5. Free-piston engine according to one of the preceding claims, wherein the hydraulic cylinder (6) via a high-pressure channel (30) with the high-pressure storage device (34) and via a low-pressure channel (38) with the low-pressure accumulator (36) can be connected, each with a check valve (32 , 40) prevents backflow from the high-pressure accumulator (34) or into the low-pressure accumulator (36).

6. Free piston engine according to claim 5, wherein the check valve (32) arranged in the high-pressure channel (30) can be bypassed via a bypass line (72), which can be bypassed or shut off by means of a directional valve (70, 86).

7. Free piston engine according to claim 6, wherein the directional valve (70) has a switching position (b) in which the bypass line (72) can be connected to the tank.

8. Free piston engine according to one of claims 5 to 7, wherein the high pressure channel (30) via a second control edge (62) of the control piston (44) can be opened.

9. Free-piston engine according to one of claims 5 to 8, wherein the control piston (44) is a stepped piston and the annular space (82) delimited by an annular end face of the control piston (44) with both the low-pressure accumulator (36) and the high-pressure accumulator device (34 ) is connectable.

10. Free piston engine according to claim 9, wherein the pressure channel (30) in a by the larger end face of the control piston (44) delimits space (78).

11. Free-piston engine according to one of the preceding claims, wherein the high-pressure accumulator (34, 98) has a medium-pressure accumulator (98) and a high-pressure accumulator (34), which can be connected to one another via a line (100) and a control valve (102), wherein the end face of the control piston (44) which is effective in the opening direction can be acted upon by the pressure in the medium pressure accumulator (34).

12. Free piston engine according to claim 11, wherein the medium pressure accumulator (94) via a further connecting line (104) and a further control valve (106) can be connected to the low pressure accumulator (36).

13. Free piston engine according to claim 5 and 11 or 12, wherein the high pressure channel (30) with the high pressure accumulator (34) is connected.

14. Free piston engine according to one of the preceding claims, characterized in that the Ubersübersventi lanordnung (44, 46, 48) is arranged coaxially to the engine piston axis.

15. Free piston engine according to one of the preceding claims, characterized in that the transmission valve arrangement

(44, 46, 48) is designed as a logic valve or as a slide valve.