EP1282766A1

EP1282766A1 - Free piston motor

Info

Publication number: EP1282766A1
Application number: EP01944926A
Authority: EP
Inventors: Rudolf SCHÄFFER
Original assignee: Bosch Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 2000-05-19
Filing date: 2001-05-15
Publication date: 2003-02-12
Anticipated expiration: 2021-05-15
Also published as: ES2245696T3; CN1214179C; WO2001088352A1; EP1282766B1; US20040065277A1; ATE300669T1; CN1440489A; US6931845B2

Abstract

A free-piston engine has a stepped piston having a larger end face thereof guided in the compression cylinder, and a smaller end face in the work cylinder. Both the work cylinder and the compression cylinder are connected with a common high-pressure accumulator for initiating the compression stroke or for charging during the expansion stroke.

Description

FREE PISTON ENGINE

description

The invention relates to a free-piston engine according to the preamble of patent 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 the drive train instead of a crank mechanism. For this purpose, the engine piston is connected to a hydraulic cylinder, via which the translational 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 performed, 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 is performed ^'by cooperation with a hydraulic piston, the 3-way diverter valve is connectable to a high-pressure reservoir or a low-pressure accumulator via a 2 /. 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 reservoir via the changeover valve, so that the further compression stroke of the engine piston 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 changeover valve, 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 switchover valve are in the millisecond range, throttling losses occur in the switchover valve when opening and closing the connection to the high-pressure accumulator, 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 free-piston type, the so-called INNAS engine, as disclosed, for example, in WO 9603576 AI.

In this INNAS free-piston engine, the hydraulic piston is designed as a stepped piston and has two active surfaces, the first larger of which is arranged in a compression cylinder, while the second smaller delimits a pump work chamber or working cylinder. The larger area is pressurized in a compression cylinder, while the working cylinder can be connected to a high-pressure accumulator or a low-pressure accumulator via check valves. This INNAS free-piston engine has a much more complex structure than the Brandl free-piston engine, so that the expenditure on device technology is relatively high.

In contrast, the object of the invention is to develop the generic free-piston engine in such a way that the expenditure on device technology is minimized. This object is achieved by a free-piston engine with the features of claim 1.

The free-piston engine according to the invention has a stepped piston, the larger end face of which is guided in the compression cylinder and the smaller end face of which is guided in the working cylinder. Both the working cylinder and the compression cylinder can be connected to a common high-pressure accumulator for initiating the compression stroke or for charging during the expansion stroke. Compared to the INNAS free-piston engine described at the outset, this variant has the advantage that only two pressure accumulators, ie a low-pressure accumulator and a high-pressure accumulator, are sufficient for operation, while in the generic INNAS free-piston engine, three pressure accumulators with the associated lines must be available. The system can thus ^" be constructed much more compactly with less expenditure on device technology, so that the manufacturing costs of the free-piston engine are reduced compared to the solutions described at the beginning.

Another advantage is that the hydraulic piston or the engine piston has an inner dead center position, which is automatically set due to the pressure conditions. At high pressure in the high-pressure accumulator, the engine piston must work against this high pressure during the expansion stroke, so that due to the balance of forces, the expansion stroke is ended earlier than when the pressure in the high-pressure accumulator is lower. Due to this shifted dead center position, the acceleration distance available during the compression stroke is correspondingly shorter in the next cycle. Since the pressure in the high-pressure accumulator acts on the larger end face during the compression stroke, this shorter acceleration distance is compensated for by the higher pressure. Chen, so that the engine piston is accelerated to approximately the same speed as at a lower pressure with a longer acceleration distance. The energy supplied to the engine piston thus remains approximately the same as the energy which is supplied to it at a lower pressure of the high-pressure accumulator and a longer acceleration path.

Another essential advantage of the solution according to the invention is that the pressure medium is sucked in practically the entire way of the hydraulic piston during the return movement of the hydraulic piston from its dead center position, while in the Brandl free piston motor described at the beginning the pressure medium is only sucked out of the low pressure accumulator reaching a predetermined acceleration of the hydraulic piston.

With this solution, in the event that the inner dead center of the engine piston is not reached, for example due to a misfire, the inner dead center can be achieved by applying the pressure in the low-pressure accumulator to the working cylinder.

In a preferred solution, both the compression space delimited by the larger end face and the work space delimited by the ring area are connected to the hydraulic accumulator during the compression stroke. During the compression stroke, pressure medium is supplied from the high-pressure accumulator and, at the same time, the pressure medium is returned from the working cylinder to the high-pressure accumulator - the piston area effective in the compression direction thus corresponds to the difference area between the larger end face and the annular surface of the piston, which is preferably designed as a differential piston. With these variants, the printing medium flows are significantly reduced compared to conventional solutions via a start valve that opens and controls the connection to the high-pressure accumulator.

A version with a differential piston builds the INNAS free-piston engine much shorter, since in the solution according to the invention the compression cylinder is used both for pressurizing during the compression stroke and for loading the high-pressure accumulator.

Instead of a differential cylinder, it is also possible to use a piston with a piston collar, the piston rod of which is guided in the working cylinder and the piston section of which has a larger diameter in the compression cylinder. To initiate the compression stroke, the annular surface of the stepped piston is connected to the high-pressure accumulator, the pressure in the low-pressure accumulator acting on the smaller end face of the piston rod, so that the compression stroke is supported by the suction of the pressure medium from the low-pressure accumulator.

In an advantageous development, the stepped piston is provided with a control edge, via which a connection to the high-pressure accumulator can be opened during the compression stroke, so that after a predetermined acceleration distance of the hydraulic piston, pressure medium is fed directly from the high-pressure accumulator into the compression cylinder, bypassing the start valve , Since the main pressure medium flow thus does not have to be passed through the start valve, the throttle losses can be reduced further.

In a particularly preferred variant, the

Free piston engine is a directional control valve, via which a start line surrounding the start valve can be opened, so that a large cross-sectional area is available. wirc to accelerate the free piston when starting the engine. This directional control valve remains open during operation of the free piston engine.

In this variant, it is preferred if the directional control valve is designed as a logic valve with a graduated logic piston. The pressure in the high-pressure accumulator can be applied to a smaller cross-sectional area of the logic piston via an upstream release valve, while the pressure in the compression cylinder is applied to the larger cross-sectional area of the logic piston.

The release valve is preferably designed as a 3/2-way valve, via which the smaller area cross section can be acted upon either with the pressure in the high-pressure dispenser or with the tank pressure.

In the event that the engine piston cannot be moved back to its outer dead center position due to a misfire or another fault, the free-piston engine can be provided with a retraction device. Here, the compression cylinder can be connected to a tank via a piston retraction arrangement, so that the piston end face effective in the direction of the outer dead center is relieved of pressure.

In a particularly preferred embodiment, the piston retraction arrangement has a check valve, in the open position of which the working cylinder is connected to the compression cylinder.

The piston retraction arrangement also has a piston retraction valve, via which the compression cylinder can be connected to the tank. According to the invention, the check valve is integrated in the hydraulic piston. This solution has the advantage that the throttle losses are minimal due to the short connection paths between the compression cylinder and the working cylinder. Furthermore, this arrangement is very compact, since no separate receptacles for the piston retraction arrangement have to be provided in the housing. The compactness can be further improved if the check valve is also integrated in the hydraulic piston.

One possibility for integrating the check valve and the check valve is that the hydraulic piston is designed in two parts with a collar and a piston rod, the collar being designed to be displaceable on the piston rod via a sliding sleeve. The collar closes a control cross-section in a displacement position, so that the connection between the compression cylinder and the working cylinder is closed. In its non-return position, the control cross section is opened accordingly.

In this constructive solution, a closing body is axially displaceably guided in an end piece of the piston rod and blocks a breakthrough in the collar in a spring-preloaded basic position at low pressure in the compression cylinder. When pressure builds up in the compression cylinder, the closing body lifts off, so that the connection between the compression cylinder and the working cylinder is only closed again by the axial displacement of the collar described above.

The stepped piston can be actively activated in the event of a fault

Move towards the outer dead center if it is in

In the direction of the outer dead center effective ring end face can be acted upon by the pressure in the high-pressure accumulator, at least one of the surfaces of the Step piston is relieved of pressure. The return is particularly simple if the ring end face on the engine piston side is designed with a larger area than the ring end face of the step piston which is effective in the direction of the inner dead center.

In order to influence the compression pressure to a certain extent, a bypass line can be provided in the low pressure channel leading to the low pressure accumulator, via which the check valve there can be bypassed. This bypass line can be shut off via a metering 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:

1 shows an embodiment of a free-piston engine with a hydraulic piston designed as a differential piston;

FIGS. 2 and 3 different operating positions of the free-piston engine from FIG. 1;

FIG. 4 shows the free-piston engine from FIG. 1 with a device for metering the compression pressure;

5 shows the free-piston engine from FIG. 1 with a piston retraction device;

6 shows an exemplary embodiment of a free-piston engine with a hydraulic piston designed as a stepped piston;

FIG. 7 shows a variant of the embodiment shown in FIG. 6 with a piston retraction device; Fig. 8 shows an embodiment of a free-piston engine with a modified starting device and a piston retraction arrangement, which is partially integrated in the hydraulic piston and

9 shows a constructive solution of the hydraulic piston from FIG. 8.

1 shows a schematic representation of a first exemplary embodiment of a free-piston engine 1. This has an engine housing 2, in the combustion cylinder 4 of which an engine piston 6 is guided. This is in operative connection with a coaxially arranged hydraulic piston 8, which is guided in an axial bore 10. An annular end face 12 of the hydraulic piston 8 delimits a working cylinder 14, while the larger end face 16 of the hydraulic piston 8 delimits a compression cylinder 18.

A pressure channel 20 and a low-pressure channel 22 open into the working cylinder 14. The latter is connected to a low-pressure accumulator 24, a pressure medium flow from the working cylinder 14 to the low-pressure accumulator 24 being prevented by a check valve 26.

The compression cylinder 18 is connected via a high-pressure conduit 28 with a high-pressure accumulator 30, the high-pressure passage 28 up as a ^'2/2-way valve 32 and is executed starting valve zusteuerbar. The pressure channel 20 opens into the high pressure channel 28. A further check valve 34 prevents flow of pressure medium from the high-pressure accumulator 30 into the working cylinder 14. The combustion cylinder 4 is provided with an outlet channel 36, via which exhaust gas can be removed from the combustion chamber 38 delimited by the engine piston 6.

The rear side of the engine piston 6 facing the hydraulic piston 8 delimits an inlet space 40 which has its minimum volume in the inner dead center position of the engine piston 6 shown. The inlet space 40 is connected to the combustion space 38 by an overflow duct 42.

The fresh air can be supplied during the compression stroke of the engine piston 6 via an inlet channel 44 with an inlet valve 46. The free-piston engine is ignited by injecting fuel via an injection valve 48 opening into the combustion cylinder.

The function of the free-piston engine shown in FIG. 1 is explained below. At the beginning of a cycle, the combustion chamber 38 is filled with fresh air, the start valve 32 is closed and the engine piston 6 and the hydraulic piston 8 are in their dead center position (IT) shown in FIG. 1.

To initiate the compression stroke, the start valve 32 is opened so that the high-pressure accumulator 30 is connected to the compression cylinder 18. The pressure acting on the larger end face 16 accelerates the hydraulic piston out of its dead center position and transfers this acceleration to the engine piston 6. The pressure medium in the working cylinder 14 is conveyed back into the pressure channel 28 via the check valve 34 and the pressure line 20. This means that the end face 16 and the annular end face 12 of the hydraulic piston 8 are acted upon by the pressure in the high-pressure accumulator 30, so that that of the surface of the piston rod corresponding face in the direction of the outer dead center (AT) is effective. The connection to the low-pressure accumulator 24 is blocked by the check valve 26.

According to FIG. 2, fresh air is sucked in via the inlet channel 44 and the opened inlet valve 46 into the enlarging inlet space 40 during the compression stroke of the engine piston 6. The acceleration of the engine piston 6 takes place against the compression pressure of the fresh air, which increases polytropically in the combustion cylinder 38. As a result, the engine piston 6 is braked and comes to a standstill at the outer dead center (AT).

As soon as the engine piston 6 is braked in its AT, fuel is injected via the injection valve 48 and ignited by the high temperature of the fresh air, so that the engine piston 6 - as shown in FIG. 3 - by the build-up of combustion pressure in the combustion chamber 38 from the AT in the direction to IT is accelerated. This acceleration is transmitted to the hydraulic piston 8 so that it is moved to the left toward its IT in accordance with FIG. 3. Due to the resulting enlargement of the annular space of the working cylinder 14, pressure medium is drawn in from the low-pressure accumulator 24 via the low-pressure duct 22 and the check valve 26. At the same time, the pressure medium in the compression cylinder 18 is displaced into the high-pressure channel 28 - the hydraulic accumulator 30 is loaded. That is, in the exemplary embodiments shown in FIGS. 1 to 3, the hydraulic accumulator 30 is loaded simultaneously with the suction of the pressure medium from the low-pressure accumulator. Since this suction takes place along the entire return movement of the hydraulic piston 8, no cavitation phenomena occur in the working space 14. During the return movement, the engine piston 6 and the hydraulic piston 8 reduce their kinetic energy against the accumulator pressure in the high-pressure accumulator 30 until they are braked in the IT. During this process, the combustion cylinder 38 is purged by the fresh gas flowing out of the inlet space 40 via the overflow channel 42. After the engine piston 6 and the hydraulic piston 8 have reached their IT, the start valve 32 is brought into its blocking position - the free-piston engine 1 is ready for the next cycle.

FIG. 4 shows a free-piston engine during the compression stroke, the exemplary embodiment described above being supplemented by a device for metering the compression energy. This device has a bypass line 50 through which the check valve 26 in the low-pressure channel 22 can be bypassed. In the bypass line 50, a metering valve 52 designed as a 2/2-way valve is provided, which blocks the bypass line 50 in its blocking position.

When the metering valve 52 is shut off, the exemplary embodiment shown in FIG. 4 corresponds to that from the previously described drawings. By opening the metering valve 52 connected to the motor control, the working space 14 can be connected directly to the low-pressure accumulator 24, so that the annular end face 12 is acted upon by the pressure in the low-pressure accumulator 24. As a result, the hydraulic piston 8 does not have to be accelerated against the pressure in the high-pressure accumulator 30 during the compression stroke, so that, for example, the supplied compression energy can be increased at the beginning of the compression stroke.

In the event of malfunctions in the control of the free-piston engine, for example in the event of a misfire, that the engine piston 6 and the hydraulic piston 8 could not be properly returned to the IT. In order to facilitate the return to the IT, the free-piston engine 1 in the variant shown in FIG. 5 is designed with a piston retraction system. This can be formed, for example, by a piston retraction valve 54 that is connected to the pressure channel 20. In a basic position of the piston retraction valve 54 denoted by a, the pressure channel 20 is connected to the high pressure channel 28 in the manner described above, so that the function corresponds to that of the above-described exemplary embodiments. If a fault occurs, the start valve 32 is closed and the piston retraction valve 54 is brought into the position shown in b, in which the high-pressure channel 28 is connected to a tank T. The pressure medium located in the compression cylinder 18 is then relaxed towards the tank T, so that the hydraulic piston 8 and thus the engine piston 6 can be moved back into its inner dead center position by the pressure of the low-pressure accumulator 24 in the working space 14.

FIG. 6 shows an exemplary embodiment of a free-piston engine 1, in which the hydraulic piston 8 is designed as a stepped piston with two piston rods 56, 58 and an annular collar 60. In this embodiment, the working cylinder 14 is delimited by the end face 62 of the piston rod 56 on the right in FIG. 6. The compression cylinder 18 is delimited by the ring end face 64 of the collar 60 facing the piston rod 56. The piston rod 58 and the left annular surface 66 of the hydraulic piston 8 delimit an annular cylinder 68 of the axial bore 10 receiving the hydraulic piston 8. As in the exemplary embodiment described above, the low-pressure accumulator 24 is connected via a low-pressure channel 22 and a check valve 26 with the working cylinder 14 adjoining the piston rod 56 connected. In this ar- Working cylinder 14 also opens the pressure channel 20 connected to the high pressure accumulator 30 with the check valve 30.

The high-pressure accumulator 30 is also connected via the high-pressure channel 28 to the compression cylinder 18 delimited by the right ring end face 64. The start valve 32 is arranged in the high-pressure channel 28. The start valve 32 can be bypassed via a bypass channel 72, in which a check valve 70 is arranged, which enables the pressure medium to flow back from the compression cylinder 18 to the high-pressure accumulator 30.

A pressure line 74, which opens into the high-pressure channel 28 downstream of the check valve 70, can be opened via the outer peripheral edge of the ring end face 64 of the ring collar 60.

Otherwise, the free-piston engine shown in FIG. 6 corresponds to that from the exemplary embodiments described above, so that further explanations are unnecessary.

To initiate the compression stroke, the start valve 32 is moved from its blocking position into its through position, so that the high-pressure accumulator 30 is connected to the compression cylinder 18 via the pressure channel 28. The pressure acting on the annular end face 64 accelerates the hydraulic piston 8, moves the engine piston 6 to its AT and compresses the fresh air present in the combustion cylinder 38. After a predetermined axial displacement of the hydraulic piston 8, the peripheral edge of the annular end face 64 opens the pressure line 74, so that the pressure medium can enter the compression cylinder 18 directly bypassing the start valve 32. This can reduce throttle loss Minimize above the start valve 32, since the pressure medium only flows through the start valve 32 at the beginning of the compression stroke. During the compression stroke, pressure medium is drawn from the low-pressure accumulator 24 into the working cylinder 14 via the low-pressure channel 22 and the check valve 26 that opens. The engine piston 6 is braked by the increasing compression pressure in the combustion chamber 38 in the AT. The start valve 32 is closed and fuel is injected via the injection valve 48, thereby igniting the resulting mixture. The engine piston 6 and the hydraulic piston 8 are accelerated from the AT to the IT, the pressure line 74 being closed when the hydraulic piston 8 moves back. The expansion movement takes place against the pressure in the working cylinder 14 and in the compression cylinder 18, so that when the check valve 34 is open, the high-pressure accumulator 30 is charged via the pressure channel 20 or via the high-pressure channel 28.

FIG. 7 shows a variant of the free-piston engine shown in FIG. 6 with hydraulic pistons 8 designed as stepped pistons, this being equipped with a piston retraction system, by means of which the engine pistons 6 and the hydraulic pistons 8 can be returned to their IT position in the event of a fault. In the exemplary embodiment shown in FIG. 7, the piston retraction system has a return duct 76 which is connected to the high-pressure accumulator 30 and which opens into the ring cylinder 68. The connection between the ring cylinder 68 and the high-pressure accumulator 30 can be shut off or opened via a switching valve 78 designed as a 2/2-way valve. In the event of a fault, for example a misfire, the ring cylinder 68 can be connected to the high-pressure accumulator 30 via the changeover valve 78, so that the ring end face 66 is acted upon by a pressure acting in the IT direction. In the exemplary embodiment shown in FIG Surface of the piston rod 58 moves smaller than that of the piston rod 56, so that the resultant force acting on the two end faces 66, 64 of the collar SO acts in the IT direction.

The pressure in the working cylinder 14 can be reduced via a relief duct 80 connecting the working cylinder 14 with the part of the low-pressure duct 22 arranged downstream of the check valve 26. This can be opened or closed via a control valve 82. That is, when the piston retraction is initiated, the control valve 82 is brought into its open position so that the pressure medium is fed into the low-pressure accumulator 24 from the working cylinder 14 via the relief channel 80 when the hydraulic piston 8 moves back.

The annular end face 66 of the hydraulic piston 8 can also be connected via a channel 84 with a further changeover valve 86 to the relief channel 80 and thus directly to the low-pressure accumulator 24, so that, for example, the back of the hydraulic piston 8 can be subjected to a lower pressure during the compression stroke. The control valve 82 is brought into its blocking position.

FIG. 8 shows a schematic representation of that area of a free-piston engine 1 in which the hydraulic piston 8 for driving the engine piston, not shown, is arranged. In the exemplary embodiment shown in FIG

Exemplary embodiment according to FIG. 4 - the low-pressure accumulator 24 is connected to the annular working space of the working cylinder 14 via a check valve 26. The check valve 26 can be bypassed via a bypass line 50 with a metering valve 52, so that the compression energy supplied at the beginning of the compression stroke by direct connection of the low pressure accumulator 24 can be influenced.

The high-pressure accumulator 30 is connected to the high-pressure channel 28 and the start valve 32 and the pressure channel 20

Compression cylinder 18 connected. In the illustrated

The embodiment is the check valve 34 in the

Hydraulic piston 8 integrated.

Similar to the embodiment shown in FIG. 5, the free-piston engine has a piston retraction arrangement 84, which, however, is formed by a check valve 86 and a retraction valve 88 in the solution shown. The check valve 86 is also integrated in the hydraulic piston 8. The withdrawal valve 88 is designed as a 2/2-way valve which, in its spring-loaded basic position, shuts off a channel 92 extending between a tank channel 90 and the pressure channel 20 and opens this connection in its switching position.

The high-pressure channel 28 can be connected directly to the compression cylinder 18 by bypassing the start valve 32 via a directional valve 94, which is integrated in the motor housing 2 of the free-piston engine 1. In the embodiment shown in Figure 8, the directional valve 94 is designed as a logic valve (2/2-way cartridge valve) with a graduated logic piston 96. The end face of the logic piston 96 with a larger cross-sectional area 98 is prestressed against a valve seat 100. In the area of this valve seat 100, a radial connection 102 is formed, which is connected to the high-pressure duct 28 via a bypass line 104. In other words, when the logic piston 96 rests on the valve seat 100, the connection between the bypass line 104 and the compression space 18 is shut off. The other end section of the logic piston 96 with a smaller cross-sectional area 106 is guided into a control chamber 108, which can be connected to the tank channel 90 or the high-pressure channel 28 via a control channel 110 and a release valve 112. In the exemplary embodiment shown, the release valve 112 is designed as a 3/2-way valve which, in its spring-preloaded basic position, connects the high-pressure channel 28 to the control channel 110. In the switching position, the connection to the high-pressure duct 28 is blocked and the control duct 110 is connected to the tank duct 90.

In addition, due to the pressure present in the control chamber 108, the logic piston 96 is also biased against the seat 104 in the closing direction by the force of a spring 113.

To start the free-piston engine, the release valve 112 is brought into its switching position, so that the smaller area cross section 106 is acted upon by the tank pressure. The spring 113 is designed so that the control piston is initially still biased against the valve seat 100 when the engine is started. The start valve 32 is opened so that the compression cylinder 18 is acted upon by the pressure in the high-pressure accumulator - the hydraulic piston 8 is accelerated by the increasing pressure. As a result, the pressure acting on the larger cross-sectional area 98 of the logic piston 96 rises, so that it opens, lifts off the valve seat 100 and the radial connection 102 and thus the connection to the high-pressure accumulator 30 is opened - the logic valve 94 opens completely.

It is advantageous in this variant that the logic piston 96 receives its energy for opening via its own control edge, so that no pilot valve is required / 88352

is. The opening movement takes place very quickly, so that the pressure in the compression cylinder 18 can be increased with high dynamics. During operation of the free-piston engine 1, the logic piston 96 remains in its open position.

To stop the free-piston engine, the start valve 32 is closed and the release valve 112 is switched to its basic position, so that the pressure in the high-pressure accumulator is applied to the smaller cross-sectional area 106 of the logic piston 96. The free piston engine 1 then comes to a standstill when the start valve 32 and the logic valve 94 are closed. In other words, in the solution described above, the logic valve 94 also acts as a check valve, via which the connection from the compression cylinder 18 to the high-pressure accumulator 30 can be controlled.

As can be seen from the schematic illustration according to FIG. 8, the blocking valve 86 is in the closing direction by the force of a closing spring 114 and in

Opening direction acted upon by the pressure in the compression cylinder 18. When the shut-off valve 86 is open, the working cylinder 14 is connected to the compression cylinder 18 via the check valve 34. Accordingly, in the case of the above-described pressure build-up in the compression cylinder 18, the shut-off valve 86 is brought into its open position, so that the pressure building up in the working cylinder 14 via the check valve 34 and the high-pressure channel 28 can be used for charging the high-pressure accumulator 30 during the compression stroke.

Figure 9 shows a possible constructive solution for

Integration of the check valve 84 and the check valve

86 in the hydraulic piston 8. Accordingly, this is a divided piston with a collar 116 and one with respect to the outer diameter of the collar 116 in diameter wrestled piston rod 118 executed. The collar 116 and the piston rod 118 are connected to one another via a sliding sleeve 120. For connection in the axial direction, the piston rod 118 has an enlarged end piece 122, which is arranged within the sliding sleeve 120. In the stop position shown, a rear stop surface 124 bears against a stop ring 126 of the sliding sleeve 120. The end piece 122 is designed with a guide bore 128 in which a closing body 130 is guided in an axially displaceable manner. This is biased towards the collar 116 by a compression spring 132. This is cup-shaped and has an opening 137 in a base 134. In the basic position shown, this opening 137 is closed by the closing body 130, which is biased against it, so that the connection between the compression cylinder 18 and the working cylinder 14 is blocked. The closing body 130 thus forms a seat 136 for the collar 116.

According to FIG. 9, the closing body 130 has compensation bores 138 through which pressure medium from the working cylinder 18 can enter a spring chamber 140. The closing body 130 has a guide pin 142 which plunges sealingly into an axial bore 144 of the piston rod 118. The force of the compression spring 132 and the area difference between the left seat-side end face and the right spring chamber-side ring end face is selected so that the closing body 130 is still biased into its closed position at a pressure in the working cylinder 18, which is below the pressure in the low-pressure accumulator 24. When a higher pressure is reached in the working cylinder 18, the closing body 130 is moved to the right against the force of the compression spring 132 until it hits a stop shoulder 146. Due to the pressure in the working cylinder 18, the collar 116 is also axially aligned with the piston rod 118. device moved to the right (view according to FIG. 9) until it runs onto the closing body 130, so that the opening 137 is blocked off. If, during the compression stroke, the pressure in the working cylinder 14 rises to a pressure> than the pressure in the compression cylinder 18, the collar 116 is lifted from the closing body 130 by the pressure difference acting on its end face and the connection between the working cylinder 14 and the compression cylinder 18 is opened - the high-pressure accumulator Loading. That is, in this embodiment, the collar 116 acts as a check valve for opening the connection between the working cylinder 14 and the compression cylinder 18. The closing body 130 with the compression spring 132 practically acts as a check valve which is brought into its open position when the pressure in the compression cylinder 18 rises. This check valve closes only when the pressure in the compression cylinder 18 is lower than the pressure in the low-pressure accumulator 24. Such a low pressure is set when the free piston is to be specifically moved back to its starting position.

In particular, the above-described solution is characterized by an extremely compact structure, the throttling losses being minimal due to the direct connection between the working and compression cylinders 14, 18. In principle, the solutions explained in FIGS. 8 and 9 can also be implemented in the exemplary embodiments described above.

The additional devices shown in the above-described exemplary embodiments can in principle be used individually or in combination in the case of the two aforementioned variants with stepped or differential pistons.

Instead of the 3/2-way valve shown in FIG. 5, a 2/2-way valve can also be used as the piston return valve 54 are used, in which case the check valve 34 should be designed to be lockable.

What is disclosed is a free-piston engine with an engine piston that can be driven via a graduated hydraulic piston. The larger diameter of the hydraulic piston is guided in a compression cylinder, while the smaller diameter is arranged in a working cylinder. During the compression stroke, the compression cylinder is connected to a high-pressure accumulator and the working cylinder to a low-pressure accumulator or a high-pressure accumulator. During an expansion stroke, the high-pressure accumulator is charged by the pressure medium displaced from the cylinder rooms.

Reference symbol list:

1 free piston engine

2 engine housing 4 combustion cylinder

6 engine pistons

8 hydraulic pistons

10 axial bore

12 ring end face 4 working cylinder 6 end face 8 compression cylinder 0 pressure channel 2 low pressure anal 4 low pressure storage 6 RV 8 high pressure channel 0 high pressure storage 2 start valve 4 RV 6 outlet channel 8 combustion chamber 0 inlet space 2 overflow channel 4 inlet channel 6 inlet valve 8 injection valve 0 bypass line 2 ^' Dosing valve 4 piston directional valve 6 piston rod 8 piston rod 0 ring collar 2 small end face 4 right ring end face 6 ring face Ring cylinder non-return valve bypass channel pressure line return channel change entil relief channel control valve piston retraction arrangement check valve return valve tank channel channel directional control valve logic piston larger area cross-section valve seat radial connection bypass line small area cross-section control chamber control channel release valve spring closing spring collar piston rod sliding sleeve end piece stop surface stop ring guide ring 137 breakthrough

138 compensating bore 140 spring chamber

142 guide pin

144 axial bore

146 stop shoulder

Claims

Expectations

1. Free-piston engine with an engine piston (6) which can be driven via a graduated hydraulic piston (8), the section with a smaller diameter in a working cylinder (14) and the section with a larger diameter in a compression cylinder (18) which is arranged during the Compression stroke can be acted upon with pressure medium from a pressure medium reservoir (30) via a start valve (32), pressure medium from a low pressure reservoir (24) being able to be sucked into the working cylinder (14), while during the Ξ expansion stroke the pressure medium in one of the cylinders (14, 18 ) can be used for charging a pressure medium store, characterized in that the pressure medium store is a high pressure store (30) which can be connected both to the working cylinder (14) and to the compression cylinder (18).

2. Free piston engine according to claim 1, wherein a larger end face (16) of the piston (8) with the high pressure accumulator (30) and a smaller ring end face (12) of the piston (8) via a check valve (34) with the high pressure accumulator (30) or Can be connected to the low-pressure accumulator (24) via a second check valve (26).

3. Free-piston engine according to claim 1, wherein the hydraulic piston (8) is a stepped piston (8) with a piston rod (56) guided in the working cylinder (14), the piston section of which having a larger diameter (60) is guided in the compression cylinder (18).

4. Free-piston engine according to claim 2 or 3, with a pressure line (74), on the one hand in an area of the high-pressure channel (28) between the start valve (32) and high-pressure accumulator (30) and on the other hand opens into the compression cylinder (18), and which can be opened during the compression stroke of the hydraulic piston (8), the section of the high-pressure channel (28) arranged between the start valve (32) and the compression cylinder (18) ) can be connected to the pressure line (74) via a line with a check valve (70).

5. Free-piston engine according to claim 3 or 4, wherein from the high-pressure channel (28) branches a return channel (76) with a changeover valve (78), and opens into a ring cylinder (68) penetrated by a further piston rod (58), so that when the valve is turned open - Switching valve (78) in the direction of the inner dead center of the engine piston (8) effective annular surface (66) can be acted upon with pressure medium.

6. Free piston engine according to claim 5, wherein the engine piston piston rod (58) is less

Has diameter than the other piston rod (56).

7. Free piston engine according to claim 2 with a directional control valve (94), via the piston (96) of which a bypass valve (104) bypassing the start valve (32) can be opened.

8. Free-piston engine according to claim 7, wherein the directional control valve (94) is a logic valve, the logic piston (96) of which is designed in a stepped manner, a smaller area cross section (106) via a release valve (112) with the pressure in the high-pressure accumulator (30) and whose larger cross-sectional area {98) is acted upon by the pressure in the compression cylinder (18).

9. Free-piston engine according to claim 8, wherein the release valve (112) is a 3/2-way valve, which in its switching positions acts on the smaller cross-sectional area (106) with the pressure in the high-pressure accumulator (30) or a pressure in a tank channel (90).

10. Free-piston engine according to one of the preceding claims, with a piston return valve arrangement (54), via which the compression cylinder can be connected to the tank (T) or to the high-pressure accumulator (30).

11. Free piston engine according to claim 10, wherein the piston retraction arrangement (54) has a check valve (86)

Connecting the working cylinder (14) to the compression cylinder (18) and a return valve (88) for connecting the compression cylinder (18) to the tank (90), the check valve (86) being integrated in the hydraulic piston (8).

12. Free-piston engine according to claim 11, wherein the check valve associated with the high-pressure accumulator (30)

(34) is also integrated in the hydraulic piston (8).

13 free-piston engine according to claim 12, wherein a larger piston diameter forming collar (160) of the hydraulic piston (8) via a sliding sleeve (120). is connected to a piston rod (118) which is guided axially displaceably in the sliding sleeve (120) with an end piece (122), the collar (116) closing a control cross section in a displacement position, so that a connection between the compression cylinders (14) and the working cylinder (18) is interrupted.

14. Free-piston engine according to claim 13, wherein in the end piece (122) a closing body (130) is guided, which is biased by means of a compression spring (132) against an opening in the bottom (134) of the collar (116), the pressure in Compression cylinder (18) is reported via compensating bores (138) of the closing body (130) in a spring chamber (140) for the compression spring (132) and the area of the closing body (130) effective in the closing direction is less than the end face of the closing body effective in the opening direction (130) is.

15. Free-piston engine according to one of the preceding claims, wherein in a low-pressure channel (22) see between the working cylinder (14) and the low-pressure accumulator (24), a non-return valve (26) bypass line (50) is provided, which via a metering valve (52 ) can be locked.