Combustion engine and gas handling system for pneumatic operation of a valve actuator

A combustion engine includes, a first controllable engine valve (8) arranged to selectively open/close a combustion chamber (7) included in the combustion engine (1), and a gas handling system arranged to drive the first engine valve (8), which gas handling system includes a closed pneumatic pressure fluid circuit, wherein the closed pressure fluid circuit includes, coupled in series with each other, a compressor (31) and a valve actuator (10) that are operatively connected to the first engine valve (8). The combustion engine is characterized by the gas handling system further including a gas accumulator (38) that is connected with the closed pressure fluid circuit via at least one gas accumulator conduit (39), which includes a controllable valve (40). A gas handling system for pneumatic control of a valve actuator is also described.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to a combustion engine suitable for powering a vehicle, such as a car or a truck, a boat etc. or a machine such as an electric power generation unit or the like. The combustion engines concerned are camshaft free piston engines, which are also known under the concept “engines with free valves”. The present invention relates in particular to a combustion engine comprising a first controllable engine valve arranged to selectively open/close a combustion chamber included in the combustion engine, and a gas handling system arranged to drive said first engine valve, which gas handling system comprises a closed pneumatic pressure fluid circuit, wherein the closed pressure fluid circuit comprises, coupled in series with each other, a compressor and a valve actuator that is operatively connected to said first engine valve.

In a second aspect, the present invention relates to a gas handling system for pneumatic operation of a valve actuator.

BACKGROUND OF THE INVENTION AND STATE OF THE ART

In a camshaft free combustion engine a pressure fluid, such as a liquid or a gas, is used to achieve a displacement/opening of one or more engine valves. This means that the camshafts, and related equipment, that conventional combustion engines use to open engine valves to let air in respective let exhaust fumes out from the combustion chamber, has been replaced by a less volume demanding and more controllable system.

In an engine that is constructed for significant angular momentum outputs, the pressure in the combustion chamber is increasing proportional to an increased angular momentum output, and the force that is required to open the valve actuator to open the, in relation to the combustion chamber inward opening, engine valve consequently also increases proportional to an increased angular momentum output. At high numbers of revolutions, such as 6-8000 rpm, a very fast opening of the engine valve is also required for the filling of air respective evacuation of exhaust fumes from the engine cylinder not to be restricted. These requirements, i.e. the need for an extremely fast opening at high frequencies in a high performance engine having high counter pressure in the combustion chamber of the engine at the opening of the exhaust valves, require the pressure of the pressure fluid upstream of the valve actuator to be high, in the order of 8-30 bar. Downstream the valve actuator, the pressure fluid has a lower pressure, in the order of 3-6 bar.

At high numbers of revolution and high engine loads, the pressure difference between the low pressure side and the high pressure side should be in the order of 15-20 bar to achieve a correct operation of the valve actuators, and when the engine is idle running, or at low numbers of revolution and low loads, the pressure difference between the low pressure side and the high pressure side only needs to be in the order of 2-5 bar. The lower pressure difference at low numbers of revolution is desirable when the pressure is increased by way of a compressor from the low pressure side to the high pressure side, and at the pressure increase, energy consumption occurs that increases concurrently with increased pressure on the high pressure side.

In situations that require fast acceleration and/or very fast change from low numbers of revolution and low load to high numbers of revolutions and high load, for example when entering on a busy main road or at a sudden overtaking of a slow moving vehicle, the pressure difference between the low pressure side and the high pressure side must immediately be increased to achieve the acceleration that the driver requires. A conventional compressor is dimensioned to be able to generate pressure differences with greatly varying magnitude, they are however not dimensioned to satisfy the requirement of immediate shifts between separate great pressure difference levels and pressure fluid flows.

Furthermore, there is inertness in the present systems to go from a great pressure difference to a small pressure difference, i.e. when the vehicle again is operated at low numbers of revolution after the short/temporary rise in numbers of revolutions/engine load, it will take time before the pressure difference and thereby the high energy consumption has decreased to a desired level.

BRIEF DESCRIPTION OF THE PURPOSE OF THE INVENTION

The aim of the present invention is to set aside the abovementioned drawbacks and shortcomings of the previously known combustion engines and to provide an improved combustion engine. A fundamental object of the invention is to provide an improved combustion engine of the initially defined type, which is arranged to be able to immediately increase the pressure difference between the low pressure side and the high pressure side by increasing the pressure on the high pressure side of the pressure fluid circuit at the need of a rapid increase in the numbers of revolution/engine load of the combustion engine.

A further object with the present invention is to provide a combustion engine that can rapidly go from a great pressure difference to a small pressure difference between the low pressure side and the high pressure side.

It is another object with the present invention to provide a combustion engine that, after each sudden increase in pressure difference, is self priming before the subsequent need for a sudden increase of pressure difference.

BRIEF DESCRIPTION OF THE FEATURES OF THE INVENTION

According to the invention, the main object is at least achieved by way of the initially defined combustion engine and of a gas handling system for pneumatic operation of a valve actuator having the features defined in the independent claim. Preferred embodiments of the present invention are further defined in the subsequent dependent claims.

According to a first aspect of the present invention, a combustion engine of the initially defined type is provided that is characterized in that the gas handling system further comprises a gas accumulator that is connected to the closed pressure fluid circuit via at least one gas accumulator conduit, which includes a controllable valve.

According to a second aspect of the present invention, a gas handling system for pneumatic operation of a valve actuator is provided comprising a closed pneumatic pressure fluid circuit, wherein the closed pressure fluid circuit comprises, coupled in series with each other, a compressor and a valve actuator. The gas handling system is characterized by comprising a gas accumulator that is connected to the closed pressure fluid circuit via at least one gas accumulator conduit, which comprises a controllable valve.

The present invention is thus based on the insight that a gas accumulator is arranged to store earlier pressure peaks to rapidly be able to supply a large volume of pressure fluid under high pressure to the closed pressure fluid circuit, for the purpose of achieving an immediate pressure increase on the high pressure side of the pressure fluid circuit.

According to a preferred embodiment of the present invention, the closed pressure fluid circuit comprises a primary pressure fluid channel that extends from the compressor to an inlet opening of the valve actuator, wherein the gas accumulator is connected to the primary pressure fluid channel via a first gas accumulator conduit, which comprises a controllable valve.

According to a preferred embodiment of the present invention, the gas accumulator is connected to said primary pressure fluid channel via a second gas accumulator conduit, which comprises a non-return valve arranged to allow a flow in a direction toward the gas accumulator. This way, it is guaranteed that when the controllable valve in the first gas accumulator conduit is closed, the pressure in the gas accumulator is always equally high as the highest pressure peak in the high pressure side of the closed fluid circuit.

According to a preferred embodiment, the compressor has a variable displacement. This means that the pressure increase of the high pressure side of the pressure fluid circuit can be sped up further by increasing the displacement of the compressor in connection with a rapidly increased number of revolutions or load. The size of the displacement is preferably controlled by the pressure difference between the upper side and lower side of the compressor pistons, i.e. the pressure ratio over the compressor.

According to a preferred embodiment, the closed pressure fluid circuit comprises a secondary pressure fluid channel that extends from the cylinder head chamber to the compressor, wherein the gas accumulator is connected with said secondary pressure fluid channel via a third gas accumulator conduit, which comprises a controllable valve. Thereto, it is preferred that a non-return valve is arranged in said secondary pressure fluid channel upstream the position where the third gas accumulator conduit discharge in the secondary pressure fluid channel, wherein the non-return valve is arranged to allow a flow in a direction toward the compressor. This leads to the average pressure on the uppers side of the compressor pistons increases, which leads to a rapid increase in the displacement of the compressor.

Further advantages with and features of the invention are evident from the remaining dependent claims and from the following detailed description of preferred embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is initially made toFIG. 1that is a schematic depiction of a part of an inventive combustion engine, generally denoted1. The combustion engine1comprises a cylinder block2with at least one cylinder3. Said cylinder block2generally comprises three or four cylinders3. In the shown embodiment reference is made only to one cylinder3, it should nevertheless be realized that he equipment described below in relation to the shown cylinder3is preferably applied to all of the cylinders of the combustion engine1, in the embodiment the combustion engine comprises more cylinders.

Furthermore, the combustion engine1comprises a piston4that is axially displaceable in said cylinder3. The movement, axial displacement back and forth, of the piston4is transferred on a conventional manner to a connection rod5connected to the piston4, the connection rod5in turn is connected to and drives a crank shaft (not shown) in rotation.

The combustion engine1also comprises a cylinder head6that together with said cylinder3and said piston4delimits a combustion chamber7. In the combustion chamber7the ignition of a mix of fuel and air occurs in a conventional manner and is not further described herein. The cylinder head6comprises at least one controllable first engine valve8, also known as a gas exchange valve. In the shown embodiment, the cylinder head also comprises a controllable second engine valve9. The one engine valve8constitutes, in the shown embodiment, an inlet valve that is arranged to selectively open/close for supply of air to the combustion chamber7, and the second engine valve9constitutes in the shown embodiment an air outlet valve, or exhaust valve, that is arranged to selectively open/close for evacuation of exhausts form the combustion chamber7.

The combustion engine1further comprises a first valve actuator, generally denoted10, that is operatively connected to said first engine valve8and that is arranged in a closed pressure fluid circuit of the combustion engine1. The valve actuator10comprises a pneumatic pressure fluid circuit with at least one inlet opening11for pressure fluid and at least one outlet opening12for pressure fluid. The pressure fluid is a gas or a gas mixture, preferably air or nitrogen gas. Air has the advantage that it is easy to change the pressure fluid or to supply more pressure fluid if the closed pressure fluid circuit leak, and nitrogen gas has the advantage that it lacks oxygen, which prevents oxidation of other elements.

In the case the combustion engine comprises several valve actuators are these arranged in parallel to one another in said closed pressure fluid circuit. Each valve actuator can be operatively connected with one or more engine valves, the combustion engine can for example comprise two air inlet valves8, which are jointly driven by the same valve actuator10. Nevertheless, it is preferred that each valve actuator operates one engine valve each to achieve the greatest possible controllability of the operation of the combustion engine1.

The description below of the combustion engine will only include one engine valve8and one valve actuator10, but it should be realized that the corresponding also applies to all engine valves and valve actuators if nothing else is said.

The combustion engine1also comprises a cylinder head chamber13that forms part in said closed pressure fluid circuit and that is delimited by said cylinder head6and at least a first cylinder head mantle14. In the shown embodiment, the cylinder head mantle14is divided in two parts, which are individually attachable to and releasable from the cylinder head6by way of bolts. The cylinder head chamber13preferably presents a volume in the order of 3-10 liter, typically in the order of 5-6 liter. In an alternative embodiment, only a cylinder head mantle14is present that, together with the cylinder head6, delimits the cylinder head chamber13.

The at least one outlet opening12of the valve actuator10is in fluid communication with the cylinder head chamber13, i.e. that the pressure fluid leaving the valve actuator10via said at least one outlet opening12flows out in the cylinder head chamber13. In those case where the combustion engine1comprises several valve actuators, all outlet openings of the valve actuators for pressure fluid discharge in the same cylinder head chamber.

Preferably, the whole of the valve actuator10is arranged in said cylinder head chamber13, and it is also preferred that the valve actuator10is releasably connected to said cylinder head mantle14, for example by a bolt16, or similar holding means. In this embodiment, the valve actuator10accordingly “hangs” in the cylinder head mantle14without being in contact with the cylinder head6. If the valve actuator10should be in contact with both the cylinder head mantle14and the cylinder head6, a construction wise disadvantageous tolerance chain is achieved.

Reference is now made toFIG. 2, which shows a schematic depiction of the valve actuator10.

The valve actuator10comprises an actuator piston disc17and an actuator cylinder21delimiting a downward open cylinder volume. The actuator piston disc17divides said cylinder volume in a first upper part19and a second lower part20and is axially displaceable in said actuator cylinder21. The actuator piston disc17forms part of an actuator piston, generally designated21, that is arranged to contact and drive said first engine valve8. The actuator piston further comprises means22for play elimination in axial direction in relation to said first engine valve8.

The play eliminating means22are preferably hydraulic, and assures that when the actuator piston disc21is in its upper turn position, the actuator piston21remains in contact with the first engine valve8when it is closed, for the purpose of correcting for assembly tolerances, heat expansion, etc. Accordingly, the axial length of the actuator piston21is adjusted by way of the play eliminating means22.

The other part20of the cylinder volume of the valve actuator10is in fluid communication with said cylinder head chamber13. This way, it is guaranteed that the same pressure acts on the actuator piston disc17from the first part19of the cylinder volume respective from the second part20of the cylinder volume when the actuator piston21is in the upper turn position. Thereby, the sealing between the actuator piston disc17and the actuator cylinder12is not critical, but some leakage can be allowed for minimizing the resistance to displacement of the actuator piston disc17, and in resting position, the actuator piston disc is not affected by changes in the low pressure level.

The valve actuator10comprises a controllable inlet valve23that is arranged to open/close the inlet opening12, a controllable outlet valve27that is arranged to open/close the outlet opening11, a hydraulic circuit, generally designated25, that in turn comprises a non-return valve26arranged to allow filling of the hydraulic circuit25, and a controllable emptying valve27arranged to control the emptying of the hydraulic circuit25. It should be pointed out that the valves in the valve actuator10are schematically depicted and can for example be constituted by sliding valves, seat valves, etc. Furthermore, several of the abovementioned controllable valves may be constituted by a single body. Each valve can further be directly or indirectly electrically controlled. With directly electrically controlled is meant that the position of the valve is directly controlled by, for example, an electro-magnetic device, and with indirect electrically controlled is meant that the position of the valve is controlled by a pressure fluid that in turn is controlled by, for example, an electro-magnetic device.

To achieve a displacement of the actuator piston disc17downward for opening the engine valve8, the inlet valve26is opened to allow a filling of pressure fluid with a high pressure in the upper part19of the cylinder volume. When the actuator piston21is displaced downward, the non-return valve26of the hydraulic circuit25opens, whereupon hydraulic liquid is sucked in and replaces the volume that the actuator piston21leaves. Thereafter, the inlet valve23is closed and the pressure fluid that has entered in the upper part19of the cylinder volume is allowed to expand, whereupon the actuator piston disc17continues its movement downward. When the pressure fluid in the upper part19of the cylinder volume is not able to displace the actuator piston disc17further, i.e. when the pressure on the under side of the actuator piston disc17and the return spring28of the engine valve8is as high as the pressure on the upper side of the actuator piston disc17, the actuator piston disc17stops. The actuator piston disc17is held (locked) in its lower position a desired amount of time by keeping the emptying valve27of the hydraulic circuit25closed at the same time as the non-return valve26of the hydraulic circuit25is automatically closed. To achieve a return movement, the outlet valve24is opened to allow an evacuation of pressure fluid from the upper part19of the cylinder volume, and additionally the emptying valve27of the hydraulic circuit25is opened, whereupon the actuator piston disc is displaced upward when the hydraulic liquid is evacuated from the hydraulic circuit25, and at the same time, the pressure fluid is evacuated from the upper part17of the cylinder volume to the cylinder head chamber13.

Reference is now made primarily toFIG. 3, which shows a partly cross-sectional schematic perspective view of, among other things, a cylinder head and cylinder head mantles.

The cylinder head mantle14comprises a pressure fluid manifold29that is connected to the at least one inlet opening11of the valve actuator10. The pressure fluid manifold29extends along the axial length of the cylinder head mantle14. Said pressure fluid manifold29forms part of a primary pressure fluid channel30that extends from a compressor31to the at least one inlet opening11of the valve actuator10. The compressor31is arranged to supply a pressure fluid under high pressure to the valve actuators. Furthermore, a secondary pressure fluid channel32(see alsoFIG. 1) extends from the cylinder head chamber13to said compressor31.

The volume of the primary pressure fluid channel30, high pressure side, shall be kept as small as possible so that the temperature of the pressure fluid will sink as little as possible from the compressor31to the valve actuator10. The volume of the cylinder head chamber13and the secondary pressure fluid channel32, low pressure side, shall on the other hand be maximized so that the pressure ratio between the low pressure side and the high pressure side is affected as little as possible when the compressor31pulls gas/pressure fluid from the low pressure side. Preferably, the volume of the cylinder head chamber13and the secondary pressure fluid channel32is at least ten times greater than the volume of the primary pressure fluid channel30, most preferably at least15times greater.

The compressor31has variable compressor volume/displacement, or by other means adjustable outflow, and generally the compressor31is driven by the crank shaft of the combustion engine1. At high numbers of revolutions and high torque output, higher pressure of the pressure fluid in the primary pressure fluid channel30is required, and at low numbers of revolutions and low torque output, lower pressure of the pressure fluid in the primary pressure fluid channel30is required. The pressure difference between the high pressure side and the low pressure side is in the order of 15-20 bar at high numbers of revolution/torque loads and in the order of 2-5 bar at low numbers of revolution and low engine loads. The compressor31is preferably of the type axial piston pump or swashplate pump, which provides a variable displacement by way of several pistons with variable stroke, where all pistons are arranged in mutually different positions in their respective cycles. The stroke is determined by the inclination of a glide plate, which acts against, and by rotation drives the pistons to perform an axial movement, and central axis of the glide plate performs a nutating motion. For each revolution the glide plate is turned, all pistons will perform one cycle. The inclination of the glide plate is thus variable/adjustable.

The pressure level on the high pressure side in in the order of 8-30 bar to, with sufficient speed, open an inward opening engine valve where a high counter pressure is present in the combustion chamber, and the pressure level on the low pressure side is in the order of 4-8 bar.

The cylinder head mantle14further comprises a hydraulic liquid manifold33that is connected with an inlet opening34of said hydraulic circuit25of the valve actuator10. The hydraulic liquid manifold33extends along the axial length of the cylinder head mantle14, parallel to the pressure fluid manifold29. A pump35, or the like, is arranged to supply a pressurized hydraulic liquid to the hydraulic liquid manifold33via a conduit36. The cylinder head mantle14further comprises all necessary electric infrastructure (not shown) for, among other things, controlling the first valve actuator10, for various sensors, etc.

Reference is now primarily made to theFIGS. 4-9, which schematically show alternative embodiments of a gas handling system according to the invention for pneumatic control of a valve actuator10, which gas handling system comprises a pneumatic closed pressure fluid circuit.

In theFIGS. 4-9, a compressor is shown to the right, the primary pressure fluid channel30(high pressure side) at the upper edge, the valve actuator10to the left, and the secondary pressure fluid channel32(low pressure side) at the lower edge. The pressure fluid thus flows counter-clockwise in the figures, which is illustrated by way of an arrow37inFIG. 4.

Essential to the present invention is that the gas handling system comprises a gas accumulator38that is connected to the closed pressure fluid circuit via at least one gas accumulator conduit, which includes a controllable valve.

Reference is now made toFIG. 4, which shows a preferred first embodiment. In this embodiment, the gas accumulator38is connected with said primary pressure fluid channel30via a first gas accumulator conduit39, which comprises a controllable valve40.

At the need of a rapid pressure increase on the high pressure side from a low pressure level to a high pressure level, for example as a response to the accelerator paddle in the vehicle being rapidly pushed down and/or that the number of revolutions rapidly increases, the controllable valve40in the first gas accumulator conduit39is opened, whereupon the closed in volume, that has a higher pressure level than the pressure level present on the high pressure side, flows into the primary pressure fluid channel30and provides an immediate pressure rise on the high pressure side. The pressure level in the gas accumulator is lowered somewhat. The volume of the gas accumulator38is preferably at least five times greater than the volume in the primary pressure fluid channel30. Preferably, the compressor31has a variable displacement31that is controlled by the pressure relation over the compressor and the pressure on the lower side of the compressor pistons, whereupon the compressor31is arranged to, at a pressure increase on the high pressure side, achieve an automatic increase of the displacement of the compressor31, which lead to a further pressure increase.

Preferably, a first pressure sensor41is connected with the gas accumulator38, and a second pressure sensor42is connected with the primary pressure fluid channel30, to ensure that the pressure level in the gas accumulator38is higher than the pressure level in the primary pressure fluid channel30before the controllable valve40in the first gas accumulator conduit39is opened. In the shown embodiment, a third pressure sensor43is also connected with the secondary pressure fluid channel32to be able to determine the pressure relation between the low pressure side and the high pressure side.

When the pressure in the gas accumulator38is used to briefly rise the pressure level in the primary pressure fluid channel30, the controllable valve40in the first gas accumulator conduit39is closed. When the pressure level on the high pressure side again shall be lowered, the controllable valve40is opened in the first gas accumulator conduit39for refilling the gas accumulator38. The compressor31is preferably active to refill the gas accumulator to a predetermined level, irrespective of the need of pressure fluid with high pressure to the valve actuator10is remaining or not.

Reference is now made toFIG. 5, which shows a second embodiment. Only differences in relation to the embodiment according toFIG. 4will be described.

In addition to the first embodiment according toFIG. 4, the combustion engine1comprises a second gas accumulator conduit44that extends between the primary pressure fluid channel30and the gas accumulator38, and that comprises a non-return valve44, which is arranged to allow a flow in a direction toward the gas accumulator38. This way, it is guaranteed that hat the controllable valve40in the first gas accumulator conduit39can be closed as soon as a desired pressure increase has been achieved in the primary pressure fluid channel30. Thereafter, the non-return valve45in the second gas accumulator conduit44guarantees that the latest achieved highest pressure peak in the primary pressure fluid channel30is forwarded to and saved in the gas accumulator38. Accordingly, a simpler and automatic priming of the gas accumulator38is achieved. Further, the second gas accumulator conduit44also comprises flow restriction means44′, which for example are implemented by way of a constriction. The purpose of the flow restriction means44′ is to delay/limit so that the increased pressure that the compressor31delivers is not at first hand used to refill the gas accumulator38.

Reference is now made toFIG. 6, which shows a third embodiment. Only differences with respect to the embodiments according toFIGS. 4 and 5will be described.

In this embodiment, and in the subsequent embodiments, a cylinder head mantle13is also shown that is arranged between the secondary pressure fluid channel32and the valve actuator10. It should nevertheless be remarked that the cylinder head chamber13can be dispensed with in the third and the subsequent embodiments, and can be included in the first and the second embodiment.

In the third embodiment according toFIG. 6, the gas handling system comprises a gas accumulator conduit47that extends between the gas accumulator38and the secondary pressure fluid channel32and that comprises a controllable valve48. The first gas accumulator conduit39that is shown in the first and second embodiments is not present in the third embodiment.

At the need for a rapid pressure increase on the high pressure side from a low pressure level to a high pressure level, the controllable valve48in the third gas accumulator conduit47is opened, whereupon the closed in volume of pressure fluid flows into the secondary pressure fluid channel32. Thereby, the compressor31will be fed with a more dense pressure fluid, which gives a more rapid increase of the displacement of the compressor31and thereby provides a more rapid pressure increase on the high pressure side. Preferably, the third gas accumulator conduit47is connected with the secondary pressure fluid channel32close to or in direct connection with the compressor, in other words, the third gas accumulator conduit47is most preferably connected with the secondary pressure fluid channel32in the interface between the compressor31and the secondary pressure fluid channel32.

Preferably, the compressor31has a variable displacement that is controlled by the pressure relation over the compressor31and the pressure on the under side of the compressor pistons, whereupon the compressor31is arranged to, at a pressure rise at the inlet of the compressor31, automatically increase the displacement of the compressor.

Reference is now made toFIG. 7, which disclose a fourth embodiment. Only differences in relation to the embodiment according toFIG. 6will be described.

In the fourth embodiment according to claim7, the second gas accumulator conduit44comprises, in addition to the non-return valve45, a controllable valve45′ to prevent a refilling of the gas accumulator38when the need for a pressure rise on the high pressure side remains.

It is further preferred that a non-return valve49is arranged in the secondary pressure fluid channel32upstream the position where the third gas accumulator conduit47discharge in the secondary pressure fluid channel32, which non-return valve49is arranged to allow a flow in the direction toward the compressor, and thus preventing that the supplied pressure fluid flows into the cylinder head chamber13.

In an alternative (not shown) embodiment, the third gas accumulator conduit47is connected directly to the compressor31and the non-return valve49is also preferably arranged in the compressor31.

The controllable valve45′ in the second gas accumulator conduit44further leads to the gas accumulator38not being refilled/primed before said controllable valve45″ is opened. This leads to the volume in which the pressure should rise is kept at a minimum, whereupon a quicker pressure rise is achieved. When the need for a high pressure in the primary pressure fluid channel30decline/cease, the controllable valve45′in the second gas accumulator conduit44is opened, whereupon pressure fluid flows into the gas accumulator38. Additionally, the displacement of the compressor31will automatically decrease, which gives an even faster pressure drop on the high pressure side.

Reference is now made toFIG. 8, which shows a fifth embodiment. Only differences in relation to earlier described embodiments will be described.

The fifth embodiment is a combination of the first embodiment according toFIG. 4and the fourth embodiment according toFIG. 7. However, this embodiment comprises no second gas accumulator conduit. The fifth embodiment provides a possibility to open and release pressure fluid from the gas accumulator38, either in the primary pressure fluid channel30, via the first gas accumulator conduit39, or in the secondary pressure fluid channel32, via the third gas accumulator conduit47.

Reference is now made toFIG. 9, which shows a sixth embodiment. Only differences with respect to the earlier embodiments will be described.

The sixth embodiment is a combination of the second embodiment according toFIG. 5and the fourth embodiment according toFIG. 7. However, this embodiment comprises no controllable valve in the second gas accumulator conduit44.

Similar to the fifth embodiment according toFIG. 8, the sixth embodiment provides a possibility to open and release the pressure fluid from the gas accumulator, either in the primary pressure fluid channel30, via the first gas accumulator conduit39, or in the secondary pressure fluid channel32, via the third gas accumulator conduit47. Additionally, the sixth embodiment provides the automatic refilling function of the second embodiment according toFIG. 5.

Conceivable Modifications of the Invention

The invention is not limited to only the abovementioned and embodiments shown in the drawings, which only have an illustrating and exemplifying purpose. This patent application is intended to cover all modifications and variants of the preferred embodiments described herein, and the present invention is consequently defined by the wording of the enclosed claims and the equipment can thus be modified in all conceivable ways within the framework of the enclosed claims.

It should also be pointed out that all information about/concerning terms such as above, below, upper, lower, etc. shall be interpreted/read with the equipment oriented in accordance with the figures, with the drawings oriented in such a way that the reference numbers can be read in a correct manner. Consequently, such terms indicates only relative relationships in the shown embodiments, which relationships can be changed if the equipment according to the invention is provided with another construction/design.

It should be pointed out that even if it is not explicitly stated that features from a specific embodiment can be combined with the features of another embodiment, this should be regarded as obvious when so is possible.