FREE PISTON ENGINE PROVIDED WITH A PURGING AIR DOSING SYSTEM

Abstract: The invention relates to a free piston engine. The air required for combustion is supplied to the combustion chamber while the exhaust gasses leave the combustion chamber via an exhaust port. In order to achieve improved purging, that is to say to compress more oxygen-rich air, purging air is dosed into the purging air chamber or the combustion chamber by means of a purging air dosing system following a signal from the control means.

Description: Free piston engine provided with a purging air dosing system The invention relates to a free piston engine in accordance with the preamble of claim 1. Free piston engines of this kind are known from, for instance, the various patent applications as filed by the applicant. The disadvantage of the known free piston engines is that after fuel combustion, the combustion gasses do not leave the combustion chamber quickly enough to be replaced by clean oxygen-rich air. As a result the amount of oxygen present in the combustion chamber is limited causing the amount of combustible fuel to be limited and consequently also the energy to be generated by a particular engine. It is the object of the invention to increase the amount of energy to be supplied by a particular engine and to that end the free piston engine also comprises a purging air dosing system which, depending on the control means, is able to supply purging air via a connecting pipe to the purging air chamber or the combustion chamber. This achieves that the moment of purging air dosing can be subject to and adapted to the stroke frequency of the engine, so that a limited amount of energy suffices to compress the purging air, and the extra oxygen fed into the combustion chamber by the purging air dosing is optimally utilized. In accordance with a first embodiment of the invention the purging air dosing system comprises a continuously operating purging air pump having a buffer means and a valve operationable by the control means . This is a simple manner to realise separate purging air dosing. In accordance with a second embodiment of the invention the purging air dosing system comprises a purging pump which can be activated by the controls and which is directly connected with the purging air chamber or via a non-return valve with the combustion chamber. This avoids the use of a quick-acting valve which is prone to malfunctioning. In accordance with a further improvement of the invention, the control means are connected to sensor means for the detection of a position of the piston, which position serves to emit a signal for the dosing of purging air. This further simplifies the control because the purging air dosing depends directly on the position of the piston. The invention is also embodied in a method of purging combustion gasses from the combustion chamber of the free piston engine in accordance with the invention, which is characterized in that the dosing of the purging air is started at an adjustable time after starting the movement of the piston. This simple method achieves that after each stroke the engine is ready for the next stroke, irrespective of the stroke frequency. The invention will now be elucidated by means of some examples of embodiments referring to a Figure, in which Fig. 1 shows a schematic representation of a first embodiment of a free piston engine provided with a purging air dosing system; Fig. 2 shows a schematic representation of a second embodiment of a free piston engine provided with a purging air dosing system; and Fig. 3 shows a schematic representation of a third embodiment of a free piston engine provided with a purging air dosing system. Identical parts in the different Figures are provided with identical reference numbers . A free piston engine 1 comprises a cylinder 2 in which a piston 3 can move from a lower dead centre, shown in Fig. 1 when the piston 3 is to the right, to the upper dead centre, shown in Fig. 1 when the piston 3 is to the left. The movement of the piston 3 is effectuated in the known manner by means of a piston drive 9. To the piston 3 an oil piston 12 is connected by means of which oil is pumped from a low-pressure pipe 11 to a high-pressure pipe 8. At 10, a hydraulic system of a user is coupled with the high-pressure pipe 8 and the low-pressure pipe 11. The piston 3 and the cylinder 2 form a combustion chamber 16 and a purging air chamber 13. The purging air chamber is provided with a purging air supply B, which supply may take place via a non-return valve 5. When the piston 3 moves from the upper dead centre to the lower dead centre and the piston 3 unblocks an inlet opening 15, this purging air flows from the purging air chamber 13 via a purging air channel 14 into the combustion chamber 16. When the piston 3 moves from the upper dead centre to the lower dead centre, it also unblocks an exhaust port 4, from which the exhaust gasses can escape in the direction C. The next operating stroke again compresses the purging air in the combustion chamber 16 and, in the known manner, by means of a fuel injection system 17, fuel is injected into the compressed air, which then ignites in the usual manner . Purging air supply B takes place through a purging air dosing system 18 which, via a purging air connection 24 and a channel, is connected to or possibly integrated with the purging air chamber 13. The purging air connection 24 is connected to a pump chamber 26 in which a movable air piston 22 is provided. When the air piston 22 is moved in a direction D, it pumps air from an air supply A via a non-return valve 23 and a non-return valve 25 provided in the piston. The purging air dosing system 18 works as follows: the movement in the direction D occurs owing to the fact that during the movement of the piston's 3 lower dead centre to the upper dead centre a resetting channel 7 comes under high pressure from the pipe 8 with the result that both a cylinder 20 and a surge chamber 21 are subjected to this pressure. The area differences of the piston 27 which are subjected to pressure will make the air piston 22 move in a direction opposite to direction D until the extreme position is reached. The surge chamber 21 has a volume or is provided with an accumulator (not shown) such that when the compressed oil expands, it moves the piston 27 in the direction D. When moving from the upper dead centre to the lower dead centre, the oil piston 12 unblocks a switch channel 6 connecting the cylinder 20 with the low pressure 11, so that the piston 27 can move in the direction D under the influence of the pressure in the surge chamber 21. This drives extra purging air into the purging air chamber 13, the amount and/or the pressure of this purging air, depending among other things on the pressure at 8 , and thus depending on the capacity of the engine and the amount of fuel combusted per stroke. Figure 2 shows a second embodiment wherein a purging air dosing system 18 is directly connected via a non-return valve 28 with the combustion chamber 16. The air piston 22 will move when during the movement of the piston 3 from the lower dead centre to the upper dead centre, the switch channel 6 is opened. At that moment the pressure at both sides of the piston 27 equalizes and owing to the area difference the air piston 22 will move, causing the air piston 22 to press purging air via a non- return valve 28 into the combustion chamber. Simultaneously new air is drawn in via an opening E. With the subsequent movement from the upper dead centre to the lower dead centre, the high pressure 8 develops in the switch pipe 6 and the air piston 22 will return to its starting position. Figure 3 shows an embodiment wherein the entire air supply A takes place via a pressure booster 29, wherein the purging air is stored in an air buffer means 30 to be dosed via a pop valve 31 into the combustion chamber 16. The pressure booster 29 may be driven in the usual manner such as, for instance, by means of an exhaust-gas turbine coupled to an exhaust port 4. Driving is also possible by means of a hydraulic engine operating on the high pressure 8, so that the power supplied by the pressure booster is proportional to the power supplied by the engine. The valve 31 is operated through the control of the engine, and the switch time can be varied in order to obtain optimal adaptation to the operational conditions of the engine . The valve is preferably a pop valve as known from, for instance, WO96/03575, by the same applicant.

Claims: CLAIMS 1. A free piston engine for the generation of energy through combustion of fuel mixed with air, comprising a combustion chamber (16) formed by, among other things, a cylinder and a piston (3) movable in the cylinder (2) from a lower dead centre to an upper dead centre, exhaust ports (4) for the exhaust of combustion gasses (C) from the combustion chamber, inlet openings (15) for the supply of combustion air into the combustion chamber, a purging air pump (3, 13; 18; 29) for bringing the combustion air in a purging air chamber (13; 30) connected with the inlet openings under overpressure, a fuel system (17) for the supply and mixing of the fuel with the combustion air, moving means (9) for the acceleration or delay of the piston and for keeping it still at its lower dead centre, provided with control means by which the duration of keeping the piston in the lower dead centre can be adjusted so that the stroke frequency can be varied, characterized in that the free piston engine also comprises a purging air dosing system (18;29-31) which, depending on the control means, is able to supply purging air via a connecting pipe to the purging air chamber (13,30) or the combustion chamber (16) . 2. A free piston engine in accordance with claim 1, characterized in that the purging air dosing system com- prises a continuously operating purging air pump (29) having a buffer means (30) and a valve (31) operationable by the control means . 3. A free piston engine in accordance with claim 1, characterized in that the purging air dosing system com- prises a purging pump (18) which can be activated by the controls and which is directly connected with the purging air chamber (13) or via a non-return valve (28) with the combustion chamber (16) . 4. A free piston engine in accordance with claim 1, 2 or 3 , characterized in that the control means are connected to sensor means (6) for the detection of a position of the piston (3,12), which position serves to emit a signal for the dosing of purging air. 5. A free piston engine in accordance with one of the preceding claims wherein the moving means are formed by a hydraulic system, characterized in that the purging air dosing system comprises a hydraulically driven purging pump (18) and/or a hydraulically operated valve (31) . 6. A free piston engine in accordance with claim 5 , characterized in that the hydraulically driven purging pump and/or the hydraulically operated valve are provided with a surge chamber (21) for compressed liquid which serves to drive the means for dosing the purging air. 7. A free piston engine in accordance with one of the preceding claims, characterized in that means (21,27; 31) are present, which make that the amount and/ or pressure of the dosed purging air is dependent on the energy converted per stroke by the free piston engine . 8. A free piston engine in accordance with claim 7, wherein the energy is converted in an oil flow whose pres- sure (8) is load-dependent, characterized in that the purging air dosing system comprises dosing means (27, 29) for the purging air, which means can be moved by oil of this pressure. 9. A method of purging combustion gasses from the combustion chamber of the free piston engine in accordance with one of the preceding claims, characterized in that the dosing of the purging air is started at an adjustable time after starting the movement of the piston. 10. A method in accordance with claim 9, character- ized in that the adjustable time is chosen such that the piston at that moment is almost at the end of its stroke to the lower dead centre. 11. A method in accordance with claim 9, characterized in that the adjustable time is chosen subject to the stroke frequency such that dosing of the purging air starts just before the next stroke. 12. A method of purging combustion gasses from the combustion chamber of the free piston engine in accordance with one of the claims 1-8, characterized in that dosing of the purging air is started when the piston, during its movement from or to the lower dead centre, has reached a predetermined position.

Inventors: ACHTEN PETER AUGUSTINUS JOHANN, ACHTEN, PETER, AUGUSTINUS, JOHANNES
Applicants: ACHTEN PETER AUGUSTINUS JOHANN, INNAS FREE PISTON BV, ACHTEN, PETER, AUGUSTINUS, JOHANNES, INNAS FREE PISTON B.V.
Application year: 1997
Main classification: F02B71
IPC codes: F02B71