Working gas circulation engine

1. A working gas circulation engine comprising:

a combustion chamber capable of expanding a working gas having a specific heat ratio higher than that of air due to a combustion between an oxidizing agent and a fuel;

a circulation path that allows the working gas to circulate from an exhaust side to a suction side of the combustion chamber and that is capable of supplying the working gas again to the combustion chamber;

a feed unit capable of feeding a gas in an inside of a pressure-reduction target section whose pressure is to be reduced, to an outside; and

a control unit that operates the feed unit to feed the gas in the inside of the pressure-reduction target section to the outside, when a pressure in the inside of the pressure-reduction target section is higher than a predetermined pressure set in advance.

2. The working gas circulation engine according to claim 1 , further comprising:

a storage unit capable of storing a gas fed by the feed unit with a pressure higher than an internal pressure of the pressure-reduction target section.

3. The working gas circulation engine according to claim 1 , wherein

the feed unit includes a feed passage that connects the inside and the outside of the pressure-reduction target section in such a manner that the gas can flow therethrough, an opening/closing unit that is provided on the feed passage and can open and close the feed passage, and a pressure-feed unit that is provided on the feed passage and applies pressure to a gas in the feed passage to feed the gas from the inside to the outside of the pressure-reduction target section.

4. The working gas circulation engine according to claim 1 , wherein

the pressure-reduction target section is the circulation path whose internal pressure possibly varies according to an operation state to become higher than the predetermined pressure.

5. The working gas circulation engine according to claim 4 , further comprising:

a cooling unit that is provided on the circulation path and cools a gas circulating in the circulation path, wherein

the feed unit can feed the gas in the inside of the circulation path to the outside at the downstream side from the cooling unit with respect to the direction of circulating the gas in the circulation path with the combustion chamber defined as a reference.

6. The working gas circulation engine according to claim 4 , further comprising:

a removing unit that is provided on the circulation path and removes the fuel in the gas generated after the combustion between the oxidizing agent and the fuel, wherein

the feed unit can feed a gas in the inside of the circulation path to the outside at the downstream side from the removing unit with respect to the direction of circulating the gas in the circulation path with the combustion chamber defined as a reference.

7. The working gas circulation engine according to claim 4 , further comprising:

a concentration detecting unit that detects a concentration of the fuel in a gas in the circulation path, wherein

the feed unit can feed a gas in the inside of the circulation path at the downstream side from a detection position of a concentration by the concentration detecting unit with respect to the direction of circulating the gas in the circulation path with the combustion chamber defined as a reference, and

the control unit inhibits a feed of the gas by the feed unit, when the concentration of the fuel detected by the concentration detecting unit is not less than a predetermined concentration set in advance.

8. The working gas circulation engine according to claim 1 , wherein

the pressure-reduction target section is an engine-body-side pressure-reduction target section that is a space other than the combustion chamber, a suction port and an exhaust port communicating with the combustion chamber which are included in an engine body, and an internal pressure of the space possibly varies according to an operation state to become higher than the predetermined pressure.

9. The working gas circulation engine according to claim 4 , wherein

the engine-body-side pressure-reduction target section includes a crank chamber that is provided to a side opposite to the combustion chamber across a piston provided so as to be capable of moving reciprocally in a cylinder bore.

10. The working gas circulation engine according to claim 8 , wherein

the feed unit can feed a gas in the inside of the engine-body-side pressure-reduction target section into the inside of the circulation path.

11. The working gas circulation engine according to claim 10 , further comprising:

a communication path that is provided separate from a feed passage of the feed unit and connects the inside of the engine-body-side pressure-reduction target section and the inside of the circulation path in such a manner that the gas can flow therethrough; and

a first preventing unit that is provided on the communication path and can prevent a flow of the gas from the inside of the circulation path to the inside of the engine-body-side pressure-reduction target section.

12. The working gas circulation engine according to claim 10 , wherein

the feed unit includes a feed passage that connects the inside and the outside of the engine-body-side pressure-reduction target section in such a manner that the gas can flow therethrough, and an adjusting unit that is provided at the upstream side from a connection portion to the feed passage of the circulation path with respect to the direction of circulating the gas in the circulation path with the combustion chamber defined as a reference, and that can adjust the pressure in the circulation path, wherein

the adjusting unit reduces a pressure in the circulation path at the downstream side from the adjusting unit so as to be capable of feeding the gas in the inside of the engine-body-side pressure-reduction target section into the inside of the circulation path.

13. The working gas circulation engine according to claim 12 , wherein

the adjusting unit adjusts an open degree of the circulation path so as to adjust a pressure in the circulation path, and

the control unit controls the adjusting unit so as to adjust an open degree of the circulation path on the basis of the temperature in the combustion chamber.

14. The working gas circulation engine according to claim 12 , wherein

the feed unit is provided on the feed passage and inhibits the flow of a gas from the inside of the circulation path to the inside of the engine-body-side pressure-reduction target section.

15. The working gas circulation engine according to claim 12 , further comprising:

an oxidizing agent supply unit that supplies the oxidizing agent to the downstream side from the adjusting unit in the circulation path with respect to the direction of circulating the gas in the circulation path with the combustion chamber defined as a reference.

16. The working gas circulation engine according to claim 12 , wherein

the control unit operates the adjusting unit of the feed unit, during the deceleration of a vehicle having the engine body provided with the combustion chamber mounted thereto or during a fuel-cut period in which the supply of the fuel from the fuel supply unit to the combustion chamber is stopped, so as to reduce the pressure at the downstream side from the adjusting unit, thereby feeding the gas in the inside of the engine-body-side pressure-reduction target section in the inside of the circulation path.