1. A downhole power system comprising:
a tubing string comprising a pressurised fluid,
a turbine for converting energy from the pressurised fluid into rotation of a shaft,
a tool powered by the turbine,
wherein a constant flow downhole assembly is arranged between the tubing string and the turbine for providing a substantially constant flow of the pressurised fluid to the turbine,
wherein the constant flow downhole assembly has an assembly axis and comprises:
a body comprising a main bore having a bore inlet and at least one bore outlet,
a hollow piston having a piston inlet and a piston outlet, said hollow piston being arranged in the main bore, and
a spring arranged in the main bore, said spring being compressed upon movement of the piston in a first direction, and
wherein the bore inlet is in fluid communication with the piston inlet and the piston inlet is smaller than the bore inlet so as to force the piston to move in the first direction.
2. A downhole power system according to claim 1, further comprising a generator arranged between the turbine and the tool, the generator comprising a rotor and a stator and the rotor being connected with the shaft.
3. A downhole power system according to claim 1, wherein the piston inlet is smaller than the bore inlet so as to force the piston to move in the first direction.
4. A downhole power system according to claim 1, wherein the piston has a piston wall adapted to partly cover the bore outlet when the piston moves in the first direction for reducing the flow of fluid into the bore outlet.
5. A downhole power system according to claim 1, wherein the piston outlet is elongated and extends along the assembly axis.
6. A downhole power system according to claim 1, wherein the main bore comprises first openings arranged upstream of the piston to allow pressurised fluid to flow in a bypass channel out through second openings and into apertures arranged in the piston wall.
7. A downhole power system according to claim 6, wherein changeable flow restrictors are arranged in the first openings.
8. A downhole power system according to claim 1, wherein the flow restrictors are nozzles.
9. A downhole power system according to claim 1, wherein the tool is a driving unit, such as a downhole tractor.
10. A downhole power system according to claim 9, wherein the driving unit comprises projectable arms having wheels.
11. A downhole power system according to claim 1, wherein the system comprises two driving units, an electrically driven driving unit and a fluid-driven driving unit.
12. A downhole power system according to claim 1, wherein the tubing string is a coiled tubing.
13. A constant flow downhole assembly for controlling a substantially constant flow rate in the downhole power system according to claim 1, said constant flow downhole assembly having an assembly axis and comprising:
a body comprising a main bore having a bore inlet and at least one bore outlet,
a hollow piston having a piston inlet and a piston outlet, and being arranged in the main bore, and
a spring arranged in the main bore, said spring being compressed upon movement of the piston in a first direction.
14. A constant flow downhole assembly according to claim 13, wherein the piston inlet is smaller than the bore inlet so as to force the piston to move in the first direction.
15. A method for providing a substantially constant flow of fluid into a turbine of the downhole power system according to claim 1, comprising the steps of:
pressurising a fluid in a tubing string,
entering the pressurised fluid into the main bore of the constant flow downhole assembly,
letting the pressurised fluid flow past the hollow piston and into the turbine until the fluid flow exceeds a predetermined level,
moving a piston by the pressurised fluid pressing on a top of the piston, and
reducing a flow area of the bore outlet by the piston moving in a first direction until the fluid flow is substantially equal to the predetermined level.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A fuel supply structure which has a fuel pump sucking fuel in a fuel tank and supplying the fuel into a fuel supply section of an engine, and a fuel hose connecting the fuel supply section and the fuel pump,
wherein the fuel supply section includes a plurality of fuel supply sections,
the fuel hose has a shared hose section provided on the fuel supply upstream side, and a plurality of individual hose sections provided on the fuel supply downstream side and branched from the shared hose section, and
at least a portion of at least any one of the shared hose section and the individual hose sections is made of an elastic body.
2. The fuel supply structure according to claim 1,
wherein the plurality of the individual hose sections includes an individual extended hose section extending from the fuel supply downstream end of the shared hose section in the extension direction of the fuel supply direction, and an individual branched hose section extending from the fuel supply downstream end of the shared hose section in the direction different from the extension direction,
wherein at least a portion of at least any one of the individual branched hose sections is made of an elastic body.
3. The fuel supply structure according to claim 1, wherein among the individual hose sections, at least a portion of the individual hose section having the smallest fuel supply amount is made of an elastic body.
4. The fuel supply structure according to claim 1, wherein the hose section made of an elastic body or a portion thereof is disposed substantially straightly.
5. The fuel supply structure according to claim 1, wherein the hose section made of an elastic body or the hose section with the elastic body portion is formed to have a larger inside diameter than the hose section without the elastic body portion.
6. The fuel supply structure according to claim 1, wherein in the entire fuel hose, the hose section not made of an elastic body and any non-elastic body portion of the hose section with the elastic body portion are made of a resin.