Injection device for metering a fluid and motor vehicle having such an injection device

1. An injection device for metering a fluid, comprising:

a valve, which has a valve needle and a valve seat;

a nozzle shaft, which surrounds the valve needle and which holds a volume of the fluid;

an inlet tube;

an inlet chamber formed by the inlet tube, which adjoins the nozzle shaft on the side of the nozzle shaft facing away from the valve and which has a flow connection to the nozzle shaft;

at least one compressible volume compensation element, which is filled with a gas, the at least one compressible volume compensation element located in the inlet chamber and is a wall lining of the inlet tube; and

a wall region, the wall region being part of the at least one compressible volume compensation element, the wall region being composed of a martensitically hardened steel;

wherein the at least one compressible volume compensation element is in contact with the fluid.

2. The injection device of claim 1 , the at least one volume compensation element further comprising regions composed of a flexible, porous plastic, wherein the pores of the plastic are filled with the gas.

3. The injection device of claim 1 , the at least one volume compensation element further comprising an inlay, wherein the inlay is arranged in the interior of the injection device in such a way that the inlay is surrounded substantially completely by the fluid.

4. The injection device of claim 1 , another volume compensation element comprising a lining of a wall of the nozzle shaft.

5. The injection device as claimed in claim 1 , the valve needle further comprising:

a gas-filled cavity within the interior of the valve needle;

wherein the valve needle is formed from martensitically hardened steel.

6. The injection device of claim 1 , wherein the injection device is used for a urea solution in an exhaust gas aftertreatment system.

7. The injection device of claim 6 , wherein the injection device is used as part of a motor vehicle.