Patent ID: 8671663

Claim:
A method for metering a fluid, pollutant-reducing medium into a motor vehicle exhaust system, comprising the steps of: supplying the fluid medium to a nozzle; introducing the fluid medium into the motor vehicle exhaust system through the nozzle; controlling at least one of a pump and a pressure relief element with pulse-width modulation; positioning the pump upstream of the nozzle; connecting an outlet of the pump to at least one of an inlet of the pump and a return line leading to a reservoir with a bypass path; positioning the pressure relief element in the bypass path; pumping fluid medium into the nozzle and increasing a pressure in the nozzle; opening the nozzle in response to the increase in pressure; injecting the fluid medium through the nozzle into the motor vehicle exhaust system at an injection site; positioning the nozzle adjacent the injection site; propelling the fluid medium through the nozzle and into the motor vehicle exhaust system with the pump in response to the increase in pressure in the nozzle; and at least in periods of time in which the pump is not in operation, flowing the fluid medium at least partially back via the bypass path from an outlet side of the pump to its inlet side or to the reservoir so that the nozzle closes in response to a drop in pressure in the nozzle.