The present invention relates to a SCR system having several doser organised in an in-line architecture.

BACKGROUND OF THE INVENTION

Multi-doser Selective Catalytic Reduction (SCR) systems are adapted to spray reagent in the exhaust gases of an internal combustion engine. Said systems have a tank filled with reagent and a pump flowing said reagent to a plurality of dosers. The dosers of said system are connected in parallel to the outlet of the pump or to a common manifold, or via "T" or "Y" junction elements. Such complex and expensive system architecture are typically provided for engines having several bank of cylinders, V6 type for instance, or requiring spray upstream and downstream the exhaust pipe.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a Selective Catalytic Reduction system (SCR system) comprising a tank, a pump, a first doser, a last doser for injecting in an exhaust pipe reagent stored in the tank and delivered by the pump to the dosers, the dosers being arranged in-line. The system further comprises a first feed pipe inter-connected between the first doser and the pump and, a last feed pipe arranged between the first doser and the last doser.

The first doser is provided with an inlet for receiving reagent from the pump and, an outlet for delivering reagent to the last doser.

The SCR system further comprises a second doser inserted in the line between the first doser and the last doser, said second doser receiving reagent from the first doser via the first feed pipe and delivering reagent to the last doser via the last feed pipe.

In a further alternative, the SCR system comprises a plurality of dosers arranged in-line one after the other wherein, the first doser in the line is the only doser to receive the reagent from the pump, all the other dosers from the second to the last receiving reagent R from the previous doser in the line.

All the dosers from the first to the last but one in the line have an inlet for receiving reagent R and, an outlet for delivering reagent to the next doser in line.

All the feed pipes of the system directly extend from an outlet, to the inlet, of a doser.

The system is free from connecting blocks, manifold, distributors, T- junction or any element adapted to divide the flow in a plurality of routes joining as many dosers. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying figure 1 which sketches a SCR system as per the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

A powertrain system comprises an internal combustion engine and an exhaust pipe wherein exhaust gases are filtered and chemically treated to remove pollutants prior to exiting the tailpipe. The powertrain system further comprises a selective catalytic reduction system 10, hereafter SCR system 10, adapted to spray a reagent R, such as urea fluid, at an injection point of the pipe.

Engines having two or more banks of cylinders, such as V6 engines, have several exhaust pipes and thus several reagent injection points. It is also common to have reagent injection in the hot part of the exhaust pipe, upstream a particulate filter and also, in the cold part of the pipe downstream said filter.

More in details in reference to the figure 1, the SCR system 10 comprises a tank 12 storing the reagent R, a pump 14 immersed in the reagent R is arranged to suck said reagent R and deliver it to a first doser 16 adapted to spray the reagent R at a first injection point PI of the exhaust pipe. To flow the reagent from the pump 14 to said first doser 16, a first feed pipe 18 is connected to the pump outlet 20 and it extend to the first doser inlet 22. Said first doser 16 is also provided with an outlet 24 connected to another feed pipe, which in the example shown is a last feed pipe 26 extending to the inlet 28 of a last doser 30 adapted to spray the reagent R at a last injection point P30 of the exhaust pipe. An electronic control unit 32, ECU, electrically connected to the dosers 16, 30 delivers command signal to said dosers also, to avoid freezing of the reagent R, or to thaw a frozen system, heater elements 34 are arranged in several points of the system, in the tank and over the length of the feed lines.

Furthermore, the dosers of the SCR system can be air cooled, as the first doser 16 shown, or liquid cooled as the last doser 30 is. Also, the pump 14 represented immersed in the tank may be arranged outside the tank with a suction line from its inlet to the reagent R.

The SCR system 10 has an in-line organisation of the dosers, the last doser 30 receiving reagent R from the first doser 16 rather than directly from the pump. The fluid connection is done by the first doser 16 that is provided with an inlet 22 and with an outlet 24. This in-line architecture advantageously simplifies and frees the system 10 from any flow dividing elements such as connection blocks, T-junction elements, manifold, distributors arranged away from the dosers between two in a feed pipe.

Such an architecture can be extended to SCR systems 10, not shown, provided with three dosers. In this case a second doser 36 is inserted in the line between the first doser 16 and the last doser 30. The first doser receives reagent R from the pump 14, the second doser 36 receives reagent R from the first doser 16 and, the last doser 30 receives reagent R from the second doser 36. Said second doser 36 is then provided, similarly to the first doser 16, with and inlet 22 and with an outlet 24.

More generally, an SCR system 10 having one pump 14, "n" dosers arranged in-line comprises "n" feed pipes, as many as injectors. The first feed pipe 18 is arranged between the pump 14 and the first doser 16 and, the other n-1 feed pipes are arranged between consecutive dosers. In such architecture of SCR system, the first doser as well as all the intermediate dosers, from the second to the last but one, are provided with an inlet 22 and with an outlet 24. The nth doser 30, last in the line, connected to said last but one doser has just an inlet 28. LIST OF REFERENCES

R reagent

P 1 first inj ection po int

P30 last injection point

10 SCR system

12 tank

14 pump

16 first doser

18 first feed pipe

20 pump outlet

22 first doser inlet

24 first doser outlet

26 last feed pipe

28 inlet of the last doser

30 last doser

32 ECU

34 heater electrical connector

36 second doser