Device for injecting an additive into the exhaust system of motor vehicle

Abstract

Device for injecting a liquid additive including an additive tank connected by an additive pipe to an injector positioned in the exhaust system of the vehicle concerned, where there is provided, on the additive pipe, a positive-displacement lift-and-force pump including a cylinder and a piston which delimits within the cylinder a pressurizing chamber, and where an electric actuator is coupled to the piston to cause it to retreat, drawing additive into the chamber from the tank and simultaneously compressing a spring that acts on the piston, such that by virtue of the spring, the forward movement of the piston, delivering additive to the injector, takes place under controlled pressure.

1 . Device for injecting an additive in the liquid state into an exhaust system of a motor vehicle with a combustion engine, the additive injection device comprising:
 an additive tank connected by an additive pipe to at least one injector positioned in the exhaust system and a means of pumping the additive being provided on the additive pipe between the additive tank and the injector, these means being capable cyclically of dispensing metered quantities of pressurized additive,   wherein the pumping means comprise a positive-displacement lift-and-force pump comprising a cylinder, a piston mounted such that the piston can move translationally in the cylinder and delimiting within this cylinder a pressurizing chamber, a motor or electromechanical actuator coupled to the piston so as to move the piston translationally, and spring means acting on the piston in a direction of forcing the additive from the cylinder in such a way that actuation of the motor or actuator in one direction causes the piston to retreat, drawing additive into the pressurizing chamber from the additive tank and simultaneously compressing the spring means, whereas the forward movement of the piston delivering the additive to the injector takes place under a controlled pressure, due to said spring means.   
   
   
       2 . Device for injecting additive according to  claim 1 , wherein the motor of the positive-displacement pump is a DC electric motor with two directions of rotation. 
   
   
       3 . Device for injecting additive according to  claim 2 , wherein the electric motor is connected via a step-down gearing to a rotary endless screw mounted along the axis of the cylinder of the pump and collaborating with the piston shaped as a nut, or with a nut connected to the piston, the piston and/or the nut being prevented from rotating. 
   
   
       4 . Device for injecting additive according to  claim 1 , wherein a sealing membrane of a “rolling” type is mounted between the piston and the cylinder of the pump in order to fluid tightly delimit the pressurizing chamber while at the same time being able to cope with the variations in volume of this chamber. 
   
   
       5 . Device for injecting additive according to  claim 1 , wherein the spring means acting on the piston in the direction of delivering the additive out of the cylinder comprise a helical compression spring mounted inside the cylinder and acting on the piston on an opposite side to the pressurizing chamber. 
   
   
       6 . Device for injecting additive according to  claim 1 , further comprising, on a delivery side of the positive-displacement pump, a three-way electrically operated valve, control of which allows the additive to be directed selectively to the injector or, conversely, to the tank in order to empty the additive pipe. 
   
   
       7 . Device for injecting additive according to  claim 6 , further comprising, for the function of emptying the additive pipe, in combination with the aforementioned electrically operated valve, a venting check valve positioned on the pipe near to the injector. 
   
   
       8 . Device for injecting additive according to  claim 1 , wherein the cylinder of the positive-displacement pump comprises heating means that work by circulating a hot fluid inside a wall of the cylinder, in line with the pressurizing chamber, these heating means defrosting the additive. 
   
   
       9 . Device for injecting additive according to  claim 6 , wherein the three-way electrically operated valve is incorporated into the pump or attached to the cylinder of this pump in such a way as to communicate with the aforementioned heating means. 
   
   
       10 . Device for injecting additive according to  claim 8 , wherein, interposed on a connection between the additive tank and the positive-displacement pump is an auxiliary reserve of additive comprising an annular chamber surrounding the cylinder of the pump region provided with the heating means, such that this auxiliary reserve also benefits from a defrosting effect. 
   
   
       11 . Device for injecting additive according to  claim 10 , wherein the auxiliary reserve of additive has a volume substantially equivalent to an amount of additive injected in an operating cycle of the pump. 
   
   
       12 . Device for injecting additive according to  claim 11 , wherein the volume is substantially equivalent to a cycle of filling the line that connects the pump to the injector