Control system of emissions of a motor vehicle

Abstract

The invention relates to a discharge solenoid valve (18b), an outlet duct (36) of which is connected to a fuel intake circuit (16) into a vehicle engine. According to the invention, the outlet duct (36) of the solenoid valve includes a substantially cylindrical portion with a smaller cross-section (38), said portion (38) with a smaller cross-section extending axially over a distance of about 0.2 to 2 millimeters.

Description

[0001] The present invention relates to a solenoid valve of a fuel evaporative emission control system as well as to an engine equipped with such a solenoid valve and a motor vehicle equipped with such an engine.

[0002] An evaporative emission control system 10 as shown in figure 1 comprises a tank 12 for recovering and temporarily trapping gaseous fuel from the fuel storage tank 14. This recovery tank 12 is connected to the engine fuel intake system 16 via a solenoid valve 18, the degree of opening of which determines the quantity of fuel vapors which is reinjected into the engine. The solenoid valve is controlled in opening and closing by a computer 20 of the vehicle which determines the optimal conditions allowing the reinjection of fuel vapors.

[0003] In the current technique, the purge solenoid valves 18 comprise an outlet pipe 22 connected to the fuel inlet which comprises a portion with reduced section 24 connected upstream and downstream to substantially frustoconical portions 26, 28 with a section widening towards the upstream and downstream, respectively ( figure 2 ). This portion 24 with reduced section or neck generally comprises an internal annular face which is curved along the axis of flow of the fluid through said portion 24. As shown in the figure 2 and well known in the state of the art, the solenoid valve 18 also comprises a movable valve 30 actuated by displacement by a coil 32 and a seat 34 for closing the circulation of fluid in the solenoid valve.

[0004] This type of configuration of the outlet pipe 22 does not allow a good compromise to be obtained between the pressure drop and the flow rate. Indeed, the variation of the dimensions of the pipe such as the section of the portion with reduced section or the dimensions of the frustoconical portions does not allow good results to be obtained since an increase in the section of the neck induces not only an increase in the flow rate but also an increase in the pressure drop whereas it would be appropriate to maximize the flow rate while minimizing the associated pressure drop.

[0005] An equivalent problem arises with the solenoid valve described in document EP1312787A1 which comprises an outlet conduit comprising a reduced portion whose dimensions do not allow the flow rate to be maximized while minimizing the associated pressure drop.

[0006] The invention proposes to provide an effective, simple and economical solution to the aforementioned problems.

[0007] To this end, it proposes a system for controlling evaporative emissions in a motor vehicle, comprising a fuel storage tank connected to a tank for retaining gaseous fuel particles, this retention tank being connected at the outlet to a solenoid valve comprising an outlet conduit connected to a fuel intake circuit in the engine, characterized in that the outlet conduit of the solenoid valve comprises a portion with a reduced section having a substantially cylindrical shape.

[0008] According to the invention, the replacement of the neck of the prior art by a zone with a reduced section having a cylindrical shape makes it possible to significantly reduce the pressure loss in the conduit while having a limited impact on the reduction in the flow rate.

[0009] According to the invention, said portion with reduced section extends axially over a distance of between approximately 0.2 and 2 millimeters and preferably over an axial distance of between 0.5 and 1 millimeter.

[0010] According to the invention, said portion with reduced section has a diameter of between approximately 2 and 7 millimeters.

[0011] According to another characteristic of the invention, the portion of pipe with reduced section is connected upstream and downstream to two frustoconical portions with section increasing in opposite directions to the portion with reduced section.

[0012] The invention also relates to a motor vehicle engine, comprising a fuel gaseous emission control system as described above.

[0013] The invention also relates to a motor vehicle comprising an engine as above.

[0014] The invention will be better understood and other details, characteristics and advantages of the invention will appear on reading the following description given by way of non-limiting example with reference to the appended drawings in which: there figure 1 , described above, is a schematic view of an evaporative pollutant emission control system; figure 2 is a schematic view of a solenoid valve for purging a fuel gaseous particle retention tank; figure 3 is a schematic view of an outlet conduit in a purge solenoid valve according to one embodiment of the invention; figure 4 is a graph representing the evolution of the flow rate as a function of the pressure drop at the outlet of the solenoid valve of the figure 2 (curve A) and in the conduit of the figure 3 (curve B); the figure 5 is a graph representing the variations in flow rate and pressure drop as a function of the length of the cylindrical portion with reduced section of the conduit of the solenoid valve according to the invention, the figure 6 is a schematic view of an outlet conduit in a purge solenoid valve according to one embodiment of the invention.

[0015] We now refer to the figure 3 and the figure 6 which represents an outlet pipe 36 of a purge solenoid valve according to the invention. The solenoid valve 18b may be, with the exception of the outlet pipe 36, identical in every respect to the solenoid valve 18a shown in figure 2 . It can be mounted in the circuit of the figure 1 in the same place as solenoid valve 18a.

[0016] According to the invention, the outlet pipe 36 comprises a portion 38 of pipe with reduced cross-section having a substantially cylindrical shape. This portion 38 is connected upstream to a frustoconical upstream portion 40 with a cross-section increasing towards the upstream and downstream to a frustoconical portion 42, 42' with a cross-section increasing towards the downstream.

[0017] According to one embodiment, visible on the figure 6 , the frustoconical portions 40, 42' are asymmetrical to each other with respect to a plane substantially perpendicular to the cylindrical portion 38.

[0018] According to one embodiment, visible on the figure 3 , the frustoconical portions 40, 42 are symmetrical to each other with respect to a plane substantially perpendicular to the cylindrical portion 38.

[0019] Furthermore, the upstream end of the upstream frustoconical portion 40 can be connected to another cylindrical portion 44 for junction with the downstream face of the valve seat. Similarly, the downstream end of the downstream frustoconical portion 42, 42' is connected to a downstream cylindrical pipe 46.

[0020] The invention thus proposes to replace the portion of pipe with reduced section of the prior art by the portion with reduced section of the figures 3 et 6 in order to minimize pressure loss while limiting flow rate degradation.

[0021] There figure 4 is a graph representing the evolution of the flow rate (for example in Kg / h) as a function of the pressure drop (for example in mbar) or pressure difference between the upstream and downstream of the solenoid valve. The curve referenced A relates to the portion 22 of the outlet pipe as shown in figure 2 and figure B relates to the portion 38 of the pipe shown in figures 3 et 6 .

[0022] As a first observation, we see that curve B has a steeper slope so that the maximum flow threshold is reached more quickly than for curve A. Thus, we can easily see on the graph of the figure 4 that for a threshold or plateau of substantially identical flow rate, the use of a portion with a reduced cylindrical section having a cylindrical shape makes it possible to maintain a substantially identical threshold flow rate while reducing the pressure loss since the start of the plateau is offset on curve B compared to curve A on the abscissa axis.

[0023] As a second observation, it is noted that although the threshold flow values ​​for curves A and B are similar, they are not identical. In this respect, it should be noted that it may be necessary to increase the diameter of the reduced-section pipe 38 compared to the neck diameter of the prior art in order to compensate for the slight drop in flow resulting from the cylindrical shape.

[0024] The graph of the figure 5 represents the evolution of the flow rate (left histogram) and the pressure drop rate (right histogram) as a function of the length of the portion 38 with reduced section of cylindrical shape. The reference is taken at 0 where we observe that there is, obviously, neither gain nor loss. As can be seen on this graph, the increase in the length of the portion 38 with reduced section is accompanied by a decrease in the flow rate, which means that the more the length of the portion 38 with reduced section is increased, the more the flow rate decreases in comparison with a portion with reduced section without a cylindrical portion, i.e. punctual or quasi-punctual. This corroborates the observation made on the figure 4, for a given length of the portion 38 with reduced section, where a decrease in the flow rate is observed between curves A and B. The increase in the length of the portion with reduced section is accompanied by a rapid decrease in the pressure drop rate up to 1 mm, the pressure drop rate then increases very slightly but the flow rate at 2 mm is lower than that obtained with 1 mm, which indicates that the optimal value of the length of the portion with reduced section is 1 mm, the decrease in pressure drop being the most significant for a relatively contained decrease in flow rate.

[0025] Said portion with reduced section has, according to the invention, a diameter of between approximately 2 and 7 millimeters.

Claims

1. Evaporative emission control system (10) in a motor vehicle, comprising a fuel storage tank (14) connected to a fuel vapor retention canister (12), this retention canister (12) being connected at its outlet to a purge solenoid valve (18b), an outlet conduit (36) of which is connected to a fuel intake circuit (16) in a vehicle engine, the outlet conduit (36) of the solenoid valve comprising a reduced cross-section portion (38) having a substantially cylindrical shape, characterized in that said reduced cross-section portion (38) extends axially over a length of 1 millimeter and has a diameter between 2 and 7 millimeters.

2. System (10) according to claim 1, wherein the reduced cross-section conduit portion (38) is connected upstream and downstream to two frustoconical portions (40, 42) with increasing cross-sections in directions opposite to the reduced cross-section portion (38).

3. Motor vehicle engine, characterized in that it comprises a system according to one of claims 1 to 2.

4. Motor vehicle, characterized in that it comprises an engine according to claim 3.

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