FR3054860A1 - PRESSURE WAVE MITIGATION DEVICE FOR THERMAL ENGINE FUEL INJECTORS - Google Patents

Abstract

The invention relates to a fuel injector (10) comprising: - a body (12), - a needle (16) positioned inside a first cavity (20), said needle (16) being mounted movable in translation between a rest position in which said needle (16) rests against a seat (22) and an active position, said body (12) comprising: - a second cavity (34), called fuel accumulation, positioned upstream of said needle (16), said accumulation cavity (34) having one end opening towards a fuel injection rail and another end opening towards a valve (40) of said needle (16), and - a pressure wave attenuation device (42) positioned within said accumulation cavity (34) decreasing an apparent length (L) of said accumulation cavity (34) for pressure waves passing through said accumulation cavity (34).

Description

Holder (s): PEUGEOT CITROEN AUTOMOBILES SA Société anonyme.

Extension request (s)

Agent (s): PEUGEOT CITROEN AUTOMOBILES SA Public limited company.

PRESSURE WAVE MITIGATION DEVICE FOR FUEL ENGINE INJECTORS.

FR 3 054 860 - A1 engine, comprising:

- a body (12),

a needle (16) positioned inside a first cavity (20), said needle (16) being mounted movable in translation between a rest position in which said needle (16) rests against a seat (22) and an active position, said body (12) comprising:

- A second cavity (34), called the fuel accumulation cavity, positioned upstream of said needle (16), said accumulation cavity (34) having one end opening towards a fuel injection rail and another end opening towards a valve (40) of said needle (16), and

- a pressure wave attenuation device (42) positioned inside said accumulation cavity (34) decreasing an apparent length (L) of said accumulation cavity (34) for pressure waves passing through said accumulation cavity (34).

The present invention relates to a device for attenuating pressure waves for fuel injectors for a thermal engine, in particular for a motor vehicle. The invention finds a particularly advantageous, but not exclusive, application with petrol type engines with direct injection.

In a manner known per se, a fuel injector comprises a body and a needle positioned inside a first cavity. The needle is mounted movable in translation between a rest position in which the needle rests against a seat so as to block the passage of fuel and an active position in which the needle is positioned at a distance from the seat so as to allow the fuel passage to the outside of the injector.

A second cavity, called the fuel accumulation cavity, is positioned upstream of the needle. This cavity makes it possible to accumulate a quantity of fuel to ensure the supply of fuel to the combustion chamber of the engine in the event of the engine computer controlling a large instantaneous flow of fuel. The accumulation cavity has one end opening towards an injection rail and another end opening towards a valve of the needle. The valve is provided with small diameter openings to allow the passage of fuel to the needle cavity. The valve also provides pressure balancing inside the injector.

The accumulation cavity being almost closed on the side of the valve and open on the side of the injection rail, it can establish waves of the quarter-wave type generating vibrations of the injector creating noise pollution for the driver and which can also disturb the vehicle's control electronics.

The invention aims to effectively remedy this drawback by proposing a fuel injector for a heat engine, in particular for a motor vehicle, comprising:

- a body,

a needle positioned inside a first cavity, the needle being mounted movable in translation between a rest position in which the needle rests against a seat so as to block a passage of fuel and an active position in which the needle is positioned at a distance from the seat so as to allow the passage of fuel, characterized in that the body comprises:

a second cavity, called the fuel accumulation cavity, positioned upstream of the needle, the accumulation cavity having one end opening towards a fuel injection rail and another end opening towards a valve of the needle, and

- a pressure wave attenuation device positioned inside the accumulation cavity decreasing an apparent length of the accumulation cavity for pressure waves passing through the accumulation cavity.

By apparent length of the cavity is meant the distance between two faces of two adjacent threads facing one another in the case where the device takes the form of a helix or between two wall faces of a chicane-style obstacle.

The invention thus makes it possible to increase the resonance frequency and therefore its damping, insofar as the resonance frequency is inversely proportional to the length of the cavity. In other words, the invention makes it possible to attenuate the pressure waves enclosed in the injector by changing the characteristics of the acoustic cavity.

In one embodiment, the pressure wave attenuation device consists of a propeller.

In one embodiment, the propeller comprises a number N of threads verifying the following relationship N = fc / fr, fc being the chosen frequency, fr being the resonant frequency of the accumulation cavity without the attenuation device of pressure waves, N being rounded to the nearest whole by its lower or higher value.

In one embodiment, the pressure wave attenuation device is constituted by baffles.

In one embodiment, the pressure wave attenuation device is mounted free or fixed on a retaining device inside the accumulation cavity.

In one embodiment, the pressure wave attenuation device is made of a polymer type material. This makes it possible to provide an additional structural damping effect linked to the properties of the material such as the Poisson's ratio.

In one embodiment, the propeller is not irregular.

According to one embodiment, an internal diameter of the accumulation cavity is greater than an internal diameter of the first cavity.

The invention also relates to a heat engine comprising at least one fuel injector as defined above.

The invention also relates to any vehicle, in particular of the automobile type, comprising such an engine.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given only by way of illustration but in no way limit the invention.

Figure 1 is a sectional representation of a fuel injector according to the present invention comprising a pressure wave attenuation device;

Figure 2 is a schematic representation of a second embodiment of the fuel injector according to the present invention.

Identical, similar, or analogous elements retain the same reference from one figure to another.

Figure 1 shows a fuel injector 10 of the heat engine, in particular for a motor vehicle. The injector 10 comprises a body 12 provided at one end with an O-ring 14 to seal with an injection rail to which the injector 10 is connected. The other end of the body 12 is located on the side from the free end of a needle 16 and is intended to be partially inserted inside the combustion chamber. A seal 18 inserted in a groove 19 of corresponding shape formed at the external periphery of the body 10 makes it possible to prevent the ascent of the combustion gases.

The needle 16 is positioned inside a first cavity 20 and mounted movable in translation between a rest position in which the needle 16 rests against a seat 22 so as to block the passage of fuel and a active position in which the needle 16 is positioned at a distance from the seat 22 so as to allow the passage of fuel towards the outside of the injector 10, in the combustion chamber of the engine.

For this purpose, the injector 10 comprises a solenoid 24 capable of moving the needle 16 from the rest position to the active position, when it is supplied by a current. The supply of the solenoid 24 is carried out via a connector 26 receiving control signals from the engine computer. When the injector 10 is no longer supplied, the needle 16 is biased towards its rest position by a return spring 28 mounted on the one hand between an anchor 30 secured to one end of the needle 16 and a device retaining 32 of the spring 28. This retaining device 32 of the spring 28 has a hollow shape to allow the passage of fuel from a second cavity 34 to a valve 40.

The second cavity 34, called the fuel accumulation cavity, is positioned upstream of the needle 16. This cavity 34 makes it possible to accumulate a quantity of fuel to ensure the supply of fuel to the combustion chamber of the engine. if the engine control unit controls a large instantaneous flow of fuel.

An internal diameter D of the accumulation cavity 34 is greater than the internal diameter D 'of the first cavity 20. In addition, the length L of the accumulation cavity 34 is less than the length L' of the first cavity 20 receiving the needle 16.

The second cavity 34 is in fluid communication with the rail via a conduit 36 in which is installed a filter 38 to trap particles of small dimensions not filtered by the fuel filter. Thus, the accumulation cavity 34 has one end opening towards the injection rail via the conduit 36 and another end opening towards the valve 40 of the needle 16 via the hollow holding device 32 and the space in which are installed the spring 28 and the anchor 30.

The valve 40 is provided with small diameter openings to allow the passage of fuel to the first cavity 20. The valve 40 also provides pressure balancing inside the injector 10.

A pressure wave attenuation device 42, for example constituted by a propeller or Archimedes screw, is positioned inside the accumulation cavity 34. This device 42 makes it possible to reduce the apparent length L of the accumulation cavity 34 for the pressure waves passing through the accumulation cavity 34. By apparent length of the cavity 34 is meant the distance d between two faces of two adjacent threads 44 opposite the one from the other in the case where the device 42 takes the form of a helix or between two faces of the walls of a baffle-style obstacle, as described in more detail below.

The pressure wave attenuation device 42 is made of a polymer type material. This makes it possible to provide an additional structural damping effect linked to the properties of the material such as the Poisson's ratio.

Thus, during the operation of the injector 10, the acoustic waves encounter obstacles formed by the walls of the threads 44 of the propeller 42 and break on these obstacles. The helical shape of the device 42 means that the transverse waves are no longer established over the total length L of the accumulation cavity 34 but over the distance difference d between two adjacent threads 44 of the device 42. The increase in the value of the resonance frequency is done in the ratio of the distances L / d.

The diameter of the core of the propeller 42 may be chosen to ensure that a cross section compatible with the operation of the injector 10 is maintained. The external diameter of the propeller 42 may be equal to or slightly less than the internal diameter D of the accumulation cavity 34. The pressure wave attenuation device 42 may be freely mounted or fixed on a retaining device inside the accumulation cavity 34.

The propeller 42 has a number N of threads 44 verifying the following relationship N = fc / fr. fc being the chosen frequency, fr being the resonant frequency of the accumulation cavity without the pressure wave attenuation device, N being rounded to the nearest whole by its lower or higher value. For example, a resonance frequency of 8kHz has been calculated. To calculate the necessary number of threads 44 of the propeller 42 in order to have a new resonant frequency of 20 kHz, we apply the formula N = 20/8, that is N = 2.5. The propeller 42 must therefore have 2 to 3 threads 44.

According to certain embodiments, the propeller 42 may be of irregular pitch according to which a spacing between the threads 44 of the propeller 42 is defined by a mathematical law, such as the method called pseudo-random binary sequence (or Pseudo random binary sequence in English).

In order to minimize the pressure drop of the fluid, a ratio between an apparent cross-sectional area of the fluid between two faces of two threads 44 of the propeller 42 from one another and an area of the cross-section of the second cavity 34 is between 1/3 and 1. In other words, the walls of the propeller 42 are relatively thin and spaced apart by a significant distance to avoid disturbing the flow of fuel inside the injector 10. Indeed, the realization of small diameter grooves or section restrictions or the installation of damping materials of the glass wool type could make it possible to attenuate the vibrations, but this would generate too great a pressure drop which would disturb the flow of fuel and therefore affect the intrinsic performance of the injector 10, in particular its instantaneous flow.

It should also be noted that the positioning of the pressure wave attenuation device 5 would not have the desired effect if it were positioned inside the cavity 20 containing the needle 16, insofar as the volume of the cavity 20 is closed by the needle in its rest state and almost closed on the side of the valve 40, so that the disturbing acoustic waves cannot be established there.

According to an alternative embodiment shown in Figure 2, the device 10 for attenuating pressure waves 42 is constituted by baffles 46. The baffles 46 may take the form of a wall in the form of a half-moon s' alternately extending over opposite angular sectors of the external periphery of the device 42 and spaced axially between them in a regular or irregular manner.

Claims (10)

1. Fuel injector (10) for a heat engine, in particular for a motor vehicle, comprising: - a body (12), - a needle (16) positioned inside a first cavity (20), said needle (16) being mounted movable in translation between a rest position in which said needle (16) rests against a seat (22) of so as to block a fuel passage and an active position 'in which said needle (16) is positioned at a distance from said seat (22) so as to allow the passage of fuel, characterized in that said body (12) comprises: - A second cavity (34), called the fuel accumulation cavity, positioned upstream of said needle (16), said accumulation cavity (34) having one end opening towards a fuel injection rail and another end opening towards a valve (40) of said needle (16), and - a pressure wave attenuation device (42) positioned inside said accumulation cavity (34) decreasing an apparent length (L) of said accumulation cavity (34) for pressure waves passing through said accumulation cavity (34). 2. Fuel injector according to claim 1, characterized in that said pressure wave attenuation device (42) consists of a propeller. 3. Fuel injector according to claim 2, characterized in that said propeller (42) comprises a number N of threads (44) verifying the following relation N = fc / fr, fc being a chosen frequency, fr being the resonant frequency of the accumulation cavity without the pressure wave attenuation device, N being rounded to the nearest whole by its lower or higher value. 4. Fuel injector according to claim 1, characterized in that said pressure wave attenuation device (42) is constituted by baffles (46). 5. Fuel injector according to any one of claims 1 to 4, characterized in that said pressure wave attenuation device (42) is mounted free or fixed on a retaining device inside said cavity accumulation (34). 6. Fuel injector according to any one of claims 1 to 5, characterized in that said pressure wave attenuation device (42) is made of a polymer type material. 7. Fuel injector according to claim 2, characterized in that said propeller 5 (42) is an irregular step. 8. Fuel injector according to any one of claims 1 to 7, characterized in that an internal diameter (D) of said accumulation cavity (34) is greater than an internal diameter (Dj of said first cavity (20 ). 9. A heat engine characterized in that it comprises at least one fuel injector (10) as defined according to any one of the preceding claims. 10. Vehicle, especially motor vehicle, characterized in that it comprises the engine according to the preceding claim.