Common rail fuel injector

Abstract

 A fuel injector which, under the control of the engine ECM, controls the fuel injection event profile by means of a shuttle valve of the injector. The shuttle valve is constructed so that axial forces generated by fuel pressure are balanced. In a preferred embodiment, the nozzle of the injector contains a needle valve seated at the top thereof, the needle valve sliding within the nozzle without touching the tip thereof.

Description

[0001] This invention is related to an electronically controlled high-pressure common rail fuel injector for injecting metered amounts of highly pressurized fuel into a cylinder of a diesel engine.

[0002] Conventional fuel injection systems employ a "jerk" type fuel system for pressurizing and injecting fuel into the cylinder of a diesel engine. A pumping element is actuated by an engine-driven cam to pressurize fuel to a sufficiently high pressure to unseat a pressure-actuated injection valve in the fuel injection nozzle. In one form of such a fuel system having an electromagnetic unit injector, the plunger is actuated by an engine driven cam to pressurize the fuel inside the bushing chamber when a solenoid is energized and the solenoid valve is closed. The metering and timing is achieved by a signal from an electronic control module (ECM) having a controlled beginning and a controlled pulse.

[0003] In another form of such a fuel system, the fuel is pressurized by an electronic or mechanical pumping assembly into a common rail and distributed to electronically controlled injectors, which inject pressurized fuel into the engine cylinders. Both the electronic pump and the injectors are controlled by the ECM signal.

[0004] One necessity for using the electronically controlled common rail results from the present and future injection pressure requirements for diesel engines which are in the neighborhood of up to a maximum of 2'000 bars. The maximum pressure capability of the conventional fuel injection system is 1'000 to 1'100 bars. Another problem with the conventional fuel injection system is the very limited flexibility and adjustability of the fuel injection characteristics. In conventional fuel injection systems, the fuel flow output adjustment can not be separated from injection pressure and every fuel flow adjustment will determine a certain injection pressure for the engine which, most of the time, is not the optimum required by the engine and generates excessive emission and fuel consumption. Also, the adjusted fuel flow will determine a certain injection rate shape which can be different from the optimum rate shape required by the engine. The electronically controlled common rail allows individual adjustments for all the fuel injection characteristics and all over the engine speed range. This flexibility characteristic only for this system allows to optimize and "tailor" the fuel system to the engine all over the speed range for the best emission and fuel consumption.

[0005] In applicant's European patent application EP 0737808, a high pressure electronic common rail fuel injector is disclosed, comprising an injector body having a fuel inlet therein; a first equalized pressure fuel chamber formed within the injector body and in fluid communication with the fuel inlet; a shuttle valve slidingly disposed within the injector body; a second fuel chamber formed within the injector body under the bottom of the shuttle valve; a nozzle coupled to the injector body; a first fuel passage fluidly coupling the second fuel chamber to the nozzle; a shuttle valve seat formed in the injector body between the first and second fuel chambers; a check ball seat formed between the second fuel chamber and a second fuel passage; a check ball loosely contained between a bottom surface of the shuttle valve and the check ball seat; and a piezoelectric shuttle valve actuator coupled to the shuttle valve, wherein activation of the piezoelectric shuttle valve actuator operates to seat the check ball on the check ball seat, thereby allowing fuel flow between the first and second fuel chambers and preventing fuel flow between the second fuel chamber and the second fuel passage, and deactivation of the piezoelectric shuttle valve actuator operates to unseat the check ball from the check ball seat, thereby allowing fuel flow between the second fuel chamber and the second fuel passage.

[0006] This fuel injector further comprises a needle valve seat formed in a distal end of the nozzle; a needle valve slidingly disposed within the nozzle; and a controllable biasing member, achieved by placing a piezoelectric actuator between the needle valve and a bias spring, applying a variable biasing force to the needle valve in a direction tending to seat the needle valve against the needle valve seat by varying an amount of control current applied to the actuator. The length of the piezoelectric actuator changes in proportion to the amount of control current applied thereto, thereby changing the bias force applied to the needle valve.

[0007] Thus, the fuel injector, under the control of the engine ECM, may control the shape of the fuel injection event profile, changing the shape of the injection event profile in proportion to the amount of control current applied. The profile is altered in relation to engine speed for reducing emission of particulates and hydrocarbons and also reducing fuel consumption.

[0008] Nevertheless, this common rail fuel injector is not free from drawbacks:

[0009] Below the shuttle valve is the above-mentioned check ball, residing within the second fuel chamber and sitting in a hemispherical recess of a spacer member. The problem with this arrangement is that pressure below the shuttle valve in the second fuel chamber acts against the shuttle valve opening force and when it exceeds a certain level, it prevents valve opening. Also, pressure coming into the second fuel chamber will lift the check ball and a part thereof will go through the central second fuel passage of the spacer member and through the fuel return line to the fuel tank, instead of going through the first fuel passage down to the nozzle.

[0010] On the other hand, in this prior art common rail fuel injector, the nozzle has a needle valve seated on a seat on the lower end of the nozzle. The high impact force created by the spring of the biasing device will pound the needle on the seat at every injection end. This may lead to deformation or even to cracks and broken tips because of the combination of high force, high temperatures and thin walls. This design is thus of poor reliability, leading to fuel leaks and broken tips. This will also limit the nozzle closing force, allowing leaks through the seat, blow back from the engines cylinder pressure through spray holes and carbon deposits on the seat.

[0011] The aim of the invention is to offer an improved electronically controlled high pressure common rail fuel injector free from the above-mentioned drawbacks.

[0012] A first object of the invention is a high pressure electronic common rail fuel injector, comprising: an injector body having a fuel inlet therein, a first fuel chamber formed within the injector body and in fluid communication with the fuel inlet, a second fuel chamber formed within the injector body, a nozzle coupled to the injector body, a first fuel passage fluidly coupling the second fuel chamber to the nozzle, a shuttle valve slidingly disposed within a bore of the injector body, and an electrically driven shuttle valve actuator coupled to the shuttle valve, wherein said shuttle valve slides between a first position allowing fuel flow, and a second position preventing fuel flow between the first and second fuel chambers, wherein said first and second chambers are defined by two annular recesses, one annular recess being formed in the side wall of the shuttle valve and the other in the side wall of said bore of the injector body, wherein said annular recesses overlap in said first position and are tightly separated in said second position.

[0013] By this arrangement, each first axial force generated by fuel pressure acting on a first shoulder of each annular recess is balanced by a second axial force generated by fuel pressure acting on a second shoulder of the annular recess. Thus, controlled fast and efficient opening/closing shuttle movements of the shuttle valve may be obtained by means of an actuator driven under control of the ECM of the vehicle.

[0014] The shuttle valve may be actuated by various types of actuators. Several actuators are known in the art. By way of an example, one may cite electromagnetic actuators, solenoid based actuators, piezoelectric actuators, etc... By virtue of the aforesaid arrangement, the injector according to the invention is not limited to a specific type of actuator.

[0015] Preferably, the fuel injector comprises a shuttle valve seat formed in the injector body between the first and second fuel chambers. In a preferred embodiment, for forming the seat, said shuttle valve has a portion of smaller diameter on one side of its annular recess and a portion of larger diameter on the other side of said recess, both diameters being matched to two inner diameters of the body surrounding said annular recess formed in the injector body.

[0016] Preferably, the fuel injector further comprises a shuttle valve actuator coupled to the shuttle valve, wherein activation of the shuttle valve actuator operates to unseat the shuttle valve from the shuttle valve seat, thereby allowing fuel flow between the first and second fuel chambers, and deactivation of the shuttle valve actuator operates to seat the shuttle valve on the shuttle valve seat, and further comprises a biasing member coupled to the shuttle valve and operative to apply a biasing force to the shuttle valve in a direction tending to seat the shuttle valve against the shuttle valve seat, thereby preventing fuel flow between the first and second fuel chambers.

[0017] In another aspect, a second object of the invention is a high pressure common rail fuel injector comprising an injector body having a fuel inlet therein, a first fuel chamber formed within the injector body and in fluid communication with the fuel inlet, a second fuel chamber formed within the injector body, a nozzle coupled to the injector body, a first fuel passage fluidly coupling the second fuel chamber to the nozzle, a shuttle valve slidingly disposed within the injector body, and an electrically driven shuttle valve actuator coupled to the shuttle valve, wherein said shuttle valve slides between a first position allowing fuel flow, and a second position preventing fuel flow between the first and second fuel chambers, said injector further comprising a needle valve seat formed in a proximal end portion of the nozzle; a needle valve slidingly disposed within the nozzle, said needle valve having a resting member at the proximal end thereof; and a biasing member operative to apply a biasing force to said resting member in a direction tending to seat said resting member against the needle valve seat.

[0018] Preferably, the needle valve has an internal passage open at the needle valve tip, fluidly coupling said first fuel passage to a fourth chamber at the tip of the nozzle.

[0019] Preferably, the tip of said needle valve slides within said fourth chamber without touching the bottom wall of the nozzle body.

[0020] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments described hereunder and illustrated by the drawings, wherein

Fig. 1 is a cross-sectional view of a first embodiment of a fuel injector according to the present invention;

Fig. 2a is a partial cross-sectional view of the first embodiment of the fuel injector with pull type actuation;

Fig. 2b is a partial cross-sectional view of a second embodiment of fuel injector with push type actuation;

Fig. 2c is a partial cross-sectional view of a third embodiment of fuel injector with pull type actuation;

Fig. 3 is a partial cross-sectional view of a standard nozzle, part of the first embodiment of the present invention, and Fig. 3a is an enlarged view of its tip;

Fig. 4 is a cross-sectional view of a fourth embodiment of the present invention;

Fig. 5 is a partial cross-sectional view of a nozzle, part of the fourth embodiment of the present invention, and Fig. 5a is an enlarged view of its tip.

[0021] Referring to Fig. 1 and 2a, there is illustrated a high pressure electronic common rail fuel injector of the present invention, indicated generally at 10. The injector 10 comprises an injector body 100 having a nozzle retainer 118. mounted to a distal end 116 thereof. A fuel inlet fitting 102 is threadingly engaged to the injector body 100 in order to receive fuel from a common rail fuel injection system (not shown). Fuel passes through a fuel inlet passage 103 into a first equalized pressure chamber 117 formed within the injector body 100.

[0022] The injector body 100 receives a slidably mounted shuttle valve 101 with a smaller lower diameter (d1) and a larger upper diameter (d2), both diameters matched to two inner diameters of the body 100. Between the portion of smaller diameter and the portion of larger diameter, the shuttle valve 101 has an annular recess 104 which receives the fuel under high pressure through the inlet passage 103. The pressure is thus contained in the first annular pressure chamber 117 defined by the inner wall of the body 100, the annular recess 104 in the shuttle valve 101, the upper shoulder 104a and the lower shoulder 104b of the recess 104. The upper shoulder 104a seals also a body seat 115 preventing the high pressure fuel from entering a second equalized annular pressure chamber 108 and a downward passage 109 to the nozzle 200. Above and next to the body seat 115, the inner body wall has an annular recess 125 defining, together with the cylindrical outer shuttle valve wall, said second annular pressure chamber 108. This configuration of the shuttle valve is illustrated in magnified detail in Fig. 2a. The second pressure chamber 108 is in fluid communication with the downward fuel passage 109 via a transverse passage 122.

[0023] It will be appreciated by those skilled in the art that fuel entering the first equalized pressure chamber 117 will create a substantially balanced upward and downward axial force on the shuttle valve 101 by means of the interaction between the pressurized fuel and the shoulders 104a and 104b. Therefore, the pressure in the incoming fuel does not create a substantial net upward or downward force on the shuttle valve 101. Likewise, the pressure of the fuel in the second pressure chamber 108 does not create any substantial net upward or downward force on the shuttle valve 101. In other words, no substantial force of this kind opposes the shuttle movement of the shuttle valve 101.

[0024] Fig. 1 and 2a show a first embodiment, the shuttle valve being actuated by a "pull" type actuator and having the seat on the upper side of the annular recess 104. The proximal end of the shuttle valve 101 is coupled to a piezoelectric actuator 106. The piezoelectric actuator 106 exhibits the property that when a current is applied thereto, it generates a movement in the longitudinal direction. Application of varying amounts of current thereto will produce varying amounts of longitudinal movement. The piezoelectric actuator 106 is contained within a cover which is sealingly engaged to the injector body 100.

[0025] A retaining ring 107 is coupled to the shuttle valve 101 in the area between the piezoelectric actuator 106 and the top of the actuator body 100. A biasing spring 105 located in an upper bore 126 of the injector body 100 is coupled between the retaining ring 107 and the lower face of the actuator 106, thereby producing a downward bias force on the shuttle valve 101. When the piezoelectric shuttle valve actuator 106 is not activated (i.e. no current is applied thereto), the bias spring 105 biases the shuttle valve 101 in a downward direction, thereby seating the shuttle valve 101 against the body seat 115. This action prevents fuel from flowing between the first pressure fuel chamber 117 and the second fuel chamber 108. In this configuration, the injector 10 is turned off, and no fuel flows to the nozzle 200.

[0026] A second bias spring 110 is held within a cylindrical hollow bore 119 in the distal portion 116 of the injector body and is compressed between the bottom of the bore 119 and the top of a spring seat 121. The bottom 120 of the spring seat 121 slides within a bore of a spacer member 111 and is fastened to the top of a needle valve 203a. Fig. 3 shows an enlarged view of the body 200a of the nozzle 200 of Fig. 1. The upper part of the needle valve 203a is slidingly engaged by a passage through the upper part of the body 200a of the injector nozzle. The lower part of the needle valve 203a is arranged to shuttle within a bore of the nozzle body 200a, said bore forming a third pressure chamber 202a. A fuel passage 201a provides fluid communication between the third pressure chamber 202a and the fuel downward passage 109, through the spacer member 111. Fig. 3a shows a more enlarged view of the tip of the nozzle body 200a. The distal end of the needle valve 203a mates with a valve seat 204a formed in the lower end of the nozzle body 200a. Mating and unmating of the needle valve 203a with the valve seat 204a controls flow of fuel from the passages 109 and 201 through the third chamber 202a and through the spray holes 205a. The injector 10 is mounted in an engine (not shown) such that fuel exiting the spray holes 205a is applied to the engine cylinders.

[0027] When the actuator 106 is energized, it lifts the shuttle valve 101 off the seat 115, opening fuel access to the second chamber 108 and to the passage 109, and down to nozzle 200. Here the high pressure fuel passes through the passage 201a into a heart shaped upper area of the third chamber 202a. The fuel pressure will lift the needle valve 203a off its seat 204a, compressing the spring 110, and thus the fuel will be injected into the engines combustion chamber through the spray holes 205a.

[0028] When the actuator 106 is de-energized, the spring 105 will seat the shuttle valve 101 on the seat 115, preventing from feeding more fuel under pressure into the passage 109, and thus the spring 110 will seat the needle valve 203a on the seat 204a, ending the injection process.

[0029] Fig. 2b shows a second embodiment of the shuttle valve, the shuttle valve being actuated by a "push" type actuator. The construction of the injector body also uses two different diameters on the plunger like shuttle valve and in the injector body and allows the introduction of a seat for sealing the fuel access to passage 109. Likewise the first embodiment, a biasing spring device (not shown) opposes the action of the actuator. A retaining surface is coupled to the shuttle valve in the area between the piezoelectric actuator and the actuator body. A biasing spring is coupled between the retaining surface and the bottom surface of the upper bore 126 of the injector body, thereby producing an upward bias force on the shuttle valve 101b, acting to retain the shuttle valve 101b engaged with its valve seat 115b, thereby preventing fuel flow from the equalized pressure chamber 117b to the second chamber 108b the fuel passage 109.

[0030] As can be seen in greater detail in the enlargement of Fig. 2b, the arrangement of the shuttle valve mechanism is similar but reverse to the arrangement of Fig. 2a. The shuttle valve 101b has a smaller upper diameter (d1) and a larger lower diameter (d2), both diameters matched to two inner diameters of the body 100b. The body seat 115b mates and unmates with the lower shoulder 104b of the annular recess 104 of the shuttle valve and the second fuel pressure chamber 108b is located below the first pressure chamber.

[0031] Those skilled in the art will easily recognize that, except the reversal positions, the working of the second embodiment is identical to the working of the first embodiment, as described herein above.

[0032] Fig. 2c shows a third embodiment of a shuttle valve arrangement, the shuttle valve being opened by an upward movement and closed by a downward movement.

[0033] The upper and lower portions of the slidable shuttle valve 101c have the same diameter (d), matching to the inner diameter of the injector body. The shuttle valve has an annular recess in front of the fuel inlet 103 for forming the first pressure chamber 117c. The inner body wall presents an annular recess, defining together with the shuttle valve outer wall a second pressure chamber 108c. The second chamber 108c is in fluid communication with a downward fuel passage 109. The annular recesses in the body wall and in the shuttle valve are offset so that the two chambers 108c and 117c are tightly separated when the actuator pushes the shuttle valve down but communicate when the actuator pulls the shuttle valve up. The shuttle valve does not push against a seat and the metal-to-metal tight clearance seals the fuel pressure. The actuator may be selected among electromagnetic actuators.

[0034] Those skilled in the art will appreciate that in all the embodiments shown in Fig. 1, 2a, 2b, 2c, the bore of the spacer member 111, the bore 119 in the distal portion of the injector body, and a chamber 123 located below the plunger shuttle valve 101 communicate with one another through a passage 124 and communicate, through a central passage 112 and a cross passage 113 in the shuttle valve 101, with the upper bore 126 receiving the spring 105 and with an outlet passage 114 to the fuel return line to the tank. Thus, fuel leakages from the high pressure chambers are collected, and building up of a high pressure condition below the shuttle valve 101 and above the needle valve 203a, which could counteract the shuttle movement of said valves, is prevented.

[0035] But contrarily to the construction disclosed by EP 0737808, the chamber 123 is not put in fluid communication with an upstream high pressure second chamber at each injection cycle by a set ball valve.

[0036] Those skilled in the art will recognize that the first pressure chamber could also be formed by an annular recess in the body wall and the second pressure chamber by an annular recess in the shuttle valve.

[0037] As an alternative to the nozzle shown in Fig. 1 and described hereinabove, according to the invention, a preferred solution is also proposed for the nozzle, using a shuttling needle having its contact seat on the upper side of the nozzle. An embodiment thereof is shown in Fig. 4 and, at enlarged scales, in Fig. 5 and 5a.

[0038] The injector shown in Fig. 4 uses the same injector body as in Fig. 1 and thus, the same numerals are used for this part of the injector without further description. Fig. 5 shows a nozzle using a needle valve 203b slidably mounted in a nozzle body 200b. The upper and lower portions of the needle valve are slidably guided in the nozzle body 200b. The middle portion of the needle valve is surrounded by a third pressure chamber 202b.

[0039] There is a large seat 204b on the upper side of the nozzle, where the nozzle body 200b is much stronger than at the lower end. The proximal portion of the needle valve 203b bears a corresponding resting member 210b. Fuel under high pressure enters the nozzle body 200b through a passage 201b and flows into the third chamber 202b, from where it passes through a cross hole 207b, down a central passage 208b in the needle valve 203b and into a fourth tip chamber 206b. Here the fuel is stopped by the tight clearance between the nozzle body 200b and needle valve 203b at the lower edge 211b of the needle, as shown in Fig. 5a.

[0040] When high fuel pressure exceeds spring's 110 pretension force, it will compress the spring 110 and lift the needle valve 203b from its seat 204b. The lower edge 211b of the needle will uncover the inside area 209b of the nozzle bore where spray holes 205b are located, allowing the fuel to be injected into the engine's combustion chamber through the spray holes 205b. When the actuator 106 is de-energized, the shuttle valve 101 is seated by the spring 105 on its seat 115 and the supply of high pressure to the nozzle is cut off. With pressure dropping inside the nozzle because fuel has been injected through spray holes 205b, when the pressure level gets lower than the spring's 110 pretension force, the needle valve 203b will be re-seated on its seat 204b and the lower edge 211b of the needle will cut off fuel to holes 205b, ending the injection process.

[0041] Those skilled in the art will recognize that the needle tip never touches the bottom wall 212b of the nozzle body 200b. As explained above, this solution eliminates nozzle leaking, cracking and tip break off. Also carbon deposits on the seat are eliminated, because the increased seat area and material resistance allow higher nozzle opening and closing pressure.

Claims

1. A high pressure electronic common rail fuel injector (10), comprising:

an injector body (100, 100b, 100c) having a fuel inlet (103) therein;

a first fuel chamber (117, 117c) formed within the injector body and in fluid communication with the fuel inlet;

a second fuel chamber (108, 108b, 108c) formed within the injector body;

a nozzle (200) coupled to the injector body;

a first fuel passage (109) fluidly coupling the second fuel chamber to the nozzle;

a shuttle valve (101, 101b, 101c) slidingly disposed within a bore of the injector body; and

an electrically driven shuttle valve actuator (106) coupled to the shuttle valve, wherein said shuttle valve slides between a first position allowing fuel flow, and a second position preventing fuel flow between the first and second fuel chambers, characterized in that said first and second chambers are defined by two annular recesses (104, 125), one annular recess (104) being formed in the side wall of the shuttle valve and the other one (125) in the side wall of said bore of the injector body, wherein said annular recesses overlap in said first position and are tightly separated in said second position.

2. A fuel injector as claimed in claim 1, wherein an annular recess (104) is formed in the shuttle valve (101, 101b, 101c) in an area facing said fuel inlet (103) in both said first and second positions.

3. A fuel injector as claimed in claim 1 or 2, wherein said shuttle valve (101c) has the same diameter on both sides of the annular recess (104) formed in said shuttle valve.

4. A fuel injector as claimed in claim 1 or 2, further comprising a shuttle valve seat (115, 115b) formed in the injector body between the first (117) and second (108, 108b) fuel chambers.

5. A fuel injector as claimed in claim 4, wherein said shuttle valve (101, 101b) has a portion of smaller diameter on one side of its annular recess (104) and a portion of larger diameter on the other side of said recess, both diameters being matched to two inner diameters of the body (100, 100b) surrounding said annular recess formed in the injector body.

6. A fuel injector as claimed in claim 4 or 5, comprising a shuttle valve actuator (106) coupled to the shuttle valve (101, 101b), wherein activation of the shuttle valve actuator operates to unseat the shuttle valve from the shuttle valve seat (115, 115b), thereby allowing fuel flow between the first (117) and the second (108, 108b) fuel chambers, and deactivation of the shuttle valve actuator operates to seat the shuttle valve on the shuttle valve seat, further comprising a biasing member (105) coupled to the shuttle valve and operative to apply a biasing force to the shuttle valve in a direction tending to seat the shuttle valve against the shuttle valve seat, thereby preventing fuel flow between the first and second fuel chambers.

7. A fuel injector as claimed in anyone of claims 1 to 6, further comprising a needle valve seat (204a) formed in a distal end of the nozzle (200);
a needle valve (203a) slidingly disposed within the nozzle; and
   a biasing member (110) coupled to the needle valve and operative to apply a biasing force to the needle valve in a direction tending to seat the needle valve against the needle valve seat.

8. A fuel injector as claimed in anyone of claims 1 to 6, further comprising a needle valve seat (204b) formed in a proximal end portion of the nozzle;
   a needle valve (203b) slidingly disposed within the nozzle, said needle valve having a resting member (210b) at the proximal end thereof; and
   a biasing member (110) operative to apply a biasing force to said resting member in a direction tending to seat said resting member against the needle valve seat.

9. A fuel injector as claimed in claim 8, wherein said needle valve (203b) has an internal passage (208b) open at the needle valve tip (211b), fluidly coupling said first fuel passage (109) to a fourth chamber (206b) at the tip of the nozzle.

10. A fuel injector as claimed in claim 9, wherein the tip of said needle valve (203b) slides within said fourth chamber (206b) without touching the bottom wall (212b) of the nozzle body (200b).

Drawing