Claims:
1 A fuel injector (100), said fuel injector (100) comprising:
an injector body (102);
a nozzle assembly (104) fitted to said injector body (102) and comprising one or more openings for injecting fuel into a combustion chamber;
characterized in that
a spring (106) within said injector body (102), said spring (106) having at least one of a variable coil diameter and a variable pitch for controlling quantity of fuel injected into said combustion chamber based on engine operating conditions.

2 The fuel injector (100) as claimed in claim 1, wherein said spring (106) is pre-loaded.
, Description:Field of the invention
[0001] The invention relates to fuel injector.
Background of the invention
[0002] Fuel injector (10) is an important component in a fuel injection system for injecting fuel into a combustion chamber of an engine. Figure 1 illustrates a cross sectional view of a fuel injector (10) in accordance with existing art. The fuel injector (10) comprises an injector body (12) which forms the outer covering of the fuel injector (10). The fuel injector (10) also includes a nozzle assembly (14) that is fitted to the injector body (12). The nozzle assembly (14) comprises a nozzle body (14a) and a needle (14b). The needle (14b) is placed inside the nozzle body (14a). The nozzle body (14a) comprises one or more holes for spraying fuel in an atomized form. A spring (16) is placed inside the injector body (12) that enables opening and closing of the spray holes by lifting the nozzle needle (14b) between open position and closed position within the nozzle body (14a). The fuel injector (10) has an inlet (18) through which fuel enters into a nozzle cavity in the nozzle body (14a). As the pressure of the fuel increases within the nozzle cavity, the nozzle needle (14b) is lifted.
[0003] According to US5769319, a closed nozzle fuel injector comprising an injector body containing an injector cavity including a nozzle cavity and an injector orifice communicating with one end of said nozzle cavity to discharge fuel into the combustion chamber, a nozzle valve element positioned in the nozzle cavity adjacent to the injector orifice, and a rate shaping control concept for varying the flow rate of fuel through said injector orifice, said rate shaping control means including a throttling passage integrally formed in said nozzle needle element for restricting the flow of fuel to said nozzle cavity to thereby vary the rate at which fuel pressure in said nozzle cavity increases.

Brief description of the accompanying drawings
[0004] Figure 1 is a cross sectional view of a fuel injector, in accordance with existing art;
[0005] Figure 2 is a cross sectional view of a fuel injector, in accordance with one embodiment of the present disclosure;
[0006] Figure 3 is a graph showing injection quantity as a function of engine speed, in accordance with an existing art; and
[0007] Figure 4 is a graph showing injection quantity as a function of engine speed, in accordance with an embodiment of the present disclosure.

Detailed description of the embodiments
[0008] Figure 2 is a cross sectional view of a fuel injector (100), in accordance with one embodiment of the present disclosure.
[0009] The fuel injector (100) comprises an injector body (102), a nozzle assembly (104) fitted to the injector body (102) and comprising one or more openings for injecting fuel into a combustion chamber. The fuel injector (100) is characterized by a spring (106) within the injector body (102), the spring (106) having at least one of a variable coil diameter and a variable pitch for controlling quantity of fuel injected into the combustion chamber based on engine operating conditions.
[0010] The structure of the fuel injector (100) is explained in detail in the below paragraphs.
[0011] The injector body (102) forms an outer covering of the fuel injector (100). The injector body (102) has a cavity (102a) that houses other components of the fuel injector (100) that is explained in the following lines.
[0012] The fuel injector (100) also comprises a nozzle assembly (104) fitted to the injector body (102). The nozzle assembly (104) comprises a nozzle body (104a), a nozzle cavity (104b) and a needle (104c). The needle (104c) is placed within the nozzle cavity (104b) The nozzle body (104a) comprises one or more orifices in fluid communication with a combustion chamber for injecting fuel present in the nozzle cavity (104b) into the combustion chamber. The needle (104c) is movable within the nozzle cavity (104b) such that the orifices are opened and closed.
[0013] An inlet (108) is housed in the injector body (102) for releasing high pressure fuel received from a fuel pump through high pressure pipe into the nozzle cavity (104b).
[0014] The nozzle assembly (104) comprises threads on its inner surface so that the nozzle assembly (104) is fitted to the injector body (102) using thread-fit mechanism.
[0015] The fuel injector (100) is characterized by a spring (106) within the injector body (102). That is, the spring (106) is placed in the cavity (102a) of the injector body (102). The spring (106) facilitates movement of the needle (104c) between the open position and the closed position within the nozzle cavity (104b) during fuel injection. Also, the spring (106) is pre-loaded when the nozzle assembly (104) is fitted to the injector body (102) using the thread-fit mechanism.
[0016] In one embodiment, the characteristic of the spring (106) is such that it has a variable coil diameter, a uniform wire diameter and a uniform pitch. Coil diameter refers to the diameter of the coils in the spring. The number of coils present in the spring is defined based on factors such as needle lift, quantity of fuel injection required and stiffness of the spring. Variable coil diameter refers to one or more coils in the spring which has a varying diameter with respect to other coils in the spring. According to this embodiment, the diameter of the coils at the top and bottom of the spring (106) is less than the diameter of the coils towards the center of the spring (106). It should be noted that, in accordance with this embodiment, the coil diameter of the spring (106) varies between the range of 3.5mm to 7.0 mm. Wire diameter refers to the diameter of the wire of the spring (106). Pitch refers to the distance between any two coils in the spring (106). Uniform pitch refers to the distance between the coils being the same.
[0017] In another embodiment, the characteristic of the spring (106) is such that it has a variable pitch, a uniform coil diameter and a uniform wire diameter. The variable pitch refers to distance between the coils being different with respect to each other and uniform coil diameter refers to the coil diameter of every coil in the spring being the same. In this embodiment, the pitch at the top and bottom of the spring (106) is less than the pitch towards the center of the spring (106). Value of the pitch in accordance with this embodiment varies between range of 1mm-2mm. However, the value of the pitch is required to be distributed with respect to each coil such that total length of the spring (106) is maintained to be nearly equal to 27.2 mm.
[0018] In yet another embodiment, the characteristic of the spring (106) is such that it has both variable coil diameter and a variable pitch with a uniform wire diameter. It should be noted that in all three embodiments, the wire diameter is uniform.
[0019] The fuel injector (100) also comprises a pressure bolt (110) that is seated on a distance piece (112) and is located in the cavity (102a) of injector body (102). The pressure bolt (110) is also used for holding the spring (106) at one end and is used for translating movement of the needle (104c) to the spring (106). The distance piece (112) is located between the injector body (102) and the nozzle assembly. The distance piece (112) is used for defining the maximum lift of the needle (104c).
[0020] The working of the fuel injector (100) is explained in detail in the below paragraphs.
[0021] Fuel from a fuel tank is pressurized using a fuel pump. The pressurized fuel is sent to the fuel injector (100). The pressurized fuel flows into the nozzle cavity (104b) through the inlet (108). The pressurized fuel therefore is accumulated in the nozzle cavity (104b). As the accumulation in the nozzle cavity (104b) occurs, the pressurized fuel exerts a force on the needle (104c). As a result the needle (104c) tends to exert a force against spring force. When the pressure exerted by the pressurized fuel exceeds the pre-loaded spring force, the spring (106) compresses and the needle (104c) is lifted thereby opening the orifices present in the nozzle cavity (104b). When the orifices are opened, pressurized fuel is injected into the combustion chamber.
[0022] As the needle (104c) is lifted, because of the presence of distance piece (112) between the injector body (102) & nozzle body (104a), the needle (104c) can move until the needle (104c) reaches the bottom surface of the distance piece (112). This controls the needle lift. The needle lift is referred to as the distance moved by the needle (104c) from the closed position towards the open position. In Figure 2, the needle is at the closed position. The needle (104c) obtains maximum lift when the top surface of the needle (104c) reaches the bottom surface of the distance piece (112). The needle guide (104d) moves within the pressure bolt (110).
[0023] As the needle (104c) is lifted against the spring force, the spring (106) begins to compress. As the spring (106) has variable coil diameter and variable pitch, rate at which the needle (104c) is lifted against the spring force, for a particular engine operating condition, varies. Such rate is also defined as the speed at which the needle (104c) is lifted. Such variation in the rate at which the needle (104c) is lifted causes variation in quantity of the fuel injected into the combustion chamber. For a particular engine operating condition, the quantity of fuel required is known using a map that is stored in a control unit. Consequently, the distance by which the needle (104c) is required to be lifted so that the required quantity of fuel is injected by the fuel injector (100) is also known. It should be noted, by using the spring (106), the rate at which the needle (104c) is lifted against the spring force varies for that particular engine operating condition, however, the height to which the needle (104c) is lifted remains the same for that particular engine operating condition. In other words, time taken by the needle (104c) to be lifted to that particular height varies due to the spring (106).
[0024] Hence, the spring (106) having variable coil diameter and variable pitch causes variable rate at which the needle (104c) is lifted against the spring force. Such variable rate of needle lift causes change in quantity of fuel injected into the combustion chamber when compared to a spring having a uniform coil diameter and uniform pitch as known in prior art. The change in the quantity of fuel injection causes reduced emissions and reduced fuel consumption for a particular engine operating condition. The change in the quantity of fuel injected into the combustion chamber is explained in detail in conjunction with Figure 3.
[0025] Figure 3 and Figure 4 are graphs showing injection quantity as a function of engine speed.
[0026] Figure 3, is a graph showing injection quantity as a function of engine speed, in accordance with a prior art. Here, the fuel injector (10) comprises a spring (16) having a uniform coil diameter, uniform pitch and a uniform wire diameter. According to graph shown in Figure 3, X-axis represents needle lift of the fuel injector (10) and Y-axis represents quantity of fuel injected into a combustion chamber.
[0027] As discussed above, the needle (14b) is movable between a closed position and an open position. The needle lift is defined as the height at which the needle (14b) is lifted with respect to the closed position.
[0028] The quantity of fuel injected into a combustion chamber is represented in terms of cc/30 seconds and the needle lift is represented in terms of millimeters.
[0029] According to graph shown in Figure 3, ramp (302) represents a linear relationship between the needle lift and the quantity of fuel injected into the combustion chamber. That is, if the needle lift is high then the quantity of fuel injected into the combustion chamber is large.
[0030] The graph shown in Figure 4, represents the quantity of fuel injected with respect to the needle lift for the fuel injector (100) with a spring (106) having at least one of a variable coil diameter and a variable pitch for controlling quantity of fuel injected into the combustion chamber based on engine operating conditions. The X-axis represents, the needle lift and is represented in terms of millimeters. The Y-axis represents, the quantity of fuel injected into the combustion chamber and is represented in terms of cc/30 seconds.
[0031] The graph (402) represents the relationship between the quantity of fuel injected and the needle lift. In the graph (402) the relationship between the quantity of fuel injected and the needle lift is non-linear. Such non linearity is obtained due to variable rate of needle lift for a particular engine operating condition (speed and torque). This is obtained by using spring (106) having variable coil diameter or variable pitch or both coil diameter and pitch being variable in nature. Such variable rate of needle lift occurs due to the spring (106) having a variable coil diameter and variable pitch. The variable rate of needle lift causes reduction in the quantity of fuel injected. Such reduction in the quantity of fuel injected results in reduced emissions and reduced fuel consumption. Hence, for a particular engine operating condition, the needle lift and the quantity of fuel injected for that needle lift is pre-defined. By using the spring (106) having variable coil diameter and variable pitch, the variable rate of needle lift occurs, thereby, altering the quantity of fuel injected into the combustion chamber. However, the height up to which needle (104c) is lifted (needle lift) still remains the same for that particular engine operating condition. That is, in other words, the speed at which the needle (104c) is lifted varies for that particular engine operating condition.
[0032] Therefore the present disclosure discloses a fuel injector (100) characterized by a spring (106) having variable coil diameter and variable pitch. By using such a spring (106), the rate of needle lift for a particular engine operating condition changes. Such variable rate of needle lift causes alteration in the quantity of fuel injected into the combustion chamber. Also, by obtaining variable rate of needle lift, the quantity of fuel injected into the combustion chamber is reduced. Hence avoiding excess fuel injection which results in increased emissions and increased fuel consumption. Hence, the fuel injector (100) disclosed in the current disclosure enables reduced emissions and reduced fuel consumption.
[0033] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments with regard to the type of injector body, type of nozzle assembly are envisaged. The scope of the invention is only limited by the scope of the claims.