A FUEL FLOW PATH FOR A VALVE GROUP OF A FUEL INJECTOR

Technical Field of the Invention

The present invention relates to a valve group used in fuel injection systems for adjusting a fuel flow path in hydraulic control units.

Prior Art

Valves are used for many applications in the field of automotive engineering, particularly in the field of injection technology. Valves are used for regulating hydraulic pressure and controlling the injection behavior of injection devices. In the field of high-pressure reservoir injection systems, especially in common rail injection systems, valves are used to control the lift of an injection valve closure member, which opens or closes injection openings.

The prior art reference, which is relevant to the technical field of the present invention is the US 2010/116910 A1 publication. It discloses a ball valve for adjusting a flow of a fluid medium. The ball valve includes a valve seat and a rounded closing element, in particular a valve ball. Furthermore, the ball valve has an inlet with a choke valve and one diffuser arranged between the choke valve and the valve seat. The diffuser includes a constriction on the side facing the valve seat.

Brief Description of the Invention

An object of the present invention is to decease cavitation erosion effects on a valve seat of a fuel injector.

A fuel injector having a fuel flow path having a total length between a valve seat and a fuel pressure control chamber comprising a length of an A-throttle, a distance between the A-throttle and the valve seat and a length of a pre-hole. The fuel flow path is arranged by shortening a length of the pre-hole and arranged by elongating a sum of the length and of the distance between the A- throttle and the valve seat in a constant total length of the fuel flow path between the valve seat and the fuel pressure control chamber in order to decrease a L1/L2 ratio. Thus, cavitation erosion risk along the cavitation erosion blocker is decreased due to the decreased L1/L2 ratio.

In a possible embodiment of the present invention, the L1/L2 ratio is between 0.15 - 0.4. Thus, a desired cavitation erosion index is obtained.

In a possible embodiment of the present invention, the decreased L1/L2 ratio is arranged by eliminating a throttle on the diffuser. Thus, an additional manufacturing process for the throttle is eliminated.

In a possible embodiment of the present invention, a chamfered hole is formed between the diffuser and the valve seat as gradually widening from the diffuser through the valve seat. Thus, a transition region for fuel flow is formed before the fuel flow reaches the valve seat.

In a possible embodiment of the present invention, a conical portion is formed between the A-throttle and the diffuser. Thus, a pressure recovery region between the A-throttle and the diffuser is provided. Therefore, pressure fluctuations causing cavitation are reduced.

In a possible embodiment of the present invention, the conical portion is gradually widening from the A-throttle through the diffuser. Thus, a mild pressure transition region between the A-throttle and the diffuser is obtained. Therefore, pressure fluctuations causing cavitation are reduced.

Brief Description of the Figures

FIG.l shows a CE-blocker having a pre-hole, an A-throttle, a diffuser, a conical portion between the A-throttle and the diffuser, a chamfered hole in a frontal view according to the present invention.

FIG.2 shows a cross-sectional view of a part of a fuel injector having a piston means, a fuel pressure control chamber, a CE-blocker and a valve element according to the prior art.

A Detail taken from FIG.2 shows a part of a CE-blocker having a pre-hole, an A- throttle, a diffuser, a throttle, a chamfered hole in a frontal view according to the prior art. FIG.3 shows a solenoid type fuel injector in a cross-sectional view and the dashed part shows the detail in the FIG.2 in the prior art.

Reference Numbers

10 Fuel injector

11 Body

12 Magnet core

13 Magnet coil

14 Magnet housing

15 Armature plate

16 Armature guidance

17 Valve spring

18 Armature bolt

19 Spring

20 Piston means

24 Valve body

26 Fuel channel

27 Needle

30 Cavitation erosion (CE) blocker

31 Pre-hole

32 A-throttle

33 Diffuser

34 Throttle

35 Chamfered hole

36 Conical portion

40 Valve element

41 Valve seat

42 Ball holder

50 Control chamber

60 Electrical connector

70 Spray hole

80 Valve nut

90 Inlet connector

V Valve longitudinal axis LI A length of the A-throttle

L2 A distance between the A-throttle and the valve seat

L3 A length of the pre-hole

H A total length between a valve seat and a fuel pressure control chamber

Detailed Description of the Invention

The present invention proposes a fuel injector (10) having a fuel flow path having a total length (H) between a valve seat (41) and a fuel pressure control chamber (50) comprising a length (LI) of an A-throttle (32), a distance (L2) between the A-throttle (32) and the valve seat (41) and a length (L3) of a pre-hole (31). The fuel flow path is arranged by shortening a length (L3) of the pre-hole (31) and arranged by elongating a sum of the length (LI) of the A-throttle (32) and of the distance (L2) between the A-throttle (32) and the valve seat (41) in a constant total length (H) of the fuel flow path between the valve seat (41) and the fuel pressure control chamber (50) in order to decrease a L1/L2 ratio.

The fuel injector (10) is a solenoid valve type fuel injector as one of embodiment of the fuel injector is shown in FIG.3. The solenoid fuel injectors (10) have an electromagnetic actuating mechanism. The actuating mechanism actuates an armature group and the armature group provides a valve closure member (i.e. a valve element (40) preferably in a ball shaped) to open and close a needle (27) of the fuel injector (10) by changing the fuel pressures.

An armature group comprising an armature bolt (18) and an armature guidance (16) are being actuated by a magnetic actuating mechanism which has a magnet coil (13), a magnet core (12) surrounding the magnet coil (13) and a magnet housing (14) where the magnet core (12) is set inside.

The magnetic actuating mechanism actuates a needle (27) of the fuel injector (10) to open and close the needle (27) for spraying fuel from spray holes (70) of the fuel injector (10). An armature guidance (16) is a part which is fixed with a valve nut (80). The function of the armature guidance (16) is to guide an armature bolt (18). The armature guidance (16) has a certain gap as a main hole and the armature bolt (18) can move inside the main hole in a vertical direction (on a valve longitudinal axis: V) to up and down. The armature bolt (18) functions as a part of magnetic actuator that opens and closes a valve group. The armature bolt (18) transfers forces to a valve element (40), keeps an A-throttle (32) closed and carries to an armature plate (15). When the armature plate (15) is pulled by a magnetic force, the armature bolt (18) moves together with the armature plate (15) upward and opens the A-throttle (32) via lifting the valve element (40). During operation of the solenoid valve fuel injector (10), the magnetic actuating mechanism actuates an armature group via energizing of the magnet coil (13) and pulls up the armature bolt (18) and the ball holder (42) by help of a valve spring (17) and a spring (19) surrounds the armature group which comprises the armature plate (15), the armature guidance (16) and the armature bolt (18). Electric current is fed through an electrical connector (60) to the magnet coil (13). Magnetic force is created and overcomes the spring (19) force exerted on armature bolt (18) and the valve element (40) rises to a defined height. High- pressure fuel flows through A-throttle (32) and under the valve element (40) and the pressure in control chamber (50) reduces. Injection starts and continues, as the valve element (40) stays open. The fuel is provided via an inlet connector (90) through inside fuel channels (26) which are formed inside a body (11) of the fuel injector (10). When the A-throttle (32) is opened, a pressurized fuel coming from the fuel channels (32) flows through a control chamber (50) and then through the A-throttle (32) to keep the A-throttle (32) open during the spraying of the fuel into a combustion chamber (not shown in the figures) of an engine block. By the pushing force of the pressurized fuel in the control chamber (50), a piston means (20) moves together with the needle (27) through the spray holes (70) and sprays the fuel. When the electrical current is cut off, the magnetic force run out and the valve spring (17) pushes and closes the valve element (40) via the armature bolt (18). Pressure in the control chamber (50) rises, closes the needle (27) via the piston means (20), and brings the injection process to the end.

Figure 1 shows a cavitation erosion (CE) blocker (30) of a valve used at a fuel injector (10) in a frontal view according to the present invention. The CE-blocker (30) has the elements of a pre-hole (31), an A-throttle (32), a conical portion (36), a diffuser (33) and a chamfered hole (35) on the fuel flow path that are ordered in a +Y direction. A length (L3) of the pre-hole (31), a length (LI) of the A-throttle (32), a distance (L2) between the A-throttle (32) and the valve seat (41), a total length (H) between a valve seat (41) and a fuel pressure control chamber (50) are also shown in Figure 1.

Figure 2 shows a cross-sectional view of a part of a fuel injector (10) having a piston means (20), a control chamber (50) in fluid communication with a CE- blocker (30), a valve element (40) having a seat on a valve seat (41) according to the prior art.

A Detail taken from Figure 2 shows a part of a C E-blocker (30) of a valve used at a fuel injector (10) in a front view according to the prior art. The elements of the CE-blocker (30) are in the order of the fuel flow path that is in +Y direction as a pre-hole (31), an A-throttle (32), a diffuser (33), a throttle (34) and a chamfered hole (35). The length (L3) of the pre-hole (31) is not as short as shown in A detail, but the length (L3) is longer as indicated in the A detail with double lines.

In the prior art, conventional valves have the disadvantage of severe erosion, particularly in the common rail type of fuel injectors (10) functioning at several thousand bar pressures. The erosion is in particular due to a cavitation in the fuel injection valve. In the valve seat (41) region of the fuel injection valves, the expansion of the fluid medium from high pressure to low pressure regions creates bubbles which results in cavitation erosion due to condensation particularly in the seat region of the valve seat (41). High-pressure peaks that occur during the implosion or explosion of cavitation bubbles cause the cavitation erosion. Therefore, closing behavior of the valve fails and malfunction in the injection behavior of the fuel injector (10) emerges.

In the prior art, in the CE-blocker (30) type of valve, bubbles mostly form in A- Throttle (32) and bubbles are carried along the diffuser (33) asymmetrically. Bubbles reaching the throttle (34) and the chamfered hole (35) accumulates on one side of the valve seat (41). There is a high risk of cavitation erosion at the valve element (40) and the valve seat (41) by implosion or explosion of the bubbles and this causes delamination on the valve seat (41) surface. There is a coating surface on the valve seat (41) and when the imploding bubbles cause deterioration on the coated surface, cavities and micro-cracks are formed on the valve seat (41). As a result, the problem of fuel leakage and back flow emerge on the valve. This problem may lead to the fuel injection failure and engine shut down.

There are also manufacturing problems during the manufacturing of the throttle (34) of the CE-blocker (30). The throttle (34) geometry, which is between the chamfered hole (35) and diffuser (33), is a very hard geometry to manufacture in terms of concentricity concern. If an eccentric geometry of the throttle (34) is formed during manufacturing process, some fuel injector body (11) can be thrown out, which decreases the production yield.

According to the present invention, simulation calculations are carried out to find parameters decisively to affect cavitation erosion. The location of cavitation damage is depended upon a variety of factors such as valve geometry and flow conditions in the fuel flow path. In particular, these parameters are fluid flow velocity, the vapor phase volume fraction and the distance (L2) between the valve seat (41) and the A-throttle (32).

There is a cavitation erosion index (CEI) defined as the ratio of the length (LI) of the A-throttle (32) to the distance (L2) between the A-throttle (32) and the valve seat (41). The value of CEI changes between 0.44 and 0.15. As the value of CEI increases the risk of cavitation erosion increases.

In a detailed description of the invention, a fuel injector (10) having a fuel flow path having a total length (H) between a valve seat (41) and a control chamber (50) comprising a length (LI) of an A-throttle (32), a distance (L2) between the A-throttle (32) and the valve seat (41) and a length (L3) of a pre-hole (31). The fuel flow path is arranged by shortening a length (L3) of the pre-hole (31) and arranged by elongating a sum of the length (LI) of the A-throttle (32) and of the distance (L2) between the A-throttle (32) and the valve seat (41) in a constant total length (H) of the fuel flow path between the valve seat (41) and the control chamber (50) in order to decrease a L1/L2 ratio. Therefore, the distance (L2) between the A-throttle (32) and the valve seat (41) is increased since the length (L3) of the pre-hole (31) is decreased while the total length (H) of the fuel flow path between the valve seat (41) and the control chamber (50) is constant. The increase in the distance (L2) reduces the L1/L2 ratio; hence, cavitation erosion index (CEI) reduces. As a result, cavitation erosion problem around the valve seat (41) and the valve element (40) is minimized. In a possible embodiment of the present invention, with design optimizations of the distance (L2) and the length (L3), the L1/L2 ratio is obtained between 0.15 - 0.4. When the L1/L2 ratio is decreased to a range between 0.15 and 0.4, cavitation erosion index (CEI) drops to an optimum level to eliminate cavitation erosion risk on the valve of the fuel injector (10).

In an embodiment of the present invention, the decreased L1/L2 ratio is arranged by eliminating a throttle (34) on the diffuser (33). The throttle (34) between the diffuser (33) and the chamfered hole (35) is formed with the aim of eliminating cavitation erosion on the valve seat (41) region and the valve element (40). When the distance (L2) between the A-throttle (32) and the valve seat (41) is elongated, the L1/L2 ratio decreases, cavitation erosion index reduces and thus, cavitation erosion problem is minimized. Therefore, there is not any requirement for manufacturing the throttle (34) on the diffuser (33). The function of decreasing cavitation erosion done by the throttle (34) is overtaken by the elongated distance (L2) on the diffuser (33). Hence, an additional manufacturing process to form the throttle (34) geometry on the diffuser (33) is eliminated. Thus, the extra load on manufacturing is terminated and the problem of throwing out eccentrically manufactured fuel injector body (11) is defeated.

In an embodiment of the present invention, a chamfered hole (35) is formed between the diffuser (33) and the valve seat (41) as gradually widening from the diffuser (33) through the valve seat (41). The minimum dimeter of the chamfered hole (35) is equal to the diameter of the diffuser (33). The diameter of the chamfered hole (35) increases gradually through the valve seat (41). An angle of the chamfered hole (35) with respect to a horizontal axis is different from an angle of the valve seat (41) with respect to the horizontal axis. The increase in the diameter of the chamfered hole (35) creates a transition region for fuel flowing in the direction of +Y. Since the pressure regulation is a very critical concern before the fuel flow hits to the valve element (40) and reaches the valve seat (41), the transition region created by the chamfered hole (35) prevents the cavitation bubbles from imploding. Thus, cavitation erosion around the valve seat (41) surface and the valve element (40) is decreased.

In an embodiment of the present invention, a conical portion (36) is formed between the A-throttle (32) and the diffuser (33). The conical portion (36) is gradually widening from the A-throttle (32) through the diffuser (33). Thus, a pressure recovery region providing a mild pressure transition region between the A-throttle (32) and the diffuser (33) is obtained. Pressure fluctuations causing cavitation are reduced. Bubble formation is reduced by the gradually widening coning zone in the conical portion (36) and cavitation erosion risk is decreased.