GB2339271A

GB2339271A - Damped valve

Info

Publication number: GB2339271A
Application number: GB9913763A
Authority: GB
Inventors: Sattish Pattanaik
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 1998-07-06
Filing date: 1999-06-14
Publication date: 2000-01-19
Also published as: GB9913763D0; DE19931026A1

Description

2339271 DAMPED LIQUID CONTROL VALVE ASSEMBLY AND HYDRAULICALLY ACTUATED

FUEL INJECTOR USING SAME The present invention relates generally to damped liquid valve assemblies, and more particularly to noise reduction in high speed control valve assemblies, such as those used in hydraulically-actuated fuel injectors having a spill controlled rate shaping device.

In one class of control valve assemblies, a valve member is moved between upper and lower valve seats during its actuation cycle. For instance, in many hydraulically actuated fuel injectors, a control valve assembly includes a poppet valve member that is moved between upper and lower conical valve seats by a solenoid and return spring.

Although the poppet valve member moves a distance on the order of only about several hundred microns, the valve member can have a substantial velocity when it impacts one of the seats. It is usually undesirable to have the valve member linger for any substantial length of time in between the upper and lower valve seats. Thus, relatively high accelerations and velocities are usually desirable when moving the valve member from one seat to the other.

However, it is also typically desirable to have impact velocities that do not cause unnecessary damage to the valve seats nor cause undesirable noise.

In most cases, damage to the valve seats can be addressed by an appropriate design and by the use of suitable materials. However, the problem of reducing noise produced by impact of the valve member on one of its seats can often prove more problematic. While noise often does not undermine the performance of a valve assembly, a consumer may perceive a problem due to the presence of noise. This noise usually reveals itself as a loud clicking that is not only annoying, but often undermines a users confidence in the valve, because the noise sometimes lends one unfamiliar with a given system the impression that the valve is not working properly.

Since impact noise is directly proportional to the square of the impact velocity, a relatively small decrease in impact velocity can result in a relatively large decrease in impact noise. For instance, a thirty percent reduction in approach velocity will correspond to more than a fifty percent reduction in impact noise. While it may be desirable to reduce impact velocity, it is often difficult to do so without undermining valve performance. In other words, reducing impact velocity without substantially increasing the time it takes to move the valve member between seats is difficult to accomplish.

The present invention is directed to over coming these and other problems associated with reducing valve member impact velocities without otherwise undermining valve performance.

In one aspect, a damped liquid control valve assembly includes a valve body that defines a first passage, a second passage, and a third passage. A valve member is positioned in the valve body and is moveable a distance between a first position in which the third passage is open to the first passage, and a second position in which the third passage is open to the second passage. The valve body and the valve member define a damping chamber, that decreases in volume when the valve member moves toward its first position. The damping chamber is filled with a liquid. The valve body defines a vent port extending between the damping chamber and a low pressure area. The vent port is sufficiently restrictive to flow that a pressure increase in the liquid in the damping chamber occurs when the valve member approaches its first position, and this pressure increase is sufficiently high that the valve member is hydraulically braked over a last portion of the moveable distance.

In another aspect, a hydraulically-actuated fuel injector includes an injector body that defines a nozzle outlet, an actuation fluid inlet, an actuation fluid drain, and an actuation passage that opens to a piston bore. A control valve member is positioned in the valve body and moveable a distance between a first position in which the actuation passage is opened to the actuation fluid drain, and a second position in which the actuation passage is open to the actuation fluid inlet. A piston positioned in the piston bore has a hydraulic surface exposed to fluid in the third passage, and is moveable between a retracted position and an advanced position. The valve body and the control valve member define a damping chamber that decreases in volume when the control valve member moves toward its first position. The valve body defines a vent port extending between the damping chamber and a low pressure area. The vent port is sufficiently restrictive to flow that a pressure increase in the liquid in the damping chamber occurs when the control valve member approaches its first position. Further more, this pressure increase is sufficiently high that the control valve member is hydraulically braked over a last portion of the moveable distance.

A fuel injector according to the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a sectioned side diagrammatic view of a hydraulically-actuated fuel injector according to the present invention.

Figure 2 is an enlarged sectioned side diagrammatic view of the control valve assembly portion of the fuel injector shown in Figure 1.

Referring now to Figures 1 and 2, a hydraulically actuated fuel injector 10 includes an injector body 12 made up of a plurality of components attached to one another in a manner well known in the art. A portion of injector body 12 is a valve body 13 that includes a control valve assembly 11. A solenoid 14 is attached to injector body 12 and includes an armature 15 attached to a poppet valve member 16 with a non-hollow fastener 17. Poppet valve member 16 is normally biased downward to close high pressure seat 23 by a poppet biasing spring 28. When solenoid 14 is energized, armature 15 pulls poppet valve member 16 upward along centerline 18 to open high pressure seat 23 and close low pressure seat 24. Thus, poppet valve member 16 includes a pair of conical valve surfaces 30 and 31 that move between high pressure seat 23 and low pressure seat 24, respectively. The distance that control valve member 16 moves between these seated positions is generally on the order of several hundred microns in a fuel injector of this type. Injector body 12 defines an actuation fluid cavity 22 that opens to a piston bore 40. When solenoid 14 is de-energized, actuation fluid cavity 20 is opened to a low pressure reservoir 37 via a drain passage 36 and an actuation fluid drain 21 past low pressure seat 24. When solenoid 14 is energized, actuation fluid cavity 22 is opened to a source of high pressure actuation fluid 35 via a high pressure supply passage 34 and an actuation fluid inlet 20 past high pressure seat 23.

In order to decrease the inertia of poppet valve member 16 and hasten its movement between valve seats 23 and 24, it is machines to include a hollow interior 29. In order to ensure proper sealing at the seats, poppet valve member 16 is guided in its up and down movement along center line 18 by a poppet guide bore 25, which is defined by a portion of valve body 13. Hollow interior 29 and a portion of guide bore 23 combine to define a damping chamber 26 that decreases in volume when poppet valve member 16 is moving downward toward high pressure seat 23.

Damping chamber 26 is preferable filled with the same liquid used as the hydraulic medium, which is typically engine lubricating oil. Because of the tight clearance between poppet valve member 16 and guide bore 25, damping chamber 26 is substantially a closed volume, except for a small diameter vent port 27 that communicates to a low pressure area 19. Vent port 27 preferably has a uniform cylindrically shaped cross section that is on the order of about 1 millimeter is diameter. Vent port 27 extends between damping chamber 26 and low pressure area 19, which in this example is outside of injector body 11.

When poppet valve member 16 is moved upward during an injection event, a vacuum is created within damping chamber 26, and additional liquid is drawn through vent port 27 into damping chamber 26. When poppet valve 16 is moving downward toward the end of an injection event, liquid within damping chamber 26 is displaced toward low pressure space 19 through vent port 27. Depending upon such factors as the compressibility of the liquid within damping chamber 26, the restrictiveness to flow of vent port 27 due to its length and diameter, and the volume of damping chamber 26, poppet valve member 16 can be hydraulically braked as it approaches high pressure seat 23. The present invention accomplishes this without substantially undermining the remaining portions of valve member's movement during an injection event. In other words, vent port 27 can produce a flow restriction to the displacement of fluid out of damping chamber 26 when poppet valve member 16 is moving near its maximum velocity as it approaches high pressure seat 23 at the end of an injection event. However, vent port 27 is preferably sized to present no such flow restriction when poppet valve member 16 is moving slower over the majority of the distance between low pressure seat 24 and high pressure seat 23.

Apart from the features of the control valve assembly 11, fuel injector 10 includes reciprocating piston 41 that is positioned in piston bore 40 and moveable between a retracted position, as shown, and a downward advanced position. Piston 41 includes a hydraulic surface 42 exposed to fluid pressure in actuation fluid cavity 22.

Fuel injector 10 also includes a plunger 43 that moves in a plunger bore 44 between a retracted position, as shown, and a downward advanced position. Piston 41 and plunger 43 are connected to move together, and both are normally biased toward their respective retracted positions by a return spring 55. When plunger 43 is pushed downward by piston 41, fuel within a fuel pressurization chamber 45 is raised to relatively high injection pressures. This high pressure fuel is pushed along nozzle supply passage 50, into nozzle chamber 54 and eventually out of nozzle outlet 51 during an injection event. The high pressure fuel hydraulically lifts needle valve member 52 to an open position against the action of a needle biasing spring 53 during an injection event. Between in3ection events, when fuel pressure is relatively low, needle return spring 53 biases needle valve member 52 downward to block nozzle outlet 51. Between injection events when plunger 43 is retracting, fresh fuel is drawn into fuel pressurization chamber 45 from source of fuel 48, through fuel supply passage 47, into fuel inlet 46 and past check valve 49.

Preferably, the fuel fluid and hydraulic medium are different liquids, such as distillate diesel fuel and lubricating oil, respectively.

Between injection events, solenoid 14 is de-energized, poppet valve member 16 is seated to close high pressure seat 23 and open low pressure seat 24, piston 41 and plunger 43 are in their retracted positions as shown, and needle valve member 52 is in its downward closed position.

Each injection event is initiated by energizing solenoid 14. This moves poppet valve member 16 upward to open high pressure seat 23 and close low pressure seat 24. Because poppet valve 16 must move some finite distance to accomplish this task, the high pressure inlet 20 must necessarily be open to low pressure drain 21 when poppet valve member 16 is between seats. In order to perform properly and prevent unnecessary losses, solenoid 14 is preferably sized to quickly move poppet valve member 60 upward to initiate the injection event.

When high pressure seat 24 opens, high pressure actuation fluid flows actuation cavity 22 and acts on hydraulic surface 42 to begin the downward stroke of piston 41 and plunger 43. This causes the pressure of fuel within fuel pressurization chamber 45 to quickly rise. When the fuel pressure exceeds a valve opening pressure sufficient to overcome needle biasing spring 53, needle valve member 52 moves upward to its open position, and fuel commences to spray out of nozzle outlet 51.

When it is desired to end the injection event, solenoid 14 is de-energized. This causes poppet valve member 16 to move downward to close high pressure seat 23 under the action of return spring 28. In most cases, poppet valve member 16 begins its downward movement from a rest position in contact with low pressure seat 24; however, in some instances, particularly at idle, the solenoid on-time may be so brief that poppet valve member 16 never comes to rest against low pressure seat 24. In some more unusual cases, poppet valve member 16 actually bounces off of the low pressure seat and moves downward toward high pressure seat 23 at a much higher rate. In any event, when poppet valve member 16 contacts high pressure seat 23, an impact noise is produced, and the source of high pressure actuation fluid is closed. When this occurs, piston 41 and plunger 43 cease their downward movement, which results in a sudden drop of fuel pressure. When the fuel pressure drops below a valve closing pressure, needle return spring 53 pushes needle valve member 52 downward to again close nozzle outlet 51 and end the injection event.

In order to decrease the noise produced when poppet valve member 16 impacts high pressure seat 23, the present invention utilizes an appropriately sized damping chamber 26 along with an appropriately sized vent port 27. As stated earlier, the volume of damping chamber 26 decreases when poppet valve member 16 moves downward. This in turn requires some amount of fluid to be displaced out of vent port 27. The rate at which the fluid is displaced through vent port 27 is related to the rate at which poppet valve member 16 is moving downward. Since the only forces acting on poppet valve member 16 when it is moving downward are produced from return spring 28 and a an opposing hydraulic force on the underside of valve member 16 due to fluid pressure in damping chamber 26. Thus, if the pressure in damping chamber 26 gets sufficiently high, the movement of poppet valve member 16 will be hydraulically braked. Those skilled in the art will appreciate that spring 28 will tend to accelerate poppet valve member 16 for the complete distance until it comes in contact with lower seat 23.

Thus, poppet valve member 16 will tend to be near its highest velocity as it approaches the lower seat. By appropriately sizing vent port 27, a flow restriction can occur when these higher velocities are reached such that pressure is increased in damping chamber 26 and poppet valve 16 is hydraulically braked as it approaches high pressure seat 23. However, vent port 27 is preferably sufficiently sized that it plays no significant part in slowing the movement poppet valve member 16 when it moves at slower rates over a majority of a distance between low pressure seat 24 and high pressure seat 23.

At the extremes, if vent port 27 were eliminated all together, poppet valve member 16 would become hydraulically locked and be unable to move downward. On the other hand, if vent port 27 were made too large, poppet valve member 16 could move at virtually any rate without creating any significant flow restriction. In addition, the overall volume of damping chamber 26 plays an important role in that the liquid therein has some ability to compress when pressure is applied. Thus, if damping chamber 26 is too large, hydraulic braking could not occur, since pressure levels could not rise significantly with the small change in volume that occurs when poppet valve member 16 moves between seats. On the other hand, if damping chamber 26 were made too small, the damping characteristics can become overly sensitive to the size and shape of vent port 27, which could undermine the ability to mass produce valves with consistent performance. In order to improve consistency and results between several produced injectors, vent port 27 preferably has a uniform diameter made using known and reliable machining techniques. Computer modeling predicts that a vent port with a diameter of about 1 millimeter can reduce approach velocities in the illustrated fuel injector by about 30%. This corresponds to an impact noise reduction of more than 50%. These noise reductions were predicted for a fuel injector having a spill controlled rate shaping device.

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Claims

1. A damped liquid control valve assembly comprising:

a valve body defining a first passage, a second passage and a third passage; a valve member positioned in said valve body and being movable a distance between a first position in which said third passage is open to said first passage, and a second position in which said third passage is open to said second passage; said valve body and said valve member defining a damping chamber that decreases in volume when said valve member moves toward said first position, and said damping chamber being filled with a liquid; said valve body defining a vent port extending between said damping chamber and a low pressure area; said vent port being sufficiently restrictive to flow that a pressure increase in said liquid in said damping chamber occurs when said valve member approaches said first position, and said pressure increase is sufficiently high that said valve member is hydraulically braked over a last portion of said distance.

2. The control valve assembly of claim 1 wherein said valve member is a poppet valve member that moves between a first seat and a second seat.

3. The control valve assembly of claim I wherein said first passage is a high pressure passage; said second passage is a low pressure passage; and said third passage is a fluid cavity containing liquid in contact with a reciprocating piston.

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4. The control valve assembly of claim 1 wherein liquid displaced from said damping chamber passes through said vent port.

5. The control valve assembly of claim 1 further comprising a compression spring operably positioned to bias said valve member toward one of said first position and said second position.

6. The control valve assembly of claim 1 wherein said vent port includes a cylindrically shaped passage.

7. The control valve assembly of claim 1 further comprising a solenoid attached to said valve body, and including an armature attached to said valve member.

8. A hydraulically driven piston and damped control valve assembly comprising:

a valve body defining a first passage, a second passage and a third passage that opens to a piston bore; a valve member positioned in said valve body and being movable a distance between a first position in which said third passage is open to said second passage, and a second position in which said third passage is open to said first passage; a piston positioned in said piston bore and having a hydraulic surface exposed to fluid in said third passage, and being moveable between a retracted position and an advanced position; said valve body and said valve member defining a damping chamber that decreases in volume when said valve member moves toward said first position, and said damping chamber being filled with a liquid; said valve body defining a vent port extending between said damping chamber and a low pressure area; said vent port being sufficiently restrictive to flow that a pressure increase in said liquid in said damping chamber occurs when said valve member approaches said first position, and said pressure increase is sufficiently high that said valve member is hydraulically braked over a last portion of said distance.

9. The hydraulically driven piston and damped control valve assembly of claim 8 wherein said valve member is a poppet valve member that moves between a high pressure seat and a low pressure seat.

10. The hydraulically driven piston and damped control valve assembly of claim 8 wherein said first passage is a high pressure passage; and said second passage is a low pressure passage.

11. The hydraulically driven piston and damped control valve assembly of claim 8 wherein liquid displaced from said damping chamber passes through said vent port.

12. The control valve assembly of claim 8 further comprising a compression spring operably positioned to bias said valve member toward one of said first position and said second position.

13. The control valve assembly of claim 8 further comprising a solenoid attached to said valve body, and including an armature attached to said valve member.

14. A hydraulically actuated fuel injector comprising:

an injector body defining a nozzle outlet, an actuation fluid inlet, an actuation fluid drain and an actuation fluid cavity that opens to a piston bore; a control valve member positioned in said injector body and being movable a distance between a first position in which said actuation fluid cavity is open to said actuation fluid drain, and a second position in which said actuation fluid cavity is open to said actuation fluid inlet; a piston positioned in said piston bore and having a hydraulic surface exposed to fluid in said actuation fluid cavity, and being moveable between a retracted position and an advanced position; said injector body and said control valve member defining a damping chamber that decreases in volume when said control valve member moves toward said first position; said injector body defining a vent port extending between said damping chamber and a low pressure area; said vent port being sufficiently restrictive to flow that a pressure increase in said liquid in said damping chamber occurs when said control valve member approaches said first position, and said pressure increase is sufficiently high that said control valve member is hydraulically braked over a last portion of said distance.

15. The hydraulically actuated fuel injector of claim 14 wherein said control valve member is a poppet valve member that moves between a high pressure seat and a low pressure seat.

16. The hydraulically actuated fuel injector of claim 15 further comprising a compression spring operably positioned to bias said control valve member toward one of said first position and said second position.

17. The hydraulically actuated fuel injector of claim 16 wherein said injector body defines a fuel inlet connected to source of fuel fluid; and said actuation fluid inlet is connected to a source of actuation fluid that is different from said fuel fluid.

18. The hydraulically actuated fuel injector of claim 17 wherein liquid displaced from said damping chamber passes through said vent port.

19. The hydraulically actuated fuel injector of claim 17 10 further comprising a solenoid attached to said injector body, and including an armature attached to said control valve member.

20. The hydraulically actuated fuel injector of claim 17 15 wherein said control valve member is a poppet valve member.

21. A hydraulically actuated fuel injector according to claim 14, substantially as described with reference to 20 the accompanying drawings.

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