1. Field of the Invention
The invention generally relates to a fuel injector and, more particularly, to a system for adjusting the sensitivity of the response time of a spool movement in a fuel injector over a wide rang of operating temperatures.
1. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a driver will deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as “grooves”) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure chamber. As the pressure in the high pressure chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
However, in such a conventional system, a response time between the injection cycles may be slow thus decreasing the efficiency of the fuel injector. Also, injection events may vary in duration. This is mainly due to the slow movement of the control valve spool. More specifically, the slow movement of the control valve spool may result in a slow activation response time to begin the injection cycle. To remedy this inadequacy, additional pressurized working fluid may be needed; however, additional energy from a high pressure oil pump must be expanded in order to provide this additional working fluid. This leads to inefficiency in the operations of the fuel injector, itself Also, the working fluid at an end of an injection cycle may not be vented at an adequate response rate due to the slow movement of the control valve spool.
A solution to the foregoing problems is the utilization of a piezoelectric actuator system as disclosed in co-pending U.S. patent application Ser. No. 10/638,322. In this system many advantages over the related art systems are provided such as, for example, providing a short control valve stroke. This shorter stroke translates into a fast response time for outflow of the inlet rail pressure, thereby the fuel injector has an increased efficiency over the related art. In this improved system the movement of the control valve stroke, e.g., control spool, is provided by working fluid acting on control surfaces of the spool assembly.
Although the system of co-pending U.S. patent application Ser. No. 10/638,322 provides many advantages over conventional systems, improvements can still be achieved. For example, response times of the spool movement due to the changes in viscosity of the working fluid over a given temperature range may be improved. As should be understood by those of ordinary skill in the art, the viscosity of the working fluid at cooler temperatures is higher than the viscosity of the working fluid at normal temperatures, e.g., 80 to 100 degrees Celsius. Thus, by having a higher viscosity of the working fluid at cold start of the engine, there may be an increase in the flow resistance especially when wall effects are taken into consideration. This may result in slow movement of the control valve spool at higher viscosity levels.
In a first aspect of the invention, a control valve for an injector includes a spool valve assembly having a spool moveable between an open position and a closed position. The spool has a first hydraulic surface and a second hydraulic surface. A first chamber is in fluid communication with the first hydraulic surface of the spool and a second chamber is in fluid communication with the second hydraulic surface of the spool. An actuator is in fluid communication with the second hydraulic surface of the spool. The actuator, in an open position, provides a fluid path to ambient such that a hydraulic force acting on the first hydraulic surface of the spool becomes greater than a hydraulic force acting on the second hydraulic surface of the spool. A flow path is in fluid communication with the second hydraulic surface to decrease a force acting on the second hydraulic surface of the spool during spool operation. This may sensitize the system, in one example, over a wide range of operating temperatures.
In another aspect of the invention, a control valve includes a control valve body having an inlet port and a spool valve assembly. The spool valve assembly includes, for example, (i) a spool moveable within a bore between a first position and a second position, (ii) a first control piston having a first diameter positioned at a first end of the spool, (iii) a second control piston having a second diameter positioned at a second end of the spool, (iv) a first control chamber formed by the first control piston and the control valve body, (v) a first fluid connection leading from the inlet to the first control chamber, (vi) a second control chamber formed between a plate and the second control piston, and (vii) a second fluid connection leading from the inlet to the second control chamber. An actuator provides a fluid passage to ambient from the second control chamber, and includes a check plate which is moveable between an open position and a close position seating against a disk. A means is provided for reducing a pressure in the second control chamber during operational conditions of the spool valve assembly.
In yet another aspect of the invention, a fuel injector is provided which includes an intensification chamber, a nozzle assembly, and a control valve assembly. The control valve assembly includes a mechanism in fluid connection with a hydraulic surface of the spool to reduce a working fluid force thereon
a and 3b show an exploded view of an actuator assembly of the invention during operational stages;
a shows a graph of an injector control signal versus time implemented by an aspect of the invention;
b shows a graph of piezo current versus time implemented by an aspect of the invention;
c shows a graph of a spool stroke versus time implemented by an aspect of the invention; and
d shows a graph of injection rate versus time implemented by an aspect of the invention.
The invention is directed to, for example, an oil activated fuel injector and more particularly to systems used with an oil activated fuel injector to increase sensitivity of a spool assembly. The control valve of the invention, in one aspect, is designed to increase efficiency of the injector by increasing response times of the spool movement at cold start. That is, the invention addresses, in one aspect, the need to sensitize the entire system to high viscosity conditions of the working fluid at cold start of the engine. In another aspect, the invention sensitizes the system throughout a range of operating conditions. The invention may also be used as a kit to retrofit already existing fuel injectors.
Referring now to
A spring 3a biases the piston 2 and the plunger 4 in a direction of arrow “A”. A high pressure fuel chamber 7 is disposed between the plunger 4 and the nozzle assembly 5, and is in fluid communication with a fuel line 8 leading to a needle assembly 9. A check valve 6 is also provided within the nozzle assembly 5 or alternatively in a disk plate 5a between the nozzle assembly 5 and the intensifier body 1. A spring 10 biases the needle assembly 9 in a direction of arrow “B”.
A valve body is generally depicted as reference numeral 115 and includes an oil or working fluid inlet 12 and a spool 13. The spool 13 includes grooves having control edges depicted generally as reference numeral 14, i.e., a first leading edge 14a and a second leading edge 14b. The valve body 115 also includes grooves, depicted generally as reference numeral 15, which lead to ambient. Working ports 16 are provided in the valve body 115, which lead to the bore chamber 3 and more specifically are in communication with the piston 2. The working ports 16 are also in fluid communication with the working fluid inlet 12 via the grooves of the spool 13 though a space 14c formed between the leading edge 14a and the working port 16 when the spool 13 is in the open position.
A control piston 17 is provided in a center bore 13a of the spool 13. A control volume chamber 18 is formed between the control piston 17 and the spool 13. A cross bore 19 provides fluid communication between the working fluid inlet 12 and the control volume chamber 18. A stop plate 20 is positioned proximate an end portion of the control piston 17, remote from the spool 13. The stop plate 20 provides a mechanism for limiting movement of the control piston 17 during cycles of the fuel injector 100.
A second control piston 22 is provided on another side of the spool, remote from the control piston 17. In one embodiment, the second control piston 22 has a larger surface area than the control piston 17. In one implementation, the second control piston 22 may be upwards of two times the diameter of the control piston 17.
The ratio of size may be 1:1.2 and upwards of 1:2 in one range, and the smaller control piston 17 may be 2.5 mm, but may be 3 mm with the second control piston 22 being 4 mm, in one illustrative implementation. The second control piston 22 is positioned proximate a plate 23 which includes an inlet throttle 26 and an outlet throttle 30.
A fluid connection 24 is provided between the working fluid inlet 12 and the inlet throttle 26, via a fluid connection 25 provided in housing 21. In one aspect of the invention, as seen in
By way of one illustrative example, at lower viscosity conditions at normal operating conditions, e.g., with the working fluid at 80 to 100 degrees Celsius, the fluid connection 25 will have no effect on the flow behavior of the working fluid and hence the force asserted against control piston 22. However, at cold start, e.g., temperatures of minus 20 degrees Celsius, the working fluid will have a higher viscosity level thus resulting in increased flow resistance. But, in the configuration of the invention, the reduced flow area or increased flow restriction provided by the fluid connection 25, upstream from the inlet, will reduce the force applied to the control piston 22. That is, the adjustment of the flow connection 25 will allow for faster discharge of the fluid behind the control piston 22 (due, in part, to less fluid buildup in chamber 29). In this manner, the pressure exerted on control piston 22 can be lower than the pressure exerted. against the control piston 17 during an opening operation, thus allowing for a more responsive control valve spool during cold start conditions. Thus, the fluid connection 25 can be used to sensitize the system during cold start.
Referring again to
The actuator assembly includes a housing-like a pot, where the piezo stack is located in the center of the pot. The piezo has substantially the same height as the pot and one end of the piezo is welded on the bottom of the pot. In a final manufacturing process the open side of the pot/piezo assembly is grounded. Once the piezo is activated, the stack expands and comes out of the pot, as discussed in more detail below. In the application of the invention, the center pin makes a relative stroke to the outer part 39 (border of the pot ). Typical strokes of this size of piezo are 20 to 50 microns. In one embodiment, the piezo actuator includes approximately 200 layers of ceramic discs, which respond to a current applied to the piezo actuator 37. It should be well understood, though, that more or less layers and other types of discs are contemplated by the invention and that the example provided herein is for illustrative purposes.
Now referring to
In
In
It should be understood that before the piezo opens the check plate 33, its low pressure side is pressurized from the center to an inner seat 51, which reduces the force requirement of the piezo. The required piezo force is dependent on the area of groove 50, the fluid pressure and the diameter of rod 40. In the configuration of
Much like the discussion with reference to the restricted fluid connection 25, this dual passage configuration will reduce the pressure on the control piston 22 during cold start conditions. But, in addition, this dual passage configuration also has the advantage of increasing the flow rate of the working fluid during normal operating conditions and thus allows for more responsiveness of the spool movement over a wide range of temperatures. In one embodiment, for high viscosity conditions, the modified check plate 33 and disk 36 may be designed to have a same flow reduction as that of the modified fluid connection at the inlet side of the spool valve assembly, as discussed above.
a-4d show graphs of the injector control signal, the piezo current, the spool stroke and the injection rate versus time, respectively. More specifically,
Still referring to
In one embodiment, the positive driver current “PC” of the piezo actuator is +10 amps and the negative driver current “NC” is −10 amps. A corresponding voltage of 150V and 0V may be applied. It should be understood by those of ordinary skill in the art that different amperages may be used depending on the specific application of the invention. For example, additional layers utilized in the piezo actuator may translate into the need for a bigger current and a smaller voltage.
Likewise, fewer layers used with the piezo actuator may translate into the need for a smaller current and a bigger voltage. However, in one implementation, a current of +/−10 amps is used with approximately 200 layers of the piezo actuator.
c and 4d show the relationship between the spool stroke and the injection rate of the fuel injector. Referring to
Referring back to
In operation, the check plate 33 and the spool valve assembly are movable between a closed position and an open position via application of the positive and negative driver current applied to the piezo actuator 37. That is, the current applied to the piezo actuator 37 is used to lengthen and shorten the piezo actuator 37, i.e., ceramic discs of the piezo actuator 37, to open and close the check plate 33 to ambient via the center pin and push rod assembly. In the open position, fluid in the control volume chamber 29 is vented to ambient via paths 52 and 53, and the pressure within the control volume chamber 18 is greater than that of the control volume chamber 29. The hydraulic forces acting on the control piston 17, being greater than the hydraulic forces acting on the second control piston 22, will then move the spool valve assembly to the open position. In this operational stage, the flow of the working fluid is considerably increased by flowing to ambient via two directions, 52 and 53. Flow restriction via the fluid connection 25 may also result in a decrease pressure in the control volume chamber 29 (resulting in a decrease in force acting on the control piston 22) thus increasing the sensitivity of the system.
When the negative driver current is applied, the check plate 33 will block ambient and the hydraulic forces acting on the second control piston 22 will increase and become greater than the hydraulic forces acting on the control piston 17 such that the spool valve assembly will be moved into the closed position. At this operational stage, due to the restricted flow passage of flow connection 25, the pressure within the control volume or chamber 29 will not be as high during cold start compared to normal operations. This is mainly due to the combination of the restricted flow path and the higher viscosity of the working fluid. During normal conditions, the restricted flow path will not affect the flow rate of the working fluid.
While the invention has been described in terms of embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.
This application is a continuation-in-part application of co-pending U.S. patent application Ser. No. 10/638,322, which is hereby incorporated by reference for all purposes as if fully set forth herein.
Number | Date | Country | |
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Parent | 10638322 | Aug 2003 | US |
Child | 10841511 | May 2004 | US |