1. Field of the Invention
The invention generally relates to a fuel injector and, more particularly, to a fuel injector having a piezoelectric actuator that provides improved rate shaping qualities and improved multiple control of the fuel injection events of the fuel injector and a method of use thereof.
2. 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 or drain 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 that 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 control valve controls the flow of working fluid from the oil rail to the intensifier chamber and hence the intensifier piston (i.e., fill position), as well as controls the flow of the working fluid from the intensifier chamber to ambient (i.e., drain position). During an injection cycle, fuel in a high-pressure chamber is placed under pressure by the intensifier piston. The high-pressure fuel will flow to the nozzle assembly where it will overcome spring forces and other hydraulic forces to lift the needle for injection of fuel into a combustion chamber.
However, simply using this type of fuel injector and the accompanying multiple process may not be adequate to reduce emissions or provide varying quantities of fuel (e.g., pilot quantity of fuel) during the combustion process. Accordingly, many types of fuel injectors have been designed which attempt to reduce emissions, from providing a pilot quantity of fuel and multiple injections to other controls. In one type of system, a piezoelectric actuator is used to control an injection cycle. For example, a piezoelectric actuator is operable to control the fuel pressure within a control chamber defined, in part, by a surface of the valve needle of the injector. This is referred to as a parasitic escape of fuel. Further, during injection, pressure waves may be transmitted along the fuel passages and lines which, in turn, may give rise to undesirable needle movement during injection and may be of sufficient magnitude to cause secondary injections. The large control chamber may cause this shortcoming.
In other known systems, additional valves, such as three way poppet valve are required in order to provide a positive fuel pressure within the control chamber. The three-way valve, in general, will control the injection cycle of the fuel injector. Being more specific, the three way valve will provide (i) fuel into the control chamber in order provide a pressure therein and maintain the needle valve in a closed position, (ii) drain the fuel from the control chamber to a drain supply line and (iii) provide fluid communication between the control chamber and the high pressure fuel line. In this manner, control of the needle valve can be maintained. These three way valves are typically spring loaded and controlled by an actuator. In this same type of system, an electronically controlled valve is required in order to allow the fuel to enter the high-pressure fuel chamber from a low-pressure fuel supply line. This electronically controlled valve is typically in the open position to allow the fuel to enter the high-pressure fuel chamber, but also allows for “bleeding” (i.e., fuel to flow from the high-pressure chamber to the low pressure supply line). To close this valve, a controller or solenoid closes the valve so that the intensifier piston can provide a high-pressure environment which, initially, will not open the needle valve due to various other counter forces such as, for example, the fuel pressure within the control chamber.
The invention is directed to overcoming one or more of the problems as set forth above.
In a first aspect of the invention, a fuel injector includes an injector body defining a nozzle outlet and a high-pressure fuel chamber. A needle valve member is mounted in the injector body and has an opening hydraulic surface substantially surrounded by a high pressure fuel line which is in fluid communication with the high-pressure fuel chamber. The needle valve member is movable between an open position and a closed position with respect to the nozzle outlet. A piezoelectric actuator is activated between an off position and an on position for positioning a control valve into one of an open position and a closed position. A control piston has a closing hydraulic surface and is positioned in mechanical communication with the needle valve member. A piston control chamber is positioned between the control valve and the closing hydraulic surface of the control piston. The piston control chamber is in fluid communication with the control valve and the high-pressure fuel chamber via throttles. A high-pressure fuel condition is maintained in the piston control chamber by fuel supplied directly from the high-pressure fuel chamber and independent of any actuation of the control valve. The high-pressure fuel condition results in a downward force acting on the closing hydraulic surface of the control piston. A pressure loss fuel condition is generated within the piston control chamber by activation of the piezoelectric actuator which moves the control valve to the open position for releasing fuel. A force on the opening hydraulic surface of the needle valve member is greater than the downward force on the closing hydraulic surface of the control piston, in the pressure loss fuel condition, thereby opening the needle valve member for producing an injection event.
In another aspect of the invention, a fuel injector includes an injector body, a control valve and an intensifier mechanism positioned within the injector body and set in motion by actuation of the control valve. A high-pressure fuel chamber is located within the injector body which provides a high-pressure fuel condition in response to an activation of the intensifier mechanism. An independently controlled hydraulically actuated fuel supply valve supplies fuel to the high-pressure fuel chamber. A high-pressure supply line is in fluid communication with the high-pressure fuel chamber and a needle valve member is mounted in the injector body and has an opening hydraulic surface surrounded at least partially by the high-pressure fuel line. A piezoelectric actuator is mounted in the injector body and independently controlled to be moved between an off position and an on position for controlling movement of a controllable valve between an open position and a closed position. A control piston has a closing hydraulic surface and is mechanically coupled to the needle valve member. A piston control chamber is in fluid communication with the high-pressure fuel line and defined by an upper end of the control piston and an interior wall of the injector body.
In still another aspect of the invention, a fuel injector includes an injector body having a high-pressure fuel chamber and a needle valve member with a hydraulic surface. A high-pressure fuel line is in fluid communication with the high-pressure fuel chamber and at least partially surrounding the hydraulic surface of the needle valve member. A control chamber is in direct fluid communication with the high-pressure fuel chamber. A controllable valve generates a high-pressure fuel condition in the high-pressure fuel chamber, the high-pressure fuel line and the control chamber. A needle valve member is mounted in the injector body and has an opening hydraulic surface at least partially surrounded by the high-pressure fuel line. A piezoelectric actuator is mounted in the injector body and is actuated between an off position and an on position by actuation of an electrically actuated controller. A pressure release valve is positionable in an open position and a closed position by actuation of the piezoelectric actuator. A first fuel line is in fluid communication with the control chamber and the high-pressure fuel chamber, the first fuel line having a first diameter. A second fuel line is in fluid communication with the pressure release valve and the control chamber and has a second diameter which is larger than the first diameter of the first fuel line. A high-pressure fuel condition is maintained in the control chamber by a fuel pressure which is generated in the high-pressure fuel chamber and independent of an initial actuation of the electronically actuated control. A low-pressure fuel condition is generated within the control chamber when the pressure release valve is in the open position.
In still another aspect of the invention, an internal combustion engine includes a combustion chamber having intake and exhaust valves and a lubrication system for lubricating components associated with the combustion chamber. A rail line and a fuel injector communicating with the combustion chamber is also provided. The fuel injector includes an injector body having an intensifier chamber in fluid communication with the rail line and an intensifier piston movable within the intensifier chamber. An independently controllable hydraulic valve supplies fuel to the high-pressure fuel chamber. A high-pressure fuel line is in fluid communication with the high-pressure fuel chamber. A needle valve member has a hydraulic surface at least partially surrounded by the high-pressure fuel line. A control chamber and a first fuel line fluidly coupled between the high-pressure chamber and the control chamber is also provided. An independently hydraulically actuated valve controls the intensifier piston. A piezoelectric actuator is mounted in the injector body and is activated between an off position and an on position by actuation of an electrically actuated controller. A pressure release valve is positionable in an open position and a closed position by actuation of the piezoelectric actuator. A second fuel line is fluidly coupled between the pressure release valve and the control chamber. A high-pressure fuel condition is provided in the control chamber independently by a fuel pressure which is generated in the high-pressure fuel chamber. A low-pressure fuel condition is generated within the control chamber when the pressure release valve is in the open position.
In yet another aspect of the invention, a method of controlling fuel injection events of a fuel injector is provided. The method includes the steps of:
The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:
a-3d show enlarged schematic portions of aspects of the fuel injector of the invention;
The invention is directed to a fuel injector having a piezoelectric actuator. In the embodiments of the invention, high-pressure fuel can be easily reached (e.g., 2200 bar and more are easily achieved) with superior rate shaping performance to the injection event. Additionally, injection quantity can be higher for both for “large” diesel engines (possible >0.5 liter/cylinder) and smaller engines with very precise control. By using the fuel injector of the invention, pilot and post injections are now possible within all injection pressures with obvious noise reduction compared to conventional systems. Additionally, rail dynamics are dampened and reduced through switch on of the intensifier valve, and cold performance will be increased with the use of diesel fuel for control of the injector.
Referring now to
The intensifier chamber 18 includes a piston and plunger assembly 18a in communication with a high-pressure fuel chamber 20. The piston and plunger assembly is in mechanical communication with a spring 19 for biasing the assembly toward the rail 14. A fuel supply line 22 is also in fluid communication with the high-pressure fuel chamber 20 via a hydraulically actuated one way ball valve 22a. And, a high-pressure fuel line 24 is in fluid communication with a first fluid line 26 and a second fluid line 28. The high-pressure fuel line 24 extends to a nozzle assembly 30 (also referred to as a needle valve member). The one way valve 22a allows fuel to enter the high-pressure fuel chamber 20, but prevents bleeding or any back flow. In view of the above discussion, it should now be recognized by those of ordinary skill in the art that the high-pressure fuel chamber 20 supplies the high-pressure fuel throughout the injector of the invention, i.e., the fluid lines 24, 26 and 28 as well as to the nozzle assembly, via the activation of the solenoid, S1. That is, the control valve 14, activated by the solenoid, S1, is used activate the high pressure within the fuel injector.
The first fluid line 26 includes a first throttle 32 and the second fluid line 28 includes a second throttle 34. In embodiments, a control valve 36 such as, for example, a 2/2 seat valve, is positioned between the second throttle 34, a piezoelectric actuator 38 (piezoelectric stack) and a drain or pressure release line 28. The pressure release line 28 is in fluidly communication with a fuel tank of low-pressure diesel reservoir. The piezoelectric actuator 38 controls the opening and closing of the control valve 36, as discussed in more detail below, and thus allows for a drain condition in a control chamber to thus provide for a pressure differential within the injector. But, it should be understood that the control valve 14 activates the high pressure throughout the injector of the invention and is mainly responsible for the control of the fuel injector of the invention. More specifically, the control valve 14 controls the activation of the intensifier piston 18 which, in turn, results in the high pressure fuel conditions within the fuel injector.
Still referring to
During the dynamic pressurization of the high-pressure port in the injector, a pre-opening of the nozzle may occur due to the arrangement of the throttles; that is, it may take some time until the volume is filled equally with pressure since the fluid is compressible, especially for higher pressures. To prevent this from happening, different methods may be used. By way of example, a larger volume may pass the first throttle 32 on the fuel line 24 down to the nozzle such that it will take longer to reach the required pressure. In still another variation, a throttle 24b may be may be placed in line 24 to build-up the pressure in line 28, or a check valve 24c (
In another variation,
In
In still another embodiment,
In
A heart or control chamber 44 surrounds the opening hydraulic surface 42 and is also in fluid communication with the high-pressure fuel line 24. A piston 46, which is part of the nozzle assembly 30, includes a piston surface 46a, preferably having a diameter of approximately 4 mm. A control piston 48 is mechanical coupled with the piston surface 46a. In embodiments, the control piston includes a closing hydraulic surface 48a which has a diameter of approximately 4.2 mm, for example, or larger than the diameter of the needle stem. A spring 50 surrounds the plunger 48 and is positioned between the piston surface 46a and a control disk 49.
Still referring to
The larger diameter of the second throttle 34, in combination with the actuation of the piezoelectric actuator 38 and opening of the valve 36, generates a pressure loss within the piston control chamber 52. This pressure loss decreases the downward forces applied on the closing hydraulic surface 48a of the control piston which, in combination with the high pressure in the high-pressure fuel line 24, allows the needle 40 to rise to begin an injection event. According to this configuration, when a voltage is applied to the piezoelectric actuator 38 and the valve 36 opens, the fuel will flow through the following flow path:
In this manner, the fuel pressure in the piston control chamber 52 can be decreased thus decreasing the forces exerted on the closing hydraulic surface 48a of the control piston 48. This creates a pressure differential between the piston control chamber 52 and the high-pressure fuel line 24; namely, the pressure within the high-pressure fuel line 24 will be greater than the pressure within the piston control chamber 52. In this manner, a force applied to the opening hydraulic surface 42 of the nozzle assembly will be greater than a force applied to the closing hydraulic surface 48a of the control piston 48. This action will then lift the needle in order to provide an injection event. By thus controlling the voltage applied to the piezoelectric actuator 38, the control of the injection event can be precisely controlled by the opening and closing of the valve 36 (i.e., the increase and decrease of pressure (forces applied to the hydraulic surfaces) within the piston control chamber 52). This can provide both pilot and post injection quantities of fuel, as well as multiple injections of fuel. Accurate rate shaping is also now possible through multiple injections with additional control valve measures on the oil side.
However, when no voltage is applied to the piezoelectric actuator 38, the pressure within the piston control chamber 52 and the high pressure fuel line 24 will approximately equalize. This is because the valve 36 is now closed and the pressure within the piston control chamber 52 will increase due to the pressure from the high-pressure fuel chamber 24. As a result, the force exerted on the closing hydraulic surface 48a of the control piston 48 in combination with the spring force will be greater than the force applied on the opening hydraulic surface 42 of the nozzle assembly 30 thus maintaining the needle 40 in the closed position.
In one approach, the piezoelectric actuator 38 may be placed near the nozzle. In one embodiment, the piezoelectric actuator 38 is placed approximately 20 mm from the nozzle itself. The placement of the piezoelectric actuator 38 proximate to the nozzle may prevent or resolve the pre-opening of the needle. The placement of the piezoelectric actuator 38 near the nozzle may be accomplished by separating the intensifier chamber from the injector, and placing the piezoelectric actuator 38 at such location. The intensifier and valve system may be combined with the rail 14, with a short “pipe” connecting between the intensifier and valve system (pump) and the nozzle. The pipe would accommodate the piezoelectric actuator 38.
In a further embodiment, the opening of the hydraulic valve, providing working fluid to the intensifier chamber, may be slowed to provide a control strategy, i.e., to distribute the pressure equally to the back side of the needle and the needle tip. This will prevent or substantially decrease the pressure or shock wave phenomenon. In one embodiment the hydraulic valve may be slowed by 4 to 5 times the normal speed, which may be approximately between 300 to 1000 microseconds. This may be accomplished by providing less or a partial current, a step current to the solenoids or a hydraulic dampening. In one known application, solenoids are supplied with 20 amps at 50 volts. This will avoid early needle opening or a pre-injection. The working fluid may be coolant, oil, fuel or other hydraulic fluids.
In Operation
In one embodiment of operation, low-pressure oil, fed by a hydraulic pump, is fed to the intensifier chamber via the hydraulic connection rail. In embodiments, the pressure control valve in either the injector or the low-pressure oil rail controls the high-pressure condition in the injector. It should be understood that the rail volume has to be high enough to provide the requisite energy required for the injection process.
To initiate the injection process, the control valve (or a single spring operated valve or a 2-way solenoid valve) moves from a closed position to the open position by, for example, an electromagnet controlled by the solenoid, S1. This type of valve and the activation thereof is well known in the art and a description is thus omitted. It is understood, though, by keeping the valve in the open position requires less power than the initial opening. By opening the valve 14, the intensifier is activated to prepare the necessary high-pressure fuel for injection. Prior to this activation, fuel is allowed into the chamber 20 via the supply line 22 and valve 22a. It is seen in at least
Now, by opening the valve 14, the oil will force the intensifier plunger and piston downward towards the high-pressure fuel chamber. Fuel will be forced through the high-pressure fuel line into the heart chamber as well as into the piston control chamber (via the first fluid line). Prior to activation of the piezoelectric actuator, the fuel pressure within the high-pressure fuel line and the piston control chamber will be substantially the same (after pressurization by the above mechanism). This will create a force on the hydraulic surface of the control piston in combination with the downward forces applied by the spring, which is greater than an upward force on the opening hydraulic surface of the nozzle assembly. In this way, the needle will be maintained in a closed position.
Although the injector is designed for multiple injections, the injection will be initiated through the activation of the piezoelectric actuator. In operation, a voltage is applied to the actuator 38 which, in turns, opens the control valve 36. Once open, a pressure loss will generate within the piston control chamber thus decreasing a force applied to the closing hydraulic surface. The high-pressure fuel in the high-pressure fuel line will flow to the control chamber and exert an upward force on the opening hydraulic surface greater than a downward force exerted by the spring and the force on the closing hydraulic surface of the control piston. The sealing member will ensure very low leakage to the nozzle assembly. The greater forces on the opening hydraulic surface of the nozzle assembly will then lift the needle to begin an injection event.
Depending on the opened amount of the valve (activated by the piezoelectric actuator), fuel pressure within the piston control chamber can be regulated thus regulating the force applied to the closing hydraulic surface of the control piston. In this manner, the needle opening distance can be regulated to provide a predetermined amount of fuel to the combustion chamber during an injection event. In other words, the loss of pressure (decrease of pressure via the larger diameter second throttle) within the piston control chamber will depend on the voltage applied to the actuator. Thus, the opening distance of the valve, which is controlled by the voltage applied to the actuator, will regulate the pressure losses within the piston control chamber. And, by regulating the pressure within the piston control chamber, the fuel pressure within the high pressure line can precisely facilitate and control the opening and closing of the needle. The high pressure is turned off when the last injection for the defined combustion cycle has taken place. The same process repeats at this point for the next cylinder by again reactivating the piezoelectric actuator.
While the invention has been described in terms of preferred 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.