Patent Application
20050252494
1. Field of the Invention
The present invention is directed to piezoelectric injection systems having a mechanism for controlling rate shape, and to methods for controlling such piezoelectric injection systems.
2. Description of Related Art
In most fuel supply systems applicable to internal combustion engines, fuel injectors are used to inject fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned adjacent the nozzle orifice for allowing fuel to be injected into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve is positioned in a nozzle cavity and biased by a nozzle spring so that when the pressure of the fuel within the nozzle cavity exceeds the biasing force of the nozzle spring, the nozzle valve element moves outwardly to allow fuel to pass through the nozzle orifices, thus marking the beginning of the injection event.
In another type of system, such as disclosed in U.S. Pat. No. 5,819,704, the beginning of injection event is controlled by a servo-controlled needle valve element. The system includes a control volume positioned adjacent an outer end of the needle valve element, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit so as to cause the movement of the needle valve element between open and closed positions. Opening of the injection control valve causes a reduction in the fuel pressure in the control volume resulting in a pressure differential which forces the needle valve open, and closing of the injection control valve causes an increase in the control volume pressure and closing of the needle valve.
Internal combustion engine designers have increasingly come to realize that substantially improved fuel supply systems are required in order to meet the ever increasing governmental and regulatory requirements of emissions abatement and increased fuel economy. Specifically, it is known that improved control of fuel metering into the combustion chamber, is essential in reducing the level of emissions generated during coombustion process while minimizing fuel consumption, for example, in combustion of diesel fuel. In addition, it is known that improved control of the rate of fuel injected during the course of an injection event, i.e. the rate shape of the injection, is also very important in reducing the level of emissions generated, especially in diesel fuel combustion. As a result, many proposals have been made to provide fuel metering control and rate shape control for closed nozzle fuel injector systems, including such systems that utilize piezoelectric fuel injectors.
For instance, U.S. Pat. No. 5,779,149 to Hayes, Jr. discloses a piezoelectric controlled common rail fuel injector. The piezoelectric actuator controls the movement of an inwardly opening poppet-type control valve for controlling the flow of fuel from a control volume and ultimately, the movement of the nozzle valve element. The reference further discloses that fuel metering is variably controlled by controlling the duration and modulation of the electrical signal that is provided to the piezoelectric actuator. Although the above-described reference provides some control over fuel metering, and thus, control over the amount of fuel injected, the reference does not provide a solution for effectively controlling rate shape of the fuel injections.
U.S. Pat. No. 6,253,736 to Crofts et al. discloses a piezoelectric fuel injector nozzle assembly having feedback control with a nozzle valve control arrangement that operates to control the movement of the nozzle valve element. The reference discloses that the nozzle valve control arrangement functions to control the quantity of the fuel metered, and also functions as a rate shaping control device for producing a predetermined time varying change in the flow rate of fuel injected into the combustion chamber during an injection event so as to improve combustion and minimize emissions. The reference further discloses that the injection rate shape is controlled by varying the voltage supplied to the piezoelectric actuator based on engine operating conditions.
U.S. Pat. No. 4,732,129 to Takigawa et al. discloses an injector with an electroexpansive actuator. The actuator voltage is controlled to ultimately vary the movement of a nozzle needle thereby enabling fuel injection at different injection rates.
U.S. Pat. No. 6,367,453 to Igashira et al. discloses a method of controlling injection rate shape by applying voltage to piezo actuator such that the injection rate increases slowly when voltage is applied to the piezo actuator and decreases rapidly when voltage is applied to the piezo actuator is stopped, thereby creating a triangular rate shape. The injector uses a three-way valve and a specific size ratio of main and sub orifices to achieve slow needle opening and quick needle closing motion.
Methods of controlling fuel injectors such as that disclosed in Crofts et al. typically provide an input signal, i.e. voltage, current, etc., to a piezoelectric element, an electromagnetic actuator, or a magnetostrictive actuator to thereby operate the fuel injector. As disclosed in Crofts et al., rate shape of fuel injections is also controlled in the same manner by changing the magnitude of the input signal. However, controlling the rate shape of fuel injections by varying the input signal in the manner known has been found to not provide the desired results in various instances when accurate rate shaping would be desirable.
Thus, despite the teachings of the art discussed above, alternative systems and methods for controlling injection rate shape using piezoelectric fuel injectors are desirable to provide further control of combustion and emissions generated by such combustion, and to further improve fuel economy. Therefore, there still exists an unfulfilled need for a piezoelectric fuel injection system having enhanced rate shape control, and a method for controlling a piezoelectric fuel injector in which enhanced rate shape is attained.
In view of the foregoing, an aspect of the present invention is a piezoelectric fuel injection system to aid in reducing exhaust emissions and improving fuel economy, especially in engines not using exhaust gas recirculation.
Another aspect of the present invention is a piezoelectric fuel injection system having enhanced rate shape control.
Still another aspect of the present invention is a method for controlling a piezoelectric fuel injection system in which enhanced rate shape is attained.
Thus, in accordance with one aspect of the present invention, a piezoelectric fuel injection system for an internal combustion engine is provided to allow injection of fuel during an injection event and comprises a piezoelectric element actuatable to inject fuel during said injection event, a power source adapted to provide voltage to said piezoelectric element, and a controller adapted to control the power source to charge the piezoelectric element to an initial voltage to begin the injection event, to decrease the voltage from the initial voltage to an intermediate voltage, and to increase the voltage from the intermediate voltage to a primary voltage to thereby control a rate of fuel injected during the injection event, wherein the initial voltage is at least approximately equal to the primary voltage. That is, the initial voltage is no less than approximately the primary voltage. The initial voltage and the primary voltage may be approximately equal. Also, the initial voltage may be greater than or equal to at least approximately 50% of a maximum voltage rating of the piezoelectric element but still at least approximately equal to the primary voltage. Preferably, the initial voltage may be greater than or equal to at least approximately 90% of the maximum voltage rating, and may be approximately equal to 100% of the maximum voltage rating. The intermediate voltage may be greater than 40% of the initial voltage and less than 70% of the initial voltage. The controller may be adapted to maintain the initial voltage for an initial voltage duration and vary the initial voltage duration to control the fuel injection rate. The controller may also be adapted to maintain the intermediate voltage for an intermediate voltage duration and vary the intermediate voltage duration to control the fuel injection rate. The controller may also be adapted to vary the intermediate voltage level to control the fuel injection rate.
The above system preferably includes a piezoelectric fuel injector actuatable to inject fuel during the injection event, with the piezoelectric element incorporated into the fuel injector body. The piezoelectric fuel injector may include an injector cavity, an injector orifice communicating with one end of the injector cavity to discharge fuel into a combustion chamber, and a nozzle valve element positioned in one end of the injection cavity adjacent the injector orifice for movement between an open position in which fuel may flow through the injector orifice into the combustion chamber and a closed position in which fuel flow through the injector orifice is blocked. The charge of the piezoelectric element to the initial voltage causes a rapid opening of the nozzle valve element and a corresponding rapid increase in the fuel injection rate, and the decrease of the voltage from the initial voltage to the intermediate voltage causes, in one embodiment, an opening of the nozzle valve element slower than the rapid opening and a slower increase in the fuel injection rate than the rapid increase, and, in another embodiment, the nozzle valve element to be maintained in a partially opened position resulting in an essentially steady state injection. Preferably, the increase of the voltage from the intermediate voltage to the primary voltage causes the nozzle valve element to move to a fully open position and the injection rate to reach a maximum level, wherein the controller is further adapted to maintain the primary voltage for a predetermined period of time.
The piezoelectric fuel injector preferably further includes a control volume positioned at one end of the nozzle valve element, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit to control fuel flow from the control volume to control movement of the nozzle valve element, wherein the piezoelectric element controls the movement of the injection control valve.
In another embodiment, the invention includes a method for implementing the present invention.
These and other aspects of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention when viewed in conjunction with the accompanying drawings.
The piezoelectric fuel injection system 2 of the illustrated embodiment includes a controller 4, e.g. electronic control unit, that is connected to a power source 6, the controller 4 being adapted to control the power source 6. The power source 6 of the piezoelectric fuel injection system 2 is connected to a fuel injector 10 and provides power thereto in the manner as further described below in accordance with the present invention. Fuel injector 10 receives fuel from a fuel source and is adapted to inject the received fuel into a combustion chamber of an internal combustion engine (not shown) during an injection event of a combustion cycle, details of the internal combustion engine and combustion cycles being known in the art and thus, being omitted herein.
Referring to
As can be appreciated by one of ordinary skill in the art by examination of
In the embodiment shown in
Nozzle valve element 20 is preferably formed from an integral piece structure and positioned in a nozzle cavity 24 and a spring cavity 26. The spring cavity 26 contains a bias spring 28 for abutment against a land 30 formed on nozzle valve element 20 so as to bias nozzle valve element 20 into a closed position as shown in
Fuel injector 10 further includes a nozzle valve control arrangement indicated generally at 38 for controlling the movement of nozzle valve element 20 between open and closed positions, the initial opening of the nozzle valve element defining the beginning of an injection event during which fuel flows through injector orifices 22 into the combustion chamber of the internal combustion engine. Specifically, nozzle valve control arrangement 38 operates to initiate, and control the movement of nozzle valve element 20 including the degree of opening and the rate of opening of nozzle valve element 20. In addition, nozzle valve control arrangement 38 operates to maintain nozzle valve element 20 in the open position for a specified duration so as to control the quantity of fuel injected. The degree of opening, the rate of opening, and the duration of opening for nozzle valve element 20 are controlled based on the operating conditions of the engine, for example, engine speed, load, throttle position, etc.
When operated in accordance with the present invention, nozzle valve control arrangement 38 controls nozzle valve element 20 to control the rate shape of the fuel injection, especially during a first portion of an injection event. This allows time varying change in the flow rate of fuel injected into the combustion chamber during an injection event. Correspondingly, such control of the rate shape allows improved fuel economy while reducing emissions.
As most clearly shown in the enlarged view of
In the illustrated embodiment, piezoelectric element 52 comprises a columnar laminated body of thin disk-shaped elements, each having a piezoelectric effect so that when a voltage is applied to the piezoelectric element 52, the elements become charged and expand along the axial direction of the column. Of course, piezoelectric element 52 may be of any type or design in other embodiments that is suitable for actuating control valve 40 in the manner described hereinbelow. The expansion of piezoelectric element 52 causes downward movement of control valve 40, via center rod 54, into an open position away from valve seat 43 thereby permitting high pressure fuel to drain from control volume 44 via the drain circuit 41 which in turn causes the opening of nozzle valve element 20 and corresponding injection of fuel through injector orifices 22. A decrease in the voltage applied to piezoelectric element 52 causes axial contraction of the element 52, upward movement of center rod 54 and corresponding movement of control valve 40 toward the closed position which in turn causes either movement of nozzle valve element 20 toward the closed position or termination of an outward movement of nozzle valve element 20 to maintain element 20 in a desired partially open position.
The amount of expansion of piezoelectric element 52 corresponds to the specific design of the elements, the voltage being controlled, for example, by controller 4, and the amount of voltage applied to the piezoelectric element. In addition, the duration and amount of voltage provided by controller 4 determines the amount of fuel injected by fuel injector 10. The voltage duration and amount or level at various stages of the injection event are controlled or varied, as discussed hereinbelow, based on the operating conditions of the engine such as engine speed, engine load, throttle position, etc. At the end of an injection event, when the voltage is turned off, i.e. zero volts are provided, piezoelectric element 52 is discharged so that it reverts back to its original position thereby causing control valve 40 to move into the closed position which causes nozzle valve element 20 to move into its closed position.
Referring again to
During operation, prior to-an injection invent, piezoelectric element 52 is de-energized causing control valve 40 to be biased into the closed position in sealing engagement against valve seat 43 by fuel pressure forces acting on the lowered distil end of control valve 40 due to the high pressure fuel in control volume 40. The fuel pressure level experienced in the injector cavity surrounding nozzle valve element 20 is also present in control volume drain circuit 41 and control volume 44 since drain flow through drain circuit 41 is blocked by control valve 40. As a result, the fuel pressure acting inwardly on nozzle valve element 20, in combination with the bias force of bias spring 28 maintains nozzle valve element 20 in its closed position blocking flow through injector orifices 22. At a predetermined time, controller 4 controls power source 6 so as to charge or energize piezoelectric element 52 with voltage to controllably cause the expansion of piezoelectric element 52 and movement of center rod 54 and control valve 40 from the closed position shown in
As previously described, use of such conventional control methods has been found to be inadequate in accurately controlling rate shape of the injections in various situations. For example, it has been found that in order to reduce exhaust emissions in diesel engines, the rate of fuel injected into the combustion chamber during an injection event should be gradually increased to a desired steady state level instead of rapidly ramping up the rate of fuel injected to the desired steady state level at the very beginning of the injection event. Moreover, it is desirable to vary and control the injection rate of fuel (rate shape) during the injection event, and especially during an initial portion of the event.
Whereas the input signal provided to a fuel injector actuator may generally be controlled to gradually change over time, such a controlled input signal does not necessarily result in fuel injection having the desired gradually changing rate shape. At least with respect to injectors having servo-controlled nozzle valves, this inability to precisely control injection rate may be attributed to the fact that although the valve actuator, such as a piezoelectric element, can respond to the input signal in a precise and rapid manner, the nozzle valve element cannot be operated in a corresponding precise and rapid manner because the nozzle valve element is operated by controlling the amount of fuel in the control volume which requires time to flow into, or out, of the control volume. Thus, conventional fuel injectors cannot readily control the injection of fuel to achieve the desired injection rate shape. As a result, too much fuel or too little fuel can be injected into the combustion chamber by the fuel injector thereby resulting in an undesirable injection rate shape and corresponding increased emissions and/or fuel consumption.
Referring to
The above-described fuel injection rate and nozzle valve element motion events are achieved by piezoelectric fuel injection system 2 of the present invention precisely controlling the movement of control valve 40 to control the pressure in control volume 44 thereby effectively and precisely controlling the movement of nozzle valve element 20. Specifically, piezoelectric fuel injection system 2 operates to control the voltage applied to piezoelectric element 52 of nozzle valve control arrangement 38 in such a manner as described hereinbelow to effectively and precisely control the expansion and contraction of the piezoelectric element 52 and thus the movement of control valve 40 to achieve the desired rate shape. The system and method of the present invention provides flexible rate shape capability for variably controlling the rate shape throughout engine operation depending on engine operating conditions by varying the voltage level and voltage duration at different times during the injection event as described hereinbelow. Thus, the present invention applies an electrical charge or voltage profile which effectively and precisely controls the movement of nozzle valve element 20 throughout the injection event to achieve a predetermined desired rate shape, such as a boot-shape.
Referring to
More specifically, upon the initiation of an injection event, the piezoelectric element 52 is charged to an initial voltage which insures a rapid partial opening of nozzle valve element 20. This initial voltage is at least equal to approximately the primary voltage. Moreover, preferably, this initial voltage is greater than or equal to at least the approximately 50% of the maximum voltage rating of the piezoelectric element 52. In the example of
The actual test results using the piezoelectric fuel injection system of the present invention to achieve a boot-shaped injection rate as shown in
Referring to
Importantly, the system and method of the present invention permits the injection rate shape to be actively adjusted and varied based on engine operating conditions during the full operating range of an engine. Specifically, the desired rate shape for any particular set of engine operating conditions can be achieved by changing one or more of three primary control parameters of the voltage provided to the piezoelectric element 52 using controller 4. Specifically, referring to
It should be noted that variations of the present invention are considered within the scope of the present invention. For example, the various voltage levels, including the initial, intermediate and primary voltage levels may vary throughout the particular stage without deviating from the present invention as long as the primary relationships between the voltage levels are maintained as described herein. Also, additional voltage levels may be included in an injection event as long as the initial, intermediate and primary voltage levels, and their magnitude relationships, are present. For example, the primary voltage may consist of two different voltage levels. Thus, the piezoelectric fuel injection system 2 of the present invention creates a voltage profile including at least three step functions to open control valve 40 to lift the nozzle valve element 20 to a partial lift position to develop a low injection rate, then partially close control valve 40 to keep nozzle valve element 20 in the partial lift position, and then more fully open control valve 40 to further lift nozzle valve element 20 to develop the full injection flow rate.
The present invention is advantageous over conventional piezo actuator control methods for injectors. One conventional control scheme applies low electrical charge rates to the piezo elements resulting in a low voltage rate. Consequently, the control valve is slow to open which causes a low pressure drop rate in the control volume and thus a delayed, slowly increasing injection rate. This conventional control scheme results in a system that is difficult to control and provides unsatisfactory injection rate control throughout engine operating conditions thereby failing to optimize emissions reduction. Another conventional control scheme initially applies a maximum voltage which is then continuously maintained until the end of the injection event causing the injection rate to ramp up quickly to the steady state injection rate. As previously described, this rapid ramp-up in the injection rate, especially during the early stage of an injection event, causes increased emissions and decreased fuel economy. The present invention permits selective, variable voltage control, and thus rate shaping throughout engine operation thereby permitting the injection flow rate to be controlled based on varying engine conditions by simple changes to specific controllable piezoelectric voltage parameters. The present invention can be operated to permits cycle-by-cycle controllable rate shaping. The present flexible and actively controllable rate shaping system, injector and method is especially advantageous on engines not having other means, such as exhaust gas recirculation, for achieving desired emission levels.
Finally, as previously noted, the present invention may be combined with other control strategies for controlling rate shape to provide further flexibility in controlling the rate shape such as a boot-shaped injection rate shape, a triangular injection rate shape, or any other desired injection rate shape.
While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto. The present invention may be changed, modified and further applied by those skilled in the art. Therefore, this invention is not limited to the detail shown and described previously, but also includes all such changes and modifications.
