The piezoelectric fuel injection system 2 of the illustrated embodiment includes a controller 4, such as an 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 100 and provides power thereto, in the manner as further described below in accordance with the present invention. The fuel injector 100 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 132 is preferably formed from an integral piece structure and positioned in a nozzle cavity 136 and a spring cavity 140. The spring cavity 140 contains a bias spring 150 for abutment against a land 133 formed on nozzle valve element 132 so as to bias the nozzle valve element 132 against a nozzle seat 138 into a closed position as shown in
Fuel injector 100 further includes a nozzle valve control assembly indicated generally at 200 for controlling the movement of nozzle valve element 132 between open and closed positions. The initial opening of the nozzle valve element 132 defines the beginning of an injection event during which fuel flows through injector orifices 134 into the combustion chamber of the internal combustion engine. Specifically, nozzle valve control assembly 200 operates to initiate, and control, the movement of nozzle valve element 132 including the degree of opening and the rate of opening of nozzle valve element 132. In addition, nozzle valve control assembly 200 operates to maintain nozzle valve element 132 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 132 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 assembly 200 controls nozzle valve element 132 to control the rate shape of the fuel injection. 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
As shown in
In the illustrated embodiment, piezoelectric element 280 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 280, the elements become charged and expand along the axial direction of the column. The preload of piezoelectric element 280 is adjustable via disc springs 284 and adjustment nut 286. Of course, piezoelectric element 280 may be of any type or, design in other embodiments that is suitable for actuating the valve plunger 231. The embodiments described herein are described with respect to a piezoelectric actuator, which provide extremely fast and reliable valve response times and are capable of more injections per cycle than other known mechanisms. However, it is apparent that devices according to the present invention may employ other electromechanical actuators. The amount of expansion of piezoelectric element 280 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 100. The voltage duration and amount or level at various stages of the injection event are controlled or varied 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, the piezoelectric element 280 is discharged so that it reverts back to its original position thereby causing valve plunger 231 to move into the closed position which causes nozzle valve element 132 to move into its closed position.
Referring again to
During operation, the start and end of injection are controlled according to pressure in the control chamber 210. Prior to an injection event, the piezoelectric element 280 is de-energized causing valve plunger 231 to be biased into the closed position with the valve plunger 231 in sealing engagemerit against the valve seat 232 by seating spring 252. It is noted, in particular, that the seating spring 252 eliminates any need to use high pressure fuel to bias the valve plunger 231 in the closed position. In this no-fuel state, the control chamber 210 receives fuel at injection pressure through the control chamber charge circuit 212. Specifically, the fuel pressure level experienced in the injector cavity 120 surrounding the nozzle valve element 132 is also present in the control chamber 210 since drain flow from the control chamber 210 to the drain circuit 240 is blocked by valve plunger 231. As a result, the fuel pressure in the control chamber 210 acting on nozzle valve element 132, in combination with the bias force of bias spring 150, maintains nozzle valve element 132 in its closed position blocking flow through injector orifices 134. The pressure in control chamber 210 provides a high seat load to minimize any leakage.
At a predetermined time, controller 4 controls power source 6 so as to charge or energize piezoelectric element 280 with voltage to controllably cause the expansion of piezoelectric element 280 and movement of center rod 282 against the drive plunger 260. The resulting movement of the drive plunger 260 increases the pressure in cavity 262, which is filled with fuel acting as a fuel, or hydraulic, linkage 263. The fuel linkage 263 in cavity 262 applies a force sufficient to overcome the force of seating spring 252 and moves the valve plunger 231 to an open position. The pressure in cavity 262 must be sufficient to overcome the biasing force of the sealing spring 252, as the sealing spring 252 provides sufficient force to seal the valve plunger 231 against the valve seat 232.
The movement of valve plunger 231 is thus controlled by controlling the voltage applied to piezoelectric element 280. Thus, the distance between the valve plunger 231 and the valve seat 232 is controlled to vary the drain flow from control chamber 210 which ultimately permits precise control over the movement of nozzle valve element 132 between its closed and open positions.
As the valve plunger 231 of the control valve 230 is lifted from the valve seat 232, fuel flows from control chamber 210 through drain circuit 240 to a low pressure drain. Simultaneously, high pressure fuel flows from control chamber charge circuit 212 and the associated orifice 213 into control chamber 210. However, since the control chamber charge circuit orifice 213 is designed with a smaller cross-sectional flow area than the drain or control valve orifice 220, a greater amount of fuel is drained from control chamber 210 than is replenished via control chamber charge circuit 212. The pressure in control chamber 210 immediately decreases. As a result of the decreasing control chamber pressure, fuel pressure forces acting on nozzle valve of element 132 due to high pressure fuel in injector cavity 120, begin to move nozzle valve element 132 against the bias force of spring 150 into an open position.
When the valve plunger 231 moves into the open position, the control chamber 210 is connected to the drain circuit 240 by a drainage assembly 290, which includes an orifice 220, a drilling or passageway 222, the valve chamber 238, and the spring cavity 250. Due to the pressure difference, fuel in the control chamber 210 travels through the drainage assembly 290 and is vented to the drilling 240 and to drain. In particular, the orifice 220 is positioned at one end of the control chamber 210, opposite the end of the injector plunger 132. The higher pressure fuel in control chamber 210 exits the control chamber 210 into the drilling 222. Because the spring cavity 250 in the embodiment of
Thus, with the valve plunger 231 in the open position, the fuel is vented from the control chamber 210, through the orifice 220 and the drilling 222, into the valve chamber 238, past the valve plunger 231 and the valve seat 232, and through spring cavity 250 and drilling 240 to drain. The resulting drop in pressure in control chamber 210 at one end of the injector plunger 132 allows the injector plunger 132 to lift away from the valve seat 138 allowing fuel flow into the engine combustion chamber.
As further shown in
When injection is ended, the piezoelectric element 280 is de-energized. The piezoelectric center rod 282 retracts and moves away from the drive plunger 211, causing the pressure in cavity 262 to drop and reducing the amount of force acting against the biasing force of the spring 252. Thus, the biasing force of spring 252 is able to push the drive plunger 211 toward the piezoelectric element 280 and move the valve plunger 231 into the closed position, with the plunger end 233 seated at the valve seat 232. As a result, the control chamber 210 is filled with high pressure fuel through charge circuit orifice 213. The high pressure in the control chamber 210 forces the injector plunger 132 to be seated against nozzle seat 138, and ends the fuel injection.
While the piezoelectric actuator 280 is de-energized, cavity 262 is filled, and maintained, with fuel from the drain 240 flowing through a check valve 242, which opens with the corresponding drop in the pressure of cavity 262. The drain pressure is maintained at a sufficient level to assure filling of the cavity 262.
Advantageously, a controlled leakage of fuel from cavity 262 past drive plunger 260, through a channel 264, allows any air to be expelled to drain. This controlled leakage and the retraction of the piezoelectric element 280 result in an increase in the volume in cavity 262, which leads to a reduction of the pressure in the cavity 262 and assists seating of the plunger 230.
The flow of fuel from the drain 240 to fill the cavity 262 provides a source of filtered and cooler fuel to form the fuel linkage 263. The fuel in the fuel linkage 263 is not trapped. Thus, the fuel from the drain 240 provides a constant source of fuel to refill the cavity 262 and to make up for any fuel that leaks from the cavity 262. This cycling of fuel and the introduction of the cleaner fuel helps minimize the damaging effects of dirt and particles that would otherwise be trapped in the cavity 262. The cleaner fuel also helps to make the fluid properties more consistent. Moreover, the cycling of fuel provides a path for heat to be dissipated, and the introduction of cooler fuel reduces changes in temperature and corresponding changes in viscosity and other temperature-dependent properties.
When piezoelectric actuator 280 is energized and the cavity 262 is pressurized, the pressure causes the check valve 242 to be seated and close connection with the drain 240. Thus, the check valve 242 prevents fuel from exiting to the drain 240 when a higher pressure is required in the cavity 262 to move the valve plunger 231 into the open position.
The fuel linkage 263 in cavity 262 changes to compensate for any dimensional difference in length between the piezoelectric element 280 and the housing 270 due to temperature. In other words, the fuel linkage 263 connects the action of the piezoelectric element 280 to the valve plunger 231. Thus, the present invention compensates for thermal growth and part tolerances through the length, or height, of the fuel linkage 263, allowing the performance of the piezoelectric element 280 to be independent of temperature.
The increased pressure in the chamber 262 or the increased stroke of the valve plunger 231 can be achieved by the relative sizing of the drive plunger 260 to the valve plunger 231 for the same actuator stroke.
There may be leakage between the valve chamber 238 and hydraulic link cavity 262 past valve plunger 231, where the fuel in valve chamber 238 is under a higher pressure. However, the valve plunger 231 has an adequate length-to-diameter ratio, or sealing length, to minimize the amount of leakage. In addition, as discussed above, the hydraulic link pressure is maintained at a pressure when the injector is not fueling, and at a much higher pressure during injection. The higher pressure in cavity 262 during injection occurs due to force applied by the piezoelectric actuator 280 on drive plunger 260 with the check valve 242 sealing the hydraulic cavity from the drain circuit 240. Accordingly, although there may be a continuous leakage path between valve chamber 238 and hydraulic link cavity 262, the pressure in hydraulic link cavity 262 reduces the pressure difference between valve chamber 238 and hydraulic link cavity 262, thus minimizing the amount of leakage.
The valve plunger 231 is actuated by a piezoelectric element 280 of nozzle valve control assembly 200 to cause movement of the valve plunger 231 and the nozzle valve element 132 into their respective open positions. When the valve plunger 231 moves into the open position, the control chamber 210 is connected to the drain circuit 240 by a drainage assembly 290, which includes an orifice 220, a drilling 222, the valve chamber 238, and the spring cavity 250. The drilling 222 in the embodiment of
Moreover, unlike
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.