JP2001173495A - Unit injector and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain highly precise fuel injection in a unit injector using a shape memory alloy as a booster actuator. SOLUTION: The unit injector 1 comprises a shape memory element 14, an injection pump 2 pressurizing fuel in a boosting chamber 9 after receiving the shrinkage of the shape memory element 14, and an injection valve 1 which injects fuel when pressurized fuel is supplied. When a fuel injection signal is received, energizing and heating to the shape memory element 14 is started, the injection time of the fuel is preset according to operating conditions, and the shape memory element 14 is energized and heated until the preset injection time has passed since the start of displacement of the shape memory element 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a unit injector and a control method thereof.

[0002]

2. Description of the Related Art A unit injector in which an injection pump section and an injection valve section are integrated has been put to practical use in diesel engines and gasoline engines. This unit injector does not have an injection pipe, so that the fuel injection system can be reduced in size, and high-pressure and high-performance fuel injection can be performed.

In such a unit injector, as described in Japanese Patent Application Laid-Open No. H11-294298, the boosting piston is generally driven by a cam drive. It has to be provided, which causes the system to be large, complicated, and costly.

Therefore, it has been considered to use a shape memory alloy that can be used as an actuator having a high energy density (output / weight) as an actuator for driving a boosting piston (hereinafter, referred to as a boosting actuator).

[0005]

[Problems to be solved by the invention]
When a shape memory alloy is used as the boost actuator,
It was necessary to repeat the heating / cooling cycle of the shape memory alloy in accordance with the injection timing, and it was difficult to perform high-precision fuel injection due to difficulty in accurate temperature control.

Further, in the case of a configuration in which the shape memory alloy is contracted by applying electric heating to a temperature equal to or higher than the transformation temperature and the fuel is pressurized and injected using the contraction displacement, the injector receives heat in the engine room after the engine is stopped. When the temperature of the fuel inside the fuel cell rises and the shape memory alloy exceeds the transformation temperature, the fuel is spontaneously injected.

[0007] The present invention has been made in view of the above technical problems, and realizes highly accurate fuel injection when a shape memory alloy is used as a boosting actuator. The purpose is to prevent injection.

[0008]

According to a first aspect of the present invention, there is provided a shape memory element which contracts when energized and heated, and is cooled and expanded by fuel, and receives fuel in the pressurized chamber by expansion of the shape memory element. A unit injector including an injection pump unit that inhales and pressurizes and discharges fuel in a pressurized chamber in response to contraction of the shape memory element, and an injection valve unit that injects fuel when the pressurized fuel is supplied. Control method, when receiving a fuel injection signal, to start energization heating to the shape memory element, to set the fuel injection time according to the operating state, from the start of the shape memory element contraction, the set injection time After the lapse of time, the current supply to the shape memory element is terminated.

According to a second aspect of the present invention, in the first aspect, the energization heating of the shape memory element is a continuous energization until the shape memory element starts contraction, and is intermittent until the set injection time elapses from the start of contraction. It is characterized by being energized.

In a third aspect based on the first or second aspect, the time until the shape memory element starts to contract is measured, and the longer the time until the shape memory element starts to contract, the longer the duty of the intermittent energization. The ratio is set to be large.

According to a fourth aspect of the present invention, in the first to third aspects, the injector includes a discharge valve for opening and closing a discharge passage in the pressurized chamber. After the engine is stopped, the exhaust valve is opened to discharge fuel in the pressurized chamber. It is characterized by discharging.

In a fifth aspect based on the fourth aspect, the discharge valve is made of a shape memory alloy whose transformation temperature is set to be equal to or higher than the fuel temperature during engine operation and equal to or lower than the transformation temperature of the shape memory element. The valve is opened above the temperature and closed below the transformation temperature.

According to a sixth aspect of the present invention, in the first to third aspects, the cooling fuel is intensively supplied to the shape memory element at the end of the injection stroke.

According to a seventh aspect of the present invention, in the sixth aspect, the injector is provided with a supply valve for opening and closing the supply passage of the cooling fuel with a delay with respect to the displacement of the shape memory element. The fuel for cooling is intensively supplied to the shape memory element.

According to an eighth invention, when energized and heated, it shrinks,
A shape memory element that is cooled and expanded by the fuel, and an injection pump that draws the fuel into the pressurized chamber when the shape memory element is expanded, and pressurizes and discharges the fuel in the pressurized chamber when the shape memory element contracts. A unit injector having an injection valve unit that injects fuel when pressurized fuel is supplied, wherein the discharge valve opens after the engine stops and discharges fuel in the pressurized chamber to a discharge passage. It is characterized by being provided in a pressurizing chamber.

In a ninth aspect based on the eighth aspect, the discharge valve is formed of a shape memory alloy whose transformation temperature is set to be equal to or higher than the fuel temperature during engine operation and equal to or lower than the transformation temperature of the shape memory element. The valve is opened as described above, and the valve is closed below the transformation temperature.

According to a tenth aspect of the present invention, there is provided a shape memory element which contracts when energized and heated, cools and expands with fuel, expands the shape memory element, sucks fuel into a pressurizing chamber, and A unit injector including an injection pump unit that pressurizes and discharges the fuel in the pressurized chamber in response to the contraction of the fuel, and an injection valve unit that injects the fuel when the pressurized fuel is supplied. It is characterized in that the cooling fuel is sometimes concentratedly supplied to the shape memory element.

According to an eleventh aspect, in the tenth aspect,
A supply valve for opening and closing the supply passage of the cooling fuel with a delay with respect to the displacement of the shape memory element, and configured to supply the cooling fuel intensively to the shape memory element at the end of an injection stroke. It is characterized by the following.

[0019]

Therefore, according to the first aspect, the shape memory element as the boosting actuator starts contracting.
That is, by controlling the fuel injection amount based on the time from the start of the fuel injection, the dead time until the shape memory element starts to be displaced is not affected, and the high-precision fuel injection amount is prevented. Control becomes possible.

According to the second aspect of the present invention, the continuous energization is performed until the shape memory element starts to be displaced, so that the dead time from when the fuel injection signal is received to when the shape memory element starts to be displaced is reduced. Thus, the responsiveness of the injector can be improved.

Further, the responsiveness of the shape memory element is affected by the temperature of the cooling fuel. According to the third aspect of the present invention, the duty ratio in the intermittent energization performed after the shape memory element starts contracting is reduced by the fuel. It is changed according to the time from the start of energization, which indirectly represents the temperature, to the start of displacement of the shape memory element, so that even if the response of the shape memory element changes due to the fuel temperature, the amount of injected fuel is kept constant. Can be kept.

According to the fourth and eighth aspects of the invention, after the engine is stopped, the valve provided in the pressurized chamber is opened, and the fuel in the pressurized chamber is discharged. Thereby, after the engine stops, the fuel temperature in the injector rises due to the heat in the engine room and the fuel injection (natural fuel injection) due to the contraction of the shape memory element can be prevented. In particular, according to the fifth and ninth aspects, it is possible to prevent natural injection of fuel with a simple configuration.

According to the sixth, seventh, tenth and eleventh aspects of the present invention, cooling fuel is intensively supplied to the shape memory element at the end of the fuel injection stroke, that is, cooling is required. Since the cooling fuel is not supplied to the vicinity of the shape memory element except when the heating is performed, the thermal efficiency at the time of energizing and overheating can be improved.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of a unit injector according to the present invention. The unit injector is roughly divided into an injection valve section 1, an injection pump section 2 for supplying high-pressure fuel to the injection valve section 1, and an injection pump section 2. And a step-up actuator unit 3 for driving the motor.

The injection valve section 1 comprises a valve element 5 for opening and closing an injection port 4 opening to a combustion chamber of an engine (not shown), and a reaction spring 6 for urging the valve element 5 in a valve closing direction. Passage 7
When high-pressure fuel is supplied through the valve body 5, the valve body 5 lifts against the spring force of the reaction force spring 6, and fuel is injected from the injection port 4 into the combustion chamber.

The injection pump unit 2 includes a pressure-raising piston 8 slidable in the axial direction, a pressure-raising chamber 9 formed at the tip of the pressure-raising piston 8, and a direction in which the pressure-raising chamber 9 expands the pressure-raising piston 8. And a reaction force spring 10 biased in the middle right direction. When the pressure-raising piston 8 is displaced in the direction of reducing the pressure-rising chamber 9 (leftward in the figure) against the spring force of the reaction force spring 10,
The fuel in the pressurizing chamber 9 is pressurized, and high-pressure fuel is supplied to the injection valve unit 1 through the passage 7. After that, when the pressure-raising piston 8 is displaced in a direction to enlarge the pressure-raising chamber 9, the passage 11
New fuel is supplied into the pressurizing chamber 9 through the check valve 12.

The boosting actuator section 3 is connected to the displacement reversing piston 13, a shape memory element 14 interposed between the flange 13a of the displacement reversing piston 13 and the intermediate wall of the injector, and connected to the displacement reversing piston 13. And a spool valve 16 connected via a portion 15. The tip of the displacement reversing piston 13 is in contact with the back surface of the pressure-raising piston 8. In the figure, reference numeral 17 denotes a contact switch for detecting the start time of contraction of the shape memory element 14.

The shape memory element 14 is made of an alloy having a shape memory effect such as Ti-Ni or Cu-Zn-Al. The shape memory element 14 contracts when the temperature exceeds the transformation temperature T1 due to electric heating or the like, and decreases when the temperature falls below the transformation temperature T1. Stretch to length. The transformation temperature T1 is set higher than the fuel temperature Tf so as to enable cooling by the fuel. The displacement characteristic of the shape memory element 14 is set according to the engine used, and FIG. 2 shows an example of the characteristic.

The contraction displacement of the shape memory element 14 is reversed by the displacement reversing piston 13, and the displacement reversing piston 13 is displaced in the left direction in FIG. At this time, the tip of the displacement reversing piston 13 pushes the back surface of the boosting piston 8, and the boosting piston 8 is displaced in a direction to reduce the boosting chamber 9 against the spring reaction force of the reaction force spring 10.

The spool valve 16 is a valve that opens and closes a passage 18 for guiding cooling fuel to the shape memory element 14, and is connected to the displacement reversing piston 13 via a connecting portion 15. The spool valve 16 opens when the shape memory element 14 is contracted and closes when the shape memory element 14 expands to its original length.

However, the connecting portion 15 and the displacement reversing piston 1
3 is connected with a play to give hysteresis to the opening / closing timing of the spool valve 16, and the spool valve 16 is not displaced for a while even when the displacement reversing piston 13 starts displacing.

The operation of the spool valve 16 will be described in detail with reference to FIG. 3. First, FIG. 3A shows a state in which the shape memory element 14 is in an extended state. In this state, the spool valve 16 is in the closed position. is there.

In this state, when the shape memory element 14 is energized and heated and contracts, the displacement reversing piston 13 starts displacing in the direction of contracting the pressurizing chamber 9 (FIG. 3 (b)).
Fuel injection is started. However, since the connecting portion 15 and the displacement reversing piston 13 are connected with play, the spool valve 16 does not yet move from the closed position in this state, and the passage 18 remains closed.

Further, when the shape memory element 14 contracts and approaches the shortest length, the spool valve 16 also starts displacing to the left (FIG. 3C), the passage 18 is opened and the cooling fuel is released. 14 is introduced.

When the heating of the shape memory element 14 is completed, the shape memory element 14 is cooled by the fuel and starts to expand.
The spool valve 16 is not displaced from the open position by the play provided between them (FIG. 3D).

Thereafter, when the shape memory element 14 expands and approaches the maximum length, the spool valve 16 also starts displacing to the right and closes the passage 18 (FIG. 3 (e)).

As described above, by providing the opening and closing timing of the spool valve 16 with hysteresis, the spool valve 16 is opened only in the extension stroke in which the shape memory element 14 is to be cooled, and cooling fuel is introduced near the shape memory element 14. Thus, the contraction process by heating the shape memory element 14 and the expansion process by cooling can be efficiently performed without heat loss.

Further, an inside opening valve 19 made of a shape memory alloy is provided in the pressure increasing chamber 9.

FIG. 4 shows a cross section of a portion where the inner opening valve 19 is provided. The inner opening valve 19 is a C-ring reed valve, which closes during engine operation as shown in FIG.
Although the fuel in the pressurizing chamber 9 is prevented from flowing out to the discharge passage 20, when the temperature in the pressurizing chamber 9 rises to a predetermined transformation temperature after the engine stops, it contracts and opens as shown in FIG. Then, the fuel in the pressurizing chamber 9 is discharged to the passage 20.

Here, the transformation temperature T2 of the shape memory alloy constituting the inner opening valve 19 is set higher than the fuel temperature Tf so that the shape memory alloy is closed during the operation of the engine, but is higher than the transformation temperature T1 of the shape memory element 14. Is also set low. Transformation temperature T
By setting 2 in this way, when the temperature of the fuel in the injector rises when the engine is stopped, the inner opening valve 19 opens before the shape memory element 14 contracts, and the fuel in the pressure boosting chamber 9 escapes to the passage 20. Therefore, occurrence of spontaneous fuel injection can be reliably prevented.

Next, a method of controlling the unit injector will be described with reference to a flowchart shown in FIG. This flow is executed by a controller (not shown) for each injection upon receiving a fuel injection signal.

To explain this, first, two timers t1 and t2 used for control are set to zero, and the timer t1 is started (step S1).
The timer t1 is used to measure the time from the start of energization until the shape memory element 14 starts contracting.
The timer t2 is used to measure the time from the start of contraction of the shape memory element 14, that is, the time from the start of fuel injection.

In step S2, the shape memory element 14
In order to quickly increase the temperature of the contact switch 1, the contact switch 1 is turned on in step S3.
Until the start of contraction of the shape memory element 14 is detected by 7, the shape memory element 14 is continuously energized.

When the start of contraction of the shape memory element 14 is detected, the process proceeds to step S4, where the timer t1 is stopped and the timer t2 is started. Thus, the time required from the start of energization to the start of contraction of the shape memory element 14 is recorded in the timer t1.

When the shape memory element 14 starts contracting, the pressure-raising piston 8 is pushed via the displacement reversing piston 13,
The fuel in the pressurizing chamber 9 is pressurized. Then, the pressurized fuel is supplied to the injection valve section 1 through the passage 7, and fuel injection into the combustion chamber is started.

At this time, since a predetermined amount of fuel is injected within a predetermined time after the shape memory element 14 starts contracting,
The value of the timer t1 is used for fuel injection. In particular,
Since the value of the timer t1 indirectly predicts the temperature of the cooling fuel flowing near the shape memory element 14,
The duty ratio X is read from a map set so that the energization duty ratio during injection increases as t1 increases. The longer the time t1, the lower the fuel temperature and the lower the shape memory element 14.
However, by increasing the duty ratio X as t1 is longer, the fuel injection amount can be kept constant regardless of the fuel temperature.

In step S5, an injection time ta set based on operating conditions such as the throttle opening and the engine speed is read.

Thereafter, the shape memory element 14 is intermittently energized with the duty ratio X until the elapsed time t2 from the start of the intermittent energization reaches the set injection time ta (step S).
6, S7), when the elapsed time t2 reaches the set injection time ta, the energization is stopped and the timer t2 is stopped (step S8).

When the power supply to the shape memory element 14 is stopped, the shape memory element 14 is cooled by the cooling fuel introduced in the vicinity. Then, when cooled below the transformation temperature, it extends to its original length, and the process is terminated.

Therefore, each time the fuel injection signal is received, the above flow is executed and fuel injection is performed. However, the shape memory element 14 starts contracting, that is, the fuel injection amount is determined by the time from the start of fuel injection. Since the control is performed, the fuel injection amount can be controlled with high accuracy without being affected by the dead time until the shape memory element 14 starts to be displaced.

Further, since the energization is continuously performed until the shape memory element 14 starts to be displaced, the time from receiving the fuel injection signal until the shape memory element 14 starts contracting is reduced, and the responsiveness of the injector is reduced. Can be improved.

Further, the responsiveness of the shape memory element 14 is affected by the temperature of the cooling fuel introduced in the vicinity thereof, but the duty ratio X in the intermittent energization performed after the shape memory element 14 starts contracting. The amount of fuel to be injected can be changed even if the response of the shape memory element 14 changes due to the fuel temperature by changing the value according to the time from the start of energization indicating the fuel temperature indirectly to the start of displacement of the shape memory element. Can be kept constant.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a unit injector according to the present invention.

FIG. 2 is an example of a characteristic diagram of a shape memory element.

FIG. 3 is a diagram for explaining an operation of a boost actuator unit.

FIG. 4 is a diagram for explaining the operation of the inward opening valve.

FIG. 5 is a flowchart illustrating a method for controlling a unit injector according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection valve part 2 Injection pump part 3 Boost actuator part 4 Injection port 5 Valve 13 Displacement reversing piston 14 Shape memory element 15 Connecting part 16 Spool valve (supply valve) 17 Contact switch 18 Passage (supply passage) 19 Opening valve (discharge) Valve) 20 passage (discharge passage)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akihiro Sakakida 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Yasuyuki Ito 2 Takara-cho 2 Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. Terms (reference) 3G060 AB06 CA02 EA01 FA00 3G301 LB12 LC10 MA20 ND41 NE23

Claims (11)

[Claims] 1. A shape memory element that contracts when heated and is cooled by fuel, expands when cooled by fuel, draws fuel into the pressurized chamber due to expansion of the shape memory element, and receives contraction of the shape memory element. A fuel injection signal that pressurizes and discharges the fuel in the pressurized chamber, and an injection valve that injects the fuel when the pressurized fuel is supplied. When the shape memory element is received, the heating of the shape memory element is started, the fuel injection time is set according to the operating state, and the power is supplied to the shape memory element after the set injection time has elapsed from the start of contraction of the shape memory element. A method for controlling a unit injector, wherein heating is terminated. 2. The method according to claim 1, wherein the shape memory element is energized and heated continuously until the shape memory element starts contracting, and intermittently until the set injection time elapses from the start of contraction. 2. The method for controlling a unit injector according to item 1. 3. The intermittent energization duty ratio is set to be longer as the time until the start of contraction of the shape memory element is measured, and the time until the start of contraction of the shape memory element is longer. 3. The method for controlling a unit injector according to 1 or 2. 4. The fuel injection system according to claim 1, wherein the injector is provided with a discharge valve for opening and closing a discharge passage in the pressurized chamber, and after the engine is stopped, the discharge valve is opened to discharge the fuel in the pressurized chamber. The control method of the unit injector according to any one of the above. 5. The exhaust valve comprises a shape memory alloy whose transformation temperature is set to be higher than the fuel temperature during engine operation and lower than the transformation temperature of the shape memory element. The method for controlling a unit injector according to claim 4, wherein the valve is closed below. 6. The method according to claim 1, wherein cooling fuel is intensively supplied to the shape memory element at the end of the injection stroke. 7. A fuel injection valve having a supply valve for opening and closing a cooling fuel supply passage with a delay with respect to a displacement of the shape memory element, so that the shape memory element is cooled intensively at the end of an injection stroke. 7. The method for controlling a unit injector according to claim 6, wherein a fuel for use is supplied. 8. A shape memory element that contracts when energized and heated, cools and expands with fuel, expands the shape memory element, draws fuel into a pressurized chamber, and receives shrinkage of the shape memory element. A unit injector comprising: an injection pump unit that pressurizes and discharges fuel in the pressurized chamber; and an injection valve unit that injects fuel when the pressurized fuel is supplied. A unit injector comprising a discharge valve for discharging fuel in a pressure increasing chamber to a discharge passage in the pressure increasing chamber. 9. The discharge valve is formed of a shape memory alloy whose transformation temperature is set to be higher than a fuel temperature during engine operation and lower than a transformation temperature of the shape memory element. The unit injector according to claim 8, wherein the valve is closed below. 10. A shape memory element, which contracts when heated and heated, and which is cooled and expanded by fuel, expands the shape memory element, draws fuel into a pressurized chamber, and receives contraction of the shape memory element. A unit injector comprising: an injection pump unit that pressurizes and discharges the fuel in the pressurized chamber; and an injection valve unit that injects the fuel when the pressurized fuel is supplied. A unit injector configured to intensively supply cooling fuel to a storage element. 11. A supply valve for opening and closing a supply passage for cooling fuel with a delay with respect to a displacement of the shape memory element,
2. The configuration according to claim 1, wherein the cooling fuel is intensively supplied to the shape memory element at the end of the injection stroke.
0. The unit injector according to 0.