Fuel supply system for internal combustion engine

In a fuel supply system, a fuel pump supplies fuel from a fuel tank to a fuel supply piping and to a back pressure introducing passage. A pressure regulator has a fuel pressure regulating chamber communicated to the fuel supply piping, and a back pressure chamber communicated to the back pressure introducing passage. When a fuel pressure in the fuel pressure regulating chamber is larger than a relief pressure that bulges the diaphragm toward the back pressure chamber, a relief valve opens a relief port to return the fuel from the fuel pressure regulating chamber to the fuel tank. The relief pressure is adjusted by controlling a fuel pressure in the back pressure chamber of the pressure regulator.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2006-90837 filed on Mar. 29, 2006, and No. 2006-102811 filed on Apr. 4, 2006, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a fuel supply system having a fuel pump and a pressure regulator that regulates a fuel discharging pressure of the fuel pump.

BACKGROUND OF THE INVENTION

In conventional fuel supply systems, a fuel pump sucks fuel from a fuel tank and supplies the fuel out of the fuel pump into an internal combustion engine. Some fuel supply systems are provided with a pressure regulator to regulate a fuel supply pressure, i.e., a pressure of the fuel at which the fuel is discharged out of the fuel supply system, as disclosed in JP-H05-321783-A, JP-H05-039763-A, JP-H06-129325-A (which has counterparts U.S. Pat. Nos. 5,359,976, 5,471,962, 5,577,482, and EP-0593053-B1, EP-0606106-B1), and JP-2002-310025-A. In general, the pressure regulators incorporated in the fuel supply systems have a construction in which a diaphragm (pressure receiving portion) partitions a fuel pressure regulating chamber from a back pressure chamber. The diaphragm is bulged by forces applied by a fuel pressure in the back pressure chamber and by a fuel pressure in the fuel pressure regulating chamber. Thus, the fuel pressure regulating chamber discharges the fuel in accordance with the fuel pressure in the back pressure chamber and the fuel pressure in the fuel pressure regulating chamber so as to regulate the fuel pressure in the fuel pressure regulating chamber. The fuel pressure in the fuel pressure regulating chamber decreases when the fuel in the fuel pressure regulating chamber is discharged, and then the fuel is supplied from the fuel pump into the fuel pressure regulating pressure of the pressure regulator, so as to regulate the fuel supply pressure of the fuel supply system.

The fuel pressure in the fuel pressure regulating chamber, which is regulated by the bulge of the diaphragm, is referred to as a set pressure of the pressure regulator hereafter. The set pressure of the pressure regulator is determined by the pressure in the back pressure chamber, a ratio between a pressure receiving area on one surface of the diaphragm, which is subjected to the pressure in the back pressure chamber and a pressure receiving area on the other surface of the diaphragm, which is subjected to the fuel pressure in the fuel pressure regulating chamber, etc. In a construction in which an elastic member such as a spring applies a biasing force onto the diaphragm, the set pressure of the pressure regulator is determined also by the biasing force of the elastic member. The pressure introduced into the back pressure chamber of the pressure regulator is: an atmospheric pressure; a negative pressure in an intake pipe (refer to JP-H06-129325-A); any one of the negative pressures in the intake pipe and the atmospheric pressure (refer to JP-H05-039763-A); a fuel pressure regulated by another pressure regulator (refer to JP-2002-310025-A), etc.

In this regard, it is recently demanded to raise the fuel supply pressure of the fuel supply system, due to the following reasons.

Firstly, high fuel supply pressure is necessary to compress and liquefy fuel vapors generated in fuel piping. For example, the fuel vapors are prone to be generated when the fuel pump is started on a condition that a fuel temperature is high. High fuel supply pressure is required especially in this condition.

Next, high fuel supply pressure is necessary to promote atomization of fuel injections into the internal combustion engine. For example, it is necessary to promote the atomization of the fuel especially when the internal combustion engine is driving at heavy load, so as to raise an output power of the internal combustion engine.

Further, it is necessary to promote atomization of fuel injections in order to decrease unburned fuel in emission gas discharged out of the internal combustion engine, and to improve startability of the internal combustion engine in low and high temperature conditions. In order to promote the atomization of fuel injections, high fuel supply pressure, at which the fuel is discharged out of the fuel supply system and supplied to fuel injection valves, is effective, in addition to refinements of the fuel injection valves such as adjustments of shapes of injection holes, etc.

When the fuel supply pressure is raised as described above, however, some disadvantages occur. For example, an operating current of the fuel pump rises and an alternator is subjected to heavy load. This decreases fuel efficiency of the vehicle, and shortens a useful life of brushes of a motor for driving the fuel pump, to decrease endurance of the fuel supply system.

In order to raise fuel supply pressure of the fuel supply system, it is necessary to raise the set pressure of the pressure regulator.

In order to raise the set pressure of the pressure regulator, the elastic member such as a spring is upsized to increase the biasing force applied onto the diaphragm, for example. However, the pressure regulator becomes bulky when the elastic member is upsized.

In this regard, JP-2002-310025-A discloses a fuel supply system in which the pressure in the back pressure chamber of a first pressure regulator, which is for regulating the fuel supply pressure of the fuel supply system, is regulated by a second pressure regulator, which is for regulating the back pressure of the first pressure regulator. By setting the set pressure of the second pressure regulator at a high value, it is possible to raise the set pressure of the first pressure regulator without upsizing the pressure regulators.

In the fuel supply system disclosed in JP-2002-310025-A, however, a pressure of excessive fuel, which is discharged out of the first pressure regulator, is adjusted and introduced into the back pressure chamber of the second pressure regulator. In this construction, a quantity of the excessive fuel, which is discharged out of the first pressure regulator in accordance with a fuel consumption quantity of the internal combustion engine, i.e., a quantity of the fuel, which is introduced into the back pressure chamber of the first pressure regulator after its pressure is regulated by the second pressure regulator, is not stable. As a result, the fuel pressure in the back pressure chamber of the first pressure regulator fluctuates depending on the fuel consumption quantity of the internal combustion engine. This causes instability of the set pressure of the first pressure regulator, i.e., instability in the fuel supply pressure of the fuel supply system, which is regulated by the first pressure regulator.

SUMMARY OF THE INVENTION

The present invention is achieved in view of the above-described issues, and has an object to provide a fuel supply system that endures in an operation to pressurize fuel at high pressure and to supply high pressure fuel.

Another object of the present invention is to provide a fuel supply system that can regulate fuel at high pressure and supply high pressure fuel without upsizing its pressure regulator.

The fuel supply system for supplying fuel from a fuel tank to a fuel supply piping has a back pressure introducing passage and a fuel pump. The fuel pump supplies the fuel from the fuel tank to the fuel supply piping and to the back pressure introducing passage. The pressure regulator is provided with a case, a diaphragm, a fuel pressure regulating port, a back pressure introducing port, a relief port, and a relief valve. The diaphragm partitions an inner space of the case into a fuel pressure regulating chamber and a back pressure chamber. The fuel pressure regulating port communicates the fuel pressure regulating chamber to the fuel supply piping. The back pressure introducing port communicates the back pressure chamber to the back pressure introducing passage. The relief port communicates the fuel pressure regulating chamber to the fuel tank. The relief valve operates in accordance with a bulging degree of the diaphragm. The relief valve opens the relief port when a fuel pressure in the fuel pressure regulating chamber is larger than a relief pressure that bulges the diaphragm toward fuel pressure regulating chamber. The relief valve closes the relief port when the fuel pressure in the fuel pressure regulating chamber is not larger than the relief pressure. The relief pressure is adjusted by controlling a fuel pressure in the back pressure chamber of the pressure regulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIGS. 1 to 4illustrate a fuel supply system100according to a first embodiment of the present invention. As shown inFIG. 1, the fuel supply system100includes a fuel pump module1, an electrical control unit (ECU)2, etc. The fuel pump module1is installed inside a fuel tank3. The fuel pump module1sucks fuel from the fuel tank3, pressurizes the fuel, and supplies the fuel to a delivery pipe (not shown). The delivery pipe is connected to fuel injectors (not shown), each of which is installed on a cylinder of an internal combustion engine to inject the fuel. The fuel supply system100according to the first embodiment is a returnless fuel supply system that is not provided with a return pipe that returns excessive fuel from a delivery pipe to the fuel tank3.

The ECU2is supplied with electric power from a battery4. The ECU2controls operation of a primary pump10, which is provided in the fuel pump module1, in accordance with a command signal that indicates optimum fuel pressure for each driving state of the engine, and fuel pressure in the delivery pipe. The ECU2controls the fuel pressure in the delivery pipe in this manner. Specifically, the ECU2controls a relay5to switch the primary pump10on and off. Further, the ECU2controls operation of the fuel injectors to adjust fuel injection quantity. The ECU2serves as a back pressure pump controller according to the present invention.

In the schematic diagram ofFIG. 1, the primary pump10is shown outside a casing11; however, the primary pump10is installed inside the casing11in practical arrangement. The casing11is supported by a lid member12that closes an opening end of the fuel tank3.

As indicated by short dashed arrow lines inFIG. 1, the fuel discharged out of the primary pump10flows through a fuel filter13in the casing11into a pressure regulator20in a normal operation time of the fuel supply system100. The fuel, a pressure of which is regulated by the pressure regulator20, is supplied out of a discharge port14, which is provided in the lid member12, to the delivery pipe. The excessive fuel, which is discharged out of the pressure regulator20, is returned to the fuel tank3.

A construction of the primary pump10is described in the following, referring toFIG. 2.

The primary pump10is an electrically driven pump, and provided with a motor portion110and a pump portion150. The motor portion110is a DC motor having brushes. The motor portion110has a construction in which a cylindrical housing112forms a motor chamber114therein, a plurality of permanent magnets116are arranged along a circumference of the housing112, and an armature118is located inside of the circular array of the permanent magnets116to be coaxial to the circular array.

When the armature118is supplied with electric power via the brushes (not shown) from the battery4, a rotation axis124, which rotates integrally with the armature118, rotationally moves an impeller152of the pump portion150. A fuel discharge port130is formed in an end cover120. The fuel is pressurized by the rotating impeller152, introduced into the motor chamber114, and discharged out of the fuel discharge port130to a flow passage in which the fuel filter13is installed within the casing11as shown inFIG. 1. The fuel discharge port130is provided with a check valve131, so as to prevent the fuel from flowing backward from the fuel discharge port130into the housing112. Thus, it is possible to keep the fuel pressure in the delivery pipe even when the primary pump10is stopped.

A construction of the pressure regulator20is described in the following, referring toFIG. 3.

The pressure regulator20includes: a back pressure side case271; a pressure regulation side case272; a rubber diaphragm273; a spring seat274; a valve guide275; a ball276; a fastening277; a valve head member278; a spring279; and a valve seat member282. The diaphragm273, the spring seat274, the valve guide275, the ball276and the valve head member278form a moving body280that is integrally displaced.

An outer circumferential portion of the rubber diaphragm273is tightly sandwiched between the back pressure side case271and the pressure regulation side case272, and an inner circumferential portion of the diaphragm273is tightly sandwiched between the spring seat274and the valve guide275. The ball276is pushed on the valve guide275by the fastening277. The valve head member278has a plate-like shape and moves integrally with the ball276. The back pressure chamber284is defined by the back pressure side case271and the moving body280. The spring279is installed in the back pressure chamber284, and biases the moving body280in a direction to seat the valve head member278onto the valve seat283of the valve seat member282.

The valve seat member282, which has a cylindrical shape, is press-fitted into and blazed to the pressure regulation side case272. The valve seat member282has a discharge passage287that extends in an axial direction thereof. The discharge passage287communicates a fuel pressure regulating chamber285with a fuel discharge port294. The valve seat283is formed on the fuel pressure regulating chamber (285)-side end of the discharge passage287. When the valve head member278is seated on the valve seat283, a communication between the fuel pressure regulating chamber285and the fuel discharge port294is interrupted. When the valve head member278is lifted apart from the valve seat283, the communication between the fuel pressure regulating chamber285and the fuel discharge port294is allowed.

A communicating hole291, which is formed on the back pressure side case271, communicates the back pressure chamber284with a fuel discharge port306of a back pressure control pump30, which is described hereafter. The pressure in the back pressure chamber284is controlled in accordance with an operation of the back pressure control pump30. The pressure in the back pressure chamber284acts on the moving body280in a direction to seat the valve head member278onto the valve seat283.

Another communicating hole292, which is formed on the back pressure side case271, is connected to a piping (not shown) that serves as a secondary fuel passage L2to lead the fuel in the back pressure chamber284to a fuel discharge passage L1, which discharges the fuel out of the fuel discharge port130of the primary pump10as shown inFIG. 1. The secondary fuel passage L2is provided with a check valve390, which serves as a secondary passage shutting valve according to the present invention. The check valve390includes a valve body388that opens and closes the secondary fuel passage L2, and a spring389that biases the valve body388in a direction to close the secondary fuel passage L2. The check valve390restricts a fuel flow in the secondary fuel passage L2to a direction from the back pressure chamber284to the fuel discharge passage L1that is connected to the fuel discharge port130of the primary pump10.

The check valve390opens the secondary fuel passage L2when a pressure difference between the pressure P1in the fuel discharge passage L1, which is connected to the fuel discharge port130of the primary pump10, and the pressure P2in the back pressure chamber284becomes larger than a set pressure. Thus, the check valve390closes the secondary fuel passage L2, and the fuel flows as indicated by short dashed arrow lines, in the normal operation time in which the primary pump10normally operates. In a high pressure operation time in which both of the primary pump10and the back pressure control pump30normally operate, the check valve390keep closing the secondary fuel passage L2, and the fuel flows as indicated by single-dotted chain arrow line inFIG. 1.

When the pressure P1in the fuel discharge passage L1becomes smaller than the pressure P2in the back pressure chamber284due to a failure of the primary pump10or some other cause, the pressure P1further decreases to make the pressure difference between the pressures P1, P2larger than the set pressure of the check valve390. Then, the check valve390opens the secondary fuel passage L2, and the fuel flows as indicated by double-dotted chain arrow line inFIG. 1.

Even if a fuel discharge quantity out of the back pressure control pump30increases on a condition that the primary pump10normally operates, the pressure P2in the back pressure P2chamber284increases, and the pressure P1in the fuel discharge passage L1also increases. Thus, the pressure difference between the pressures P1, P2does not become larger than the set pressure of the check valve390, and the secondary fuel passage L2is kept closed. Accordingly, while the primary pump10normally operates, the secondary fuel passage L2is kept closed even if the fuel discharge quantity out of the back pressure control pump30increases.

FIG. 5depicts an example of relationship between fuel discharging pressure and fuel discharge quantity of the back pressure control pump30in accordance with driving voltage (and driving current) applied to the back pressure control pump30. As indicated by solid lines inFIG. 5, the fuel discharge quantity decreases as the fuel discharging pressure P2increases. On a condition that the fuel discharge quantity is constant, the fuel discharging pressure P2increases as the driving voltage (and the driving current) increases. Accordingly, when the back pressure control pump30starts driving in a state that the secondary fuel passage L2is closed by the check valve390, the fuel discharge quantity gradually decreases and the fuel discharging pressure gradually increases as the time is elapsed. When the fuel discharge quantity becomes zero, the fuel discharging pressure P2becomes constant at pressures P21, P22as shown inFIG. 5. The pressure P21when the driving voltage is 8V (when the driving current is 4 A) is smaller than the pressure P22when the driving voltage is 12V (when the driving current is 6 A). Thus, it is possible o regulate the pressure P2in the back pressure chamber284by adjusting the driving voltage applied to the back pressure control pump30. A broken line in the graph ofFIG. 5indicates a relationship between the pressure P2and the driving current on a condition that the fuel discharge quantity of the back pressure control pump30is zero.

A communicating hole293, which is formed on the pressure regulation side case272, communicates the fuel pressure regulating chamber285with the fuel discharge passage L1that connected to the fuel discharge port130of the primary pump10. The pressure in the fuel pressure regulating chamber285is equal to the fuel discharging pressure of the primary pump10, and acts on the moving body280in a direction to lift the valve head member278apart from the valve seat283. The pressure regulation side case272has the fuel discharge port294on an opposite side from the back pressure side case271, to discharge the excessive fuel.

The pressure regulator20regulates the pressure of the fuel that flows out of the fuel filter13into the fuel discharge passage L1at a predetermined high pressure (600 kPa, for example), by discharging the excessive fuel out of the fuel discharge port294in accordance with the fuel discharge quantity of the primary pump10. The value of the above-mentioned high pressure is determined in accordance with the pressure in the back pressure chamber284, which is controlled by the operation of the back pressure control pump30, and corresponds to a relief pressure according to the present invention. The fuel, the pressure of which is regulated at the high pressure, is supplied from the fuel discharge passage L1to the delivery pipe on the engine side.

The valve head member278in the valve head the pressure regulator20is located at a position so as to balance a force, which is applied by the fuel pressure in the back pressure chamber284onto the moving body280in a direction to seat the valve head member278onto the valve seat283, a force, which is applied by the fuel pressure in the fuel pressure regulating chamber285onto the moving body in a direction to lift the valve head member278apart from the valve seat283, and a biasing force, which is applied by the spring (biasing member)279onto the moving body in a direction to seat the valve head member278onto the valve seat283.

When the fuel discharge quantity from the primary pump10into the fuel pressure regulating chamber285becomes large, the force, which moves the moving body280in a direction to lift the valve head member278apart from the valve seat283, increases, and then the valve head member278lifts off the valve seat283. When the valve head member278is lifted off the valve seat283, the excessive fuel is discharged out of the fuel pressure regulating chamber285to the fuel discharge port294. The opening clearance between the valve head member278and the valve seat283changes in accordance with a quantity of the excessive fuel, to balance the fuel pressure in the fuel pressure regulating chamber285with the pressure in the back pressure chamber284and the biasing force of the spring279, and to regulate the fuel pressure in the fuel pressure regulating chamber285. The excessive fuel discharged out of the fuel discharge port294returns into the fuel tank3.

A construction of the back pressure control pump30is described in the following, referring toFIG. 4.

The back pressure control pump30is electrically driven one, and provided with a pump portion312, and a motor portion314that rotationally drive the pump portion312. The motor portion314of the back pressure control pump30has an output power smaller than that of the motor portion110of the primary pump10. In the first embodiment, a pump having a maximum discharge quantity of 80-150 liters per hour is suitable for the primary pump10, and a pump having a maximum discharge quantity of approximately 30 liters per hour is suitable for the back pressure control pump30.

The pump portion312is a turbine pump (centrifugal pump) having pump cases320,322and an impeller324. The pump cases320,322house the impeller (rotational member) rotatably therein. C-shaped pump passages302are formed between the pump case320and the impeller324and between the pump case322and the impeller324. The fuel in the fuel tank3is sucked through a fuel suction port303, which is formed on the pump case320, pressurized by a rotation of the impeller324, and pressure-supplied to the motor portion314. The fuel pressure-supplied to the motor portion314flows through a fuel passage304, which is provided between a stator core330and a rotor360, and supplied out of the fuel discharge port306to the back pressure chamber284of the pressure regulator20.

The motor portion314is an inner rotor brushless motor. The motor portion314includes the stator core330, a pair of insulators340and a pair of coils348. The stator core330is formed of coil cores332. The coil core332has teeth334that extend in radial directions, and peripheral cores336that extend along a circumference on a radially outer side of the teeth334. Each of the insulators340is press-fitted on both axial end sides of the coil cores332. Each of the insulators340has a bobbin groove, in which conducting wires are wound to form the coils348.

The rotor360has a rotation axis362and permanent magnets306, and the rotor360is rotatably installed inside an inner circumference of the stator core330. The permanent magnets306form eight magnetic pole portions365that are aligned to surround the rotation axis362. The eight magnetic pole portions365are magnetized to provide positive and negative magnetic poles on their circumferences that face the coil cores332so that the positive and negative magnetic poles alternately surround the rotation axis362.

A switching circuit (not shown) switches driving current supplied to the coil348, so as to control magnetic pole generations of the coils348. In order to switch the driving current supplied to the coils348to rotate the rotor360, it is necessary to detect rotational position of the rotor360. The rotational position of the rotor360is detected by a detecting device such as a Hall device, for example, and the driving current is switched in accordance with detection signals of the detecting device. Alternatively, it is also possible to detect the rotational position of the rotor360by energizing some of the coils348, and detecting induction electromotive forces generated in the other coils348(for example, by energizing four coils among totally six coils, and detecting the induction electromotive forces generated in the other two coils). The switching circuit may be incorporated in the back pressure control pump30. In another way, the switching circuit may be installed outside the back pressure control pump30(in the ECU2, for example).

When electric power is supplied from the battery4to the coil348, the rotation axis362, which rotates integrally with the rotor360, rotates the impeller324of the pump portion312. The fuel is pressurized by the rotating impeller324, introduced into a motor chamber, and discharged out of the fuel discharge port306, which is formed in an end cover352, to the communicating hole293of the pressure regulator20shown inFIG. 3. The fuel discharge port306is not provided with any check valve, differently from the primary pump10in which the fuel discharge port130is provided with the check valve131. Thus, when the back pressure control pump30stops, the fuel in the back pressure chamber284of the pressure regulator20flows backward in the back pressure control pump30, and discharged through the pump passage302and the fuel suction port303into the fuel tank3.

The ECU2is provided with a CPU, a ROM, a RAM, an input circuit, an output circuit, etc. (not shown). When electric power is supplied from the battery4to the ECU2, the ECU2controls the operations of the primary pump10and the back pressure control pump30, pursuant to a control procedure shown inFIG. 6. In this control procedure, the fuel discharging pressure of the primary pump10, which is regulated by the pressure regulator20, is controlled by the operation of the back pressure control pump30. In a fall back operation time (limp home operation time) due to a failure of the primary pump10or some other reason, the back pressure control pump30supplies the fuel from the fuel tank3, instead of the delivery pipe the primary pump10. Namely, the control procedure shown in the flow chart ofFIG. 6switches the fuel supply system100between the fall back operation and an operation to regulate the fuel discharging pressure of the primary pump10.

(1) Firstly, the ECU2starts the control procedure at a predetermined pump operation monitoring timing, and determines whether an error of the primary pump10has been detected or not in a step40. Specifically, the fuel supply system100can detect the error of the primary pump10by the ECU2in a step60, and sets a flag F to1to memorize the error of the primary pump10. Then, the ECU2determines whether the flag F is1or not in the step40.
(2) Next, the ECU2determines a starter motor for starting the engine is working or not in a step42, and further determines the engine is at a heavily loaded state or not in a step44. If the ECU2determines that the starter motor is working, i.e., the engine is in starting state in the step42, the ECU2operates the back pressure control pump30in a middle mode by applying a predetermined driving voltage (or driving current) to the back pressure control pump30in a step56, and operates the primary pump10at the same time by activating the relay5in a step58.

If the ECU2determines that the starter motor is not working in the step42and further determines that the engine is at heavily loaded state in the step44, the ECU2operates the back pressure control pump30in a low mode by applying another predetermined driving voltage (or driving current) to the back pressure control pump30, and operates the primary pump10at the same time in the step58. The heavily loaded state of the engine includes an accelerating state of a vehicle, for example.

(3) If the ECU2determines that the flag F is not1in the step40, that the starter motor is not working in the step42, and that the engine is not in heavily loaded state in the step44, the ECU2stops the back pressure control pump30in a step46. Then, if the ECU2determines that the engine is driving in a step48, the ECU2starts the primary pump10or keeps operating the primary pump10, by activating the relay5in the step58. That is, the fuel supply system100is in the normal operation time in the step58.

If the ECU2determines that at least one branch condition is not satisfied in the steps40,42,44, the ECU2starts the back pressure control pump30in any one of the steps54,56,64. That is, when the primary pump10is not in failure and the engine is starting or driving in heavily loaded state, the pressure in the back pressure chamber284increases, and the pressure P1in the fuel discharge passage L1, which is connected to the fuel discharge port130of the primary pump10, increases. If the engine is in normally loaded state, the pressure in the back pressure chamber284remains small, and the pressure P1in the fuel discharge passage L1, which is connected to the fuel discharge port130of the primary pump10, is not increased. InFIG. 6, “FP2” indicates the back pressure control pump30, and “FP1” indicates the primary pump10.

(4) As described above, the ECU2changes the fuel discharging pressure of the back pressure control pump30in accordance with conditions of the fuel supply system100when it drives the back pressure control pump30. When the flag F is set to1and any failure is present in the primary pump10, etc., the ECU2operates the back pressure control pump30in a high mode in the step64, in which the fuel discharging pressure and the fuel discharge quantity of the back pressure control pump30is maximized.
(5) When the ECU2determines that no failure is present in the primary pump10, etc., and that the starter motor is working and the engine is starting, the ECU2operates the fuel supply system100in the middle mode in the step56, in which the fuel discharging pressure of the back pressure control pump30is smaller than in the high mode. Thus, the pressure in the back pressure chamber284is larger than in a state in which the back pressure control pump30is stopped in the step46. As a result, the pressure P1in the fuel discharge passage L1, which is connected to the fuel discharge port130of the primary pump10, is set to a large value.
(6) When the ECU2determines that no failure is present in the primary pump10, etc., and that the engine is driving in a state that the starter motor is stopping, the ECU2operates the fuel supply system100in the low mode in the step54, in which the fuel discharging pressure of the back pressure control pump30is smaller than in the middle mode. Thus, the pressure in the back pressure chamber284is larger than in a state in which the back pressure control pump30is stopped in the step46, and smaller than in the middle mode. As a result, the pressure P1of the fuel discharge passage L1, which is connected to the fuel discharge port130of the primary pump10, is set to a value larger than when the back pressure control pump30is stopping, and smaller than in the middle mode.
(7) After the process of the step46, the ECU2determines whether the engine is driving or not in the step48. If the ECU2determines that the engine is not driving in the step48, the ECU2releases the relay5in the step50so as to stop the primary pump10.
(8) After the process of the step58, the ECU2determines whether the primary pump10is normally operating or not on a condition that the relay5is activated in the step60. As shown inFIG. 1, the fuel supply system100is provided with a failure detector15that detects a failure of the primary pump10. The ECU2detects the failure of the primary pump10in accordance with a detection signal sent from the failure detector15. In the first embodiment, the failure detector15detects a driving voltage of the primary pump10. The ECU2determines that the failure of the primary pump10(e.g., a break in the wiring) when the driving voltage is smaller than a predetermined set value.
(9) If the ECU2determines that the primary pump10is in normal operation in the step60, the ECU2sets the flag F to0in a step52. If the ECU2determines that the primary pump10is not in normal operation in the step60, the ECU2sets the flag F to1in a step62. After the processes of the step52,62, the control procedure of the primary pump10and the back pressure control pump30is finished.
(10) After the process of the step64, the ECU2determines in a step66whether an ignition switch (not shown) is turned on or not. If the ECU2determines that the ignition switch is turned on, the control procedure is finished. If the ECU2determines that the ignition switch is turned off, the ECU2determines that a fall back operation is not necessary, and stops the operation of the back pressure control pump30in a step68. Then, the ECU2sets the flag F to0in a step70, and completes the control procedure.

Advantages of the fuel supply system100according to the first embodiment are described in the following. The fuel supply system100is provided with the back pressure control pump30for supplying the fuel to the back pressure chamber284of the pressure regulator20, in addition to the primary pump10for supplying the fuel to the delivery pipe. Accordingly, the fuel supply system100can adjust the fuel pressure in the back pressure chamber284by controlling the fuel discharging pressure of the back pressure control pump30. Further, when the primary pump10is in normal operation, the normal operation of the ECU2, which serves as the back pressure pump controller according to the present invention, switches the fuel discharging pressure of the primary pump10in the steps46,54,56inFIG. 6. Thus, the fuel supply system100can adjust the pressure P1of the fuel discharge passage L1of the primary pump10, in accordance with the driving conditions of the engine, which are detected in the steps42,44.

Especially in the returnless fuel supply system100, relatively large fuel discharging pressure of the primary pump10is required. This raises an operating current of the primary pump10, to cause malfunctions to raise a load acting on the alternator, to shorten a useful life of the brushes of the primary pump10, etc. Accordingly, the fuel supply system100according to the present embodiment, which is provided with the back pressure control pump30, prevents the above malfunctions and is suitable for the returnless fuel supply system100, because the fuel supply system100according to the present embodiment can raise the fuel discharging pressure only in a required time, so as to improve durability of the fuel supply system100.

Further, the fuel supply system100according to the first embodiment is provided with the secondary fuel passage P2, which leads the fuel discharged out of the back pressure control pump30to the fuel discharge passage L1of the primary pump10. Thus, even when the primary pump10is in failure, the fuel supply system100can supply the fuel from the back pressure control pump30via the secondary fuel passage L2to the delivery pipe. Accordingly, the back pressure control pump30of the fuel supply system100according to the first embodiment is provided with a fall back function (limp home function) when the primary pump10is in failure.

Furthermore, in the fuel supply system100according to the first embodiment, the secondary fuel passage L2is connected to the back pressure chamber284. Thus, the fuel supply system100requires a means that closes the secondary fuel passage L2when the primary pump10is normally operating, and opens the secondary fuel passage L2when the primary pump10is in failure. In this regard, the fuel supply system100according to the first embodiment is provided with the check valve390, which serves as a secondary passage shutting valve according to the present invention, in the secondary fuel passage L2. Thus, when a pressure in the fuel discharge side of the primary pump10becomes smaller than a predetermined value, it is determined that the primary pump10is in failure, and the check valve390opens the secondary fuel passage L2. Relatively to a construction provided with a failure detecting means and an electromagnetic valve so that the electromagnetic valve opens the secondary fuel passage L2when the failure detecting means detects a failure of the primary pump10, the fuel supply system100according to the present embodiments uses the relatively low-cost check valve390serving as the shut-off valve, to decreases a manufacturing cost of the fuel supply system100.

Still further, the fuel supply system100according to the first embodiment, the secondary fuel passage L2is provided with the check valve390, which serves as the secondary passage shutting valve according to the present invention, and the check valve390limits a fuel flow in the secondary fuel passage L2to a direction from the back pressure chamber284to the fuel discharge passage L1of the primary pump10. Then, the check valve390opens the secondary fuel passage L2when a difference between the pressure in the fuel discharge side of the primary pump10and the pressure in the back pressure chamber284becomes larger than a set pressure.

In this manner, the fuel supply system100according to the first embodiment incorporates the check valve390that is relatively cheep with respect to electromagnetic valve, to decrease the manufacturing cost of the fuel supply system100.

Still further, in the fuel supply system100according to the first embodiment, a turbine pump having no seal function is used for the pump portion312of the back pressure control pump30. Thus, when the fuel supply system100is switched from the high pressure fuel supplying operation in which both of the primary pump10and the back pressure control pump30are in normal operations (as indicated by single-dotted chain arrow line inFIG. 1) to the normal operation in which only the primary pump10is in normal operation (as indicated by short-dashed line inFIG. 1), the operation of the back pressure control pump30is stopped to flow the fuel in the back pressure chamber284backward in the back pressure control pump30and discharged through the pump passage302and the fuel suction port303into the fuel tank3. Thus, the fuel pressure in the back pressure chamber284is easily decreased to switch the fuel supply system100from the high pressure fuel supplying operation to the normal operation.

Second Embodiment

In the following is described a fuel supply system102according to a second embodiment of the present invention, referring toFIG. 7. In the second embodiment, the same referential numerals as in the first embodiment is assigned to components substantially as same as in the first embodiment, and those components are not redundantly described. A construction of the fuel supply system102according to the second embodiment differs from that in the first embodiment in the following points.

The fuel supply system102according to the second embodiment is not provided with the secondary fuel passage L2in the first embodiment, and does not perform the fall back operation (limp home operation) utilizing the back pressure control pump30. Further, the communicating hole292formed on the back pressure side case271of the pressure regulator20is connected to a piping (not shown). As shown inFIG. 7, this piping is provided with a fuel return passage L3that returns the excessive fuel out of the back pressure control pump30to the fuel tank3.

On the fuel return passage L3is installed a pressure regulating valve392, which is different from the pressure regulator20in the first embodiment. The pressure regulating valve392is provided with: a case393; a diaphragm that partitions an internal space of the case393into an outflow chamber395and an inflow chamber396; a valve body397that opens and closes a communicating passage communicating the outflow chamber395to the inflow chamber396; and a spring398that is installed in the outflow chamber395and biases the valve body397in a direction to close the communicating passage. The outflow chamber395is communicated to the fuel return passage L3, and the inflow chamber396is communicated to the back pressure chamber284of the pressure regulator20.

The pressure regulating valve392regulates the fuel discharging pressure of the back pressure control pump30to a predetermined constant value. Thus, the fuel pressure in the back pressure chamber284is regulated to the constant value with accuracy, and the fuel discharging pressure of the primary pump10is adjusted with accuracy.

The piping that forms the fuel return passage L3is connected to another piping (not shown) that has a relief passage L4. The relief passage L4is provided with an orifice391. Thus, when the back pressure control pump30stops, the fuel in the back pressure chamber284is discharged out of the relief passage L4, so that the fuel pressure in the back pressure chamber284easily decreases, to switch the high pressure fuel supplying operation (as indicated by single-dotted chain arrow line inFIG. 7) to a normal operation (as indicated by short-dashed broken arrow line inFIG. 7). Accordingly, in the fuel supply system102according to the present invention, which is provided with the relief passage L4, a pump having sealing function such as a gear pump can be used for the pump portion312of the back pressure control pump30.

Third Embodiment

In the following is described a fuel supply system104according to a third embodiment of the present invention, referring toFIG. 8. In the third embodiment, the same referential numerals as in the first embodiment is assigned to components substantially as same as in the first embodiment, and those components are not redundantly described. A construction of the fuel supply system104according to the third embodiment differs from that in the second embodiment in the following points. That is, the construction of the fuel supply system104according to the third embodiment is formed by eliminating the orifice391in the construction in the second embodiment, and a turbine pump is used for the pump portion312of the back pressure control pump30as in the first embodiment.

By using the turbine pump, when the fuel supply system104is switched from the high pressure fuel supplying operation (indicated by single-dotted chain arrow line inFIG. 8) to the normal operation (indicated by short-dashed arrow line), the back pressure control pump30stops, and the fuel in the back pressure chamber284flows backward in the back pressure control pump30and discharged through the pump passage302and the fuel suction port303into the fuel tank3, even without the orifice391. Accordingly, the fuel pressure in the back pressure chamber284easily decreases, so as to switch the fuel supply system104from the high pressure fuel supplying operation to the normal operation.

Fourth Embodiment

In the following is described a fuel supply system106according to a third embodiment of the present invention, referring toFIGS. 9,10. In the fourth embodiment, the same referential numerals as in the first embodiment is assigned to components substantially as same as in the first embodiment, and those components are not redundantly described. A construction of the fuel supply system106according to the fourth embodiment differs from that in the third embodiment in the following points. That is, the construction of the fuel supply system106according to the fourth embodiment is formed by substituting a check valve390for the pressure regulating valve392in the construction in the third embodiment.

FIG. 10illustrates a variation of the fuel discharging pressure of the back pressure control pump30when the fuel discharge quantity of the back pressure control pump30increases due to a switch from the normal operation to the high pressure fuel supplying operation. In the graph ofFIG. 10, a solid line illustrates a relationship between the fuel discharge quantity and the fuel discharging pressure when the check valve390is used as in the fourth embodiment, and a single-dotted chain line illustrates the relationship between the fuel discharge quantity and the fuel discharging pressure when the pressure regulating valve392is used as in the third embodiment.

As shown inFIG. 10, the fuel discharging pressure changes steeply when the check valve390is used than when the pressure regulating valve392is used. Accordingly, when the fuel pressure in the back pressure chamber284is changed and the pressure P1of the fuel discharge passage L1of the primary pump10is changed, the pressure P1is changed with smaller accuracy in the fourth embodiment than in the third embodiment. However, when it is not required to control the change of the pressure P1of the primary pump10, it is possible to use the check valve390as in the fourth embodiment, so as to reduce the manufacturing cost of the fuel supply system106with respect to that in the third embodiment in which the pressure regulating valve392is used.

Fifth Embodiment

In the following is described a fuel supply system108according to a fifth embodiment of the present invention, referring toFIG. 11. In the fifth embodiment, the same referential numerals as in the first embodiment is assigned to components substantially as same as in the first embodiment, and those components are not redundantly described. A construction of the fuel supply system108according to the fourth embodiment differs from that in the first embodiment in the following points. That is, the construction of the fuel supply system108according to the fourth embodiment is formed by eliminating the secondary fuel passage L2and the check valve390in the first embodiment.

By changing the driving voltage (or driving current) applied to the back pressure control pump30, the fuel discharging pressure of the back pressure control pump30changes, and the fuel pressure in the back pressure chamber284also changes. Specifically, as shown inFIG. 5, the pressure P21on a condition that the driving voltage is 8V (or the driving current is 4V) is smaller than the pressure P22on a condition that the driving voltage is 12V (or the driving current is 6 A). Thus, it is possible to adjust the pressure P2of the back pressure chamber284by regulating the driving voltage (or the driving current). Accordingly, it is possible to eliminate the secondary fuel passage L2and the check valve390, so as to reduce the number of parts for forming the fuel supply system108.

Modifications of First to Fifth Embodiments

The failure detector15in the first to fifth embodiments detects the driving current of the primary pump10, and the ECU2determines that a failure (e.g., pump lock-up, wire breakage) of the primary pump10exists when the driving current is larger than or smaller than a predetermined set value. In this regard, it is also possible to calculate a rotational speed of the armature118based on a change of inductive electromotive force generated in the primary pump10, and determine whether a failure of the primary pump10exists or not, based on a relation between a driving voltage applied to the primary pump10and the rotational speed of the armature118.

Sixth Embodiment

FIG. 12depicts a fuel supply system410according to a sixth embodiment of the present invention. The fuel supply system410supplies fuel stored in a fuel tank (not shown) to a fuel rail402. The fuel rail402is communicated to fuel injection valves404for respective cylinders of an internal combustion engine406.

[Construction of Fuel Supply System]

A fuel pump420of the fuel supply system410is an electrically driven turbine pump that rotates an impeller by an electrically driven motor so as to suck and pressurize the fuel. The fuel pump420is installed in the fuel tank (not shown).

The fuel pump420sucks the fuel stored in the fuel tank through a fuel suction port421, pressurizes the fuel, and discharges the fuel out of a fuel discharge port422. A pressure regulator440regulates a fuel discharging pressure of the fuel pump420. The fuel discharged out of the fuel pump420flows through a piping600and supplied to the fuel rail402. A construction of the pressure regulator440is described hereafter in detail.

The piping600is communicated to a back pressure chamber610of the pressure regulator440by a piping602, which serves as a back pressure introducing passage according to the present invention. In the piping602is installed a shut-off valve430, which serves as a back pressure introducing valve according to the present invention. A fuel pressure regulating chamber612of the pressure regulator440is communicated to the piping600by a piping604.

The shut-off valve430is an electromagnetic valve. When the shut-off valve430is opened, the fuel discharged out of the fuel pump420flows through the shut-off valve430to piping602, and introduced into the back pressure chamber610of the pressure regulator440.

A back pressure chamber620of a pressure regulator490is opened to atmospheric air. A fuel pressure regulating chamber622of the pressure regulator490is communicated via a piping606to the piping602at a point between the shut-off valve430and the back pressure chamber610. The piping606is provided with an orifice607that restricts a fuel flow quantity introduced from the piping602to the fuel pressure regulating chamber622. The pressure regulator490regulates a fuel pressure between the shut-off valve430and the back pressure chamber610in the piping602. Namely, the pressure regulator490regulates a fuel pressure in the back pressure chamber610. The orifice607is installed to restrict and decrease a fuel discharge quantity out of the fuel pressure regulating chamber622when the pressure regulator490regulates the fuel pressure in the back pressure chamber610of the pressure regulator440.

A fuel discharging pipe608, which serves as a relief passage according to the present invention, is connected to the piping602at a point between a branch point of the piping606and the back pressure chamber610. An end of the fuel discharging pipe608, which is opposite from the other end connected to the piping602, is opened to a space inside the fuel tank. In the fuel discharging pipe608is installed an orifice609. The orifice609is installed to decrease a fuel discharge quantity flown through the piping602and discharged out of the fuel discharging pipe608when the shut-off valve430is opened to introduce the fuel discharged out of the fuel pump420through the piping602to the back pressure chamber610of the pressure regulator440.

An engine control unit (ECU)500, which serves as a fuel supply controller according to the present invention, is formed of a CPU, a ROM and a RAM (not shown). The ECU500turns on and off an electric power supply to the fuel pump420so as to control an operation of the fuel pump420by letting the CPU execute a control program stored in the ROM. The ECU500also turns on and off the electric power supply to the shut-off valve430so as to open and close the shut-off valve430in accordance with driving states of the internal combustion engine406.

A construction of the above-mentioned pressure regulator440is described in detail in the following, referring toFIG. 13. A pressure regulation side case444of the pressure regulator440is swaged to a back pressure side case442. An outer circumferential portion of a diaphragm450and a pinching member452are tightly swaged to the pressure regulation side case444. An inner circumferential portion the diaphragm450is tightly sandwiched between a valve guide454and a spring seat456. A ball458is fitted to a depressed portion455of the valve guide454. The ball458has a flat surface459on an opposite side from a portion fitted to the depressed portion455. The flat surface459is in contact with a disk-like shaped valve head member460. A cylindrical support member470is fixed to the pressure regulation side case444. A cylindrical valve seat member472is fixed to an inner wall of the support member470so as to protrude toward the valve head member460. A spring (elastic member)462is installed in a spring chamber served by the back pressure chamber610. The spring462applies a biasing force to the diaphragm450, the valve guide454, the spring seat456, the ball458and the valve head member460in a direction toward the valve seat member472.

A connection pipe480communicates the back pressure chamber610in the back pressure side case442to the piping602. The fuel in the piping602flows through the connection pipe480, and is introduced into the back pressure chamber610. A connection pipe482communicates the fuel pressure regulating chamber612in the pressure regulation side case444to the piping604. The fuel in the piping600flows through the piping604and the connection pipe482, and is introduced into the fuel pressure regulating chamber612. A relief pipe484is fixed to an inside of the support member470on a side opposite from the valve seat member472. When the valve head member460is lifted apart from the valve seat member472, the fuel in the fuel pressure regulating chamber612is discharged out of the relief pipe484into the fuel tank.

[Starting Time and Normally Operating Time of Internal Combustion Engine]

In the following is described an operation of the fuel supply system410. The ECU500sets a fuel injection pressure of the fuel injection valves404to a high pressure or to a low pressure, in accordance with the driving states of the internal combustion engine406, which is detected by sensors (not shown). In a starting time of the internal combustion engine406, for example, it is desirable to set the pressure of the fuel, which is supplied to the fuel injection valves404, to the high pressure. This is to promote atomization of sprayed fuel in low temperature condition, and also to promote the atomization of the sprayed fuel and to suppress vapor generation in the fuel in high temperature condition. When a load applied to the internal combustion engine is relatively small during a constant-speed driving time of vehicle, for example, the pressure of the fuel supplied to the fuel injection valves404can be set to the low pressure. The pressure of the fuel supplied to the fuel injection valves404is switched to the high pressure or to the low pressure by opening and closing operation of the shut-off valve430controlled by the ECU500.

(1) When the fuel pump420is started on a condition that an electric power supply to the shut-off valve430is turned off and the shut-off valve430is closed, for example, the pressure of the fuel, which is supplied through the piping600to the fuel rail402, increases as indicated by a solid line620inFIG. 14. A dashed line inFIG. 14indicates a fuel pressure variation in the piping602corresponding to an opening and closing operation of the shut-off valve430. When the shut-off valve430is closed, the piping602is blocked and the fuel discharged out of the fuel pump420is not introduced into the back pressure chamber610of the pressure regulator440. The piping602is opened to the atmospheric air via the fuel discharging pipe608, so that the pressure in the back pressure chamber610is approximately equal to the pressure of the atmospheric air. The piping600,604introduce the fuel discharged out of the fuel pump420to the fuel pressure regulating chamber612of the pressure regulator440.

Thus, the diaphragm450is displaced (bulged) in accordance with a difference between a force F1, which acts onto the diaphragm450in a direction to seat the valve head member460on the valve seat member472, and a force F2, which acts onto the diaphragm450in a direction to lift the valve head member460apart from the valve seat member472. The force F1is a resultant of a force applied by the pressure of the fuel in the back pressure chamber610, which corresponds to the atmospheric pressure, and a biasing force of the spring462. The force F2is applied by the pressure of the fuel discharged out of the fuel pump420and introduced into the fuel pressure regulating chamber612.

When the force F1is equal to or larger than the force F2, the valve head member460is seated on the valve seat member472, and the fuel in the fuel pressure regulating chamber612is not discharged out of the discharge pipe484. When the pressure in the fuel pressure regulating chamber612rises and the force F1becomes smaller than the force F2, the valve head member460is lifted apart from the valve seat member472, and the fuel in the fuel pressure regulating chamber612is discharged out of the discharge pipe484. Then, the pressure of the fuel in the fuel pressure regulating chamber612, i.e., the pressure of the fuel, which is discharged out of the fuel pump420and supplied through the piping600to the fuel rail402, decreases.

(2) Next, as shown inFIG. 14, when the electric power supply to the shut-off valve430is started to open the shut-off valve430on a condition that the fuel pump420is driving, the fuel discharged out of the fuel pump420is introduced not only to the fuel pressure regulating chamber612but also to the back pressure chamber610of the pressure regulator440through the piping602. In this time, the pressure of the fuel introduced in the back pressure chamber610is set to a pressure larger than the atmospheric pressure by the pressure regulator490. Thus, the force F1becomes smaller than the force F2, and the diaphragm450is displaced (bulged) against the pressure applied by the fuel pressure in the back pressure chamber610. Then, the fuel pressure in the fuel pressure regulating chamber612when the valve head member460is lifted apart from the valve seat member472becomes larger than the fuel pressure when the shut-off valve430is opened and the fuel discharged out of the fuel pump420is not introduced into the back pressure chamber610. That is, the set pressure of the pressure regulator440is raised. As a result, as shown inFIG. 14, when the shut-off valve430is opened, the fuel pressure in the fuel pressure regulating chamber612, i.e., the pressure of the fuel that is discharged out of420and supplied through the piping600to the fuel rail402is larger than that when the shut-off valve430is closed.
(3) When the shut-off valve430is switched from opening state to closing state, the fuel discharged out of the fuel pump420stops being introduced into the back pressure chamber610. Then, the fuel in the piping602is discharged out of the fuel discharging pipe608, and the pressure in the back pressure chamber610decreases approximately to the atmospheric pressure. As a result, the set pressure of the pressure regulator440is decreased, and the fuel discharging pressure of the fuel pump420is set to the low pressure. Accordingly, the pressure of the fuel, which is supplied from the fuel pump420to the fuel rail402, decreases.

In this manner, the ECU500controls the opening and closing operations of the shut-off valve430in accordance with the driving states of the internal combustion engine406, so as to switch the pressure of the fuel supplied to the fuel rail402between the high pressure and the low pressure.

[Stopping Time of Internal Combustion Engine]

In the following is described an operation of the fuel supply system when the internal combustion engine406is stopping, referring to a flow chart shown inFIG. 15.

The ECU500determines whether the internal combustion engine406is stopping or not, in a step700. If the internal combustion engine406is stopping, the ECU500determines whether the shut-off valve430is opened or closed in a step702. If the shut-off valve430is closed, the ECU500stops the electric power supply to the fuel pump420to stop the fuel pump420in a step706. When the fuel supply sump420is stopped while the shut-off valve430is closed as mentioned above, the piping600is blocked by the shut-off valve430and a check valve (not shown) that is installed in and in the fuel discharge port422of the fuel pump420, so as to prevent the fuel from leaking from the piping600and the fuel rail402. Accordingly, a decrease of a residual pressure in the piping600and in the fuel rail402is limited, to improve a startability of the internal combustion engine406. Further, by limiting the decrease of the residual pressure in the piping600and in the fuel rail402, it is possible to suppress the vapor generation in the piping600and in the fuel rail402especially when the internal combustion engine406is stopped on a condition that the fuel temperature is relatively high. Accordingly, the startability of the internal combustion engine406is further improved.

If the ECU500determines that the shut-off valve430is opening in the step702, the ECU500stops the electric power supply to the shut-off valve430to open the shut-off valve430, in a step704. After opening the shut-off valve430, the ECU500stops the electric power supply to the fuel pump420to stop the fuel pump420in the step706.

When the fuel pump420is stopped on a condition that the shut-off valve430is opening, the fuel in the piping600is discharged through the piping602and the fuel discharging pipe608in a period from the stop of the fuel pump420and a valve open of the shut-off valve430, and the fuel pressure in the piping600and in the fuel rail402can decrease.

In this regard, it is possible to stop the fuel pump420to maintain the fuel pressure in the piping600and in the fuel rail402, by stopping the fuel pump420after closing the shut-off valve430if the shut-off valve430is opened. Thus, the fuel supply system410limits a decrease of the residual pressure in the piping600and in the fuel rail402, and suppresses the vapor generation in the piping600and in the fuel rail402, so as to improve the startability of the internal combustion engine406.

In the above-described fuel supply system410according to the sixth embodiment, the set pressure of the pressure regulator440is increased without raising the biasing force of the spring462, by introducing the fuel discharged out of the fuel pump420into the back pressure chamber610of the pressure regulator440for regulating the fuel discharging pressure of the fuel pump420. Accordingly, it is possible to raise the fuel discharging pressure of the fuel pump420without upsizing the spring462and the pressure regulator440.

When the fuel is introduced into the back pressure chamber610in order to raise the set pressure of the pressure regulator440, the fuel discharge quantity of the fuel pump420is stable relative to a quantity of the excessive fuel of the internal combustion engine406, for example. Accordingly, the pressure regulator440can regulate the fuel discharging pressure of the fuel pump420stably to reduce a fluctuation in the fuel discharging pressure.

Further, the fuel pressure introduced into the back pressure chamber610of the pressure regulator440is adjusted by another pressure regulator490. Thus, it is possible to change the pressure of the fuel introduced into the back pressure chamber610of the pressure regulator440, by changing the set pressure of the pressure regulator490by adjusting a biasing force of the spring in the pressure regulator490. That is, the set pressure of the pressure regulator440is adjusted by changing the set pressure of the pressure regulator490, so that it is possible to change the fuel discharging pressure of the fuel pump429, which is regulated by the pressure regulator440.

Seventh Embodiment

FIG. 16schematically depicts a fuel supply system412according to a seventh embodiment of the present invention. In the seventh embodiment, the same referential numerals as in the sixth embodiment is assigned to components substantially as same as in the sixth embodiment, and those components are not redundantly described.

In the fuel supply system412shown inFIG. 16, the pressure of the fuel introduced into the back pressure chamber610of the pressure regulator440is regulated not by the pressure regulator490as in the sixth embodiment, but by an orifice603that is provided in the piping602. By adjusting an opening diameter of the orifice203, it is possible to adjust the pressure of the fuel that is introduced into the back pressure chamber610of the pressure regulator440.

Eighth Embodiment

FIG. 17depicts a pressure regulator520of a fuel supply system according to an eighth embodiment of the present invention. In the eighth embodiment, the same referential numerals as in the sixth embodiment is assigned to components substantially as same as in the sixth embodiment, and those components are not redundantly described.

The fuel supply system according to the eighth embodiment is provided with the pressure regulator520instead of the pressure regulator440in the sixth embodiment. An orifice522is formed on a back pressure side case442of the pressure regulator520. The orifice522acts in the same manner as the orifice609installed in the piping602of the fuel supply system410according to the sixth embodiment. Thus, the fuel supply system according to the eighth embodiment is not provided with the fuel discharging pipe608and the orifice609, which are provided in the fuel supply system410according to the sixth embodiment shown inFIG. 12.

As described above, in the fuel supply system according to the eighth embodiment, the orifice522, which releases the pressure in the back pressure chamber610of the pressure regulator520to an atmospheric air when the shut-off valve430is closed, is provided in the pressure regulator520. Thus, a construction of piping of the fuel supply system is simplified. Further, when the shut-off valve430is opened, the back pressure chamber610of the pressure regulator520is regularly provided with fuel, so that the fuel does not stagnate in the back pressure chamber610. Thus, it is possible to prevent parts that are exposed to a space in the back pressure chamber610from corrosion.

Modifications of the Sixth to Eighth Embodiments

In the sixth to eighth embodiments, the pressure of the fuel introduced into the back pressure chamber610of the pressure regulator440,520is regulated by the pressure regulator490or by the orifice603. However, it is also possible to introduce the fuel discharged out of the fuel pump420directly into the pressure regulator440,520neither via the pressure regulator490nor via the orifice603.

In the sixth to eighth embodiments, the shut-off valve430opens and closes the piping602to switch the set pressure of the pressure regulator440,520to the high pressure or to the low pressure. However, it is possible to specify the set pressure of the pressure regulator440,520regularly to the high pressure, without installing the shut-off valve430in the piping602.

In the sixth to eighth embodiments, when the shut-off valve430is closed from a state in which the shut-off valve430is opened, the fuel in the back pressure chamber610is discharged through the orifice609installed in the fuel discharging pipe608or through the orifice522provided in the pressure regulator520, to release the pressure in the back pressure chamber610of the pressure regulator440,520to the atmospheric air. In this regard, it is also possible to decrease the pressure in the back pressure chamber610by gradually releasing the fuel from the back pressure chamber without using the fuel discharging pipe608nor using the orifice522.

In the fuel supply system in which the set pressure of the pressure regulator440,520is changed by opening and closing the shut-off valve430as described in the above sixth to eighth embodiments, it is desirable to detect faulty in pressure regulation based on an electric signal sent by a fuel pressure sensor and/or the driving current applied to the fuel pump420and notify the faulty to a driver of vehicle when the fuel discharging pressure of the fuel pump420cannot be regulated to a target pressure due to failures of parts and the like.