P3P2012416AU DESCRIPTION FUEL SUPPLY DEVICE 5 TECHNICAL FIELD The present invention relates to a fuel supply device, and more particularly, to a fuel supply device applied to a multicylinder diesel engine. 10 BACKGROUND ART Japanese Laid-Open Patent Publication No. 2009-102990 discloses an example of a typical fuel supply device. The 15 fuel supply device of the document is connected to a plurality of first injectors, which inject fuel into each first combustion chamber of a first cylinder group, and a plurality of second injectors, which inject fuel into each second combustion chamber of a second cylinder group, in a 20 multicylinder diesel engine. The fuel supply device of the document supplies fuel from a fuel tank to each first injector and each second injector. Each first injector and each second injector may be a piezo-injector, which employs a piezo element as an actuator that opens and closes an 25 injection hole. The fuel supply device in the document includes a medium pressure pump, which is described as a feed pump in the document, and a high pressure pump. The medium pressure pump 30 adjusts the fuel from the fuel tank to a medium pressure and delivers the medium-pressure fuel to a medium pressure passage. The high pressure pump adjusts the fuel, which is delivered through the medium pressure passage, to a high pressure, which is higher than the medium pressure, and 35 delivers the high-pressure fuel to a high pressure passage. 1 P3P2012416AU The high pressure passage is connected to a common rail. A first high pressure passage connects the common rail to each first injector. A second high pressure passage connects the common rail to each second injector. 5 A first return passage, which is connected to each first injector, is capable of transporting surplus fuel from each first injector. A second return passage, which is connected to each second injector, is capable of transporting surplus 10 fuel from each second injector. A first connection passage and a first recovery passage branch from the first return passage at a first branching point. The first connection passage is connected to the medium pressure passage. The first recovery passage is connected to the fuel tank. A 15 second connection passage and a second recovery passage branch from the second return passage at a second branching point. The second connection passage, like the first connection passage, is connected to the medium pressure passage. The second recovery passage, like the first 20 recovery passage, is connected to the fuel tank. A first back pressure valve is arranged in the first recovery passage, and a second back pressure valve is arranged in the second recovery passage. The first back 25 pressure valve is capable of applying back pressure to the first injectors, and the second back pressure valve is capable of applying back pressure to the second injectors. Additionally, a first check valve is arranged in the first connection passage, and a second check valve is arranged in 30 the second connection passage. The first check valve permits the supply of fuel from the medium pressure passage to the first return passage and impedes the supply of fuel from the first return passage to the medium pressure passage. The second check valve permits the supply of fuel from the 35 medium pressure passage to the second return passage and 2 P3P2012416AU impedes the supply of fuel from the second return passage to the medium pressure passage. A valve opening pressure of the first check valve is set to be lower than the back pressure of the first back pressure valve. A valve opening pressure 5 of the second check valve is set to be lower than the back pressure of the second back pressure valve. In the fuel supply device of the document, fuel is drawn from the fuel tank by the medium pressure pump and delivered 10 to the high pressure pump. Then, the fuel, which is delivered to the medium pressure passage, is adjusted to a higher pressure than the medium pressure by the high pressure pump and delivered to the common rail through the high pressure passage. The high-pressure fuel, which is 15 accumulated in the common rail, is injected from the first injectors into the first combustion chambers of the first cylinder group in the engine and from the second injectors into the second combustion chambers of the second cylinder group in the engine. 20 The surplus fuel in each first injector is transported to the fuel tank through the first return passage and the first recovery passage. The surplus fuel in each second injector is transported to the fuel tank through the second 25 return passage and the second recovery passage. Under this situation, the pressure of the first return passage side acts against the pressure of the fuel tank side at the first back pressure valve, and the pressure of the 30 second return passage side acts against the pressure of the fuel tank side at the second back pressure valve. The first back pressure valve opens when the pressure difference between the pressure of the first return passage side and the pressure of the fuel tank side becomes larger than the 35 back pressure that is set by an urging force of a spring of 3 P3P2012416AU the first back pressure valve. The second back pressure valve opens when the pressure difference between the pressure of the second return passage side and the pressure of the fuel tank side becomes larger than the back pressure 5 that is set by an urging force of a spring of the second back pressure valve. In this manner, the surplus fuel, which is exposed to the atmospheric pressure through the first back pressure valve and the second back pressure valve, is returned to the fuel tank. 10 During operation of the engine, when the fuel tank becomes empty, that is, when fuel runs out, bubbles enter the first return passage of the first injectors, which are piezo-injectors, and the second return passage of the second 15 injectors, which are piezo-injectors. This decreases the pressures of the first return passage and the second return passage. In this condition, when the tank is refilled with fuel and the engine is restarted, the first injectors and the second injectors cannot inject fuel. 20 Therefore, in the fuel supply device of the document, when the fuel tank is refilled with fuel and the engine is restarted, the medium pressure pump supplies fuel to the first return passage through the first connection passage 25 and supplies fuel to the second return passage through the second connection passage. In the first check valve, the pressure of the medium pressure pump side in the first connection passage acts against the pressure of the first return passage side. In the second check valve, the pressure 30 of the medium pressure pump side in the second connection passage acts against the pressure of the second return passage side. Then, when the pressure difference between the pressure of the medium pressure pump side and the pressure of the first return passage side becomes larger than the 35 valve opening pressure that is set by the urging force of 4 P3P201241GAU the spring of the first check valve, the first check valve opens. When the pressure difference between the pressure of the medium pressure pump side and the pressure of the second return passage side becomes larger than the valve opening 5 pressure that is set by the urging force of the spring of the second check valve, the second check valve opens. In this manner, the fresh fuel is supplied to the first return passage under a pressure that is higher than the valve opening pressure of the first check valve, and supplied to 10 the second return passage under a pressure that is higher than the valve opening pressure of the second check valve. The valve opening pressure of the first check valve is set to be lower than the back pressure of the first back 15 pressure valve, and the valve opening pressure of the second check valve is set to be lower than the back pressure of the second back pressure valve. Therefore, the back pressure of the first back pressure valve acts on the fuel in the first return passage, and the back pressure of the second back 20 pressure valve acts on the fuel in the second return passage. This obtains the pressure of the first return passage, which is needed for fuel injection from the first injector, and the pressure of the second return passage, which is needed for fuel injection from the second injector. 25 However, when the engine is restarted after fuel replenishment, high-pressure fuel, which is supplied by the high pressure pump, exists in the common rail, the first high pressure passage, and the second high pressure passage. Thus, the fuel supply device of the document enables the 30 first injectors and the second injectors to inject fuel again. PRIOR ART DOCUMENT 35 PATENT DOCUMENT 5 P3P2 012416AU Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-102990 5 SUMMARY OF THE INVENTION PROBLEMS THAT ARE TO BE SOLVED BY THE INVENTION The fuel supply device in Japanese Laid-Open Patent 10 Publication No. 2009-102990 includes the first return passage, which connects the first cylinder group to the fuel tank, and the second return passage, which connects the second cylinder group to the fuel tank. Further, the first back pressure valve and the first check valve are provided 15 for the first return passage, and the second back pressure valve and the second check valve are provided for the second return passage. Thus, in the above fuel supply device, a volume 20 difference and a pressure loss difference are easily produced between the first return passage and the second return passage. A valve opening pressure difference and a flow characteristic difference are easily produced between the first check valve and the second check valve. A back 25 pressure difference and a flow characteristic difference are easily produced between the first back pressure valve and the second pressure valve. Consequently, in the above fuel supply device, an injection time difference and an injection amount difference are easily produced between the first 30 injector and the second injector. This may influence the engine starting performance, fuel efficiency, output, an emission performance, and so on. To avoid such situations, a control may be executed so that priority for injection is given to one of the first injector and the second injector 35 over the other one. Alternatively, a control may be executed 6 P3P2012416AU to correct the difference in the injection amount between the first injectors and the second injectors. Further, the tolerance of components may be decreased. However, these actions would raise the manufacturing costs. In the fuel 5 supply device of document 1, fuel injection is controlled so that the first injectors have priority over the second injectors by setting the valve opening pressure of the first check valve, which is arranged in the first connection passage, to be lower than the valve opening pressure of the 10 second check valve, which is arranged in the second connection passage. As a result, injection always needs to be started from the first cylinder group. The above fuel supply device includes a large number of 15 components. This increases the fuel supply device in size and weight, and raises component costs and management costs. Further, an increase in the number of assembling steps raises the manufacturing costs. It is thus difficult to install the fuel supply device in a vehicle or the like. 20 MEANS FOR SOLVING THE PROBLEM It is an object of the present disclosure to provide a fuel supply device capable of starting an engine with high 25 quality while lowering the manufacturing costs and obtaining superior properties for installation in a vehicle or the like. In one aspect of the present disclosure, a fuel supply 30 device is connected to a plurality of first injectors and a plurality of second injectors. The fuel supply device supplies fuel from a fuel tank to each of the first injectors and each of the second injectors. The first injectors inject the fuel into a first fuel chamber of a 35 first cylinder group of an engine. The second injectors 7 P3P2012416AU inject the fuel into a second fuel chamber of a second cylinder group of the engine. Each of the first injectors and each of the second injectors are piezo-injectors. The fuel supply device includes a medium pressure pump, a high 5 pressure pump, a high pressure passage, a first return passage, a second return passage, a recovery passage, a back pressure valve, a medium pressure passage, a connection passage, and a check valve. The medium pressure pump is capable of adjusting the fuel from the fuel tank to a medium 10 pressure and delivering the medium-pressure fuel. The high pressure pump is capable of adjusting the fuel to a high pressure, which is higher than the medium pressure, and delivering the high-pressure fuel. The high pressure passage connects the high pressure pump to each of the first 15 injectors and each of the second injectors. The first return passage is connected to each of the first injectors and capable of transporting surplus fuel from each of the first injectors. The second return passage is connected to each of the second injectors and capable of transporting surplus 20 fuel from each of the second injectors. The recovery passage joins the first return passage and the second return passage at a junction and returns the surplus fuel to the fuel tank. The back pressure valve is arranged in the recovery passage and capable of applying a back pressure to each of the first 25 injectors and each of the second injectors. The medium pressure passage is connected to the medium pressure pump. The connection passage connects the medium pressure passage to one of the first return passage, the second return passage, and a portion of the recovery passage upstream from 30 the back pressure valve. The check valve is arranged in the connection passage and has a lower opening valve pressure than the back pressure. The check valve permits the supply of fuel from the medium pressure passage to the first return passage and the second return passage and impedes the 35 opposite. 8 P3P2012416AU The fuel supply device of this aspect employs the recovery passage that joins the first return passage and the second return passage at the junction, and returns the 5 surplus fuel to the fuel tank through the recovery passage. Therefore, even if a volume difference and a pressure loss difference exists between the first return passage and the second return passage, a volume difference and a pressure loss difference do not exist in the first recovery passage. 10 That is, in this aspect, the influence of the return passages on the recovery passage is smaller than that in document 1. In this aspect, the back pressure valve is arranged in 15 the recovery passage that joins the first return passage and the second return passage at the junction. As a comparative example, if different back pressure valves are arranged in the first return passage and the second return passage, a back pressure difference and a flow characteristic 20 difference may be produced between the two back pressure valves. In contrast, in the fuel supply device of the present disclosure, such a back pressure difference and a flow characteristic difference do not exist. 25 In this aspect, the check valve, which has a lower opening valve pressure than the back pressure, is arranged in the connection passage, which is connected to the medium pressure passage. The medium pressure passage is connected, through the connection passage, to one of the first return 30 passage, the second return passage, and the portion of the recovery passage upstream from the back pressure valve. In document 1, different check valves are arranged in two return passages. In contrast, the fuel supply device of the present disclosure includes only one return passage with the 35 single check valve. Therefore, an opening valve pressure 9 P3P2012416AU difference and a flow characteristic difference that are produced when a plurality of check valves are used do not exist in this aspect. 5 This limits the injection time difference and the injection amount difference of the first injector and the second injector. Therefore, the engine easily achieves superior starting capability, fuel efficiency, output, emission properties, and so on. In the fuel supply device of 10 the present disclosure, there is no need for a complicated control of the injectors. This allows for a relatively moderate tolerance for components. Thus, the manufacturing costs may be reduced. 15 In this aspect, the fuel supply device includes a small number of components. This allows for the fuel supply device to be reduced in size and weight. In addition to decreasing component costs and management costs, a decrease in the number of assembling steps lowers the manufacturing costs. 20 This realizes a fuel supply device having superior properties for installation in a vehicle or the like. Therefore, in the fuel supply device of this aspect, the engine may be started with high quality while lowering the 25 manufacturing costs and obtaining superior properties for installation in a vehicle or the like. In the present disclosure, in addition to a diesel engine, a gasoline engine may be used as a multicylinder 30 engine. When the fuel supply device in this aspect is used in a diesel engine, a common rail may be arranged between the high pressure pump and each first injector and between the high pressure pump and each second injector. 35 In one aspect of the present disclosure, the engine 10 P3P2012416AU includes an addition valve that adds the fuel to raise the exhaust temperature of the engine. The medium pressure passage connects the medium pressure pump to the addition valve. A filter in an exhaust gas purification catalyst may 5 collect particulate matter, which is emitted by the engine. In this situation, when a certain amount of particulate matter is deposited in the filter, the addition valve adds fuel to the exhaust gas to raise the temperature of the filter. This burns the deposited particulate matter and 10 regenerates the filter. In this aspect, the medium pressure pump is connected to the addition valve through the medium pressure passage. This eliminates the need for a special medium pressure passage that connects the medium pressure pump to the addition valve, and allows for a smaller fuel 15 supply device to be realized. In one aspect of the present disclosure, one of the first return passage and the second return passage includes a first portion, which extends from the check valve toward 20 each of the first injectors, and a second portion, which extends from the check valve toward each of the second injectors. The longer one of the first portion and the second portion has a larger cross-sectional passage area than the other one of the first portion and the second 25 portion. In one aspect of the present disclosure, one of the first return passage and the second return passage is connected to the connection passage at a connecting point. 30 The first portion extends from the connecting point toward each of the first injectors, and the second portion extends from the connecting point toward each of the second injectors. When the first portion is longer than the second portion, the cross-sectional passage area of the first 35 portion is larger than that of the second portion. When the 11 P3P2012416AU second portion is longer than the first portion, the cross sectional passage area of the second portion is larger than that of the first portion. 5 In one aspect of the present invention, the cross sectional passage area of the connection passage is larger than that of the shorter one of the first portion and the second portion. In these aspects, in addition to the advantages that the above fuel supply device obtains, the 10 volume difference and the pressure loss difference between the first return passage and the second return passage may be further reduced from that in document 1. In one aspect of the present invention, the first return 15 passage and the second return passage are configured so that the length from the check valve to each of the first injectors and the length from the check valve to each of the second injectors are the same. In this aspect, the volume difference and the pressure loss difference between the 20 first return passage and the second return passage may be further reduced from that in document 1. This allows for a smaller fuel supply device to be realized. BRIEF DESCRIPTION OF THE DRAWINGS 25 Fig. 1 is a schematic diagram showing the structure of a fuel supply device of a first embodiment. Fig. 2 is a schematic diagram showing the structure of a 30 fuel supply device of a second embodiment. Fig. 3 is a schematic diagram showing the structure of a fuel supply device of a third embodiment. 35 EMBODIMENTS OF THE INVENTION 12 P3P2012416AU First to third embodiments of the present disclosure will now be described with reference to the drawings. 5 First Embodiment As shown in Fig. 1, a fuel supply device of a first embodiment is connected to four first injectors la to Id and a plurality of second injectors le to lh. The first 10 injectors la to 1d inject fuel into each first combustion chamber of a first cylinder group L in a multicylinder diesel engine. The second injectors le to lh inject fuel into each second combustion chamber of a second cylinder group R in the diesel engine. The fuel supply device of the 15 first embodiment supplies fuel from a fuel tank 3 to the first injectors la to id and the second injectors le to lh. Each of the first injectors la to ld and the second injectors le to lh is a piezo-injector, which employs a piezo element, and functions as an actuator that opens and 20 closes an injection hole. In the fuel supply device of the first embodiment, the fuel tank 3 is connected to a supply pump 5 through a supply pipe 7. A fuel filter 9 is arranged in the supply pipe 7. 25 The supply pump 5 incorporates a medium pressure pump 5a and a high pressure pump 5b. The medium pressure pump Sa adjusts the fuel from the fuel tank 3 to a medium pressure of a few megapascals, and 30 delivers the fuel to medium pressure pump pipes 5c and 5d. The high pressure pump 5b is connected to the medium pressure pump Sa through the medium pressure pump pipe Sc. The high pressure pump 5b is capable of adjusting the fuel, which is delivered through the medium pressure pump pipe 5c, 35 to a high pressure of a few hundred megapascals. A primary 13 P3P201241GAU high pressure pipe 11 is in communication with a discharge unit of the high pressure pump 5b. A medium pressure pipe 13 is connected to the medium pressure pump Sa through the medium pressure pump pipe 5d. 5 A first common rail 15 is connected to the high pressure pump 5b through the primary high pressure pipe 11. A second common rail 19 is connected to the first common rail 15 through a secondary high pressure pipe 17. The first common 10 rail 15 is connected to the first injectors la to id through the first high pressure pipes 21a to 21d, respectively. The second common rail 19 is connected to the second injectors le to lh through the second high pressure pipes 21e to 21h, respectively. The primary high pressure pipe 11, the first 15 common rail 15, and the first high pressure pipes 21a to 21d correspond to a first high pressure passage. The primary high pressure pipe 11, the first common rail 15, the secondary high pressure pipe 17, the second common rail 19, and the second high pressure pipes 21e to 21h correspond to 20 a second high pressure passage. The first high pressure passage and the second high pressure passage correspond to a high pressure passage through which fuel flows under a high pressure. 25 A first medium pressure pipe 13a and a connection pipe 13b branch from the medium pressure pipe 13 at a first branching point A. A second medium pressure pipe 13c and a first connection pipe 31a branch from the connection pipe 13b at a second branching point B. A first addition injector 30 23a, which serves as a first addition valve, is connected to the first medium pressure pipe 13a. A second addition injector 23b, which serves as a second addition valve, is connected to the second medium pressure pipe 13c. The first addition injector 23a and the second addition injector 23b 35 are each arranged at the upstream side of a diesel 14 P3P2012416AU particulate filter (DPF) in an exhaust gas purification catalyst. The medium pressure pump pipes 5c and 5d, the medium pressure pipe 13, the first medium pressure pipe 13a, the second medium pressure pipe 13c, and the connection pipe 5 13b correspond to a medium pressure passage through which fuel flows under a medium pressure. Each of the first injectors la to 1d is connected to a first return pipe 25 that defines a first return passage. 10 Each of the second injectors le to lh is connected to a second return pipe 27 that defines a second return passage. The first return pipe 25 is connected to a second connection pipe 31b at a connecting point C. The first return pipe 25 is connected to the second return pipe 27 and a first 15 recovery pipe 39 at a junction D, which is downstream of the connecting point C. The first recovery pipe 39 extends from the junction D to a back pressure valve 29. The first return pipe 25, the second return pipe 27, and the first recovery pipe 39 form a return passage, which transports fuel. 20 The first connection pipe 31a and the second connection pipe 31b form a connection passage, which connects the medium pressure passage to the return passage. A check valve 33 is arranged between the first connection pipe 31a and the 25 second connection pipe 31b. The check valve 33 permits the supply of fuel from the first connection pipe 31a to the second connection pipe 31b and impedes the supply of fuel from the second connection pipe 31b to the first connection pipe 31a. The opening valve pressure of the check valve 33 30 is set to be lower than the pressure of the return passage. The first return pipe 25 is capable of transporting surplus fuel from the first injectors la to ld. Also, the second return pipe 27 is capable of transporting surplus 35 fuel from the second injectors le to lh. The back pressure 15 P3P2012416AU valve 29 is capable of applying a back pressure, which is used to operate the first injectors la to ld and the second injectors le to lh. The downstream side of the back pressure valve 29 is connected to the second recovery pipe 37. The 5 first recovery pipe 39 and the second recovery pipe 37 form a recovery passage, which returns fuel to the fuel tank 3. The supply pump 5 is connected to the second recovery pipe 37 through a drain pipe 35a. The drain pipe 35a is connected to the fuel tank 3 through a portion of the second recovery 10 pipe 37. Drain pipes 35b and 35c are connected to the second common rail 19. The second common rail 19 is connected to the drain pipe 35a through the drain pipe 35b, and also connected to the drain pipe 35a through the drain pipe 35c. 15 In the fuel supply device of the first embodiment, fuel from the fuel tank 3 is drawn through the supply pipe 7 into the medium pressure pump Sa of the supply pump 5. During this process, foreign matter is removed from the fuel by the fuel filter 9. The fuel, which is drawn by the medium 20 pressure pump Sa, is delivered to the high pressure pump 5b of the supply pump 5 and adjusted to a high pressure. The high-pressure fuel is delivered into the first common rail 15 through the primary high pressure pipe 11. The fuel from the first common rail 15 is delivered into the second common 25 rail 19 through the secondary high pressure pipe 17. The high-pressure fuel, which is accumulated in the first common rail 15, is injected into the first combustion chambers of the first cylinder group L in the engine by the 30 first injectors la to ld. The high-pressure fuel, which is accumulated in the second common rail 19, is injected into the second combustion chambers of the second cylinder group R in the engine by the second injectors le to lh. 35 The surplus fuel in the first injectors la to ld is 16 P3P2012416AU transported to the fuel tank 3 after passing through the first return pipe 25, the first recovery pipe 39, the back pressure valve 29, and the second recovery pipe 37. The surplus fuel in the second injectors le to lh is transported 5 to the fuel tank 3 after passing through the second return pipe 27, the first recovery pipe 39, the back pressure valve 29, and the second recovery pipe 37. Under this situation, in the back pressure valve 29, the 10 pressure at the side of the first recovery pipe 39 acts against the pressure at the side of the fuel tank 3. The back pressure valve 29 opens when the pressure difference between side of the first recovery pipe 39 and the side of the fuel tank 3 becomes larger than the pressure used to 15 operate the first injectors la to id and the second injectors le to lh. In this manner, the surplus fuel is exposed to the atmospheric pressure through the back pressure valve 29 and returned to the fuel tank 3. 20 During operation of the engine, when the fuel tank becomes empty, that is, when fuel runs out, bubbles enter the first return passage, which is connected to the first injectors la to ld, and the second return passage, which is connected to the second injectors le to lh. The first 25 injectors la to id and the second injectors le to le are piezo-injectors. This decreases the pressures of the first return passage and the second return passage. In this condition, when the tank is refilled with fuel and the engine is restarted, the first injectors la to id and the 30 second injectors le to lh cannot inject fuel. Therefore, in the fuel supply device of the first embodiment, when the fuel tank is refilled with fuel and the engine is restarted, the medium pressure pump 5a supplies 35 fuel to the first return pipe 25 through the connection pipe 17 P3P2012416AU 13b, the first connection pipe 31a, and the second connection pipe 31b. The fuel, which is supplied to the first return pipe 25, is also supplied to the second return pipe 27 from the junction D. 5 Under this situation, in the check valve 33, the pressure at the side of the first connection pipe 31a connected to the medium pressure pump 5a acts against the pressure at the side of the second connection pipe 31b 10 connected to the first return pipe 25. The check valve 33 opens when the pressure at the side of the medium pressure pump 5a, that is, the side of the first connection pipe 31a, becomes larger than a force obtained by adding the pressure at the side of the first return pipe 25, that is, the side 15 of the second connection pipe 31b, to the spring force of the check valve 33. In this manner, the fresh fuel from the fuel tank 3 is supplied to the first return pipe 25 and the second return pipe 27 under a pressure that is higher than the valve opening pressure of the check valve 33. 20 The advantages of this embodiment will now be described below. (1) The opening valve pressure of the check valve 33 is 25 set to be lower than the back pressure of the back pressure valve 29, that is, the pressure that opens the back pressure valve 29. Thus, the back pressure of the back pressure valve 29 acts on the fuel in the first return pipe 25 and the fuel in the second return pipe 27. This obtains the pressure of 30 the first return pipe 25, which is used for fuel injection from the first injectors la to ld, and the pressure of the second return pipe 27, which is used for fuel injection from the second injectors le to lh. 35 (2) When the fuel tank 3 is refilled with fuel and the 18 1987959v1 P3P201241GAU engine is restarted, the high pressure pump 5b supplies high-pressure fuel to the first common rail 15, the second common rail 19, the first high pressure pipes 21a to 21d, and the second high pressure pipes 21e to 21h. Thus, the 5 fuel supply device of the first embodiment enables the first injectors la to 1d and the second injectors le to lh to inject fuel again. (3) During this process, the fuel supply device of the 10 first embodiment returns the surplus fuel from the first injectors la to ld and the second injectors le to lh to the fuel tank 3 through the first recovery pipe 39 and the second recovery pipe 37. The pipe length L2 from the check valve 33 to the second injectors le to lh is greater than 15 the pipe length L1 from the check valve 33 to the first injectors la to ld. The length Ll is the total of the length of the second connection pipe 31b and the length of the upstream portion of the first return pipe 25 from the connecting point C. The length L2 is the total of the length 20 of the second connection pipe 31b, the length of the downstream portion of the first return pipe 25 from the connecting point C, and the length of the second return pipe 27. In the first embodiment, the first return pipe 25 includes a first portion 25a, which extends from the check 25 valve 33 to the first injectors la to 1d, and a second portion 25b, which extends from the check valve 33 to the second injectors le to lh. Specifically, the first portion 25a extends from the connecting point C toward the first injectors la to 1d, and the length L1 is the total of the 30 length of the second connection pipe 31b and the length of the first portion 25a. The second portion 25b extends from the connecting point C toward the second injectors le to lh, and the length L2 is the total of the length of the second connection pipe 31b, the length of the second portion 25b, 35 and the second return pipe 27. In document 1, a different 19 1987959v1 P3P2012416AU recovery passage is connected to each return passage. In contrast, in the first embodiment, the first return pipe 25 and the second return pipe 27 joined into the single first recovery pipe 39 at junction D. Therefore, even if a volume 5 difference and a pressure loss difference exist between the first return pipe 25 and the second return pipe 27, the volume difference and the pressure loss difference do not exist in the first recovery pipe 39. That is, in the first embodiment, influence of the return passage on the recovery 10 passage is smaller than that in document 1. (4) In the fuel supply device of the first embodiment, the back pressure valve 29 is arranged at the downstream side of the first recovery pipe 39, that is, the side of the 15 fuel tank 3. As a comparative example, if different back pressure valves are arranged in the first return passage and the second return passage, a back pressure difference and a flow characteristic difference may be produced between the two back pressure valves. In contrast, in the first 20 embodiment, only a single back pressure valve 29 is arranged in the first recovery pipe 39 that is a portion of a single recovery passage. Therefore, since the first embodiment employs only a single back pressure valve 29, a back pressure difference and a flow characteristic difference do 25 not exist. (5) Further, in the fuel supply device of the first embodiment, the check valve 33, which has a lower opening valve pressure than the back pressure of the back pressure 30 valve 29, is arranged between the first connection pipe 31a and the second connection pipe 31b. Document 1 uses two return passages, each of which includes a check valve. However, the first embodiment uses only the single return passage, which includes the single check valve 33. 35 Therefore, in the first embodiment, a valve opening pressure 20 1987959vl P3P2012416AU difference and a flow characteristic difference, which are produced when a plurality of check valves are employed, do not exist. 5 (6) In this manner, the fuel supply device of the first embodiment includes the single check valve 33 and the single back pressure valve 29. This limits the injection time difference and the injection amount difference of the first injectors la to ld and the second injectors le to lh. 10 Therefore, the engine easily achieves superior starting capability, fuel efficiency, output, emission properties, and so on. Consequently, in the fuel supply device of the first embodiment, there is no need for a complicated control of the injectors. This allows for a relatively moderate 15 tolerance for components. Thus, the manufacturing costs may be reduced. (7) The fuel supply device of the first embodiment includes a small number of components. This allows for the 20 fuel supply device to be reduced in size and weight. In addition to decreasing component costs and management costs, a decrease in the number of assembling steps lowers the manufacturing costs. This realizes a fuel supply device having superior properties for installation in a vehicle or 25 the like. Consequently, according to the fuel supply device of the first embodiment, the engine may be started with high quality while lowering the manufacturing costs and obtaining 30 superior properties for installation in a vehicle or the like. (8) The fuel supply device of the first embodiment connects the first addition injector 23a to the first medium 35 pressure pipe 13a, and the second addition injector 23b to 21 1987959v1 P3P2012416AU the second medium pressure pipe 13c. Thus, without using a special medium pressure passage, when a certain amount of particulate matter is deposited in a DPF, the first addition injector 23a and the second addition injector 23b add fuel 5 to the exhaust gas to raise the temperature of the DPF. In other words, in the first embodiment, the medium pressure pump 5a is connected to the addition valves, that is, the first addition injector 23a and the second addition injector 23b, through the medium pressure passage. This eliminates 10 the need for a special medium pressure passage that connects the medium pressure pump 5a to the addition valves. Thus, the first embodiment realizes a smaller fuel supply device. Second Embodiment 15 As shown in Fig. 2, in the fuel supply device of the second embodiment, like the first embodiment, the pipe length L2 from the check valve 33 to the second injectors le to lh is greater than the pipe length Ll from the check 20 valve 33 to the first injectors la to ld. However, in the fuel supply device of the second embodiment, a cross-sectional passage area of the second portion 25b of the first return pipe 25, which is located 25 closer to the first recovery pipe 39 than the connecting point C, and a cross-sectional passage area of the second return pipe 27a are larger than a cross-sectional passage area of the first portion 25a of the first return pipe 25 between the connecting point C and the first injectors la to 30 ld. Additionally, the cross-sectional passage area of the second connection pipe 31c and the cross-sectional passage area of the first recovery pipe 39a are the largest among the first return pipe 25, the second return pipe 27a, the first recovery pipe 39a, and the second connection pipe 31c. 35 Otherwise, the structure of the second embodiment is to the 22 1987959v1 P3P2012416AU same as the first embodiment. (9) Thus, in addition to the advantages of the fuel supply device of the first embodiment, the fuel supply 5 device of the second embodiment allows for further reduction in the volume difference and the pressure loss difference between the first return pipe 25 and the second return pipe 27a as compared with document 1. 10 Third Embodiment As shown in Fig. 3, in the fuel supply device of the third embodiment, the second connection pipe 31d is connected to the first return pipe 25 at a connecting point 15 E. The first return pipe 25 and the second return pipe 27 are configured so that a length L3 from the check valve 33 to the first injectors la to ld and a length L4 from the check valve 33 to the second injectors le to lh are the same. Otherwise, the structure of the third embodiment is 20 the same as the first embodiment. (10) Thus, the fuel supply device of the third embodiment allows for further reduction in the volume difference and the pressure loss difference between the 25 first return pipe 25 and the second return pipe 27a as compared with document 1. The present disclosure is described through the first to third embodiments. However, the present disclosure is not 30 restricted to the first to third embodiments. The present disclosure may be modified within the scope and equivalence of the appended claims. For example, the connection passage does not have to be 35 connected to the first return pipe 25. Instead, the 23 1987959vl P3P2012416AU connection passage may be connected to the second return pipe 27 and the first recovery pipes 39 and 39a. The present disclosure has industrial applicability and 5 may be applied to a vehicle or the like that includes a diesel engine. In this specification, the terms "comprise", "comprises", "comprising" or similar terms are intended to 10 mean a non-exclusive inclusion, such that a system, method or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed. 15 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge. 20 24 1987959v1 P3P2012416AU DESCRIPTION OF REFERENCE SIMBOLS 5 L: First Cylinder Group la to ld: First Injector R: Second Cylinder Group le to lh: Second Injector 3: Fuel Tank 10 5a: Medium Pressure Pump 5b: High Pressure Pump 11, 15, 17, 19, 21a to 21d, 21e to 21h: High Pressure Passage (11: Primary High Pressure Pipe, 15: First Common Rail, 17: Secondary High Pressure Pipe, 19: Second Common 15 Rail, 21a to 21d: First High Pressure Pipe, 21e to 21h: Second High Pressure Pipe) 25: First Return Passage (First Return Pipe) 27: Second Return Passage (Second Return Pipe) D: Junction 20 37, 39: Recovery Passage (37: Second Recovery Pipe, 39: First Recovery Pipe) 29: Back Pressure Valve 5c, 5d, 13, 13a, 13c, 13b: Medium Pressure Passage (5c, 5d: Medium Pressure Pump Pipe, 13a: First Medium Pressure 25 Pipe, 13c: Second Medium Pressure Pipe, 13b: Connection Pipe) 31a, 31b: Connection Passage (First Connection Pipe, Second Connection Pipe) 33: Check Valve 30 23a: First Addition Valve (First Addition Injector) 23b: Second Addition Valve (Second Addition Injector) 25 1987959vl