CN113494401B

CN113494401B - Driving device of fuel pump

Info

Publication number: CN113494401B
Application number: CN202110284497.4A
Authority: CN
Inventors: 楢本和昭
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2020-03-19
Filing date: 2021-03-17
Publication date: 2023-05-26
Anticipated expiration: 2041-03-17
Also published as: JP7047005B2; CN113494401A; JP2021148081A

Abstract

The invention provides a driving device of a fuel pump, which can not wastefully utilize the power of an internal combustion engine, can improve the operation efficiency of the fuel pump, and ensures that the pumping flow rate of the fuel pump is not more or less than the required flow rate. The present invention is a fuel pump driving device for driving a high-pressure fuel pump (5) that pumps fuel to a fuel injection valve (11) side after pressurizing the fuel using power of an internal combustion engine (3), comprising: a transmission (4) provided between a crankshaft (3 a) of the internal combustion engine (3) and a drive shaft (22 a) of the high-pressure fuel pump (5) and transmitting the power of the internal combustion engine (3) to the drive shaft (22 a) after shifting; and a speed ratio setting unit that sets a speed ratio (gear stage) of the transmission (4) such that a pump-out flow rate QFPMP of the fuel pumped out from the high-pressure fuel pump (5) exceeds a required flow rate QFPMD of the fuel required by the internal combustion engine (3) (fig. 5).

Description

Driving device of fuel pump

Technical Field

The present invention relates to a driving device for a fuel pump for driving a fuel pump for supplying fuel to a fuel injection valve after pressurizing the fuel in an internal combustion engine.

Background

As a conventional driving device for a fuel pump, for example, a structure disclosed in patent document 1 is known. In patent document 1, the fuel pump is a rotary fuel pump, and is coupled to a crankshaft of an internal combustion engine, and the fuel pump is driven to rotate by power of the internal combustion engine. Specifically, the driving device includes: a crankshaft sprocket connected to the crankshaft via a drive gear and a driven gear; a pump drive sprocket disposed in the vicinity of the camshaft and coupled to the crankshaft sprocket via a timing chain; and a drive shaft which is provided concentrically with the pump drive sprocket and is coupled to the pump shaft of the fuel pump.

In this configuration, when the internal combustion engine is operated to rotate the crankshaft, the power of the internal combustion engine is transmitted to the drive shaft via the crankshaft sprocket, the timing chain, and the pump drive sprocket, and is further transmitted from the drive shaft to the pump shaft of the fuel pump, thereby driving the fuel pump. According to the above configuration, the fuel pump is shifted with respect to the crankshaft by a predetermined speed ratio determined by the speed ratio of the drive gear to the driven gear and the speed ratio of the crankshaft sprocket to the pump drive sprocket.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2010-255529

Disclosure of Invention

Problems to be solved by the invention

Fig. 9 shows a normal fuel flow rate characteristic corresponding to the rotation speed (engine speed) NE of the internal combustion engine. First, the required flow rate QFCMD of fuel required for an internal combustion engine (for example, a supercharged engine) increases sharply in a low rotation speed region as the engine rotation speed NE increases, while decreases gradually in a medium-high rotation speed region. In contrast, the pump-out flow rate QFPMP0 of the fuel pump increases sharply in the low rotation speed region and increases gradually in the medium-high rotation speed region as the engine rotation speed NE increases.

According to the above characteristics, the pump-out flow rate QFPMP0 is very close to the required flow rate QFCMD (with a small margin) in the vicinity of the peak rotational speed NEP in the low rotational speed region corresponding to the peak value of the required flow rate QFCMD. Therefore, the fuel pump specification (such as the build and the capacity) is set so that the pump-out flow rate QFPMP0 reliably exceeds the required flow rate QFCMD around the peak rotation speed NEP. However, in this case, in the medium-high rotation speed region, the pump-out flow rate QFPMP0 greatly exceeds the required flow rate QFCMD, the margin becomes excessively large, the power of the internal combustion engine is wastefully consumed, and the operation efficiency of the fuel pump is lowered.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a driving device for a fuel pump that can improve the operation efficiency of the fuel pump by not wastefully using the power of an internal combustion engine and can ensure that the pump-out flow rate of the fuel pump is not too high relative to the required flow rate.

Means for solving the problems

In order to achieve the object, the invention according to claim 1 is a fuel pump driving device for driving a fuel pump (in the embodiment (hereinafter, the same applies to the present invention) that pumps fuel to a fuel injection valve 11 side after pressurizing the fuel using power of an internal combustion engine 3, comprising: a transmission (transmission 4, continuously variable transmission 4A) provided between a crankshaft 3a of the internal combustion engine 3 and a drive shaft 22a of the fuel pump, for shifting the power of the internal combustion engine 3 and transmitting the shifted power to the drive shaft 22a; and a speed ratio setting unit (ECU 2, fig. 5, fig. 8) that sets a speed ratio (gear stage, target speed ratio RTTGT) of the transmission such that a pump-out flow rate QFPMP of the fuel pumped out from the fuel pump exceeds a required flow rate QFCMD of the fuel required by the internal combustion engine 3.

In this driving device, the fuel pump is driven using the power of the internal combustion engine. Further, a transmission is provided between a crankshaft of the internal combustion engine and a drive shaft of the fuel pump, and power of the internal combustion engine is transmitted to the drive shaft of the fuel pump after being changed in speed by the transmission. According to the present invention, the gear ratio of the transmission is set such that the pump-out flow rate of the fuel pumped out from the fuel pump exceeds the required flow rate of the fuel required for the internal combustion engine. According to such a setting of the gear ratio, the power of the internal combustion engine can be utilized without waste, and the operation efficiency of the fuel pump can be improved, so that the pump-out flow rate of the fuel pump can be ensured to be small and small relative to the required flow rate.

The invention according to claim 2 is the fuel pump driving device according to claim 1, further comprising rotation speed detecting means (crank angle sensor 41) for detecting the rotation speed NE of the internal combustion engine 3, wherein the gear ratio setting means sets the gear ratio at a lower speed side as the detected rotation speed NE of the internal combustion engine 3 is higher (step 12 of fig. 5 and 8).

As described with reference to fig. 9, in the case where the gear ratio is fixed, the pump-out flow rate of the fuel pump approaches the required flow rate from the internal combustion engine in the low rotation speed region, and the margin with respect to the required flow rate is small, whereas in the medium-high rotation speed region, the margin with respect to the required flow rate is large. In view of such a relationship, according to this configuration, the higher the detected rotational speed of the internal combustion engine is, the lower the speed ratio is set. Thus, the higher the rotational speed of the internal combustion engine, that is, the larger the margin of the pump-out flow rate with respect to the required flow rate, the lower the speed ratio is set. Therefore, according to this margin, the pump-out flow rate exceeding the required flow rate can be ensured while reducing the power of the internal combustion engine for driving the fuel pump and the actual pump-out flow rate, and the above-described effects of claim 1 can be more favorably obtained.

The invention according to claim 3 is the fuel pump driving device according to claim 2, characterized in that the transmission is constituted by a stepped transmission (transmission 4) that changes the transmission ratio stepwise, and the transmission ratio setting means sets the transmission ratio to a high speed when the rotation speed NE of the internal combustion engine 3 is equal to or less than the predetermined rotation speed NREF, and sets the transmission ratio to a low speed when the rotation speed NE of the internal combustion engine 3 is greater than the predetermined rotation speed NREF (fig. 5).

According to this configuration, when the rotational speed of the internal combustion engine is equal to or less than the predetermined rotational speed, that is, when the margin of the pump-out flow rate with respect to the required flow rate is small, the speed ratio is set to the high speed stage, whereby the rotational speed of the drive shaft of the fuel pump can be further increased, the pump-out flow rate can be increased, and the margin with respect to the required flow rate can be improved. On the other hand, when the rotational speed of the internal combustion engine is greater than the predetermined rotational speed, that is, when the margin of the pump-out flow rate with respect to the required flow rate is large, the speed ratio is set to the low speed stage, whereby the rotational speed of the drive shaft of the fuel pump can be further reduced, the pump-out flow rate can be reduced, and the margin with respect to the required flow rate can be compressed, so that the fuel pump can be operated more efficiently.

The invention according to claim 4 is the fuel pump driving device according to claim 2, wherein the transmission is constituted by a continuously variable transmission 4A that steplessly changes the transmission ratio, and the transmission ratio setting means steplessly sets a target transmission ratio RTTGT that is a target of the transmission ratio RT in accordance with the rotation speed NE of the internal combustion engine 3 (step 12 of fig. 8).

According to this configuration, the transmission is constituted by a continuously variable transmission, and a target speed ratio, which is a target of the speed ratio, is steplessly set in accordance with the rotation speed of the internal combustion engine. This makes it possible to control the gear ratio of the transmission more finely, to ensure that the pump-out flow rate of the fuel pump is not too high or too low relative to the required flow rate, and to obtain the above-described effects of claim 1 with higher accuracy.

Drawings

Fig. 1 is a diagram schematically showing the overall structure of a fuel pump and a driving device thereof to which the present invention is applied.

Fig. 2 is a diagram schematically showing a transmission.

Fig. 3 is a diagram schematically showing a fuel pump.

Fig. 4 is a block diagram showing a control device that controls the fuel pump.

Fig. 5 is a flowchart showing a setting process of the gear stage of the transmission.

Fig. 6 is a graph schematically showing an image of the pump-out flow rate characteristic of the fuel pump obtained by the control process of fig. 5 together with the comparative example.

Fig. 7 is a diagram schematically showing a continuously variable transmission used as a transmission in embodiment 2.

Fig. 8 is a flowchart showing a process of setting the gear ratio according to embodiment 2.

Fig. 9 is a graph schematically showing the pump-out flow rate characteristics of a fuel pump driven by a conventional driving device.

Description of the reference numerals

1. A drive device of the high-pressure fuel pump;

2 ECU (speed ratio setting unit);

3. an engine (internal combustion engine);

3a crankshaft;

4. a transmission;

4A continuously variable transmission (transmission);

5. a high-pressure fuel pump (fuel pump);

11. a fuel injection valve;

22a drive shaft (drive shaft of fuel pump);

41. crank angle sensor (rotation speed detecting unit);

NE engine speed (engine speed of internal combustion engine);

NREF specifies the rotational speed;

pump-out flow rate of the QFPMP high-pressure fuel pump;

QFCMD requires flow;

RT speed ratio;

RTTGT target speed ratio.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Reference numeral 5 in fig. 1 denotes a high-pressure fuel pump, and the driving device 1 includes an internal combustion engine (hereinafter referred to as an "engine") 3 as a driving source, a transmission 4 that changes the power of the engine 3, and a pump driving cam 22 that is provided on a drive shaft 22a connected to the transmission 4 and drives the high-pressure fuel pump 5.

The engine 3 is, for example, a gasoline engine for a vehicle (not shown), and has a plurality of cylinders (not shown). Each cylinder is provided with a fuel injection valve 11 and a spark plug 12 (see fig. 4), and fuel is directly injected from the fuel injection valve 11 into the combustion chamber. The fuel injection valve 11 is connected to the high-pressure fuel pump 5 via a delivery pipe (not shown), and is supplied with high-pressure fuel from the high-pressure fuel pump 5. The mixed gas generated in the combustion chamber is ignited by a spark from the spark plug 12 to be combusted, thereby generating power of the engine 3, and the power is output from the crankshaft 3 a. The operation of the fuel injection valve 11 and the ignition plug 12 is controlled by the ECU 2 described later.

As shown in fig. 2, the transmission 4 is constituted by a stepped transmission having 2 gear trains and setting the shift stage to a low speed stage or a high speed stage. The transmission 4 includes an input shaft 6 integrally coupled to a crankshaft 3a of the engine 3, a low-speed gear 7L and a high-speed gear 7H disposed on the input shaft 6, an output shaft 8 extending parallel to the input shaft 6 and coupled to a drive shaft 22a of the high-pressure fuel pump 5, and a low-speed gear 9L, a high-speed gear 9H and a synchronizer clutch S disposed on the output shaft 8.

The low-stage gear 7L and the high-stage gear 7H are provided integrally with the input shaft 6, and the number of teeth of the gear 7H is larger than the number of teeth of the gear 7L. On the other hand, the low-speed gear 9L and the high-speed gear 9H are rotatably provided on the output shaft 8. The number of teeth of the gear 9H is smaller than the number of teeth of the gear 9L, and the two

gears

9L, 9H mesh with the

gears

7L, 7H on the input shaft 6, respectively.

The synchronizer clutch S is moved along the output shaft 8 by the sleeve Sa to set the shift stage to the low speed stage or the high speed stage. The operation of the synchronous clutch S is controlled by the ECU 2 (see fig. 4). Specifically, when the gear stage is set to the low gear stage, the synchronizer clutch S is moved to the left in fig. 2, and the low gear stage gear 9L is engaged with the output shaft 8. Thus, the gear 9L and the gear 7L for a low gear stage on the input shaft 6 meshed therewith set the gear stage to a low gear stage. As a result, the power input from the engine 3 to the input shaft 6 is transmitted to the drive shaft 22a of the high-pressure fuel pump 5 after shifting at a high gear ratio (low-speed side gear ratio) determined by the gear ratios of the

gears

7L, 9L.

On the other hand, when the gear stage is set to the high gear stage, the synchronizer clutch S is moved rightward in fig. 2, and the high gear stage gear 9H is engaged with the output shaft 8. Thus, the gear 9H and the gear 7H on the input shaft 6 engaged therewith set the gear stage to the high-low gear stage. As a result, the power of the engine 3 is transmitted to the drive shaft 22a after shifting at a low gear ratio (high-speed-side gear ratio) determined by the gear ratios of the

gears

7H, 9H.

The high-pressure fuel pump 5 uses the engine 3 as a driving source, and further pressurizes the low-pressure fuel pressurized by the low-pressure fuel pump (not shown) to a high pressure and supplies the high-pressure fuel to a delivery pipe of the fuel injection valve 11.

As shown in fig. 3, the high-pressure fuel pump 5 includes a plunger 23 slidably disposed in the pressurizing chamber 21 and engaged with the pump drive cam 22, and a spring 24 for biasing the plunger 23 toward the pump drive cam 22. As described above, the pump drive cam 22 is provided integrally with the drive shaft 22a. With the above configuration and the pump driving cam 22 having 2

cam mountains

22b, 22b equally spaced in the circumferential direction, the plunger 23 reciprocates 2 times in equal cycles in the pressurizing chamber 21 every one rotation of the driving shaft 22a.

Further, a suction port 25 and a pump outlet 26 communicating with the pressurizing chamber 21 are formed in the high-pressure fuel pump 5. Suction port 25 is connected to a low pressure fuel pump, and pump outlet 26 is connected to delivery pipe 16.

A check valve 27 is provided between the pressurizing chamber 21 and the pump outlet 26. The check valve 27 is composed of a valve body 27a and a spring 27b that biases the valve body 27a toward the pressurizing chamber 21. The check valve 27 opens when the pressure of the fuel in the pressurizing chamber 21 is greater than the fuel pressure of the delivery pipe, allowing the fuel to be pumped out of the pump outlet 26, and otherwise closes, preventing backflow of the fuel into the pressurizing chamber 21.

A relief control valve 28 is provided between the pressurizing chamber 21 and the suction port 25. The relief control valve 28 is constituted by a solenoid 29, a plunger 30 having a valve element 31 at its tip and driven by the solenoid 29, a spring 32 for biasing the plunger 30 toward the pressurizing chamber 21, and the like. The relief control valve 28 is normally open, and is maintained in an open state by the urging force of the spring 32 when the solenoid 29 is not energized, so that the suction port 25 is opened, whereas the relief control valve 28 is closed to close the suction port 25 when the solenoid 29 is energized.

In the high-pressure fuel pump 5 having the above configuration, the relief control valve 28 is controlled to be in an open state during the descent of the plunger 23 (when retracting from the pressurizing chamber 21) by the pump driving cam 22 and the spring 24, and thereby fuel is sucked into the pressurizing chamber 21 from the low-pressure fuel pump side through the suction port 25. On the other hand, during the rising of the plunger 23, the relief control valve 28 is closed by energization, and thereby the fuel in the pressurizing chamber 21 is pressurized, and the pressure thereof rises. Then, when the pressure of the fuel in the pressurizing chamber 21 exceeds the fuel pressure of the delivery pipe, the check valve 27 opens, whereby the fuel in the pressurizing chamber 21 is pumped out to the delivery pipe 16 via the pump outlet 26.

When the plunger 23 is lifted, the relief control valve 28 is maintained in an open state until the middle of the lifting, and then when the plunger is closed, the fuel in the pressurizing chamber 21 flows back to the fuel tank (not shown) from the open suction port 25 until the relief control valve 28 is closed. Further, after the relief control valve 28 is closed, the fuel is pumped out at a point in time when the pressure of the fuel in the pressurizing chamber 21 exceeds the fuel pressure of the delivery pipe, according to the closing timing. The operation of the relief control valve 28 described above is controlled by the ECU 2 (see fig. 4).

A crank angle sensor 41 (see fig. 4) is provided to the crankshaft 3a of the engine 3. The crank angle sensor 41 outputs a CRK signal as a pulse signal in accordance with the rotation of the crankshaft 3 a. The CRK signal is generated for each predetermined crank angle (e.g., 30 degrees). The ECU 2 calculates the rotation speed (hereinafter referred to as "engine rotation speed") NE of the engine 3 based on the CRK signal.

Further, a detection signal indicating an operation amount (hereinafter referred to as "accelerator opening") AP of an accelerator pedal (not shown) of the vehicle is input from an accelerator opening sensor 42 to the ECU 2.

The ECU 2 is constituted by a microcomputer (not shown) constituted by CPU, RAM, ROM, an input/output interface (both not shown), and the like. The ECU 2 executes engine control including control of fuel injection by the fuel injection valve 11 and ignition timing by the ignition plug 12 in accordance with a control program stored in the ROM based on detection signals from the above-described sensors 41 to 42, and the like. In the present embodiment, the process of setting the gear stage of the transmission 4 is performed particularly for controlling the pump-out flow rate at which the fuel is pumped out from the high-pressure fuel pump 5.

Fig. 5 shows this gear stage setting process. This process is repeatedly performed at predetermined intervals. In the present process, first, in step 1 (hereinafter, referred to as "S1"), it is determined whether or not the detected engine speed NE is equal to or less than the predetermined speed NREF. The predetermined rotational speed NREF is set to a value close to the peak rotational speed NEP (rotational speed at which the required flow rate QFCMD changes from increasing to decreasing) shown in fig. 6, for example.

When the answer of step 1 is yes and the engine speed NE is in the low rotation speed range equal to or lower than the predetermined rotation speed NREF, the transmission speed of the transmission 4 is set to the high speed (step 2), and the present process is terminated. As described above, by setting the speed change stage of the transmission 4 to the high speed stage in the low speed region, the rotational speed of the drive shaft 22a further increases, and as a result, as shown in fig. 6, the pump-out flow rate QFPMP of the high-pressure fuel pump 5 increases, whereby a margin with respect to the required flow rate QFCMD can be ensured.

On the other hand, when the answer of step 1 is no and the engine speed NE is in the medium-high speed region where the predetermined speed NREF is greater, the speed change stage of the transmission 4 is set to the low speed stage (step 3), and the present process is ended. As a result, the rotational speed of the drive shaft 22a is further reduced by setting the speed change stage of the transmission 4 to the high speed stage in the medium-high speed region, and as a result, as shown in fig. 6, the pump-out flow rate QFPMP of the high-pressure fuel pump 5 is reduced as compared with the conventional pump-out flow rate QFPMP0 (broken line), whereby an excessive margin with respect to the required flow rate QFCMD can be compressed, and the high-pressure fuel pump 5 can be operated more efficiently.

Next, embodiment 2 of the present invention will be described with reference to fig. 7 and 8. Fig. 7 shows a continuously variable transmission 4A serving as a transmission in embodiment 2. The continuously variable transmission 4A is a hydraulic belt type transmission, and includes an input shaft 41 integrally connected to a crankshaft 3a of the engine 3, a drive pulley 42 provided on the input shaft 41, an output shaft 43 extending parallel to the input shaft 41 and connected to the drive shaft 22a, a driven pulley 44 provided on the output shaft 43, a transmission belt 45 wound around the two

pulleys

42 and 44, and DR solenoid valves 46 and DN solenoid valves 47 for changing the pulley widths of the drive pulley 42 and the driven pulley 44, respectively.

The drive pulley 42 has movable portions 42a and fixed portions 42b that face each other. The movable portion 42a is attached to the input shaft 41 so as to be movable in the axial direction and not rotatable, and the fixed portion 42b is fixed to the input shaft 41. The opposing surfaces of the movable portion 42a and the fixed portion 42b are inclined, and V-shaped grooves for winding the transmission belt 45 are formed. The groove width of the groove is changed by controlling the hydraulic pressure supplied to the DR oil chamber 42c on the rear surface side of the movable portion 42a by the DR solenoid valve 46.

The driven pulley 44 is configured in the same manner as the driving pulley 42. That is, the driven pulley 44 has a movable portion 44a and a fixed portion 44b that face each other. The movable portion 44a is attached to the output shaft 43 so as to be movable in the axial direction and not rotatable, and the fixed portion 44b is fixed to the output shaft 43. The movable portion 44a and the fixed portion 44b have inclined surfaces on opposite sides thereof, and a V-shaped groove is formed for winding the transmission belt 45. The groove width of the groove is changed by controlling the hydraulic pressure supplied to the DN oil chamber 44c on the rear surface side of the movable portion 44a by the DN solenoid valve 47. The operations of the DR solenoid valve 46 and the DN solenoid valve 47 are controlled by the ECU 2.

As described above, in the continuously variable transmission 4A, the ECU 2 controls the 2

solenoid valves

46 and 47 to steplessly change the groove widths and the effective diameters of the 2 pulleys 42 and 44, whereby the ratio between the rotation speed NDR of the driving pulley 42 and the rotation speed NDN of the driven pulley 44, that is, the transmission ratio RT (=ndr/NDN), is steplessly set. As a result, the power input from the engine 3 to the input shaft 41 is transmitted to the drive shaft 22a after being steplessly changed in the gear ratio RT.

Next, a process of setting the gear ratio of the continuously variable transmission 4A will be described with reference to fig. 8. This process is repeatedly executed by the ECU 2 at predetermined intervals. In the present process, first, in step 11, the required flow rate QFCMD of the fuel required for the engine 3 is calculated. The required flow rate QFCMD is calculated by, for example, searching a predetermined map (not shown) based on the required torque TRQCMD and the engine speed NE of the engine 3. Further, the required torque TRQCMD is calculated based on the accelerator opening AP and the engine speed NE.

Next, in step 12, a predetermined target speed ratio map is searched for based on the engine speed NE and the above-described required flow rate QFCMD, whereby a target speed ratio RTTGT, which is a target of the speed ratio RT of the continuously variable transmission 4A, is calculated, and the present process is terminated. Although not shown, the target gear ratio map is obtained as follows: from the engine speed NE and the required flow rate QFCMD, a gear ratio that ensures that the pump-out flow rate QFPMP of the high-pressure fuel pump 5 is not too large or too small relative to the required flow rate QFCMD is obtained in advance by experiments or the like, and the gear ratio is mapped as a target gear ratio RTTGT.

Therefore, by setting the target speed ratio RTTGT by the setting process of fig. 8 described above and controlling the speed ratio RT of the continuously variable transmission 4A with this target speed ratio set, as in embodiment 1, a margin of the pump-out flow rate QFPMP of the high-pressure fuel pump 5 with respect to the required flow rate QFCMD can be ensured in the low rotation speed region, and the margin can be compressed in the medium-high rotation speed region, so that the high-pressure fuel pump 5 can be operated more efficiently. Further, since the speed ratio RT is steplessly controlled, the control of the high-pressure fuel pump 5 can be performed more finely and with high accuracy.

The present invention is not limited to the embodiments described above, and can be implemented by various means. For example, as the transmission, a gear type 2-speed transmission 4 is used in embodiment 1, and a hydraulic belt type continuously variable transmission 4A is used in embodiment 2. The invention is not limited thereto and any type and configuration of transmission can be used. For example, the transmission 4 according to embodiment 1 may be increased in the number of shift stages to 3 or more, and an electric belt type continuously variable transmission may be used instead of the hydraulic belt type continuously variable transmission 4A according to embodiment 2.

The high-pressure fuel pump 5 of the embodiment is of a type including the relief control valve 28, but the configuration thereof is arbitrary. The structure of the detail can be changed as appropriate within the scope of the gist of the present invention.

Claims

1. A driving device for a fuel pump which uses power of an internal combustion engine to drive the fuel pump, the fuel pump pressurizing and pumping fuel out to a fuel injection valve side, characterized in that,

the driving device of the fuel pump comprises:

a transmission that is provided between a crankshaft of the internal combustion engine and a drive shaft of the fuel pump, and that changes speed of power of the internal combustion engine and transmits the power to the drive shaft; and

a speed ratio setting unit that sets a speed ratio of the transmission such that a pump-out flow rate of the fuel pumped out from the fuel pump exceeds a required flow rate of the fuel required by the internal combustion engine, and the larger a margin of the pump-out flow rate with respect to the required flow rate, the lower the speed ratio is set.

2. The driving device for a fuel pump according to claim 1, wherein,

the driving device of the fuel pump further includes a rotation speed detecting unit that detects a rotation speed of the internal combustion engine,

the transmission ratio setting unit sets the transmission ratio to a lower speed side as the detected rotational speed of the internal combustion engine is higher.

3. The driving device for a fuel pump according to claim 2, wherein,

the transmission is constituted by a stepped transmission that changes the gear ratio stepwise,

the speed ratio setting means sets the speed ratio to a high speed level when the rotational speed of the internal combustion engine is equal to or less than a predetermined rotational speed, and sets the speed ratio to a low speed level when the rotational speed of the internal combustion engine is greater than the predetermined rotational speed.

4. The driving device for a fuel pump according to claim 2, wherein,

the transmission is constituted by a continuously variable transmission that steplessly changes the gear ratio,

the speed ratio setting unit steplessly sets a target speed ratio that is a target of the speed ratio, based on the rotation speed of the internal combustion engine.