JP2000213433A - Engine with common rail type fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a peak of load to engine by setting a fuel forcedly feeding timing by a high pressure fuel supply pump to a timing in which a cam shaft driving torque is negative. SOLUTION: In a high pressure fuel supply pump in a common rail type fuel injection system, the number of times in which a high pressure fuel is forcedly fed in one combustion cycle is set equal to the number of cylinders, and a fuel forcedly feeding timing by a high pressure fuel supply pump is set to a timing in which a cam torque A required for rotating and driving a cam shaft provided with a cam for driving an inlet valve and an exhaust valve becomes negative. Accordingly, an overlap between a peak of a driving torque B of the high pressure fuel supply pump and a peak of the driving torque A of the cam shaft is prevented to reduce a peak of load, and load for a timing belt used for taking out a motive power from an engine output shaft is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine provided with a common rail type fuel injection system in which fuel is pumped to a common rail by a high pressure fuel supply pump and fuel supplied from the common rail is injected from an injector into a combustion chamber.

[0002]

2. Description of the Related Art Conventionally, a common rail fuel injection system is known as a fuel injection system applied to an engine such as a diesel engine. The common rail fuel injection system stores a working fluid for fuel injection control pressurized to a predetermined pressure by a fuel supply pump in a common rail, and transfers the fuel stored in the common rail from an injector operated by a solenoid valve to a corresponding combustion chamber. This is a fuel injection system capable of increasing the injection pressure and injecting conditions such as fuel injection timing and injection amount to be optimally controlled in accordance with the operating state of the engine. The controller included in the system controls the fuel pressure in the common rail and the operation of the solenoid valve provided in each injector according to the operating condition of the engine so that the pressurized fuel is injected in each injector under the above optimum injection conditions. Is controlling.

An outline of a common rail type fuel injection system will be described with reference to FIG. The fuel supply to the plurality of injectors 1 is supplied from the common rail 2 through a fuel supply pipe 3 constituting a part of a fuel flow path. The fuel sucked up from the fuel tank 4 via the filter 5 by the feed pump 6 and pressurized to a predetermined suction pressure is sent to the high-pressure fuel supply pump 8 through the fuel pipe 7. The high-pressure fuel supply pump 8 is a so-called plunger-type fuel supply pump for a supply, is driven by, for example, an engine, boosts fuel to a high pressure determined based on an operation state, and supplies the fuel to the common rail 2 through a fuel pipe 9. Then, the fuel is stored in the common rail 2 in a state where the pressure is raised to a predetermined pressure. In general, a plurality of injectors 1 are provided according to the type of the engine (the number of cylinders). Under the control of the controller 12, fuel is injected into a corresponding combustion chamber at an optimum injection timing with an optimum fuel injection amount. I do. Since the injection pressure of the fuel injected from the injector 1 is substantially equal to the pressure of the fuel stored in the common rail 2, the pressure in the common rail 2 is controlled to control the injection pressure.

[0004] The fuel relieved from the fuel injection pump 8 by the flow control valve 14 is returned to the fuel tank 4 through the return pipe 10. Further, of the fuel supplied to each injector 1 from the fuel supply pipe 3, the fuel not consumed for injection into the combustion chamber is also supplied to the fuel tank 4 through the return pipe 11.
Is returned to. Controller 12 which is an electronic control unit
The engine includes an engine cylinder discrimination sensor and a crank angle sensor for detecting the engine speed, an accelerator depression sensor for detecting the accelerator depression, a water temperature sensor for detecting the coolant temperature, and a pressure detection for the intake pipe. For example, detection signals from various sensors for detecting an operating state of the engine such as an intake pipe pressure sensor for inputting the information are input. The controller 12 controls a solenoid valve provided in the injector 1 based on these detection signals so that the engine output becomes an optimum output in accordance with the operating state, and controls the fuel injection conditions of the injector 1, that is, the fuel injection. Controls timing and injection volume. The common rail 2 is provided with a pressure sensor 13. The controller 12 receives a detection signal of the fuel pressure in the common rail 2 detected by the pressure sensor 13, and keeps the fuel pressure in the common rail 2 constant or the engine pressure. The discharge flow rate of the high-pressure fuel supply pump 8 is controlled so as to be a predetermined pressure in accordance with the operation state of.

FIG. 3 is a sectional view schematically showing a cylinder head including an engine valve operating mechanism and a combustion chamber intake / exhaust mechanism. The cross section shown in FIG. 3 is a plane orthogonal to a camshaft constituting a valve operating mechanism for a certain cylinder.
Lower surface 20a of cylinder head 20, cylinder block 2
A combustion chamber 22 is formed by one cylinder bore 21a and the top surface of a piston (not shown). Cylinder head 2
0, corresponding to the combustion chamber 22, the intake valve 23 and the exhaust valve 2
4 are provided. The intake valve 23 and the exhaust valve 24 have a valve stem 25 and a valve head 26 attached to the tip of the valve stem 25, respectively. Between the cylinder head 20 and the spring receiver 27 attached to the base end of the valve stem 25, the valve stem 25 is set at the base end, that is, the intake valve 23.
Alternatively, a coil-shaped return spring 28 that urges the exhaust valve 24 in the closing direction is interposed so as to surround the valve stem 25. On the cylinder head 20, a valve mechanism 30 driven by an output shaft of the engine to operate the intake valve 23 and the exhaust valve 24 is provided. The valve train 30 is provided with a pair of mutually parallel camshafts 31 and 32 that are rotationally driven by a drive torque extracted from an output shaft of the engine via, for example, a gear transmission mechanism. Cam 3 that rotates integrally with camshafts 31 and 32, respectively
The tappet 29 between the intake valve 23 and the exhaust valve 24 is pressed by the valves 3 and 34, and the valve stem 25 is pushed in against the urging force of the return spring 28, and the valve head 26 is moved to the valve seats 35 and 3.
6, the intake port 37 or the exhaust port 38 is opened. In order to operate the intake valve 23 and the exhaust valve 24, the cams 33, 34 provided on the camshafts 31, 32 are operated by the valves 23,
It is necessary to apply a driving torque to the camshafts 31 and 32 so as to push the valve stem 25 of the camshaft 24 against the urging force of the return spring 28.

Generally, a three-cylinder diesel engine is
Compared to a cylinder diesel engine, the peak value of the camshaft drive torque tends to be higher. FIG.
At a certain engine speed, the relationship between the crank angle and the driving torque in one combustion cycle of the engine is shown, where the horizontal axis is the crank angle of the first cylinder (0 to 720 degrees) and the vertical axis is the camshaft driving torque. It is a graph.
A camshaft driving torque in a three-cylinder engine is indicated by a solid line D, and a camshaft driving torque in a four-cylinder engine is indicated by a broken line E. The tendency of the three-cylinder diesel engine is that the cam angle at the time of the maximum lift of the intake valve 23 of a certain cylinder and the cam angle at the time of the maximum lift of the exhaust valve 24 of another cylinder are close to each other, and the intake and exhaust are close to each other. This is because the operation timings of the valves 23 and 24 exist substantially independently without interference with each other.

FIG. 10 shows an intake valve 23 and an exhaust valve 2 in a four-cylinder diesel engine with the crank angle as a horizontal axis.
4 is a map showing the operation timing of No. 4. In FIG. 10, # 1 to # 4 indicate the cylinder numbers in which the intake valve 23 or the exhaust valve 24 is open, and the period during which the intake valve 23 or the exhaust valve 24 is open is indicated by the horizontal axis. It is indicated by parallel running lines. With two rotations of the crank, four steps of intake, compression, explosion, and exhaust are sequentially performed from the first cylinder # 1 to the fourth cylinder # 4. As can be seen from FIG. 10, the fourth cylinder # 4
And the opening operation period of the intake valve 23 in the third cylinder # 3 almost overlaps.
Similarly, the operation period of the exhaust valve 24 in the second cylinder # 2, the opening operation period of the intake valve 23 of the fourth cylinder # 4, and the first cylinder # 1
, The opening period of the intake valve 23 of the second cylinder # 2, and the exhaust valve 2 of the third cylinder # 3.
The operation period of No. 4 and the operation period of the intake valve 23 in the first cylinder # 1 almost overlap each other. Therefore, when the cam lift of the exhaust valve 24 of a certain cylinder becomes the maximum,
The timing almost coincides with the time when the cam lift of the intake valve 23 of another cylinder becomes maximum.

However, the profiles of the cams 33 and 34 are cams formed in a convex mountain shape around the rotation. Therefore, in a four-cylinder engine, for example, as shown in FIG. Valve 24 and fourth cylinder #
In the intake valve 23 of No. 4, the camshafts 31, 3 respectively
2 is a drive-side crank angle period for opening the intake valve 23 and the exhaust valve 24 against the spring force of the return spring 28 in a substantially first half period (the exhaust valve 24 of the second cylinder # 2).
During the period of 302 degrees to 366 degrees, and the period of 354 degrees to 404 degrees for the intake valve 23 of the fourth cylinder # 4).
Exhaust valve 24 of fourth cylinder # 4 and intake valve 2 of third cylinder # 3
3 is a period in which the camshafts 31 and 32 are driven by the restoring force of the return springs 28 of the intake and exhaust valves 23 and 24, respectively. In a four-cylinder engine, the driving torque required for the camshafts 31, 32 to drive the intake / exhaust valves 23, 24 of some cylinders is determined by the return of the intake / exhaust valves 23, 24 of other cylinders operating immediately before. Since the torque produced by the restoring force of the spring 28 is offset, the peak value of the driving torque is reduced.

FIG. 5 shows a three-cylinder diesel engine having an intake valve 2 with the crank angle of the first cylinder # 1 as the horizontal axis.
3 is a map showing the operation timings of No. 3 and the exhaust valve 24.
In FIG. 5, the coordinates and symbols are the same as those used in FIG. As can be understood from the operation timings of the intake and exhaust valves 23 and 24 shown in FIG. 5, in the three-cylinder engine, the exhaust valve 24 in the other cylinder is operated almost simultaneously with the operation of the intake valve 23 in one cylinder. Despite the timing, there is substantially no period in which the operating periods of the intake and exhaust valves in different cylinders overlap one after another. Therefore, in a three-cylinder diesel engine, the camshafts 31, 32
When the intake and exhaust valves 23 and 24 in one cylinder are to be operated at substantially the same time, the torque for driving the intake and exhaust valves 23 and 24 is provided by the return spring of the intake and exhaust valves in the immediately preceding other cylinder. As shown in FIG. 4, the camshaft 3 is not offset by the driven torque.
The torque for driving 1, 32 shows a large value.

The graph shown in FIG. 4 is obtained by adjusting the peak of each lift amount at the crank angle marked with a black circle at the operation timing of the intake / exhaust valve shown in FIG.
It is produced by adding and combining the curves shown in FIG. FIG.
Is a graph showing the relationship (curve) between the rotation angle of the camshaft 31, that is, the cam angle and the amount of displacement of the valve stem 25 of the intake valve 23 in the axial direction. The displacement of the valve stem 25 indicates the amount of deflection of the return spring 28 provided on the intake valve 23. FIG. 7 is a graph showing a relationship (curve) between the cam angle and the driving torque of the intake valve 23. The range in which the amount of displacement of the valve stem 25 of the intake valve 23 occurs (from 0 degree cam angle to 1 degree)
20 degrees), the first half of the range
The driving torque is positive, corresponding to the fact that the cam 33 attached to the first valve 1 works to deflect the return spring 28 provided on the intake valve 23. The latter half of the range is from the return spring 28 provided on the intake valve 23 to the camshaft 31.
Corresponds to the fact that is driven to rotate, the driving torque is negative.

FIG. 8 is a graph showing the relationship (curve) between the rotation angle of the camshaft 32, that is, the cam angle and the amount of displacement of the valve stem 25 of the exhaust valve 24 in the axial direction.
The displacement of the valve stem 25 indicates the amount of deflection of the return spring 28 provided on the exhaust valve 24. FIG. 9 is a graph showing the relationship (curve) between the cam angle and the drive torque of the exhaust valve 24. Although there are slight differences in the curves depending on the cam profiles of the cam 34 for operating the exhaust valve 24 and the cam 33 for operating the intake valve 23, FIGS. 8 and 9 show changes similar to FIGS. 6 and 7, respectively. ing.

In the common rail fuel injection system, when fuel is pumped to the common rail 2 by the fuel supply pump 8, it is not necessary to time the compression step and the combustion step of all the cylinders of the engine so as not to overlap at all. Impossible. The compression process and the combustion process are a series of successive operations, and the compression process and the combustion process require 360 degrees of crank angle for one cylinder. In a three-cylinder engine, the timing is designed so that the compression process and the combustion process do not overlap at all.
Although a cam angle of 0 degrees (= 360 degrees × 3) is required, in the case of a four-stroke engine, one cycle is completed at a crank angle of 720 degrees, so that the compression process and the combustion process are heavy in any cylinder. I have to be. As a result, in any cylinder, the combustion cycle is determined so that the combustion process and the compression process in the next cylinder equally overlap.

In the common rail type fuel injection system, a high pressure fuel pump 8 for supplying fuel to the common rail 2 is provided.
Is obtained from the output shaft of the engine via a transmission mechanism, similarly to the drive of the camshafts 31 and 32. Therefore, when the driving torque consumed by the camshafts 31 and 32 increases, the driving torque required in total increases, and the durability of the belt deteriorates when a timing belt, particularly a timing belt is employed as a transmission mechanism,
It is necessary to take measures such as increasing the belt width. Also,
As a result, there is a problem that the overall length of the engine is increased.

In a fuel injection device for pumping fuel to a common rail by a high-pressure fuel supply pump, the timing at which the output torque during the combustion process of the engine reaches a peak substantially coincides with the timing at which fuel is pumped by the plunger of the high-pressure fuel supply pump. (Japanese Patent Application Laid-Open No. 9-2222056) has been proposed. By specifying such a fuel pumping time, the engine vibration and rotation fluctuation are reduced. When the fuel is pumped to the common rail by the high-pressure fuel supply pump immediately after the injector is opened and the common rail pressure slightly decreases, the effect of the decrease in the common rail pressure deteriorates the injection characteristics of the fuel injected from the injector. It is disclosed that the fuel discharge timing is set by the high-pressure fuel supply pump every time fuel is injected from the injector.

Further, by setting the timing of pumping the fuel from the high-pressure fuel supply pump to the common rail within a period during which the engine generates a positive torque when any of the cylinders is in the combustion / expansion process. Either cylinder does not superimpose the load torque generated by driving the high-pressure fuel supply pump during the load torque in the compression stroke, and reduces the fluctuations in the combined torque that is the final output of the engine, thereby reducing engine noise and vibration. An accumulator type fuel injection device has been proposed (Japanese Patent Application Laid-Open No. 9-217664).

[0016]

From the graph of the camshaft driving torque in the three-cylinder engine shown in FIG. 4, it can be seen that the driving torque is always fluctuating but becomes negative in one combustion cycle. It can be seen that occurs three times as many as the number of cylinders, with the same phase difference, and in the same pattern. Therefore, the pumping of the high-pressure fuel supply pump using the timing at which the camshaft drive torque is negative in this way contributes to the reduction of the total drive torque peak value required for the output shaft of the engine. There is a problem that can be done.

[0017]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems. In a high-pressure fuel supply pump in which one combustion cycle performs three-time fuel pumping, the camshaft drive torque is determined by the fuel pumping timing. By adjusting to the negative timing, the peak value of the total torque of the torque required for driving the camshaft and the torque required for driving the high-pressure fuel pump is reduced, and the peak load torque generated in the timing train is reduced. It is an object of the present invention to provide an engine having a common rail fuel injection system capable of improving the durability of the engine.

The present invention has been made in order to achieve the above object.
It is configured as follows. That is, the present invention provides a high-pressure fuel supply pump driven by torque taken from an output shaft of an engine to pump fuel to a common rail.
An injector that injects fuel supplied from the common rail into a combustion chamber of the engine, an intake valve that opens and closes an intake port that opens to the combustion chamber, an exhaust valve that opens and closes an exhaust port that opens to the combustion chamber, A valve mechanism having a camshaft driven by a torque taken out from the output shaft and a cam provided on the camshaft to drive the intake valve and the exhaust valve to open and close; The present invention relates to an engine provided with a common rail type fuel injection system, in which fuel is fed at a timing at which torque for driving the camshaft becomes negative.

According to the present invention, as described above, the output torque is taken out from the output shaft by the operation of the engine to rotate the camshaft, and the operation cam provided on the camshaft is provided with the intake valve and the exhaust valve. By operating the valve at a predetermined timing, intake to the combustion chamber in each cylinder and exhaust of combustion gas generated by combustion are performed. Simultaneously with the operation of the intake and exhaust valves, the output shaft of the engine drives a high-pressure fuel supply pump via a transmission mechanism, and fuel is pumped to the common rail by the high-pressure fuel supply pump. Since the fuel is pumped by the high-pressure fuel supply pump when the driving torque for driving the camshaft becomes negative, the total driving torque of the driving torque for driving the camshaft and the driving torque for driving the high-pressure fuel supply pump is calculated. The peak value is reduced.

In the engine provided with the common rail type fuel injection system, the engine is a four-cycle engine, and the number of times of fuel pumping from the high pressure fuel supply pump to the common rail per two revolutions of the output shaft of the engine is the same as that of the engine. Is set so as to be equal to the number of cylinders disposed at The engine is a three-cylinder engine having three cylinders.

In the engine having the common rail type fuel injection system, the peak timing of the torque for driving the high-pressure fuel supply pump substantially coincides with the peak timing of the negative torque for driving the camshaft. As a result, the peak of the torque for driving the high-pressure fuel supply pump is reduced by the negative torque for driving the camshaft.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of an engine having a common rail fuel injection system according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing a change in driving torque consumed for driving a cam shaft with respect to a crank angle (first cylinder) and driving of a high-pressure fuel supply pump with respect to a crank angle (first cylinder) in a three-cylinder diesel engine provided with a common rail fuel injection system according to the present invention. 6 is a graph showing a change in driving torque to be applied.

The common rail type fuel injection system itself and the valve train applied to the engine according to the present invention are the same as the system schematically shown in FIG. 2 or the valve train shown in FIG. 3, respectively. Description is omitted. Assuming that the engine is a four-cycle engine, the high-pressure fuel supply pump 8 is reduced to half the output speed of the engine and driven to rotate via the transmission mechanism in the same manner as when the intake and exhaust valves 23 and 24 are driven. Is done. The fuel pressurized in the pump chamber of the high-pressure fuel supply pump 8 is discharged to the common rail 2 under the control of a flow control valve and the like.

As can be seen from the graph of the change in drive torque with respect to the crank angle shown in FIG.
The drive torque required to drive the motors 1 and 32 fluctuates three times as shown by B with respect to the crank rotating twice. The driving torque A required to drive the high-pressure fuel supply pump 8 is set to be generated in a phase opposite to the torque B for driving the camshafts 31 and 32.
That is, the fuel pressure feeding timing by the high-pressure fuel supply pump 8 is set so as to match the timing at which the driving torque of the camshafts 31 and 32 becomes negative.

The drive torque required to drive the high-pressure fuel supply pump 8 to pump the fuel to the common rail 2 and the drive torque required to drive the camshaft are such that the values of the two drive torques are always opposite. Are in opposite phase relationship. Therefore, the driving torque for driving the pump 8 and the torque for driving the camshafts 31 and 32 are always canceled each other, and the torque acting as a load on the output shaft of the engine is reduced.

The pressure feed timing of the high-pressure fuel supply pump 8 is controlled by a flow control valve 14 attached to the high-pressure fuel supply pump 8 based on a control signal from the controller 12. The high-pressure fuel supply pump 8 usually has a structure in which the plunger is stroked to increase the pressure of the fuel sucked into the pump chamber and send it out. The stroke timing of the plunger in the high-pressure fuel supply pump 8 and the timing at which the driving torque of the camshafts 31 and 32 in the valve mechanism 30 becomes negative are determined, for example, between the output shaft of the engine and the input shaft of the high-pressure fuel supply pump 8. By setting the rotation phase in the timing transmission mechanism that connects between them, they are set to be mechanically matched. In particular, the camshafts 31, 3
By matching the timing at which the drive torque of No. 2 gives a negative peak and the timing of giving a positive peak value of the drive torque required for pumping of the high-pressure fuel supply pump 8, the two drive torques are most efficiently canceled out. be able to.

The flow control valve 14, which is controlled based on a signal from the controller 12, can supply the fuel increased in pressure by the stroke of the plunger to the common rail 2 in a required amount at a required time. as a result,
The pressure of the common rail 2 can be controlled by the pumped fuel. The flow control valve 14 returns the fuel to the fuel tank 4 through the return pipe 10 at a time other than supplying the fuel to the common rail 2 even when the plunger is in the pressure feeding step.

[0028]

The engine provided with the common rail fuel injection system according to the present invention has the following effects because it is configured as described above. That is, according to the engine provided with the common rail type fuel injection system according to the present invention, the high pressure fuel supply pump driven by the torque taken out from the output shaft of the engine to pump the fuel to the common rail, and the fuel supplied from the common rail to the An injector that injects into the combustion chamber of the engine, an intake valve that opens and closes an intake port that opens into the combustion chamber, an exhaust valve that opens and closes an exhaust port that opens into the combustion chamber, and is driven by torque extracted from the output shaft of the engine And a cam valve provided on the camshaft for driving the intake valve and the exhaust valve to open and close. Since the driving torque was negative, the torque required for driving the camshaft and the high A torque required for driving the fuel pump is canceled, it is possible to reduce the peak value of the load torque to the engine. That is, the peak load torque generated in the timing train from the output shaft of the engine is reduced, and the load applied to the timing train, especially the timing belt, can be reduced, and the durability thereof can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in drive torque between a high-pressure fuel supply pump and a camshaft in an engine including a common rail fuel injection system according to the present invention.

FIG. 2 is a view schematically showing a conventional common rail fuel injection system.

FIG. 3 is a schematic cross-sectional view of a cylinder head including a conventional engine valve operating mechanism and a combustion chamber intake / exhaust mechanism.

FIG. 4 is a graph showing a relationship between a crank angle and a driving torque in one combustion cycle of the engine.

FIG. 5 is a map showing operation timings of an exhaust valve and an intake valve with respect to a crank angle in a three-cylinder engine.

FIG. 6 is a graph showing a relationship between a cam angle and a lift amount of a valve stem of an intake valve.

FIG. 7 is a graph showing a relationship between a cam angle and a driving torque of an exhaust valve.

FIG. 8 is a graph showing a relationship between a cam angle and a lift amount of a valve stem of an exhaust valve.

FIG. 9 is a graph showing a relationship between a rotation angle of a cam shaft and a driving torque of an exhaust valve.

FIG. 10 is a map showing operation timings of an exhaust valve and an intake valve with respect to a crank angle in a four-cylinder engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injector 2 Common rail 8 High pressure fuel supply pump 12 Controller 14 Flow control valve 22 Combustion chamber 23 Intake valve 24 Exhaust valve 25 Valve stem 28 Return spring 30 Valve mechanism 31, 32 Camshaft 33, 34 Cam

Claims (4)

[Claims] A high-pressure fuel supply pump driven by torque taken from an output shaft of an engine to pump fuel to a common rail; an injector for injecting fuel supplied from the common rail into a combustion chamber of the engine;
An intake valve that opens and closes an intake port that opens to the combustion chamber, an exhaust valve that opens and closes an exhaust port that opens to the combustion chamber, a camshaft driven by torque taken out from the output shaft of the engine, and a camshaft. A valve mechanism having a cam for driving the opening and closing of the intake valve and the exhaust valve, wherein the timing for pumping the fuel by the high-pressure fuel supply pump is determined by the timing when the torque for driving the camshaft becomes negative. An engine equipped with a common rail fuel injection system. 2. The engine is a four-stroke engine, and the number of times of fuel pumping from the high-pressure fuel supply pump to the common rail per two revolutions of the output shaft of the engine is equal to the number of cylinders provided in the engine. An engine provided with the common rail fuel injection system according to claim 1, comprising: 3. The engine according to claim 2, wherein the number of cylinders is three. 4. The method according to claim 1, wherein a peak timing of the torque for driving the high-pressure fuel supply pump substantially coincides with a peak timing of the negative torque for driving the camshaft. An engine provided with the common rail fuel injection system according to claim 1.