WO2008029240A1

WO2008029240A1 - Engine system

Info

Publication number: WO2008029240A1
Application number: PCT/IB2007/002477
Authority: WO
Inventors: Eiichi Hioka
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2006-08-29
Filing date: 2007-08-29
Publication date: 2008-03-13
Anticipated expiration: 2009-02-28
Also published as: JP2008057349A

Abstract

A cam (1125), which opens/closes an intake valve, is provided on an intake camshaft (1120), and is further provided with a VVT mechanism (2000) that uses an electric motor as an actuator. The intake camshaft (1120) and an exhaust camshaft (1130) are connected to a crankshaft via a timing chain (1005). A pump cam (1150) that drives a high-pressure fuel pump is provided on the exhaust camshaft (1130), instead of being provided on the intake camshaft (1120). With this arrangement, a resistance to the rotation of the electric motor is not increased even when the high-pressure fuel pump is operated, because the rotational load of the intake camshaft (1120) is not increased by the operation of the high-pressure pump.

Description

ENGINE SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention [00011 The invention relates generally to an engine system, and, more specifically, to an engine system provided with a variable valve timing system that uses an electric motor as an actuator.

2. Description of the Related Art

[0002] A variable valve timing (VVT) system that changes the phase (i.e., crank angle), at which an intake valve or an exhaust valve is opened/closed, based on the engine operating state has been used. Such variable valve timing system changes the phase of the intake valve or the exhaust valve by rotating a camshaft, which opens/closes the intake valve or the exhaust valve, relative to, for example, a sprocket. The camshaft is rotated hydraulically or by means of an actuator, for example, an electric motor. [0003] A structure in which an auxiliary is driven by the rotational force of a camshaft that is rotated in accordance with the rotation of an engine has been used.

[0004] For example, Japanese Patent Application Publication No. JP-2005-23942 (JP-A-2005-23942) describes a high-pressure fuel pump that is driven by a pump-driving cam provided on a camshaft of an exhaust valve. According to JP-A-2005-23942, the high-pressure fuel pump promotes an increase in the fuel pressure from when start-up of an engine is initiated, and driving signals are transmitted to the high-pressure fuel pump at least two times during the period from when a signal output from a crank angle sensor is detected until when the phase of the crank angle detected by a crank angle sensor is synchronized with the phase of the cam angle detected by a cam angle sensor, which detects the position of the pump driving cam, so as to reduce the time required to start up the engine, decrease the toxic substance contained in the exhaust gas, and increase the engine power. In addition, according to JP-A-2005-23942, a variable valve timing system is provided on a camshaft of an intake valve, and a pump driving cam is provided on the camshaft of the exhaust valve.

[0005] FIG. 12 in Japanese Patent Application Publication No. JP- 10-176508 (JP-A-10-176508) indicates the structure in which an intake camshaft, provided with a pump cam that drives a fuel injection pump, is further provided with a variable valve timing mechanism that changes the rotational phase of the intake camshaft in a valve operating system for an internal combustion engine. More specifically, in the valve operating system for an internal combustion engine according to JP-A-10-176508, because the pump cam is arranged on the camshaft of which the rotational phase is changed by the variable valve timing mechanism, even when the variable valve timing system changes the rotational phase of the camshaft, the fluctuation in the torque of the camshaft and the fluctuation in the pump driving torque are synchronized with each other in terms of the angle phase. This prevents amplification of the fluctuation in the valve driving torque due to the fluctuation in the pump driving torque.

[0006] Japanese Patent Application Publication No. JP-2003-343381 (JP-A- JP-2003-343381) describes a high pressure supply pump which does not exert an influence on the operation of a continuous phase control system that corresponds to a variable valve timing system. Because a pump unit is driven by a pump cam that rotates together with a sprocket wheel, the operation load of the pump is not applied to a camshaft. [0007] Japanese Patent Application Publication No. JP-2004- 100556

(JP-A-2004- 100556) describes an example of an auxiliary that is driven by a camshaft. JP-A-2004- 100556 describes a structure in which a negative-pressure pump, which produces a negative pressure in an intake pipe even when the opening amount of a throttle valve is large, is driven by a cam provided on the camshaft. [0008] With a variable valve timing system that hydraulically drives a camshaft, the variable valve timing control is sometimes not executed as accurately as it should be, in a cold environment or at the time of engine starting. Such inconvenience is caused due to insufficient hydraulic pressure used to drive the camshaft or slow response of the camshaft to the hydraulic control in such occasions. To obviate such inconveniences, a variable valve timing system that drives a camshaft by means of an electric motor has been suggested.

[0009] In a system that changes the phase of a camshaft using the rotation of an electric motor, reducing the resistance to the rotation of the electric motor greatly contributes to downsizing of an actuator. More specifically, if the resistance to the rotation of the electric motor is higher, the size of the electric motor increases to maintain a certain rate at which the valve timing changes. This may cause inconveniences such as an increase in the space for the electric motor, an increase in the production cost, and a reduction in the fuel efficiency.

SUMMARY OF THE INVENTION

[0010] The invention provides a more compact electric motor which is used as an actuator of a variable valve timing system included in an engine system that further includes an auxiliary which is driven by the rotation of a camshaft. [0011] An aspect of the invention relates to an engine system which includes an engine that produces drive power by burning fuel; an intake valve and an exhaust valve that are provided in the engine, and that are opened/closed by respective camshafts that include a first camshaft and a second camshaft; a variable valve timing system; and an auxiliary that is driven by the rotational force of the second camshaft. The variable valve timing system has a changing mechanism that includes an electric motor which serves as an actuator. The changing mechanism changes opening/closing timing of one of the intake valve and the exhaust valve by changing the rotational phase of the first camshaft, which drives the one of the intake valve and the exhaust valve, relative to the rotational phase of a crankshaft by an amount of change corresponding to the rotational speed of the electric motor relative to the rotational speed of the first camshaft. The auxiliary is driven by the rotational force of the second camshaft that drives the other of the intake camshaft and the exhaust camshaft, which is not provided with the variable valve timing system.

[0012] The engine system according to the aspect of the invention includes the intake valve and the exhaust valve that are driven by the respective camshafts, and the camshafts include the first camshaft and the second camshaft. With the engine system described above, the energy used to drive the auxiliary is obtained by the rotation of the second camshaft, not by the rotation of the first camshaft that is provided with the variable valve timing system that uses the electric motor as the actuator. Accordingly, the resistance to the rotation of the electric motor is not increased even when the auxiliary is driven, because the resistance to the rotation of the first camshaft, on which the variable valve timing system is provided, is not increased even when the auxiliary is driven. Accordingly, the amount of electric power required to achieve the same operation amount of the actuator (the rotational speed of the electric motor) is smaller when the energy used to drive the auxiliary is obtained by the rotation of the second camshaft than when the energy used to drive the auxiliary is obtained by the rotation of the first camshaft. Therefore, it is possible to reduce the size of the electric motor 2060, which is required to maintain a predetermined rate at which the opening/closing timing of the valve changes. This makes it possible to downsize the system and to improve the fuel efficiency due to reduction in the amount of electric power consumed by the variable valve timing system.

[0013] In the aspect of the invention, the auxiliary may be a fuel pump that is driven in accordance with die rotation of a cam that is provided on the second camshaft. Thus, the fuel pump, which is the auxiliary, is driven efficiently without increasing the size of the electric motor that serves as the actuator of the variable valve timing system.

[0014] In the aspect of the invention, the auxiliary may be a negative-pressure pump that is driven in accordance with the rotation of the second camshaft.

[0015] Thus, negative-pressure pump, which is the auxiliary, is driven efficiently without increasing the size of the electric motor that serves as the actuator of the variable valve timing system.

[0016] According to the aspect of the invention, it is possible to reduce the size of the electric motor in the engine system that includes the variable valve timing system which uses the electric motor as the actuator, and the auxiliary that is driven by the rotation of the camshaft. As a result, it is possible to downsize the system and to improve fuel efficiency due to a reduction in the amount of electric power consumed by the variable valve timing system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of an embodiment with reference to the accompanying drawings, wherein the same or corresponding elements will be denoted by the same reference numerals and wherein: FIG. 1 is a view schematically showing the structure of a vehicle engine provided with a variable valve timing system according to an embodiment of the invention; FIG 2 is a graph showing the map that defines the phase of an intake camshaft; FIG 3 is a cross-sectional view showing an intake VVT mechanism; FIG 4 is a cross-sectional view taken along the line IV-IV in FIG 3; FIG 5 is a first cross-sectional view taken along the line V-V in FIG 3;

FIG 6 is a second cross-sectional view taken along the line V-V in FIG 3; FIG 7 is a cross-sectional view taken along the line VII-VII in FIG 3; FIG 8 is a cross-sectional view taken along the line VIII- VIII in FIG 3; FIG. 9 is a graph showing the speed reduction ratio that the elements of the intake VVT mechanism realize in cooperation;

FIG 10 is a graph showing the relationship between the phase of a guide plate relative to a sprocket and the phase of the intake camshaft;

FIG 11 is a schematic block diagram illustrating the configuration of the control over the phase of an intake valve, executed by the variable valve timing system according to the embodiment of the invention;

FIG 12 is a block diagram illustrating the structure of a high-pressure fuel pump that is an example of an auxiliary;

FIG 13 is a schematic view illustrating the arrangement of a pump cam that drives the high-pressure fuel pump; FIG. 14 is a schematic view illustrating the arrangement of a negative-pressure pump that is another example of an auxiliary; and

FIG. 15 is a schematic view illustrating the arrangement of a drive shaft of the negative-pressure pump.

DETAILED DESCRIPTION OFTHE EMBODIMENT

[0018] Hereafter, an embodiment of the invention will be described with reference to the accompanying drawings. In the following description, the same or corresponding elements will be denoted by the same reference numerals. The names and functions of the elements having the same reference numerals are also the same. Accordingly, the descriptions concerning the elements having the same reference numerals will be provided only once below. [0019] First, a vehicle engine provided with a variable valve timing system according to the embodiment of the invention will be described with reference to FIG 1.

[0020] An engine 1000 is an eight-cylinder V-type engine including a first bank 1010 and a second bank 1012 each of which has four cylinders therein. Note that, the variable valve timing system according to the embodiment of the invention may be applied to any types of engines. Namely, the variable valve timing system may be applied to engines other than an eight-cylinder V-type engine.

[0021] Air that has passed through an air cleaner 1020 is supplied to the engine 1000. A throttle valve 1030 adjusts the amount of air supplied to the engine 1000. The throttle valve 1030 is an electronically-controlled throttle valve that is driven by a motor. [0022] The air is introduced into a cylinder 1040 through an intake passage 1032. The air is then mixed with fuel in a combustion chamber formed within the cylinder 1040. The fuel is injected from an injector 1050 directly into the cylinder 1040. Namely, the injection hole of the injector 1050 is positioned within the cylinder 1040.

[0023] The fuel is injected into the cylinder 1040 in the suction stroke. The time at which the fuel is injected need not be in the suction stroke. The description concerning the embodiment of the invention will be provided on the assumption that the engine 1000 is a direct-injection engine where the injection hole of the injector 1050 is positioned within the cylinder 1040. In addition to the injector 1050 for direct-injection, an injector for port-injection may be provided. Alternatively, only an injector for port-injection may be provided.

[0024] The air-fuel mixture in the cylinder 1040 is ignited by a spark plug 1060, and then burned. The burned air-fuel mixture, namely, the exhaust gas is purified by a three-way catalyst 1070, and then discharged to the outside of the vehicle. A piston 1080 is pushed down due to combustion of the air-fuel mixture, whereby a crankshaft 1090 is rotated. Typically, the number of revolutions per minute (rpm)) of a rotating body, for example, a shaft is usually referred to as the rotational speed, the term "rotational speed" will be used in the following description.

[0025] An intake valve 1100 and an exhaust valve 1110 are provided on the top of the cylinder 1040. The intake valve 1100 is driven by an intake camshaft 1120, and the exhaust valve 1110 is driven by an exhaust camshaft 1130. The intake camshaft 1120 and the exhaust camshaft 1130 are connected to each other by, for example, a chain or a gear, and rotate at the same number of revolutions (at one-half the number of revolutions of the crankshaft 1090). [0026] The phase (opening/closing timing) of the intake valve 1100 is controlled by an intake WT mechanism 2000 which is fitted to the intake camshaft 1120. The phase (opening/closing timing) of the exhaust valve 1110 is controlled by an exhaust VVT mechanism 3000 which is fitted to the exhaust camshaft 1130.

[0027] In the embodiment of the invention, the intake camshaft 1120 and the exhaust camshaft 1130 are rotated by the VVT mechanisms 2000 and 3000, respectively, whereby the phase of the intake valve 1100 and the phase of the exhaust valve 1110 are controlled. However, the method for controlling the phase is not limited to this.

[0028] The intake WT mechanism 2000 is operated by an electric motor 2060 (shown in I⁷IG 3). The electric motor 2060 is controlled by an electronic control unit .

8

(ECU) 4000. The magnitude of electric current passing through the electric motor 2060 is detected by an ammeter (not shown) and the voltage applied to the electric motor 2060 is detected by a voltmeter (not shown), and a signal indicating the magnitude of electric current and a signal indicating the voltage are transmitted to the ECU 4000. The exhaust VVT mechanism 3000 is hydraulically driven.

(0029] The ECU 4000 receives signals indicating the rotational speed and the crank angle of the crankshaft 1090, from a crank angle sensor 5000. The ECU 4000 also receives a signal indicating the phase of the intake camshaft 1120 and a signal indicating the phase of the exhaust camshaft 1130 (the positions of these camshafts in the rotational direction), from a camshaft position sensor 5010.

[0030] In addition, the ECU 4000 receives a signal indicating the temperature of a coolant for the engine 1000 (the coolant temperature) from a coolant temperature sensor 5020, and a signal, indicating the amount of air supplied to the engine 1000, from an airflow meter 5030. [0031] The ECU 4000 controls the throttle valve opening amount, the ignition timing, the fuel injection timing, the fuel injection amount, the phase of the intake valve 1100, the phase of the exhaust valve 1110, etc. based on the signals received from the above-mentioned sensors and the maps and programs stored in memory (not shown) so that the engine 1000 is brought into the desired operating state. [0032] According to the embodiment of the invention, the ECU 4000 successively sets the target phase of the intake valve 1100 appropriate for the current engine operating state with reference to the map that defines the target phase in advance using parameters indicating the engine operating state, typically, using the engine speed NE and the intake air amount KL. Generally, multiple maps, used to set the target phase of the intake valve 1100 at multiple coolant temperatures, are stored.

[0033] Hereafter, the intake WT mechanism 2000 that is driven by the electric motor 2060 will be described in more detail. Note that, the exhaust WT mechanism 3000 may have the same structure as the intake WT mechanism 2000 described below, and the intake VVT mechanism 200 may be hydraulically driven. [0034] As shown in FIG 3, the intake VVT mechanism 2000 includes a sprocket 2010, a cam plate 2020, link mechanisms 2030, a guide plate 2040, a speed reducer 2050, and the electric motor 2060. An electric-motor EDU (Electronic Drive Unit) 4100 used to control the electric motor 2060 is formed integrally with the electric motor 2060. [0035] The sprocket 2010 is connected to the crankshaft 1090 via, for example, a chain. The rotational speed of the sprocket 2010 is one-half the rotational speed of the crankshaft 1090, as in the case of the intake camshaft 1120 and the exhaust camshaft 1130. The intake camshaft 1120 is provided such that the intake camshaft 1120 is coaxial with the sprocket 2010 and rotates relative to the sprocket 2010. [0036] The cam plate 2020 is connected to the intake camshaft 1120 with a first pin

2070. In the sprocket 2010, the cam plate 2020 rotates together with the intake camshaft 1120. The cam plate 2020 and the intake camshaft 1120 may be formed integrally with each other.

[0037] Each link mechanism 2030 is formed of a first arm 2031 and a second arm 2032. As shown in FIG 4, that is, a cross-sectional view taken along the line IV-IV in

FIG 3, paired first arms 2031 are arranged in the sprocket 2010 so as to be symmetric with respect to the axis of the camshaft 1120. Each first arm 2031 is connected to the sprocket 2010 so as to pivot about a second pin 2072.

[0038] As shown in FIG 5, that is, a cross-sectional view taken along the line V-V in FIG 3, and FIG 6 that shows the state achieved by advancing the phase of the intake valve 1100 from the state shown in FIG 5, the first arms 2031 and the cam plate 2020 are connected to each other by the second arms 2032.

[0039] Each second arm 2032 is supported so as to pivot about a third pin 2074, with respect to the first arm 2031. Each second arm 2032 is supported so as to pivot about a fourth pin 2076, with respect to the cam plate 2020.

[0040] The intake camshaft 1120 is rotated relative to the sprocket 2010 by the pair of link mechanisms 2030, whereby the phase of the intake valve 100 is changed. Accordingly, even if one of the link mechanisms 2030 breaks and snaps, the phase of the intake valve 1100 is changed by the other link mechanism 2030. [0041] As shown in FIG 3, a control pin 2034 is Fitted on one face of each link mechanism 2030 (more specifically, the second arm 2032), the face being proximal to the guide plate 2040. The control pin 2032 is arranged coaxially with the third pin 2074. Each control pin 2034 slides within a guide groove 2042 formed in the guide plate 2040. [0042] Each control pin 2034 moves in the radial direction while sliding within the guide groove 2042 formed in the guide plate 2040. The movement of each control pin 2034 in the radial direction rotates the intake camshaft 1120 relative to the sprocket 2010. [0043] As shown in FIG 7, that is, a cross-sectional view taken along the line Vπ-VII in FIG 3, the guide groove 2042 is formed in a spiral fashion such that the control pin 2034 moves in the radial direction in accordance with the rotation of the guide plate 2040. However, the shape of the guide groove 2042 is not limited to this.

[0044] As the distance between the control pin 2034 and the axis of the guide plate 2040 increases in the radial direction, the phase of the intake valve 1100 is more delayed. Namely, the amount of change in the phase corresponds to the amount by which each link mechanism 2030 is operated in accordance with the movement of the control pin 2034 in the radial direction. Note that, as the distance between the control pin 2034 and the axis of the guide plate 2040 increases in the radial direction, the phase of the intake valve 1100 may be more advanced.

[0045] As shown in FIG 7, when the control pin 2034 reaches the end of the guide groove 2042, the operation of the link mechanism 2030 is restricted. Accordingly, the phase at which the control pin 2034 reaches the end of the guide groove 2042 is the most advanced phase or the most delayed phase of the intake valve 1100.

[0046] Multiple recesses 2044 are formed in one face of the guide plate 2040, the face being proximal to the speed reducer 2050. The recesses 2044 are used to connect the guide plate 2040 and the speed reducer 2050 to each other.

[0047] The speed reducer 2050 is formed of an externally-toothed gear 2052 and an internally-toothed gear 2054. The externally-toothed gear 2052 is fixed to the sprocket 2010 so as to rotate together with the sprocket 2010.

[0048] Multiple projections 2056, which are fitted in the recesses 2044 of the guide plate 2040, are formed on the internally-toothed gear 2054. The internally-toothed gear 2054 is supported so as to be rotatable about an eccentric axis 2066 of a coupling 2062 of which the axis deviates from an axis 2064 of the output shaft of the electric motor 2060.

[0049] FIG 8 shows a cross-sectional view taken along the line VIH-VIII in FIG. 3. The internally-toothed gear 2054 is arranged such that part of the multiple teeth thereof mesh with the externally-toothed gear 2052. When the rotational speed of the output shaft of the electric motor 2060 is equal to the rotational speed of the sprocket 2010, the coupling 2062 and the internally-toothed gear 2054 rotate at the same rotational speed as the externally-toothed gear 2052 (the sprocket 2010). In this case, the guide plate 2040 rotates at the same rotational speed as the sprocket 2010, and the phase of the intake valve 1100 is maintained.

[0050J When the coupling 2062 is rotated about the axis 2064 relative to the externally-toothed gear 2052 by the electric motor 2060, the entirety of the internally-toothed gear 2054 turns around the axis 2064, and, at the same time, the internally-toothed gear 2054 rotates about the eccentric axis 2066. The rotational movement of the internally-toothed gear 2054 causes the guide plate 2040 to rotate relative to the sprocket 2010, whereby the phase of the intake valve 1100 is changed.

[0051] The phase of the intake valve 1100 is changed by reducing the relative rotational speed (the operation amount of the electric motor 2060) between the output shaft of the electric motor 2060 and the sprocket 2010 using the speed reducer 2050, the guide plate 2040 and the link mechanisms 2030. Alternatively, the phase of the intake valve 1100 may be changed by increasing the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010. The output shaft of the electric motor 2060 is provided with a motor rotational angle sensor 5050 that outputs a signal indicating the rotational angle (the position of the output shaft in its rotational direction) of the output shaft. Generally, the motor rotational angle sensor 5050 produces a pulse signal each time the output shaft of the electric motor 2060 is rotated by a predetermined angle. The motor rotational angle sensor 5050 detects the rotational speed of the output shaft of the electric motor 2060 (hereinafter, simply referred to as the "rotational speed of the electric motor 2060" where appropriate) based on the signal output from the motor rotational angle sensor 5050.

[0052] As shown in FIG. 9, the speed reduction ratio R (θ) that the elements of the intake VVT mechanism 2000 realize in cooperation, namely, the ratio of the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket

2010 to the amount of change in the phase of the intake valve 1100 may take a value corresponding to the phase of the intake valve 1100. According to the embodiment of the invention, as the speed reduction ratio increases, the amount of change in the phase with respect to the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 decreases.

[0053] When the phase of the intake valve 1100 is within the first region that extends from the most delayed phase to CAl, the speed reduction ratio that the elements of the intake WT mechanism 2000 realize in cooperation is R 1. When the phase of the intake valve 1100 is within the second region that extends from CA2 (CA2 is the phase more advanced than CAl) to the most advanced phase, the speed reduction ratio that the elements of the intake WT mechanism 2000 realize in cooperation is R2 (Rl > R2).

[0054] When the phase of the intake valve 1100 is within the third region that extends from CAl to CA2, the speed reduction ratio that the elements of the intake VVT mechanism 2000 realize in cooperation changes at a predetermined rate ((R2 - RI) / (CA2 -CA1)).

[0055] The effects of the thus configured intake VVT mechanism 2000 of the variable valve timing system according to the embodiment of the invention will be described below.

[0056] When the phase of the intake valve 1100 (the intake camshaft 1120) is advanced, the electric motor 2060 is operated to rotate the guide plate 2040 relative to the sprocket 2010. As a result, the phase of the intake valve 1100 is advanced, as shown in FIG 10.

[0057] When the phase of the intake valve 1100 is within the first region that extends from the most delayed phase to CAl, the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 is reduced at the speed reduction ratio Rl. As a result, the phase of the intake valve 1100 is advanced.

[0058] When the phase of the intake valve 1100 is within the second region that extends from CA2 to the most advanced phase, the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 is reduced at the speed reduction ratio R2. As a result, the phase of the intake valve 1100 is advanced.

[0059] When the phase of the intake valve 1100 is delayed, the output shaft of the electric motor 2060 is rotated relative to the sprocket 2010 in the direction opposite to the direction in which the phase of the intake valve 1100 is advanced. When the phase is delayed, the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 is reduced in the manner similar to that when the phase is advanced. When the phase of the intake valve 1100 is within the first region that extends from the most delayed phase to CAl, the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 is reduced at the speed reduction ratio Rl. As a result, the phase is delayed. When the phase of the intake valve 1100 is within the second region that extends from CA2 to the most advanced phase, the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 is reduced at the speed reduction ratio R2. As a result, the phase is delayed. [0060] Accordingly, as long as the direction of the relative rotation between the output shaft of the electric motor 2060 and the sprocket 2010 remains unchanged, the phase of the intake valve 1100 may be advanced or delayed in both the first region that extends from the most delayed phase to CAl and the second region that extends from the

CA2 and the most advanced phase. In this case, in the second region that extends from CA2 and the most advanced phase, the phase is advanced or delayed by an amount larger than that in the first region that extends from the most delayed phase to CAl.

Accordingly, the second region is broader in the phase change width than the first region.

[0061] In the first region that extends from the most delayed phase to CAl, the speed reduction ratio is high. Accordingly, a high torque is required to rotate the output shaft of the electric motor 2060 using the torque applied to the intake camshaft 1120 in accordance with the operation of the engine 1000. Therefore, even when the electric motor 2060 does not produce a torque, for example, even when the electric motor 2060 is not operating, the rotation of the output shaft of the electric motor 2060, which is caused by the torque applied to the intake camshaft 1120, is restricted. This restricts the deviation of the actual phase from the phase used in the control, which is likely to occur, for example, when the engine is stopped. In addition, occurrence of an undesirable phase change is restricted when the supply of electric power to the electric motor 2060 that serves as the actuator is stopped. [0062] When the phase of the intake valve 1100 is within the third region that extends from CAl to CA2, the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 is reduced at the speed reduction ratio that changes at a predetermined rate. As a result, the phase of the intake valve 1100 is advanced or delayed. [0063] When the phase of the intake valve 1100 is shifted from the first region to the second region, or from the second region to the first region, the amount of change in the phase with respect to the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 is gradually increased or reduced. Accordingly, an abrupt stepwise change in the amount of change in the phase is restricted to restrict an abrupt change in the phase. As a result, the phase of the intake valve 1100 is controlled more appropriately.

[0064] With the variable valve timing system according to the embodiment of the invention described above, when the phase of the intake valve 1100 is within the first region that extends from the most delayed phase to CAl, the speed reduction ratio that the elements of the intake WT mechanism 2000 realize in cooperation is Rl . When the phase of the intake valve 1100 is within the second region that extends from CA2 to the most advanced phase, the speed reduction ratio that the elements of the intake WT mechanism 2000 realize in cooperation is R2 that is lower than the speed reduction ratio Rl. Accordingly, as long as the direction of the relative rotation between the output shaft of the electric motor 2060 and the sprocket 2010 remains unchanged, the phase of the intake valve 1100 may be advanced or delayed in both the first region that extends from the most delayed phase to CA 1 and the second region that extends from the CA2 and the most advanced phase. In this case, in the second region that extends from CA2 and the most advanced phase, the phase is advanced or delayed by an amount larger than that in the first region that extends from the most delayed phase to CA 1. Accordingly, the second region is broader in the phase change width than the first region. In the first region that extends from the most delayed phase to CAl, the speed reduction ratio is high. Accordingly, the rotation of the output shaft of the electric motor 2060, which is caused by the torque applied to the intake camshaft 1120 in accordance with the operation of the engine 1000, is restricted. This restricts the deviation of the actual phase from the phase used in the control. Accordingly, the phase is changed in a broader range, and controlled more accurately.

[0065] FIG 11 is a schematic block diagram illustrating the configuration of the intake valve phase control executed by the variable valve timing system according to the embodiment of the invention.

[0066] As shown in FIG 11, the engine 1000 is configured such that the power is transferred from the crank shaft 1090 to the intake camshaft 1120 and the exhaust camshaft 1130 via the sprocket 2010 and a sprocket 2012, respectively, by a timing chain 1005 (or a timing belt), as previously described with reference to FIG 1. The camshaft position sensor 5010 that outputs a cam angle signal Piv each time the intake camshaft 1120 rotates by a predetermined cam angle is fitted on the outer periphery of the intake camshaft 1120. The crank angle sensor 5000 that outputs a crank angle signal Pea each time the crankshaft 1090 rotates by a predetermined crank angle is fitted on the outer periphery of the crankshaft 1090. The motor rotational angle sensor 5050 that outputs a motor rotational angle signal Pmt each time the electric motor 2060 rotates by a predetermined rotational angle is fitted to a rotor (not shown) of the electric motor 2060. These cam angle signal Piv, crank angle signal Pea and motor rotational angle signal Pmt are transmitted to the ECU 4000. [0067] The ECU 4000 controls the operation of the engine 1000 based on the signals output from the sensors that detect the operating state of the engine 1000 and the operation conditions (the pedal operations performed by the driver, the current vehicle speed, etc.) such that the engine 1000 produces a required output power. As part of the engine control, the ECU 4000 sets the target value of the phase of the intake valve 1100 and the target value of the phase of the exhaust valve 1110 based on the map shown in FIG 2. In addition, the ECU 4000 prepares the rotational speed command value Nmref for the electric motor 2060 that serves as the actuator for the intake VVT mechanism 2000. [0068] The rotational speed command value Nmref is set based on the relative rotational speed between the output shaft of the electric motor 2060 and the sprocket 2010 (the intake camshaft 1120), which corresponds to the operation amount of the actuator, as described in detail below. The electric-motor EDU 4100 controls the rotational speed of the electric motor 2060 based on the rotational speed command value Nmref indicated by a signal from the ECU 4000.

[0069] Next, the arrangement of an auxiliary that is driven in accordance with the rotation of the camshaft will be described.

[0070] FIG 12 is a block diagram illustrating the structure of a high-pressure fuel pump 1200 that is an example of such auxiliary. [0071] As shown in FIG 12, a low-pressure fuel pump 1170 sucks fuel up from a ftαel tank 1165, and discharges the fuel under a predetermined pressure (predetermined low pressure). The low-pressure fuel pump 1170 pressurizes the fuel that will be sentto a low-pressure fuel passage 1190 through a fuel filter 1175 and a fuel pressure regulator 1180. The fuel pressure regulator 1180 is opened, when the fuel pressure in the low-pressure fuel passage 1190 is going to increase. As a result, a returning passage through which the fuel is returned to the fuel tank 1165 is formed. The fuel which is present near the fuel pressure regulator 1180 and which is part of the fuel present in the low-pressure fuel passage 1190, more specifically, the fuel that has just sucked by the low-pressure fuel pump 1170 is returned to the fuel tank 1165. As a result, the fuel pressure in the low fuel passage 1190 is maintained at a predetermined value.

[0072] The high-pressure fuel pump 1200 is provided on a cylinder head (not shown).

The high-pressure fuel pump 1200 reciprocates a plunger 1220 arranged within a pump cylinder 1210 using the rotation of a pump cam 1150 that is provided on the exhaust camshaft 1130. The high-pressure fuel pump 1200 further includes a high-pressure pump chamber 1230, which is defined by the pump cylinder 1210 and the plunger 1220, a gallery 1245 that is connected to the low fuel pressure passage 1190, and an electromagnetic spill valve 1250. The electromagnetic spill valve 1250 is an on-off valve which provides/shuts off communication between the gallery 1245 and the high-pressure pump chamber 1230.

[0073] The outlet of the high-pressure fuel pump 1200 is connected to a delivery pipe (not shown) through a high-pressure fuel passage 1260. The fuel is supplied to the injector 1050 in FIG 1 through the delivery pipe. A check valve 1240 is provided in the high-pressure fuel passage 1260. The check valve 1240 prevents the fuel from flowing back toward the high-pressure fuel pump 1200. The inlet of the high-pressure fuel pump 1200 is connected to the low-pressure fuel pump 1170, which is provided in the fuel tank 1165, through the low-pressure fuel passage 1190.

[0074] In the suction stroke in which the lift amount of the plunger 1220 decreases in accordance with the rotation of the pump cam 1150, the volume of the high-pressure pump chamber 1230 increases as the plunger 1220 is lifted down. During the suction stroke, the electromagnetic spill valve 1250 is kept open. When the electromagnetic spill valve 1250 is kept open, communication is provided between the gallery 1245 and the high-pressure pump chamber 1260. Accordingly, during the suction stroke, the fuel is sucked into the high-pressure pump chamber 1230 from the low-pressure fuel passage through the gallery 1245.

[0075] In the discharge stroke in which the lift amount of the plunger 1220 increases in accordance with the rotation of the pump cam 1150, the volume of the high-pressure pump chamber 1230 decreases as the plunger 1220 is lifted up. During the discharge stroke, open/closed state of the electromagnetic spill valve 1250 is controlled based on open/closed state control signals from an ECU (not shown).

[0076] When the electromagnetic spill valve 1250 is open in the discharge stroke, the fuel sucked into the high-pressure pump chamber 1230 flows back toward the low-pressure fuel passage 1190 through the gallery 1245, because communication is provided between the gallery 1245 and the high-pressure pump chamber 1230. More specifically, the fuel is not sentto the high-pressure fuel passage 1260, but is returned to the low-pressure fuel passage 1190 through the gallery 1245.

[0077] On the other hand, when the electromagnetic spill valve 1250 is closed, communication between the gallery 1245 and the high-pressure pump chamber 1230 is shut off. Accordingly, the fuel pressurized during the discharge stroke does not flow back to the gallery 1245, but is sent to the high-pressure fuel passage 1260. In other words, the amount and pressure of the fuel discharged from the high-pressure fuel pump

1200 is controlled based on the ratio between the time period in which the electromagnetic spill valve 1250 is open and the time period in which the electromagnetic spill valve 1250 is closed (duty ratio).

[0078] As shown FIG. 13, a cam 1125 that opens/closes the intake valve 1100 is provided on the intake camshaft 1120. Similarly, a cam 1135 that opens/closes the exhaust valve 1110 is provided on the exhaust camshaft 1130. The intake camshaft 1120 and the exhaust camshaft 1130 are connected to the crankshaft 1090 (shown in HG 1) by the timing chain 1005. In addition, the variable valve timing mechanism 2000 is provided to the intake camshaft 1120, as described above.

[0079] The pump cam 1150 that drives the high-pressure fuel pump 1200 shown in FIG 12 is provided on the exhaust camshaft 1130. With this arrangement, the operation of the high-pressure fuel pump 1200 does not increase the resistance to the rotation of the electric motor 2060, which serves as the actuator of the VVT mechanism 2000, because the rotational load of the intake camshaft 1120 provided with the WT mechanism 2000 is not increased by the operation of the high-pressure fuel pump 1200. Accordingly, the amount of electric power required to achieve the same rotational speed of the electric motor 2060 is smaller when the pump cam 1150 is provided on the exhaust camshaft 1130 than when the pump cam 1150 is provided on the intake camshaft 1120. Therefore, it is possible to reduce the size of the electric motor 2060, which is required to maintain a predetermined rate at which the intake valve phase changes. This makes it possible to downsize the system and to improve the fuel efficiency due to reduction in the amount of electric power consumed by the variable valve timing system.

[0080] FIG 14 shows an engine system that is formed by providing a negative-pressure pump 1400 to the engine system shown FIG 1. The negative-pressure pump 1400 is another example of an auxiliary that is driven by the camshaft.

[0081] The negative-pressure pump 1400 is provided in order to produce a negative pressure in an intake pipe even when the opening amount of the throttle valve is large.

The negative-pressure pump 1400 needs to be provided in, for example, an engine system provided with a variable valve lift mechanism, which controls the amount of air introduced to a combustion chamber by variably controlling of the lift amount of the intake valve while maintaining a large throttle valve opening amount. For example, a configuration in which the valve lift amount is continuously changed, a configuration in which the valve lift amount is changed in two stages, or a configuration in which the valve(s) of one or some of all cylinders is (are) opened may be applied to the variable valve lift mechanism.

[0082] As shown FIG 14, a negative-pressure supply passage 1330 is connected to a surge tank 1022. Through the negative-pressure supply passage 1330, a negative pressure produced in the surge tank 1022 is supplied to a brake booster 1310. In the negative-pressure supply passage 1330, a check valve 1340 that controls a flow of the gas from the surge tank 1022 to the brake booster 1310 is provided. In addition, a negative-pressure supply passage 1350, through which a negative pressure from the negative-pressure pump 1400 is supplied, is connected to the brake booster 1310. In the negative-pressure supply passage 1350, a check valve 1360 that controls a flow of the gas from the negative-pressure pump 1400 to the brake booster 1310 is provided. The negative-pressure pump 1400 is operated by the rotation of a pump drive shaft 1160.

[0083] The brake booster 1310 is connected to a brake pedal 1320. The brake booster 1310 reduces the force required to depress the brake pedal 1320, and creates a larger braking force with respect to the operation amount of the brake pedal 1320 by using the negative pressure supplied from the surge tank 1022 and the negative pressure supplied from the negative-pressure pump 1400. [0084] As shown FIG. 15, the pump drive shaft 1160 of the negative-pressure pump

1400 is connected to the exhaust camshaft 1130. The pump drive shaft 1160 of the negative-pressure pump 1400 rotates in accordance with the rotation of the exhaust camshaft 1130.

(0085] With this arrangement, the operation of the low-pressure fuel pump 1400 does not increase the resistance to the rotation of the electric motor 2060, which serves as the actuator of the VVT mechanism 2000, because the rotational load of the intake camshaft 1120 provided with the VVT mechanism 2000 is not increased by the operation of the low-pressure fuel pump 1400. Accordingly, the amount of electric power required to achieve the same rotational speed of the electric motor 2060 is smaller when the pump drive shaft 1160 is connected to the exhaust camshaft 1130 than when the pump drive shaft 1160 is connected to the intake camshaft 1120. Therefore, it is possible to reduce the size of the electric motor 2060, which is required to maintain a predetermined rate at which the intake valve phase changes. This makes it possible to downsize the system and to improve the fuel efficiency due to reduction in the amount of electric power consumed by the variable valve timing system.

[0086] In the embodiment of the invention, the high-pressure fuel pump and the negative-pressure pump have been described as examples of the auxiliaries driven by the camshaft. However, the invention is not limited to these examples. That is, the invention is applicable to any engine systems which include a variable valve timing system that uses an electric motor as an actuator and that is provided to one of an intake valve and an exhaust valve, and an auxiliary that is driven by a cam or a drive shaft provided to a camshaft, regardless of which of the intake valve and the exhaust valve is provided with the variable valve timing system driven by the electric motor, and regardless of the type of the auxiliary. [0087] The embodiment of the invention that has been disclosed in the specification is to be considered in all respects as illustrative and not restrictive. The technical scope of the invention is defined by claims, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

CLAIMS (PCT)

1. An engine system, characterized by comprising: an engine that produces drive power by burning fuel; an intake valve and an exhaust valve that are provided in the engine, and that are opened/closed by respective camshafts that include a first camshaft and a second camshaft; a variable valve timing system that includes a changing mechanism that changes opening/closing timing of one of the intake valve and the exhaust valve by changing a rotational phase of the first camshaft, which drives the one of the intake valve and the exhaust valve, relative to a rotational phase of a crankshaft by an amount of change corresponding to a rotational speed of an electric motor, which serves as an actuator, relative to a rotational speed of the first camshaft, and an auxiliary that is driven by a rotational force of the second camshaft that drives the other of the intake camshaft and the exhaust camshaft, which is not provided with the variable valve timing system.

2. The engine system according to claim 1, wherein the auxiliary is a fuel pump that is driven in accordance with a rotation of a cam that is provided on the second camshaft.

3. The engine system according to claim 1, wherein the auxiliary is a negative-pressure pump that is driven in accordance with a rotation of the second camshaft.

4. The engine system according to any one of claims 1 to 3, wherein the variable valve timing system is provided to change the opening/closing timing of the intake valve, and the auxiliary is driven by a rotational force of the camshaft that opens/closes the exhaust valve.