Patent Grant
8844481
The present invention relates to a variable valve apparatus for varying the open/close timing or lift amount of engine valves in an internal combustion engine.
Japanese Laid-Open Patent Publication No. 2002-168105 discloses a variable valve apparatus for an automotive internal combustion engine, which includes a camshaft arranged on an exhaust side (referred to as “exhaust camshaft”), a fixed cam integrally mounted on the exhaust camshaft so as to drive an exhaust valve, a control shaft arranged on an intake side, a control cam fixed to the control shaft, a swing cam swingably mounted on the control shaft, a rocker arm swingably supported by the control cam, an eccentric drive cam integrally mounted on the exhaust camshaft and connected to the swing cam through the rocker arm and link members so as to drive an intake valve via the swing cam and an actuator for controlling the rotational phase of the control shaft (control cam) to change the operating position of the rocker arm and thereby vary the position of contact of the swing cam with a valve lifter of the intake valve. In this configuration, the variable valve apparatus is capable of varying the valve lift characteristics of the intake valve while reducing its height dimension for improvement in mountability.
In the above conventional type of variable valve apparatus, however, the eccentric drive cam and the fixed cam serve as an intake valve drive cam and an exhaust valve drive cam, respectively. The relationship between the valve lift characteristics of the intake and exhaust valves is uniquely defined as both of the intake valve drive cam and the exhaust valve drive cam are integrally mounted on the same camshaft. In other words, the relationship between the valve timing of the intake valve and the valve timing of the exhaust valve may largely deviate from its theoretical relationship depending on the operating angle of the intake valve. This can cause problems such as increase in pumping loss and excessive increase in residual gas.
In view of the above problems, it is an object of the present invention to provide a variable valve apparatus capable of, while maintaining good mountability on an internal combustion engine, securing good relationship between the open/close timing of first and second engine valves even though the operating angle of the second engine valve becomes changed.
According to one aspect of the present invention, there is provided a variable valve apparatus for an internal combustion engine, comprising: a control shaft rotatably arranged on a cylinder head of the internal combustion engine; a camshaft rotatably arranged on the cylinder head of the internal combustion engine and having a first camshaft member to which rotation of a crankshaft of the internal combustion engine is transmitted and a second camshaft member inserted and supported in an axial hole of the first camshaft member such that the first and second camshaft members are rotatable relative to each other; a rotary cam mounted on the second camshaft member so as to rotate together with the second camshaft member and allow opening and closing operations of an exhaust valve; an eccentric drive cam mounted on the first camshaft member so as to rotate together with the first camshaft member; a rocker arm swingably supported on the control shaft and caused to swing with rotation of the eccentric drive cam; a swing cam swingably supported on the control shaft and caused to swing with swinging movement of the rocker arm and allow opening and closing operations of an intake valve; a control cam formed eccentrically on the control shaft so as to rotate together with the control shaft, change an operating position of the rocker arm according to a rotational phase of the control shaft and thereby vary the amount of swinging movement of the swing cam; a phase control mechanism adapted to control a rotational phase of the second camshaft member relative to the first camshaft member; and an actuator for rotating the control shaft.
According to another aspect of the present invention, there is provided a variable valve apparatus for an internal combustion engine, comprising: a control shaft rotatably arranged on a cylinder head of the internal combustion engine; a camshaft rotatably arranged on the cylinder head of the internal combustion engine and having a first camshaft member to which rotation of a crankshaft of the internal combustion engine is transmitted and a second camshaft member inserted and supported in an axial hole of the first camshaft member such that the first and second camshaft members are rotatable relative to each other; a phase control mechanism disposed at one end of the camshaft and adapted to control a rotational phase of the second camshaft member relative to the first camshaft member; a rotary cam mounted on one of the first and second camshaft members so as to rotate together with the one of the first and second camshaft members and allow opening and closing operations of an exhaust valve; an eccentric drive cam mounted on the other of the first and second camshaft members so as to rotate together with the other of the first and second camshaft members; a rocker arm swingably supported on the control shaft and caused to swing with rotation of the eccentric drive cam; a swing cam swingably supported on the control shaft and caused to swing with swinging movement of the rocker arm and allow opening and closing operations of an intake valve; a control cam formed eccentrically on the control shaft so as to rotate together with the control shaft, change an operating position of the rocker arm according to a rotational position of the control shaft and thereby control the amount of swinging movement of the swing cam; and an actuator for rotating the control shaft.
According to still another aspect of the present invention, there is provided a variable valve apparatus for an internal combustion engine, comprising: a control shaft rotatably arranged on an cylinder head of the internal combustion engine; a camshaft rotatably arranged on an cylinder head of the internal combustion engine and having a first camshaft member to which rotation is transmitted from the internal combustion engine and a second camshaft member with a center thereof passing through the first camshaft member; a phase control mechanism disposed at one end of the camshaft and adapted to control a rotational phase of the second camshaft member relative to the first camshaft member; a rotary cam mounted on one of the first and second camshaft members so as to rotate together with the one of the first and second camshaft members and allow opening and closing operations of either one of intake and exhaust valves; a drive cam mounted on the other of the first and second camshaft members so as to rotate together with the other of the first and second camshaft members; a transmission mechanism for converting rotation of the drive cam to swinging movement and transmitting the swinging movement; a swing cam swingably supported on the control shaft and caused to swing with the swinging movement of the transmission mechanism and allow opening and closing operations of the other of the intake and exhaust valves; a control member integrally mounted on the control shaft and adapted to control the amount of the swinging movement of the transmission mechanism according to an operating position thereof; and an actuator for rotating the control shaft.
In each of the above aspects of the present invention, the camshaft is double-structured with the first and second camshaft members, by one of which the rotary cam is driven to operate the first engine valve and by the other of which the swing cam is driven to operate the second engine valve; and the relative rotational phase of the first and second camshaft members is controlled by the phase control mechanism. It is therefore possible according to the present invention to, while securing good mountability of the variable valve apparatus on the internal combustion engine, prevent inconvenience on the relationship between the open/close timing of the first and second engine valves even though the operating angle of one of the second engine valve becomes changed.
The other objects and features of the present invention will also become understood from the following description.
The present invention will be described in detail below by way of the following first to fourth embodiments, in which like parts and portions are designated by like reference numerals to thereby omit repeated descriptions thereof. Herein, each of the first to fourth embodiments specifically refers to a variable valve apparatus for an internal combustion engine in which each cylinder has two intake valves and two exhaust valves.
As shown in
The exhaust camshaft 10 is arranged as a drive shaft in a front-rear direction of the engine and is rotatably attached by bolts 7 to brackets 6 on an upper side of the engine cylinder head 1. A pulley 4, around which a timing belt 5 is wound, is disposed on a front end of the exhaust camshaft 10.
In the first embodiment, the exhaust camshaft 10 has a double structure formed with a hollow outer camshaft member 13 (as a first camshaft member) and a solid inner camshaft member 14 (as a second camshaft member) as shown in
The rotary cams 11 are provided in a pair per engine cylinder and is integrally mounted on the outer camshaft member 13, at positions axially corresponding to respective exhaust valves 3, so as to rotate together with the outer camshaft member 13. As shown in
The eccentric drive cams 12 are integrally mounted on the inner camshaft member 14, at positions between the adjacent engine cylinders and adjacent to lateral sides of the rotary cams 11 but axially apart from the exhaust valve lifters 3a, so as to rotate together with the inner camshaft member 14. As shown in
The control shaft 31 is arranged in parallel with the exhaust camshaft 10 and rotatably attached by bolts to brackets 8 on the upper side of the engine cylinder head 1.
The control cams 32 are fixed as control members to the control shaft 31 at positions corresponding to the eccentric drive cams 12. As shown in
As will be explained later, the control shaft 31 and the control cams 32 constitute a part of the variable valve event and lift mechanism 30 to adjust the control amount of the variable valve event and lift mechanism 30.
The swing cams 21 are provided in a pair per engine cylinder and is swingably supported on the control shaft 31 at positions axially corresponding to respective intake valves 2. In the first embodiment, the swing cams 21 have a different shape from the raindrop shape of the rotary cams 11. More specifically, the swing cams 21 have rounded cam surfaces 21a and base circle surfaces 21b as shown in
The transmission mechanism 20 is adapted to convert rotation of the eccentric drive cams 12 to linear movement and transmit the linear movement as a driving force to the swing cams 21. In the first embodiment, the transmission mechanism 20 has a rocker arm 22, a link arm 23 and a link rod 24 per engine cylinder as shown in
As shown in
The link arm 23 is formed into a linear shape and arranged along a width direction of the engine so as to extend between the exhaust camshaft 10 and the control shaft 31 and link the one end 22b of the rocker arm 22 to the eccentric drive cam 12. In the first embodiment, the link arm 23 has a large-diameter base end portion 23a and a small-diameter protruding end portion 23b protruding from the base end portion 23a as shown in
The link rod 24 is formed into a short straight shape so as to link the other end 22c of the rocker arm 22 to the cam nose portion 21c of one of the pair of the swing cam 21. As shown in
The variable valve event and lift mechanism 30 is adapted to vary the valve lift characteristics (lift amount/operating angle) of the intake valves 2 by controlling the rotational phase of the control shaft 31 (control cams 32), changing the operating position of the rocker arms 22 and thereby varying the position of contact of the swing cams 21 with the intake valve lifters 2a. As shown in
The actuator 33 is disposed on a front end portion of the engine cylinder head 1 and operated under various control signals from an electronic control unit so as to cause rotation of the control shaft 31 within a given angular range according to engine operating conditions.
In the first embodiment, the control shaft 31 is controlled to a middle lift position such that the lift amount (operating angle) of the intake valves 2 is set to a middle lift amount L2 (middle operating angle D2) at the time of start of the engine as shown in
The phase control mechanism 40 is adapted as a phase control mechanism and disposed between the outer and inner camshaft members 13 and 14 at a rear end of the exhaust camshaft 10 so as to cause relative rotation between the outer and inner camshaft members 13 and 14.
As shown in
In the first embodiment, the vane rotor 42 is controlled to a middle phase position (i.e., the inner camshaft member 14 is controlled to a middle phase position relative to the outer camshaft member 13; see
Further, an engagement hole 43a is formed in one of the vanes 42b; and a lock pin 43b is elastically retained by a spring (not shown) on a lateral side of the vane 42b. The engagement hole 43a and the lock pin 43b constitutes a known type of lock mechanism 43 to prevent free movement of the vane rotor 42 upon engagement of the lock pin 43b in the engagement hole 43 in the first embodiment. By the operation of the lock mechanism, the inner camshaft member 14 can rotate in synchronism with the outer camshaft member 13 while being maintained at the middle phase position relative to the outer camshaft member 13. In the first embodiment, the lock mechanism 43 is adapted to, when the vane rotor 42 is controlled to the middle phase position upon satisfaction of the engine stop conditions, hydraulically move the lock pin 43b into in the engagement hole 43a under the elastic force of the spring and thereby restrict the rotation of the vane rotor 42 relative to the housing 41.
As shown in
In this integral configuration, each of the rotary cams 11 is formed with two pieces, one of which is a base circle cam lobe 15 located on a base end side to define a base circle region and the other of which is a lift cam lobe 16 located on a cam nose side to define a lift region, as shown in
As shown in
As the inner shaft member 14 is sandwiched between the cam lobes 15 and 16 with an outer circumferential surface of the inner shaft member 14 slightly spaced apart from the cam lobes 15 and 16, the rotary cam 11 can be easily and simply fixed by the fixing pin 17 to the inner shaft member 14.
For the insertion of the fixing pin 17, a pin insertion hole 14a is formed radially through the inner camshaft member 14. The pin insertion hole 14a has an inner diameter slightly smaller than the outer diameter of the fixing pin 17 such that the fixing pin 17 is held in a press fitted state in the pin insertion hole 14a of the inner camshaft member 14 for improvement in support rigidity.
It is alternatively feasible to fit the fixing pin 17 loosely in the pin insertion hole 14a of the inner camshaft member 14 with a slight radial clearance left between the fixing pin 17 and the pin insertion hole 14a. This allows slight play between the inner camshaft member 14 and the fixing pin 17 so that, even if there occurs a deviation between the center of the outer camshaft member 13 and the center of the inner camshaft member 14, such a deviation can be absorbed by the radial clearance for smooth rotation of the rotary cams 11 (cam lobes 15 and 16) together with the inner camshaft member 14 relative to the outer camshaft member 13.
By contrast, a pair of opposing pin insertion slits 13a are formed in the outer camshaft member 13 at positions facing opening ends of the pin insertion hole 14a for the insertion of the fixing pin 17. The pin insertion slits 13a have some length along a circumferential direction of the outer camshaft member 13 so as to allow a given amount of relative rotation between the outer and inner camshaft members 13 and 14. Namely, the relative rotation of the outer and inner camshaft members 13 and 14 is allowed within the range of movement of the fixing pin 17 in the pin insertion slits 13a and is restricted by contact of the fixing pin 17 with ends of the pin insertion slits 13a.
The operations of the variable valve apparatus according to the first embodiment will be explained in more detail below with reference to
When the eccentric drive cam 12 rotates together with the exhaust camshaft 10, the rotation of the eccentric drive cam 12 is converted to liner movement of the link arm 23. By such linear movement of the link arm 23, the rocker arm 22 swings to move the link rod 24 and thereby cause swinging movement of the swing cams 21. The intake valves 2 are opened and closed by swinging movement of the swing cams 21. At this time, the valve lift characteristics of the intake valves 2 are controlled by the variable valve event and lift mechanism 30 according to the operating conditions of the engine. As mentioned above, the lift amount (operating angle) of the intake valves 2 is set to the middle lift amount L2 (middle operating angle D2) as shown in
On the other hand, when the rotary cams 11 rotate together with the exhaust camshaft 10, the exhaust valves 3 are opened and closed with the rotation of the rotary cams 11. As no variable valve event and lift mechanism is provided to the exhaust valves 3, the valve lift characteristics of the exhaust valves 3 are fixed at the same level depending on the cam profile of the rotary cams 11 as shown in
In consequence, there is almost no valve overlap between the intake valves 2 and the exhaust valves 3; and the close timing of the intake valves 2 is set near the bottom dead center (BDC) of the engine piston at the time of start of the engine. This allows improvement in intake fill efficiency by reduction in residual gas and by increase in effective compression ratio so that the engine can achieve high torque output and good startability.
When the engine is placed in a low-speed, low-load operating state after the engine start, the control shaft 31 is rotated by the actuator 33 in such a manner that the large thickness portion 32a of the control cam 32 is located upwardly as mentioned above and as shown in
In the case where the exhaust valves 3 are conventionally driven by the rotary cams (such as those mentioned above) with the use of no variable valve event an lift mechanism and no phase control mechanism, both of the lift amount and open/close timing of the exhaust valves 3 are fixed. As the valve lift curve (open/close timing) of the exhaust valves 3 is maintained at the middle phase T2, the close timing of the exhaust valves 3 is set near the top dead center (TDC) of the engine piston. By contrast, the open timing of the intake valves 2 is retarded relative to the TDC. As a result, there occurs a negative valve overlap OL where both of the intake and exhaust valves 2 and 3 are kept closed during the time period from the close timing of the exhaust valves 3 to the open timing of the intake valves 2. During such a negative valve overlap period, the negative pressure in the engine cylinder increases with the downward movement of the engine piston. This leads to deterioration in fuel efficiency due to increase in pumping loss.
In view of the above conventional problem, the phase control mechanism 40 is operated to rotate the inner camshaft member 14 to the retard side relative to the outer camshaft member 13 by the supply of hydraulic pressure to the retard hydraulic chambers Pr such that the open/close timing of the exhaust valves 3 is set to a retarded phase T1 in the low-speed, low-load operating state where the lift amount of the intake valves 2 is set to the small lift amount L1 in the first embodiment. Under this phase retard control, the close timing of the exhaust valves 3 and the open timing of the intake valves 2 are brought nearer to each other so as to reduce the time period TL from the close timing of the exhaust valves 3 to the open timing of the intake valves 2 (negative valve overlap period). It is thus possible to limit increase in negative cylinder pressure and prevent increase in pumping loss for improvement of fuel efficiency. It is also possible to increase the expansion stroke of the engine piston for improvement of fuel efficiency as the open timing of the exhaust valves 3 is retarded to the BDC side under the phase retard control.
When the engine is placed in a high-speed, high-load operating state with increase in engine rotation speed, the control shaft 31 is rotated by the actuator 33 in such a manner that the large thickness portion 32a of the control cam 32 is located downwardly as shown in
In the case where the exhaust valves 3 are conventionally driven by the rotary cam with no phase control mechanism, the valve lift curve (open/close timing) of the exhaust valves 3 is maintained at the middle phase position T2 so as to cause a large overlap OL between the close timing of the exhaust valves 3 and the open timing of the intake valves 2 as mentioned above. During such a large valve overlap period, a large amount of exhaust gas flows into the engine cylinder. This leads to deterioration in intake fill efficiency due to increase in residual gas so that the engine fails in desired high-rotation torque output.
In the first embodiment, the phase control mechanism 4 is operated to rotate the inner camshaft member 14 to the advance side relative to the outer camshaft member 13 by the supply of hydraulic pressure to the advance hydraulic chambers Pa such that the open/close timing of the exhaust valves 3 is set to an advanced phase T3 in the high-speed, high-load operating state where the lift amount of the intake valves 2 is set to the large lift amount L3. Under this phase advance control, the valve overlap OL between the intake valves 2 and the exhaust valves 3 can be reduced. It is thus possible to limit the flow of exhaust gas into the engine cylinder and achieve desired high-rotation torque output by improve in intake fill efficiency. It is also possible to obtain reduction in exhaust discharge loss, which becomes a problem in the high-speed operating range, for desired high-rotation torque output as the open timing of the exhaust valves 3 is advanced under the phase advance control.
As described above, the exhaust camshaft 10 is double-structured with the outer and inner camshaft members 13 and 14; and the relative rotation of the outer and inner camshaft members 13 and 14 is controlled by the phase control mechanism 40 in the first embodiment. By the combined adoption of such a double-structured exhaust camshaft 10 with the phase control mechanism 40, the variable valve apparatus is configured to the open/close timing of the exhaust valves 3 within the range of T1 to T3 according to the lift amount L1, L2, L3 (operating angle D1, D2, D3) of the intake valves 2 and avoid the above-mentioned conventional problems. In the first embodiment, the variable valve apparatus has a specific configuration in which the eccentric drive cam 12 is mounted on and driven by the exhaust camshaft 10 to apply a driving force to the swing cams 21 through the transmission mechanism 20 and allow opening and closing operations of the intake valves 2 as mentioned above. The variable valve apparatus is therefore able to secure good mountability due to such a specific configuration and, at the same time, optimize good relationship between the open/close timing of the intake valves 2 and the open/close timing of the exhaust valves 3 according to the operating angle of the intake valves 2.
The peak lift phase of the intake valves 2 is slightly changed with increase in the lift amount of the intake valves 2 under the condition of θ1<θ3 where θ1 is the angle of the link arm 23 in the small-lift control state of
In the exhaust camshaft 10, the outer camshaft member 13 is located upstream of the inner camshaft member 14 on the torque transmission path from the engine crankshaft to the engine valves and is less susceptible to torsional deformation. As the eccentric drive cams 12 are integrally formed on such an outer camshaft member 13 to drive the intake valves 2 via the transmission mechanism 20 and the swing cams 21, the valve lift curve (change of operating angle) of the intake valves 2 can be stabilized effectively and securely. Furthermore, the eccentric drive cams 12 can be supported with high support rigidity for further stabilization of the valve lift curve (change of operating angle) of the intake valves 2 as each of the eccentric drive cams 12 is integral with the relatively highly rigid outer camshaft member 13.
Relief portions are continuously formed in the exhaust camshaft 10 (outer camshaft member 13) on axially opposite sides of the eccentric drive cam 12 so as to extend over axial width ranges U as shown in
The variable valve apparatus according to the first embodiment may be modified in such a manner that the base circle cam lobe 15 and lift cam lobe 16 of the rotary cam 11 are coupled and fixed together by a plurality of bolts 18 as shown in
As described above, the cam lobes 15 and 16 are fixed together by the combined use of the bolts 18 with the fixing pin 17 in the present modified embodiment. This makes it possible to improve not only the fixing strength of the cam lobes 15 and 16 but also the support rigidity of the rotary cams 11. As the adhesion of the cam lobes 15 and 16 increases, the precision of mating of the cam lobe mating surfaces 15a and 16a can be improved for smooth rotation (sliding) of the cam lobes 15 and 16 relative to the outer camshaft member 13. The variable valve apparatus improves in durability by such secure fixing of the rotary cams 11.
The variable valve apparatus according to the second embodiment is structurally similar to that according to the first embodiment, except that: each of the eccentric drive cams 12 is formed separately from the outer camshaft member 13 of the exhaust camshaft 10; and each of the rotary cams 11 is formed in one piece as shown in
As the eccentric drive cams 12 are formed separately from the outer camshaft member 13, the rotary cams 11 can be fitted around the exhaust camshaft 10 from one end side. This makes it possible to form the rotary cam 11 with one-piece structure, rather than two-piece structure of two cam lobes 15 and 16, for improvements in strength and support rigidity and thereby possible to secure further stabilization of the valve lift curve of the exhaust valves 3 by smooth rotation (sliding) of the rotary cams 11.
As in the case of the first embodiment, the fixing pin 17 is inserted in the rotary cams 11 and the outer and inner camshaft members 13 and 14 so as to allow rotation of the inner camshaft member 14 together with the rotary cams 11 relative to the outer camshaft member 13 in the second embodiment. The circumferential length of the pin insertion slits 13a of the outer camshaft member 13 is set in such a manner that each of the pin insertion slits 13a has an opening formed with a given angle Y larger than a rotational angle X of the fixing pin 17 relative the outer camshaft member 13 (i.e. a phase change angle of the phase control mechanism 40) during relative rotation of the outer and inner camshaft members 13 and 14. Even when the vanes 42b collide with the respective shoes 41a due to e.g. overshoot (that is, the outer and inner camshaft members 13 and 14 rotate relative to each other by an maximum amount), there is a slight clearance C left between the fixing pin 17 and the pin insertion slits 13a so that the fixing pin 17 does not come into contact with ends of the pin insertion slits 13. This makes it possible to secure the strength of the fixing pin 17 and the strength of the pin insertion slits 13a and prevent noise caused by collision of the fixing pin 17.
In the second embodiment, the inner camshaft member 14 has a hollow shape formed with an oil gallery 14b along the axial direction thereof such that oil flows through the oil gallery 14b and then flows out through a slight clearance between the fixing pin 17 and the pin insertion hole 14a to lubricate sliding surfaces between the outer and inner camshaft members 13 and 14 and between the outer camshaft member 13 and the rotary cams 11 for smooth rotation of the exhaust camshaft 10 and the rotary cams 11.
The variable valve apparatus according to the third embodiment is structurally similar to that according to the first embodiment, except that another valve timing control (VTC) mechanism 44 is disposed on the end of the exhaust camshaft 10 opposite from the end on which the phase control mechanism 40 is disposed as shown in
The phase control mechanism 44 is formed with the same structure as the phase control mechanism 40 and is located between the pulley 4 and the exhaust camshaft 10 so as to cause relative rotation between the pulley 4 and the outer camshaft member 13 of the exhaust camshaft 10. As mentioned above, the phase control mechanism 40 is operated to change the rotational phase of the inner camshaft member 14 to the retard side relative to the outer shaft member 13 in the small-lift control state (the amount of swinging movement of the swing cams 21 is decreased). On the other hand, the phase control mechanism 44 is operated to change the rotational phase of the outer camshaft member 13 to the advance side relative to the engine crankshaft in the small-lift control state.
By adoption of such two phase control mechanisms 40 and 44, the variable valve apparatus is configured to vary both of the open/close timing of the intake valves 2 and the open/close timing of the exhaust valves 3 within a give phase range Tx as shown in
In the third embodiment, the open timing of the exhaust valves 3 is also advanced under the phase advance control of the phase control mechanism 44. It is conceivable that such phase advance control would cause decrease in expansion load in the engine cylinder. However, the expansion ratio of the engine is merely decreased by a slight amount due to the phase advance control as the open timing of the exhaust valves 3 is near the BDC. The influence of the advanced open timing of the exhaust valves 3 on the fuel efficiency is thus relatively small. On the whole, the fuel efficiency improvement effect of the advanced close timing of the intake valves 2 exceeds the influence of the advanced open timing of the exhaust valves 2 so as to obtain further improvement in fuel efficiency as mentioned above.
The variable valve apparatus according to the fourth embodiment is structurally similar to that according to the first embodiment, except that the variable valve apparatus is provided with an intake camshaft 50 as an independent drive shaft to drive intake valves 51 and 52 (hereinafter referred to as “first and second intake valves”) per engine cylinder; and the transmission mechanism 20 is disposed between the intake camshaft 50 and the control shaft 31 as shown in
As shown in
In the fourth embodiment, the intake camshaft 50 has a double structure formed with a hollow outer camshaft member 13 (as a first camshaft member) and a solid inner camshaft member 14 (as a second camshaft member) as in the case of the exhaust camshaft 10 of the first embodiment. The outer camshaft member 13 is supported rotatably on the bearings 9 such that rotation of the engine crankshaft is transmitted to one end of the outer camshaft member 13 via a pulley and a timing belt (not shown). The inner camshaft member 14 is inserted rotatably and coaxially through an axial hole of the outer camshaft member 13.
The swing cams 21 are rotatably supported on the intake camshaft 50 at positions axially corresponding to the first intake valves 51 of the respective engine cylinders.
The rotary cams 11 are mounted on the intake camshaft 50 at positions axially corresponding to the second intake valves 52 of the respective engine cylinders. Each of the rotary cams 11 is formed with one-piece structure as in the case of the first embodiment (see
The eccentric drive cams 12 are mounted on the intake camshaft 50 (outer camshaft member 13) on sides of the swing cams 21 opposite from the rotary cams 11. Each of the eccentric drive cams 12 has a center n offset by a predetermined amount γ from a center m of the intake camshaft 50. A shaft insertion hole 12a is formed in the eccentric drive cam 12 along an axial direction of the intake camshaft 50 (i.e. a thickness direction of the eccentric drive cam 12) such that the intake camshaft 50 is inserted and press fitted in the shaft insertion holes 12a of the eccentric drive cams 12 so as to allow rotation of the outer camshaft member 13 together with the eccentric drive cams 12.
In the variable valve event and lift mechanism 30, the eccentric control cams 32 are fixed on the control shaft 31 as shown in
The transmission mechanism 20 is provided with the rocker arm 22, the link arm 23 and the link rod 24 per engine cylinder.
The rocker arm 22 is disposed above the intake camshaft 50 (swing cam 21) and rotatably supported on the eccentric body portion 32a of the control cam 32. A cam insertion hole 22a is formed in the center base portion of the rocker arm 22 so that the rocker arm 22 is swingably supported on the control cam 32 by insertion of the control cam 32 into the cam insertion hole 22a.
The link arm 23 is arranged to link one end 22b of the rocker arm 22 to the eccentric drive cam 12. The link arm 23 has a large-diameter base end portion 23a formed on one end thereof and a small-diameter protruding end portion 23b formed on the other end thereof protrudingly from the base end portion 23a and fitted to the one end 22b of the rocker arm 22 by the pin 25. A cam insertion hole 23c is formed in the center of the base end portion 23a of the link arm 23 so that the link arm 23 is rotatably fitted around the eccentric drive cam 12 by insertion of the eccentric body portion 12b of the eccentric drive cam 12 into the cam insertion hole 23c. The protruding end portion 23b of the link arm 23 is formed with a pin insertion hole 23d and rotatably connected to the one end 22b of the rocker arm 22 by fitting a pin 25 into the pin insertion hole 23d and the pin insertion hole of the one end 22b of the rocker arm 22.
The link rod 24 is bent-shaped and arranged to link the other end 22c of the rocker arm 22 to the swing cam 21. The one end 24a of the link rod 24 is rotatably connected to the end 22c of the rocker arm 22 by a pin 26, whereas the other end 24b of the link rod 24 is rotatably connected to the cam nose portion 21c of the swing cam 21 by a pin 27.
The phase control mechanism 40 is disposed between the outer and inner camshaft members 13 and 14 of the intake camshaft 50 and formed with the same structure as in the first embodiment so as to control relative rotation of the outer and inner camshaft member 13. In the forth embodiment, the phase control mechanism 40 is adapted to lock the vane rotor 42 in a most retarded phase position under the engine stop conditions.
The operations of the variable valve apparatus according to the fourth embodiment will be explained below.
When the eccentric drive cam 12 rotates together with the outer camshaft member 13 of the intake camshaft 50, the rotation of the eccentric drive cam 12 is converted to liner movement of the link arm 23. By such linear movement of the link arm 23, the rocker arm 22 swings to move the link rod 24 and thereby cause swinging movement of the swing cam 21. The first intake valve 51 of each engine cylinder is opened and closed by swinging movement of the swing cam 21. At this time, the valve lift characteristics of the first intake valves 51 are controlled by the variable valve event and lift mechanism 30 according to the engine operating conditions. At the time of start of the engine, the lift amount (operating angle) of the first intake valves 51 is set to a middle lift amount L2 (middle operating angle D2) as shown in
On the other hand, the second intake valve 52 of each engine cylinder is opened and closed with the rotation of the rotary cam 11 when the rotary cam 11 rotates together with the inner camshaft member 14 of the intake camshaft 50. The lift amount of the second intake valves 52 is fixed at a middle lift amount L2; and the valve lift curve (open/close timing) of the second intake valves 52 is set to a most retarded phase T1 at the time of start of the engine.
The valve lift characteristics of the first intake valves 51 are thus substantially the same as those of the second intake valves 52 at the time of start of the engine. In consequence, there is almost no valve overlap between the first and second intake valves 51 and 52 and the exhaust valves; and the close timing of each of the first and second intake valves 51 and 52 is set near the BDC. This allows improvement in intake fill efficiency by reduction in residual gas and by increase in effective compression ratio so that the engine can achieve high torque output and good startability as in the case of the first embodiment.
When the engine is placed in a low-speed, low-load operating state after the engine start, the control shaft 31 is rotated by the actuator 33 in such a manner that the large thickness portion 32a of the control cam 32 is located upwardly as shown in
In view of such a problem, the phase control mechanism 40 is operated to rotate the inner camshaft member 14 to the advance side relative to the outer camshaft member 13 so as to advance the open/close timing of the second intake valves 52 to a middle phase T2 in the low-speed, low-load operating state where the lift amount of the intake valves 2 is set to the small lift amount L1 in the fourth embodiment. Under this phase advance control, the close timing of the second intake valves 52 is set to the same timing as the close timing of the first intake valves 51. It is thus possible to secure sufficient reduction in pumping loss for improvement in fuel efficiency.
In the fourth embodiment, the open timing of the second intake valves 51 is also advanced under the phase advance control. It is conceivable that such phase advance control would cause deterioration in combustion efficiency as the internal EGR increases with valve overlap OL in the low-load operating state. However, there occurs a swirl due to a difference between the open timing of the first intake valves 51 and the open timing of the second intake valves 52. As the internal EGR increases under the intake swirl effect, it is possible to prevent deterioration in combustion efficiency and thereby obtain further reduction in pumping loss and increase in specific heat ratio of air-fuel mixture for further improvement in fuel efficiency.
When the engine is placed in a high-speed, high-load operating state with increase in engine rotation speed, the cycle time of the engine becomes shortened. In this state, the control shaft 31 is rotated by the actuator 33 in such a manner that the large thickness portion 32a of the control cam 32 is located downwardly as shown in
In the fourth embodiment, the phase control mechanism 40 is operated to further rotate the inner camshaft member 14 to the advance side relative to the outer camshaft member 13 so as to advance the open/close timing of the second intake valves 52 to an advanced phase T3 in the high-speed, high-load operating state where the lift amount of the intake valves 2 is set to the large lift amount L3. Under this phase advance control, the open timing of the second intake valves 52 is set nearer to the open timing of the first intake valves 51. It is thus possible to limit the swirl effect in the early intake stage and prevent deterioration in intake fill efficiency so that the engine can achieve high torque output.
As described above, the intake camshaft 50 is double-structured with the outer and inner camshaft members 13 and 14; and the relative rotation of the outer and inner camshaft members 13 and 14 is controlled by the phase control mechanism 40 in the fourth embodiment. By the combined adoption of such a double-structured intake camshaft 50 with the phase control mechanism, the variable valve apparatus is configured to vary the open/close timing of the second intake valves 51 within the range of T1 to T3 according to the lift amount L1, L2, L3 (operating angle D1, D2, D3) of the first intake valves 51 and is therefore able to avoid the above-mentioned conventional problems and optimize good relationship between the open/close timing of the first intake valves 51 and the open/close timing of the second intake valves 52.
If the double-structured intake camshaft 50 is not adopted in the variable valve apparatus, two camshafts (corresponding to the outer and inner camshaft members 13 and 14) need to be provided and spaced apart from each other in the width direction or height direction of the engine. In this case, the mountability of the variable valve apparatus decreases with increase in the dimension of the variable valve apparatus in the engine width or height direction.
In the fourth embodiment, by contrast, the intake camshaft 50 has a double structure in which the outer and inner camshaft members 13 and 14 (first and second camshaft members) are coaxial with each other as mentioned above. As the dimension of the variable valve apparatus in the engine width or height direction can be made relatively small, the variable valve apparatus is able to secure good mountability in the fourth embodiment as in the case of the first embodiment.
The entire contents of Japanese Patent Application No. 2012-34608 (filed on Feb. 21, 2012) are herein incorporated by reference.
Although the present invention has been described with reference to the above exemplary embodiments, the present invention is not limited to these exemplary embodiments. Various modification and variation of the embodiments described above will occur to those skilled in the art in light of the above teachings.
In the present invention, the intake valve 2, 51 is preferably operated by the swing cam 21 as in the first to fourth embodiments although the swing cam 21 can be used to operate either the intake valve or the exhaust valve.
In the first to fourth embodiments, the variable valve event and lift mechanism 30 is adapted to change the operating position of the swing cams 21 with rotation of the control shaft 31. However, the variable valve event and lift mechanism 30 is not limited to the above configuration and may alternatively be adapted to change the operating position of the swing cam 21 by axial movement of the control shaft 31 as disclosed in Japanese Laid-Open Patent Publication No. 2011-174416.
Further, each of the drive cams 12 is eccentric in shape in the first to fourth embodiments. The drive cams 12 are not however limited to such an eccentric shape and may alternatively be e.g. egg-shaped as disclosed in Japanese Laid-Open Patent Publication No. S55-137305.
Although the fixing pin 17 is used as relative rotation preventing means to prevent rotation of the rotary cams 11 relative to the inner camshaft member 14 (i.e. to allow the rotary cams 11 to rotate together with the inner camshaft member 14) in the first to fourth embodiments, the relative rotation preventing means is not limited to the fixing pin 17. It is alternatively feasible to insert a hexagonal shaft into the inner camshaft member 14 and thereby prevent relative rotation of the rotary cams 11 by the hexagonal shaft as disclosed in SAE-860537.
In the first to fourth embodiments, the rotation of the engine crankshaft is transmitted to the outer camshaft member 13 via the pulley and timing belt. Alternatively, it is feasible to use the inner and outer camshaft members 14 and 13 as the first and inner camshaft members, respectively, and transmit the rotation of the engine crankshaft to the inner camshaft member 14. In this case, the phase control mechanism 40 is adapted to control the rotational phase of either the rotary cams 11 or the eccentric drive cams 12 fixed to the outer camshaft member 13.
Although the rotary cams 11 (with which the variable valve event and lift mechanism 30 is not associated) are fixed to the inner crankshaft member 14 in the first to third embodiments, the eccentric drive cams 12 (with which the variable valve event and lift mechanism 30 is associated) may alternatively be fixed to the inner crankshaft member 14. In such a case, the variable valve apparatus is configured to control the lift amount of the intake valves 2 by the variable valve event and lift mechanism 30 to the small lift amount L1 in
In the first to third embodiments, the link arm 23 is adopted to convert the rotation of the eccentric drive cam 12 to the swinging movement of the rocker arm 22; and the control shaft 31 is located nearer to the intake valve 2 than a midpoint between the intake valve 2 and the exhaust valve 3 on the engine cylinder head 1. In this configuration, the valve lift characteristics of the intake valve 2 can be varied to control the operating factors directly related to the combustion of fuel in the engine (such as intake swirl and pumping loss) for improvement in fuel efficiency. It is alternatively feasible to locate the control shaft 31 at a position nearer to the exhaust valve 3 than a midpoint between the intake valve 2 and the exhaust valve 3 on the engine cylinder head 1 so that the valve lift characteristic of the exhaust valve 3 can be varied for exhaust emission improvement and other merits.
In the fourth embodiment, the double-structured intake camshaft 50 and the phase control mechanism 40 are adopted to optimize the open/close timing of the first and second intake valves 51 and 52 in each engine cylinder. It is alternatively feasible to adopt the same camshaft/phase control configuration in order to optimize the open/close timing of first and second exhaust valves in each engine cylinder. For example, the variable valve apparatus may be provided with a double-structured exhaust camshaft and a phase control mechanism so as to vary the valve lift phase of the second exhaust valve according to the valve lift characteristics of the first exhaust valve. In such a case, the valve lift curve of the first exhaust valve can be started during the intake stroke after the end of the valve lift curve of the second exhaust valve. This has a merit of allowing a large amount of residual gas to be accurately introduced through the first exhaust valve during the intake stroke as compared to the case of introducing residual gas by the valve overlap. The operating angle of the first exhaust valve can also be varied during the intake stroke according to the engine operating conditions. It is thus possible to achieve high levels of NOx and fuel efficiency improvement in the internal combustion engine e.g. diesel engine.
The scope of the present invention is defined with reference to the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-034608 | Feb 2012 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4397270 | Aoyama | Aug 1983 | A |
| 5645020 | Yamada | Jul 1997 | A |
| 6568361 | Hara et al. | May 2003 | B2 |
| 8210143 | Meusel et al. | Jul 2012 | B2 |
| 8443499 | Clever et al. | May 2013 | B2 |
| Number | Date | Country |
|---|---|---|
| 55-137305 | Oct 1980 | JP |
| 2002-168105 | Jun 2002 | JP |
| 2011-174416 | Sep 2011 | JP |
| Entry |
|---|
| A. C. Elrod et al., “Development of a Variable Valve Timed Engine to Eliminate the Pumping Losses Associated with Throttle Operation”, SAE Technical Paper Series, International Congress and Exposition, Detroit, Michigan, Feb. 24-28, 1986, No. 860537. |
| Number | Date | Country | |
|---|---|---|---|
| 20130213329 A1 | Aug 2013 | US |
