The present invention relates to improvements in a cam mechanism having forced-valve-opening/closing cams and cam-profile setting method for the valve-opening/closing cams.
Among the internal combustion engines known today are ones provided with a valve operating device of a forced-valve-opening/closing type that forcibly drives air intake and exhaust valves by means of cams directly or via rocker arms.
Such a valve operating device of the forced-valve-opening/closing type requires both cams for opening the valves (i.e., valve-opening cams) and cams for closing the valves (i.e., valve-closing cams). In the case where the valves are driven by means of these valve-opening and valve-closing cams directly or via rocker arms, some clearances are provided between the valve-opening and valve-closing cams and the valves in consideration of respective machining or manufacturing accuracy and assembling accuracy, thermal expansion/shrinkage, etc. of the valves, rocker arms, cams and other valve operating component parts.
The above-mentioned clearances can be represented by a valve lift amount difference between a valve lift curve that is indicative of relationship between a rotation angle of the valve-opening cam and a valve lift amount, and a valve lift curve that is indicative of relationship between a rotation angle of the valve-closing cam and a valve lift amount, as will be explained below.
The valve lift curve 306 of the valve-closing cam is a curve plotted by displacing the above-mentioned valve lift curve 301 upwardly by a clearance CC, and it has two inflexion points 307 and 308 and maximum lift point 309.
The valve speed curve 311, which is obtained by differentiating one of the above-mentioned valve lift curves 301 and 306, has a maximum speed point 312 corresponding to the inflexion points 302 and 307 of the valve lift curves 301 and 306, a zero speed point 313 corresponding to the maximum lift points 304 and 309 of the curves 301 and 306, and a minimum speed point 314 corresponding to the inflexion points 303 and 308 of the curves 301 and 306.
Although separate valve speed curves are obtained separately in correspondence with the valve lift curves 301 and 306, only one of the valve speed curves 311 is shown and described here because the valve speed curves corresponding to the valve lift curves 301 and 306 are of the same shape.
The above-mentioned maximum speed point 312 is a “jumping point” where the follower (provided directly on the air intake valve or exhaust valve or on the rocker arm) moves or jumps away from (i.e., disengages from) the operating surface (i.e., cam surface) of the valve-opening cam. Further, reference numeral 316 in
Similarly, the above-mentioned minimum speed point 314 is a “jumping point” where the follower moves or jumps away from the cam surface of the valve-closing cam. Further, reference numeral 318 in
The valve acceleration curve 321, which is obtained by differentiating the above-mentioned valve speed curve 311, has a zero acceleration point 322 corresponding to the maximum speed point 312 of the valve speed curve 311, a minimum acceleration point 323 corresponding to the zero speed point 313 of the valve speed curve 311, and a zero acceleration point 324 corresponding to the minimum speed point 314 of the valve speed curve 311.
Although separate valve acceleration curves are obtained separately from the valve speed curves obtained in correspondence with the valve lift curves 301 and 306 as noted above, only one of the valve acceleration curves 321 is explained because the two valve acceleration curves are of the same shape.
As stated above, the clearance CC is provided between the valve lift curves 301 and 306. Thus, in the case where the valves are driven by the cams directly, the intake valve and exhaust valve first temporarily move away from the valve-opening cam and valve-closing cam and then collide with the cams, because of the provision of the clearance CC between the cams. In the case where the valves are driven by the cams via the rocker arms, on the other hand, the rocker arms first temporarily move away from the valve-opening cam and valve-dosing cam and then collide with the cams, because of the provision of the clearance CC between the cams. Thus, in both of the cases, unwanted sound noise would be produced by the provision of the clearances between the cams.
Particularly, the inflexion point 302 of the valve lift curve 301 is where the operated member (i.e., the air intake valve, exhaust value or rocker arm), slidably contacting the valve-opening cam, moves away from the operating surface of the valve-opening cam, and the inflexion point 308 of the valve lift curve 306 is where the operated member (i.e., the air intake valve, exhaust value or rocker arm), slidably contacting the valve-closing cam, moves away from the operating surface of the valve-closing cam; thus, the valve speeds take maximum absolute values at these inflexion points. Consequently, at these inflexion points, speeds at which the operated members collide with the operating surfaces of the valve-opening and valve-closing cams become great, which would result in increased sound noise.
In order to prevent such unwanted sound noise, there have been proposed, for example in Japanese Patent Application Laid-Open Publication No. SHO-60-108513 (hereinafter referred to as “Patent Literature 1”) or No. HEI-6-221119 (hereinafter referred to as “Patent Literature 2”), an improved valve operating device and cam-profile setting method for an internal combustion engine of the forced-valve-opening/closing type, which are characterized in that the clearance between the valve lift curve of the valve-opening cam and the valve lift curve of the valve-closing cam is partly narrowed.
More specifically, in the cam curve D, the jump start point PD is located more rearward, in a rotational direction of the cam, than an inflexion point PB of the cam curve B, namely, closer to the maximum lift point PE of the cam curve B, and a point at which the slipper of the rocker arm jumps from the jump start point PD toward the cam curve A is not only located closer to the maximum lift point PE than an inflexion point PA2 of the cam curve A but also set in a first region “L”, as counted from the inflexion point PB, among four equally-divided regions of a range from the inflexion point PB to the maximum lift point PE of the cam curve B. Further, PA1 in
Further, in
Between the valve lift curve E and valve lift curve G, there are formed a clearance C0 (e.g., C0=0.25 mm for the air intake valve or C0=0.35 mm for the exhaust valve) in the valve-opening state, clearance C1 (e.g., C1 is about 0.05 mm) at a cam rotation angle J where the direction of the valve train's inertial force changes, and clearance C2 (=C1) at the time of a maximum valve lift.
With the technique shown in
With the technique shown in
In view of the foregoing prior art problems, it is an object of the present invention to achieve cost reduction and performance enhancement of an internal combustion engine by setting relatively great clearances between valve-opening and valve-closing cams and air intake and exhaust valves in a predetermined range of cam rotation angles.
It is another object of the present invention to minimize unwanted sound noise in a valve operating device of the forced-valve-opening/closing type by lessening collision between air intake and exhaust valves, or followers provided on rocker arms, and valve-opening and valve-closing cams.
According to a first aspect of the present invention, there is provided a cam mechanism having improved valve-opening and valve-closing cams for forcibly driving an air intake valve and exhaust valve. Basic valve lift curve of the valve-opening cam, indicative of relationship between cam rotation angles and valve lift amounts of the valve-opening cam is plotted in a graph where the vertical axis represents valve lift amounts of the air intake valve and exhaust valve and the horizontal axis represents cam rotation angles, and a basic valve lift curve of the valve-closing cam, indicative of relationship between cam rotation angles and valve lift amounts of the valve-closing cam is plotted in the graph by offsetting the basic valve lift curve of the valve-opening cam in a valve-lift-amount increasing direction. No-load valve lift correction curves of the valve-opening and valve-closing cams are set by offsetting a no-load curve section of the basic valve lift curve of the valve-opening cam, along which a corresponding one of the followers for actuating an air intake valve and exhaust valve does not slide, away from the basic valve lift curve of the valve-closing cam and by offsetting a no-load curve section of the basic valve lift curve of the valve-closing cam, along which the follower does not slide, away from the basic valve lift curve of the valve-opening cam, or by modifying the offset no-load curve sections into desired shapes. Respective normal valve lift curves of the valve-opening and valve-closing cams are formed by connecting the corresponding no-load valve lift correction curves with remaining sections of the corresponding basic valve lift curves; thus, a greater clearance can be provided between the normal valve lift curves of the valve-opening and valve-closing cams. The cam profiles of the valve-opening and valve-closing cams are set on the basis of such normal valve lift curves.
With the increased clearance between given sections of the normal valve lift curves of the valve-opening and valve-closing cams, the present invention can eliminate the need for high-accuracy management of the clearance between these sections of the normal valve lift curves of the valve-opening and valve-closing cams, and thereby eliminate the need for enhancing the manufacturing accuracy and assembling accuracy of various component parts of the valve operating device; as a result, the present invention can achieve significant cost reduction of the internal combustion engine. Further, with the increased clearance, the present invention can reduce viscosity resistance and agitation resistance of lubricating oil between the valve-opening and valve-closing cams and the corresponding follower and thereby enhance the performance, such as the output and fuel efficiency, of the internal combustion engine.
Preferably, the basic valve lift curve of the valve-opening cam and the basic valve lift curve of the valve-closing cam each have a middle curve section of a high mountain shape. Two cam rotation angle ranges including mountain base portions of each of the basic valve lift curves of the valve-opening and valve-closing cams are set as first and second ramp sections, and one of two cam rotation angle ranges, including mountain hillside portions of each of the basic valve lift curves, where the follower of the air intake valve or exhaust valve shifts from the valve-opening cam to the valve-closing cam, is set as a first shift section while the other of the two cam rotation angle ranges, where the follower shifts from the valve-closing cam to the valve-opening cam, is set as a second shift section. Another cam rotation angle range including a mountain top portion of each of the basic valve lift curves being is as a great lift section. The normal valve lift curve of the valve-opening cam is formed by connecting together: the no-load valve lift correction curve of the valve-opening cam, formed by offsetting the great lift section of the basic valve lift curve of the valve-opening cam in a valve-lift-amount decreasing direction; the first and second shift sections of the basic valve lift curve of the valve-opening cam; and the first and second ramp sections of the basic valve lift curve of the valve-opening cam; the cam profile of the valve-opening cam is set on the basis of the normal valve lift curve. Similarly, the normal valve lift curve of the valve-closing cam is formed by connecting together: the no-load valve lift correction curve of the valve-closing cam, formed by the first and second ramp sections of the basic valve lift curve of the valve-closing cam being offset in the valve-lift-amount increasing direction; the first and second shift sections of the basic valve lift curve of the valve-closing cam; and the great lift section of the basic valve lift curve of the valve-closing cam; thus, the cam profile of the valve-closing cam is set on the basis of the normal valve lift curve of the valve-closing cam.
In the great lift section, the clearance between the normal valve lift curves of the valve-opening and valve-closing cams can be increased by the great lift section of the basic valve lift curve of the valve-opening cam being offset in the valve-lift-amount decreasing direction. In the first and second ramp sections, the clearance between the normal valve lift curves of the valve-opening and valve-dosing cams can be increased by the first and second ramp sections of the basic valve lift curve of the valve-closing cam being offset in the valve-lift-amount increasing direction. Thus, the clearance has to be managed with high accuracy only in the first and second shift sections; namely, the clearance need not be managed with high accuracy in the other sections than the first and second shift sections. Consequently, high machining or manufacturing accuracy and assembling accuracy is required of the various component parts of the valve operating device, which can thereby achieve significant cost reduction of the internal combustion engine. Further, with the increased clearance, the present invention can reduce the viscosity resistance and agitation resistance of the lubricating oil between the valve-opening and valve-closing cams and the corresponding follower and thereby enhance the performance, such as the output and fuel efficiency, of the internal combustion engine.
According to a second aspect of the present invention, a valve lift amount difference is provided between a basic valve lift curve of a valve-opening cam indicative of a relationship between the cam rotation angles and valve lift amounts of the valve-opening cam and a basic valve lift curve of a valve-closing cam indicative of relationship between the cam rotation angles and valve lift amounts of the valve-closing cam. There are set, with respect to the basic valve lift curves of the valve-opening and valve-closing cams, ultimate valve lift curves of the valve-opening and valve-closing cams each including, as cam rotation angle ranges, a first shift section where a corresponding one of the followers for actuating the air intake valve and exhaust valve jumps away from the valve-opening cam and lands on the valve-closing cam and a second shift section where the follower jumps away from the valve-closing cam and lands on the valve-opening cam. Basic speed difference is determined which is indicative of a difference between jumping and landing speeds of the follower on a basic valve speed curve determined from the basic valve lift curves of the valve-opening and valve-closing cams, and an ultimate speed difference is determined which is indicative of a difference between jumping and landing speeds of the follower on an ultimate valve speed curve determined from the ultimate valve lift curves of the valve-opening and valve-closing cams. The respective cam profiles of the valve-opening and valve-closing cams are set in such a manner that the ultimate speed difference is smaller than the basic speed difference.
The first and second shift sections are provided on each of the ultimate valve lift curves of the valve-opening and valve-closing cams. In the first shift section, the corresponding follower jumps away from the surface of the valve-opening cam and lands on the surface of the valve-closing cam, while, in the second shift section, the corresponding follower jumps away from the surface of the valve-closing cam and lands on the surface of the valve-opening cam. The basic valve speed curve is determined from the basic valve lift curves of the valve-opening and valve-closing cams, and the basic speed difference is determined which is indicative of the difference between the jumping and landing speeds of the follower on the basic valve speed curve. Further, the ultimate valve speed curve is determined from the ultimate valve lift curves of the valve-opening and valve-closing cams, and the cam profiles are set such that the ultimate speed difference between jumping and landing speeds of the follower on the ultimate valve speed curve is smaller than the basic speed difference. Thus, the speed at which the follower collides against the valve-closing or valve-opening cam can be reduced; as a consequence, the colliding impact and hence sound noise can be significantly reduced. Consequently, even if the clearance between the ultimate valve lift curves of the valve-opening and valve-closing cams is formed into a relatively great size, it is possible to reduce the speed at which the follower collides against the valve-opening or vale-closing cam in the first and second shift sections and thereby lessen the colliding compact; as a result, the present invention can suppress production of sound noise while minimizing the cost.
Preferably, the cam profiles are set in such a manner that, in the first and second shift sections, the absolute value of the valve speed at a peak of the ultimate valve speed curve is set to be smaller than the absolute value of the valve speed at a peak of the basic valve speed curve, and that the absolute values of the landing speeds on the ultimate valve speed curve in the first and second shift sections are kept at values higher speed-curve positions than the corresponding absolute values of the landing speeds on the basic valve speed curve. The peak of the basic valve speed curve corresponds to an inflexion point of the basic valve lift curve, and this inflexion point is a point where the follower jumps away from the valve-opening or valve-closing cam. Similarly, the peak of the ultimate valve speed curve corresponds to an inflexion point of the ultimate valve lift curve, and this inflexion point is a point where the follower jumps away from the valve-opening or valve-closing cam.
With the arrangement that, in the first and second shift sections, the absolute value of the valve speed at the peak of the ultimate valve speed curve is set to be smaller than the absolute value of the valve speed at the peak of the basic valve speed curve, the jumping speed on the ultimate valve speed curve can be limited appropriately. Further, with the arrangement that the absolute values of the landing speeds on the ultimate valve speed curve in the first and second shift sections are kept constant at respective values corresponding to higher speed-curve positions than the corresponding absolute values of the landing speeds on the basic valve speed curve—more specifically, the absolute value of the landing speed on the valve speed curve in the first shift section (positive speed region) is kept at a constant value greater than the corresponding absolute value of the landing speed of the basic valve speed curve while the absolute value of the landing speed on the valve speed curve in the second shift section (negative speed region) is kept at a constant value smaller than the corresponding absolute value of the landing speed of the basic valve speed curve—, the landing speed on the ultimate valve lift curve can be increased, so that the ultimate speed difference between the jumping speed and the landing speed can be reduced. As a result, the colliding speed at which the follower collides the valve-closing or valve-opening cam, and hence the colliding impact, cam can be significantly reduced.
According to a third aspect of the present invention, there is provided an improved method for setting cam profiles of valve-opening and valve-closing cams for forcibly driving an air intake valve and exhaust valve, which the comprises: a first step of plotting a basic valve lift curve on the basis of a predetermined lift amount required of the air intake valve or exhaust valve and a valve speed curve from the basic valve lift curve; a second step of determining a basic speed difference between a jumping speed and a landing speed, on the basic speed curve, when a corresponding one of followers for actuating the air intake valve and exhaust valve jump away from the valve-opening cam and land on the valve-closing cam or when the follower jumps away from the valve-closing cam and lands on the valve-opening cam, and plotting an improved valve speed curve such that an improved speed difference between jumping and landing speeds, on the improved valve speed curve, of the follower is smaller than the basic speed difference; a third step of adjusting integrated values of the valve speeds indicated by the improved valve speed curve to integrated values of the valve speeds indicated by the basic valve speed curve while maintaining the improved speed difference, to thereby obtain an ultimate valve speed curve; and a fourth step of plotting an ultimate valve lift curve on the basis of the ultimate valve speed curve.
With the second step of plotting the improved valve speed curve such that the improved speed difference is smaller than the basic speed difference, the colliding speed at which the follower collides against the valve-closing or valve-opening cam, and hence the colliding impact, can be significantly reduced. Further, with the third step of adjusting the integrated values of the valve speeds of the improved valve speed curve to the integrated values of the valve speeds of the basic valve speed curve while maintaining the improved speed difference, the shape of the ultimate valve lift curve can be adjusted to agree with or approach the shape of the basic valve lift curve, except in sections including a range where the follower jumps away from the valve-opening cam and lands on the valve-closing cam or where the follower jumps away from the valve-closing cam and lands on the valve-opening cam.
Certain preferred embodiments of the present invention will hereinafter be described in detail, by way of example only, with reference to the accompanying drawings, in which:
The valve operating device 15 includes a cam shaft 18 rotatably mounted on a cylinder head body 17, a rocker shaft 21 mounted on the cylinder head body 17, a rocker arm pivotably mounted on the rocker shaft 21 and drivable by the cam shaft 18, the air intake valve 12 connected via a connection mechanism 23 to an end of the rocker arm 22 for opening and closing an air intake port 24 of the cylinder head body 17, and the exhaust valve 13 connected to an end of a rocker arm (not shown) for opening and closing an exhaust port 26 of the cylinder head body 17. Reference numeral 31 represents a combustion chamber communicating with the air intake port 24 and exhaust port 26, and 32 represents an ignition plug projecting into the combustion chamber 31.
The cam shaft 18 has a disk section 41 formed thereon in such a manner as to intersect the axis of the shaft 18, and a cam groove section 42 is formed in a surface 41a of the disk section 41.
Cam follower 22a formed at the distal end of the rocker arm 22 is inserted in the cam groove 42, and the cam groove section 42 has a valve-opening cam 44 for opening the air intake valve 12 and a valve-closing cam 45 for closing the air intake valve 12. The valve-opening cam 44 and valve-closing cam 45 slidingly contact the above-mentioned follower 22a. Reference numerals 47 and 48 represent valve guides. Separate followers 22a are provided in corresponding relation to the air intake vale 12 and exhaust valve 13.
The valve operating device 65 includes a cam shaft 67 rotatably mounted on a cylinder head body 61a, rocker shafts 71 and 72 mounted on the cylinder head body 61a, a valve-opening rocker arm 73 and valve-closing rocker arm 74 pivotably mounted on the rocker shafts 71 and 72 and driveable by the cam shaft 67, and the air intake valve 62 driveable by the rocker arms 73 and 74 for opening and closing the air intake port 76. Reference numeral 78 represents a combustion chamber that communicates with the air intake port 76 when the air intake valve 62 is opened.
The cam shaft 67 is provided with a valve-opening cam 81 for driving the valve-opening rocker arm 73, and a valve-closing cam 82 for driving the valve-closing rocker arm 74. Reference numeral 81a represents a valve-opening cam surface slidingly contacting the valve-opening rocker arm 73, and 82a represents a valve-opening cam surface slidingly contacting the valve-closing rocker arm 74.
The valve-opening rocker arm 73 has a cam-side sliding surface 73a slidingly contacting the valve-opening cam 81, and a valve-side sliding surface 73b slidingly contacting an end section 62A of the air intake valve 62.
The valve-closing rocker arm 74 has a cam-side sliding surface 74a slidingly contacting the valve-closing cam 82, and a valve-side sliding surface 74b slidingly contacting the end section 62A of the air intake valve 62.
The end section 62A of the air intake valve 62 has a valve-opening-side sliding surface 62a that slidingly contacts the valve-side sliding surface 73b of the valve-opening rocker arm 73, and a valve-closing-side sliding surface 62b that slidingly contacts the valve-side surface 74b of the valve-closing rocker arm 74.
In the instant embodiment, the end section 62A of the air intake valve 62 corresponds in function to the follower 62a in the embodiment of
Valve lift curve 101 of the valve-opening cam is different from the valve lift curve 301 of
Valve lift curve 111 of the valve-closing cam is different from the valve lift curve 306 of
The cam rotation angle range α1-α2 in the valve lift curve 101 and 111 will hereinafter be referred to as “first shift section”, while the cam rotation angle range α4-α5 in the valve lift curves 101 and 111 will hereinafter be referred to as “second shift section”. The above-mentioned slanted linear portions 101A and 111A are parallel to each other, and slanted linear portions 101B and 111B are parallel to each other.
Valve lift amount difference, i.e. clearance CC, between the valve lift curves 101 and 111 is, for example, 0.1 mm, and the same clearance CC is set in the first shift section and second shift section. Namely, in the instant embodiment, the clearance CC between the valve lift curves 101 and 111 in the first and second shift sections is greater than the clearance in the conventionally-known device shown in
The above-mentioned cam rotation angle range α1-α2 is a range where the inflexion points 302 and 307 of the valve lift curves 301 and 306 of
The cam rotation angle range α1-α2 in the valve speed curve 121 obtained by differentiating the valve lift curve 101 or 111 is in the form of a horizontal linear section 121A, and the cam rotation angle range α4-α5 in the valve speed curve 121 obtained by differentiating the valve lift curve 101 or 111 is in the form of a horizontal linear section 121B.
The horizontal linear section 121A is where the valve speed is kept at a constant value lower than the peak in the positive-speed region of the valve speed curve 121, i.e. the peak in the positive-speed regions or maximum speed point 312 of the valve speed curve 311 of
The horizontal linear section 121B is where the valve speed is maintained at a constant absolute value lower than the peak in the negative-speed region of the valve speed curve 121, i.e. the peak in the negative-speed region or minimum speed point 314 of the valve speed curve 311 of
In
Difference between a jumping speed of the follower (valve speed) at the jumping point 123 and a landing speed of the follower (valve speed) at the landing point 124 is indicated by ΔV1.
In the instant embodiment, the valve speed V1 at the jumping point 123 is set to be lower than a valve speed at the jumping point 312 (see also
Similarly, in
Difference between a jumping speed of the follower at the jumping point 127 and a landing speed of the follower at the landing point 128 is indicated by ΔV2.
In the instant embodiment, the absolute value of the valve speed V2 at the jumping point 127 is set to be lower than the absolute value of a valve speed at the jumping point 314 (
The valve acceleration curve 125 obtained by differentiating the valve speed curve 121 has, in the cam rotation angle range α1-α2, a linear section 125A where the valve acceleration is kept constant at a zero value in correspondence with the linear section 121A of the valve speed curve 121, and has, in the cam rotation angle range α4-α5, a linear section 125B where the valve acceleration is kept constant at a zero value in correspondence with the linear section 121B of the valve speed curve 121.
In the inventive example shown in (a) of
Once the follower 22a reaches the inflexion point 103 while sliding along the valve lift curve 101 of the valve-opening cam 44 as indicated by arrows, it moves away from the inflexion point 103 at the jumping speed V1 (see
In the comparative example shown in (b) of
Once the follower 22a reaches the inflexion point 302 while sliding along the valve lift curve 301 of the valve-opening cam as indicated by arrows, it moves away from the inflexion point 302 at the jumping speed VU (see
In the inventive example shown in (c) of
In the comparative example shown in (d) of
More specifically, the following operation takes place in the inventive example shown in (a) of
Further, the follower 22a lands on the valve lift curve 306 at a great incidence angle θi11, and thus, a valve speed component of the follower 22a, perpendicular to the colliding surface of the valve lift curve 306, increases, which would also increase the colliding impact.
By contrast, in the inventive example shown in (a) of
Further, the follower 22a lands on the linear portion 111A of the valve lift curve 111 at an incidence angle θi1 smaller than the incidence angle θi11 in the comparative example shown in (b) of
The cam rotation angle range α1-α2 in the aforementioned example will hereinafter be referred to as “first shift section” because the follower 22a shifts from the valve lift curve 101 to the valve lift curve 111.
Similar operation takes place in the inventive example shown in (c) of
Further, the follower 22a lands on the valve lift curve 301 at a great incidence angle θi12, and thus, a valve speed component of the follower 22a, perpendicular to the colliding surface of the valve lift curve 301, increases, which would also increase the colliding impact.
By contrast, in the inventive example shown in (c) of
Further, the follower 22a lands on the linear portion 101B of the valve lift curve 101 at an incidence angle θi2 smaller than an incidence angle θi12 in the comparative example shown in (d) of
The cam rotation angle range α4-α5 in the aforementioned example will hereinafter be referred to as “second shift section” because the follower 22a shifts from the valve lift curve 111 to the valve lift curve 101.
The valve lift curve 131 of the valve-opening cam is different from the valve lift curve 301 of
The valve lift curve 141 of the valve-closing cam is different from the valve lift curve 306 of
The above-mentioned cam rotation angle range α1-α2 is a range where the inflexion points 302 and 307 of the valve lift curves 301 and 306 of
The cam rotation angle range α1-α2 in the valve speed curve 151 obtained by differentiating the valve lift curve 131 or 141 is in the form of a slanted linear section 151A, and the cam rotation angle range α4-α5 in the valve speed curve 151 is in the form of a slanted linear section 151B.
The slanted linear section 151A is a portion where the valve speed is lower than the peak of the valve speed curve 151, i.e. lower than the maximum speed point 312 of the valve speed curve 311 (
The slanted linear section 151B is a portion where the absolute value of the valve speed is lower than the peak in the negative-speed region of the valve speed curve 151, i.e. lower than the minimum speed point (i.e., peak in the negative-speed region) 314 of the valve speed curve 311 (
In
Difference between a jumping speed of the follower (valve speed) at the jumping point 153 and a landing speed of the follower (valve speed) at the landing point 154 is indicated by ΔV3.
In the instant embodiment, the valve speed at the jumping point 153 is set to be lower than the valve speed at the jumping point 312 (see also
Similarly, in
Difference between a jumping speed of the follower at the jumping point 157 and a landing speed of the follower at the landing point 158 is indicated by ΔV4.
In the instant embodiment, the absolute value of the valve speed at the jumping point 157 is set to be smaller than the absolute value of the valve speed at the jumping point 314 (see also
The valve acceleration curve 155 obtained by differentiating the valve speed curve 151 has, in the cam rotation angle range α1-α2, a linear section 155A where the valve acceleration is kept constant at a negative value in correspondence with the linear section 151A of the valve speed curve 151, and has, in the cam rotation angle range α4-α5, a linear section 155B where the valve acceleration is kept constant at a positive value in correspondence with the linear section 151B of the valve speed curve 151.
In the inventive example shown in (a) of
Once the follower 22a reaches the inflexion point 133 while sliding along the valve lift curve 131 of the valve-opening cam 44 as indicated by arrows, it moves away from the inflexion point 133 at the jumping speed V3 (see
In the comparative example shown in (b) of
In the inventive example shown in (c) of
In the comparative example shown in (d) of
More specifically, the following operation takes place in the inventive example shown in (a) of
By contrast, in the inventive example shown in (a) of
Further, the follower 22a lands on the second-order curved portion 141A of the valve lift curve 111 at an incidence angle θi3 smaller than the incidence angle θi11 in the comparative example shown in (b) of
Similar operation takes place in the inventive example shown in (c) of
By contrast, in the inventive example shown in (c) of
First step of the cam-profile setting process shown in (a) of
Second step of the cam-profile setting process shown in (b) of
Third step of the cam-profile setting process shown in (c) of
That the integrated valve speed value of the improved valve speed curves 241A and 241B agrees with or approach the integrated valve speed value of the basic valve speed curve 311 means that a difference between the integrated valve speed value of the basic valve speed curve 311 and the integrated valve speed value of the improved valve speed curves 241A and 241B falls within a range of 0-10% of the integrated valve speed value of the basic valve speed curve 311.
Fourth step of the cam-profile setting process shown in (a) of
Fifth step of the cam-profile setting process shown in (b) of
In the figure, reference character 161 indicates a valve lift curve of the valve-opening cam having a middle curve section of a high mountain shape, which represents a modification of the valve lift curve 101 shown in
The valve lift curve 161 includes a first basic lift section 162 in the cam rotation angle range β1-β4, linear second connection section 163 in the cam rotation angle range β4-β5, great list section 164 in the cam rotation angle range β5-β7, linear third connection section 166 in the cam rotation angle range β7-β8, and second basic lift section 167 in the cam rotation angle range β8-β11. The first basic lift section 162 and second basic lift section 167 correspond to a part of the valve lift curve 101 shown in
The valve lift curve 171 includes a first correction ramp section 172 in the cam rotation angle range β1-β2, linear first connection section 173 in the cam rotation angle range β2-β3, basic lift section 174 in the cam rotation angle range β3-β9, linear fourth connection section 176 in the cam rotation angle range β9-β10, and second correction ramp section 177 in the cam rotation angle range β10-β11. The basic lift section 174 corresponds to a part of the valve lift curve 111 shown in
The cam rotation angle includes: a first ramp section in the cam rotation angle range β1-β3 including mountain base portions of the valve lift curves 161 and 171; first shift section in the cam rotation angle range β3-β4 including mountain hillside portions of the valve lift curves 161 and 171; great lift section in the cam rotation angle range β4-β8 including maximum lift points 168 and 309 that are peaks of the valve lift curves 161 and 171 and neighborhoods of the maximum lift points 168 and 309; second shift section in the cam rotation angle range β8-β9 including mountain hillside portions of the valve lift curves 161 and 171; and second ramp section in the cam rotation angle range β9-β11 including the other mountain base portions of the valve lift curves 161 and 171.
The valve lift curve 161 includes a second connection section in the cam rotation angle range β4-β5, and a third connection section in the cam rotation angle range β7-β8. The valve lift curve 171 includes a first connection section in the cam rotation angle range β2-β5, and a fourth connection section in the cam rotation angle range β9-β10.
Clearance CA between the above-mentioned first basic lift section 162 of the valve lift curve 161 and the first correction ramp section 172 of the second valve lift curve 171, clearance CB between the above-mentioned second basic lift section 167 and the second correction ramp section 177 and clearance CD between the above-mentioned great lift section 164 and the basic lift section 174 are each set, for example, at 0.5 mm (i.e., CA=CB=CD=0.5 mm).
Namely, because the clearances CA, CB and CD between the valve lift curve 161 of the valve-opening cam and the valve lift curve 171 of the valve-closing cam are set to be greater than a clearance CC in the other sections than the first shift section and the second shift section of the cam rotation angle, it is not necessary to enhance the machining or manufacturing accuracy of the cam surfaces of the valve-opening and valve-closing cams except for cam surfaces corresponding to the first and second shift sections and the machining or manufacturing accuracy of component parts disposed between the cam surfaces and the air intake and exhaust valves, with the result that component parts, including the cam shaft, of the valve operation system can be reduced significantly.
In the figure, reference character 181 indicates a valve lift curve of the valve-opening cam having a middle curve section of a high mountain shape, which represents a modification of the valve lift curve 131 shown in
The valve lift curve 181 includes a first basic lift section 182 in the cam rotation angle range β1-β4, second connection section 163, great lift section 164, third connection section 166, and second basic lift section 187 in the cam rotation angle range β8-β11. The first basic lift section 182 and second basic lift section 187 correspond to a part of the valve lift curve 131 shown in
The valve lift curve 191 includes a first correction ramp section 172, first connection section 173, basic lift section 194 in the cam rotation angle range β3-β9, fourth connection section 176, and second correction ramp section 177. The basic lift section 194 corresponds to a part of the valve lift curve 141 shown in
Clearance CE between the above-mentioned first basic lift section 182 of the valve lift curve 181 and the first correction ramp section 172 of the second valve lift curve 191, clearance CF between the above-mentioned second basic lift sections 187 and the second correction ramp section 177 and clearance CG between the above-mentioned great lift section 164 and the basic lift section 194 are each set at 0.5 mm (i.e., CE=CF=CG=0.5 mm).
Namely, because the clearances CE, CF and CG between the valve lift curve 181 of the valve-opening cam and the valve lift curve 191 of the valve-dosing cam are greater than a clearance CC in the other sections than the first shift section and the second shift section, it is not necessary to enhance the machining or manufacturing accuracy of the cam surfaces of the valve-opening and valve-closing cams except for the cam surfaces of the cams corresponding to the first second shift sections and the machining or manufacturing accuracy of component parts disposed between the cam surfaces and the air intake and exhaust valves, with the result that component parts, including the cam shaft, of the valve operation system can be reduced significantly.
The first and second ramp sections in the cam rotation angle include mountain base portions of the valve lift curves 181 and 191, the first and second shift sections include mountain hillside portions of the valve lift curves 181 and 191, and the great lift section in the cam rotation angle includes maximum lift points 188 and 309 that include peaks of the valve lift curves 181 and 191 and neighborhoods of the maximum lift points 188 and 309
The valve lift curve 181 also includes a second connection section in the cam rotation angle range β4-β5, and a third connection section in the cam rotation angle range β7-β8. The valve lift curve 191 also includes a first connection section in the cam rotation angle range β2-β3, and a third connection section in the cam rotation angle range β7-β8, and a fourth connection section in the cam rotation angle range β9-β10.
Normal valve lift curve 201 of the valve-opening cam is different from the valve lift amount curve 301 of the valve-opening cam shown in
The first and second ramp curves 202 and 204 overlap the valve lift amount curve 301 shown in
Normal valve lift curve 211 of the valve-closing cam is different from the valve lift amount curve 306 of the valve-closing cam shown in
The first ramp correction curve 212 includes an end curve section 216 offset from a corresponding part of the valve lift amount curve 306 shown in
As shown in (b) and (d) of
Namely, the cam rotation angle range θ1-θ3 of the valve lift curve 301, and the cam rotation angle range below the angle θ1 and cam rotation angle range above the angle θ3 of the valve lift curve 306 are ranges where the follower 22a does not slide.
Referring back to
Thus, it may be said that the intermediate curve section 206 is formed by offsetting most of the no-load curve section 331 in the valve-lift-amount decreasing direction, the end curve section 216 is formed by offsetting most of the no-load curve section 332 in the valve-lift-amount increasing direction and the end curve section 218 is formed by offsetting most of the no-load curve section 333 in the valve-lift-amount increasing direction.
At the jumping point 312 and landing point 316 of the valve speed curve (basic valve speed curve) 311 of the valve-opening cam shown in
Namely, according to the present invention, in the cam rotation angle range where the follower slides, one of the valve lift curves 301 and 306, along which the follower slides, is used as-is. But, in the cam rotation angle range where the follower does not slide, the great valve lift correction curve 203, first ramp correction curve 212 and second ramp correction curve 214 are set as no-load valve lift slide curves by one of the valve lift curves 301 and 306 along which the follower does not slide being offset away from the other of the valve lift curves 306 and 301, the normal valve lift curve 201 of the valve-opening cam is set with the first ramp curve 202, great lift correction curve 203 and second ramp curve 204, and the cam profile of the valve-opening cam is determined on the basis of the normal valve lift curve 201; in addition, the normal valve lift curve 211 of the valve-closing cam is set with the first ramp correction curve 212, great lift curve 213 and second ramp correction curve 214, and the cam profile of the valve-closing cam is determined on the basis of the normal valve lift curve 211.
Namely, because the no-load-side basic valve lift curve section, along which the follower does not slide, is offset away from the other basic valve lift curve, the present invention can increase the clearance between the normal valve lift curves of the valve-opening and valve-closing cams, to thereby reduce viscosity resistance and agitation resistance of lubricating oil between the cam of the non-sliding side and the corresponding follower and greatly reduce friction between the cam and the sliding portion of the follower.
Further, no high dimensional accuracy is required of the follower and cam of the non-sliding side; namely, no high-accuracy management is required of the clearance between the valve-opening cam and the valve-closing cam, so that it is possible to eliminate the need for enhancing the cam manufacturing accuracy and assembling accuracy and thus achieve significant cost reduction.
Normal valve lift curve 221 of the valve-opening cam has, in the cam rotation angle range θ1-θ3, a section modified, relative to the valve lift curve 301 of the valve-opening cam shown in
The middle correction curve 223 may be any desired curve, such as an algebraic curve that can be expressed easily with a mathematical expression, or a free curve that has continuity and is difficult to express with a mathematical expression.
Normal valve lift curve 231 of the valve-dosing cam has, in the cam rotation angle range below θ1 and cam rotation angle range above θ3, sections modified, relative to the valve lift curve 306 of the valve-closing cam, into a shape such that the modified sections are greater in valve lift amount than the corresponding sections of the curve 306 shown in
The end correction curves 232 and 234 may each be any desired curve, such as an algebraic curve that can be expressed easily with a mathematical expression, or a free curve that has continuity and is difficult to express with a mathematical expression.
As described above in relation to
Further, as described above in relation to
With the aforementioned arrangements, portions of the clearance between the normal valve lift curve 161 of the valve-opening cam 44 and the normal valve lift curve 171 of the valve-closing cam 45 can be set to increased sizes. Thus, the clearance has to be managed with high accuracy only in the first and second shift sections; namely, the clearance need not be managed with high accuracy in the other sections than the first and second shift sections. Consequently, high machining or manufacturing accuracy and assembling accuracy is required of the various component parts of the valve operating device 15, which can thereby achieve significant cost reduction of the internal combustion engine 10.
Further, with the size increase of the clearance, the viscosity resistance and agitation resistance of the lubricating oil between the valve-opening and valve-closing cams 44 and 45 and the followers 22a can be effectively reduced, so that the performance, such as the output and fuel efficiency, of the internal combustion engine 10 can be significantly enhanced.
Note that, whereas the preferred embodiment has been described above in relation to the case where the first, second, third and fourth connection sections 173, 162, 166 and 176 are formed as straight lines, the present invention is not so limited and these connection sections 173, 162, 166 and 176 may be formed as curved lines that smoothly connect to adjoining lines.
Further, whereas the first correction ramp section 172 in the preferred embodiment has been described above as formed by offsetting upwardly the ramp section in the cam rotation angle range β1-β2 of the first basic lift section 162 and the second correction ramp section 177 has been described above as formed by offsetting upwardly the ramp section from the cam rotation angle range β10-β11 of the second basic lift section 167, the present invention is not so limited; for example, the first correction ramp section 172 may be formed continuously with the first connection section 173 with the clearance between the first connection section 173 and the first basic lift section 162 gradually increasing in size in a direction from the cam rotation angle β3 toward the cam rotation angle β1, and the second correction ramp section 177 may be formed continuously with the fourth connection section 176 with the clearance between the fourth connection section 176 and the second basic lift section 167 gradually increasing in size in a direction from the cam rotation angle β9 toward the cam rotation angle β11.
Further, as described above in relation to
With the aforementioned arrangements, it is possible to reduce the colliding speed at which the follower 22a collides against the valve-opening or valve-closing cam 44 or 45 in the first and second shift sections even in the case where the clearance between the lift curves 101 and 111 of the valve-opening and valve-closing cams 44 and 45. Because the impact at the time of the collision can be lessened in this manner, the present invention can effectively minimize production of noise sound while minimizing the necessary cost.
Further, the cam profiles are set in such a manner that, in the first and second shift sections, the absolute value of the valve speed at the jumping point 123 as the peak of the ultimate valve speed curve 121 is set to be smaller than the absolute value of the valve speed at the maximum speed point 312 as the peak of the basic valve speed curve 311, and that the absolute values of the landing speeds on the valve speed curve 121 in the first and second shift sections are kept at constant values corresponding to higher speed-curve positions than the corresponding absolute values of the landing speeds on the basic valve speed curve 311; more specifically, the absolute value of the landing speed on the valve speed curve 121 in the first shift section (i.e., positive speed region) is kept at a constant value greater than the corresponding absolute value of the landing speed of the basic valve speed curve 311, while the absolute value of the landing speed on the valve speed curve 121 in the second shift section (i.e., negative speed region) is kept at a constant value smaller than the corresponding absolute value of the landing speed of the basic valve speed curve 311. In this way, not only the jumping speed V1 of the follower 22a on the valve speed curve 121 is limited, but also the landing speed of the follower 22a on the valve speed curve 121 is increased. Thus, it is possible to decrease the speed difference ΔV1 between the jumping speed V1 and landing speed of the follower 22a, so that the colliding speed of the follower 22a against the vale-opening or valve-closing cam 44 or 45 can be reduced and thus the impact at the time of the collision can be effectively lessened.
Furthermore, as described above in relation to
With the aforementioned second step, it is possible to reduce the colliding speed at which the follower 22a collides against the valve-opening cam 44 or valve-closing cam 45, to thereby lessen the colliding impact. Further, with the third step, which adjusts the integrated values of the valve speeds indicated by the improved valve speed curves 241A and 241B to the integrated values of the valve speeds indicated by the valve speed curve 311 while maintaining the improved speed difference ΔV1, it is possible to cause the shape of the ultimate valve lift curve 101 to agree with or approach the shape of the valve lift curve 301, except in a section that includes the range where the follower 22a jumps away from the valve-opening cam 44 and lands on the valve-closing cam 45 or where the follower 22a jumps away from the valve-closing cam 45 and lands on the valve-opening cam 44.
The embodiment shown in
The valve operating device and cam-profile setting method of the present invention are suitably applicable to forced-valve-opening/closing cams for an internal combustion engine.
Number | Date | Country | Kind |
---|---|---|---|
P2006-308110 | Nov 2006 | JP | national |
P2006-339071 | Dec 2006 | JP | national |
Number | Name | Date | Kind |
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20030106515 | Kondo | Jun 2003 | A1 |
Number | Date | Country |
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60-108513 | Jun 1985 | JP |
6-221119 | Aug 1994 | JP |
Number | Date | Country | |
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20080110425 A1 | May 2008 | US |