JPH01300005A - Processing method for cam shaft for valve system - Google Patents

Abstract

PURPOSE:To make the quality control easy by the simultaneous processing, at least, of the base circle part of a first speed correspondent cam of a grinding tool which rotates around the same axial line with the cam in a mechanism where the free connection in a pair of first speed correspondent cam and second speed correspondent cam is possible. CONSTITUTION:A pair of low speed cams 3a, 3b and a single highspeed cam 4 provided between them are mounted on a cam shaft 2 which synchronically rotates with a crank shaft. Rotation of this cam shaft 2 opens and closes a pair of suction valves provided on each air cylinder through a pair of direct- action rocker rocker arms 5, 7 and a floating rocker arm 6. Each of the rocker arms 5-7 can be freely shifted to the condition where they monolithically oscilate and to the condition where they relatively displace by a connecting device 14 mounted in a hole penetrated through the central part of these rocker arms. In a valve system like this, a grinding tool 40 which rotates around the same axial line is made to process, at least, the base circle part of a pair of the low speed cams 3a, 3b.

Description

Detailed Description of the Invention [Objective of the Invention] <Industrial Application Field> The present invention relates to an internal combustion engine having a switching device that changes the operating state of an intake valve or an exhaust valve in stages according to the rotational speed of an internal combustion engine. This invention relates to a method for machining a camshaft for a horizontal valve train of an engine.

<Prior Art> The combustion chamber of a four-stroke internal combustion engine is equipped with an intake valve and an exhaust valve in order to supply the air-fuel mixture to the combustion chamber and discharge combustion gas at predetermined timings. ,this·
Both valves are normally biased in the valve closing direction by a valve spring provided so as to surround the valve stem.

Furthermore, both of these valves are forcibly pushed open against the biasing force of the valve spring mentioned above by a cam that is integrally installed on a camshaft that is connected and driven from the engine's crankshaft using a belt, pulley, etc. It is made possible to do so.

On the other hand, in order to improve the filling efficiency of air-fuel mixture into the combustion chamber over a wide range of rotational speeds, various techniques have been proposed for changing the operating state of a valve in accordance with the rotational speed of the engine.

As such a valve operation state switching device, for example, in Japanese Patent Application Laid-Open No. 16111/1983 by the present applicant, there is a device having a shape corresponding to a pair of intake valves or an exhaust valve, respectively, and corresponding to the low speed rotation range of the engine. A pair of low-speed cams and a single high-speed cam with a shape corresponding to the high-speed rotation range of the engine are integrally arranged adjacent to a camshaft that is driven to rotate in synchronization with the rotation of the engine. A pair of direct-acting rocker arms that do not engage directly with the valve but slide on the low-speed cam and a floating rocker arm that slides on the high-speed cam via a floating biasing means are arranged adjacent to the rocker shaft so that they can be relatively angularly displaced. However, an internal combustion engine is provided in which a connecting means is installed inside each rocker arm to enable switching between a state in which these rocker arms are integrally connected and a state in which relative angular displacement between the direct-acting and floating rocker arms is allowed. A valve operating state switching device has been proposed. As a means for this connection, screws 1 to 1 are slid into guide holes arranged inwardly so as to communicate between each rocker arm, and this piston is hydraulically driven so that it straddles the same dirt floor between the adjacent rocker arms. A structure that allows rocker arms to be connected to each other is disclosed in the same specification.

According to the above structure, when the cam slipper of each rocker arm is in sliding contact with the base circle of the corresponding cam, the pistons are displaced to a position that straddles the adjacent rocker arms, thereby connecting the double-ended lock arms to each other. be done. Therefore, in order to ensure smooth operation of the piston, it is necessary to make the coaxial precision of the guide holes of the three rocker arms extremely high, which poses the problem of complicating quality control.

Therefore, in the specification of Japanese Patent Application No. 62-336596, the present applicant has proposed a method that enables smooth switching operation without extremely reducing the manufacturing tolerances of each component that constitutes the valve mechanism. Therefore, we proposed a structure in which the guide hole of the floating rocker arm disposed at the center is set to be somewhat larger than the guide hole of the direct-acting rocker arm disposed on both sides.

<Problems to be Solved by the Invention> However, according to this structure, since the cumulative error between the direct-acting rocker arm and the floating rocker arm is absorbed by the clearance between the guide hole and the piston, Depending on the situation, errors may accumulate in the direction of increasing backlash. Therefore, there is a risk that the effective lift of the cam in the high-speed rotation range may be reduced, or that a knocking noise may be generated.

The present invention has been made to improve the disadvantages of the prior art, and its main purpose is to provide an improved valve mechanism that eliminates as much as possible the factors that reduce the coaxial precision of the guide hole. The object of the present invention is to provide a method of machining a camshaft for use.

[Structure of the Invention] <Means for Solving the Problems> According to the present invention, at least three parts having a connecting means that can be selectively connected when mutually adjacent parts are in a predetermined positional relationship are provided. The valve is installed at the intake port or exhaust bow of the combustion chamber and is normally biased closed by a spring means. A valve mechanism for an internal combustion engine comprising a pair of first speed compatible cams each given a correspondingly different cam profile and a second speed compatible cam sandwiched between the pair of first speed compatible cams. 1. A method for machining a camshaft for a valve mechanism, characterized in that at least a base circle portion of the pair of first speed compatible cams is simultaneously machined with a grinding tool rotating on the same axis. This is achieved by providing a method for machining a camshaft.

In this way, the pair of cams that provide the same operating conditions to the pair of cam followers are formed with substantially the same tolerance. Therefore, it is possible to prevent the cumulative error between the pair of cam followers that engage with the pair of cams from increasing.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, a pair of intake valves 1a and 1b are provided in the internal combustion engine body (not shown). These intake valves 1a and 1b are located at 1/2 of the crankshaft (not shown).
A pair of low-speed cams 3a, 3 having a predetermined profile and integrally provided on the camshaft 2 which are synchronously driven at two speeds.
b, a single high-speed cam 4, and each low-speed cam 3a and 3b
The opening/closing operation is performed by the action of a pair of linear motion rocker arms 5 and 7 as cam followers that engage with each other to perform a rocking motion, and a floating rocker arm 6 that engages with the high-speed cam 4 to perform a rocking motion. has been done. Further, this internal combustion engine is equipped with a pair of exhaust valves (not shown), which are driven to open and close in the same manner as the intake valves 1a and 1b described above.

Each rocker arm 5 to 7 is connected to the camshaft 2 below the camshaft 2.
They are pivotally supported adjacent to each other so as to be swingable on a rocker shaft 8 which is fixedly installed in parallel to the rocker shaft 8 .

Of these, both direct-acting rocker arms 5 and 7 have basically the same shape, their bases are pivoted to rocker shafts 8, and their free ends extend above each intake valve 1a and 1b, respectively. has been done. Additionally, tappet screws 9a and 9b that abut the upper ends of the respective intake valves 1a and 1b are screwed into the free ends of both the direct-acting rocker arms 5 and 7 so as to be movable forward and backward.・9b is
They are each prevented from loosening by lock nuts 10a and 10b.

The floating rocker arm 6 is pivotally supported on a rocker shaft 8 between the two translational rocker arms 5 and 7. The floating rocker arm 6 extends slightly from the rocker shaft 8 toward the middle of the intake valves 1a and 1b, and as shown in FIG. 6a is formed on the upper surface of the free end, and a radius 11 to the cylinder is formed.
The upper end surface of the glue lid 12, which serves as a floating biasing means that slides into a guide hole 11a formed in the guide hole 11a, is in contact with the lower surface thereof.

The lifter 12 has a cylindrical shape with a bottom, and the diameter of the bottom wall thereof is reduced, and accordingly, a stepped portion 12a is formed inside. Inside the lifter 12, there is a small diameter spring 13a with a relatively small spring constant and a large diameter spring 13b with a relatively large spring constant.
2b is held in place and contracted. As a result, the floating rocker arm 6 is resiliently biased so that its cam slipper 6a is always in sliding contact with the high-speed cam 4.

As described above, the camshaft 2 is rotatably supported above the engine body, and the low-speed cams 3a and 3b and the high-speed cam 4 are integrally connected. As clearly shown in FIG. 3, the low-speed cams 3a and 3b are designed for use in the low-speed rotational range of the engine, which basically consists of a base circle portion B1 that is a perfect circle and a high portion L1 that has a relatively small lift. The cam slippers 5a and 7a are formed in a matching cam profile and are formed on the upper surface of each linear motion rocker arm 5 and 7.
The outer peripheral surfaces thereof can be brought into sliding contact with each other. In addition, the high-speed cam 4 is adapted to the high-speed rotation range of the engine, consisting of a base circle portion B2, which is also basically a perfect circle, and a high portion L2, which has a larger lifting height over a wider angle than the low-speed cams 3a and 3b. As described above, the outer peripheral surface of the rocker arm 6 is in sliding contact with the cam slipper 6a of the floating rocker arm 6. Note that the lifter 12 is not shown in FIG. 3.

Each of these rocker arms 5 to 7 is
A connecting device 14 (to be described later) installed in a hole drilled through the center of the rocker shaft 8 in parallel with the rocker shaft 8 allows switching between a state in which the rocker can swing integrally and a state in which it can be relatively displaced. It's like that.

On the other hand, a retainer 15a is provided at the upper part of each intake valve 1a, 1b.
- 15b are provided respectively. At the same time, between the retainers 15a and 15b and the engine body, a valve spring 1 surrounding the stem portion of each intake valve 1a and 1b is installed.
6a and 16b are interposed, respectively, and are used to elastically bias each intake valve 1a and 1b in the normally closed direction, that is, upward in FIG. 3.

As clearly shown in FIGS. 4 and 5, a first guide hole 17 that opens toward the floating rocker arm 6 side is bored in one of the first translational rocker arms 5 in parallel with the rocker shaft 8. There is. A reduced diameter portion 18 is formed on the bottom side of the first guide hole 17, and a stepped portion 19 is formed accordingly.

A second guide hole 20 communicating with the first guide hole 17 of the first translational rocker arm 5 is bored through the floating rocker arm 6 between both sides thereof.

The other second translational rocker arm 7 has a second guide hole 20.
A third guide hole 21 communicating with is bored. The bottom side of the third guide hole 21 is formed with a stepped portion 22 and a small diameter portion 23, similar to the first guide hole 17, and a through hole 24 is further formed in the bottom wall of these portions. Inside the first to third guide holes 17, 20, and 21, there is a first piston 25 that can move between a position where the first translational rocker arm 5 and the floating rocker arm 6 are connected and a position where the connection is released. , a second piston 26 that is movable between a position where the floating rocker arm 6 and the second translational rocker arm 7 are connected and a position where the connection is released; a stopper 27 that defines the moving distance of both the pistons 25 and 26; A coil spring 28 is installed to constantly bias the pistons 25 and 26 toward the disconnection position.

The first piston 25 slides into the first guide hole 17 and the second guide hole 20, thereby defining a hydraulic chamber 29 between the bottom surface of the first guide hole 17 and the end of the first piston 25. , there is. Further, a pair of passages 30 and 31 are bored in the rocker shaft 8 and communicate with a hydraulic pressure supply device (not shown).

The first linear-acting rocker arm 5 is then Regardless of the swing state of the hydraulic oil supply passage 30, hydraulic oil supplied from one hydraulic oil supply passage 30 can be introduced into the hydraulic chamber 29 as necessary. The pivot portions of the rocker arms 5 to 7 are lubricated by the lubricating oil supplied from the other lubricating oil supply passage 31.

The axial dimension of the first piston 25 is such that when one end thereof comes into contact with the stepped portion 19 in the first guide hole 17, the other end does not protrude from the side surface facing the floating rocker arm 6 of the first translational rocker arm 5. is set to .

The second piston 26 has an axial dimension equal to the entire length of the second guide hole 20 so that it can slide into the second guide hole 20 and the third guide hole 21 .

The stopper 27 has a disk portion 27a formed at one end that slides into the third guide hole 21, and a guide rod 27b inserted into the through hole 24 at the other end. Further, between the disk portion 27a of the stopper 27 and the bottom of the small diameter portion 23 of the third guide hole 21, the coil spring 28 described above is provided surrounding the guide rod 27b.
has been reduced. This coil spring 28 is connected to the hydraulic chamber 29
It is designed to bend when the hydraulic pressure acting on it reaches a certain predetermined value or more.

At the same time, in the coupling device 14, in order to smoothly and reliably fit the first piston 25 into the second guide hole 20 during the coupling operation, a floating rocker arm 6 is provided as shown in FIG. A partially spherical chamfered portion 34a is formed around the entire circumference of the end of the first piston 25 facing the side, and a tapered chamfered portion is formed around the open end of the floating rocker arm 6 facing the first translational rocker arm 5 side. 35a is formed over the entire circumference. Similarly, a partially spherical chamfered portion 34b is formed around the entire circumference of the end of the second piston 26 facing the second translational rocker arm 7 side, and a partially spherical chamfered portion 34b is formed around the entire circumference of the second piston 26 facing the second translational rocker arm 7 side. 2 Direct-acting rotsuka arm 7
A tapered chamfered portion 35b is formed around the entire circumference of the opening end.

Next, the operating procedure of the apparatus described above will be explained.

In the middle and low speed range of the engine, the supply of hydraulic pressure to the hydraulic oil supply passage 30 is cut off by closing a control valve (not separately shown). Then, each piston 25 and 26
are aligned in the guide holes 17 and 20, respectively, as shown in FIG. 4, by the biasing force of the coil spring 28, so that the rocker arms 5 to 7 can be angularly displaced relative to each other.

When the coupling device 14 is in the uncoupled state, the rotation of the camshaft 2 causes the first and second direct-acting rocker arms 5 and 7 to slide into sliding contact with the low-speed cams 3a and 3b. At the same time, the intake valves 1a and 1b are driven to open and close by retarding their opening timing and advancing their closing timing, and also by reducing the lift +-i. At this time, the floating rocker arm 6 swings due to sliding contact with the high-speed cam 4, but this swinging action has no effect on the operation of both intake valves 1a and 1b.

On the other hand, lubricating oil is constantly pumped into the fluid passage 31.
The rocker shirt h8 and each of the rocker arms 5 to 7 are lubricated through oil holes (not shown).

During high-speed operation of the engine, by opening the control valve, the hydraulic oil supply passage 30 and the communication hole 3 of the rocker shaft 8 are
Hydraulic pressure is supplied to the hydraulic chamber 29 of the coupling device 14 through the oil passage 3 and the oil passage 32 . As a result, as shown in FIG. 5, the first piston 25 moves toward the floating rocker arm 6 against the pressing force of the coil spring 28, and the second piston 26 is pushed by the first piston 25 and moves toward the second piston 25. Move to the linear motion rocker arm 7 side. As a result, one end of the stopper 27 is connected to the stepped portion 19.
The first and second pistons 25 and 26 move together until they come into contact with the first piston 25, the first direct-acting rocker arm and the floating rocker arm 6 are connected, and the second piston 26
The floating rocker arm 6 and the second translational rocker arm 7 are connected in three or more ways, and each rocker arm 5 to
7 are connected to each other by the connecting device 14, the amount of swing of the floating rocker arm 6 in sliding contact with the high-speed cam 4 is the largest, so the first and second translational rocker arms 5 and 7 are It swings together with the floating rocker arm 6. Therefore, both the intake valves 1a and 1b are driven to open and close at the same time, with their opening timings being advanced and their closing timings being delayed and their lift amounts being increased, according to the cam profile of the high-speed cam 4.

Here, as shown in FIG. 6, the base circle diameters D1 and DI' of the low-speed cams 3a and 3b are equal, and there is a deviation of dl between these and the base circle diameter D2 of the high-speed cam 4. Assuming that the cam slipper 5 of each rocker arm 5 to 7
a to 7a are the base circular portions B1 of each cam 3a, 3b, and 4
- When at B2, the guide hole center C2 of the floating rocker arm 6 moves d2 (d2') toward the camshaft 2 side corresponding to the deviation d1 from the guide hole center C1 CI' of both the linear motion rocker arms 5 and 7. However, it will always be eccentric.

On the other hand, assuming that the tappet clearance is 0 for each direct-acting rocker arm 5, 7 that is in direct contact with the valve stem end of each intake valve 1a, 1b, in this case, each direct-acting rocker arm 5, 7 is in direct contact with the valve stem end of each intake valve 1a, 1b. 7 movement is each low speed cam 3
a and 3b profiles and each valve spring 16a and
16b, and it can be said that there are almost no elements that cause rattling.

On the other hand, when the floating rocker arm 6 is in sliding contact with the base circular portion B of the high-speed cam 4, the large diameter spring 13b in the lifter 12 is in a state of free length, and the stepped portion 1 in the lifter 12 is in a state of free length.
There is a gap between retainer 2b and retainer 12a. Therefore,
In this state, only the small diameter spring 13a whose spring constant is set to be relatively small is contracted, and the floating rocker arm 6
It is possible to oscillate it slightly.

Taking this point into consideration, and assuming that the first piston 25 tries to push out the second piston 26 due to the pressure P in the hydraulic chamber 29, the direct-acting rocker arms 5 and 7 will have a pressing force F1 of the valve springs 16a and 16b. However, the floating rocker arm 6 is equipped with a relatively small small diameter spring 13.
Since only the pressing force F2 of a is acting, the floating rocker arm 6 can be displaced downward by the thrust force of the first piston 25.

That is, as mentioned above, the guide hole centers C1 and CI on both sides
' are on the same axis, even if there is some deviation between the intermediate guide hole centers C2, the floating rocker arm 6 will be displaced by the plunge force of both pistons 25 and 26, and the second guide hole 26 will be eccentric. is corrected, and each rocker arm 5
It can be seen that ~7 concatenations can be achieved.

Next, the base circle diameters D1 and D1' of the cams 3a and 3b for both paper speeds.
Let us assume that there is a deviation between the two.

In this case, the guide hole center C2 of the floating rocker arm 6
The deviation d2 of the guide hole center C1 of the first translational rocker arm 5 with respect to the guide hole center C1 of the second translational rocker arm 7
The deviation d2' of I' will be different, and depending on the amount of deviation, the floating rocker arm 6 will not be able to be displaced, and a smooth connection operation will not be achieved.

As can be seen from the above description, in the valve train in the above embodiment, the three rocker arms are connected by the piston moving across the guide holes of the adjacent rocker arms. Therefore, at least the centers C1 and C1 of the guide holes of both the linear motion rocker arms 5 and 7 arranged on both sides.
'If the pistons 25 and 26 are not exactly coaxial, the pistons 25 and 26 cannot move.

By the way, as is well known, the parts that make up the valve mechanism are:
Although they are manufactured based on predetermined tolerances, for example, if a hole part whose finishing tolerance is on the plus side and a shaft part whose finishing tolerance is on the minus side are combined, the clearance between the two will become excessive, causing play. It is possible that Moreover, in the opposite case, smooth operation may be hindered. In order to prevent this, it is necessary to appropriately select each part according to its finishing accuracy and combine them so that the cumulative error is minimized, which makes quality control extremely complicated.

Therefore, in the present invention, by simultaneously machining the low-speed cams 3a and 3b on both sides of the high-speed cam 4 using a common grinding tool, the finished tolerance of the base diameter of both paper-speed cams 3a and 3b can be adjusted. They are made as equal as possible.

As shown in FIG. 7, the grinding tool 40 is a known type of grinding wheel made by melting and molding alumina material, and is generally disk-shaped. Grinding surfaces 41a and 41b corresponding to both paper speed cams 3a and 3b of the camshaft 2, which is a product, are formed, and an escape route 42 is formed in the intermediate portion thereof to avoid contact with the high speed cam 4.

A drive shaft 43 on which this grinding tool 40 is placed parallel to the camshaft 2
The cam profile is machined by numerical control by pressing it against the cam surface while rotating it at the top.

Incidentally, as shown in FIG. 8, the grinding surfaces 41a and 41b of the grinding tool 40 are simultaneously shaped by a common dresser 44.

Above, only the example in which the base circle diameters are machined to be equal has been described, but the coaxial accuracy of each guide hole is determined by the relative relationship with the height of the cam slipper surface of the rocker arm, and the base circle diameters of both cams are not necessarily determined. It goes without saying that the finishing tolerances of both cams are not limited to being equal, but that it is sufficient that the finishing tolerances of both cams are equal.

[Effects of the Invention] As described above, according to the present invention, it is possible to process the pair of rocker arms disposed on both sides to have substantially equal tolerances, and it is possible to suppress the accumulation of dimensional errors related to the coupling device. . Therefore, it is extremely effective in reducing possible play in the coupling device and increasing its smoothness of operation, while at the same time making it possible to somewhat relax control tolerances and simplify quality control. , which has a great effect on reducing manufacturing costs.

[Brief explanation of the drawing]

FIG. 1i is a top view of a valve train having a valve operating state switching device constructed based on the present invention. FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1. FIG. 3 is a view in the direction of the ■ arrow in FIG. 1. FIG. 4 is a sectional view taken along the line IV--IV in FIG. 3 showing the state of low-speed operation. FIG. 5 is a cross-sectional view similar to FIG. 4 showing the state of high-speed operation. Figure 6 shows V [-V
FIG. FIG. 7 is a schematic diagram showing a cam grinding process, and FIG. 8 is a schematic diagram showing a grinding tool shaping process. 1a, 1b...Intake valve 2...Camshaft 3a, 3b...
...Low speed cam 4...High speed cam 5...First linear motion rocker arm 6...Idle 20 lock arm 7...Second translation rocker arm 5a, 6a, 7a...Cam slipper 8...・Rocker shafts 9a, 9b...Tappet screws 10a, 10b...Lock nuts 11...Cylinder head lla...Guide holes 12・
...Lifter 12a...Step part 12b...Retainer 13a...Small diameter spring 13b...Large diameter spring
14... Connecting device 15a, 15b... Retainer 16a, 1.6 b... Valve spring 17...
First guide hole 18...Small diameter part 1.9...Step part
20... Second guide hole 21... Third guide hole 22... Step part 23... Small diameter part 24...
Through hole 25...first screw 1~n 26...second piston 27...slue 1~flange 28...coil spring 29...hydraulic chamber 30...hydraulic oil supply passage 3
1... Lubricating oil supply passage 32... Oil passage 33... Communication holes 34a, 34b... Partially spherical surface fitting portions 35a, 35b
...Tapered chamfer portion 40...Grinding tool 41a, 41b...Grinding surface 42...Escape plan 43...Drive shaft 44...
Dresser Patent Applicant Honda Motor Co., Ltd. Representative Patent Attorney Yo Oshima - Figure 1 Figure 2 / Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] (1) A spring means installed at the intake port or exhaust port of the combustion chamber in cooperation with at least three cam followers having connection means that can be selectively connected when mutually adjacent parts are in a predetermined positional relationship. A pair of first speed compatible cams provided with different cam profiles corresponding to the rotational speed range of the engine, and the pair of first speed compatible cams, in order to stepwise switch the valve open operation state of the valve energized to close the valve. A method of machining a camshaft for a valve mechanism of an internal combustion engine, which is formed by serially installing a second speed compatible cam sandwiched between cams, wherein at least a base circular portion of the pair of first speed compatible cams is A method for machining a camshaft for a valve mechanism, characterized in that the machining is performed simultaneously using a grinding tool that rotates on the same axis.