GB2138093A - Rocker arm for internal combustion engine - Google Patents

Abstract

A method of manufacturing a rocker arm (1) for an internal combustion engine comprising integrally casting a chip (1003) of sintered iron alloy with an arm member of aluminum alloy, forming a thin film over the surface of the chip (1003), forming a porous anodic oxide film on the arm member, electrolysing it in a solution of ammonium thiomolybdate to form molybdenum sulfide inside the pores. The rocker arm (1) preferably has a clearance adjuster unit (1004) provided therein, no linears being required around the clearance adjuster unit (1004). A second aspect is a rocker arm of aluminum alloy with molybdenum sulfide in the pores of a porous anodic oxide film thereon and a cam follower portion of a relatively hard and friction resistant material. <IMAGE>

Description

SPECIFICATION Rocker arm for internal combustion engine The present invention concerns a rocker arm comprising movable valve systems for internal combustion engines and a method of manufacture therefor.

As the inlet and exhaust valves of internal combustion engines become worn through use, it is necessary to periodically repair and/or replace the sliding surfaces or to adjust the voids. Friction between the valve seat and the valve face would cause the upper end of the valve to be pushed toward the rocker arm by the valve spring, and result in a state where the rocker arm would constantly press the valve down and deteriorate the air tightness of the cylinder. Friction between the upper end face of the valve and the contact surface of the rocker arm would increase the void between the two, resulting in increased noise and lowered output. Therefore, a zero clearance adjuster of oil hydraulic type is used to keep the contact between the rocker arm and the valve constantly in optimal condition.

The prior art rocker arm is structured as shown in Figure 1 wherein a rocker arm 1 is placed over a rocker arm shaft 300 to swing correspondingly to the rotation of a cam 500 and to vertically move the axial end of an inlet (or exhaust) valve 400 via a zero clearance adjuster 3. The zero clearance adjuster 3 is mounted in a cylinder member formed in the rocker arm. To prevent the cylinder becoming prematurely deformed because of insufficient rigidity, there is formed a cylindrical liner 2 made of iron or copper. This type of system is widely used today as rocker arms made of light alloy metals are favored in order to decrease inertia for incrementing engine speed.

In other words, the liner is necessary for the following reasons: (1) When the oil pressure supply fails due to leakage such as when the engine stops, the body 1 30 of the zero clearance adjuster 3 slides only in the minute range of 0--2 nm which is the automatic void adjustment range for the valves, and therefore prevents smooth lubrication of fluid body; (2) As the contact point of a projection 131 at the end of the body 130 and the axial end of the valve 400 move accompanying the swinging movement of the rocker arm 1 during valve actuation, the body 1 30 is subjected to intermittent side pressures and inclines inside the void at the junction of the cylinder which in turn causes metallic contacts. When light alloys are used in such a construction, they tend to become damaged (scuffing and sticking).

Processing steps for the cylinder member for mounting the zero clearance adjuster for using the liner are 1) inserting the liner under pressure and 2) finishing the inner diameter.

Grinding conditions, etc. must be changed to suit both the liner which is made of iron or copper and the cylinder bottom which is made of light alloy. This requires complex and multiple steps in addition to the increased weight of the liner.

Thus, it would be desirable to provide an aluminum alloy rocker arm with increased resistance to damage by providing a hard and more wear-resistant surface. In particular it would be desirable for such rocker arms not to require cylinder liners for the clearance adjuster units.

The present invention aims at offering an inexpensive method of manufacturing rocker arms which withstand damage and wear Accordingly, the present invention provides a method of manufacturing an aluminum alloy rocker arm, comprising providing on the rocker arm a cam follower portion of a sintered iron alloy, providing a removable protective layer on the external surface of said cam follower portion, forming a porous anodic oxide film on the surface of the rocker arm, forming molybdenum sulfide in the pores in the oxide film and then removing the protective layer.

The present invention further aims at offering rocker arms which withstand damage and wear.

Thus, in another aspect there is provided a rocker arm formed of aluminum alloy having thereon a porous anodic oxide film in the pores of which there is formed molybdenum sulfide, and having a cam follower portion of a relatively hard and friction resistant material.

The rocker arm of the invention preferably has a cam follower portion of ceramics or sintered iron alloy. Chips of such material are now generally used with aluminum alloy rocker arms.

It is particularly useful for the rocker arm to have therein a cylinder or other receiving hole for receiving a clearance adjuster unit, the cylinder or receiving hole having a porous anodic oxide film on its internal surface with molybdenum sulfide in the pores.

The rocker arm of the invention may be made by providing on an aluminum alloy rocker arm a cam follower portion of a relatively hard and frictionresistant material, and forming a porous anodic oxide film on the surface of the rocker arm and then forming molybdenum sulfide in the pores in the oxide film.

In the attached drawings, Figure 1 shows a front view of a conventional rocker arm as mounted on the zero clearance adjuster; Figure 2 is a view to explain the movement of a rocker arm manufactured according to the present invention; and Figure 3 is a front view of a rocker arm embodying the present invention.

In Figures 2 and 3, a rocker arm 1 comprises an arm member 1001 and cam fol lower portion of a relatively hard and frictionresistant material in the form of a sintered alloy chip 1003 which is integrally cast with said arm 1001 and slidably abuts on the lift surface 501 and the clearance surface 502 provided on a cam 500. The chip 1003 thus provides the cam follower surface. As no liners are used on the zero clearance adjuster 3, a cylinder 1000 therefor in the tappet end of the arm has a somewhat smaller diameter than a conventional one.

As shown by hatched portion A in Figure 3, in the treatment of the rocker arm the chip 1003 and its periphery are masked, while the remaining portion of the rocker arm 1001 is given alumite processing to provide a solid lubricant, The masking is performed by immersing the portion A in a solution of plastics or paraffin, and subsequently taking it out to cool and solidify in the atmosphere. This will achieve a plastics or soldered coating quite simply.

There are shown three portions which specifically require alumite processing in Figure 3.

The first is the wall 1 000a of the cylinder 1000 against which the body 103 of the zero clearance adjuster slidably abuts, and the second is the cylinder top 1 000b upon which the valve acts as a spacer 110 (to be referred to later) slidably abuts thereon. The third portion is the inner surface 1 002a of the axial hole 1002 into which a rocker arm shaft 300 (to be referred to later) is slidably inserted. There are formed alumite layers of a predetermined depth, e.g. 10-40 m, on the wall surface 1000a, the cylinder top 1000b, the inner peripheral surface 1002a, so forth.

The method of manufacturing the above mentioned embodiment is now discussed.

ADC12 (JIS) aluminum alloy is used to diecast the arm member 1001. A sintered iron alloy chip 1003 is set in advance inside the metal die and the chip 1003 and its vicinity are integrally cast with the arm 1001.

The chip 1003 and its surrounding arm member 1001 alone of thus diecast arm member 1001 are immersed for about 2 seconds in a heated molten solution (e.g.

150--160"C) of thermoplastic resin (resin comprising paraffin and polyethylene (melting point: 130 C, for example)) and then left to cool. A thin thermoplastic coating of 2-3 mm thickness is thus formed on the chip 1003.

Similar to the technology disclosed in Japanese Patent Publication No. 56-4155, the arm member 1001 is directly electrolyzed in a mixed acid bath containing an aqueous solution of sulfuric acid and oxalic acid to form a porous anodic oxide film on the surface of the arm member 1001, and then the resultant film is washed with water. The arm member 1001 is then immersed in an aqueous solution of nitric acid to activate the surface of the arm 1001 and then washed with water. The arm member 1001 as anode is electrolyzed employing a DC current with a carbon rod as a cathode in an aqueous solution of ammonium thiomolybdate, preferably heated to 15--20"C, and subsequently washed with water.

The arm member 1001 is then immersed in hot water, for example of 40"C, to soften the thin thermoplastic resin film, thus facilitating peening by the operator of the thin film from the chip 1003 and the surrounding arm member 1001. Molybdenum sulfide will then be formed and fill the minute pores of anodic oxide film on the arm member 1001. A zero clearance adjuster unit 1004 assembled in advance is then inserted into the cylinder 1000 to complete the rocker arm 1.

As minute pores of alumite coating on the surface of the arm member 1001 (excluding the chip 1003) are filled with molybdenum sulfide, the friction coefficient becomes as low as 1 /2-1 /3 of that which has been simply given byalumite processing. Additionally, the surface hardness reaches about Hv 400 and improves the friction resistance. Thus, the zero clearance adjuster unit 1004 smoothly slides inside the cylinder member 1000 into which it has been inserted, does not cause damage such as scuffing and sticking, and in particular smoothens activation when the engine is started or stopped. The sliding surface 1 002a abutting the rocker arm shaft 300 of the arm member 1001 is also alumite processed as the cylinder member 1000 and molybdenum sulfide is formed.Therefore, the rotation against the shaft 300 of the rocker arm 1 is smooth, and mechanical losses are smaller and durability is improved.

Since the chip 1003 and its vicinity have been given alumite processing in an electrolytic solution after coating with thermoplastic resin, and molybdenum sulfide has been formed, it is possible to prevent dissolution of the chip 1003 into the electrolytic solution during the processing stage. As the coating can be obtained only by immersing the chip 1003 and its vicinity in liquid thermoplastic resin, the coating layer (thin film) may be peeled manually or by using a simple tool by the operator by immersing the same in the hot water of ca. 40"C and waiting until the layer becomes softened.

With improved friction resistance and hardness, the arm member 1001 does not become damaged so early even without a liner.

Non-use of the liner will reduce the weight of the movable valves, which in turn increases the level of the revolution number which may cause bouncing. This further reduces bouncing during the normal operation and decreases the weight of the engine itself.

In the above mentioned embodiment, the chip 1003 was formed with sintered iron alloy and therefore was coated with thermoplastic resin before processing being subjected to alumite. If the chip 1003 were formed with ceramics, coating would not be necessary.

Such chips of sintered iron alloy or ceramics are known per se, since they are in general use with aluminum alloy rocker arms. Following explanation is given referring to Figure 2 in respect of the construction and operation of the zero clearance adjuster and the rocker arm incorporating it. In Figure 2, the rocker arm 1 is axially mounted on a rocker arm shaft 300 and actuates an inlet valve 400 which opens/ closes an inlet port (not shown). The rocker arm 1, in other words, is arranged in a seesaw fashion with the rocker arm shaft 300 as a support axis between a cam axis 500 and the inlet/exhaust valve 400.

The arm member 1001 includes the zero clearance adjuster 3 formed by inserting the cylinder member 1000 provided on the side 1 a opposite to the valve over a zero clearance adjuster unit 1004. The zero clearance adjuster unit 1004 comprises a spacer 110, a body 130 and a plunger 180. The arm member 1001 forms a convex cam follower surface 700 on the side 1 00b opposite to the cam 500, and swings in the direction of an arrow B as it is pressed by the lift surface 501 of the cam as the cam 500 is driven.

The cylinder top 1 000b is formed spherically with its center of curvature aligning the center line 1 of the cylinder, and is slidably abutted with a spacer 110 formed with a curved surface 100 opposite to the cylinder bottom which has approximateny the same shape as the cylinder top 1 000b or its center of curvature Q aligning the center line I of the cylinder (hereinafter referred to simply as the spacer spherical surface). The spacer 110 has a surface 1 20 opposite to the press member on the side opposite to the spacer spherical surface 110, and there is bored a through hole 111 at the center thereof.The spacer 110 therefore rotatably slides against the cylinder top 1 000b in respect of said center of curvature Q. Against the wall 1 000a of the cylinder 1000 is inserted slidably the body 1 30 as the body of a cylindrical lifer, and the projection 1 31 at the end of the body 1 30 abuts against the upper end surface 140 of the valve projecting from an opening 800.

The side of the cylinder top 1 000b of the body 1 30 is positioned apart from the side of said cylinder, thereby forming a void 1 50 between the two. The void 1 50 communicates with an oil passage 160, and the oil with a predetermined pressure is supplied from a center oil port 1 70 of a hollow rocker arm shaft 300 to the zero clearance adjuster 3 via the oil passage 1 60. The center of the cylinder top 1 000b and the passage 160 communicate with each other to thereby conduct sliding of the cylinder top 1000b and the spacer spherical surface 100 with less resistance.A cylindrical plunger 1 80 is slidably inserted inside the body 1 30. The plunger 180 has a hollow chamber 181 inside, with its end slidably abutting on the opposite surface 1 20 of the pressing member of the spacer and forming a member 183 (hereinafter referred to merely as the head) opposite to the projection 131 of the body. The head 183 and the projection 1 31 of the body are respectively provided with opposing surfaces to form an oil pressure chamber 190. The chamber 1 90 is connected to the hollow chamber 181 of the plunger via an oil port 184. The oil port 184 is so constructed as to open/close by the check valve mounted inside the oil pressure chamber 190.A ball 201 larger than the diameter of the oil port 184 of the check valve, a spring 202 for the check valve to press the ball 201 elastically against the side of the oil port 184, and a support frame 203 supporting the spring 202 to press the same against the head 1 83 of the plunger are provided for this construction. The pressure chamber 1 90 is further provided with a spring 210 (hereinafter referred to merely as an adjust spring) which presses the projection 1 31 against the side of the upper end 140 of the valve so as to keep the projection 1 31 of the body and the plunger head 1 83 apart. This adjust spring 210 supports by pressure the support frame 203 at its engaging edge against the head 183.

Following is the explanation on activation of the zero clearance adjuster 5. From the center oil port 1 70 of the rocker arm shaft as a source of oil pressure supply is applied the oil pressure on the cylinder head void 1 50 via the oil passage 160, and the oil pressure is transmitted to the hollow chamber 1 81 via the through hole 111 of the spacer. The oil pressure of the hollow chamber 1 81 is applied on the ball 201 via the oil port 184.

The ball 201 moves to the side of the oil pressure chamber 190 only when it receives a force bigger than that of the spring 202 as oil pressure, and supplies the oil on the side of the hollow chamber 1 81 to the oil pressure chamber 190. The ball 201 then closes the oil port 184 by the force of the spring 202 as the pressure of the chamber 190 approximates that on the side of the hollow chamber 181, and prevents the oil inside the oil pressure chamber 1 90 from returning out of the oil port 184 even when the pressure on the chamber side 1 90 changes to high. If oil of a predetermined pressure is supplied to the chamber 1 90 from the side of the passage 1 60 when the engine is being driven, the plunger 1 80 presses at its upper end the spacer 110 abuttingly, and the body abuts the projection 1 31 against the upper end face 140 of the valve axis.In this case, so long as the cam follower surface 700 of the rocker arm 1 faces opposite the side of the clearance surface 502 as it departs from the lift surface 501 of the cam, the plunger 180 and the body 1 30 are extendably activated along the direction of the center line I of the cylinder by the oil pressure and the adjust spring 210 so as to fill all the voids between the opposing surface 1 20 of the spacer's pressure member and the upper end surface 140 of the valve axis.

On the other hand, when the cam follower surface 700 is under the pressure of the lift surface 501 of the cam, the plunger 180 and the body 1 30 which have been extended to the maximum by the control spring 210 between the surface opposite the pressure member of the spacer 120 and the upper end surface 140 of the valve axis do not act to shorten the distance between the two by the pressure of the chamber 1 90 when compressed in the direction of the center line I of the cylinder.

When the rocker arm 1 rotates in the clockwise direction, the projecting member 1 31 of the body receives from the upper end surface 140 of the valve a counterforce in the direction of the center of curvature P of the projection 1 31. The projection concurrently receives a friction force caused by the movement of the point of contact of its surface with respect to the upper end surface 140 of the valve as the rocker arm 1001 moves clockwise. An eccentric load is applied on the body 1 30 as a total of these forces, as well as a rotational moment around the center of curvature P, and a sideways force caused thereby. The body 1 30 therefore moves to incline toward the void Cb between itself and the wall 1000a.Functions of the void Ca between the body 1 30 and the plunger 180 are set at a value smaller than the void Cb, and the plunger 180 inclines integrally with the body 130.

The spherical surface of the spacer 110 slides over the cylinder top 1 000b in respect of the center of curvature Q thereof and becomes activated. This will transmit the pressure on the side of the body 1 30 approximately uniformly to the side of the cylinder top 1000b. The body 1 30 which has received the said pressure slides over the opposite surface 1 20 of the pressure member of the spacer along with the plunger 180, abuts against the inner wall of the liner 2, and transmits its side pressure uniformly. When the spacer 110 becomes somewhat inclined around the center of curvature Q, the upper end of the plunger 180 becomes more easily slidable over the surface 120. As the center of curvature Q of the spacer's spherical surface 100 is only very slightly spaced from the center of curvature P of the projection 131, when the spacer 110 receives the rotational moment, the body 130 and the plunger 180 can easily rotate integrally, and the sliding movement against the cylinder top 1 000b of the spacer 110 also becomes smooth.

The above explanation also applies when the rocker arm 1001 rotates counterclockwise. The body 130 inclines in a direction reverse to that above, and the spacer 110 also moves in the reverse direction to achieve a similar action.

Claims (16)

1. A method of manufacturing an aluminum alloy rocker arm, comprising providing on the rocker arm a cam follower portion of a sintered iron alloy, providing a removable protective layer on the external surface of said cam follower portion, forming a porous anodic oxide film on the surface of the rocker arm, forming molybdenum sulfide in the pores in the oxide film and then removing the protective layer.

2. A method as claimed in Claim 1 wherein the molybdenum sulfide is formed by electrolysing the rocker arm in a solution containing ammonium thiomolybdate.

3. A method as claimed in Claim 1 or Claim 2 wherein the protective layer is a thin film.

4. A method as claimed in Claim 3 wherein the thin film is provided by immersing the cam follower portion in a molten solution of thermoplastic resin and allowing it to cool to thereby form a thin film of the resin on the cam follower portion.

5. A method as claimed in Claim 4 wherein the thermoplastic resin comprises a paraffin and polyethylene and the thin film is removed by heating it and peeling off the thereby softened film.

6. A method as claimed in any one of the preceding claims wherein the cam follower portion is provided as a chip of the relatively hard material.

7. A method as claimed in any one of the preceding claims wherein the cam follower portion is integrally cast with the rocker arm.

8. A method as claimed in any one of the preceding claims wherein a cylinder for receiving a clearance adjuster unit is formed in the tappet end of the rocker arm prior to the formation of the anodic oxide film and the clearance adjuster unit is inserted into the cylinder after the formation of the anodic oxide film.

9. A method substantially as hereinbefore described of manufacturing an aluminum alloy rocker arm having a porous anodic oxide film on its surface, the pores of which have molybdenum sulfide therein.

10. A rocker arm whenever manufactured by a process as claimed in any one of the preceding claims.

11. A rocker arm formed of aluminum alloy having thereon a porous anodic oxide film in the pores of which there is formed molybdenum sulfide, and having a cam follower portion of a relatively hard and friction resistant material.

1 2. A rocker arm as claimed in Claim 11 wherein the relatively hard material comprises ceramics or sintered iron alloy.

1 3. A rocker arm as claimed in Claim 1 2 having a cylinder formed in its tappet end for receiving a clearance adjuster unit.

14. A rocker arm as claimed in Claim 1 3 wherein a clearance adjuster unit is inserted in the cylinder.

1 5. A rocker arm as claimed in Claim 11 substantially as hereinbefore described.

16. An internal combustion engine which comprises a rocker arm as claimed in any one of Claims 10 to 15.