GB2162608A

GB2162608A - Valve drive train for an internal combustion engine

Info

Publication number: GB2162608A
Application number: GB08514800A
Authority: GB
Inventors: Makoto Nakamura
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1984-06-12
Filing date: 1985-06-11
Publication date: 1986-02-05
Also published as: GB8514800D0; JPS611812A

Abstract

One end of a rocker arm (4) has a receiving hole (21). A hydraulic valve lifter (5) includes a cup-shaped casing (20) and an internal structure accommodated in the casing (20). The casing (20) fits in the receiving hole (21) and is made of a material which is harder than that of the rocker arm. For example, the rocker arm may be of light metal such as aluminium alloy or reinforced resin and that of the casing of a harder material such as steel or ceramics. <IMAGE>

Description

SPECIFICATION Valve drive train for an internal combustion engine Background of the invention This invention relates to a valve drive train for an internal combustion engine including a hydraulic valve lifter.

Many engines now use hydraulic valve lifters which provide zero valve clearance. This type of lifter is very quiet in operation, producing no "click" (or tappet noise, as it is called). As a rule, this type of valve lifter requires no adjustment in normal service.

In some hyraulic valve lifters, a rocker arm has a blind bore accommodating a tappet piston and a sleeve. The sleeve abuts the closed end of the bore. The tappet piston is urged relative to the sleeve into continuous contact with one end of a valve stem. During lift of the valve, reaction force is transmitted to the rocker arm via the sleeve. Accordingly, the surface of the rocker arm in contact with the sleeve is subjected to the reaction impulses.

In cases where the rocker arm is made of a light metal, such as aluminum alloy, the closed end of the bore tends to wear quickly under the reaction impulses.

In cases where the rocker arm is made of a harder metal. such as cast iron or steel, in order to prevent excessive wear of the closed end of the bore, the valve drive train is relatively heavy so that the maximum engine speed is limited considerably.

Summary of the invention It is an object of this invention to provide a lightweight, wear-resistant valve drive train including a hydraulic valve lifter.

A valve drive train of this invention includes a rocker arm having an end formed with a receiving hole. A hydraulic valve lifter includes a cup-shaped casing and an internal structure accommodated in the casing. The casing fits in the receiving hole and is made of a hard material.

Brief description of the drawings Figure 1 is a sectional view of a valve drive train according to an embodiment of this invention.

Figure 2 is a sectional view of a first modification to the embodiment of Figure 1.

Figure 3 is a sectional view of a second modification to the embodiment of Figure 1.

Corresponding and like elements are denoted by the same reference characters throughout the drawings.

Description of the preferred embodiments With reference to Figure 1, an engine cylinder head has an integral cam bracket 1 supporting a rotatable camshaft 2. A tubular rocker shaft 3 is supported along one edge of the cam bracket 1. A rocker arm 4, preferably made of a lightweight material such as an aluminum alloy or reinforced resin, is pivotally mounted on the rocker shaft 3.

The rocker arm 4 has an input end 4A which contacts anf follows the surface of an operative lobe 2A on the camshaft 2 as the camshaft rotates. An output end 4B of the rocker arm 4 engages an end 6 of the stem of an engine inlet valve or outlet valve via a hydraulic valve lifter 5.

The hydraulic valve lifter 5 includes a cupshaped casing 20 made of a hard material, such as steel or ceramics. One end of the casing 20 is open and has an outwardly-projecting annular flange 20A. The other end of the casing 20 is closed by a bottom wall 20B integral with the cylindrical walls of the casing 20. The casing 20 fits snugly into a cylindrical receiving bore 21 extending through the output end 4B of the rocker arm 4. Both ends of the casing 20 extend out of the bore 21.

The flange 20A abuts surfaces of the rocker arm 4 around the end of the bore 21 proximal to the valve stem 6. The area of contact between the flange 20A and the rocker arm 4 is much greater than the area of contact between the end face of the sleeve 9 and the casing bottom wall 20B.

Therefore, the forces developed when actuating the engine valve as the camshaft 2 rotates are transmitted between the casing 20 and the rocker arm 4 over a large enough area to minimize wear.

A snap ring 23 securely fitting around the closed end of the casing 20 abuts surfaces of the rocker arm 4 defining the other end of the bore 21. Thus, the casing 20 is fixed to the rocker arm 4 by means of the flange 20A and the snap ring 23. The snap ring 23 also prevents separation of the casing 20 and the rocker arm 4 while the rocker arm 4 is being mounted on the rocker shaft 3 or while the rocker shaft 3 and rocker arm 4 combination is being mounted on the cam bracket 1 during assembly of the engine.

The casing 20 defines a blind bore 20C coaxially accommodating a slidable cup-shaped tappet piston 7 and an inner sleeve 9. The tappet piston 7 has a cylindrical shell fitting snugly but slidably between the casing 20 and the sleeve 9. The closed end, or head 7A, of the tappet piston 7 rests in contact with the end of the valve stem 6. One end 9A of the sleeve 9 abuts the bottom wall 20B of the casing 20. The sleeve 9 is preferably made of a hard material, such as steel or ceramics. The sleeve 9 and the bottom wall 20B define an oil reservoir 8 within the sleeve 9. A pressure chamber 10 is defined between the head 7A of the tappet piston 7 and the sleeve 9. The sleeve 9 has an inwardly-extending annular projection which defines a communication passage 9B connecting the oil reservoir 8 and the pressure chamber 10.A conventional check valve 11 includes a spring-loaded valve ball for blocking and unblocking the communication passage 9B. The valve ball is movably diposed within a retainer (no reference character). A helical spring 12 disposed within the pressure chamber 10 urges the tappet piston 7 toward the valve stem 6 relative to the sleeve 9.

Pressurized hydraulic fluid, that is, oil from an engine oil pump (not shown) flows between the cam shaft 2 and the cam bracket 1 and then enters a passage 14 in the cam bracket 1. The oil moves from the passage 14 to a bearing section 4D of the rocker arm 4 via an axial passage 15 and a radial passage 16 through the rocker shaft 3.

An oil passage 13 extending through the rocker arm 4 has an inlet communicating with the bearing section 4D and an outlet communicating with an annular passage 13A in the rocker arm 4. A passage 22 extending through the cylindrical walls of the casing 20 connects the annular passage 13A to an annular groove (no reference character) in the tappet piston 7 which leads to a ring gap (no reference character) between the casing 20 and the sleeve 9. This ring gap is exposed to the oil reservoir 8 via grooves 9C in the end of the sleeve 9 adjoining the bottom wall 20B of the casing 20.

Hydraulic fluid flows from the bearing section 4D into the oil reservoir 8 via these passages, grooves, and gap.

When the engine valve is closed, pressurized fluid from the engine oil pump is forced into the oil reservoir 8. As the oil enters the reservoir 8, it acts on the check valve 11 and forces the valve 11 to open. Oil now passes the check valve 11 and enters the pressure chamber 10 within the tappet piston 7. The tappet piston 7 is therefore forced downwards until it comes into contact with the valve stem 6. This action eliminates any valve clearance between the head 7A of the tappet piston 7 and the end of the valve stem 6.

When the cam lobe 2A forces the rocker arm 4 in the direction of opening the engine valve, the valve lifter 5 is moved downwards. Since there is no valve clearance, there is no tappet noise. As the valve lifter 5 moves downwards, oil pressure in the pressure chamber 10 suddenly increases, causing the check valve 11 to close. The oil is therefore trapped in the pressure chamber 10, and the valve lifter 5 acts as a simple integral element. Accordingly, the valve lifter 5 moves downwards as an assembly and causes the engine valve to open.

When the cam lobe 2A allows the rocker arm 4 to be returned by a valve spring (no reference character) in the direction of closing the engine valve, the oil pressure in the pressure chamber 10 drops and the check valve 11 opens. Pressurized oil from the engine oil pump is again forced past the check valve 11 to replaced whatever oil may have leaked from the pressure chamber 10.

When the engine valve opens, reaction force F is transmitted from the valve stem 6 to the tappet piston 7. This reaction force F is then transmitted to the casing 20 via the spring 12 and the sleeve 9.

The bottom wall 20B of the casing 20 in contact with the sleeve 9 bears the reaction force F. The reaction force F is conducted from the casing 20 to the rocker arm 4 via the flange 20A of the casing 20. Thus, the flange 20A also bears the reaction force F. In this way, the reaction force F is transmitted to the rocker arm 4 via the wide contacting surfaces of the rocker arm 4 and the flange 20A of the hard casing 20. This limits wear on the rocker arm 4.

Since the rocker arm 4 is made of a lightweight material, the maximum engine speed can be acceptably high.

Figure 2 shows a modification to the embodiment of Figure 1. In this modification, a cap 24 is used in place of the snap ring 23. The cap 24 is press-fitted onto the distal end of the casing 20 and abuts the output end 4B of the rocker arm 4.

Figure 3 shows another modification to the embodiment of Figure 1. In this modification, the output end 4B of the rocker arm 4 has a blind bore 21 accommodating the casing 20. The diameter of the blind bore 21 is essentially the same as the outside diameter of the casing 20 so that the casing 20 snugly fits into the bore 21. The part of the walls of the rocker arm 4 defining the floor 21A of the blind bore 21 abuts the entire end face 20D of the casing 20. Thus, the casing 20 engages the rocker arm 4 via the large contact surfaces 21A and 20D. The flange 20A (see Figure 1) may be omitted from this modification.

When the engine valve opens, the reaction force F is transmitted from the valve stem 6 to the casing 20 as in the embodiment of Figure 1. The reaction force F is then conducted to the rocker arm 4 across the contact surfaces, that is, the surface 21A of the rocker arm 4 and the surface 20D of the casing 20. This limits the wear on the rocker arm 4.

Claims

1. A valve drive train for an internal combustion engine, comprising: (a) a rocker arm having an end formed with a receiving hole; and (b) a hydraulic valve lifter including a cup-shaped casing and an internal structure accommodated in the casing, the casing fitting in the receiving hole and being made of a hard material.

2. A valve drive train for an internal combustion engine, comprising: (a) an engine valve; (b) a rocker arm having a receiving hole; (c) a hydraulic valve lifter including a cup-shaped casing and an internal structure accommodated in the casing, the casing fitting in the receiving hole and being made of a hard material, the internal structure disposed between and contacting both of the engine valve and a closed end of the casing; and (d) means for engaging the casing with the rocker arm.

3. The valve drive train of claim 2, wherein the engaging means comprises a flange formed on another end of the casing and abutting the rocker arm.

4. The valve drive train of claim 2, wherein the receiving hole is a blind bore, and wherein the engaging means comprises an outer surface of the closed end of the casing abutting a wall of the rocker arm defining a floor of the blind bore.

5. The valve drive train of claim 2, wherein the receiving hole extends through the rocker arm, and the closed end of the casing projects from the receiving hole, and further comprising a snap ring fitting around the projected end of the casing and abutting the rocker arm.

6. The valve drive train of claim 2, wherein the receiving hole extends through the rocker arm, and the closed end of the casing projects from the receiving hole, and further comprising a cap 24 press-fitted onto the projecting end of the casing and abutting the rocker arm.

7. A valve drive train for an internal combustion engine comprising: (a) a pivotable rocker arm made of a rigid, lightweight material and in which a receiving hole is formed in one end distal from its pivotal axis; (b) first means for driving the rocker arm to pivot reciprocally in synchronism with engine rotation; (c) a cup-shaped tappet piston received in the receiving hole, the closed end of said tappet piston opposing a free end of an engine valve; (d) second means for resiliently holding said tappet piston in continuous contact with the engine valve; and (e) a cup-shaped casing made of a wear-resistant material, received fixedly in the receiving hole in direct contact with the rocker arm, and cooperating with said tappet piston to encapsulate and retain said second means, whereby impulses imparted to the tappet piston and second means during reciprocal movement of the rocker arm are borne by the wear-resistant casing.

8. A valve drive train for an internal combustion engine, substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.