JPH0726927A - Variable valve timing mechanism - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the rigidity of the rocker arm of the variable valve timing mechanism. [Structure] A base end 9'c of a piston 9'for connecting a rocker arm 5 and a rocker arm 7 has a large diameter and is slidably fitted into a large-diameter portion 4c of a piston hole 4b of a rocker shaft 4. Piston holes 4 on both ends of piston 9 '
The rocker arm 7 is supported by b and the large diameter portion 4c to reduce the flexure due to the valve load and improve the rigidity of the rocker arm 7.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a variable valve timing mechanism.

[0002]

2. Description of the Related Art A variable valve timing mechanism is provided with two types of cams, one for low speeds and the other for high speeds, which have different profiles, on a cam shaft. This mechanism uses hydraulic pressure to switch between a low-speed rocker arm and a high-speed rocker arm. The low speed cam is smaller than the high speed cam, and both valve overlap and lift are smaller.

By adopting a variable valve timing mechanism,
It is possible to improve the output torque of the engine in the high speed range while maintaining the low speed and high torque of the practical engine in the low speed range. As such a variable valve timing mechanism, various structures have been proposed.
The applicant has previously proposed a variable valve timing mechanism as shown in FIGS. 3 and 4.

3 and 4, the variable valve timing mechanism 1 includes two intake valves 2 and 3 and a T-type rocker arm 5 integrated with rocker shafts 4 and 4'for opening and closing the intake valves 2 and 3. A low-speed rocker arm 6, a high-speed rocker arm 7 and a T-type rocker arm 5 built-in, and a piston 8 for connecting the low-speed rocker arm 6 or the high-speed rocker arm 7 to the T-type rocker arm 5.
9 and a low speed cam 14 provided on the cam shaft 13,
It is composed of a high speed cam 15 and the like.

The rocker shafts 4 and 4'at both ends of the T-shaped rocker arm 5 are rocker shaft journals 12 and 12 '.
Oil pressure PL is rotatably supported on the piston 8 through the oil passages 12'a and 4'a provided on the journal 12 'and the rocker shaft 4'and the oil pressure PL is applied to the piston 8 by the oil passages of the journal 12 and the rocker shaft 4. Piston 9 through 12a, 4a
The hydraulic pressure PH is supplied to.

The base ends 6a, 7a of the low-speed rocker arm 6 and the high-speed rocker arm 7 are connected to the rocker shafts 4 ', 4'on both sides of the T-shaped rocker arm 5 via shaft holes 6b, 7b, respectively.
Is pivotally supported at each base end thereof, and roller bearings 10, 11 are pivotally supported at each tip end thereof. These roller bearings 10 and 11 are provided with low speed cams 14 and
It abuts on the high speed cam 15 and rolls. The low-speed rocker arm 6 and the high-speed rocker arm 7 include a lost motion assembly (not shown) arranged on the base ends 6a, 7a side.
As a result, the roller bearings 10, 11 become
It is always in contact with the high speed cam 15.

In the low speed rotation range of the engine, the piston 8 is fitted into the piston hole 6c of the low speed rocker arm 6 by the spring force of the spring 17 ', and the T-shaped rocker arm 5 and the low speed rocker arm 6 are connected and integrated. The intake valves 2 and 3 are driven by the low speed cam 14 via the low speed rocker arm 6 and the T-shaped rocker arm 5. At this time, the piston 9 retracts due to the spring force of the spring 17, and the high-speed rocker arm 7 moves to the T-shaped rocker arm 5
It is possible to swing freely by releasing the connection with. The roller bearing 11 is in contact with the high speed cam 15 by the lost motion assembly.

In the high speed rotation range of the engine, the piston 9 is pushed out against the spring force of the spring 17 by the hydraulic pressure and fitted into the piston hole 7c of the high speed rocker arm 7, and the high speed rocker arm 7 and the T-shaped rocker arm are engaged. 5, the intake valves 2 and 3 are driven by the high-speed cam 15 through the high-speed rocker arm 7 and the T-type rocker arm 5 so as to be integrated. In this high speed rotation range, the piston 8 may be hydraulically retracted against the spring force of the spring 17 'to release the connection between the low speed rocker arm 6 and the T-shaped rocker arm 5.

Further, the pistons 8 and 9 are both retracted so that T
It is also possible to stop the operation of the intake valves 2, 3 by releasing the connection between the mold rocker arm 5, the low speed rocker arm 6 and the high speed rocker arm 7, that is, to suspend the cylinder.

[0010]

By the way, in the variable valve timing mechanism 1 described above, the piston hole 4b of the rocker shaft 4, as shown in the enlarged view of FIG.
A hole 4c is formed in a concentric and slightly enlarged manner so as to interpose a spring 17 between the opening end of the piston 9 and the flange 9b provided at the base end of the piston 9 from the opening end to the center. For this reason, when the tip of the piston 9 is fitted into the piston hole 7c of the high-speed rocker arm 7 when the T-shaped rocker arm 5 and the high-speed rocker arm 7 are coupled, the portion that guides the piston 9 of the rocker arm 4 is the piston hole 4
It becomes a part of b and it is close to a cantilever state, the deflection of the piston 9 is large when receiving a valve load at the time of valve opening, the rigidity of the high speed rocker arm 7 is insufficient, and the valve system dynamic characteristic performance such as valve bounce is poor. As a result, there is a problem that the engine performance is adversely affected.

The present invention has been made in view of the above points, and reduces the bending of the coupling piston when receiving a valve load at the time of opening the valve to improve the rigidity of the rocker arm to improve the dynamic performance of the valve system. It is an object of the present invention to provide a variable valve timing mechanism designed to be improved.

[0012]

To achieve the above object, according to the present invention, a piston hole is concentrically provided in a diametrical direction of a rocker shaft of a first rocker arm to slidably insert a piston. The piston is pushed out against the spring force of a spring compressed between the large diameter portion of the piston hole and the base end of the piston, and the tip end of the second rocker arm pivotally supported by the rocker shaft is pivotally supported. In a variable valve timing mechanism that fits into a piston hole and connects the two, a large diameter portion that slidably fits into a large diameter portion of the piston hole is provided at the base end of the piston, and the piston hole is provided during the coupling. The structure is such that both ends of the piston are supported by.

[0013]

When the piston is pushed out from the piston hole of the rocker shaft and the tip of the piston fits into the piston hole of the second rocker arm, the large diameter portion of the base end fits into the large diameter portion of the piston hole. And both ends are supported by the piston holes. This reduces the flexure of the piston when receiving the valve load, and increases the rigidity of the second rocker arm.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The same or corresponding members as those shown in FIGS. 3 and 4 are designated by the same or corresponding reference numerals, and the description thereof will be omitted. In FIG. 1, a variable valve timing mechanism 1'is a T-type rocker arm 5 that opens and closes an intake valve.
Is a low-speed rocker arm 6, a high-speed rocker arm 7,
A low speed cam and a high speed cam (not shown) provided in the T-type rocker arm 5 for connecting the low speed rocker arm 6 or the high speed rocker arm 7 to the T type rocker arm 5 and the cam shaft. No.) etc. The rocker shafts 4 and 4'of the T-shaped rocker arm 5 are rotatably supported by rocker shaft journals (not shown).

The piston hole 4b of the rocker shaft 4, which pivotally supports the high-speed rocker arm 7 of the T-shaped rocker arm 5, has a roller 11 having a hole 4a at the center from the opening end facing the roller 11 side.
The diameter is slightly increased to reach the inner surface 4a 'on the opposite side (far side), and the hole 4c is slightly larger than the piston hole 4b. In this way, the rocker shaft 4 is concentrically formed with the piston hole 4b and the hole (large diameter portion) 4c having a diameter slightly larger than the piston hole 4b.

On the other hand, the piston 9'has the same length as the diameter of the rocker shaft 4 or slightly shorter than the diameter, and the shaft portion 9'a slides into the piston hole 4b of the rocker shaft 4. It is movably fitted and the base end 9'c is the shaft 9 '.
It has a diameter slightly larger than a and is formed in a shape that slidably fits into the hole 4c. This causes the piston 9'to
The vicinity of the tip of the shaft portion 9'a is supported by the piston hole 4b, and the base end (large diameter portion) 9'c is supported by the hole 4c. That is, the piston 9 '
Both ends are supported by the rocker arm 4.

A spring 17 is interposed between the hole 4c and the piston 9 '. This spring 17
Is loosely fitted onto the piston 9 ', and one end of the piston hole 4
The other end of the stepped surface 4d between the b and the piston hole 4c is pressed into contact with the end surface of the base end 9'c of the piston 9'which faces the stepped surface 4d, and is contracted between the two. The spring 17 acts to pull the piston 9 ′ into the piston holes 4 b and 4 c of the rocker shaft 4.

The operation will be described below. In the low speed rotation range of the engine, the piston 8 is fitted into the piston hole 6c of the low speed rocker arm 6 by the spring force of the spring 17 ', and the T-shaped rocker arm 5 and the low speed rocker arm 6 are joined together to form a unit for the low speed The cam drives the intake valve via the low speed rocker arm 6 and the T-shaped rocker arm 5.

In the high speed rotation range of the engine, as shown in FIG. 2, the piston 9'is pushed out by the hydraulic pressure against the spring force of the spring 17 and the tip thereof is fitted into the piston hole 7c of the high speed rocker arm 7. The high-speed rocker arm 7 and the T-type rocker arm 5 are joined and integrated, and the intake valve is driven through the high-speed rocker arm 7 and the T-type rocker arm 5 by a high-speed cam (not shown).

Then, as shown in FIG. 2, the piston 9 '
In the state where the T-shaped rocker arm 5 and the high-speed rocker arm 7 are connected, the tip of the shaft portion 9'a fits into the piston hole 7c of the high-speed rocker arm 7, and the vicinity of the tip of the shaft portion 9'a is rocker. The shaft 4 is supported by the piston hole 4b, and the base end 9'b is supported by the hole 4c. That is, both ends of the piston 9'are supported by the piston holes 4b and 4c. As a result, the piston 9 ′ has less bending when receiving a valve load when the valve is opened, and the rigidity of the high speed rocker arm 7 is increased accordingly, and the dynamic characteristic performance of the valve train is improved.

[0021]

As described above, according to the present invention, a piston hole is provided concentrically in the diameter direction of the rocker shaft of the first rocker arm, and the piston is slidably fitted and inserted into the large diameter portion of the piston hole. And a second end in which the piston is pushed out against the spring force of a spring compressed between the piston and the base end of the piston, and the tip of the piston is pivotally supported by the rocker shaft.
In a variable valve timing mechanism that is fitted into a piston hole of a rocker arm and connects the two, a large diameter portion that slidably fits into a large diameter portion of the piston hole is provided at the base end of the piston, and Since the both ends of the piston are supported by the piston hole, it is possible to reduce the deflection of the piston due to the valve load when the valve is opened, and as a result, the rigidity of the second rocker arm is increased. Therefore, there is an effect that the dynamic characteristic performance of the valve train is improved and the engine performance is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a variable valve timing mechanism according to the present invention.

FIG. 2 is an enlarged view of a main part of the variable valve timing mechanism shown in FIG.

FIG. 3 is a perspective view of a conventional variable valve timing mechanism.

4 is a sectional view taken along the line IV-IV in FIG.

FIG. 5 is an enlarged view of a main part of FIG.

[Explanation of symbols]

 1'Variable valve timing mechanism 4, 4'Rocker shaft 4b, 4c Piston hole 5 T-type rocker arm 6 Low speed rocker arm 7 High speed rocker arm 8, 9'Piston 9'a Shaft part 9'c Large diameter part (base end)

Claims (1)

[Claims] 1. A piston hole is concentrically provided in a diametrical direction of a rocker shaft of a first rocker arm, and a piston is slidably inserted into the piston hole, and the piston hole is contracted to a large diameter portion of the piston hole and to a base end of the piston. In a variable valve timing mechanism for pushing a piston against a spring force of an installed spring to fit a tip of the piston into a piston hole of a second rocker arm pivotally supported by the rocker shaft to couple the two. A variable diameter characterized in that a large diameter portion slidably fitted in a large diameter portion of the piston hole is provided at a base end of the piston, and both ends of the piston are supported by the piston hole at the time of the coupling. Valve timing mechanism.