JPH04132807A - Valve system for engine - Google Patents

Abstract

PURPOSE:To heighten the responsiveness of a variable valve timing mechanism as well as to achieve the reliability of an engine by installing a helical piston, changing the rotational phase of a camshaft, and a return spring, energizing this helical piston in the return direction, respectively. CONSTITUTION:In an internal structure of a valve timing mechanism 10, a ringlike helical piston 35 is interposed between this internal structure and a cover body 36 on the circumference of a center block 34. In addition, a return spring 40 is installed in an interval between the helical piston 35 and a casing 27 at the back of this piston. When oil is supplied by way of an interconnecting passage 38 and a conducting passage 39 and hydraulic pressure works on the helical piston 35, an exhaust side camshaft 3 and a pulley 11 are relatively rotated. Accordingly, there is produced a phase difference between the camshaft 3 and the pulley 11 and thereby on-off timing for an exhaust valve 18 is made variable. Thus, operating responsiveness in the variable valve timing mechanism is heightened and simultaneously the extent of operating reliability at time of high speed rotation is thus securable.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a valve operating system for an engine in which a hydraulically operated variable valve timing mechanism is attached to a camshaft of the engine.

(Prior technology) Conventionally, when driving a camshaft using an engine's valve mechanism, a variable valve timing mechanism is attached to the camshaft drive mechanism to change the rotational phase between the crankshaft and the camshaft. For example, a technology for changing the valve timing of an exhaust valve or an intake valve according to the operating condition is disclosed in Utility Model Application Publication No. 82-5771.
This is known as seen in Publication No. 1.

For example, in order to achieve both idle stability and output performance in the mid-to-high speed range, the variable valve timing mechanism described above is used to reduce the valve overlap at idle and increase the valve overlap in the mid-to-high speed range. It is best to control the It is also possible to control the valve timing of the intake valve to be delayed at high engine speeds, and use the intake inertia resulting from the late closing of the intake to improve the intake air filling efficiency and increase the output.

(Problem to be Solved by the Invention) However, the variable valve timing mechanism in the valve train as described above has a helical spline formed to change the rotational phase of the camshaft. It is necessary to ensure the responsiveness and reliability of the operating condition.

That is, when the rotation speed is low, the generated oil pressure is low and the variable valve timing mechanism cannot be turned on by this oil pressure, so it is necessary to set the operating range so that the variable valve timing mechanism is turned on in a region where the rotation speed has increased to a certain extent. In addition, when the oil temperature rises, the generated oil pressure decreases even if the engine speed is the same.Furthermore, as the engine speed increases, the drive torque of the camshaft also increases, ensuring reliable operation even when this high drive torque is generated. is required.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a valve train for an engine that improves the operational response of a variable valve timing mechanism and ensures operational reliability at high engine speeds. .

(Means for Solving the Problems) In order to achieve the above object, the valve train of the present invention employs hydraulic operation that changes the rotational phase of the camshaft by introducing hydraulic pressure so that the valve timing of the intake valve or the exhaust valve is delayed. The variable valve timing mechanism has a helical piston that moves in the axial direction of the camshaft under the action of introduced hydraulic pressure to change the rotational phase of the camshaft via a helical spline. The helical piston also has a return spring that urges the helical piston in the return direction, and a shaft that applies the spring force of the return spring to the helical piston in the same direction as the hydraulic pressure as the camshaft rotates at high rotations. This is configured to be weaker than the directional propulsion force.

(Function and Effect) In the above-mentioned valve train, the closing timing of the exhaust valve or intake valve is delayed by turning on the variable valve timing mechanism, and the variable valve timing mechanism is always turned on at high rotation speeds. This setting is made to increase output by increasing valve overlap or closing the intake air late. In addition, in conjunction with this, the axial propulsive force that acts on the helical piston in the same direction as the hydraulic pressure acting direction is provided in the same direction as the movement direction of the helical piston and the rotational drive of the camshaft when hydraulic pressure is introduced, and the return spring is By setting the spring force to be weaker than the axial propulsion force that acts on the helical piston at high rotations, which is the on-operation range, the helical piston remains turned on even when the oil temperature is high and the oil pressure decreases at these high rotations. The variable valve timing mechanism is moved in the direction to ensure the ON operation of the variable valve timing mechanism, increasing reliability.In addition, since the return spring is weak, the response of the ON operation of the variable valve timing mechanism is increased in the medium rotation range, etc. This makes it possible to achieve engine reliability and high output.

(Example) The present invention will be described in detail below with reference to the drawings.

Figure 1 shows a V-type 6-cylinder DOH equipped with an embodiment of a valve train.
It is a plan view of the cylinder head 4 of one bank IA in the C engine 1, and in this bank IA, three cylinders are provided with a four-valve structure (two valves on the intake side, two valves on the exhaust side), and each cylinder has a A pair of camshafts 2 and 3 for opening and closing intake and exhaust valves are disposed in parallel to each other above a cylinder head 4 and supported by bearings 5...5 and 6.

Further, an inter-cam gear 7.8 is attached to one end side (front end side) of each of the intake side camshaft 2 and the exhaust side camshaft 3, and the meshing of both the cam gears 7.8 causes the two camshafts to , 3 rotate synchronously, and this inter-cam gear 7.8 is housed in a gear chamber 9 formed at the end of the cylinder head 4. Further, the front end portion of the exhaust side camshaft 3, which includes the inter-cam gear 8, projects outward from the cylinder head 4, and a cam pulley 11 is attached to the projecting end via the variable valve timing mechanism 10 (
A timing belt 12 is wound around the cam pulley 11 (detailed structure will be described later), and a cam pulley of the other bank (not shown) and a crank pulley fixed to the crankshaft.

Therefore, when the timing belt 12 is driven by the crankshaft, the exhaust side camshaft 3 is rotated, and the rotation of the camshaft 3 is transmitted to the intake side camshaft 2 via the inter-cam gear 7.8.

Next, as shown in FIG. 5, a combustion chamber 14 is formed on the lower surface of the cylinder head 4 corresponding to each cylinder, and this combustion chamber 14 has an intake port 15 and an exhaust port 16.
An intake valve 17 and an exhaust valve 18 are installed in each opening. The cylinder head 4 also has a tappet hole 19 corresponding to the intake valve 17 and a tappet hole 2 corresponding to the exhaust valve 18.
0 are arranged in two rows, and these tappet holes 19°2
A packet-type tappet 21.21 is inserted into the hole. In this tappet 21.21, the intake valve 17 and the exhaust valve 1
The upper ends of each of the valve stems 17a and 18a of 8 are connected, and these tappets 21 are connected to a hydraulic valve lash mechanism 2.
2 is built-in.

Further, the tappet 21.21 is connected to the valve spring 2.
3.23, this tappet 21.
The cam surfaces 2a of the camshafts 2 and 3 are disposed directly above each other.

3a and when the tappet 21.21 slides in the tappet hole 19.20 for valve opening/closing operation, the valve lash mechanism 22.22 automatically adjusts the valve lash.

The tappet holes 19 and 20 on the intake side and the exhaust side are provided with first and second oil passages 41 according to the arrangement described later.
．． 42, hydraulic oil is supplied by a supply hole 24.24 to a groove 25 formed in the circumferential surface of the tappet 21.21, and from the groove 25 into the interior of the tappet 21 through a hole 26 opened in the circumferential surface of the tappet. and is supplied to the valve lash mechanism 22. Also, the oil is in the groove 25 on the other hand.
Lubricate between the tappet 21.21 and the tappet hole 19.20.

On the other hand, the above-mentioned variable valve timing mechanism 10 is hydraulically operated, and engine lubricating oil from an oil pump (not shown) of the engine is supplied to the inside of the exhaust camshaft 3 from the rear end of the exhaust camshaft 3 according to the operating condition through an oil path (described later). The opening and closing timing of the exhaust valve 18 can be varied by changing the rotational phase of the exhaust side camshaft 3.
This changes the overlap period with 7.

The detailed structure of this variable valve timing mechanism 10 will be explained based on FIGS. 1 and 4. A cylindrical casing 27 is rotatably fitted around the outer circumference of the end of the exhaust side camshaft 3, and a cover unit 36 is integrally fastened to the front end side of the casing 27 by bolts (not shown). The cam pulley 11 is attached to the cam pulley 11 by a bolt 29, and is rotated integrally by a timing belt 12. Further, in the casing 27, the journal portion 27a is supported by the front end bearing portion 6 of the cylinder head 4, the camshaft 3 is supported by the bearing portion 6, and the exhaust side camshaft is supported by the rear portion of the journal portion 27a. The gear 8 between the cams of No. 3 is inserted by keyway coupling,
It is fixed with a nut 28.

In the front end bearing portion 6 of the casing 27, large-diameter recessed portions 6a and 6b are formed on both sides, and the inter-cam gear 8 is fitted into the rear recessed portion 6a by force when tightening the nut 28. The protruding step portion 27b provided on the journal portion 27a of the casing 27 is in contact with the side end surface of the bearing portion 6, and the convex step portion 27b provided on the journal portion 27a of the casing 27 is fitted into the front recessed step portion 6b. It is in contact with the side end surface of 6. In other words, the bearing part 6
is sandwiched between the cam gear 8 and the casing 27 from both sides, thereby determining the thrust of the casing 27 of the variable valve timing mechanism 10, that is, the fixed side. Note that the convex step portion 27b of the casing 27
The surrounding area is sealed by an oil seal 32.

On the other hand, in the internal structure of the valve timing mechanism 10, a center block 34 is connected to the end of the camshaft 3 by an end bolt 33, and a ring-shaped helical piston 35 is connected to the cover integral 36 on the outer periphery of the center block 34. is interposed. Further, the cover unit 36 is formed to cover the ends of the end bolt 33 and the helical piston 35.

Helical splines inclined in opposite directions are formed on the inner and outer circumferences of the helical piston 35, and the helical piston 35 is movable in the axial direction of the camshaft 3 via the inner and outer helical splines. 34 and a cover unit 36.

Further, a return spring 40 is disposed between the back of the helical piston 35 and the casing 27.

When the cam pulley 11 is rotationally driven, the cover unit 36, the helical piston 35 and the center block 3
4 are rotated integrally, and the exhaust side camshaft 3 is also rotationally driven in the same direction. In addition, the intake side camshaft 2 has
Driving force is transmitted from an inter-cam gear 8 fixed to a casing 27 that rotates together with the cam pulley 11 to the inter-cam gear 7 on the intake side.

A hollow passage 37 is formed through the center of the exhaust side camshaft 3 in the axial direction, and a communication passage 38 is formed through the center of the end bolt 33 in communication with the hollow passage 37. The oil supplied from the valve timing mechanism 37 is introduced into the variable valve timing mechanism 10 through the communication path 38. And the above communication path 3
A conduit passage 39 is provided inside the end of the cover unit 36 to communicate with the open end of the helical piston 35 and to cause oil to be introduced into the front end surface of the helical piston 35 to act on the front end surface of the helical piston 35. The spring force of the spring 40 acts against the oil pressure.

Therefore, in the variable valve timing mechanism 10, when no oil pressure is introduced, the helical piston 35 is in the OFF state in which it is pressed and biased rightward in FIG. 4 by the force of the return spring 40. When oil is supplied from the state through the communication path 38 and the guide path 39 and hydraulic pressure acts on the helical piston 35,
The helical piston 35 moves axially to the left in FIG. 4 against the return spring 40, and becomes in the on state.

Since the center block 34 and the cover unit 36 located inside and outside of the helical piston 35 are respectively engaged with the helical piston 35 via the helical spline, the movement of the helical piston 35 in the axial direction causes the center block 34 to 34 and the cover unit 36 rotate relative to each other.

Therefore, the exhaust side camshaft 3 and the pulley 11 rotate relatively, and the camshaft 3 and the cam pulley 1
A phase difference occurs between the exhaust valve 18 and the exhaust valve 18.
The opening/closing timing of this will be changed. Conversely, when the introduction of hydraulic pressure to the variable valve timing mechanism 10 is stopped and the hydraulic pressure acting on the helical piston 35 is released, the helical piston 35 returns to the tip side by the spring force of the return spring 40. Return to the original opening/closing timing.

In this manner, the variable valve timing mechanism 10 switches the opening/closing timing of the exhaust valve 18 in two stages depending on the presence or absence of supplied hydraulic pressure.

The above switching is performed according to the rotation speed of the engine 1, and by delaying the opening/closing timing in the high rotation range and increasing the valve overlap, acceleration performance in both the low rotation range and the high rotation range of the engine is improved. becomes possible.

By the way, the exhaust side camshaft 3 is indicated by the arrow B in FIG.
As shown, it is set to rotate counterclockwise when viewed from the back side. Correspondingly, as the helical piston 35 moves backward in the axial direction due to the action of hydraulic pressure, the camshaft 3 is moved in such a manner that the rotational phase of the camshaft 3 is shifted in a retarded direction, that is, in a clockwise direction opposite to the above. The direction of inclination of the helical spline formed on the outer periphery of the central block 34, which is integral with the camshaft 3, is as shown in FIG.

In addition, when the engine is stopped, the helical piston 3
5 is moved forward by a return spring 40, but when it is driven to rotate with the rotation of the engine, the helical piston 35 is moved in the direction of inclination of its helical spline according to the driving load accompanying the opening and closing operation of the exhaust valve 18. An axial propulsive force acts in response to this, and this axial propulsive force is in the direction of moving the helical piston 35 backward, which is the same direction as the hydraulic pressure. The axial propulsive force increases as the driving torque of the camshaft 3 increases as the engine speed increases.

The spring force of the return spring 40 that biases the helical piston 35 in the forward direction is set to be weaker than the axial propulsive force of the helical piston 35 during high rotation.

As shown in FIG. 8, the above relationship is such that as the engine speed increases, the axial propulsive force of the helical piston 35 increases on the high speed side as shown by curve E, and this characteristic On the other hand, the return spring 40 is designed so that the spring force G is equal to the axial propulsive force when the engine rotation speed is a set value N on the high rotation side. Therefore, when the engine speed exceeds the set value N, the helical piston 35 automatically moves backward against the return spring 40 due to its axial thrust even without the action of hydraulic pressure, retarding the camshaft 3. This is to shift the rotational phase in the direction. Note that at normal oil temperatures, the generated oil pressure increases as the engine speed increases, as shown by curve F, but at high oil temperatures, it decreases as shown by curve F' in response to a decrease in viscosity, and the helical oil pressure increases. Although the operating force of the piston 35 decreases, stable on-operation can be obtained in the high rotation range due to the axial propulsion force.

By the way, the bearing portions 5 of the camshafts 2 and 3 mentioned above...
-5, 6. The oil supply structure to the valve lash mechanism 22 and the variable valve timing mechanism 10 is constructed as follows.

That is, as shown in FIG.
and the exhaust side camshaft 3, two oil passages 4, a first and a second oil passage, are arranged in the longitudinal direction of the cylinder head 4.
1.42 are formed in parallel, among which the first oil passage 4
1 communicates with the intake side valve lash mechanism 22 of each cylinder through the supply hole 24 explained in FIG. 5 to supply oil, while it communicates with the exhaust side valve lash mechanism 22 through the second oil passage 42. supply oil.

Further, the rear end of the first oil passage 41 located on the intake side is
At the end of the shaft opposite to the inter-cam gear 7, it communicates with a hollow passage 44 formed at the center of the intake camshaft 2 via a communication passage 43 provided in the bearing part 5. In addition, the intake camshaft 2 is provided with through holes 45 that supply oil from a plurality of locations in the longitudinal direction of the hollow passage 44 to each bearing portion 5 .

Furthermore, with respect to the second oil passage 42 located on the exhaust side, a third oil passage 46 is formed parallel to the passage 42 at an outside position of the cylinder head 3 sandwiching the exhaust side camshaft 3. 3 oil passage 46 and second oil passage 42
and communicate with the cylinder through an orifice 47 formed in the rad 4 at the rear end side. The third oil passage 46 is provided with a through hole 48 for supplying oil to each bearing portion 5 of the exhaust side camshaft 3.

Further, the second oil passage 42 is connected to the hollow passage 37 of the exhaust side camshaft 3 by a control valve 49 at its rear end side which is communicated with the orifice 47 . This control valve 49 controls the oil supply to the variable valve timing mechanism 10 in conjunction with the on/off of the solenoid 50, and as shown in FIGS. 6 and 7,
It has a valve chamber 51 with which the second oil passage 42 communicates, a plunger 52 of a solenoid 50 is inserted into the valve chamber 51, a valve body 53 is equipped on the plunger 52, and the valve chamber 51 and the camshaft 3 are provided with a valve body 53. A supply passage 54 and a discharge passage 55 are formed across the bearing portion 5 at. Furthermore, a drain passage 56 is communicated with the valve chamber 51 .

When the solenoid 50 is in the ON state (FIG. 6), the valve body 53 resists the force of the spring 57 that biases the valve in the valve closing direction.
slides forward, and the oil flowing into the valve chamber 51 flows from the hole 58 provided in the valve body 53 to the supply passage 54 and is supplied to the hollow passage 37 of the camshaft 3. In this case, the discharge passage 55 and the drain passage 56 are closed by the valve body 53.

Further, when the solenoid 50 is off (FIG. 7), the valve body 53 slides backward by the force of the spring 57, and the valve body 53
The communication between the supply passage 54 and the valve chamber 51 is cut off, and the discharge passage 55 and the drain passage 56 are connected to the valve chamber 51.
will be communicated to. Therefore, the oil that has been supplied to the valve timing mechanism 10 is discharged from the hollow passage 37 to the drain passage 56 via the control valve 49.

Oil is supplied to the first and second oil passages 41, 42 from an oil pump (not shown). That is, in FIG. 1 and FIG. 3, the first and second oil passages 41 and 42 are
An oil chamber 60 is formed between them. Then, pressure-fed oil from the oil pump is fed from below to the oil chamber 60 by a jido 61, and from this oil chamber 60, the oil is distributed and supplied to the first and second oil passages 41.42 on both sides by branch passages 62.63. be done.

Note that the ground passage 61 is connected to the oil chamber 60 in a tangential direction, and the branch passages 62 and 63 are led out from the oil chamber 60 in a tangential direction. With this structure, the oil flowing in and out of the oil chamber 60 generates a vortex within the oil chamber 60, the air contained in the oil is separated, and this separated air is transferred to the upper air vent hole 60.
is discharged from.

By the way, a cam pulley 11 is attached to the front end of the exhaust side camshaft 3 and is rotationally driven by a belt 12, and a large load based on belt tension acts downward on the front end of the camshaft 3, causing the front end bearing to 6, the lubrication conditions become stricter.

In this embodiment, in order to ensure lubricity in the front end bearing 6, the third oil passage 46 is formed to a position below the gear chamber 9, as shown in FIG. A passage 65 is provided to supply oil between the front end bearing portion 6 and the journal portion 27a of the casing 27. Note that the front ends of the first and second oil passages 41 and 42 are closed.

In the above oil path, from the oil pump to the oil chamber 6
The oil sent to the first
The oil is distributed to the second oil passages 41, 42, flows through these oil passages 41, 42, and is supplied to the valve lash mechanism 22 of each cylinder for operation. In addition, the first oil passage 4
1 flows into the hollow passage 44 of the intake-side camshaft 2 from the communication passage 43, and is supplied to each bearing portion 5 for lubrication while flowing through the hollow passage 44 toward the front end side.

On the other hand, a portion of the oil in the second oil passage 42 is released from the control valve 49.
When the engine is turned on, it flows into the hollow passage 37 of the exhaust side camshaft 3, and is supplied from the hollow passage 37 to the variable valve timing mechanism 10 for the on operation. Further, the other part of the oil in the second oil passage 42 passes through the orifice 47 to adjust its flow rate and flows into the third oil passage 46, and flows into each bearing portion 5 and front end bearing portion of the exhaust side camshaft 3. 6 for lubrication.

In addition, due to the above oil path configuration, the valve lash mechanism 2
2 and the variable valve timing mechanism 10 to obtain responsiveness and stability of operation.

Further, in the V-type engine 1, the bank IA is provided at an angle with respect to the horizontal line A shown in FIG.

Therefore, when the engine 1 is stopped, the oil in the oil chamber 60, the first oil passage 41, and the hollow passage 44 is discharged downward from the path 61, but the oil in the second and third oil passages 42, 46 and the exhaust side Since the hollow passage 37 is located below the oil chamber 60, the oil is not discharged and remains filled. As a result, lubricity on the exhaust side, which is subject to a large load, is quickly ensured when the engine is started.

Although the above embodiment shows an example in which the valve timing of the exhaust valve 18 is delayed at high speeds, the present invention is also applicable to a case where the valve timing of the intake valve 17 is delayed at high speeds.

[Brief explanation of the drawing]

FIG. 1 shows a V equipped with a valve train according to an embodiment of the present invention.
Figure 2 is a side view of the same cylinder head, Figure 3 is a rear view of the cylinder head partially cut away, and Figure 4 is a specific example of the variable valve timing mechanism. 5 is a cross-sectional rear view of the intake/exhaust port portion of the cylinder head, FIG. 6 is a sectional view of the control valve portion during ON operation, and FIG. 7 is a sectional view of the control valve portion during OFF operation. The cross-sectional view and FIG. 8 are characteristic diagrams showing the relationship between the axial thrust of the helical piston, the generated oil pressure, and the set value of the spring force of the return spring with respect to the engine speed. 1... Engine, 3... Exhaust side camshaft, 4... Cylinder head, 10...
...Variable valve timing mechanism, 11...Cam pulley, 12...Timing belt, 17...
...Intake valve, 18...Exhaust valve, 2
7...Casing, 34...Center block, 35...Helical piston, 36...Curve/cover integrated, 40...Return spring, 3
7...Hollow passage, 42...Oil passage, 4...Control valves, 50...Solenoid. Figure 4 Funeral map Figure 7

Claims (1)

[Claims] (1) An engine valve train equipped with a hydraulically operated variable valve timing mechanism that changes the rotational phase of a camshaft so that the valve timing of an intake valve or an exhaust valve is delayed by introducing hydraulic pressure, wherein the variable valve The timing mechanism has a helical piston that moves in the axial direction of the camshaft under the action of the introduced hydraulic pressure to change the rotational phase of the camshaft via a helical spline, and also urges the helical piston in the return direction. It has a return spring, and the spring force of the return spring is set to be weaker than the axial propulsive force that acts on the helical piston in the same direction as the oil pressure as the camshaft rotates at high rotations. Engine valve train.