JPH0425412B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a valve train for an automobile engine or the like that has a function of automatically changing the valve timing of an intake valve.

(B) Prior art A typical reciprocating engine in which the intake valve closes at an earlier timing (see broken line a in Figure 1) has standard valve timing (see solid line b in Figure 1). ), it is possible to obtain higher engine torque in the low speed rotation range, but
There is a tendency for torque to drop significantly in the medium to high speed range. On the other hand, when the intake valve is set to close at a later time (see the dashed line c in Figure 1), the torque drop in the medium to high speed range is lower than when the valve timing is standard. Although it is rare, there is a tendency that sufficient torque cannot be obtained in the low speed rotation range. Therefore, in order to obtain high torque over the entire rotational speed range, the valve train for driving the intake valves must have a function that advances or retards the valve timing according to the engine rotational speed. desirable.

As a prior art related to a valve train developed to meet such demands, there is a die technique as shown in previously filed Utility Application No. 56-59075 (see U.S. Pat. There is one in which a timing pulley is attached to a camshaft so that it can freely rotate by a predetermined angle in the circumferential direction, and the shaft is provided with a spring member that urges the pulley to rotate in a direction that increases the bubble timing. That is, this system was devised by focusing on the tendency that the torque required to drive the camshaft increases approximately in proportion to the increase in engine rotational speed, and in the high-speed rotation range, the spring member As the deflection increases, the bubble timing is automatically retarded. However, with this type of configuration, it is necessary to provide a spring member attachment part, a stopper, etc. on the camshaft side, so not only the pulley but also the camshaft must be newly designed, and the camshaft must have a retard function. There are disadvantages in that the rate of common parts with existing standard engines decreases, leading to increased costs, and it cannot be easily applied to existing engines.

(c) Purpose of the Invention The present invention has been made in view of the above circumstances, and is capable of maintaining engine torque at a high value over the entire rotational speed range, and has a structure with a small number of parts. It is an object of the present invention to provide an engine valve train that is extremely simple and can be easily applied to existing engines.

(d) Structure of the Invention In order to achieve the above object, the present invention includes a first rotating body fixed to a crankshaft or a camshaft, and a transmission member such as a pulley, sprocket, or gear constituting a valve train. a second rotary body which is provided so as to be movable in the axial direction with respect to the first rotary body and has a transmission element on its outer periphery; a pair of cam grooves formed to become gradually shallower toward the outer end; a weight that is engaged between the two cam grooves and is slidable in a substantially radial direction along the two cam grooves; an elastic body that presses the rotating bodies in a direction toward each other and centripetally urges the weight toward the inner end side of the cam groove, The present invention is characterized in that the outer end of the cam groove of the rotary body is provided so as to be deviated in the rotation advancing direction from the outer end of the second rotary body.

(E) Embodiment An embodiment of the present invention will be described below with reference to FIGS. 2 to 7.

Timing pulleys 3 and 4, which are transmission members, are mounted on the crankshaft 1 and camshaft 2 of the engine, respectively, and these pulleys 3,
A timing belt 5 is stretched between the belts 4 and 4, and the rotational force of the crankshaft 1 in the direction of arrow x is transmitted to the camshaft 2 via the pulley 3, belt 5, and pulley 4. Note that the timing pulley 3 on the drive side is a normal one,
It is fixed to the crankshaft 1 via a key 6. On the other hand, the timing pulley 4 on the driven side is connected to a first rotating body 7 fixed to the camshaft 2.
, a second rotating body 8 provided so as to be movable in the axial direction with respect to the first rotating body 7, and a pair of cam grooves 9 provided on opposing surfaces of both of these rotating bodies 7, 8, respectively. 10, a steel ball 12 as a weight engaged between both the cam grooves 9 and 10, and a wave spring 13 as an elastic body that presses both the rotating bodies 7 and 8 in the direction toward each other. Become. The first rotating body 7 consists of a hub 7a that fits on the outer periphery of the end of the camshaft 2, and a disk portion 7b that projects from the outer periphery of the hub 7a. and is fixed to the camshaft 2 using bolts 15. Further, the second rotating body 8 is a hub 7 of the first rotating body 7.
a disc portion 8a rotatably fitted to the outer periphery of a;
A cylindrical portion 8 integrally formed on the outer periphery of this disk portion 8a
A transmission element, that is, teeth 8c with which the timing belt 5 meshes are provided on the outer periphery of the cylindrical portion 8b. The cam groove 9 is oval-shaped and is provided in the end surface of the disk portion 7b of the first rotary body 7 in a substantially radial direction, so that one half of the ball 12 can fit into the cam groove 9. The cross section is shaped like a semicircular arc. This cam groove 9 is
It is set to become gradually shallower from the inner end 9a to the outer end 9b. Further, the cam groove 10
is an oval shape provided in a portion of the disc portion 8a of the second rotating body 8 corresponding to the cam groove 9, and has a cross section so that the other half of the ball 12 can fit therein. It is shaped like a semi-circular arc. The cam groove 10 is also set to become gradually shallower from the inner end 10a to the outer end 10b. Incidentally, the engraving directions of both the cam grooves 9 and 10 are slightly different from each other. That is, in this embodiment, the outer end 9b of the cam groove 9 is connected to the cam groove 1.
The outer end 10b of the outer end 10b is set to be deviated by a required amount in the rotation advancing direction. Note that 16 is a snap spring for locking the wave spring 13. Further, a plurality of sets (for example, 3 to 6 sets) of the cam grooves 9, 10 and the balls 12 are provided at equal angular intervals in the circumferential direction.

With such a configuration, the centrifugal force acting on the ball 12 is small in the low-speed rotation range where the rotational speed of the crankshaft 1 and the camshaft 2 is low, so that the ball 12 is rotated as shown in FIGS. 3 and 4. As shown in FIG. 2, the cam grooves 9 and 10 are held at the inner ends 9a and 10a of each cam groove 9 and 10, respectively. That is, since the first rotary body 7 and the second rotary body 8 are biased toward each other by the elastic force of the wave spring 13, the ball 12 is pushed into the both cam grooves 9 by the biasing force. , 10, but these cam grooves 9, 10 have outer ends 9b, 10.
It is designed to become shallower gradually in the b direction. Therefore, a centripetal force acts on the ball 12 due to the clamping pressure and the change in the depth of the cam grooves 9, 10, and in a low speed rotation range where the centripetal force overcomes the centrifugal force, the ball 12 are held at the inner ends 9a, 10a of the gum grooves 9, 10. When the rotational speed of the engine increases from this state and the centrifugal force acting on the ball 12 exceeds a certain value, the ball 12 expands the distance between the two rotating bodies 7 and 8 and moves outward of the cam grooves 9 and 10. End 9
b, 10b, and is held at a position that balances the centripetal force described above. At this time, a phase difference occurs between the two rotating bodies 7, 8 due to the difference in the inclination of the two cam grooves 9, 10 in the rotational direction, and the valve timing is delayed by that amount. When rotating at maximum speed, the balls 12 reach the outer ends 9b, 10b of the cam grooves 9, 10, as shown in the imaginary line in FIG. 3 and in FIG. 5, and the valve timing becomes the most delayed state. . When the speed is decelerated from this state, the centrifugal force acting on the ball 12 decreases, and the ball 12 is returned toward the inner ends 9a, 10a by the centripetal force generated by the wave spring 13 mentioned above. Figure 6 shows
FIG. 7 shows the relationship between the rotation speed of the crankshaft 1 and the valve timing in this embodiment, and FIG. 7 shows the difference between the valve timing in the low speed rotation range and the valve timing in the high speed rotation range.

In this way, according to the valve train according to the present invention, the pressing force of the wave spring 13 and the cam grooves 9, 10
By appropriately selecting the shape, etc. of the intake valve, the valve timing of the intake valve can be automatically controlled. However, as in this embodiment, it is easy to control the valve timing to retard the transition from a low speed rotation range to a high speed rotation range, and in this way, the intake inertia can be utilized. Since the closing timing of the intake valve can be delayed only in the high-speed rotation range where it is possible, the output characteristics in the high-speed rotation range can be effectively improved without deteriorating the performance in the middle and low speed rotation ranges. Moreover, this valve train has a very simple structure with a small number of parts, and can be expected to work reliably. Moreover, there is no need to perform any special processing on the camshaft 2, etc. Therefore, it is possible to reduce costs by increasing the proportion of common parts with standard engines that do not have a valve timing control function, and it can also be easily applied to existing engines by simply replacing the pulleys. It has the advantage of being able to

In addition, in the above embodiment, a case was explained in which the shape of the cam groove was set so that the valve timing could be retarded in a high-speed rotation range, but the invention recited in claim 1 is not necessarily limited to such a structure. Of course, various modifications are possible, such as retarding the valve timing only in the idling operating range or in the idling operating range and the high speed rotation range.

Further, in the above embodiments, the case where the transmission member is a timing pulley on the camshaft side has been described, but it goes without saying that the present invention is not limited to this. For example, the present invention may be applied to a pulley on the crankshaft side. It's okay. Alternatively, instead of a pulley, the present invention can be similarly applied to a sprocket, gear, etc. for tensioning a chain.

Furthermore, the weight is not limited to a ball, but may also be a roller or the like.

(f) Effects Because the present invention has the above-described configuration, it is possible to maintain engine torque at a high value over the entire rotational speed range, and the structure is simple and highly reliable. It is possible to provide an engine valve train that can be easily applied to engines and the like.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the relationship between engine torque and rotational speed. Figures 2 to 7 show an embodiment of the present invention, in which Figure 2 is a partially cutaway front view, Figure 3 is an enlarged side sectional view showing the main parts, and Figures 4 and 5 are operational views. An explanatory diagram, FIG. 6 is a characteristic explanatory diagram showing retard characteristics, and FIG. 7 is a diagram showing valve timing. 1... Crankshaft, 2... Camshaft, 4... Transmission member (timing pulley), 7...
...First rotating body, 8... Second rotating body, 9, 10
...Cam groove, 12 ... Weight (ball), 13
...Elastic body (wave spring).

Claims (1)

[Scope of Claims] 1. A system in which the rotational force of a crankshaft is transmitted to a camshaft for opening and closing intake valves via paired transmission members such as pulleys, sprockets, or gears supported by both shafts, respectively. , at least one transmission member,
a first rotating body fixed to the shaft; a second rotating body that is movable in the axial direction with respect to the first rotating body and has a transmission element on its outer peripheral portion; A pair of cam grooves are provided on the opposing surfaces of the rotating body, and at least one of the cam grooves is formed to become gradually shallower toward the outer end. The cam groove comprises a weight that can be slid in a substantially radial direction and an elastic body that presses both of the rotating bodies in a direction toward each other and centripetally urges the weight toward the inner end of the deepened cam groove. A valve train for an engine, characterized in that the phases of the two rotating bodies can be mutually changed by outward movement of the weight due to centrifugal force. 2 In a system in which the rotational force of the crankshaft is transmitted to the camshaft for opening and closing the intake valves through a pair of transmission members such as pulleys, sprockets, or gears supported by both shafts, at least one of the transmission members is parts,
a first rotating body fixed to the shaft; a second rotating body that is movable in the axial direction relative to the first rotating body and has a transmission element on its outer peripheral portion; A pair of cam grooves are provided on the opposing surfaces of both rotating bodies, and at least one of the cam grooves is formed to become gradually shallower toward the outer end. a weight that can be slid in a substantially radial direction; and an elastic body that presses the two rotating bodies in a direction toward each other and centripetally biases the weight toward the inner end of the deepened cam groove. and an outer end of the cam groove of the first rotating body is offset in a rotation advancing direction from an outer end of the cam groove of the second rotating body. Valve train.