JPH04187807A - Valve system for engine - Google Patents

Abstract

PURPOSE:To exhibit performance of an engine to the maximum by forming a cam profile of a cam in such a manner as to continuously change it in the axial direction, and steplessly and continuously selecting the cam profile for operating a valve. CONSTITUTION:In a cam profile 14 of a cam 5, the projecting height of a projection portion 15 is gradually increased from the side end surface of a timing pulley 4 toward the direction indicated by an arrow P. The top portion of the projection portion 15 is such formed that the circumferential position thereof is gradually displaced in the rotational direction of a camshaft 3. Movement of the cam 5 in the axial direction of the camshaft 3 can change a valve lift quantity and a valve timing. A controller 8 drivingly controls a control motor 9 on the basis of a detection signal output from an engine speed sensor 26a or the like, to move the cam 5 via a pushing arm 25, thus selecting the cam profile 14. Therefore, performance of an engine can be exhibited to the maximum.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a valve mechanism for an engine.

[Conventional technology]

For example, the cylinder head of a four-stroke gasoline engine is provided with an intake valve for taking in the fuel mixture and an exhaust valve for discharging the gas burned within the cylinder. A valve mechanism is provided for opening and closing in synchronization with the stroke or intake stroke. Generally, the valve mechanism in a gasoline engine transmits the rotation of the crankshaft to the camshaft via a timing boolean, and a cam provided on the camshaft causes a valve lifter to reciprocate, and in synchronization with each stroke, the intake valve and It is configured so that the exhaust valve can be opened and closed by lifting it. By the way, as mentioned above, the intake valve and exhaust valve are configured to open and close in synchronization with the intake stroke or exhaust stroke of the engine, but the degree of opening of the valve (effective valve area) and the valve opening degree (effective valve area) By changing the opening/closing timing (valve timing), engine performance changes significantly. For example, in a low-speed rotation range, the piston speed decreases and the air-fuel mixture sucked into the combustion chamber loses its momentum, so the engine tends to lack torque. In this case, by setting the valve opening of the intake valve small to narrow the cross-sectional area through which the fuel mixture passes and increase the flow velocity of the fuel mixture, intake efficiency can be increased and torque can be increased. On the other hand, in high-speed rotation ranges, the piston speed increases the force of the fuel mixture being sucked in, but the time the intake valve is open during each intake stroke becomes shorter, so the intake amount of the fuel mixture becomes insufficient. This limits the engine output. In this case, it is preferable to set the opening degree of the valve as large as possible so that a large amount of the fuel mixture can be taken in. Further, the valve timing needs to be set so as to minimize piston work loss and pump loss, and to effectively utilize the kinetic energy of intake and exhaust gas. For example, during the intake stroke, as the engine speed increases, the time the valve is open becomes shorter, but the kinetic energy of the fuel mixture flowing into the cylinder increases. By setting the timing earlier than the top dead center and setting the closing timing somewhat later, it is possible to suck in a large amount of fuel mixture.This allows the output in the high rotation range to be further improved.As mentioned above, Even if the engine is the same, there is an optimal valve opening and valve timing depending on the engine speed, engine load, etc., and if it is possible to select the above valve opening and valve timing according to the engine operating condition. In recent years, various variable valve mechanisms have been proposed that can change the valve opening degree or valve timing depending on the operating conditions of the engine.

[Problems to be Solved by the Invention] As mentioned above, many variable valve mechanisms have been proposed that allow the valve opening degree or valve timing to be changed in accordance with engine operating conditions such as engine speed. In these conventional variable valve mechanisms, it is not possible to steplessly and continuously change the valve opening degree and valve timing depending on the engine rotation speed and the like. In other words, conventional variable valve mechanisms have, for example, provided multiple valves and changed the number of valves that are open depending on the engine speed, thereby substantially changing the valve opening degree. A method is adopted in which the valve timing is changed by changing the phase of the cam attached. However, these variable valve mechanisms are configured so that the valve opening degree or valve timing is switched when the engine speed or the like exceeds a certain value. Therefore, the valve opening degree or valve timing can only be changed in steps over several stages. However, the optimum valve opening degree and the optimum valve timing continuously change depending on engine operating conditions such as engine speed, engine load, and radiator water temperature. Therefore, in the conventional variable valve mechanism described above, it cannot be said that optimal control of the valve opening degree and valve timing is performed, and it cannot be said that the performance of the engine is fully brought out. The present invention was devised under the above-mentioned circumstances, and solves the above-mentioned conventional problems, and continuously adjusts the valve opening degree and valve timing of engine valves according to engine speed, load, etc. The object of the present invention is to provide a valve train that can be varied steplessly and in a variable manner to maximize engine performance under all operating conditions. [Means for Solving the Problems] In order to solve the above problems, the present invention takes the following technical measures. That is, the present invention is a valve operating mechanism for an engine that opens and closes a valve by a cam provided on a camshaft. The cam surface is movable in the axial direction of the camshaft, and by moving the cam in the axial direction of the camshaft, the cam profile for operating the valve can be selected steplessly. It is characterized by being configured as follows.

[Operation and effects of the invention]

The valve train according to the present invention moves a cam having a cam surface in which a cam profile in a plane perpendicular to the axis at each axial position changes continuously in the axial direction in the axial direction of a camshaft, and obtains a desired cam profile. The engine valve is configured to be driven by the engine valve. The above cam has a continuous cam profile that provides optimal valve timing and valve lift (valve opening degree) depending on all engine operating conditions, and moves the above cam in the axial direction of the camshaft. This allows the valve to be opened and closed by selecting the optimum cam profile depending on the operating condition of the engine. For example, in the low speed range of the engine, by setting the valve lift of the intake valve small, the effective cross-sectional area of the valve is reduced, increasing the flow velocity of the fuel mixture and reducing the momentum of the fuel mixture flowing into the combustion chamber. can be increased. Thereby, the torque characteristics in the low speed rotation range can be improved. On the other hand, in the high speed range of the engine, the time that the intake valve is open is set for a long time, and the amount of valve lift is increased to increase the effective cross-sectional area of the nozzle. This makes it possible to increase the output in the high-speed rotation range.In other words, it is possible to drive the engine by selecting the optimal valve lift amount and valve timing according to the engine operating condition. Moreover, the cam profile of the cam according to the present invention is formed to change continuously in the axial direction.Therefore, it is possible to steplessly and continuously select the cam profile for operating the valve. Therefore, the engine can be driven while continuously and steplessly changing the valve lift amount and valve timing based on changes in engine speed, engine load, radiator water temperature, etc. This makes it possible to maximize engine performance in response to changing operating conditions.Also, by simply moving the cam in the axial direction of the camshaft, the valve lift amount and valve timing can be changed at the same time. As a result, the structure is extremely simple and it is easy to perform highly accurate control. [Explanation of Embodiments] Hereinafter, embodiments of the valve mechanism according to the present invention will be described with reference to Figs. 1 to 1O. A detailed explanation will be given based on the following. Fig. 1 is a diagram showing a schematic configuration of a valve train according to this embodiment. In general, a valve train of an engine opens and closes a plurality of intake valves and exhaust valves. However, in Fig. 1, a mechanism for driving one intake valve is shown in order to explain the operation of the valve. A so-called DOHC (DOHC) in which a set of camshafts 3 is provided above the cylinder head 2.
The present invention is applied to a double overhead camshaft (double overhead camshaft) type valve train, in which the cam 5 cannot be rotated relative to the camshaft 3 to which rotational force from a crankshaft (not shown) is transmitted via the timing pulley 4. The valve lifter 7 of the intake valve 6 is directly reciprocated by the rotation of the cam 5. Further, in this embodiment, the cam 5 is fitted onto the camshaft 3 so as to be non-rotatable but slidable in the axial direction, and the cam 5 is connected to a control motor controlled by a control device 8. By sliding the cam profile 9 in the axial direction of the camshaft 3, the cam profile 14 for operating the intake valve 6 can be selected. As shown in FIG. 2, the cam 5 according to this embodiment has a cam profile 1 in a plane perpendicular to the axis at each position in the axial direction.
The shaft hole 12 is provided with a cam surface 10 that changes continuously in the axial direction, and an inner circumferential spline 11 is formed in the shaft hole 12. The cam 5 is fitted onto an outer circumferential spline 13 formed on the camshaft 3 so that it cannot rotate relative to the camshaft 3 and is slidable in the axial direction. In the cam profile 14 of the cam 5 in this embodiment, as shown in FIGS. The cam profile 14 is formed to change continuously at each position in the axial direction of the camshaft 3, and by moving the cam 5 in the axial direction of the camshaft 3, a desired cam profile 14 can be selected. The intake valve 6 according to this embodiment, as shown in FIG.
A valve lifter 7 is directly reciprocated by the cam 5, and a valve head 18 is provided at the tip of the valve lifter 7 to open and close the intake port 17 of the cylinder head 2.
and a valve spring 19 that imparts elasticity to the valve lifter 7 and the valve head I7. The valve lifter 7 includes a valve stem 20 to which the valve head 18 is fixed, and a valve stem 20 to which the valve head 18 is fixed.
The cam follower 21 is provided at the base end of the cam follower 21. The end surface of the cam follower 21 is formed into a spherical shape, and is configured to be easily driven by the cam profile 14 of the cam 5. The valve spring 19 is connected to a retainer 22 provided at the end of the valve stem 20 and the cylinder head 2.
It is interposed in a compressed state between the valve lifter 7 and the seat surface 23 of the valve lifter 7, and is configured to apply an elastic pressing force to the valve lifter 7 via the retainer 22. When the valve is closed, the valve head 18 is brought into close contact with the valve seat 24 with a predetermined pressure, while when the valve is opened, the cam follower 21 is elastically pressed against the cam surface 10.
The valve lifter 7 is configured to follow the profile 14 of the cam 5. Further, the valve mechanism 1 in this embodiment includes a push arm 25 that clamps the cam 5 from both sides in the axial direction and presses the cam 5 to move it in the axial direction, and a push arm 25 that moves the push arm 25 in the axial direction of the camshaft 3. A control motor 9, a control device 8 that controls the movement of the control motor 9, and various sensors 26a, 26b that detect engine operating conditions such as the engine rotation speed.
26c. 26d. The pushing arm 25 has an arm portion 25 that is approximately U-shaped in plan view.
a, and a driving part 25b extending from the arm part 25a in a direction perpendicular to the axis of the camshaft 3 and having a female feed screw 27a formed therein parallel to the camshaft 3, and rotated by a control motor 9 to be described next. feed screw 27b
is configured to be able to move in the axial direction of the camshaft 3 by being screwed into the female feed screw 27a. The control motor 9 is controlled by an output signal output from the control device 8, and can move the push arm 25 to a predetermined axial position by rotating the feed screw 27b a predetermined number of rotations. . The control device 8 includes the various sensors 26a, 26b...
- A cam profile 14 that drives the control motor 9 based on input signals from the cam profile 14 to provide optimal valve timing and valve lift amount in the operating state of the engine.
The cam 5 is moved via the pushing arm 25 so that the valve lifter 7 is reciprocated. In this embodiment, a cam position sensor 28 is provided to detect the axial position of the push arm 25, and feeds back the movement position of the cam 5 to the control device 8 to ensure a reliable cam position. It is configured so that it can be controlled. In this embodiment, the rotation speed sensor 26a shown in FIG.
In addition, a radiator water temperature sensor 26b. Various sensors such as a load sensor 26c that detects the load state of the engine and a speed sensor 26d that detects the vehicle speed are connected to the control device 8, and these sensors 26a, 26
Control signals from the motors b, 26c, 26d are input to the image production device 8, and the control motor 9 is controlled based on these control signals. Next, the operation of the valve train 1 of this embodiment will be explained. The cam profile 14 of the cam 5 according to this embodiment is the third
As shown in the figures to FIG. 5, the protrusion 15 extends from the side end surface of the timing pulley 4 in the direction of arrow P in FIG.
As the protrusion height (Hl, H2°Hl) of the protrusion 15 gradually increases, the circumferential position of the top 0 of the protrusion 15 (θ3.θ2.
θ, ) is formed to be gradually displaced in the rotational direction of the camshaft 3 (direction of arrow T), and by moving the cam 5 in the axial direction of the camshaft 3, the valve lift amount and pulp timing are adjusted. be changed. That is, as shown in FIG. 6, when the engine rotates at a low speed, the cam profile 14a with a small valve lift amount H1 is selected, and as the engine speed increases, the cam 5 is moved in the direction of the arrow Q, and the cam profile 14a is By sequentially selecting profiles 14b and 14c, the valve lift amount is increased from H1 to H2H. Conversely, as the engine speed decreases, the cam is moved in the direction of arrow P to reduce the valve lift amount. When the engine rotates at a low speed, the speed of the piston in the cylinder becomes low, and the rotational speed of the camshaft 3 also becomes low, so that the pulp opening time tends to become long. Therefore, it is difficult to forcefully introduce the fuel mixture into the combustion chamber, and there is a tendency for torque to be insufficient in a low speed range and for rotation to be unstable. In this embodiment, as shown in FIGS. 3 and 6, the cam profile +4a selected in the low speed rotation range of the engine is set to be smaller than the operating angle θ of the cam 5, and the valve lift amount H1 is also set small. By reducing each operation 01 of the cam 5,
The opening time of the pulp can be shortened and the work loss of the piston can be lowered. Further, since the valve lift amount H1 is small, the flow path of the fuel mixture is narrowed, the flow velocity of the mixture can be increased, and the mixture can be forcefully introduced into the combustion chamber. As a result, it can be expected that the engine rotation will be stabilized during idling, etc., and that the torque in the low speed rotation range will be improved. On the other hand, in a high-speed rotation range of the engine, the rotational speed of the camshaft 3 increases, the time during which the intake pulp is open becomes shorter, and the flow rate of the fuel mixture increases. Therefore, in the high-speed rotation range of the engine, it is desirable to set the pulp opening time to be long and to increase the lift amount so that a large amount of air-fuel mixture can be introduced into the combustion chamber. In this embodiment, as shown in FIGS. 5 and 6, the cam profile 14c of the cam 5 used in the high-speed rotation range is such that the operating angle θ is increased to set the pulp opening time to be long. , the valve lift amount H2 is set large. Furthermore, in this embodiment, the protruding portions 15 of
The circumferential position of the apex 0 of the cam profile 14a is displaced from θ2 to θ in the rotational direction of the cam 5 (direction of arrow T) with respect to the apex position of the cam profile 14a. Further, the lift start point S of the pulp is also displaced in the rotation direction of the cam 5,
As the engine speed increases, the pulp lift start time is brought forward. As a result, in a high-speed rotation range, it becomes possible to draw in a large amount of fuel mixture while utilizing the inertia of the fuel mixture, and the engine output can be further increased. In this embodiment, the cam profile 14 is selected by the control device 8 driving and controlling the control motor 9 based on the detection signal from the rotation speed sensor 26a, etc. This is done by moving the . Therefore, the engine can be operated by automatically setting the valve lift amount and valve timing that are optimal for the operating state of the engine. Furthermore, in this embodiment, since the cam profile 14 for opening and closing the pulp can be selected steplessly, the sensors 26a, 26b, . . . detect the engine rotation speed, engine load, radiator water temperature, etc. The engine can be driven without steplessly and continuously changing the valve lift amount and valve timing based on changes in the detection signals. This makes it possible to maximize engine performance in response to ever-changing operating conditions. 7 to 9 show examples of changes in valve lift amount and valve timing of each valve when the valve operating mechanism according to the present invention is applied to an intake valve and an exhaust valve. FIG. 7 shows the results in the low speed rotation range of the engine, and as the engine speed increases, the rotation speed changes sequentially as shown in FIGS. 8 and 9. As shown in these figures, in the low speed rotation range, the amount of lift is small and the opening time of the intake and exhaust valves is short. on the other hand,
As the rotational speed increases, the valve lift amount increases and the valve open time also increases. In addition, the so-called overlap time, in which the intake pulp and exhaust valve are open at the same time, is made longer as the speed increases.
The kinetic energy of intake and exhaust is used to increase intake and exhaust efficiency. As shown in these figures, in the valve train according to the present embodiment, the valve lift amount and valve timing can be changed simultaneously, steplessly and continuously, so that the intake pulp and exhaust gas flow can be changed. You can freely adjust the relationship between the valve timing. As mentioned above, in this embodiment, the cam profile 14 of the cam 5 can be selected continuously according to the engine speed, etc., and can also be automatically selected by the control device, so that any The optimum valve timing and valve lift amount can be selected under the operating conditions. FIG. 10 shows the relationship between rotational speed and output in an engine to which the present invention is applied and a conventional engine. In this figure, a dashed line 29 indicates an output curve of a normal engine not equipped with a variable valve mechanism, a broken line 30 indicates an output curve of an engine equipped with a conventional variable valve mechanism, and a solid line 31 indicates an output curve of an engine equipped with a valve mechanism according to the present invention. Each represents the output curve of the engine. As shown in this figure, the output curve 31 of the engine equipped with the valve mechanism according to the present invention has uniform output over the entire rotation range of the engine, which is different from the output curve 30 of the engine equipped with the conventional variable valve mechanism. As shown in the figure, the output does not decrease at the predetermined rotational speed n at which valves and the like are switched. Therefore, the performance of the engine can be maximized depending on the operating state of the engine from a low speed rotation range to a high speed rotation range. Although the above 1θ diagram shows an example in which the engine output is controlled to be maximum, it is also possible to select the cam profile so that the fuel efficiency is the highest depending on each engine rotation range. be. The present invention is not limited to the above-described embodiments. In the embodiments, the present invention is applied to a so-called DOHC type valve train, but the present invention can also be applied to other valve train mechanisms such as a 5OHC type. Further, in the embodiment, only one intake pulp opening/closing mechanism has been shown and described, but it goes without saying that the present invention can be applied to a valve operating mechanism that simultaneously drives a plurality of intake pulps and exhaust valves. Further, in this embodiment, the cam 5 is configured to slide in the axial direction of the camshaft 3, but the cam may be fixed to the camshaft and the camshaft itself may be moved. Furthermore, the cam profile is not limited to the embodiments, and can be set to exhibit desired engine characteristics depending on the type of engine, application, purpose of use, etc. Also, a control device 8 serves as a mechanism for moving the cam 5.
The control motor 9 was configured to be driven by
Other control mechanisms such as mechanical control based on engine speed etc. may also be employed.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an embodiment of a valve mechanism according to the present invention, Fig. 2 is an external perspective view of a cam according to the present invention, and Fig. 3 is a cross section taken along the line ■-■ in Fig. 2. 4 is a sectional view taken along the line IV-IV in FIG. 2, FIG. 5 is a sectional view taken along the line V-■ in FIG. 2, and FIG. Figures 7 to 9 are explanatory diagrams showing the relationship between the valve lift amount and valve timing of the intake pulse section and exhaust valve when the valve train according to the present invention is adopted, and Figure 10 is an illustration showing the relationship between the engine output and engine rotation. It is a diagram showing the relationship with numbers. DESCRIPTION OF SYMBOLS 1... Valve train mechanism, 3... Camshaft, 5... Cam, 6... Valve, 10... Cam surface, 14a, 14
b, +40...cam profile.

Claims (1)

[Claims] (1) An engine valve mechanism that opens and closes valves using a cam installed on a camshaft, the cam being a cam whose cam profile in a plane perpendicular to the axis changes continuously in the axial direction at each axial position. The cam has a surface and is movable in the axial direction of the camshaft, and is configured such that by moving the cam in the axial direction of the camshaft, a cam profile for operating the valve can be selected steplessly. An engine valve mechanism characterized by: