Phase varying device of engine

The present invention relates to a phase varying device of an engine of an automobile that transmits rotation of a crankshaft of the automobile engine to a camshaft for opening/closing an intake valve or an exhaust valve of the engine and varies open/close timing of the intake valve or the exhaust valve according to an operating condition such as an engine load and revolutions.

As this type of phase varying device, one as disclosed in the following Patent Document 1 proposed by the present inventor et al. has been known. This is shown in FIG. 7.

The phase varying device is used in a manner fitted to an unillustrated engine case (a cover for the phase varying device) since the intake valve or the exhaust valve is opened/closed, and includes an annular outer casing section 10 having a sprocket 12 to which a driving force of a crankshaft of an engine is transmitted by an unillustrated chain, an annular inner casing section 20 arranged coaxially with the outer casing section 10, capable of rotating relatively to the outer casing section 10, and forming a part of a camshaft 2, an intermediate member 30 interposed between the outer casing section 10 and the inner casing section 20 while being respectively engaged with the outer casing section 10 and the inner casing section 20 through helical splines and moving in an axial direction thus varying the phase of the inner casing section 20 with respect to the outer casing section 10, and an electromagnetic brake 40 being an electromagnetic control means provided at a side of the inner casing section 20 opposite the side where the camshaft 2 is disposed and moving the intermediate member 30 in the axial direction. On the camshaft 2, provided is a cam 2a for opening/closing one of the intake valve or exhaust valve.

The outer casing section 10 is composed of the sprocket 12 provided with a ring-shaped concave portion 13 at an inner periphery thereof, an inner flange plate 14 closely adhered to a side surface of the sprocket 12 and designing a flange engagement groove 13A in cooperation with the concave portion 13, and a spline case 16 fixing the inner flange plate 14 to the sprocket 12 by tightening together and formed with a spline engagement portion 17 with the intermediate member 30 at an inner circumference thereof. By a large-diameter concave portion at an opening side of the concave portion 13 of the outer casing section 10 and a small-diameter concave portion 13b at an inner side of the concave portion 13, a step portion 13c facing directly to an outer periphery of a flange 24 at the side of the inner casing section 20 is provided between both concave portions 13a and 13b. The sprocket 12, inner flange plate 14, and spline case 16 are integrated by a tightening screw 11, which therefore facilitates formation of the flange engagement groove 13A and the spline engagement portion 17 in the spline case 16.

In addition, a small-diameter sprocket 12A is fixedly fitted to the outer casing section 10, and although not illustrated, the small-diameter sprocket 12A is coupled with a sprocket of the phase varying device for opening/closing the other of the intake valve or exhaust valve by a chain, for controlling both the intake valve and exhaust valve.

Meanwhile, female and male helical splines 32 and 33 are provided on inner and outer circumferential surfaces of the intermediate member 30, male helical splines 23 are provided on an outer peripheral surface of the inner casing section 20, and female helical splines are formed at the spline engagement portion 17 of an inner circumferential surface of the spline case 16. Moreover, the inner and outer splines 32 and 33 of the intermediate member 30 are provided as helical splines in opposite directions so that a slight movement of the intermediate member 30 in the axial direction can greatly vary the phase of the inner casing section 20 with respect to the outer casing section 10. A male screw portion 31 is formed on the outer circumferential surface of the intermediate member 30.

The electromagnetic brake 40 is composed of an electromagnetic clutch 42 for which an electromagnet (electromagnetic coil) 62 is provided in a clutch case 60 and a friction material 66 is fixedly fitted to the clutch case surface, a rotary drum 44 made of a ferromagnetic material for receiving a braking force from the friction material 66 of the electromagnetic clutch 42, and a torsion coil spring 46 axially interposed between the rotary drum 44 and the outer casing section 10. Pins 68 are engaged with holes provided in the engine case, so that the electromagnetic clutch 42 is supported on the engine case so as to be movable in the axial direction but not be rotatable. The rotary drum 44 is supported so as to be rotatable on the inner casing section 20 by a bearing 22 and is formed with a female screw portion 45 to be screwed with the male screw portion 31 of the intermediate portion 30. When the rotary drum 44 rotates relatively to the outer casing section 10, the intermediate member 30 moves in the axial direction as a result of the work of both screw sections 45 and 31.

When the electromagnetic clutch 42 is off, since the braking force does not work on the rotary drum 44, the rotary drum 44 and outer casing section 10 are fixed at their initial positions by the torsion coil spring 46, the outer casing section 10, inner casing section 20, intermediate member 30, and rotary drum 44 integrally rotate, and no phase difference occurs between the outer casing section 10 and the inner casing section 20. Then, since the inner casing section 20 has been coupled to the camshaft 2 and the outer casing section 10 has been coupled with a crank pulley provided on the crankshaft by a chain, the intake valve or exhaust valve can be opened/closed at a normal timing according to rotation of the crankshaft.

When the electromagnetic clutch 42 is turned on, a frictional braking force acts on the friction material 66 provided on the electromagnetic clutch 42 and the rotary drum 44. When the braking force acts on the rotary drum 44, the rotary drum 44 experiences a rotational delay with respect to the outer casing section 10, the intermediate member 30 moves rightward in FIG. 7 as a result of the work of the spring portions 31 and 45, and owing to the inner and outer helical splines 32 and 33 of the intermediate member 30, the inner casing section 20 rotates relatively to the outer casing section 10, so that the phase difference between both varies. Then, the rotary drum 44 is held at a position where the braking force balances with a spring force of the torsion coil spring 46. By controlling current to be supplied to the electromagnet of the electromagnet clutch 42, the inner casing section 20 and outer casing section 10 can be controlled to have a desired phase difference. Thereby, the open/close timing of the intake valve or exhaust valve can be appropriately varied.

When the electromagnetic clutch 42 is again turned off, the braking force no longer works on the rotary drum 44, the intermediate member 30 rotates to its initial position as a result of the action of the torsion coil spring 46 and moves leftward in FIG. 7 to the initial position as a result of the work of the screw portions 31 and 45. Then, the inner casing section 20 rotates to an initial position in a reverse direction with respect to the outer casing section 10 to eliminate the phase difference between both, and the intake valve or exhaust valve is opened/closed at a normal timing.

Meanwhile, friction torque adding members 51 and 55 are interposed between the flange 24 of the inner casing section 20 and sides of the flange engagement groove 13A of the outer casing section 10 so as to increase friction torque of a relative sliding portion between the outer casing section 10 and the inner casing section 20 and suppress gear rattle of the tooth portions hitting against each other from occurring at the helical spline engagement portions 23, 32, 33, and 17 between the intermediate member 30 and the outer casing section 10 and inner casing section 20.

Moreover, the phase varying device is internally supplied with engine oil through an inlet 73a of the camshaft 2, an oil channel in the camshaft 2, and an outlet 73b. The engine oil that has exited the outlet 73b is supplied to a sliding surface between the friction material 66 provided on the surface of the electromagnetic clutch 42 and the rotary drum 44 so as to prevent overheating between the friction material 66 and the rotary drum 44 owing to friction (see the following Patent Document 1 for details).

As described above, in the abovementioned phase varying device, when the sliding surface temperature reaches a high temperature owing to frictional heat on the relative sliding surface between the friction material 66 and the rotary drum 44, there is a possibility that the surface of the friction material generally formed of a porous material clogs up with reactants and insoluble contents of additives such as an antioxidant, a friction adjuster, and a detergent/dispersant dispersed in the engine oil and friction torque generated at the friction material 66 and rotary drum 44 is lowered, so that a cooling mechanism to allow the engine oil to flow between the friction material 66 and the rotary drum 44 is indispensable. Since the cooling mechanism is formed, the phase varying device has a complicated structure, thus resulting in a high cost, wherein a problem resides.

The present invention has been made in view of the problems described above and an object thereof is to prevent heat generation owing to friction in a phase varying device of an automobile engine.

In order to achieve the aforementioned object, according to a first aspect of the invention, in a phase varying device of an engine including: an outer casing section having a sprocket to which rotation of a crankshaft of the engine is transmitted; an inner casing section capable of rotating relatively to the outer casing section and coupled with a camshaft for opening/closing an intake valve or an exhaust valve of the engine; and an intermediate member meshing with the outer casing section and the inner casing section through helical splines, relative rotation being generated between the outer casing section and the inner casing section by moving the intermediate member in an axial direction thus varying an open/close timing of the intake valve or the exhaust valve, the phase varying device of an engine is provided with an electromagnetic control means having a rotary drum being screwed on the intermediate member and provided as a permanent magnet and an electromagnetic clutch for braking the rotary drum.

According to a second aspect of the invention, in the first aspect of the invention, a plurality of magnetic poles are formed on the rotary drums, and by arranging electromagnets in the electromagnetic clutch so that magnetic poles corresponding to the magnetic poles are also formed and changing polarity of the electromagnets with an appropriate phase relative to the magnetic poles of the rotary drum, the rotary drum is braked or accelerated.

According to a third aspect of the invention, in the first or second aspect of the invention, the electromagnetic clutch is disposed in proximity to an interior side surface of the rotary drum.