Valve timing control device for internal combustion engine

A front plate for a valve timing control device is produced which comprises a plate part that closes a front opening of a housing body to seal operation oil chambers in the housing body and a cylindrical part that is integral with and projected forward from an opened central portion of the plate part and after production of the front plate, an annular part of a front surface of the plate part near a root portion of the cylindrical part is pressed, by a press machine, toward a rear surface of the plate part against a supporting tool that intimately supports the rear surface of the plate part, so that the rear surface of the plate part has an improved flatness at an annular area surrounding the opening of the front plate thereby to increase a sealability between the plate part and the front opening of the housing body.

TECHNICAL FIELD

The present invention relates to a valve timing control device for an internal combustion engine, which varies and controls the open/close timing of intake or exhaust valves in accordance with a vehicle operation condition.

BACKGROUND ART

One known valve timing control device for an internal combustion engine is described in the after-mentioned Patent Document-1.

The known device will be briefly described in the following. The device comprises a housing member that receives a torque from a crankshaft and has therein a plurality of operation oil chambers extending around an inner cylindrical surface of the housing, a front plate that includes a plate part closing at its rear surface a front open part of the housing member and a cylindrical part formed on a central portion of a front surface (outer end surface) of the plate part, a vane rotor that is received in the housing member and rotatable in a given range in both the most delayed angle side and most advanced angle side relative to the housing member and has four vanes for grouping the operation oil chambers into delayed angle operation oil chambers and advanced angle operation oil chambers, and a torsion spring that is partially received in the cylindrical part of the front plate and has one end engaged to a front edge of the cylindrical part and the other end engaged to the vane rotor.

The torsion spring is arranged to bias the vane rotor in the advanced angle side by its biasing force, and by controlling the open/close timing of the exhaust valves in the advanced angle side for improving the engine startability.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF INVENTION

Problems to be Solved by Invention

In the known valve timing control devices such as one mentioned hereinabove, the front open part of the housing member is dosed by the rear surface of the plate part of the front plate for sealing the plurality of operation oil chambers. However, it is difficult to sufficiently increase the accuracy of a side clearance between the rear surface of the plate part of the front plate and a counterface surface of the vane rotor that axially faces the rear surface of the plate part.

That is, when the front plate with the cylindrical part is formed entirely by press-forming, shaping the cylindrical part by applying a burring press to a central portion of the plate part inevitably brings about production of so-called sagging between a base part of the cylindrical part and the central portion of the plate part. With such sagging, a central portion of the rear surface of the plate part is rippled or bent, which may cause deterioration in accuracy of the side clearance and increase leakage of the operation oil from the operation oil chambers.

The present invention is provided by taking the drawback of the known valve timing control devices into consideration and provides a valve timing control device for an internal combustion engine, which is constructed to have a high sealing accuracy by increasing a surface area of a circular central part of the rear surface of the plate part of the front plate.

Means for Solving the Problems

The invention defined by claim1is a valve timing control device for an internal combustion engine, which comprises a housing body to which a torque is transmitted from a crankshaft, at least one of axial ends of the housing body being opened; a vane rotor that includes a rotor fixed to the camshaft, a plurality of vanes provided on the rotor, the vanes being operatively engageable with a plurality of shoes projected from an inner cylindrical surface of the housing body thereby to constitute delayed angle operation chambers and advanced angle operation chambers, the vane rotor being selectively rotated in a delayed angle side or an advanced angle side relative to the housing body in response to charging or discharging of an operation oil to or from the delayed and advanced angle operation chambers; a front plate including a discal plate part that closes the axial open end of the housing body at its rear surface thereby sealing all of the delayed and advanced angle operation chambers and a cylindrical part that is integrally projected outward from a peripheral edge of a through opening formed in a central portion of the discal plate part; and a torsion spring that has one end engaged to the rotor and the other end engaged to the cylindrical part thereby to constantly bias the vane rotor in one of opposed rotation directions relative to the housing body, the valve timing control device being characterized in that an annular part of a front surface of the plate part near a root portion of the cylindrical part is pressed toward the rear surface of the plate part to produce a recess and during the pressing, an inner area of the rear surface of the plate part, which is placed at a position corresponding to the position where the recess is produced, is supported against the pressing force, so that the annular area and an inner cylindrical surface of the cylindrical part are shaped to have a generally right angled cross section.

Effects of Invention

According to the invention, the sealing accuracy of the rear surface of the plate part can be increased by increasing a surface area of the circular central part of the rear surface of the plate part by suppressing production of the sagging at the circular central part of the rear surface of the plate part. As a result, undesired leakage of the operation oil from the operation oil chambers can be suppressed.

EMBODIMENTS FOR CARRYING OUT INVENTION

In the following, an embodiment of the valve timing control device for an internal combustion engine according to the present invention will be described in detail with reference to the accompanying drawings. In the illustrated embodiment, there is employed a type in which the control device is applied to a valve actuating device for exhaust valves.

First Embodiment

As is seen fromFIGS. 1 and 2, the valve timing control device (VTC) for an internal combustion engine comprises a sprocket1that is a drive rotation member driven by a crankshaft (not shown) through a timing chain, a camshaft2that is arranged to make a rotation relative to the sprocket1, a phase varying mechanism3that is arranged between the sprocket1and the camshaft2to vary a relative rotation phase between them1and2and a hydraulic circuit4that actuates the phase varying mechanism3.

The sprocket1is made of an iron-based metal and shaped like a thicker disc, and has on a periphery thereof a gear portion1aaround which the above-mentioned timing chain is wound, and has at a central portion thereof a supporting opening1bthrough which an outer cylindrical surface of the camshaft2is rotatably supported. Furthermore, the sprocket1is formed at four equally spaced radially outer portions thereof with respective internally threaded openings1cto which after-mentioned four bolts9are engaged. The sprocket1can serve as a rear cover that closes a rear opening of an after-mentioned housing5.

The camshaft2is rotatably supported by a cylinder head (not shown) through camshaft bearings and integrally formed at given axial portions thereof with egg-shaped cams for making open/close operation of the exhaust valves, and the camshaft2is formed at one axial end2athereof with a bolt inserting hole2binto which a shaft portion6aof a cam bolt6is inserted in an axial direction to fix an after-mentioned vane rotor7to the camshaft2. A leading end of the bolt inserting hole2bis formed with an internal thread (not shown) to which an external thread formed on a leading end of the cam bolt6is engaged.

As is seen fromFIGS. 1 to 3, the phase varying mechanism3comprises a housing5that has therein operation oil chambers, a vane rotor7that is a driven rotation member fixed to one end of the cam shaft2through the cam bolt6and swingably rotatably received in the housing5, and four delayed angle hydraulic chambers10or the delayed angle operation oil chambers and four advanced angle hydraulic chambers11or the advanced angle operation oil chambers that are each defined between each of four (first to fourth) shoes8ato8dintegrally formed on an cylindrical inner surface of an after-mentioned cylindrical housing body5a.

The housing5comprises the cylindrical housing body5athat is made of a sintered metal, a front plate12that closes a front opening of the housing body5a, and the sprocket1that closes a rear opening of the housing body5ato serve as a rear cover. The housing body5a, the front plate12and the sprocket1are tightly joined together by the four bolts9that pass through bolt openings8erespectively formed in the shoes8ato8d.

The front plate12is integrally produced by pressing a carbon steel plate with a press machine and a specialized press method, and as is seen fromFIGS. 1, 2 and 4 to 6, comprises a circular plate part13and a cylindrical part14integrally formed on a central part of the circular plate part13via the press-forming.

The plate part13is formed at a central part thereof with a relatively large through opening13athat forms a part of the cylindrical part14, and to a hole edge of the through opening13aprovided at a front surface13d, there is integrally connected the cylindrical part14. That is, the cylindrical part14is projected forward from a rear surface side13eof the plate part13while being bent, and an inner diameter of the through opening13ais the same as that of an inner cylindrical surface14aof the cylindrical part14, and the through opening13aand the cylindrical part13are coaxially and continuously connected.

The plate part13is formed at equally spaced four peripheral portions thereof with respective bolt openings13bthrough which the bolts9pass, and each bolt opening13bis formed, at a hole edge thereof on the front surface13d, with a tapered annular recess with which a base part of the shaft of the bolt9is engaged. Furthermore, around the tapered annular recess of each bolt opening, there is formed an annular seat surface13conto which a rear surface of a head9aof the bolt9is seated.

The cylindrical part14is projected forward from the front surface13dof the plate part13by a given distance, and a leading end14bof the cylindrical part14has a tapered surface14cthe vertical section of which is circular-arc in shape, and the cylindrical part14is provided with a circular-arc shaped cut14dat a position that corresponds to a position taken by an after-mentioned widest first vane18awhen it is turned in a circumferential direction within a given range. The cylindrical part14is further provided at a circumferentially opposed end of the cut14dwith a first spring engaging groove14ethat is an engaging portion.

As is seen fromFIGS. 4 and 9, the first spring engaging groove14eis shaped nearly rectangular, and the groove14eextends inward, while curving, from a projection14fformed on a front end14bof the cylindrical part14, and extends linearly from one end of the curved part, and extends, while curving, from one end of the linear part. The first spring engaging groove14eis a groove to which a first engaging end32aof an after-mentioned torsion spring32is engaged from a circumferential direction, and the projection14ffunctions to prevent disengagement of the first engaging end32aof the torsion spring32from a front part of the engaging groove14e.

As is seen fromFIG. 10, the first spring engaging groove14ehas, at one inside edge of the inner cylindrical surface of the cylindrical part14, that is, at the inside edge to which the first engaging end32ais engaged, a convex surface14g.

As is seen fromFIGS. 6 to 8, the connecting portion between the plate part13and cylindrical part14has a unique structure. This unique structure is produced through an after-mentioned press forming.

That is, by pressing a root portion of the cylindrical part14relative to the plate part13toward the rear surface side13eby an after-mentioned pressing punch, there is produced an annular recess16around an annular area of the front surface13dof the plate part13. During this pressing, the rear surface13eof the plate part13is entirely supported by an after-mentioned cylindrical supporting tool41against the pressing force.

With the above-mentioned process, an annular area13fof the rear surface13eis pressed or shifted toward the axis of cylindrical part14(viz., in the direction of the arrow ofFIG. 7), so that the annular area13fis shaped to have a right angled cross section increasing its outer surface area while sufficiently reducing the length L between a hole edge13gof the annular area13fand the inner cylindrical surface14aof the cylindrical part14. Accordingly, a tapered annular surface13hproduced between the hole edge13gof the annular area13fand the inner cylindrical surface14aof the cylindrical part14has a sufficiently small taper angle.

Although the above-mentioned annular recess16is of an endless type provided around the outer surface of the root of the cylindrical part14, the annular recess16is not always necessary to extend entirely around the root. That is, the annular recess16may have a cut portion or cut portions in the entire length.

The vane rotor7is integrally constructed of for example a sintered metal, and as is seen fromFIGS. 1 to 3, comprises a rotor17that is connected to the camshaft2by the cam bolt6inserted through a bolt inserting bore7aformed in an axially middle portion of the rotor, and four, that is, first to fourth vanes18ato18dthat are radially outwardly projected from equally spaced portions (viz., spaced by 90 degrees) of an outer cylindrical wall of the rotor17.

The rotor17is shaped generally cylindrical and has at a radially outer part of a front surface of the rotor an annular groove17aand at a rear surface of the rotor a circular engaging bore17bto which a leading end2bof the camshaft2is tightly engaged. An inner surface of the annular groove17bis formed with a second spring engaging groove17cthat extends (radially) toward the axis of the bolt inserting bore7a.

As is seen fromFIG. 1, the rotor17has, at the side directed toward the camshaft2, an axially rear surface that slidably contacts with an opposing front surface of the sprocket1leaving a minute clearance therebetween. While, an axially front surface of the rotor slidably contacts with an opposing rear surface13eof the plate part13of the front plate12leaving a minute clearance therebetween, so that the rotor establishes a sealing function against both the front surface of the sprocket1and the rear surface13eof the plate part13.

While, as is seen fromFIGS. 2 and 3, the first to fourth vanes18ato18dare each put between adjacent two of the shoes8ato8d, and the vanes are each provided at a rounded outer wall thereof with a groove for holding a sealing member15athat slidably contacts the inner cylindrical surface of the housing body5awhile establishing sealing therebetween. While, the shoes8ato8dare each provided at a top surface thereof with a groove to hold a sealing member15bthat slidably contacts an outer cylindrical surface of the rotor17while establishing sealing therebetween. Each of the vanes18ato18dhas opposed end surfaces in the width direction thereof (viz., axial direction of a rotor shaft) which slidably and respectively contact the front surface of the sprocket1and the rear surface13eof the plate part13leaving a minute clearance therebetween, so that the vanes establish a sealing against both the front surface of the sprocket1and the rear surface13eof the plate part13.

The first vane18ain the vanes18ato18dis shaped like a fan with a largest width when viewed from the side and has the largest weight, and the three vanes18bto18dother than the first vane18ahave each a width smaller than that of the first vane18a. Because the first vane18ais largest in weight, the center Y of gravity (viz., the oval illustrated by hatched line) of the vane rotor7is placed at a position shifted toward the first vane18afrom the center point P1.

As will be understood from the dot-dash line ofFIG. 3, when the vane rotor7is rotated in the most delayed angle direction, one side surface of the first vane18ais moved in a circumferential direction and finally brought into contact with an opposing surface of the first shoe8athereby to limit the rotational position of the vane rotor in the most delayed angle side. Furthermore, as will be understood from the solid line, when the vane rotor is rotated in the most advanced angle direction, the other side surface of the first vane18ais moved in a circumferential direction and finally brought into contact with an opposing surface of the second shoe8bthereby to limit the rotational position of the vane rotor in the most advanced angle side. Thus, the first vane18aand the first and second shoes8aand8bthus constitute a stopper that limits both the most delayed and most advanced angles positions of the vane rotor7.

During the above-mentioned movement of the vane rotor, the second to fourth vanes18bto18dare kept away from their opposing surfaces of the shoes8cand8dwithout contacting the same. Accordingly, a so-called contact accuracy between the first vane18aand each of the first and second shoes8aand8bis increased and since the speed in feeding the hydraulic pressure to the delayed and advanced angle hydraulic chambers10and11is increased, the rotation responsiveness of the vane rotor7in normal and reverse directions is increased.

The delayed angle hydraulic chambers10and the advanced angle hydraulic chambers11are respectively connected to the hydraulic circuit4through first and second connecting holes10aand11athat extend in the rotor17in radial direction.

The hydraulic circuit4is a circuit that selectively feeds or discharges the hydraulic oil to or from the delayed and advanced angle hydraulic chambers10and11, and as is seen fromFIG. 1, the hydraulic circuit4comprises a delayed angle oil passage19that feeds and discharges the hydraulic pressure to and from each of the delayed angle hydraulic chambers10through the first connecting hole10a, an advanced angle oil passage20that feeds and discharges the hydraulic pressure to and from each of the advanced angle hydraulic chambers11through the second connecting hole11a, and an oil pump21that feeds the hydraulic pressure to the oil passages19and20and an electromagnetic switch valve22that switches the flow of the delayed and advanced angle oil passages19and20in accordance with an operation condition of the engine. The oil pump21is of a common type, such as a trochoid pump or the like which is rotated or driven by the crankshaft of an engine.

The delayed angle oil passage19and the advanced angle oil passage20have respective ends connected to passage ports of the electromagnetic switch valve22, and the other ends of the passages19and20are connected through a cylinder head (not shown) and a cylinder block (not shown) to an interior of the camshaft2constituting delayed and advanced angle passage portions19aand20athat extend axially in parallel with each other.

The delayed angle passage portion19ais connected to the delayed angle hydraulic chambers10through the first connecting holes10a, and the advanced angle passage portion20ais connected to the advanced angle hydraulic chambers11through the connecting holes11a.

As is seen fromFIG. 1, the electromagnetic switch valve22is of a type having two positions and three ports and so constructed that upon control by an electronic controller (not shown), a spool valve (not shown) slidably movably arranged in a valve body is moved in a forward or rearward direction to connect a discharge passage21aof the oil pump21to one of the oil passages19and20and simultaneously connect the other oil passage19or20to a drain passage23.

An intake passage21bof the oil pump21and the drain passage23are connected to interior of an oil pan24. The discharge passage21aof the oil pump21has at its downstream portion a filtration filter25and is connected at the downstream portion to a main oil gallery M/G that feeds the oil to mutually sliding and contacting portions of the internal combustion engine. The oil pump21is equipped with a flow rate control valve26that controls the oil discharged from the discharge passage21ato a suitable amount by discharging an excessive part of the oil to the oil pan24.

The electronic controller is equipped with a computer which, by receiving information signals from a crank angle sensor (not shown), an air flow meter, an engine cooling water temperature sensor, a throttle valve open degree sensor, and a cam angle sensor that detects a current rotation phase of the camshaft, estimates the current operation condition of the engine, and by outputting a control pulse signal to an electromagnetic coil of the electromagnetic switch valve22, controls the shift position of a spool valve of the electromagnetic switch valve22thereby to carry out a desired switching of the above-mentioned passages.

Between the first vane18aand a rear cover1bof the sprocket1, there is arranged a lock mechanism that is able to lock the vane rotor7at the most advanced angle position relative to the housing5.

As is seen fromFIGS. 1 to 3, the lock mechanism comprises a lock pin28that is slidably received in a hole27formed in and extending axially in the first vane18aand is projectable toward the rear cover1b, a lock opening29that is formed in a radially middle portion of the rear cover1band engageable with a leading end28aof the lock pin28to lock the vane rotor7, and an engaging/disengaging mechanism that engages or disengages the leading end28aof the lock pin28to or from the lock opening29.

The lock pin28with the leading end28ais entirely shaped cylindrical so that engagement of the lock pin28with the lock opening29in the axial direction is easily made, and a coil spring30is provided and compressed between a bottom of an axially extending bore formed in the lock pin28and the rear surface13eof the front plate12for biasing the lock pin28in a projecting direction (viz., the direction for establishing the engagement).

The lock opening29is sized larger in diameter than the leading end portion of the lock pin28and placed at a position circumferentially eccentric toward the advanced angle hydraulic chamber11, so that upon engagement with the lock pin28, a relative converting angle between the housing5and the vane rotor7takes a value that corresponds to the most advanced angle position. At a side portion of the lock opening29, that is, at a position that is one stage lower than the position of the lock opening29, there is formed a circular-arc shaped pressure receiving chamber31that is smaller in diameter than the lock pin28.

The engaging/disengaging mechanism comprises the above-mentioned coil spring30that biases the lock pin28in the projecting direction, and a disengagement hydraulic circuit (not shown) that feeds the pressure receiving chamber31with a hydraulic pressure to move back the lock pin28. In the disengagement hydraulic circuit, there is arranged a system by which the hydraulic pressure selectively fed to the delayed and advanced angle hydraulic chambers10and11is led to the pressure receiving chamber31through given oil holes for moving or biasing the lock pin28in a backward direction.

Within a space defined by the plate part13, the cylindrical part14and the annular groove17aof the rotor17, there is installed a torsion spring32that biases the vane rotor7in a timing advancing direction relative to the housing5.

As is seen fromFIGS. 1 and 2, the torsion spring32comprises a coiled spring body part, a first engaging end portion32athat extends radially outward from one end of the spring body part and a second engaging end portion32bthat extends radially inward from the other end of the spring body part.

The coiled spring body part is almost entirely received in the through opening13aand the cylindrical part14, and an axially inside part of the spring body part is received and arranged in the annular groove17aof the rotor17.

The second engaging end portion32bis engaged to the first spring engaging groove14efrom a circumferential direction and the second engaging end portion32bis engaged and fixed to the second spring engaging groove17cof the rotor17from an axial direction. Due to the spring force of the torsion spring32, the vane rotor7is constantly biased to rotate in a timing advancing direction.

The torsion spring32is constructed to reduce its diameter when the vane rotor7is turned in a timing delaying direction relative to the housing5.

[Method for Producing the Front Plate]

The front plate12is produced by carrying out a series of press forming steps depicted byFIGS. 11A to 11F.

First, as is seen fromFIG. 11A, a carbon steel base metal12′ for the front plate12is shaped into a circular plate by a press machine (not shown). The circular plate thus provided has at its central portion a cylindrical part forming opening14h′ that is used for forming a cylindrical part14′.

Then, as is seen fromFIGS. 11B and 11C, an annular portion of the circular plate that surrounds the cylindrical part forming opening14h′ is gradually pressed upward to produce an integral unit that includes a plate part13′ and a cylindrical part14′ (Burring Method). Due to this pressing step, an inner cylindrical part14iof a junction portion (or root portion) between the plate body13′ and the cylindrical part14′ inevitably brings about production of so-called sagging.

Then, as will be understood fromFIG. 11D, the base metal12′ for the front plate12thus formed is set on and fitted to a mounting base40that has at a position corresponding to the cylindrical part14′ an inserting hole40a, and a supporting tool41is inserted into the cylindrical part14′ from above. The supporting tool41is shaped like a stepped cylindrical member and has a smaller diameter leading end portion41ahaving an outer diameter smaller than an inner diameter of an inner cylindrical surface14a′ of the cylindrical part14′ and, upon insertion of the supporting tool, the leading end portion41aof the tool is placed closely to the inner cylindrical surface14a′. Under this condition, a stepped part41cdefined between larger and smaller diameter portions41band41aof the supporting tool41is arranged to axially face a leading end surface14b′ of the cylindrical part14′ keeping a minute clearance therebetween.

Then, with the above-mentioned condition being kept, by using a press punch42arranged around the supporting tool41, an outer cylindrical wall14jof the root of the cylindrical part14′ is pressed downward as is indicated by the arrows. As is seen from the drawing provided at a right side ofFIG. 11D, a center bore42aof the press punch42has, around its lower edge, a sharply sloped annular press edge part42b, and when the outer cylindrical wall14jis pressed down by the press edge part42bin the direction of the arrows, the plate part13produces the above-mentioned annular recess16around the inner cylindrical part thereof.

That is, when the pressing force for forming the annular recess16is applied to the given portion, the inner cylindrical portion of the plate part13′ and the root area part of the cylindrical part14′ are pressed radially inward. During this pressing, the inner cylindrical surface14a′ of the root portion of the cylindrical part14′ and an inner cylindrical surface of the plate part13′ near a through opening13a′ are intimately supported by an outer cylindrical surface of the supporting tool41and an upper surface of the mounting base40near the inserting hole40aagainst the pressing force.

Accordingly, the material of the plate part13placed around the through opening13a′ is shifted in the direction of the arrow ofFIG. 8, that is, toward the axis of the cylindrical part14, so that as is seen fromFIG. 7, the annular area13fof the rear surface side13eof the plate part is shifted toward the axis of the cylindrical part14. With such shifting, the annular area13fof the rear surface side13eof the plate part13is shaped to have a right-angled cross section increasing the inner surface area thereof. Thus, the above-mentioned undesired sagging caused by the initial pressing is eliminated.

Then, as is seen fromFIG. 11E, a punch43is hitted radially outward (in the direction of the arrow) against a given portion of the cylindrical part14from inside, and thus, as is seen fromFIG. 10, there are produced the above-mentioned cut14dand the first spring engaging groove14e. The punch43has a convex front end surface43aradius of curvature of which is almost the same as that of the cylindrical part14, and during the punching, an upper edge43bof the front end surface43amoves radially outward from the side of axis of the cylindrical part14(viz., from the inside) for forming the first spring engaging groove14eby punching. With such movement, the above-mentioned arc surface14gis formed at the inside edge as is shown inFIG. 10.

Then, the base metal12′ for the front plate12is subjected to a heat treatment at a given temperature for a give time, and then, as is seen fromFIG. 11F, a hole punching process is applied to equally spaced portions of the peripheral part of the plate part13for forming four bolt openings13bat the peripheral part. Then, by using a coining process, each bolt opening13bhas at an outer edge part thereof the above-mentioned annular seat surface13c.

Then, the rear surface13eof the plate part13and the leading end surface14bof the cylindrical part14are put between front and rear polishing devices44aand44bto carry out a so-called double disc polishing. With this polishing, the rear surface13ecan have a high surface roughness for increasing a side clearance accuracy between it and the above-mentioned roller17.

With the above-mentioned steps, a series of forming work for forming the front plate12is completed.

[Operation Effects of the Valve Timing Control Device of the Embodiment]

As is seen fromFIG. 3, at the time of starting the engine, the vane rotor7is biased toward the most advanced angle position by the spring force of the torsion spring32and the leading end28aof the lock pin28is engaged with the lock opening29retaining the vane rotor7at an advanced angle position that is optimal for effecting the engine starting. Accordingly, the valve timing of the exhaust valves is stably controlled to the most advanced angle side. Thus, when an engine starting is carried out due to ON-switching of the ignition switch, a satisfied engine startabillity is exhibited.

When, after the engine starting, the engine is operated in a low speed load range, de-energization of the electromagnetic coil of the electromagnetic switching valve22is kept by the electronic controller. With this, connection between an exhaust passage18aof the oil pump21and the delayed angle oil passage19is established and connection between the advanced angle oil passage20and the drain passage23is established.

Thus, the operation oil discharged from the oil pump21is led into the delayed angle hydraulic chambers10through the delayed angle oil passage19causing the delayed angle hydraulic chambers10to show a higher pressure, and at the same time, the operation oil in the advanced angle hydraulic chambers11is led into the oil pan22through the advanced angle oil passage20and the drain passage23causing the advanced angle hydraulic chambers11to show a lower pressure.

At this time, the operation oil led into the delayed angle hydraulic chambers10is led into both the pressure receiving chamber31and the lock opening29through the above-mentioned disengagement hydraulic circuit thereby causing the chamber31and the lock opening29to have a higher pressure, and thus, the lock pin28is moved back to disengage the leading end28afrom the lock opening29resulting in a free rotation of the vane rotor7.

Accordingly, in accordance with increase of the volume of the delayed angle hydraulic chambers10, the vane rotator7is turned left in the drawing (viz., in the delayed angle direction) as is indicated by a dot-dash line inFIG. 3, so that one side surface of the first vane18ais brought into contact with an opposing surface of the first shoe8athereby to restrain the vane rotor7at the most advanced rotation angle position. With this, the vane rotor7or the chamber shaft2changes its rotation angel relative to the housing5in the delayed angle toward the most delayed angle side.

Due to rotation of the vane rotor7in the delayed angle side relative to the housing5, the torsion spring32is deformed in a diameter reducing direction.

When, then, the engine operation is shifted for example to a high rotation load range, a control current is outputted to the electromagnetic switch valve22from the electronic controller, so that the discharge passage21ais connected to the advanced angle oil passage20and at the same time the delayed angle oil passage19is connected to the drain passage23. With such connection, the operation oil in the delayed angle hydraulic chambers10is discharged thereby to cause the chambers10to show a lower pressure, and the operation oil is led into the advanced angle hydraulic chambers11thereby to cause the chambers11to show a higher pressure. During this, due to the flow of the operation oil from the advanced angle hydraulic chambers11to the pressure receiving chamber31through the above-mentioned disengagement hydraulic circuit, the lock pin28is disengaged from the lock opening29and keeps the disengaged condition.

Accordingly, as is indicated by the solid line inFIG. 3, the vane rotor7is turned toward the advanced angle side relative to the housing5, so that the other side surface of the first vane18ais brought into contact with an opposing surface of the second shoe8bthereby to retain the vane rotor7at the most advanced angle rotation side. With this, the camshaft2is shifted in rotation timing to the most advanced angle side relative to the housing5. As a result, the open/close timing of the exhaust valves is controlled to the most advanced angle side, and thus, the output of the engine in the high rotation high load range can be improved.

At a time just before stopping the engine, the operation oil in the hydraulic chambers10and11is discharged to the oil pan22through the drain passage23, and thus, the hydraulic pressure in both the pressure receiving chamber29and the lock opening29is lowered too. Thus, due to the spring force of the torsion spring32aapplied to the camshaft2, the vane rotor7is turned toward the most advanced angle side and due to spring force of the coil spring30, the lock pin28is projected causing its leading end28ato engaged with the lock opening29.

Since a relative positioning in a circumferential direction of the housing between the lock pin28and the lock opening29is assuredly made at the time of assembling the parts, the engagement of the lock pin28with the lock opening29is smoothly achieved.

Furthermore, since, in the embodiment, the front plate12is integrally produced by pressing a relatively thin iron-based metal plate via press forming, a light-weight production of the front plate is assuredly possible and the work for manufacturing the front plate is simple, which can bring about a cost reduction.

Furthermore, in the embodiment, for formation of the annular recess16on the inner cylindrical part of the front surface13dof the plate part13, the root portion of the cylindrical part14is pressed by the press punch42, so that the annular area13fof the rear surface13eis shaped to have a right angled cross section increasing its inner outer surface area. With this feature, the sagging is eliminated and thus a sealing surface can be increased, and thus, the sealing accuracy of the side clearance between the plate part and the axially other end surface of the rotor17can be sufficiently increased.

Since enlargement of the outer surface area of the annular area13fof the rear surface13eis carried out by co-operation work between the press punch42and the supporting tool41not by abrasive machining, the forming cost can be reduced.

Furthermore, since the inside edge of the first spring engaging groove14eis shaped to have the arc surface14g, damages that would appear on the outer surface of the first engaging end portion32aof the torsion spring32when the first engaging end portion32ais kept engaged with the first spring engaging groove14ecan be eliminated.

Furthermore, because of provision of the tapered to annular surface13hbetween the inside hole edge13gof the annular area13fand the inner cylindrical surface14aof the cylindrical part14, the deformation of the torsion spring32in a diameter expanding direction can be neatly received by a space defined by the tapered annular surface13h, and thus, a smoothed deformation of the torsion spring32is achieved. Furthermore, due to provision of the space, interference of the outer surface of the torsion spring32with the inner cylindrical surface14aof the cylindrical part14is suppressed and thus, damages of the outer surface of the torsion spring and generation of noises can be suppressed.

Furthermore, since the annular seat surface13cof the plate part13is formed also by the press forming, cost can be reduced as compared with that in the abrasive machining.

Furthermore, in the embodiment, due to provision of the widest first vane18aof the vane rotor7, the center of gravity of the vane rotor is offset to the side of the first vane18a, and at the same time due to provision of the cut14dand the first spring engaging groove14eof the cylindrical part14, the center of gravity of the front plate12is offset to one side that is opposite to the other side where the cut14dand the first spring engaging groove14eare provided, and thus, an excessive weight caused by the first vane18ais cancelled.

Accordingly, a weight balancing in entire construction of the valve timing control device is sufficiently achieved without providing the third vane18cwith a balancing weight or the like that is positioned opposite to the position where the first vane18ais provided, and due to provision of the cut14dand the first spring engaging groove14e, light weighting of the device is obtained.

It is to be noted that the present invention is not limited to the construction of the above-mentioned embodiment. That is, the construction is changeable within the concept of the invention.