US20130125846A1

US20130125846A1 - Variable cam phaser for automobile engine

Info

Publication number: US20130125846A1
Application number: US13/697,908
Authority: US
Inventors: Michihiro Kameda; Masayasu Nagado; Masaaki Niiro
Original assignee: Nittan Valve Co Ltd
Current assignee: Nittan Corp
Priority date: 2010-05-18
Filing date: 2010-05-18
Publication date: 2013-05-23
Also published as: EP2573336B1; KR20130072190A; CN102859126A; JPWO2011145175A1; EP2573336A1; WO2011145175A1; EP2573336A4; JP5616440B2

Abstract

The invention provides a variable cam phaser for an automobile engine, equipped with a self-locking mechanism which is simpler in structure, cost effective, and easy to manufacture. The self-locking mechanism includes: a eccentric circular members (12) integral with the camshaft (6) and a support groove (15) for supporting the eccentric circular members from the both sides thereof at positions offset from the camshaft axis towards the eccentric cam center; a lock plate integrally held with the control rotor by means of a coupling mechanism; and a cylindrical portion belonging to the drive rotor in which the lock plate is inscribed. The self-locking mechanism prevents an unexpected change in the phase angle caused by an external disturbing toque transmitted to the camshaft via the crankshaft of the engine.

Description

TECHNICAL FIELD OF THE INVENTION

This invention relates to a variable cam phaser for an automobile engine for varying the relative phase angle between the crankshaft of the engine and the camshaft of the apparatus to change open/close timing of valves of the engine, the apparatus equipped with a self-locking mechanism for preventing an unexpected change in the phase angle caused by an external disturbing torque transmitted from the valve.

BACKGROUND ART

Such variable cam phaser as stated above equipped with a self-locking mechanism for preventing such unexpected change in phase angle is disclosed in Patent Document 1 listed below. This Patent Document 1 teaches a multiplicity of eccentric circular members (eccentric circular cam 110, first link 111, second link 112) each member having an eccentric center and arranged at a prescribed axial position of the camshaft such that the four centers of the eccentric members function as a whole as a four-link mechanism 108. By putting a brake on the four-link mechanism 108 with a first or second electromagnetic clutch 105 or 106, respectively, via a first or second control rotor 102 or 103, respectively, the phase angle of the drive rotor 101, operable connected to the camshaft and crankshaft, can be changed relative to the camshaft.
This four-link mechanism 108 can vary the relative phase angle between the camshaft and crankshaft (drive rotor 101) in the phase advancing or retarding direction through rotations of the eccentric circular cam 110 integral with the camshaft, first link 111 rotatably supported by the eccentric circular cam 110, and second link 112 rotatably supported by the first link 111 about their pivots in association with a braked movement of either the first or second control rotor 102 or 103, respectively.
On the other hand, when the camshaft is subjected to an external disturbing torque arising from a reaction of a valve spring and transmitted to the drive rotor 101, the first link 111 is pressed against a guide groove 113 of the first link formed in the drive cylinder 115 of the drive rotor 101, so that the circular eccentric members 110-112 are unrotatably fixed, thereby preventing the camshaft from changing its phase angle relative to the drive rotor 101. The variable cam phaser disclosed in Patent Document 1 has a self-locking mechanism for preventing any phase angle change caused by such external disturbing torque as discussed above.

PRIOR ART DOCUMENT

PATENT DOCUMENT 1 PCT/JP2009/61327

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Since the self-locking mechanism disclosed in Patent Document 1 has a four-link mechanism 108, the self-locking mechanism must achieve self-locking function with a required accuracy of the four-link mechanism 108. As a consequence, the self-locking mechanism turns out to be very complex and costly. Thus, a need exists to provide a simple self-locking mechanism.
It is, therefore, an object of the present invention to provide a structurally simpler and more cost effective variable cam phaser for automobile engine having a self-locking mechanism.

Means for Solving the Problem

An inventive variable cam phaser for an automobile engine as recited in claim 1 includes:
a drive rotor driven by the crankshaft of the engine;
a control rotor;
a camshaft coaxial with the drive rotor and adapted to rotatably support the drive rotor;
a torque means for providing the control rotor with a torque for rotating the control rotor relative to the drive rotor;
a phase angle varying mechanism for varying the relative phase angle between the drive rotor and the control rotor in accord with the relative rotation of the control rotor relative to the drive rotor; and a self-locking mechanism mounted in the phase varying mechanism for preventing a phase change from occurring between the drive rotor and the camshaft caused by an unexpected cam torque appearing on the camshaft, the variable cam phaser characterized in that the self-locking mechanism comprises:
an eccentric circular cam integral with the camshaft; and
a lock plate having

- a support groove for supporting, at positions further offset from the camshaft axis in the direction (referred to as eccentric direction) from the camshaft axis towards the cam center of the eccentric circular cam, the periphery of the eccentric circular cam from both sides thereof,
- a coupling mechanism for transmitting the relative rotational torque from the control rotor to the eccentric circular cam, and

a cylindrical body formed integral with the drive rotor and circumscribing the periphery of the lock plate.
(Function) Upon receipt of an external disturbing torque from a valve, the lock plate in rotation together with the camshaft is subjected to a substantially radial force via the support groove that is adapted to immovably holding the eccentric circular cam integral with the camshaft, and hence the lock plate is pressed against the cylinder of the drive rotor. As a consequence, the drive rotor and the camshaft both driven by the crankshaft are interlocked and prohibited from undergoing a relative rotation by the external disturbing torque, thereby keeping the phase angle between them unchanged.
As recited in claim 2, the phase angle varying apparatus of claim 1 may be configured such that:
the support groove extends in a radial direction of the lock plate;
the eccentric circular cam is provided on the outer periphery thereof with a lock plate bush; and
the lock plate bush has on the opposite sides of the outer periphery thereof a pair of flat faces spaced apart across the line of eccentric direction and supported by the support groove.
(Function) With the eccentric circular cam held in the support groove and with the lock plate bush kept in surface contact with the support groove via the paired flat faces, the contact stress generated on the wall of the support groove is reduced as compared with the stress that would be otherwise generated if the eccentric circular cam were in direct contact with the support groove. As a result, substantially no uneven friction wear will take place in contacting surfaces, which allows the lock plate and eccentric circular cam to be kept in good condition without suffering a backlash or play, which in turn facilitates prompt generation and transmission of a pressure between the lock plate and the cylinder of the drive rotor under an external disturbing torque.
As recited in claim 3, the variable cam phaser of claim 2 may be further configured such that the lock plate is divided into two parts by a pair of slits each extending from the support groove to the periphery of the lock plate.
(Function) When the eccentric circular cam is held in surface contact with the support groove of the lock plate via the lock plate bush, it may happen that the torque that causes the lock plate to rotate relative to the cylinder under an external disturbing torque becomes dominant over the radial force that forces the lock plate against the cylinder of the drive rotor, thereby rendering the self lock mechanism inoperable. However, when the lock plate is divided into two part by the slits extending from the support groove to the periphery of the lock plate, the relative torque generated on one of the divided lock plate constituent members is not well transmitted to the other member. As a consequence, under an external disturbing torque, the torque generated on the entire lock plate is reduced. Accordingly, the pressure exerted to the drive rotor cylinder of the lock plate is enhanced.
As recited in claim 4, the variable cam phaser of claim 3 may be configured such that one of the two slits may be provided with means for providing a force to widen that slit (said means hereinafter referred to as urging means).
(Function) By providing one of the slits with such force to widen one of the slits, the gaps that are formed during manufacture between the lock plate and drive rotor cylinder and between the lock plate bush and the support groove are reduced, thereby reducing the plays of members of the self-locking mechanism during self-locking operation. That is, a pressure needed to force the lock plate against the drive rotor cylinder can be instantaneously generated under an external disturbing torque.
As recited in claim 5, the variable cam phaser of claim 2 may be configured such that the lock plate is provided with two slits extending from the support groove to the periphery of the lock plate and that the radius of curvatures of the lock plate on the opposite sides thereof across the line of eccentric direction are slightly larger than the inner radius of the cylinder circumscribing the lock-plate.
(Function) The lock plate inscribed in the cylinder has a slightly larger radius of curvature than the inner radius of the cylinder, and is acted upon by a radially inward forces exerted by the cylinder. As a consequence, the gaps between the lock plates and the drive rotor cylinder and between the lock plate bush and the support groove, formed by manufacturing errors for example, are still reduced. That is, in this configuration, as in the configuration defined in claim 4, clearances (plays) of members of self-locking mechanism are reduced during a self-locking operation under an external disturbing torque, and thud a required pressure to the drive rotor cylinder of the lock plate is instantly generated.
As recited in claim 6, the variable cam phaser defined in claim 4 or 5 may be further configured such that the lock plate bush is divided into two parts by a pair of slits.
(Function) In this configuration, as defined in claim 6, since a force is exerted on each of the divided members of the lock plate bush by the urging means via the lock plate, gaps that are formed between the divided lock plate bushes and the eccentric circular cam can be reduced in size than the gaps formed with undivided lock plate bushes, so that the plays of self-locking constituent members are still reduced. That is, a pressure created by an external disturbing torque is instantly transmitted to the drive rotor cylinder. This implies that precision requirement for the eccentric circular cam and rock plate bush can be relaxed and hence the production costs of the self-locking mechanism can be reduced.
Further, as recited in claim 7, the variable cam phaser defined in any one of claims 2 through 6 may be configured such that the flat faces of the lock plate bushes are a pair of stepped faces projecting to the right and left with respect to the line of eccentric direction, and that the stepped faces are offset in the eccentric direction away from the cam center towards the eccentric axis of the cam center.
(Function) Strictly speaking, a gap due to manufacturing error is formed between the support groove and the respective lock plate bushes. However, when the flat faces are stepped and abutted against the rock plate at positions offset from the cam center of the eccentric circular cam, the arcuate moving distance traveled by the flat faces before they come into contact with the support groove under an external disturbing torque is reduced as compared with the case where the planes are not stepped. In other words, plays of the rock plate bushes are still minimized then, so that a still instantaneous pressure is generated and transmitted to the drive rotor cylinder of the lock plates under an external disturbing torque.
Still further, as recited in claim 8, the variable cam phaser defined in any one of claims 1 through 7 may be configured such that the coupling mechanism consists of coupling members each engaging with one of paired coupling holes formed in the control rotor and with one of paired coupling holes formed in the rock plate; and that a minute clearance is provided between each coupling member and an associated coupling hole of either the control rotor or the lock plate.
(Function) If the positional relationship between the control rotor and the lock plate is set too strict, a manufacturing error may make it difficult to press the lock plate against the drive rotor cylinder under an external disturbing torque. By providing a minute clearance between each of the coupling members and the associated hole, the lock plate is less restricted to move in the radial direction, which makes it easy for the lock plate to be pressed against the drive rotor cylinder under an external disturbing torque.

Results of the Invention

The variable cam phaser for automobile engine defined in claim 1 has a self-locking mechanism which is simpler in structure and cost effective than conventional one in that the mechanism consists of such members as a drive rotor cylinder, disc shaped lock plate, and support groove.
The variable cam phaser in accordance with claim 2 is equipped with a self-locking mechanism having an improved self-locking function and durability.
The variable cam phaser in accordance with any one of claims 3 through 8 has a still improved self-locking function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective figure of a variable cam phaser for an automobile engine in accordance with a first embodiment of the invention, as viewed from the front end thereof.

FIG. 2 is an exploded perspective figure of the apparatus of FIG. 1, as viewed from the rear end thereof.

FIG. 3 is a front view of the apparatus of the first embodiment (excluding cover 70).

FIG. 4 is a cross section taken along line A-A of FIG. 3.

FIG. 5 is a cross section taken along line E-E of FIG. 4.

FIG. 6 shows cross sections of the apparatus taken along line B-B of FIG. 4 (FIG. 6( a)) and along line C-C of FIG. 4 (FIG. 6( b)).

FIG. 7 illustrates a self-locking mechanism of the first embodiment.

FIG. 8 is a cross section of a self-loci mechanism in accordance with a second embodiment of the invention, taken long a line that corresponds to line E-E of FIG. 4.

FIG. 9 illustrates a variation of a spring member used in the second embodiment.

FIG. 10 illustrates a variation of the lock plates.

FIG. 11 is a cross section of a self-locking mechanism in accordance with a third embodiment of the invention, taken along a line that corresponds to line E-E of FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will now be described in detail by way of example with reference to the accompanying drawings. variable cam phaser shown in the respective embodiments are installed in an automobile engine, adapted to transmit the rotation of the crankshaft of the engine to the camshaft of the apparatus to open/close air suction/exhaustion valves of the engine in synchronism with the crankshaft so that the valve timing of the air suction/exhaustion valves is changed in accord with such parameters of the operating conditions of the engine as an engine load and rpm.
Referring to FIGS. 1 through 6, there is shown a structure of a first embodiment of the invention. A variable cam phaser 1 comprises a drive rotor 2 driven by the crankshaft, a first control rotor 3 (referred to as control rotor in claim 1), a camshaft 6 (FIG. 4), torque means 9, a phase angle varying mechanism 10, and a self-locking mechanism 11. The end of the apparatus having a second electromagnetic clutch shown in FIG. 1 will be hereinafter referred to as the front end, while the end having the drive rotor 2 will be referred to as the rear end. The rotational direction (clockwise direction) of the drive rotor 2 about the axis L0 of the camshaft as viewed from the front end will be referred to as phase advancing direction D1, and the opposite rotational direction (counterclockwise direction) will be referred to as phase retarding direction D2.
The drive rotor 2 consists of a sprocket 4 and a drive cylinder 5 having a cylinder 20, integrated together with a multiplicity of bolts 2 a. The camshaft 6 shown in FIG. 4 is immovably and coaxially integrated with the rear end of a center shaft 7 by means of a bolt 37 screwed into a threaded female hole 6 a formed in the front end of the camshaft and the central circular hole 7 e of the center shaft 7.
The first control rotor 3 is a generally bottomed cylinder having a flange portion 3 a at the front edge thereof, a cylindrical portion 3 b extending rearward, and a bottom 3 c. The bottom 3 c has a central circular throughhole 3 d, a pair of pin holes 28, an arcuate groove 30 extending along a circle of a given radius about the central axis L0 (the groove hereinafter referred to as arcuate groove 30), and a guide groove 31 whose radius decreases in the phase advancing direction D1 about the central axis L0 (the groove hereinafter referred to as oblique guide groove 31).
The center shaft 7 is a contiguous body comprising a first cylindrical portion 7 a, flange portion 7 b, second cylindrical portion 7 c, eccentric circular cam 12 having a cam center L1 eccentrically offset from the camshaft axis L0, and a third cylindrical portion 7 d, arranged along the axis L0 in the order mentioned from the rear end towards the front end. The drive rotor 2 comprises a sprocket 4 and a drive cylinder 5 which are integrated together by means of bolts 2 a. Provided between the sprocket 4 and the drive cylinder 5 is a center shaft 7, which has a flange portion 7 b. The center shaft 7 also has first and second cylindrical portions 7 a and 7 c, respectively, which are fitted in the circular hole 4 a of the sprocket 4 and in the circular hole 5 a of the drive cylinder 5 a, respectively, so that the drive rotor 2 is rotatably mounted on the camshaft 6 via the center shaft 7. The third cylindrical portion 7 d is fitted in the central circular hole 3 d of the first control rotor 3. It is noted that the drive rotor 2, first control rotor 3, camshaft 6, and center shaft 7 are coaxial with the axis L0.
The torque means 9 consists of a first electromagnetic clutch 21 for providing the first control rotor 3 with a first torque (braking torque to retard the control rotor 3 relative to the drive rotor 2), and a reverse rotation mechanism 22 for providing the first control rotor 3 with a second torque which is opposite in direction with respect to the first torque.
The phase angle varying mechanism 10 includes the center shaft 7 (rotatably supporting the drive rotor 2), self-locking 11, and a coupling mechanism 16, and is adapted to couple the first control rotor 3 unrotatably with the camshaft 6.
The self-locking mechanism 11 is arranged between the drive rotor 2 and center shaft 7 so as to prevent a phase angle disturbance from occurring between the drive rotor 2 and camshaft 6 under an external disturbing torque applied to the camshaft 6 by a valve spring (not shown). The self-locking mechanism 11 consists of the eccentric circular cam 12 of the center shaft 7, lock plate bush 13 and lock plate 14, and the cylinder 20 of the drive rotor 2.
The lock plate bush 13 has a circular hole 13 a for receiving therein the eccentric circular cam 12 of the center shaft 7, and is provided on the opposite sides thereof with a pair of flat faces 23 and 24, as shown in FIGS. 1 and 5. The lock plate bush 13 is rotatably mounted on the periphery of the eccentric circular cam 12 such that the two flat faces 23 and 24 are maintained substantially parallel with respect to a line L2 connecting the camshaft axis L0 and the cam center L1 as shown in FIG. 5.
The lock plate 14 is generally disk shaped and has a substantially rectangular support groove 15 extending along a diameter. The lock plate 14 consists of a pair of two constituent members 14 a and 14 b divided by a pair of slits 25 and 26 formed at the opposite narrow sides 15 a and 15 b of the support groove 15 and extending to the circumference of the lock plate 14. The flat faces 23 and 24 of the lock plate bush 13 are held in contact with the long sides 15 c and 15 d of the support groove 15.
The periphery of the lock plate 14 is inscribed in the cylindrical portion 20 of the drive cylinder 5. The flat faces 23 and 24 of the lock plate bush 13 are sandwiched between the long sides (15 c and 15 d) of the support groove 15. Under this condition, the portion of the periphery of the eccentric circular cam 12 eccentrically offset (from the cam center L1) beyond a line L3 that passes through the cam center L1 perpendicularly to the line L2 is supported by the support groove 15 via the lock plate bush 13.
The coupling mechanism 16 consists of a pair of coupling pins 27, a pair of first pin holes 28 formed in the bottom 3 b of the first control rotor 3, and a pair of second pin holes 29 each formed in the respective constituent members 14 a and 14 b of the lock plate 14. Each of the coupling pins 27 is fixedly fitted at one end thereof in either the first pin hole 28 or second pin hole 29, but at the other end loosely fitted in the other first pin hole or second pin hole with a minute gap between pin and the hole. The lock plate 14 is pressed against the inner circumferential surface 20 a of the cylinder 20 of the drive cylinder 5 and unrotatably held therein when an external disturbing torque is transmitted thereto, as described in detail later. The minute gap provided in either the first or second pin hole 28 or 29 is to circumvent a difficulty of pressing the lock plate 14 against the inner circumferential surface 20 a if the lock plate 14 is fixed to the first control rotor 3.
The lock plate 14, inscribed in the cylinder 20 of the drive cylinder 5 and holding the lock plate bush 13 therein, is unrotatably integrated with the first control rotor 3 by means of the coupling pins 27 inserted the first and second pin 28 and 29. As a consequence, the center shaft 7 (camshaft 6) is unrotatably integrated with the first control rotor 3 via the eccentric circular cam 12, lock plate bush 13 and lock plate 14.
The camshaft 6 becomes integral with the first control rotor 3 under an external disturbing torque exerted by the torque means 9, and undergoes a relative rotation relative to the drive rotor 2 in either the phase-advancing direction D1 or phase retarding direction D2. As a result, the phase angle between the camshaft 6 and drive rotor 2 (or a crankshaft, not shown) is changed, thereby changing the valve timing.
It is noted here in connection with the torque means 9 that the first electromagnetic clutch 21 is firmly secured inside the engine (not shown) ahead of the first control rotor 3. When the front end 3 e of the flange portion 3 a is attracted by the first electromagnetic clutch 21 onto the friction member 21 a of the first electromagnetic clutch 21, the first control rotor 3 is retarded in rotation relative to the drive rotor 2 rotating in D1 direction.
The reverse rotation mechanism 22 consists of the arcuate groove 30 and the oblique guide groove 31 of the first control rotor 3, a second control rotor 32, a disk shaped pin guide plate 33, a second electromagnetic clutch 38 for putting a brake on the second control rotor 32, first and second link pins 34 and 35, and a ring member 36.
The second control rotor 32 is arranged inside the cylindrical portion 3 b of the first control rotor 3 and rotatably mounted on the coaxial third cylindrical portion 7 d of the center shaft 7 that passes through the central circular throughhole 32 a of the second control rotor 32. The second control rotor 32 is provided in a rear section thereof with a stepped eccentric circular hole 32 b, whose center of is offset from the camshaft axis L0. The ring member 36 is slidably inscribed in the stepped eccentric circular hole 32 b.
The disc shaped pin guide plate 33 is arranged inside the cylindrical portion 3 b of the first control rotor 3 and between the bottom 3 c and second control rotor 32 such that the pin guide plate 33 is rotatably supported by the third cylindrical portion passing through the central circular throughhole 33 a of the pin guide plate 33. The pin guide plate 33 has a groove 33 b and a guide groove 33 c that extends independently of the circular throughhole 33 a in substantially opposite radial directions (the guide grooves hereinafter referred to as radial guide grooves). The radial groove 33 b is formed in correspondence with the arcuate groove 30 and extends from a position near the central circular throughhole 33 a to the periphery of the pin guide plate. The radial guide groove 33 c is formed in correspondence with the oblique guide groove 31 and extends to a point near the periphery.
A thin round shaft 34 a and a thick hollow shaft 34 b integrated with the thin round shaft 34 a at the front end of the thin round shaft 34 a constitutes a first link pin 34. The thick hollow shaft 34 b is supported on both sides thereof by the radial groove 33 b. The rear end of the thin round shaft 34 a passes through the arcuate groove 30 and support groove 15, and is securely fixed to a mounting hole 5 b of the drive cylinder 5. On the other hand, the thin round shaft 34 a can move in the arcuate groove 30 between the opposite ends of the arcuate groove 30.
A second link pin 35 consists of a first member 35 c which is made up of a thin shaft 35 a integrally connected to the rear end of a thick round shaft 35 b, a first hollow shaft 35 d, a second hollow shaft 35 e, and a third hollow shaft 35 f. The first through third hollow shafts 35 d-35 f are mounted in sequence on the thin round shaft 35 a and retained together at their rear ends. The thick round shaft 35 b is inserted in the support groove 15. The first hollow shaft 35 d has an arcuate periphery that can fit the oblique guide groove 31, and is movable along the oblique guide groove 31 with its upper and lower sides supported by the oblique guide groove 31. The second hollow shaft 35 e has a cylindrical shape and is movable along the radial guide groove 33 c with its opposite sides held by the radial guide groove 33 c. The third hollow shaft 35 f has a cylindrical shape and is rotatably fitted in the circular hole 36 a formed in the ring member 36.
It is noted that a holder 39 and a washer 40 each having a central circular hole 39 a and 40 a, respectively, are placed on the leading end of the third cylindrical portion 7 d of the center shaft 7 The holder 39, washer 40, and center shaft 7 are securely fixed to the camshaft 6 with the bolt 37 screwed into a threaded bore 6 a through the circular holes 39 a, 40 a, and 7 e. As a result, all the elements between the drive rotor 2 and the second control rotor 2 inclusive, arranged round the periphery of the center shaft 7, are securely fixed together between the flange portion 6 b of the camshaft 6 and the holder 39. The axial clearance of these elements can be optimized by adjusting the thickness of the washer 40. Arranged in front of the bolt and the first and second electromagnetic clutches 21 and 38, respectively, is a cover 70.
The operation of the torque means 9 for changing the phase angle between the camshaft 6 and drive rotor 2 (and the crankshaft not shown) will now be described. Normally, the first control rotor 3 is in rotation in D1 direction (FIG. 6) together with the drive rotor 2 When the first control rotor 3 is attracted by, and abutted against, the first electromagnetic clutch 21 for braking, the center shaft 7 (camshaft 6) is retarded in D2 direction together with the integrated first control rotor 3, relative to the drive rotor 2 which is rotating in D1 direction. As a consequence, the phase angle of the camshaft 6 relative to the drive rotor 2 (and of the crankshaft not shown) is varied in the phase retarding direction D2, thereby changing the open/close timing of the valve.
Under this condition, the first hollow shaft 35 d of the second link pin 35 moves in the oblique guide groove 31 in substantially the clockwise direction D3 (FIG. 6( c)), and the second hollow shaft 35 e moves in the radial guide groove 33 c in D4 direction towards the axis L0 (FIG. 6( b)). Thus, the third hollow shaft 35 f shown in FIG. 6( a) provides the ring member 36 with a torque that causes the ring member 36 to slide within the circular hole 32 b. The thin round shaft 34 a moves in the arcuate groove 30 in the clockwise direction D1. The opposite ends 30 a and 30 b of the arcuate groove 30 serve as stoppers for stopping the thin hollow shaft 34 a that comes into abutment with the ends.
On the other hand, the second control rotor 32 is normally in rotation in D1 direction together with the drive rotor 2 (FIG. 6( a)) As the second electromagnetic clutch 38 is activated, the front end 32 c of the second control rotor 32 is attracted onto the friction member 38 a, resulting in a rotational delay of the second control rotor 32 in D2 direction relative to the first control rotor 3. In response to the eccentric rotation of the stepped eccentric circular hole 32 b in D2 direction within the ring member 36 shown in FIG. 6( a), the ring member 36 slidably rotates in the stepped eccentric circular hole 32 b. In response to the movement of the ring member 36, the second hollow shaft 35 e shown in FIG. 6( b) moves in the radial direction D5 within the radial guide groove 33 c together with the third hollow shaft 35 f and first hollow shaft 35 d. In this case, the first control rotor 3 shown in FIG. 6( c) is acted upon by a torque in the direction opposite to the torque generated by the first electromagnetic clutch 21. This torque is exerted, via the wall of the oblique groove 31, by the first hollow shaft 35 d moving in the oblique groove 31 in the substantially counterclockwise direction D6, causing the first control rotor 3 to be rotated in the phase advancing direction D1 still more relative to the drive rotor 2 rotating in D1 direction. Accordingly, the phase angle of the camshaft 6 relative to the drive rotor 2 (and crankshaft not shown) is advanced in D1 direction back to the original phase angle, thereby restoring the open/close timing of the valve.
Next, operation of the self-locking mechanism 11 will now be described in detail. The phase angle of the center shaft 7 (and of the camshaft 6) relative to the drive rotor 2 (and of the crankshaft not shown) is determined by a rotation of the first control rotor 3 in the phase advancing direction D1 or retarding direction D2 relative to the drive rotor 2, as described above. However, if an external disturbing torque is transmitted from a valve spring (not shown) to the camshaft 6, the relative phase angle between the camshaft and drive rotor 2 is changed, which will result in an unexpected deviation in open/close timing of the valve. The self-locking mechanism 11 of this embodiment takes advantage of such external disturbing torque to prevent such phase angle deviation.
FIG. 7 illustrates how a self-lock function takes place between the periphery (14 c and 14 d) of the lock plate 14 and the cylinder 20 of the drive cylinder 5 when an external disturbing torque is transmitted to rotate the camshaft 6 (center shaft 7) in clockwise direction D1 or counterclockwise direction D2.
When the camshaft 6 and the center shaft 7 are subjected to an external disturbing torque in the phase retarding direction D2 or phase advancing direction D1, the eccentric circular cam 12 is acted upon by a torque that causes the cam center L1 to be eccentrically rotated about the camshaft axis L0 in either D2 direction or D1 direction. Assume now that: the cam axis L1 is eccentrically offset from the camshaft axis L0 by a distance s; line L2 passes through the axis L0 and cam center L1; and line L3 passing through the cam center L1 is perpendicular to line L2; and line L3 intersects the eccentric circular cam 12 at point P1. Under this condition, when the eccentric circular cam 12 is subjected to a torque in the in D2 direction, the guide plate bush 13 is acted upon by a force F1 exerted by the eccentric circular cam 12 at the intersection point P1 in the direction of line L3. When the eccentric circular cam 12 is acted upon by an external disturbing torque in D1 direction, the lock plate bush 13 is acted upon by a force F2 exerted by the eccentric circular cam 12 at intersection point P2 along line L3 (directed from cam center L1 to intersection point P2).
It is noted that the forces F1 and F2 are transmitted along line L3 from the lock plate bush 13 to the lock plate 14 via the flat faces 23 and 24 in surface contact with the respective long sides 15 c and 15 d of the support groove 15. These forces F1 and F2 are further transmitted from peripheries of the constituent members 14 a and 14 b, respectively, of the lock plate 14 to the inner circumferential surface 20 a of the drive cylinder 5 at points P3 and P4 where line L3 meets the peripheries of the constituent members 14 a and 14 b.
Local frictional forces arise at points P3 and P4 from the forces F1 and F2 between the inner circumferential surface 20 a of drive cylinder 5 and the peripheries 14 c and 14 d that prevent a relative rotation of drive cylinder 5 relative to the lock plate 14. These local frictional forces can be determined as follows. Denoting by L4 the tangential lines of the respective peripheries of the constituent members (14 c and 14 d) at the intersection points P3 and P4; by L5 a line perpendicular to line L3; by L6 a line perpendicular to line L4; by θ1 and θ2 the angles (hereinafter referred to as friction angles) of lines L5 and L6 at the intersection points P3 and P4, respectively. with respect to the tangential line L4; and by μ the friction coefficient of the frictional surface, the forces acting on the drive rotor 2 at the intersection points P3 and P4, respectively, that may cause a phase angle deviation between the drive rotor 2 and camshaft 6 are given by F1*sin θ1 and F2*sin θ2, respectively. The local frictional forces preventing slides that may occur between the inner circumferential surface 20 a and the peripheries 14 c and 14 d are given by μμF1*cos θ1 and μ*F2*cos θ2, respectively.
When the frictional forces exceed the forces that can incur a phase angle chance, the drive cylinder 5 and the lock plate 14 are firmly secured to each other. Then, the lock plate bush 13 and the eccentric circular cam 12 (center shaft 7) are also immovably secured to each other. As a consequence, the control rotor 2 and camshaft 6 are immovably locked to each other under the external disturbing torque, thereby resulting in no relative phase change between them.
In the case when the following conditions
F1*sin θ1<μ*F1*cos θ1
and F2*sin θ2<μ*F2*cos θ2
are satisfied, the local frictional forces preventing the sliding motion of the lock plate 14 with respect to the drive cylinder 5 exceeds the force that can cause an angular phase change, so that a self-locking function is established between them. Thus, by setting the friction angles θ1 and θ2 such that
θ1<tan⁻¹μ and θ2<tan⁻¹μ,
the self-locking takes place between the drive rotor 2 (or the crankshaft not shown) and the camshaft 6 under an external disturbing torque, thereby preventing a change in phase-angle.
It is noted that if the lock plate bush 13 having flat faces 23 and 24 is inserted between the eccentric circular cam 12 and support groove 15, the contact stresses that appear on the support groove 15 in surface contact with the long sides 15 c and 15 d will be reduced. However, the self-locking function can be established even if the eccentric circular cam 12 is held in the support groove 15 with the line L2 passing through the axis L0 and L1 aligned with the long sides 15 c and 15 d substantially in parallel thereto. Thus, the lock plate bush 13 may be omitted.
Next, referring to FIG. 8, there is shown a self-locking mechanism 41 in accordance with a second embodiment of the invention. The self-locking mechanism 41 has substantially the same elements as the first self-locking mechanism 11 except that lock plate bush 42 and lock plate 43 have different shapes from the corresponding lock plate bush and lock plate of the first embodiment. A spring member 44 corresponds to the urging means of claim 4.
Specifically, the lock plate bush 42 is similar in shape to the lock plate bush 13 of the first embodiment, except that the lock plate bush 42 has no flat faces like 23 or 24. In the second embodiment, the lock plate 43 is provided with a slit 46 and a slit 47 for mounting a spring member 44. Thus, the slit 47 is larger than the slit 46. Other features of the lock plate 43 are the same as those of the lock plate 14.
The lock plate bush 42 is mounted on the eccentric circular cam 12 that passes through the circular hole 42 a of the lock plate 42. The lock plate bush 42 has a substantially elongate rectangular support groove 45 extending in a substantially diametrical direction. The lock plate bush 42 is divided into two constituent members 43 a and 43 b by a pair of linear slits that extend radially outwardly from the short sides 45 a and 45 b of the support groove 45 to the periphery of the lock plate 43. The slit 46 has the same shape as the slit 25 of the lock plate 14 of the first embodiment, but the slit 47 differs from the slit 26 of the first embodiment in that the slit 47 has a larger width than slit 46.
Mounted in the slit 47 is a spring member 44, which has an arcuate convex portion 44 a and curved portions 44 b and 44 c at the opposite ends of the arcuate convex portion 44 a, where the width of the arcuate convex portion 44 a is larger than the that of the slit 47. A spring member 44 provides the constituent members 43 a and 43 b with a force for widening the width of the slit 47 when its arcuate convex portion 44 a is fitted in the slit 47 and the curved portions 44 b and 44 c are supported by the constituent members 43 a and 43 b. As a consequence, in the self-locking mechanism 41, any gaps introduced during manufacture between the peripheries 43 c and 43 d of the constituent members 43 a and 43 b and the inner circumferential surface 20 a of the drive cylinder 5, and between the lock plate bush 42 and support groove 45 are reduced, thereby reducing plays of these members, and hence improving the pressure transmission to the inner circumferential surface 20 a of the lock plate 43 in self-locking action. Thus, a positive self-locking function is established.
An external disturbing torque is transmitted from the cam center L1 of the eccentric circular cam 12 to the inner circumferential surface 20 a of drive cylinder 5 along line L3, and generates forces F1 and F2 at the intersection points P7 and P8, which forces are transmitted from the lock plate bush 42 to the respective constituent members 43 a and 43 b through line contact between the lock plate bush 42 and the lock plate constituent members 43 a and 43 b at the intersection point P5 and P6 of the tangential line L3 with the periphery of the lock plate bush 42. Further, these forces acts on the inner circumferential surface 20 a of the drive cylinder 5 at the intersection points P7 and P8 of line L3 with the peripheral surface (43 c and 43 d). In this case, as in the first embodiment, by setting the friction angles between the tangential lines passing through the intersection point P7 and P8 and the line perpendicular to line L3 (the friction angles corresponding to the friction angles θ1 and θ2 defined in the first embodiment) in the range a self-locking function is established between the lock plate 43 and the cylinder 20 of the drive cylinder 5 under an external disturbing torque.
It is noted that the urging means for widening the width of the slit 47 is not limited to the 44 as shown in FIG. 8: it may alternatively be a trapezoidal member 48 a and a spring member 48 b as shown in FIG. 9( a) and (b). As shown in FIG. 9( a), the lock plate 43 has cut-away portions 47 a and 47 b that narrows in diameter along the camshaft axis L0 and towards the periphery of the slit 47. A trapezoidal member 48 a is arranged between the cut-away portions 47 a and 47 b. The trapezoidal member 48 a is provided in the periphery thereof with a recess 48 c for receiving a spring member 48 b corresponding to the spring member 44. The trapezoidal member 48 a is acted upon by a spring force exerted by the spring member 48 b in the direction D7 towards the axis L0. This force will act on the faces of the cut-away portions 47 a and 47 b at right angle thereto, thereby widening the slit 47.
As shown in FIG. 9( b), a C-shaped leaf spring 49 for compressing the lock plate constituent members 43 a and 43 b is arranged round the peripheries of the lock plate constituent members so as to widen the width of the slit 47 and narrow the width of the slit 46. The C-shaped leaf spring 49 is arranged such that its opening is aligned with the slit 46 between the lock plate constituent members 43 a and 43 b. Further, the left half portion of the C-shaped leaf spring 49 shown in FIG. 9( b) may be fixed to the constituent member the 43 b with the right half of the C-shaped leaf spring 49 while the right half portion mounted on the constituent member 43 b so that the constituent member 43 b is urged to rotate in the D2 direction relative to the constituent member 43 a. Thus, the peripheries of the lock plate constituent members 43 a and 43 b are urged to move towards the inner circumferential surface 20 a of the drive cylinder 5 by the C-shaped leaf spring 49. As a consequence, gaps formed between the inner circumferential surface 20 a of the drive cylinder 5 and the peripheries 43 c and 43 d of the lock plate 43, and between a lock plate bush 50 and the support groove 45 as well due to manufacturing errors, are reduced by the urging force of the C-shaped leaf spring 49, and so are the plays of the associated elements.
As shown in FIG. 9( b), the lock plate bush 50 may be split into two lock plate bush constituent members 50 a and 50 b separated by slits 50 c and 50 d formed along line L2. When the lock plate bush 50 is divided, the gaps formed between the inner periphery 50 e of the lock plate bush 50 and the outer periphery of the eccentric circular cam 12 due to manufacturing errors are still reduced, thereby further reducing plays of the constituent members and providing still effective self-locking function. Since plays of the locking members due to manufacturing errors can be reduced with the urging means as shown in FIGS. 8 and 9, precision requirements for the eccentric circular cam 12, lock plate bush 42 and 50, and for rock plate 43 can be relaxed to lower the production cost.
This lock plate may be made in the form of a C-shaped object 51 having an opening or slit 53 that extends from a support groove 52 to the outer periphery 51 a of the C-shaped object 51 as shown in FIG. 10, wherein the outer diameter of the C-shaped object 51 (as measured along line L3) can be made slightly larger than the inner diameter of the inner periphery 20 a of the cylinder 20 so that the inner periphery 20 a are constantly pushed radially outward (in the direction of d2 and d3 in FIG. 10). In this configuration, the same self-locking function as described above in connection with FIGS. 8 and 9 can be obtained without the spring member.
Next, referring to FIG. 11, there is shown another self-locking mechanism for use with an automobile variable cam phaser in accordance with a third embodiment of the invention. The self-locking mechanism 61 has essentially the same structure as the second self-locking mechanism 41 except that the spring member 44 is removed from the washer 40 and that the lock plate bush 42 is replaced by a lock plate bush 62 having a different configuration.
The lock plate bush 62 has a pair of right and left stepped faces 63 and 64, respectively, each having a flat face 62 a/62 b and stepped portion 62 c/62 d projecting therefrom to the right/left.
The lock plate bush 62 is mounted on the eccentric circular cam 12 coaxially with the eccentric circular cam 12 that passes through the circular hole 62 e of the lock plate bush 62 such that the stepped faces 63 and 64 are parallel to line L2 extending from the axis L0 toward the L1. On the other hand, the stepped faces 63 and 64 are mounted on the eccentric circular cam 12 in a symmetric fashion with respect to line L2 and offset from the cam center L1. In other words, provided in a region of the lock plate 62 further offset from the intersection points C1 and C2 where line L3 intersects the flat faces 62 a and 62 b, are the stepped faces 63 and 64 projecting to the right and left of the flat faces 62 a and 62 b. Line L7 connecting the centers of the flat faces 63 and 64 is substantially parallel to line L3, and intersects line L2 at a right angle at point C3 which is eccentrically further offset from the camshaft axis L0 than the cam center L1. The stepped faces 63 and 64 are held in position by the long sides 45 a and 45 b of the support groove 45.
As the eccentric circular cam 12 is acted upon by a force in D2 direction or D1 direction due to an external disturbing torque, the long sides 45 a and 45 b of the support groove 45 are respectively subjected to outward forces oriented to the left and right direction, respectively, along line L7, across the stepped faces 63 and 64 which are in surface contact with long sides 45 a and 45 b of the support groove 45 at positions further offset than the cam center L1 of the eccentric camshaft 12. Furthermore, the forces F3 and F4 are transmitted from the lock plate 43 to the inner circumferential surface 20 a of the drive cylinder 5 at the intersection points P9 and P10 where line L7 intersects the outer peripheries 43 c and 43 d of the lock plate constituent members 43 a and 43 b, respectively. Thus, these forces are transmitted from the cylinder 20 of the drive cylinder 5 to the lock plate 43. In this case, by setting the friction angles θ1 and θ2 between the tangential lines at intersection points P9 and P10 and the line perpendicular to line L7 to satisfy
θ1<tan⁻¹μ,θ2<tan⁻¹μ
in the same manner as the friction angles defined in the first embodiment, a self-locking function is established between the lock plate 43 and the cylinder 20 of the drive cylinder 5 by an external disturbing torque.
It is noted that minute gaps exist between the stepped faces 63 and 64 and the support face 45 due to manufacturing errors. In the third embodiment, however, the stepped faces 63 and 64 are in contact with the support face 45 at further offset positions than the cam axis L1 of the eccentric circular cam 12 that they exhibit less plays in the self-locking mechanism as compared with the first embodiment in which the eccentric circular cam 12 only has non-stepped flat faces 23 and 24. This is due to the fact that, if such minute gaps exist, an external disturbing toque facilitates the flat faces to move round the axis L0 until the flat faces come into contact with the support groove 45, whereby the stepped faces 63 and 64 (offset from the cam center L1) are in contact with the support groove 15 at positions further offset from the cam center L1 than the non-stepped faces 23 and 24 of the eccentric circular cam 12 of the first embodiment, so that the distance from the point of surface contact to the rotational axis is longer in the third embodiment than in the first embodiment. As a consequence, fluctuations in phase angle caused by the gaps are more reduced in the third embodiment for a given gap than in the first embodiment. As a result, by reducing the plays involved in the self-locking mechanism, the pressure that acts on the cylinder 20 of the lock plate 43 under an external disturbing torque is enhanced, thereby securing the function of the self-locking mechanism. This is true if the spring member 44 is removed from the slit 47.

BRIEF DESCRIPTION OF SYMBOLS

1 variable cam phaser for automobile engine
2 drive rotor
3 first control rotor (control rotor of claim 1)
6 camshaft
9 torque means
10 phase angle varying mechanism
11 self-locking mechanism
121 eccentric circular cam
13 lock plate bush
14 lock plate
14 a and 14 b lock plate constituent members
15 support groove
16 coupling mechanism
20 cylindrical portion
23 & 24 a pair of flat faces
25 & 26 a pair of slits
27 coupling members
28 coupling holes of control rotor
29 coupling holes of lock plate
44 means (spring member)
50 lock plate bush
51 C-shape lock plate
53 slit
63 & 64 stepped face
L0 camshaft axis
L1 cam center of eccentric circular cam

Claims

1. A variable cam phaser for an automobile engine including:

a drive rotor driven by the crankshaft of the engine;

a control rotor;

a camshaft coaxial with the drive rotor and adapted to rotatably support the drive rotor;

a torque means for providing the control rotor with a torque for rotating the control rotor relative to the drive rotor;

a phase angle varying mechanism for varying the relative phase angle between the drive rotor and the control rotor in accord with the relative rotation of the control rotor relative to the drive rotor;

and a self-locking mechanism mounted in the phase varying mechanism for preventing a phase change from occurring between the drive rotor and the camshaft caused by an unexpected cam torque appearing on the camshaft, the variable cam phaser characterized in that the self-locking mechanism comprises:

an eccentric circular cam integral with the camshaft; and

a lock plate having

a support groove for supporting, at positions further offset from the camshaft axis in the direction (referred to as eccentric direction) from the camshaft axis towards the cam center of the eccentric circular cam, the periphery of the eccentric circular cam from both sides thereof,

a coupling mechanism for transmitting the relative rotational torque from the control rotor to the eccentric circular cam, and

a cylindrical body formed integral with the drive rotor and circumscribing the periphery of the lock plate.

2. The variable cam phaser according to claim 1, wherein

the support groove extends in a radial direction of the lock plate;

the eccentric circular cam is provided on the outer periphery thereof with a lock plate bush; and

the lock plate bush has on the opposite sides of the outer periphery thereof a pair of flat faces spaced apart across the line of eccentric direction and supported by the support groove.

3. The variable cam phaser according to claim 2, wherein the lock plate is divided into two parts by a pair of slits each extending from the support groove to the periphery of the lock plate.

4. The variable cam phaser according to claim 3, wherein one of the two slits may be provided with urging means for providing a force to widen that slit.

5. The variable cam phaser according to claim 2, wherein

the lock plate is provided with two slits extending from the support groove to the periphery of the lock plate; and

the radius of curvatures of the lock plate on the opposite sides thereof across the line of eccentric direction are slightly larger than the inner radius of the cylinder circumscribing the lock-plate.

6. The variable cam phaser according to claim 4, wherein the lock plate bush is divided into two parts by a pair of slits.

7. The variable cam phaser according to claim 3, wherein

the flat faces of the lock plate bush are a pair of stepped faces projecting to the right and left to the line of eccentric direction; and

the stepped faces are offset in the eccentric direction away from the cam center towards the eccentric axis of the cam center.

8. The variable cam phaser according to claim 3, wherein

the coupling mechanism consists of coupling members each engaging with one of paired coupling holes formed in the control rotor and with one of paired coupling holes formed in the rock plate; and

a minute clearance is provided between each coupling member and an associated coupling hole of either the control rotor or the lock plate.

9. The variable cam phaser according to claim 5, wherein the lock plate bush is divided into two parts by a pair of slits.

10. The variable cam phaser according to claim 4, wherein

the flat faces of the lock plate bush are a pair of stepped faces projecting to the right and left to the line of eccentric direction; and the stepped faces are offset in the eccentric direction away from the cam center towards the eccentric axis of the cam center.

11. The variable cam phaser according to claim 5, wherein

12. The variable cam phaser according to claim 6, wherein

13. The variable cam phaser according to claim 4, wherein

14. The variable cam phaser according to claim 5, wherein

15. The variable cam phaser according to claim 6, wherein

16. The variable cam phaser according to claim 7, wherein