Abstract
A rocker arm includes an outer arm defining a bore; an inner arm which pivots relative to the outer arm, the inner arm defining a stop surface; a lost motion spring which biases the inner arm to pivot relative to the outer arm in a first direction; and a lock pin that slides within the bore between a coupled position in which the lock pin prevents the inner arm from pivoting relative to the outer arm past a predetermined position in a second direction which is opposite of the first direction and a decoupled position in which the lock pin permits the inner arm to pivot relative to the outer arm past the predetermined position in the second direction; such that the lock pin and the stop surface act together to limit the extent to which the inner arm pivots relative to the outer arm in the first direction.
Claims
1. A rocker arm for transmitting rotational motion from a camshaft to opening and closing motion of a combustion valve in an internal combustion engine, said rocker arm comprising: an outer arm defining a lock pin bore; an inner arm which selectively pivots relative to said outer arm, said inner arm defining a stop surface; a lost motion spring which biases said inner arm to pivot relative to said outer arm in a first direction; and a lock pin disposed within said lock pin bore such that said lock pin slides within said lock pin bore between 1) a coupled position in which said lock pin prevents said inner arm from pivoting relative to said outer arm past a predetermined position of said inner arm relative to said outer arm in a second direction which is opposite of said first direction and 2) a decoupled position in which said lock pin permits said inner arm to pivot relative to said outer arm past said predetermined position in said second direction; wherein said lock pin and said stop surface act together to limit the extent to which said inner arm pivots relative to said outer arm in said first direction.
2. The rocker arm as in claim 1 wherein said lock pin and said stop surface act together to limit the extent to which said inner arm pivots relative to said outer arm in said first direction both when said lock pin is in said coupled position and when said lock pin is in said decoupled position.
3. The rocker arm as in claim 1 wherein: said lock pin bore extends along, and is centered about, a lock pin bore axis; said lock pin includes a first lock pin section which is centered about said lock pin bore axis and which engages said inner arm in said coupled position, thereby preventing said inner arm from pivoting relative to said outer arm past said predetermined position of said inner arm relative to said outer arm in said second direction; and said lock pin includes a travel limiter which extends along, and is centered about, a travel limiter axis which is parallel to and laterally offset from said lock pin bore axis and which engages said stop surface, thereby limiting the extent to which said inner arm pivots relative to said outer arm in said first direction.
4. The rocker arm as in claim 3, wherein said travel limiter has a cross-sectional shape of a circle when sectioned by a plane that is perpendicular to said travel limiter axis.
5. The rocker arm as in claim 3 further comprising a means for anti-rotation which prevents rotation of said lock pin within said lock pin bore about said lock pin bore axis.
6. The rocker arm as in claim 3 wherein said inner arm defines an inner arm aperture which circumferentially surrounds said travel limiter when said lock pin is in said coupled position.
7. The rocker arm as in claim 6 wherein said lock pin is retracted from said inner arm aperture when said lock pin is in said decoupled position.
8. The rocker arm as in claim 6 wherein: said inner arm selectively pivots relative to said outer arm about a pivot axis; and said inner arm aperture extends along, and is centered about, an inner arm aperture axis which is normal to said pivot axis.
9. The rocker arm as in claim 6 further comprising a means for anti-rotation which prevents rotation of said lock pin within said lock pin bore about said lock pin bore axis.
10. The rocker arm as in claim 3 wherein said travel limiter axis is laterally offset from said lock pin bore axis in said second direction.
11. The rocker arm as in claim 3 wherein a cross-sectional area of said travel limiter taken perpendicular to said travel limiter axis is less than a cross sectional area of said first lock pin section taken perpendicular to said lock pin bore axis.
12. A rocker arm for transmitting rotational motion from a camshaft to opening and closing motion of a combustion valve in an internal combustion engine, said rocker arm comprising: an outer arm defining a lock pin bore; an inner arm which selectively pivots relative to said outer arm, said inner arm defining a stop surface; a lost motion spring which biases said inner arm to pivot relative to said outer arm in a first direction; and a lock pin disposed within said lock pin bore such that said lock pin slides within said lock pin bore between 1) a coupled position in which said lock pin prevents said inner arm from pivoting relative to said outer arm past a predetermined position of said inner arm relative to said outer arm in a second direction which is opposite of said first direction and 2) a decoupled position in which said lock pin permits said inner arm to pivot relative to said outer arm past said predetermined position in said second direction; wherein said lock pin and said stop surface act together to limit the extent to which said inner arm pivots relative to said outer arm in said first direction; wherein said inner arm defines an inner arm aperture which circumferentially surrounds said lock pin when said lock pin is in said coupled position.
13. The rocker arm as in claim 12 wherein said lock pin is retracted from said inner arm aperture when said lock pin is in said decoupled position.
14. The rocker arm as in claim 12 wherein: said inner arm selectively pivots relative to said outer arm about a pivot axis; and said inner arm aperture extends along, and is centered about, an inner arm aperture axis which is normal to said pivot axis.
Description
BRIEF DESCRIPTION OF DRAWINGS
(1) This invention will be further described with reference to the accompanying drawings in which:
(2) FIG. 1 is an isometric view of a rocker arm in accordance with the present invention;
(3) FIG. 2 is a cross-sectional view of the rocker arm of FIG. 1, taken through a first plane that is perpendicular to an axis about which an inner arm of the rocker arm pivots relative to an outer arm of the rocker arm, shown in a decoupled state;
(4) FIG. 3 is the cross-sectional view of FIG. 2, now showing the rocker arm in a coupled state;
(5) FIG. 4 is an isometric, partially exploded view of the rocker arm;
(6) FIG. 5 is an isometric view of a lock pin of the rocker arm;
(7) FIG. 6 is an isometric view of the inner arm of the rocker arm; and
(8) FIG. 7 is an isometric view of the rocker arm, shown with a retainer of a latching arrangement removed.
DETAILED DESCRIPTION OF INVENTION
(9) Referring initially to FIGS. 1-3, a rocker arm 10 in accordance with the invention is illustrated where rocker arm 10 is either a two-step rocker arm or a deactivation rocker arm, which may generically be referred to as a switchable rocker arm. Rocker arm 10 is included in valve train (not shown) of an internal combustion engine (not shown) in order to translate rotational motion of a camshaft (not shown) to reciprocating motion of a combustion valve (not shown). Rocker arm 10 includes an inner arm 12 that is pivotably disposed in a central opening 16 of an outer arm 14. Inner arm 12 selectively pivots within outer arm 14 about a pivot shaft 18 which is centered, and extends along, a pivot axis 18a. Inner arm 12 includes a contact surface illustrated as a roller 20 carried by a roller shaft 22 that is supported by inner arm 12 such that roller 20 and roller shaft 22 are centered about a roller shaft axis 24. Roller 20 is configured to follow a lobe of the camshaft, for example a high-lift lobe, to impart lifting motion on a respective combustion valve. A bearing 26 may rotatably support roller 20 on roller shaft 22 for following a cam lobe of a lifting cam of an engine camshaft (not shown). Bearing 26 may be, for example, a plurality of rollers or needle bearings. Roller shaft 22 is fixed to inner arm 12, by way of non-limiting example only by staking each end of roller shaft 22 in order to cause each end of roller shaft 22 to be increased in diameter to prevent removal from inner arm 12. Outer arm 14 includes two walls 28 positioned parallel to each other such that walls 28 are perpendicular to roller shaft axis 24 and such that walls 28 are spaced apart from each other to define central opening 16 therebetween. Outer arm 14 also includes followers 30 such that one follower 30 is fixed to each wall 28. As shown, followers 30 may be sliding surfaces, but may alternatively be rollers. Followers 30 are configured to follow respective lobes of the camshaft, for example low-lift lobes which impart lifting motion on a respective combustion valve or null lobes which do not impart lifting motion on a respective combustion valve. A lost motion spring 32 acts between inner arm 12 and outer arm 14 to pivot inner arm 12 away from outer arm 14 in a first direction. A socket 34 for pivotably mounting rocker arm 10 on a lash adjuster (not shown) is included at a first end 14a of outer arm 14 while a pad 36 for actuating a valve stem (not shown) is included at a second end 14b of outer arm 14. A latching arrangement 38 disposed within outer arm 14 at first end 14a thereof selectively permits inner arm 12 to pivot relative to outer arm 14 about pivot shaft 18 and also selectively prevents inner arm 12 from pivoting relative to outer arm 14 about pivot shaft 18. While the follower of inner arm 12 has been illustrated as roller 20, it should be understood that the follower of inner arm 12 may alternatively be a sliding surface as shown in U.S. Pat. No. 7,305,951 to Fernandez et al. Similarly, while followers 30 of outer arm 14 have been illustrated as sliding surfaces, it should be understood that followers 30 may alternatively be rollers as shown in U.S. Pat. No. 7,305,951. It should also be understood that the followers of inner arm 12 and outer arm 14 may all be rollers or may all be sliding surfaces.
(10) Rocker arm 10 is selectively switched between a coupled state and a decoupled state by latching arrangement 38. In the coupled state as shown in FIG. 3, inner arm 12 is prevented from pivoting relative to outer arm 14 past a predetermined position of inner arm 12 relative to outer arm 14 in a second direction, shown as clockwise in FIG. 3, which is opposite from the first direction. In this way, in the coupled state, inner arm 12, and therefore roller shaft 22, is coupled to outer arm 14, and rotation of the lifting cam is transferred from roller 20 through roller shaft 22 to pivotal movement of outer arm 14 about the lash adjuster which, in turn, reciprocates the associated valve. In the decoupled state as shown in FIG. 2, inner arm 12 is able to pivot relative to outer arm 14 past the predetermined position in the first direction. In this way, in the decoupled state, inner arm 12, and therefore roller shaft 22, is decoupled from outer arm 14. Thus, roller shaft 22 does not transfer rotation of the lifting cam to pivotal movement of outer arm 14, and the associated valve is not reciprocated. Rather, inner arm 12 together with roller 20 and roller shaft 22 reciprocate within central opening 16, thereby compressing and uncompressing lost motion spring 32 in a cyclic manner such that lost motion spring 32 biases inner arm 12 to pivot relative to outer arm 14 in the first direction, shown as counterclockwise in FIG. 2.
(11) Latching arrangement 38 will now be described in greater detail with continued reference to FIGS. 1-3, and now with additional reference to FIGS. 4-7. Latching arrangement 38 includes a connecting bore 40 which is centered about and extends along a connecting bore axis 40a into outer arm 14 such that connecting bore 40 is centered about connecting bore axis 40a. Connecting bore 40 extends from the outer surface of outer arm 14 to a connecting bore floor 42 which terminates connecting bore 40. Connecting bore floor 42 may be perpendicular to connecting bore axis 40a as shown. Connecting bore 40 may comprise multiple diameters, however, the cross-sectional shape of connecting bore 40 taken perpendicular to connecting bore axis 40a at any point along connecting bore axis 40a is preferably a circle.
(12) Latching arrangement 38 also includes an oil supply bore 44 which is centered about, and extends along an oil supply bore axis 44a. The cross-sectional shape of oil supply bore 44 taken perpendicular to oil supply bore axis 44a at any point along oil supply bore axis 44a is preferably a circle, with the exception of where oil supply bore 44 meets socket 34 which provides for a non-symmetric cross-sectional shape. Oil supply bore 44 extends from socket 34 to connecting bore 40 such that oil supply bore 44 opens into connecting bore 40 through connecting bore floor 42. In this way, oil supply bore 44 provides fluid communication from socket 34 to connecting bore 40 and communicates pressurized oil to connecting bore 40. As is conventional in hydraulically actuated switchable rocker arms, oil supply bore 44 receives oil from the lash adjuster which is received within socket 34. As shown, oil supply bore axis 44a may be parallel to connecting bore axis 40a, however, oil supply bore axis 44a may alternatively be oblique to connecting bore axis 40a. Also as shown, oil supply bore axis 44a may be offset from connecting bore axis 40a in a direction perpendicular to connecting bore axis 40a.
(13) Latching arrangement 38 also includes a lock pin bore 46 which is centered about, and extends along, a lock pin bore axis 46a. Lock pin bore 46 extends from central opening 16 to connecting bore 40 such that lock pin bore 46 opens into connecting bore 40 through connecting bore floor 42. Lock pin bore 46 may comprise multiple diameters, however, the cross-sectional shape of lock pin bore 46 taken perpendicular to lock pin bore axis 46a at any point along lock pin bore axis 46a is preferably a circle, with the exception of where lock pin bore 46 meets central opening 16 which provides for a non-symmetric cross-sectional shape. As shown, lock pin bore axis 46a is preferably parallel to connecting bore axis 40a. Also as shown, lock pin bore axis 46a may be offset from connecting bore axis 40a in a direction perpendicular to connecting bore axis 40a. As such, when oil supply bore axis 44a is parallel to connecting bore axis 40a, oil supply bore axis 44a is also parallel to lock pin bore axis 46a and when oil supply bore axis 44a is oblique to connecting bore axis 40a, oil supply bore axis 44a is also oblique to lock pin bore axis 46a. As illustrated in the figures, lock pin bore 46 and oil supply bore 44 are located laterally relative to each other and communicate with each other via connecting bore 40, i.e. oil supply bore 44 does not open directly into lock pin bore 46 and vice versa.
(14) Lock pin bore 46 will now be described in greater detail. Lock pin bore 46 includes a first lock pin bore section 46b which is proximal to, and opens into connecting bore 40 through connecting bore floor 42. Lock pin bore 46 also includes a second lock pin bore section 46c which is proximal to, and opens into central opening 16. Second lock pin bore section 46c is preferably smaller in diameter than first lock pin bore section 46b. Lock pin bore 46 also includes a third lock pin bore section 46d which is immediately axially adjacent to second lock pin bore section 46c such that third lock pin bore section 46d is axially between first lock pin bore section 46b and second lock pin bore section 46c. Third lock pin bore section 46d is preferably larger in diameter than second lock pin bore section 46c, thereby forming a first lock pin bore shoulder 46e where third lock pin bore section 46d meets second lock pin bore section 46c. Third lock pin bore section 46d is preferably smaller in diameter than first lock pin bore section 46b. Lock pin bore 46 may also include a fourth lock pin bore section 46f which is immediately axially adjacent to third lock pin bore section 46d and to first lock pin bore section 46b such that fourth lock pin bore section 46f is axially between first lock pin bore section 46b and third lock pin bore section 46d. Fourth lock pin bore section 46f is larger in diameter than first lock pin bore section 46b and third lock pin bore section 46d, thereby forming a second lock pin bore shoulder 46g where fourth lock pin bore section 46f meets third lock pin bore section 46d.
(15) Latching arrangement 38 also includes a lock pin 48 within lock pin bore 46 which slides along lock pin bore axis 46a between a coupled position shown in FIG. 3 and a decoupled position shown in FIG. 2 based on the magnitude of oil pressure supplied through oil supply bore 44. Lock pin 48 includes a first lock pin section 48a which is located within first lock pin bore section 46b such that first lock pin section 48a extends along, and is centered about, lock pin bore axis 46a. First lock pin section 48a is cylindrical and sized to mate with first lock pin bore section 46b in a close sliding fit which allows lock pin 48 to move axially within lock pin bore 46 while substantially preventing lock pin 48 from moving in a direction perpendicular to lock pin bore axis 46a and also substantially preventing oil from leaking between the interface of first lock pin section 48a and first lock pin bore section 46b. In this way, first lock pin section 48a acts as a hydraulic piston which allows pressurized oil from oil supply bore 44 to urge lock pin 48 into the coupled position shown in FIG. 3. In order to allow this relationship, first lock pin section 48a and first lock pin bore section 46b may need to be machined in a finish grinding operation to obtain suitable tolerances and surface finishes. As will be readily recognized by those of ordinary skill in the art, substantially preventing oil from leaking between the interface of first lock pin section 48a and first lock pin bore section 46b is an indication that some leakage may occur while still allowing sufficient pressure to act upon first lock pin section 48a to urge lock pin 48 into coupled position shown in FIG. 3. Any oil that may leak past the interface of first lock pin section 48a and first lock pin bore section 46b may be vented out of outer arm 14 through a vent passage that will not be further described herein. Lock pin 48 also includes a second lock pin section 48b which is supported within second lock pin bore section 46c such that second lock pin section 48b extends along, and is centered about lock pin bore axis 46a. Second lock pin section 48b includes a flat 48c thereon which is engaged by a complementary surface of a dowel pin 50 which is fixed within a complementary outer arm aperture 14c of outer arm 14 which extends into lock pin bore 46. In this way, dowel pin 50 extends into lock pin bore 46 thereby substantially preventing rotation of lock pin 48 about lock pin bore axis 46a. Consequently, flat 48c and dowel pin 50 act together as a means for anti-rotation of lock pin 48 about lock pin bore axis 46a. Second lock pin section 48b is cylindrical, with the exception of flat 48c, and sized to mate with second lock pin bore section 46c in a close sliding fit which allows lock pin 48 to move axially within lock pin bore 46 while substantially preventing lock pin 48 from moving in a direction perpendicular to lock pin bore axis 46a. When lock pin 48 is positioned in the coupled position shown in FIG. 3, a portion of second lock pin section 48b extends into central opening 16 and engages inner arm 12. While not shown, the tip of second lock pin section 48b which engages inner arm 12 may include a flat which engages inner arm 12. Lock pin 48 also includes a third lock pin section 48d which joins first lock pin section 48a and second lock pin section 48b such that third lock pin section 48d is smaller in diameter than first lock pin section 48a and second lock pin section 48b, thereby forming a lock pin shoulder 48e where third lock pin section 48d meets first lock pin section 48a. However, in an alternative, third lock pin section 48d may be omitted and lock pin shoulder 48e is formed where second lock pin section 48b meets first lock pin section 48a. Third lock pin section 48d extends along, and is centered about lock pin bore axis 46a such that third lock pin section 48d is cylindrical. Lock pin 48 also includes a fourth lock pin section 48f, hereinafter referred to as travel limiter 48f, which extends from second lock pin section 48b in a direction that is away from first lock pin section 48a such that second lock pin section 48b is located between third lock pin section 48d and travel limiter 48f. While travel limiter 48f is shown as being cylindrical, it should be understood that travel limiter 48f may be other shapes as well. Unlike first lock pin section 48a, second lock pin section 48b, and third lock pin section 48d which extend along, and are centered about, lock pin bore axis 46a, travel limiter 48f extends along, and is centered about, a travel limiter axis 48g which is parallel to, and laterally offset from, lock pin bore axis 46a. It should be noted that travel limiter axis 48g is laterally offset from lock pin bore axis 46a in the same direction that inner arm 12 moves when inner arm 12 compresses lost motion spring 32, i.e. the second direction. It should also be noted that a cross-sectional area of travel limiter 48f taken perpendicular to travel limiter axis 48g is less than a cross-sectional area of first lock pin section 48a taken perpendicular to lock pin bore axis 46a. Travel limiter 48f and its related function will be described in greater detail later.
(16) Latching arrangement 38 also includes a return spring 52 within lock pin bore 46 which urges lock pin 48 into the uncoupled position shown in FIG. 2. Return spring 52 circumferentially surrounds third lock pin section 48d and a portion of second lock pin section 48b such that return spring 52 is held in compression between first lock pin bore shoulder 46e and lock pin shoulder 48e. In this way, when the pressure of oil acting on first lock pin section 48a is sufficiently low, return spring 52 urges lock pin 48 into the uncoupled state shown in FIG. 2. Conversely, when the pressure of oil acting on first lock pin section 48a is sufficiently high, lock pin 48 is urged by the oil pressure into the coupled state as shown in FIG. 3 whereby return spring 52 is compressed. As shown in FIG. 3, second lock pin bore shoulder 46g limits the travel of lock pin 48 in the coupled state by providing a surface for lock pin shoulder 48e to contact.
(17) Latching arrangement 38 also includes a retainer 54 located within connecting bore 40 such that retainer 54 closes connecting bore 40 to define a chamber 56 within connecting bore 40 axially between retainer 54 and connecting bore floor 42 which provides fluid communication between oil supply bore 44 and lock pin bore 46. It should be noted that FIG. 7 is shown with retainer 54 removed in order to obtain a clear view of connecting bore 40, oil supply bore 44, and lock pin bore 46 viewed looking in the direction of connecting bore axis 40a. As shown in FIGS. 2 and 3, retainer 54 may be cup-shaped with an annular wall 54a centered about connecting bore axis 40a and an end wall 54b closing off the end of annular wall 54a that is proximal to connecting bore floor 42. Annular wall 54a is sized to mate with connecting bore 40 in an interference fit relationship which prevents oil from passing between the interface of annular wall 54a and connecting bore 40. End wall 54b includes a central section 54c surrounded by a peripheral section 54d such that central section 54c extends axially toward connecting bore floor 42 to a greater extent than peripheral section 54d. In this way, peripheral section 54d ensures that chamber 56 is sufficiently large to ensure adequate oil flow and pressure from oil supply bore 44 to lock pin bore 46. As shown, central section 54c may be perpendicular to connecting bore axis 40a while peripheral section 54d is oblique relative to connecting bore axis 40a such that peripheral section 54d tapers away from connecting bore floor 42 when moving from where peripheral section 54d meets central section 54c to where peripheral section 54d meets annular wall 54a. As best seen in FIG. 2, central section 54c acts as a travel stop for lock pin 48 when lock pin 48 is in the decoupled position such that lock pin 48 abuts the central section 54c while lock pin 48 is separated from peripheral section 54d when lock pin 48 is in the decoupled state. While the interference fit of annular wall 54a with connecting bore 40 may be sufficient to maintain the position of retainer 54 within connecting bore 40, additional retention may be desired. As shown, a clip 58 may be provided in a groove 60 of connecting bore 40 to ensure that the position of retainer 54 within connecting bore 40 is maintained. Alternative methods may be used to ensure retainer 54 that the position of retainer 54 within connecting bore 40 is maintained, for example, adhesives, welding, crimping, staking or combinations thereof.
(18) In order to limit the extent to which inner arm 12 pivots relative to outer arm 14 in the first direction, i.e. counterclockwise as viewed in FIGS. 2 and 3, inner arm 12 includes a stop surface 12a upon which travel of inner arm 12 is limited by travel limiter 48f of lock pin 48 when lost motion spring 32 causes inner arm 12 to pivot relative to outer arm 14 in the first direction. However, due to travel limiter 48f of lock pin 48 being smaller in diameter than second lock pin section 48b and also due to travel limiter 48f being centered about travel limiter axis 48g which is laterally offset from lock pin bore axis 46a in the same direction that inner arm 12 moves when inner arm 12 compresses lost motion spring 32, i.e. the second direction, clearance is provided to allow inner arm 12 to pivot in the second direction when lock pin 48 is in the decoupled position as shown in FIG. 2. Stop surface 12a is partly defined by a recess 12b which extends part way into inner arm 12 and which receives second lock pin section 48b when lock pin 48 is in the coupled position as shown in FIG. 3. However, second lock pin section 48b reacts against a portion of recess 12b that is 180 around the perimeter of recess 12b from the portion against which travel limiter 48f reacts. An inner arm aperture 12c extends further into inner arm 12 such that inner arm aperture 12c initiates at the bottom of recess 12b and such that inner arm aperture 12c extends along, and is centered about, an inner arm aperture axis 12d which is normal to pivot axis 18a. It should be noted that inner arm aperture axis 12d is shown coincident with travel limiter axis 48g in FIGS. 2 and 3, however inner arm aperture axis 12d will pivot relative to travel limiter axis 48g as inner arm 12 pivots relative to outer arm 14, but inner arm aperture axis 12d will remain normal to pivot axis 18a. Inner arm aperture 12c further defines stop surface 12a and receives travel limiter 48f when lock pin 48 is in the coupled position as shown in FIG. 3 such that inner arm aperture 12c circumferentially surrounds travel limiter 48f when lock pin 48 is in the coupled position, where it should be noted that travel limiter 48f is retracted from inner arm aperture 12c when lock pin 48 is in the decoupled position. In this way, travel limiter 48f is able to engage stop surface 12a to limit the extent to which inner arm 12 pivots relative to outer arm 14 in the first direction when lock pin 48 is both in the coupled position and the decoupled position.
(19) While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.
