Patent Application
20090308339
The present invention relates to switchable valve train members for internal combustion engines for supporting a roller finger follower or a pushrod in a combustion valve train; more particularly, to a switchable hydraulic lash adjuster or a switchable valve lifter that is switchable between a first mode wherein valve actuation is permitted and a second mode wherein valve actuation is prevented; and most particularly, to a sub-assembly for a switchable member wherein a latchable pin housing is selectively latched to a sub-assembly body by a single transverse locking pin, and wherein the pin housing is prevented from rotation within the adjuster body, and wherein axial mechanical lash in the sub-assembly is easily set during assembly thereof without requiring repeated assembly and disassembly of the sub-assembly.
Switchable valve train devices are well known in the engine arts for selectively permitting or preventing the opening of an associated engine combustion valve. See, for example, U.S. Pat. No. 7,263,956 B1 (“the '956 patent”) wherein a pin housing of a switchable valve lifter (SVL) is slidably disposed within an outer body bore. Opposing dual, flatted locking pins having a compression spring therebetween are disposed in a transverse bore in the pin housing for extending radially to engage an annular locking shelf in the body bore. Pressurized oil is applied selectively to the outer ends of the pins to retract the pins into the pin housing, allowing the pin housing to slide in the body bore in lost motion. The dual locking pin concept, as disclosed in the '956 patent, offers several benefits over the prior art single locking pin concept. For example, the valve train load that is transferred through the switchable device during valve lift is supported by two locking pins instead of one and the overall diameter of the device may be reduced since load bearing lengths may be shared by both sides of the body and pin housing. This dual flatted locking pin construction disclosed in the '956 patent has been adapted to other valve train members such as switchable hydraulic lash adjusters (SHLA).
An additional known problem in prior art SHLAs having dual locking pins is that side-loading of the pin housing with respect to the body is significantly greater than in prior art SVLs wherein forces are nearly parallel to the axis of the SVL. This is because a hydraulic lash adjuster supports and is a pivot point for a roller finger follower (RFF), and force vectors imposed on the RFF by an associated cam lobe during opening and closing of such a valve are not entirely parallel to the axis of the SHLA. Because the pin housing of a prior art SHLA is not constrained from rotation within the SHLA body, there are orientations of the pin housing with respect to the sideloading wherein the entire axial load is carried by a single locking pin during certain periods during the valve lift event.
A separate issue in prior art SHLAs is the need for a precise setting of the internal axial lash (mechanical lash) between the pin housing and adjuster body with the pin in locked position. It is important that the locking pin be given sufficient clearance to engage reliably and securely; however, if too much clearance is permitted, the SHLA will be noisy and will experience excessive wear. Also, too much clearance will adversely effect the opening timing of the associated valve since, in the valve opening direction, the pin housing must first traverse the mechanical lash before the switchable valve train can even begin to open the associated valve. Because the stack-up of manufacturing tolerances of the individual lash adjuster components cannot provide a consistent, as-built mechanical lash, a means for adjusting the mechanical lash of each SHLA must be provided. Typically, in the prior art, each SHLA is at least partially assembled and the gross axial lash is measured. The required clearance is then subtracted from the gross axial lash and a graded shim of the resulting thickness is inserted into the SHLA, typically after first disassembling the partially-assembled device.
What is needed in the art is an improved SHLA wherein the axial load is reliably carried by a single locking pin and wherein the gross mechanical lash may be easily measured and a desired mechanical lash may be set without disassembly of the device.
It is a principal object of the present invention to provide a reliable single-pin SHLA or SVL.
It is a further object of the invention to reduce the manufacturing complexity and cost of a SHLA or SVL.
Briefly described, a sub-assembly for a switchable valve train device, which may be either a SHLA or a SVL, includes a pin housing slidably disposed in a body and having a transverse bore. A stepped plug has a major diameter portion that is full-fitting in the transverse bore and a minor diameter portion extending beyond the surface of the pin housing to engage a longitudinal slot in a wall of the body to prevent rotation of the pin housing within the body. The upper end of the slot limits axial travel of the pin housing and thus participates in setting mechanical lash in the device.
The plug also acts as a seat for a compression spring. A locking pin is disposed in the transverse bore against the spring for extension beyond the pin housing to engage a locking port formed in a wall of the body opposite the longitudinal slot. Because the pin housing is prevented from rotation within the body, the orientation of the locking pin to the locking port is maintained.
The locking pin and the locking port are provided with mating flats to distribute the locked load. The locking pin is prevented from rotation within the cross-bore by action of an anti-rotation cross pin to maintain the rotational orientation of the locking pin flat to the locking port flat.
Mechanical lash is readily set by use of a gage tool during assembly via selection of a locking pin having an appropriate thickness.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
As noted above, the construction and functionality of SVLs and SHLAs are very similar. Although the following presentation is directed to an improved single-pin SHLA, the disclosed principles of construction are equally applicable to an improved single-pin SVL. Prior art is found in two single-pin SVL disclosures.
Referring to
The disclosed SVL 10 has at least the shortcomings that would exist if the locking arrangement were used in a single-pin SHLA.
First, operating experience has shown that a round pin disposed in a round port suffers from undesirably rapid wear to the pin and/or port because of the relatively short bearing length of the mating bore and because the pin and port have essentially line contact as a result of a deliberate difference in diameters that allows the pin to enter the port reliably. The result is that, as the wear occurs, the internal mechanical lash between the pin housing and the body increases undesirably. The increased lash results in objectionably noisier operation of the engine, but more importantly, results in a later valve opening point and a progressively lower valve lift.
Second, there is no apparent method for conveniently setting internal mechanical lash during assembly of SVL 10 as shown in the '175 patent.
Third, the axial positions of upper end 35 of slot 32 and locking port 38 define the amount of internal mechanical lash and are subject to variation in manufacturing tolerances of pin housing 24, plug 30, and body 18, making the amount of lash in any given unit, and hence the precise point of opening and lift of an associated valve, unreliable.
Referring to
While a means has been provided in SVL 10′ for setting mechanical lash, SVL 10′ has the other shortcomings as SVL 10 recited above, especially since it utilizes a cylindrical locking pin 36′ having a circular cross-section that locks into a round locking port 38′ formed in bore 20′ of body 18′. As noted above, this shortcomings would also exist if the locking arrangement were used in a single-pin SHLA.
As an improvement over a single locking pin design, switchable valve train members in the prior art employ dual opposing locking pins, as disclosed in the '956 patent, which arrangement provides greater locking stability and reliability than a single-pin arrangement. Experience has shown, however, that a dual-pin arrangement can have a drawback in certain applications. As noted above, because the pin housing is free to rotate within the body of a prior art SHLA having dual locking pins for engagement with an annular locking shelf, there are orientations of the pin housing with respect to an associated RFF wherein the entire axial load is carried by only one of the two locking pins during periods of the valve lift event, the force balance within the SHLA prevents contact of the opposite pin with the locking shelf due to the component of force applied to the pin housing that is transverse to the axis of the body. Further, as the diameter of the pin housing is reduced for packaging purposes, the transverse length of the bore in the pin housing also becomes smaller, leading to shorter pins having a reduced length/diameter ratio, resulting in increased potential for cocking and wear of the pins, thereby reducing the stiffness of the locking mechanism.
Referring now to
In one aspect of the present invention, a locking port 138 formed in a wall of body 118 is provided with a locking ledge 150 for receiving a mating flat 152 on locking pin 136. The use of a broad planar contact area between the pin and the body overcomes the prior art wear problem wherein a locking pin having a circular cross-section engages a circular bore of a slightly larger diameter as noted above. This arrangement requires that locking pin 136 be prevented from rotation about its own axis, which is readily accomplished in many ways by providing an additional flat (not visible) on the side of pin 136 and a mating flat-ended cross-pin (not visible) disposed in pin housing 124, substantially as disclosed in U.S. Pat. No. 6,513,470 (“the '470 patent”) directed to a SVL, the relevant disclosure of which is herein incorporated by reference. Note that if the rotational orientation of the body of a SHLA or SVL relative to the receiving bore in the engine is critical, such as, for example, for maintaining roller alignment with a cam lobe in the case of a roller SVL or for oil port alignment in either a SHLA or SVL, a means for locating the body in the receiving bore, as known in the art, may be provided.
Further, locking port 138 is provided with an additional notch 154 to allow locking pin 136 to be installed through port 138 after pin housing 124 is inserted into body 118, the benefits of which are described below.
Referring now to
Next, a gage tool 156 is inserted (
Plug 130 is then urged back into transverse bore 128 and pin housing 124 is raised a small distance, without disassembly, to permit gage tool 156 to be withdrawn (
Sub-assembly 100 is now fully assembled with the correct internal mechanical lash and is ready for subsequent insertion of a prior art lash adjusting mechanism 26 (
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
