Patent Description:
An overhead cam switching roller finger follower is designed to switch between two motion modes. A spring biases an inner arm with respect to an outer arm so that the inner arm returns to a starting position. It is difficult to set the starting position of the inner arm because of variances in spring strength and tolerance stack up. So, it is desirable to set the starting position with means for accommodating variances and stack up.

<CIT> relates to a switching roller finger follower wherein a stop pin is provided for limiting the relative rotation between the inner arm assembly and the outer arms around the pivot axle connecting the inner arm assembly and the outer arms. Similar switching roller finger followers are known from <CIT> and <CIT>.

The invention relates to a switching roller finger follower as defined in claim <NUM>.

Additional objects and advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure. The objects and advantages will also be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claimed invention.

Reference will now be made in detail to the examples which are illustrated in the accompanying drawings. Directional references such as "left" and "right" are for ease of reference to the figures.

This application provides lash adjustment structures and techniques for an overhead cam switching roller finger follower ("SRFF"), sometimes called a "rocker arm. " While a <NUM>-roller rocker arm is shown in the figures, it is possible to use the techniques disclosed herein with other SRFFs, such as those comprising slider pads instead of rollers. As an example of these alternative SRFFS, the outer rollers can be replaced with slider pads. Alternatively or additionally, the inner roller can be replaced with a slider pad. And, the disclosed lash adjustment structures and techniques can be used with these alternative SRFFs.

A strategy was developed to provide a stop of motion between the inner arm assembly <NUM> and outer arms <NUM>, <NUM> on a Switching Roller Finger Follower (SRFF). The design involves a single stop pin <NUM>, select fit for size to manage lash and set a starting position, passing through the inner arm assembly <NUM> and contacting shoulders <NUM>, <NUM> on both inner sides of the outer arms. The stop pin <NUM> is retained by outer roller retainers <NUM> and is crowned on the ends <NUM>, <NUM> to prevent sticking during operation. The stop pin <NUM> can be assembled in the SRFF as by drop-in assembly through bores <NUM>, <NUM> in-line with the shoulders <NUM>, <NUM>.

In a SRFF, lash management is an important design consideration. In a <NUM> lobe SRFF, such as the <NUM>-roller rocker arm shown in the Figures, there are two areas where lash is introduced in the rocker arm: at the latch <NUM> of the latch assembly <NUM>; and between the inner roller assembly <NUM> and the outer rollers <NUM>, <NUM>. The lash at the latch <NUM> can result from the return spring, or as drawn with two return springs <NUM>, <NUM>, pushing the latching arm <NUM> of the inner arm assembly <NUM> above the latch <NUM> so that the latching arm <NUM> doesn't drag against the latch <NUM> during latch assembly actuation. This "latch lash" can vary forces pushing up on the overhead cam and can cause uneven presentation of the inner roller assemblies <NUM> to the overhead cam rail when a series of such SRFFs are assembled into a valvetrain.

The "roller lash" between the inner roller assembly <NUM> and outer arm rollers <NUM>, <NUM> can be a difference in where the inner roller <NUM> aligns with respect to an overhead cam versus where the outer rollers <NUM>, <NUM> align with respect to that overhead cam. Said in broader terms, the second kind of lash is related to a difference in outer arms <NUM>, <NUM> position with respect to inner arm assembly <NUM> position.

The design of the stop pin <NUM> manages both kinds of lash. The design uses a stop pin <NUM> in an inner port <NUM> through an axle <NUM> of the inner roller assembly <NUM>. As shown, the axle <NUM> is fitted to inner arms <NUM>, <NUM>, such as at opening <NUM>, so that axle <NUM> is stationary with respect to the inner arms. Optional needle bearings <NUM> can surround axle <NUM>. Outer layer of inner roller assembly <NUM> is a roller <NUM> that is acted on by an overhead cam during use. The stop pin <NUM> sets the location of the outer diameter of the roller <NUM> relative to the outer arms, which is a calibratable location corresponding to the starting position.

The stop pin <NUM> is select fit for size to achieve the proper lash. By "select fit," the stop pin <NUM> can vary from customer application to customer application to adjust the lash and set the starting position of the inner arm assembly <NUM> with respect to the outer arms <NUM>, <NUM>. If more lash is desired or if the roller assembly <NUM> should have a starting position lowered, the stop pin <NUM> can comprise a larger diameter D to draw the inner arm down closer to the latch <NUM>. If less lash is desired or if the starting position should be raised closer to the overhead cam, the pin can comprise a smaller diameter D, which increases the gap G between stop pin <NUM> and inner port <NUM> and enables the inner roller assembly <NUM> to be biased closer to the overhead cam. At times, there are variances even in the stop pins themselves, requiring exchange of stop pins sold or manufactured as "same size. " Gap G persists despite which stop pin is select fit so that the stop pin can slide into the axle <NUM> without being stuck, as would occur with an interference, friction, or press-fitting. Gap G can be a clearance fitting, and gap G can result in a large clearance between axle <NUM> and stop pin <NUM>. Grinding or other machining or manufacturing techniques can be used to form the different sized stop pins <NUM>.

The unitary stop pin <NUM> and pin selection and alternative exchange techniques improve over the art because the "same size" stop pins, even if requiring exchange, are cheaper pieces to stock and exchange than some other components of the SRFF. Even if exchanging the stop pin, the SRFF is not scrapped in total due to tolerance stack up. And, having an array of different sized stop pins is a low scrap way to provide customer-specific variation without complete re-design or re-manufacture of the SRFF. While part count stock overall may increase for manufacture of some SRFFs, the part count of the SRFF itself remains low and the quantity of scrap during manufacture can be restricted to the stop pins and thereby total scrap can be kept low.

The inner roller assembly <NUM> can be installed with respect to the outer arm assembly with a pivot axle <NUM> provided to set relative motion therebetween. The outer arm assembly can comprise a valve end <NUM> and a pivot end <NUM>. The pivot end <NUM> can comprise a latch body for receiving the latch assembly <NUM> herein shown as an electromechanical latch, though numerous alternative latch assemblies exist such as hydraulic and mechanical latch assemblies. A hydraulic lash adjuster cup <NUM> is shown for when a hydraulic lash adjuster is mounted to the SRFF. The pivot end can pivot on the HLA during engine system use.

The valve end <NUM> can comprise the pivot axle <NUM> and an integrally formed valve seat or a valve seat insert <NUM> for mounting a stem end of a valve. Valve seat insert can comprise, among numerous valve seat insert alternatives, a valve surface <NUM> for seating valve stem end, valve guides <NUM>, <NUM> for constraining valve stem end, and mounting cusps <NUM> for securing the valve seat <NUM> with respect to the pivot axle <NUM>.

At least one return spring biases the stop pin <NUM> toward the inner shoulders <NUM>, <NUM> so as to bias the inner arm assembly <NUM> toward the starting position. While pivot end return springs or a single return spring on the pivot axle <NUM> among other variations of return spring arrangements can be used in alternative SRFFs, the illustrated example comprises valve end return springs <NUM>, <NUM> coiled around the pivot axle <NUM>. Spring caps <NUM> can secure the return springs in place. The outer arms <NUM>, <NUM> can comprise bias points, or shoulders <NUM>, <NUM>, for biasing ends <NUM>, <NUM> of the return springs. Inner arms <NUM>, <NUM> can comprise inner arm extensions <NUM>, <NUM> comprising notches <NUM> configured for biasing other ends <NUM>, <NUM> of the return springs. An outer arm connector <NUM> can span across the valve end <NUM> of the outer arms <NUM>, <NUM> and restrict the motion of the inner arm assembly <NUM> with respect to the outer arms as by abutting the inner arm extensions <NUM>, <NUM> at an extrema of lost motion movement of the inner arm assembly <NUM>. Numerous return spring alternatives and return spring mounting alternatives are compatible with the disclosure to return the inner arm assembly <NUM> to a starting position with respect to outer arms.

The inner sides of the outer arms <NUM>, <NUM> can be formed with inner grooves <NUM>, <NUM> to serve as pump-down guides for the stop pin <NUM>. During lost motion travel of the stop pin <NUM>, it can move through the inner grooves <NUM>, <NUM> as the inner arms <NUM>, <NUM> pivot within the outer arms <NUM>, <NUM>. The crowned ends <NUM>, <NUM> slide against the inner grooves <NUM>, <NUM> without sticking when the overhead cam actuates to move an unlatched inner arm assembly <NUM>, and the stop pin <NUM> returns to a position abutting shoulders <NUM>, <NUM> when the overhead cam is at base circle or when the inner arm assembly <NUM> is latched. Because of the clearance fit and gap G, the stop pin <NUM> can move, and the inner grooves can guide the stop pin without causing the inner arm assembly pivoting motion to be dependent on the outer arms motion.

The latch assembly <NUM> comprises the latch <NUM>, and the latch is selectively movable from a latched position shown in <FIG> to an unlatched position shown in <FIG>. Unlatched position retracts latch <NUM> into the latch body <NUM> joining the outer arms <NUM>, <NUM>. In the latched position, the inner arm assembly <NUM> is latched to move dependent with the outer arms <NUM>, <NUM>. "Dependent with" means that the outer arms and inner arm assembly move together. The overhead cam actuates on the SRFF and pushes on the SRFF. The gap G closes during actuation, but the latching arm <NUM> is latched against latch <NUM> and the forces from the overhead cam press the latched SRFF to move dependently. Via control of the latch assembly (hydraulic, mechanical or electro-mechanical) the latch can be selected to move to an unlatched position unlatching the inner arm assembly to pivot independent of the outer arms. The stop pin <NUM> can move in inner grooves <NUM>, <NUM>, but the pivoting motion is "independent," meaning that the outer arms <NUM>, <NUM> are no longer joined in a way that transfers overhead cam forces to the inner arm assembly <NUM>. When considering the stop pin <NUM> spanning between the pair of outer arms <NUM>, <NUM> and through the inner port <NUM>, the stop pin <NUM> is configured pivotable independent of the outer arms, and the stop pin can pivot independently of the outer arms when the latch <NUM> is in the unlatched position.

The stop pin <NUM> is "select fit," which can comprise having a stock of stop pins of different diameters D. Depending upon the chosen customer lash, stop pins of one diameter or another can be inserted into bores <NUM>, <NUM> in the outer arms <NUM>, <NUM> and into axle <NUM> to set the starting position. Likewise, if assembly measurements indicate the inner arm assembly <NUM> should move with respect to the outer arms, due to tolerance stack up or other variances, the stop pins <NUM> can be exchanged or selected to achieve a desired starting position. A gauge, mount, caliper, or other calibration device or technique can be used to aid in selecting an appropriate diameter stop pin <NUM>.

The bores <NUM>, <NUM> aligned with the inner port <NUM> of hollow axle <NUM> achieve a design that is conducive to the select fit process. Once the stop pin of appropriate diameter is installed in the hollow port, the retention of the stop pin <NUM> is accomplished by utilizing retainers <NUM>. The retainers can achieve multiple functions of retaining the stop pin <NUM> inside the SRFF, providing a sliding surface for the ends <NUM>, <NUM> of the stop pin <NUM>, and securing the outer rollers <NUM>, <NUM>.

Retainers <NUM> can be pressed into bores <NUM>, <NUM> in cantilevered posts <NUM>, <NUM> on the outer arms <NUM>, <NUM>. The retainers <NUM> can be identical, as drawn, or can be "left handed" and "right handed" as when the bores are not identically sized, as when stop pin <NUM> is installed or exchanged from only one side of the SRFF instead of from either side as drawn. A flat head <NUM> can be used for a low footprint and can be used to retain the outer rollers <NUM>, <NUM> in position on the cantilevered posts <NUM>, <NUM>. A shank <NUM> with a crowned end <NUM> can seat in the bore <NUM> or <NUM>. The crowned end <NUM> provides a non-stick surface against with the stop pin ends <NUM>, <NUM> can slide. When the inner arm assembly <NUM> moves down, the stop pin <NUM> moves out of the range of the retainers <NUM>. To keep the stop pin <NUM> aligned when the inner arm assembly <NUM> moves back to the starting position, the ends <NUM> of the stop pin <NUM> can be crowned to ensure that the stop pin is centered if the stop pin contacts the retainer <NUM> on its way back.

The SRFF can be used in a Type II overhead cam valvetrain. A lash adjuster can be seated beneath the latch assembly <NUM>. The latch can be, for example, hydraulic, electromechanical, mechanical, among variations. When the SRFF is latched, the inner arm assembly <NUM> and outer arms <NUM>, <NUM> move together with the cam lobe to provide motion to the affiliated valve. When the latch <NUM> on the SRFF is unlatched, the inner arm assembly <NUM> moves downward with the cam lobe relative to the outer arms <NUM>, <NUM>. Depending on the cam lobe arrangement, the outer arms can remain stationary or can provide a variable valve actuation ("VVA") functionality. The pivot axle <NUM> can connect the inner arm assembly <NUM> to pivot with respect to the pair of outer arms <NUM>, <NUM> from the starting position to a "lost motion" position. Valve deactivation (lack of motion) or early or late opening or closing can be accomplished by selecting the "lost motion" position and the functionality ascribed thereto. Variables comprise, among others, the presence or absence of outer rollers or outer sliders, the shape and number of overhead lobes, and the location of the inner arm assembly with respect to the outer arms.

Methods of select-fitting a stop pin within a switching roller finger follower can comprise biasing an inner arm assembly <NUM> toward a starting position with respect to an outer arm. A calibratable device, such as a gauge, caliper, micrometer, chuck, or other testing device, can be applied to the SRFF to gauge where the inner arm assembly is with relation to a preselected starting position. A stop pin of a diameter that sets the inner arm assembly in the starting position can be selected. As above, this can comprise selection from a stock of stop pins of different diameters. The stop pin can be inserted within the inner arm assembly <NUM> to set the inner arm assembly at the starting position. The starting position can be re-gauged with the calibratable device. If needed, the stop pin can be exchanged with a selected second stop pin to re-set the starting position.

In an alternative select-fitting or lash setting method, inner arm assembly <NUM> is biased toward a starting position with respect to an outer arm. The starting position is gauged with a calibratable device. Because the inner arm assembly already comprises a stop pin, the stop pin is exchanged with a second stop pin of a diameter that re-sets the starting position of the inner arm assembly.

Claim 1:
A switching roller finger follower, comprising:
an inner arm assembly (<NUM>) comprising an axle (<NUM>) and an inner port (<NUM>) through the axle; a pair of outer arms (<NUM>, <NUM>) surrounding the inner arm assembly, each of the outer arms comprising a bore (<NUM>, <NUM>) and an inner shoulder (<NUM>, <NUM>) on an inner side facing the inner arm assembly, wherein the bores in the outer arms are in-line with the inner shoulders;
a pivot axle (<NUM>) connecting the inner arm assembly to the outer arms, the pivot axle configuring the inner arm assembly to pivot between the inner sides of the outer arms from a starting position to a lost motion position;
a latch assembly (<NUM>) comprising a latch (<NUM>) selectively movable between a latched position latching the inner arm assembly to move dependent with the outer arms and an unlatched position unlatching the inner arm assembly to pivot between the inner sides of the outer arms;
a stop pin (<NUM>) spanning between the inner sides of the outer arms and through the inner port, the stop pin comprising a clearance fit with the inner port, and the stop pin configured to pivot between the inner sides of the outer arms;
a pair of retainers (<NUM>) seated in each respective bore, wherein the pair of retainers cover the respective bores so that the stop pin cannot exit the bores in the outer arms; and
at least one return spring (<NUM>, <NUM>) biasing the stop pin toward the inner shoulders so as to bias the inner arm assembly toward the starting position,