Granted Patent B2

US 9,429,047 · App. 14/076,480 · Granted Aug 30, 2016

Abstract

Claims (98)

1. A method, comprising:

receiving, at a computing device including one or more processors, parameters for a rocker arm and a valve of an engine and a contact point path defining a plurality of contact points between a pad of the rocker arm and a tip of the valve at various rotation angles of the rocker arm, the engine including a camshaft having a lobe operable to actuate the rocker arm via a follower or follower/pushrod, the valve having a stem and a guide;

calculating, at the computing device, one or more metrics based on the contact point path, the one or more metrics including at least one of (i) a valve tip wear metric and (ii) a stem-to-guide collision energy of the valve;

outputting, at the computing device, the one or more metrics;

receiving, at the computing device and based on the one or more metrics, an adjustment to the contact point path from a user to obtain a modified contact point path that satisfies a design objective of decreased valve tip wear or decreased valve tick, the modified contact point path causing at least one of the one or more metrics to decrease below a respective predetermined threshold;

determining, at the computing device, custom contours for the rocker arm pad and the camshaft lobe based on the modified contact point path;

based on the custom contours for the rocker arm pad and the camshaft lobe, generating, at the computing device, a set of instructions for machining a custom contoured rocker arm pad and a custom contoured camshaft lobe; and

transmitting, from the computing device and to machining components via a network, the set of instructions, wherein receipt of the set of instructions is configured to cause the machining components to machine the custom contoured rocker arm pad and the custom contoured camshaft lobe.

2. The method of claim 1 , wherein determining the custom contour for the rocker arm pad includes calculating, at the computing device, a curvature of the rocker arm pad at each point along the contact point path by calculating:

κ

2

=

1

(

ⅆ

r

ⅆ

n

)

⁢

cos

⁡

(

η

-

α

)

,

where κ 2 represents the curvature of the rocker arm pad at a specific contact point, r represents a radial distance from a pivot point of the rocker arm to the specific contact point, η represents an angular coordinate of the specific contact point, and α represents an initial angle between a plane of the valve tip and a plane connecting an initial contact point and the rocker arm pivot point.

3. The method of claim 1 , wherein calculating the one or more metrics based on the contact point path includes calculating the valve tip wear metric, which includes:

calculating, at the computing device, a sliding velocity between the rocker arm pad and the valve tip at each contact point along the contact point path based on the rocker arm parameters and the valve parameters;

determining, at the computing device, a contact stress between the rocker arm pad and the valve tip at each contact point along the contact point path based on the rocker arm parameters; and

calculating, at the computing device, the valve tip wear metric based on a product of the sliding velocities and the contact stresses.

4. The method of claim 3 , wherein calculating the sliding velocity between the rocker arm pad and the valve tip at a specific contact point along the contact point path includes calculating:

υ (12) =r ω sin(η−α)

where υ (12) represents the sliding velocity, r represents a radial distance from a pivot point of the rocker arm to the specific contact point, η represents an angular coordinate of the specific contact point, ω represents a change rate of change of η, and α represents an initial angle between a plane of the valve tip and a plane connecting an initial contact point and the rocker arm pivot point.

5. The method of claim 3 , wherein determining the contact stress between the rocker arm pad and the valve tip at a specific contact point along the contact point path includes calculating, at the computing device, the contact stress based on an average contact pressure between the rocker arm pad and the valve tip for a single valve cycle, wherein the average contact pressure is based on a weighted average of a force applied by the rocker arm at a plurality of different engine loads.

6. The method of claim 1 , wherein determining the custom contour for the rocker arm pad includes calculating, at the computing device, the stem-to-guide collision energy of the valve, wherein the stem-to-guide collision energy represents a kinetic energy imparted by the valve as it pivots about a bottom corner of its guide, and wherein the stem-to-guide collision energy is based on the rocker arm parameters, the valve parameters, and the contact point path.

7. The method of claim 6 , wherein the modified contact point path decreases the stem-to-guide collision energy of the valve below an acceptable valve stem-to-guide collision energy threshold.

8. The method of claim 6 , wherein the stem-to-guide collision energy is calculated based on valve stem diameter, valve guide diameter, valve guide length, a location of a center of mass of the valve, an unguided cold length of the valve, and a friction coefficient for assessing Coulomb friction between the valve tip and the rocker arm pad.

9. The method of claim 1 , wherein the custom contour for the camshaft lobe companions with the custom contour for the rocker arm pad to produce the modified contact point path.

10. The method of claim 1 , wherein calculating the custom contour for the camshaft lobe is further based on:

(i) a relationship s(φ) between an arc-length distance s along a surface of the rocker arm pad as measured from its zero-lift contact point with the valve tip and a rotation angle of the camshaft φ,

(ii) a first interpolating spline η(φ) that represents an angular velocity of the rocker arm as a function of the rotation angle of the camshaft φ, where η represents an angular coordinate of a specific contact point,

(iii) a first derivative dη/dφ of the first interpolating spline η(φ) that represents an angular velocity of the rocker arm as a function of the rotation angle of the camshaft φ, and

(iv) a second derivative d 2 η/d 2 φ of the first interpolating spline η(φ) that represents the angular acceleration of the rocker arm, where φ represents a rotation angle of the camshaft.

11. The method of claim 10 , wherein the relationship s(φ) is calculated by:

selecting, at the computing device, a number N of equally-spaced points over a range of φ where a camshaft lift profile l(φ) is non-zero;

determining, at the computing device, a value of s for each value of φ using the following zero-finding routine:

min

φ

⁢

l

⁡

(

ϕ

i

)

+

Δ

⁢

⁢

y

max

-

h

0

-

min

s

⁢

r

⁡

(

s

i

)

·

sin

⁡

(

τ

⁡

(

s

i

)

)

=

0

,

where i represents an index ranging from 1 to N, Δy max represents a y-coordinate of a contact point of the valve tip when the valve is at maximum lift, and h 0 represents the maximum lift displacement of the valve stem within its guide;

creating, at the computing device, a second interpolating spline that defines a function s(φ)s, for i=1. . . N; and

creating, at the computing device, the first interpolating spline η(φ) that defines η as a function of φ from (φ i , η(s(φ i )).

12. The method of claim 11 , further comprising calculating, at the computing device:

Δy max = r 0 sin(−α)+h 0 ,

where r 0 represents a radial distance from the a pivot point of the rocker arm to an initial contact point between the rocker arm pad and the valve tip, α represents an initial angle between a plane of the valve tip and a plane connecting the initial contact point and the rocker arm pivot point, and where l(φ)−h 0 =0 at maximum valve lift.

13. The method of claim 1 , wherein the respective predetermined thresholds correspond to at least one of (i) increased valve life or more even valve tip wear and (ii) inaudible valve tick.

Assignments (8)