ACTING FORCE TRANSMISSION DEVICE FOR USE WITH VALVE MECHANISM AND METHOD OF MANUFACTURING THE SAME

Abstract

An acting force transmission device for use with a valve mechanism of an engine includes an acting force transmission member that transmits an acting force to a valve to open/close the valve. A support shaft is provided in the acting force transmission member. An annular roller is directly mounted on an outer periphery of the support shaft. The roller is adapted to rotate when subjected to a cam force exerted by a cam and is adapted to transmit the cam force to the acting force transmission member as the acting force. A ratio d/D of an inner diameter d to an outer diameter D of the annular roller is not less than 0.7.

Claims

1. An acting force transmission device for use with a valve mechanism of an engine, the acting force transmission device comprising; an acting force transmission member for transmitting an acting force to a valve to open/close the valve; a support shaft provided in the acting force transmission member; and an annular roller directly mounted on an outer periphery of the support shaft, the roller adapted to rotate when subjected to a cam force exerted by a cam and adapted to transmit the cam force to the acting force transmission member as the acting force, wherein a ratio d/D of an inner diameter d to an outer diameter D of the annular roller is not less than 0.7.

2. The acting force transmitting device of claim 1 wherein the support shaft is mounted on the acting force transmission member.

3. The acting force transmitting device of claim 2 wherein the annular roller comprises an inner periphery that opposes the outer periphery of the support shaft.

4. The acting force transmitting device of claim 2 wherein lubrication is realized between the inner periphery of the annular roller and the outer periphery of the support shaft near a domain of elastohydrodynamic lubrication.

5. The acting force transmitting device of claim 4 wherein the lubrication is realized at an engine revolution per minute of 600 rpm.

6. The acting force transmission device of claim 1 wherein the ratio d/D is 0.95.

7. A method of manufacturing an acting force transmission device for use with a valve mechanism of an engine, the acting force transmission device comprising: an acting force transmission member for transmitting an acting force to a valve to open/close the valve; a support shaft mounted on the acting force transmission member; and an annular roller directly mounted on an outer periphery of the support shaft and adapted to rotate when subjected to a cam force exerted by a cam and adapted to transmit the cam force to the acting force transmission member as the acting force; wherein the method comprises a step of configuring the annular roller such that a ratio d/D of an inner diameter d to an outer diameter D of the roller is not less than 0.7.

8. The method of claim 7, further comprising: directly and rotatably mounting the annular roller onto the support shaft.

9. A rocker arm structure for use with a valve mechanism of an engine, comprising: an arm for transmitting an acting force to an action transmitting end thereof and adapted to transmit the action to a valve in order to open/close the valve; a support shaft projecting laterally from the arm at a position of the arm offset from the action transmitting end toward an opposite end of the arm; and an annular roller rotatably mounted on the outer periphery of the support shaft, the roller rotated by a cam force exerted by a cam onto an outer periphery thereof to transmit the cam force to the support shaft so as to transmit the cam force to said action transmitting end via the arm, whereas contact stress P depends on a contact width (Wm), while the sliding speed V depends on an inner diameter (DRin) of the roller, wherein the contact width Wm of the outer periphery of the support shaft in contact with the inner periphery of the roller and the inner diameter (DRin) of the roller are configured such that a product PV remains in a domain of hydrodynamic lubrication even when an rpm of the engine is at an rpm less than a predetermined middle rpm level, where P is a contact stress exerted by the inner periphery of the roller to the outer periphery of the support shaft in contact with the roller, and V is a sliding speed V of the inner periphery of the roller relative to the outer periphery of the support shaft.

10. The acting force transmitting device of claim 9 wherein the support shaft is mounted on the arm.

11. The acting force transmitting device of claim 10 wherein the support shaft is directly and rotatably mounted onto the arm.

12. The acting force transmitting device of claim 11 wherein the annular roller comprises an inner periphery that opposes the outer periphery of the support shaft.

13. The acting force transmitting device of claim 10 wherein lubrication is realized between the inner periphery of the annular roller and the outer periphery of the support shaft near a domain of elastohydrodynamic lubrication.

14. A method of manufacturing a rocker arm structure that comprises: an arm for transmitting, to one end thereof serving as an action transmitting end, an acting force that acts on a valve to open/close the valve; a support shaft projecting laterally from the arm at a position offset from said one end towards the other end of the arm; and an annular roller rotatably mounted on the outer periphery of the support shaft, the roller rotated by a cam force exerted by a cam onto an outer periphery thereof to transmit the cam force to the support shaft so as to transmit the cam force to said action transmitting end via the arm; wherein the method comprises configuring a contact width (Wm) of the outer periphery of the support shaft in contact with the inner periphery of the roller and the inner diameter (DRin) of the roller such that a product PV remains in a domain of hydrodynamic lubrication even when an rpm of the engine is at an rpm less than a predetermined middle rpm level, where P is a contact stress exerted by the inner periphery of the roller to the outer periphery of the support shaft in contact with the roller, and V is a sliding speed V of the inner periphery of the roller relative to the outer periphery of the support shaft.

15. The method of claim 14, further comprising: directly and rotatably mounting the annular roller onto the support shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0020] FIG. 1 shows a structure of a rocker arm in accord with the first example of the disclosure.

[0021] FIG. 2 is a cross section taken along line X2-X2 in FIG. 1;

[0022] FIG. 3 is a plan view of a rocker arm in accord with the first example of the disclosure.

[0023] FIG. 4 is a brief longitudinal cross section of a rocker arm in accord with the first example of the disclosure.

[0024] FIG. 5 illustrates a method of determining the inner diameter and the central contact width of the inner periphery of the roller.

[0025] FIG. 6 illustrate alternative method of determining the inner diameter and the central width of the inner periphery of the roller.

[0026] FIG. 7 compares characteristics of canonical rocker arms having a normal contact width and a reduced contact width.

[0027] FIG. 8 compares characteristics of canonical rocker arms having a reduced inner roller diameter and an increased inner roller diameter.

[0028] FIG. 9 compares cam torques of a canonical rocker arm and a standard rocker arm equipped with needle bearings as functions of engine rpm in all range of rpm. FIG. 9 also shows a relationship between engine rpm and lubrication mode of a canonical rocker arm structure.

[0029] FIG. 10 is a diagram comparing cam torques involved in a standard rocker arm equipped with needle bearings, a canonical rocker arm (with d/D=0.44), and a rocker arm embodying the disclosure (d/D=0.75) in all rpm domains in regard to the second example of the disclosure,

[0030] FIG. 11 shows Stribeck curves for the respective rocker arms.

[0031] FIG. 12 is a plan view of a acting force transmission device in the form of a rocker arm in regard to the second example of the disclosure.

[0032] FIG. 13 is a cross section of the acting force transmission device taken along line X4-X4 in FIG. 12.

DETAILED DESCRIPTION

[0033] Below the examples of the present disclosure are explained in details based on the drawings. The first example of the present disclosure is explained in reference to FIGS. 1 through 9. In order to achieve the first object of the disclosure above, in reference to FIGS. 1 through 3, a rocker arm structure for use with a valve mechanism of an engine includes an arm (4) for transmitting, to an action transmitting end of the arm (the end referred to as action transmitting end), an acting force that acts on a valve (2) to open/close the valve (2). A support shaft (5) projects laterally from the arm (4) at a position offset from said one end towards the other end of the arm (4). An annular roller (6) is rotatably mounted on the outer periphery of the support shaft (5). The roller is rotated by a cam force exerted by a cam (C) onto an outer periphery thereof to transmit the cam force to the support shaft (5) so as to transmit the cam force to said action transmitting end via the arm (4) (as shown in FIGS. 1 through 3).

[0034] A contact width Wm (defined to be the axial width of the outer periphery of the support shaft (5) in contact with the inner periphery of the roller (6)) and the inner diameter (DRin) of the roller are configured such that a product PV remains in a domain of hydrodynamic lubrication when the rpm of the engine is less than a predetermined middle level, where P is the contact stress exerted by the inner periphery of the roller (6) to the outer periphery of the support shaft (5) in contact with the roller, and V is the sliding speed V of the inner periphery of the roller relative to the outer periphery of the support shaft (5). It is noted that the contact stress P depends on the contact width Wm, while the sliding speed V depends on the inner diameter (DRin) of the roller. (Refer to FIGS. 4 through 6).

[0035] It is noted that in FIGS. 1 through 6, reference numeral 2a indicates a valve stem; 5b an outer periphery of a support shaft; 6i an inner periphery of a roller; 6im a central portion of the inner periphery of the roller; 7 a portion of opposing paired upright walls (of the arm (4)); 8 a valve-pressing portion; 9 a lush adjuster support; 9a a semi-spherical recess; 10 a lush adjuster; B axial length of the roller 6; and DRout outer diameter of the roller.

[0036] In order to achieve the second object of the disclosure above the manufacturing method of the rocker arm according to the example is the following.

[0037] A method of manufacturing a rocker arm structure of an engine that comprises: an arm (4) for transmitting an acting force to one end thereof (said end hereinafter referred to as action transmitting end) adapted to transmit the action to a valve (2) in order to open/close the valve (2); a support shaft (5) projecting laterally from the arm (4) at a position of the arm offset from said action transmitting end towards the other end of the arm (4); and an annular roller (6) rotatably mounted on the outer periphery of the support shaft (5), the roller rotated by a cam force exerted by a cam (C) onto an outer periphery thereof to transmit the cam force to the support shaft (5) so as to transmit the cam force to said action transmitting end via the arm (4),

[0038] The method comprises configuring a contact width Wm of the outer periphery of the support shaft (5) in contact with the inner periphery of the roller (6) and the inner diameter (DRin) of the roller such that a product PV remains in a domain of hydrodynamic lubrication when the rpm of the engine is less than a predetermined middle level, where P is the contact stress exerted by the inner periphery of the roller (6) to the outer periphery of the support shaft (5) in contact with the roller, and V is the sliding speed V of the inner periphery of the roller relative to the outer periphery of the support shaft (5), whereas the contact stress P depends on the contact width Wm, while the sliding speed V depends on the inner diameter (DRin) of the roller.

[0039] According to the rocker arm of the example, in view of the fact that the contact stress (P) exerted by the inner periphery of the roller (6) to the outer periphery of the support shaft (5) in rotation at a given rpm (FIG. 7) is related to the axial width (Wm) of the outer periphery of the support shaft (5) in contact with the inner periphery of the roller (6) and that the speed (V) of the inner periphery of the roller (6) sliding relative to the outer periphery of the support shaft (5) at a given rpm (FIG. 8) is related to the inner diameter (DRin) of the roller (6), the contact width (Wm) and the inner diameter (DRin) of the roller are set such that the product (PV) remains in a domain of hydrodynamic lubrication even when the rpm of the engine is less than a predetermined middle level, where P is the contact stress exerted by the inner periphery of the roller (6) to the outer periphery of the support shaft (5) in contact with the roller (6), and V is the sliding speed of the inner periphery of the roller (6). Thus, when the rocker arm structure (3) is operated under a condition that engine oil is sprayed or showered onto the valve mechanism, engine oil enters spaces between the support shaft (5) and the roller (6). As a result, friction between the support shaft (5) and the roller (6) takes place in a domain of hydrodynamic lubrication if the engine rpm is not less than the above mentioned predetermined rpm level. Then, utilizing the inventive rocker arm (3), the cam torque can be better confirmed to the cam torque experienced in a conventional rocker arm structure that utilizes needle bearings, even when the engine rpm is in a low or middle rpm domains. (See a diagram shown in the lower half of FIG. 5.)

[0040] According to the manufacturing method of the rocker arm of the example, the above rocker arm can be manufactured by setting the axial contact width (Wm) of the outer periphery of the support shaft (5) in contact with the inner periphery of the roller (6) and setting the inner diameter DRin of the roller (6) such that the product (PV) of a contact stress P exerted by the inner periphery of the roller (6) to the outer periphery of the support shaft (5) in contact with the roller, and a sliding speed V of the inner periphery relative to the outer periphery of the roller (6), remains in a domain of hydrodynamic lubrication even when the rpm of the engine is less than a predetermined middle level.

[0041] Next the second example of the present disclosure is explained in reference to FIGS. 10 through 13. The example is based on the following findings of the present inventor obtained in a sequence of researches:

[0042] (1) A Stribeck curve can be obtained for each of bearing-free rollers of a rocker arm having different d/D ratio, where d is the inner diameter and D is the outer diameter of the roller rotatably but directly mounted on a support shaft (FIGS. 3 and 4),

[0043] (2) Stribeck curves show that friction coefficients of the rollers decrease with the increasing ratio d/D;

[0044] (3) Given an engine rpm, Hersey Number, defined to be v/p, where is viscosity, v is the speed of the roller relative to the shaft, and p is a load per unit area, increases with the increasing ratio d/D.

[0045] (4) As shown in any of Stribeck curves, the roller can achieve a friction coefficient as large as that of a standard rocker arm (having needle bearings) even in a low rpm domain, provided that the ratio d/D is not less than a predetermined value.

[0046] From FIG. 11 sufficiently small cam torque equivalent to a roller rocker arm (acting force transmission device) having a needle bearing with engine speed of 600 rpm can be obtained when ratio d/D of an inner diameter d to an outer diameter D of the roller is not less than 0.7.

[0047] The example is achieved on the basis of the findings above. Thus, it is an object of the example to provide an acting force transmission device for use with a valve mechanism, the acting force transmission device comprising an acting force transmission member for transmitting the acting force to a valve to open/close the valve. A support shaft mounted on the acting force transmission member. An annular roller is directly mounted on the outer periphery of the support shaft. The roller is adapted to rotate when subjected to a cam force exerted by a cam onto an outer periphery of the annular roller to transmit the cam force to the acting force transmission member as the acting force. The acting force transmission device has friction performance close to that of a conventional acting force transmission device equipped with needle bearings as much as possible even in a low and a middle rpm domain.

[0048] Further object of the example is to provide a method of manufacturing the inventive acting force transmission device mentioned above.

[0049] In order to achieve the above object, in reference to FIGS. 12 through 13, there is provided in accordance another aspect of the disclosure a method of manufacturing an acting force transmission device 20 (rocker arm) that comprises: an acting force transmission member 21 for transmitting an acting force to a valve to open/close the valve; a support shaft 22 mounted on the acting force transmission member 21; and an annular roller 23 directly mounted on the outer periphery of the support shaft 22, the roller 23 adapted to rotate when subjected to a cam force exerted by a cam onto the outer periphery thereof to transmit the cam force to the acting force transmission member 21.

[0050] The method includes a step of configuring the roller 23 to have an inner diameter d and an outer diameter D such that the ratio d/D of d to D is not less than 0.7. The upper limit of the ratio d/D can appropriately be configured with dimensions, strength, etc. required for each part considered, about 0.95 for example.

[0051] The manufacturing method of the acting force transmission device for use with valve mechanism according to the example is structured as following.

[0052] The acting force transmission device 20 comprises an acting force transmission member 21 for transmitting an acting force to a valve to open/close the valve. A support shaft 22 is mounted on the acting force transmission member 21. An annular roller 23 is directly mounted on an outer periphery of the support shaft 22 and adapted to rotate when subjected to a cam force exerted by a cam and adapted to transmit the cam force to the acting force transmission member 21 as the acting force,

[0053] The method comprises a step of configuring the roller 23 such that a ratio d/D of an inner diameter d to an outer diameter D of the roller 23 is not less than 0.7.

[0054] According to the acting force transmission for use with valve mechanism 20 of the example, it is possible to realize lubrication between the inner periphery of the roller 23 and the outer periphery of the support shaft 22 near a domain of elastohydrodynamic lubrication (EHL) even at a low rpm (600 rpm for example) if the ratio d/D of the inner diameter d to the outer diameter D of the inventive roller is set to not less than 0.7 in accord with the inventor's findings, so that the inventive acting force transmission device achieves nearly the same friction performance as a conventional device equipped with needle bearings even under a middle/low engine rpm domain (FIG. 11).

[0055] According to the manufacturing method of the acting force transmission for use with valve mechanism 20 of the example, it is possible to have lubrication between the inner periphery of the roller 23 and the outer periphery of the support shaft 22 take place in a domain close to elastohydrodynamic lubrication (EHL) by setting the ratio d/D of the inner diameter d and outer diameter D of the inventive roller 23 to not less than 0.7 even under a middle/low engine rpm domain (600 rpm for example).

[0056] The foregoing description has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.