Patent Application
20090000579
The present disclosure relates to valve trains, and more particularly to a valve train having overload features.
The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Internal combustion engines typically include an arrangement of pistons and cylinders located within an engine block. In a four stroke engine, each cylinder has at least two valves. These valves control the flow of air to the combustion cylinders and allow for venting of combustion exhaust gasses. A simple valve arrangement includes an intake valve and an exhaust valve, each actuated by a valve train. The valve train typically includes a camshaft with cam followers that actuate respective pushrods and rocker assemblies. The rocker assemblies in turn actuate respective intake and exhaust valves.
Though unlikely, it is possible that during operation of the valve train, a failure may occur in one of the various components. One such failure could include a mistimed event. A mistimed event may occur when the intake valve in an engine employing cylinder deactivation is inadvertently reactivated before the activation of the exhaust valve. In this scenario, the intake valve is forced open against combustion and exhaust gasses under large amounts of pressure. These gasses may create as much as 19.5 kN of force and cause failures in expensive and/or difficult to replace components within the valve train or engine. Accordingly, it is desirable that the valve train is designed to fail at controlled locations in order to prevent more extensive damage to the valve train and/or engine during a mistiming event
In one aspect of the present invention, a valve train for use in an engine is provided. The valve train includes a rocker arm assembly having a valve side arm and a cam side arm. A valve is coupled to the engine and is in contact with the valve side arm. A pushrod is reciprocatable by a camshaft and is in contact with the cam side arm. An overload feature is located on at least one of either the rocker arm assembly or the pushrod. The overload feature has a reduced cross-sectional area calibrated to activate at a predefined load.
In another aspect of the present invention, the overload feature is located on the pushrod.
In yet another aspect of the present invention, the pushrod includes a first wall portion with a first thickness and a second wall portion within the overload feature with a second thickness, and wherein the second thickness is less than the first thickness.
In yet another aspect of the present invention, the second wall portion is located proximate to an end of the pushrod that contacts the cam side lever arm.
In yet another aspect of the present invention, the rocker arm assembly includes an annular extension that defines a bore, and the overload feature includes a first slot and a second slot located on the annular extension.
In yet another aspect of the present invention, the first slot and the second slot are located on opposite sides of the annular extension.
In yet another aspect of the present invention, the first slot reduces a cross-sectional area through the annular extension a first amount and the second slot reduces a cross-sectional area through the annular extension a second amount that is different than the first amount.
In yet another aspect of the present invention, the rocker arm assembly further includes a bolt that couples the rocker arm assembly to the engine, and wherein the overload feature is located on the bolt.
In yet another aspect of the present invention, the bolt includes a cylindrical shaft having a portion with a first cross-sectional area and a portion within the overload feature and having a second cross-sectional area less than the first cross-sectional area.
In still another aspect of the present invention, a rocker arm assembly for use in a valve train having a pushrod and a valve is provided. The rocker arm assembly includes a rocker body, a valve side arm extending from the rocker body and in contact with the valve, and a cam side arm extending from the rocker body opposite the valve side arm and in contact with the pushrod. A slot is located in the cam side arm and has a size calibrated such that the cam side arm will fail at a predefined load.
In yet another aspect of the present invention, the slot is circular.
In yet another aspect of the present invention, the circular slot is located in a first surface of the rocker arm and the pushrod contacts a second surface of the rocker arm opposite the first surface.
In yet another aspect of the present invention, the circular slot is aligned with the pushrod.
In yet another aspect of the present invention, the rocker arm assembly further includes a pair of side slots extending from the circular slot.
In yet another aspect of the present invention, the side slots extend from opposite sides of the circular slot along the length of the second rocker arm.
In yet another aspect of the present invention, the rocker arm assembly further includes a fluid port formed in the top surface of the second rocker arm and located within the circular slot.
In yet another aspect of the present invention, a failure occurs when the pushrod pushes through the circular slot of the second rocker arm.
In yet another aspect of the present invention, the second rocker arm grips the pushrod if the pushrod pushes through the circular slot in the second rocker arm during a failure.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
Referring now to
The internal combustion engine 10 also includes a valve train 20 according to the principles of the present invention. The valve train 20 includes a camshaft 22 which is received and supported for rotation in a bore 24 within the engine block 12. In the particular example provided, the cylinders 14 are arranged in a V-type arrangement and the camshaft 22 is located at the bottom of the “V”. However, it should be appreciated that various other cylinder 14 and camshaft 22 arrangements may be employed with the present invention.
The valve train 20 also includes a pushrod 26, a rocker arm assembly 28, and at least one inlet valve 29. The camshaft 22 includes an inlet cam 30 that engages a hydraulic roller lifter 32 at an end of the pushrod 26. The pushrod 26 is coupled at an opposite end thereof to the rocker assembly 28. The rocker assembly 28 is in turn coupled to the inlet valve 29. The inlet valve 29 is biased by a biasing member 31, illustrated as a spring in the particular example provided.
During operation of the valve train 20, rotation of the camshaft 22 and the inlet cam 30 reciprocates the hydraulic roller lifter 32 and the pushrod 26. The pushrod 26 then actuates the rocker assembly 28 such that the rocker assembly 28 oscillates on a supporting shaft 33 about a pivot axis 34. The pivot axis 34 is parallel to the axis of the camshaft 24. As the rocker assembly 28 is actuated by the reciprocating pushrod 26, the rocker assembly 28 opens and closes the inlet valve 29. The inlet valve 29 is in communication with the cylinder 14 and allows air intake into the cylinder 14 as the camshaft 22 rotates and the pushrod 26 reciprocates.
An exhaust valve train 36 is also illustrated with the engine 12. The exhaust valve train 36 includes an exhaust pushrod 38 (the top of which is shown) that is reciprocated by an exhaust cam 40 on the camshaft 22. The exhaust pushrod 38 in turn oscillates an exhaust rocker arm 42, which reciprocates an exhaust valve 44. The exhaust valve train 36 operates in a manner similar to the valve train 20, though the opening and closing of the exhaust valve 44 is out of synch with the opening and closing of the pair of inlet valves 29.
With reference to
The pushrod 26 also includes an overload feature 60. The overload feature 60 includes a reduction in the thickness of the wall 46 of the pushrod 26 along a second wall portion 49 of the pushrod 26. Accordingly, the wall 46 of the overload feature 60 has a second thickness, indicated by reference number 62, through the second wall portion 49 that is less than the first thickness 54. In this way, the cross-sectional area through the overload feature 60 is less than the cross-sectional area through the remainder of the pushrod 26. In the particular example provided, the thickness of the wall 46 is reduced through the overload feature 60 by removing material from the outer surface 50 of the wall 46. Alternatively, the thickness of the wall 46 may be reduced through the overload feature 60 by removing material from the inner surface 48 of the wall 46. The overload feature 50 acts as a “fuse” for the valve train 20. More specifically, the reduced cross-sectional area of the wall 46 at the overload feature 60 (the second wall portion 49) has a compressive strength less than that of the wall 46 along the rest of the pushrod 26 (the first wall portion 47). Accordingly, if the pushrod 26 is subjected to a predefined compressive load or force that exceeds the strength of the pushrod 26 through the overload feature 60, then the overload feature 60 activates and the pushrod 26 will separate or bend at a point within the overload feature 60. The load or force at the overload feature 60 that results in activation may be calibrated by adjusting the cross-sectional area of the wall 46 at the overload feature 60. The overload feature 60 is preferably located proximate to the rocker arm assembly 28 such that during activation of the overload feature 60, the pushrod 26 may be extracted from the engine 10 with minimal difficulty.
Turning now to
The rocker arm assembly 28 further includes an overload feature 84 located on the cam side lever arm 76. The overload feature 84 includes a circular slot 86 formed in the top surface 78 on the cam side lever arm 76. The circular slot 86 encircles the fluid port 82 and is positioned such that the circular slot 86 is approximately aligned with the end of the pushrod 26 on the bottom surface 80 of the cam side lever arm 76. A pair of side slots 88A and 88B extend out from the circular slot 86 on opposite sides. The side slots 88A and 88B are preferably positioned such that they extend along the length of the cam side lever arm 76. In the particular example provided, the side slot 88A extends to an end or tip of the cam side lever arm 76 and the side slot 88B extends towards the rocker body 70. The overload feature 84 acts as a “fuse” for the valve train 20. More specifically, the slots 86, 88A, and 88B cooperate to reduce the cross-sectional area of the cam side lever arm 76 thereby reducing the strength of the cam side lever arm 76 through that cross-sectional area. Accordingly, if the pushrod 26 is subjected to a predefined compressive load that exceeds the strength of the cam side lever arm 76 at the overload feature 84, then the overload feature 84 will activate and the pushrod 26 will punch through the cam side lever arm 76 near the circular slot 86. The cam side lever arm 76 will also preferably separate or bend between the side slot 88B and the rocker body 70. During such an activation, the cam side lever arm 76 will grip the pushrod 26 as the pushrod 26 pushes through the cam side lever arm 76, thereby preventing the pushrod 26 from coming free within the engine 10. The depths or sizes of the slots 86, 88A, and 88B into the cam side lever arm 76 may be sized such that the pushrod 26 will push through the cam side lever arm 76 at a calibrated, predefined load or force.
With reference to
The rocker arm assembly 90 also includes an overload feature 104 located on the annular extension 94A. It should be appreciated that the overload feature 104 may alternatively be located on the annular extension 94B or on both annular extensions 94A and 94B without departing from the scope of the present invention. The overload feature 104 includes a first slot 106A and a second slot 106B. The slots 106A and 106B are located on opposite sides of the annular extension 94A. Each slot 106A and 106B extend from an outer edge 107 of the annular extension 94A radially inward towards the pivot axis 34. The slots 106A and 106B reduce a wall thickness of the annular extension 94A a predefined amount. The overload feature 104 acts as a “fuse” for the valve train 20. More specifically, the reduced cross-sectional area of the annular extension 94A at the overload feature 104 has a strength less than that of the rest of the annular extension 94A. Accordingly, if during a mistiming event the pushrod 26 subjects the rocker arm assembly 90 to a load or force that exceeds the strength of the annular extension 94A through the overload feature 104, then the overload feature 104 will activate and accordingly the annular extension 94A will separate or bend at a point within the overload feature 104. The amount of load or force that results in activation at the overload feature 104 may be calibrated by adjusting the depths or sizes of the slots 106A and 106B which in turn change the cross-sectional area through the annular extension 94A and therefore the strength through that cross-sectional area. In a preferred embodiment, the slots 106A and 106B have different depths and sizes such that the first slot 106A reduces the cross-sectional area or wall thickness of the annular extension 94A a first amount and the second slot 106B reduces the cross-sectional area or wall thickness of the annular extension 94A a second amount that is different than the first amount. Accordingly, the annular extension 94A will separate at one of the slots 106A or 106B before separating at the other. Therefore, the annular extension 94A will stay attached at whichever of the cross-sectional areas through the slots 106A or 106B has greater strength. This feature prevents a portion of the annular extension 94A from coming completely free of the rocker arm assembly 28 and moving loose within the engine 10.
Turning now to
The center bolt 110 further includes an overload feature 120 located on the cylindrical shaft 112. The overload feature 120 includes a reduction in the diameter of the cylindrical shaft 112. Accordingly, the cylindrical shaft 112 through the overload feature 120 has a second diameter, indicated by reference number 122, that is less than the first diameter 118 such that the cross-sectional area through the overload feature 120 is less than the cross-sectional area through the remainder of the cylindrical shaft 112. The overload feature 120 acts as a “fuse” for the valve train 20. More specifically, the reduced cross-sectional area of the cylindrical shaft 112 at the overload feature 120 has a strength less than that along the rest of the cylindrical shaft 112. Accordingly, if during a mistiming event the pushrod 26 subjects the rocker arm assembly 90 and therefore the center bolt 110 to a load or force that exceeds the strength of the center bolt 110 through the overload feature 120, then the overload feature is activated and accordingly the center bolt 110 will break or separate at a point within the overload feature 120. The amount of load or force that results in activation at the overload feature 120 may be calibrated by adjusting the cross-sectional area of the cylindrical shaft 112 at the overload feature 120.
Preferably, only one of the overload features 60, 84, 104, and 120 described throughout the several views will be employed in any given application. However, it should be appreciated that any number or combination may be employed without departing from the scope of the present invention.
The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
