Engine having variable lift valvetrain

A rocker arm may include a first arm defining a first longitudinal bore and a second arm defining a second longitudinal bore. The rocker arm may house a locking assembly including a first actuation pin extending through a first radial passage in the rocker arm, a second actuation pin extending through a second radial passage in the rocker arm, and a first lock pin located in the first longitudinal bore between the first and second actuation pins. An actuation assembly may be engaged with the first and second actuation pins and may be linearly displaceable between first and second actuation positions. The first and second arms may be rotatable relative to one another when the actuation assembly is in the first actuation position and may be fixed for rotation with one another when the actuation assembly is in the second actuation position.

FIELD

The present disclosure relates to engines having variable valve lift mechanisms.

BACKGROUND

Engine assemblies may include multi-step lift mechanisms to provide variable valve lift during engine operation. The multi-step lift mechanism may be actuated by a hydraulic system to switch between the various lift modes. The use of hydraulic actuation may increase oil demand for an engine, resulting in increased oil pump size and/or the inclusion of additional hydraulic systems.

SUMMARY

An engine assembly may include an engine structure, a camshaft, a rocker arm, a locking assembly and an actuation assembly. The camshaft may be rotationally supported on the engine structure and may define a longitudinally extending rotational axis and may include first and second cam lobes. The rocker arm may be rotationally supported on the engine structure.

The rocker arm may include first and second arms. The first arm may be engaged with the first lobe of the camshaft and a first engine valve and may define a first longitudinal bore. The second arm may be adjacent the first arm and engaged with the second lobe of the camshaft and may define a second longitudinal bore. The locking assembly may include a first actuation pin extending through a first radial passage in the rocker arm, a second actuation pin extending through a second radial passage in the rocker arm, and a first lock pin located in the first longitudinal bore between the first and second actuation pins. The actuation assembly may be linearly displaceable between first and second actuation positions and may include a first actuation member engaged with the first actuation pin and a second actuation member engaged with the second actuation pin. The first and second arms may be rotatable relative to one another when the actuation assembly is in the first actuation position and may be fixed for rotation with one another by the first lock pin when the actuation assembly is in the second actuation position.

The rocker arm may additionally include a third arm engaged with a third lobe of the camshaft and a second engine valve and may define a third longitudinal bore. The locking assembly may include a second lock pin located in the second longitudinal bore. The second lock pin may be located in the second and third longitudinal bores to fix the second and third arms for rotation with one another when the actuation assembly is in the second actuation position.

DETAILED DESCRIPTION

Examples of the present disclosure will now be described more fully with reference to the accompanying drawings. The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

With reference toFIGS. 1 and 2, an engine assembly10is illustrated. The engine assembly10may include an engine structure12, a camshaft assembly14, a valve actuation assembly16and valves18. The camshaft assembly14(FIG. 2) has been removed from the engine structure inFIG. 1in order to better illustrate the valve actuation assembly16. In the present non-limiting example, the engine assembly10is shown as an overhead camshaft engine. However, the present disclosure is not limited to overhead camshaft arrangements and applies equally to cam-in-block arrangements where a single camshaft includes both intake and exhaust lobes. It is further understood that the present disclosure applies equally to intake and exhaust valve actuation assemblies.

The engine structure12may include a cylinder head rotationally supporting the camshaft assembly14and supporting the valve actuation assembly16and valves18. The camshaft assembly14may include a camshaft20and a cam phaser assembly22. The camshaft20may form a concentric camshaft including first and second shafts24,26and first and second sets of lobes28,30. The second shaft26may be coaxial with and rotatable relative to the first shaft24. More specifically, the second shaft26may be rotationally supported within the first shaft24.

The first set of lobes28may be fixed for rotation with the first shaft24and the second set of lobes30may be rotatable relative to the first shaft24and fixed for rotation with the second shaft26. In the present non-limiting example, the first and second sets of lobes28,30are illustrated as either all intake lobes or all exhaust lobes. However, as indicated above, the present disclosure is not limited to such arrangements and applies equally to configurations where the lobes form both intake and exhaust lobes.

The cam phaser assembly22may be coupled to the camshaft20to rotate the first and second lobes28,30relative to one another. However, the present disclosure is not limited to engines including cam phasers. It is further understood that the present disclosure is not limited to concentric camshaft arrangements and applies equally to camshafts where the first and second lobes28,30are rotationally fixed relative to one another.

With reference toFIGS. 1 and 3, the valve actuation assembly16may include a valve lift assembly32and an actuation assembly34. The valve lift assembly32may include a shaft36mounted to the engine structure12, rocker arms38rotationally supported on the shaft36, and a locking assembly40located within the rocker arms38. The shaft36may define a longitudinal bore42and arcuate slots44extending radially through an outer circumferential surface into the bore42.

With additional reference toFIGS. 4-6, the rocker arms38may each include first, second, and third arms46,48,50. The second arm48may be located axially between the first and third arms46,50. The first and third arms46,50may be engaged with the first lobes28of the camshaft20and the second arms48may be engaged with the second lobes30of the camshaft20. The first, second, and third arms46,48,50may include mounting bores52,54,56, respectively, at first ends thereof and the first and third arms46,50may include valve engagement regions58,60, respectively, at second ends thereof. The shaft36may extend through the mounting bores52,54,56and rotationally support the rocker arm38thereon. While illustrated as including three arms, it is understood that the present disclosure is not limited to such arrangements. By way of non-limiting example, the present disclosure applies equally to arrangements having two arms.

Additionally, the first arm46may define a first longitudinal bore62, the second arm48may define a second longitudinal bore64, and the third arm50may define a third longitudinal bore66. The shaft36, mounting bores52,54,56and first, second, and third longitudinal bores62,64,66may be parallel to the rotational axis of the camshaft20. The locking assembly40may be located in the first, second and third longitudinal bores62,64,66. The locking assembly40may include first and second actuation pins68,70and first, second and third lock pins72,74,76. The first and second actuation pins68,70may be perpendicular to the first, second and third lock pins72,74,76. The first actuation pin68may extend through a first radial passage78in the rocker arm38and the second actuation pin70may extend through a second radial passage80in the rocker arm38. In the present non-limiting example, the first radial passage78is defined in the first arm46and extends into the first longitudinal bore62and the second radial passage80is defined in the third arm50and extends into the third longitudinal bore66. The first and second radial passages78,80may be aligned with corresponding slots44in the shaft36.

The first lock pin72may be located between and engaged with the first actuation pin68and the second lock pin74. The third lock pin76may be located between and engaged with the second actuation pin70and the second lock pin74. In the present non-limiting example, the first actuation pin68includes a ramped (angled) surface82engaged with a ramped (angled) surface84on a first end of the first lock pin72to translate radial displacement of the first actuation pin68into axial displacement of the first lock pin72. Similarly, the second actuation pin70includes a ramped surface86engaged with a ramped surface88on a first end of the third lock pin76to translate radial displacement of the second actuation pin70into axial displacement of the third lock pin76. A first end of the second lock pin74may be engaged with the first lock pin72and a second end of the second lock pin74may be engaged with the third lock pin76.

With reference toFIGS. 1 and 3, the actuation assembly34may include an actuator90, an actuation rod92, first and second actuation members94,96, first and second stop members98,100and biasing members102. The actuator90may be engaged with the actuation rod92and may provide linear displacement of the actuation rod92. In the present non-limiting example, the actuator90is an electric motor. The use of an electric motor may provide a more robust system that is insensitive to oil pressure fluctuations (i.e., at start-up/shutdown or hot/cold operating conditions). However, the present disclosure is not limited to such arrangements and applies equally to any actuator capable of providing linear displacement of the actuation rod92. The actuation members94,96, first and second stop members98,100and biasing members102may be similar along the actuation rod92. Therefore, a single first actuation member94, second actuation member96, first stop member98, second stop member100and biasing member102will be described.

With reference toFIGS. 4-6, the first and second actuation members94,96may be located on the actuation rod92between the first and second stop members98,100and the biasing member102may be located between the first and second actuation members94,96. The first and second stop members98,100may be axially fixed to the actuation rod92. The first and second actuation members94,96may be slidably disposed on the actuation rod92between the first and second stop members98,100. The biasing member102may urge the first and second actuation members94,96outward from one another. More specifically, the biasing member102may urge the first actuation member94toward the first stop member98and the second actuation member toward the second stop member100. The first actuation member94may include a ramped (angled) surface104expanding radially outward along its axial extent in a direction from the first stop member98to the second stop member100and the second actuation member96may include a ramped surface106expanding radially outward along its axial extent in a direction from the second stop member100to the first stop member98.

During operation, the rocker arms38may be switched between first and second lift modes by the actuation assembly34. The first lift mode may provide a first valve opening and the second lift mode may provide a second valve opening that is different than the first valve opening. In the present non-limiting example, the first lobes28may displace the first and third arms46,50relative to the second arm48during the first lift mode and the second lobes30may displace the first, second and third arms46,48,50with one another during the second lift mode. The default (initial) lift mode may be varied by changing the starting location of the actuation rod92.

Linear displacement of the actuation rod92may switch the rocker arms38between first and second lift modes. The first lift mode is illustrated inFIG. 4and the second lift mode is illustrated inFIG. 6.FIG. 5illustrates a transition between the first and second lift modes. As seen inFIG. 4, the first and second actuation pins68,70, and the first, second and third lock pins72,74,76may be in a first lock position during the first lift mode. In the first lock position, the end of the first lock pin72engaged with the second lock pin74may be located outside of the second longitudinal bore64and the end of the second lock pin74engaged with the third lock pin76may be located outside of the third longitudinal bore66to provide relative rotation between the first, second and third arms46,48,50.

As seen inFIG. 6, the first and second actuation pins68,70, and the first, second and third lock pins72,74,76may be in a second lock position during the second lift mode. In the second lock position, the first lock pin72may be located in both the first and second longitudinal bores62,64and the second lock pin74may be located in both the second and third longitudinal bores64,66to fix the first, second and third arms46,48,50for rotation with one another. More specifically, the end of the first lock pin72engaged with the second lock pin74may be located within the second longitudinal bore64and the end of the second lock pin74engaged with the third lock pin76may be located within the third longitudinal bore66when in the second lock position.

The first actuation pin68may be located radially outward relative to the first lock position when in the second lock position and the second actuation pin70may be located radially outward relative to the second lock position when in the first lock position. The outward radial displacement of the first actuation pin68may displace the first, second and third lock pins72,74,76axially to switch from the first lift mode to the second lift mode. The axial displacement of the first, second and third lock pins72,74,76may displace the second actuation pin70radially inward. The first actuation pin68may be displaced by the first actuation member94. The actuation rod92may be displaced from a first actuation position to a second actuation position to displace the locking assembly40from the first lock position to the second lock position. The actuation rod92may be displaced from the second actuation position to the first actuation position to return the locking assembly40to the first lock position.

In the first actuation position, seen inFIG. 4, the first actuation pin68may be engaged with a first region of the first actuation member94and the second actuation pin70may be engaged with a first region of the second actuation member96. In the second actuation position, seen inFIG. 6, the actuation rod92may be linearly displaced relative to the first actuation position, displacing the first and second actuation members94,96relative to the first and second actuation pins68,70and providing engagement between the first actuation pin68and a second region of the first actuation member94and engagement between the second actuation pin70and a second region of the second actuation member96.

The second region of the first actuation member94may have a greater radial extent than the first region thereof and the second region of the second actuation member96may have a lesser radial extent than the first region thereof. As a result, the first actuation member94may displace the first actuation pin68radially outward as the first actuation pin68travels along the ramped surface104from the first region to the second region. The outward radial displacement of the first actuation pin68displaces the first, second and third lock pins72,74,76into the second lock position and displaces the second actuation pin70radially inward. When the actuation rod92is displaced back to the first actuation position, the first, second and third lock pins72,74,76may be returned to the first lock position by the second actuation pin70.

As seen inFIG. 5, the actuation assembly34may provide a transition between the first and second actuation positions when the rocker arm38is in the second lift mode and the first and third arms46,50are displaced relative to the second arm48. When first and third arms46,50are displaced relative to the second arm48, the first and third longitudinal bores62,66may not be aligned with the second longitudinal bore64due to an engagement with a peak region of the first lobes28, preventing axial displacement of the first lock pin72into the second longitudinal bore64and displacement of the second lock pin74into the third longitudinal bore66. When the actuation rod92is displaced to the second actuation position during the misalignment condition discussed above, the first actuation member94may remain in the first actuation position.

The displacement of the action rod92displaces the first and second stop members98,100and the second actuation member96, compressing the biasing member102and urging the first actuation member94outward against the first actuation pin68. When the first, second and third longitudinal bores62,64,66are aligned again (i.e., when the first and third arms46,50are engaged with a base circle region of the first lobes28), the first actuation member94is displaced by the biasing member102and forces the first actuation pin68radially outward, displacing the first, second and third lock pins72,74,76and the second actuation pin70to the second lock position.

The valve actuation assembly16may be assembled using the tool120illustrated inFIGS. 7-10. The tool120may define a rocker arm housing122receiving the rocker arm38and a coupling mechanism124. The rocker arm38may contain the locking assembly40before being located in the rocker arm housing122. The rocker arm38may be secured to the tool120via an engagement between the locking assembly40and the coupling mechanism124of the tool120.

The mounting bores52,54,56of the first, second and third arms46,48,50may be aligned with one another and the second longitudinal bore64of the second arm48may be offset from the first and third longitudinal bores62,66. The first lock pin72may be located in the first longitudinal bore62and the third lock pin76may be in the third longitudinal bore66when the rocker arm38is in the rocker arm housing122. The first and third lock pins72,76may initially extend inward from the first and third longitudinal bores62,66toward one another. The second lock pin74may be located in the second longitudinal bore64.

In the present non-limiting example, the rocker arm38may define additional radial passages126,128opposite the first and second radial passages78,80, respectively. When the locking assembly40is secured in the rocker arm housing122, the first actuation pin68may extend through the radial passage126and the second actuation pin70may extend through the radial passage128.

The coupling mechanism124may include actuation member130and first and second gear members132,134. The actuation member130may include a shaft136having a helical gear138engaged with the first gear member132and the first gear member132may be engaged with the second gear member134. The first gear member132may include a first arm140engaged with the first lock pin72and the second gear member134may include a second arm142engaged with the third lock pin76.

During assembly, the tools120and rocker arms38may be positioned relative to the engine structure12to provide alignment between bores (not shown) in the engine structure12and the mounting bores52,54,56of the rocker arms38. The shaft42may then be inserted into the bores in the engine structure12and the mounting bores52,54,56of the rocker arms38. The actuation assembly34may be located within the shaft bore42before or after installation of the shaft36.

After the shaft36is inserted into the bores in the engine structure12and the mounting bores52,54,56of the rocker arms38, the actuation member130may be depressed, resulting in rotation of the first and second gear members132,134from a first position (FIG. 9) to a second position (FIG. 10). As the first and second gear members132,134are rotated, the first and second arms140,142displace the first and third lock pins72,76outward from one another and the first and second actuation pins68,70radially into the shaft bore42. The second arm48may then be rotated to provide alignment between the first, second and third longitudinal bores62,64,66. The assembly tool120may then be removed from the rocker arm38.

The terms “first”, “second”, etc. are used throughout the description for clarity only and are not intended to limit similar terms in the claims.