Engine variable camshaft timing phaser with planetary gear set

An engine variable camshaft timing phaser (10) includes a sprocket (12), three ring gears (26, 28, 30), multiple planet gears (24), and a sun gear (22). The sprocket (12) receives rotational drive input from an engine crankshaft. One or more of the three ring gear(s) (26, 28, 30) receives rotational drive input from the sprocket (12) and rotates with the sprocket (12), and the remaining ring gear(s) (26, 28, 30) transmit rotational drive output to an engine camshaft (62). All three of the ring gears (26, 28, 30) engage with the planet gears (24). And the sun gear (22) also engages with the planet gears (24). In operation, relative rotational speeds between the sprocket (12) and the sun gear (22) causes the engine camshaft (62) to advance or retard engine valve opening and closing.

TECHNICAL FIELD

The present disclosure generally relates to variable valve timing (VVT) for internal combustion engines, and more particularly relates to variable camshaft timing (VCT) phasers.

BACKGROUND

Variable valve timing (VVT) systems are commonly used with internal combustion engines—such as those found in automobiles—for controlling intake and exhaust valve opening and closing. The VVT systems can help improve fuel economy, reduce exhaust emissions, and enhance engine performance. One type of VVT system employs a variable camshaft timing (VCT) phaser. In general, VCT phasers dynamically adjust the rotation of engine camshafts relative to engine crankshafts in order to advance or retard the opening and closing movements of intake and exhaust valves.

SUMMARY

In one embodiment, an engine variable camshaft timing phasing includes a sprocket, a first ring gear, multiple planet gears, a sun gear, a second ring gear, and a third ring gear. The sprocket receives rotational drive input from an engine crankshaft. The first ring gear receives rotational drive input from the sprocket. Each of the planet gears is engaged with the first ring gear. The sun gear is engaged with each of the planet gears and is driven by an electric motor. The second ring gear is engaged with each of the planet gears, and the third ring gear is engaged with each of the planet gears. In operation, relative rotational movements between the sprocket and the sun gear caused by the electric motor advances or retards the accompanying engine valve opening and closing.

In another embodiment, an engine variable camshaft timing phaser includes a sprocket, three ring gears, multiple planet gears, and a sun gear. One or more of the ring gear(s) receives rotational drive input from the sprocket. Each of the planet gears is engaged with all three of the ring gears. And the sun gear is engaged with each of the planet gears. Loads transmitted to each of the planet gears from the ring gears are substantially balanced across an axial extent of each of the planet gears. The substantially balanced loads preclude misalignment of the planet gears relative to the ring gears.

In yet another embodiment, an engine variable camshaft timing phaser includes a sprocket, a first ring gear, multiple planet gears, a sun gear, a second ring gear, a third ring gear, and a plate. The sprocket receives rotational drive input from an engine crankshaft. The first ring gear receives rotational drive input from the sprocket. Each of the planet gears makes teeth-to-teeth meshing with the first ring gear. The sun gear makes teeth-to-teeth meshing with each of the planet gears, and the sun gear is driven by an electric motor. The second ring gear makes teeth-to-teeth meshing with each of the planet gears, and the third ring gear makes teeth-to-teeth meshing with each of the planet gears. The plate receives rotational drive input from the second ring gear and receives rotational drive input from the third ring gear. The plate transmits rotational drive output to an engine camshaft. The first ring gear and each of the planet gears mesh at a first axial section of each of the planet gears. Similarly, the second ring gear and each of the planet gears mesh at a second axial section of each of the planet gears. And the third ring gear and each of the planet gears mesh at a third axial section of each of the planet gears. The first axial section of each of the planet gears is situated in-between the second and third axial sections of each of the planet gears. In operation, in order to angularly displace the engine camshaft in a first direction relative to the sprocket, the electric motor drives the sun gear at a greater rotational speed than the rotational speed of the sprocket. And in order to angularly displace the engine camshaft in a second direction relative to the sprocket, the electric motor drives the sun gear at a lesser rotational speed than the sprocket.

DETAILED DESCRIPTION

The figures illustrate embodiments of a variable camshaft timing phaser10(hereafter “phaser”) that is equipped in an internal combustion engine for controlling intake and exhaust valve opening and closing in the engine. More particularly, the phaser10dynamically adjusts the rotation of the engine's camshaft relative to the engine's crankshaft in order to advance or retard the opening and closing movements of the intake and exhaust valves. Internal combustion engines are perhaps most commonly found in automobiles, but are also found in other applications. While described in greater detail below, in general the phaser10has a planetary gear set with three ring gears that more readily balance loads across planet gears and hence preclude misalignment of the planet gears. In some instances this means that a carrier assembly for supporting the planet gears may be omitted. As an aside, the terms axially, radially, circumferentially, and their related forms are used herein with reference to the generally circular and annular and cylindrical components of the phaser10, unless otherwise indicated.

The phaser10is a multi-piece assembly with components that work together to transfer rotation from the accompanying engine's crankshaft and to the engine's camshaft, and that can work together to angularly displace the camshaft relative to the crankshaft for advancing and retarding engine valve opening and closing. The phaser10can have different designs and constructions depending upon, among other factors, the application in which the phaser is employed, production and manufacturing considerations and capabilities, and the crankshaft and camshaft that it works with. In the embodiment presented inFIGS. 1 and 2, for example, the phaser10includes a sprocket12, a planetary gear set14, and a plate16.

The sprocket12receives rotational drive input from the engine's crankshaft and rotates about an axis X1. A timing chain or a timing belt can be looped around the sprocket12and around the crankshaft so that rotation of the crankshaft translates into rotation of the sprocket via the chain or belt. Other techniques for transferring rotation between the sprocket12and crankshaft are possible. At an exterior, the sprocket12has a set of teeth18for mating with the timing chain, with the timing belt, or with another component. In different examples, the set of teeth18can include thirty-eight individual teeth, forty-two individual teeth, or some other quantity of teeth spanning continuously around the circumference of the sprocket12. In the embodiment presented here, the sprocket12has a housing20spanning axially from the set of teeth18. The housing20is a cylindrical wall that surrounds parts of the planetary gear set14. Near its terminal and open end, the housing20has several cutouts21that are spaced circumferentially therearound.

Still referring toFIGS. 1 and 2, the planetary gear set14includes a sun gear22, planet gears24, a first ring gear26, a second ring gear28, and a third ring gear30. The sun gear22is connected to an electric motor32(FIG. 1) and is driven by the electric motor for rotation about the axis X1. The connection between the sun gear22and the electric motor32can be made in a way that transmits rotation from the electric motor to the sun gear; a pin and slot is one example of such a connection. The sun gear22engages with the planet gears24and has a set of teeth34at its exterior for making direct teeth-to-teeth meshing with the planet gears. In different examples, the set of teeth34can include twenty-six individual teeth, thirty-seven individual teeth, or some other quantity of teeth spanning continuously around the circumference of the sun gear22. In the embodiment presented here, the sun gear22is an external spur gear, but could be another type of gear. A cylindrical wall36spans from the set of teeth34for interconnecting with the electric motor32.

As described in greater detail below, the planet gears24rotate about their individual rotational axes X2when in the midst of bringing the engine's camshaft to and from its advanced and retarded angular positions. When not advancing or retarding, the planet gears24revolve together around the axis X1with the sun gear22and with the ring gears26,28,30. In the embodiment presented here, there are a total of three discrete planet gears24that are similarly designed and constructed with respect to one another, but there could be other quantities of planet gears such as two or four or six. However many there are, each of the planet gears24can engage with all three of the first, second, and third ring gears26,28,30, and each planet gear can have a set of teeth38at its exterior for making direct teeth-to-teeth meshing with the ring gears. In different examples, the set of teeth38can include twenty-one individual teeth, or some other quantity of teeth spanning continuously around the circumference of each of the planet gears24. The set of teeth38at each planet gear24spans axially across the respective planet gear for an axial width W. The teeth38can extend fully across the total axial extent of each planet gear24as illustrated, though need not.

To hold the planet gears24in place at the interior of the phaser10, a carrier assembly40may be provided. But as set forth below, in some embodiments the carrier assembly40may be omitted. When provided, the carrier assembly40can include a first plate42at one end, a second plate44at the other end, and cylinders46linking the plates for making a connection between them—these items are perhaps depicted best inFIG. 4. Bolts48fasten with internal threads of the cylinders46, and bolts50fasten with pins51(FIG. 6) that mount the planet gears24and serve as a hub. And although not illustrated, washers can be inserted in-between the components of the carrier assembly40. Still, in other embodiments not depicted, the first and second plates could be matching halves that come together for connection without discrete cylinders, or the first and second plates could be unitary extensions of each other.

Referring now particularly toFIG. 2, the first ring gear26receives rotational drive input from the sprocket12so that the first ring gear and sprocket rotate together about the axis X1in operation. In this embodiment, the first ring gear26and sprocket12are connected together. The connection can be made in different ways, including by the example illustrated inFIGS. 1 and 2with the cutouts21and tabs52. The tabs52are radially-outwardly projections of the first ring gear26and are inserted into the cutouts21. For every cutout21, there can be corresponding tab52. Still, other connections could involve bolts, rivets, and/or welds, or the first ring gear26could be a unitary extension of the sprocket12. The phrases “rotational drive input” and “rotational drive output” as used herein are intended to encompass these connection and unitary possibilities. The first ring gear26engages with the planet gears24and has a set of teeth54at its interior for making direct teeth-to-teeth meshing with the planet gears24. The teeth54mesh with the teeth38of the planet gears24along a first axial section S1of each planet gear. Unlike previously-described sets of teeth, the set of teeth54project radially-inwardly relative to the annular and disk-like shape of the first ring gear26. In different examples, the set of teeth54can include eighty individual teeth, or some other quantity of teeth spanning continuously around the circumference of the first ring gear26. In the embodiment presented here, the first ring gear26is an internal spur gear, but could be another type of gear. And in installation, the first ring gear26is sandwiched axially between the second and third ring gears28,30, and is in this sense the middle ring gear.

The second ring gear28is connected to the plate16and drives rotation of the plate about the axis X1. The connection can be made in different ways, including by the example ofFIGS. 1 and 2with bolts56. There can be three bolts56fastened through the second ring gear28and into the plate16and spaced around their circumferences. Still, as before, other connections could involve more or less bolts, rivets, and/or welds, or the second ring gear28could be a unitary extension of the plate16. The second ring gear28engages with the planet gears24and has a set of teeth58at its interior for making direct teeth-to-teeth meshing with the planet gears. The teeth58mesh with the teeth38of the planet gears24along a second axial section S2of each planet gear. The set of teeth58project radially-inwardly relative to the annular and disk-like shape of the second ring gear28. In different examples, the set of teeth58can include seventy-seven individual teeth, or some other quantity of teeth spanning continuously around the circumference of the second ring gear28. With respect to each other, the number of teeth between the first and second ring gears26,28can differ by a multiple of the number of planet gears24. So for instance, the set of teeth54can include eighty individual teeth, while the set of teeth58can include seventy-seven individual teeth—a difference of three individual teeth for the three planet gears24in this example. In another example with six planet gears, the set of teeth54could include seventy individual teeth, while the set of teeth58could include eighty-two individual teeth. Satisfying this relationship furnishes the advancing and retarding capabilities by imparting relative rotational movement and relative speed between the first and second ring gears26,28. In the embodiment presented here, the second ring gear28is an internal spur gear, but could be another type of gear. And in installation as shown best inFIG. 2, the second ring gear28is situated on the camshaft-side of the phaser10relative to the other two ring gears26,30.

Like the second ring gear28, the third ring gear30is connected to the plate16and drives rotation of the plate about the axis X1. The connection can be made in different ways, including by the example ofFIGS. 1 and 2with the bolts56. As before, the bolts56fasten through the third ring gear30and into the plate16; the bolts56do not fasten through the first ring gear26as shown inFIG. 2. Still, as before, other connections could involve more or less bolts, rivets, and/or welds, or the third ring gear30could be a unitary extension of the plate16. The third ring gear30may be similarly designed and constructed as the second ring gear28. The third ring gear30engages with the planet gears24and has a set of teeth60at its interior for making direct teeth-to-teeth meshing with the planet gears. The teeth60mesh with the teeth38of the planet gears24along a third axial section S3of each planet gear. The set of teeth60project radially-inwardly relative to the annular and disk-like shape of the third ring gear30. The set of teeth60can include seventy-seven individual teeth, or some other quantity of teeth spanning continuously around the circumference of the third ring gear30; the number of teeth for the third ring gear can be the same as that for the second ring gear28. And as before, the number of teeth between the first and third ring gears26,30can differ by a multiple of the number of planet gears24. In the embodiment presented here, the third ring gear30is an internal spur gear, but could be another type of gear. And in installation as depicted best inFIG. 1, the third ring gear30is situated on the electric-motor-side of the phaser10relative to the other two ring gears26,28.

Together, the three ring gears26,28,30constitute a split ring gear construction for the planetary gear set14.

Referring now particularly toFIG. 2, the plate16can be connected to an engine camshaft62and drives rotation of the camshaft about the axis X1. The connection can be made in different ways, including by way of a bolt64. As set forth above, the plate16can also be connected to the second and third ring gears28,30via the bolts56. In the embodiment presented here, the plate16has a first sleeve portion66, a second sleeve portion68, and a flange portion70. The first sleeve portion66is a cylindrical wall that is inserted into the cylindrical wall36of the sun gear22and that receives the bolt64. The first sleeve portion66and cylindrical wall36can be slightly spaced apart from each other so they can independently rotate. The second sleeve portion68can guide connection with the engine camshaft62. And the flange portion70can resemble a disk, and has three bolt holes72that are internally threaded for fastening with the bolts56.

When put in use, the phaser10transfers rotation from the engine crankshaft and to the engine camshaft62, and, when commanded by a controller, can angularly displace the camshaft with respect to its normal operating position to an advanced angular position and to a retarded angular position. Under normal operation and without valve advancing or retarding, the sprocket12is driven to rotate about the axis X1by the engine crankshaft in a first direction (e.g., clockwise or counterclockwise) and at a first rotational speed. Since the first ring gear26is connected to the sprocket12, the first ring gear also rotates in the first direction and at the first rotational speed. Concurrently, the electric motor32drives the sun gear22to rotate about the axis X1in the first direction and at the first rotational speed. With these conditions, the sprocket12, sun gear22, first and second and third ring gears26,28,30, and plate16all rotate together in unison in the first direction and at the first rotational speed. Also, the planet gears24revolve together around the axis X1in the first direction and at the first rotational speed, and do not rotate about their individual rotational axes X2. Put differently, there is no relative rotational movement or relative rotational speed among the sprocket12, sun gear22, planet gears24, ring gears26,28,30, and plate16in normal operation. Due to this lack of relative rotational movement and speed, frictional losses that may otherwise occur between the gears are minimized or altogether eliminated.

In one example, in order to bring the engine camshaft62to the advanced angular position, the electric motor32drives the sun gear22momentarily at a second rotational speed that is slower than the first rotational speed of the sprocket12. This causes relative rotational movement and relative rotational speed between the sun gear22and sprocket12. And because the second and third ring gears28,30have a different number of individual teeth with respect to the first ring gear26, the second and third ring gears move rotationally relative to the first ring gear. At the same time, the planet gears24rotate about their individual rotational axes X2. The exact duration of driving the sun gear22at the second rotational speed will depend on the desired degree of angular displacement between the engine camshaft62and the sprocket12. Once the desired degree of angular displacement is effected, the electric motor32will once again be commanded to drive the sun gear22at the first rotational speed. The engine camshaft62hence remains at the advanced angular position while the sun gear22is driven at the first rotational speed under these conditions.

Conversely, to bring the engine camshaft62to the retarded angular position from the normal operating position, the electric motor32drives the sun gear22momentarily at a third rotational speed that is faster (contrary to the second rotational speed) than the first rotational speed of the sprocket12. Relative rotational movements and speeds are once again caused between the sun gear22and sprocket12, and between the second and third ring gears28,30and the first ring gear26. The remaining functionalities are similar to those described immediately above. Still, in another example, to advance the angular position, the second rotational speed could be faster than the first rotational speed; and to retard the angular position, the third rotational speed could be slower than the first rotational speed; this functionality depends on the number of teeth of the ring gears.

During these operations, the three ring gears26,28,30transmit loads to the planet gears24. It has been found that if these loads differ from one another, the planet gears24can become misaligned and tip off-axis and the axes X2can become out of parallel with the axis X1. To preclude these drawbacks, the planetary gear set14has been designed and constructed to transmit substantially balanced loads across the planet gears24. The first ring gear26transmits a first load to each of the planet gears24across the first axial section S1. The second ring gear28transmits a second load to each of the planet gears24across the second axial section S2, and likewise the third ring gear30transmits a third load to each of the planet gears across the third axial section S3. The first load may have a different magnitude than the second and third loads, and the second load may have the same magnitude as the third load. Further, as illustrated inFIG. 2, the first, second, and third axial sections S1, S2, and S3have axial widths that can be approximately equal to each other. And added together, the axial sections S1, S2, and S3can approximately equal the axial width W of the planet gears24. As a result of at least some of these relationships, the loads transmitted to the planet gears24are substantially equally distributed across the planet gears24, and misalignment does not occur and the axes X2remain parallel to the axis X1. Still, the loads can be balanced by other arrangements not depicted in the figures. For instance, the second and third axial sections S2, S3could have axial widths that are equal to each other but not equal to the axial width of the first axial section S1. Also, when added up the axial sections S1, S2, and S3need not equal the axial width W of the planet gears24, and/or the axial sections S1, S2, and S3could have axial spaces between them.

Since the loads are substantially balanced and misalignment does not occur, the carrier assembly40can be omitted from the design and construction of the phaser10. While the carrier assembly40is used for other purposes, one function it provides is to maintain the alignment of the planet gears24. Because the alignment can be maintained instead by the substantially balanced loads, the carrier assembly40and its plates42,44, cylinders46, bolts48,50, pins, and other components can be altogether removed from the phaser10in some embodiments. Eliminating these parts means that the phaser10can be lighter in weight and less costly in production. Moreover, the substantially balanced loads presents opportunities for reducing the size of the sets of teeth detailed above for the different gears. In some instances, larger sets of teeth were utilized to accommodate and counteract the misalignment and tipping previously experienced. The reduced size can consequently more readily satisfy packaging demands that are oftentimes inflexible in automotive applications.

FIGS. 3-6present another embodiment of the phaser10. Since many components of this embodiment are similar to what has been described for the embodiment ofFIGS. 1 and 2, the same reference numerals are being used inFIGS. 3-6for the components. In this embodiment too, the phaser10includes the sprocket12, the planetary gear set14, and the plate16. And as before, the planetary gear set14includes the sun gear22, the planet gears24, and the first, second, and third ring gears26,28,30. The descriptions provided for these components with reference to the embodiment ofFIGS. 1 and 2apply for this embodiment ofFIGS. 3-6and are incorporated herein without repeating the descriptions. Only the differences between the embodiments will be described.

The sprocket12, plate16, and ring gears26,28,30ofFIGS. 3-6are connected to one another in a different arrangement than described before. InFIGS. 3-6, the sprocket12has a set of three lugs80with internally threaded bolt holes for fastening with bolts82. The lugs80are block-like structures that project axially away from a face surface of the sprocket12. The lugs80are circumferentially spaced apart with respect to one another. The bolts82are also fastened through internally threaded bolt holes of tabs84of the first ring gear26. In this way the sprocket12and first ring gear26are connected together. There are three tabs84to correspond to the three lugs80. In this embodiment, the tabs84are rectangular unitary extensions of the first ring gear26and project axially outwardly away from an annular body of the first ring gear. Like the lugs80, the tabs84are circumferentially spaced apart with respect to one another. The lugs80and tabs84need not be equally spaced apart around their respective circumferences. Referring particularly toFIG. 4, the lug80and tab84demarcated with the prime symbol ( ) are set angularly farther apart from the other two lugs80and tabs84without the prime symbol. In a specific example, the lug80and tab84are each spaced one-hundred-and-thirty-five degrees (135°) angularly apart from the lugs80and tabs84around the circumference on both of their sides. Accordingly, the neighboring lugs80and tabs84are spaced ninety degrees (90°) angularly apart with each other. Still, other examples of angular spacings are possible.

Similarly, the second ring gear28has a set of three tabs86spaced around its circumference, and the third ring gear30has a set of three tabs88spaced around its circumference. Unlike the tabs84of the first ring gear26, the tabs86and88are set equally angularly apart with respect to one another around their respective circumferences. In a specific example, the tabs86,88are spaced one-hundred-and-twenty degrees (120°) angularly apart from one another. Still, other examples of angular spacings are possible. Furthermore, spacers90can be provided for inserting between the tabs86,88in installation. Since the first ring gear26is sandwiched by the second and third ring gears28,30, the spacers90fill the resulting gap between their tabs86,88when brought over each other. The bolts56are fastened through internally threaded bolt holes of the tabs86,88and of the spacers90. The bolts56are also fastened into internally threaded bolt holes of tabs92of the plate16for connecting the second and third ring gears28,30to the plate. The tabs92are designed and constructed similarly to the tabs86,88. Lastly, as illustrated inFIG. 4, the phaser10in this embodiment can include a snap ring94and a D-ring washer96.

As perhaps best depicted inFIGS. 3 and 5, the tabs84and lugs80are angularly offset from the tabs86,88,92and spacers90. The angular offset accommodates angular displacement when the phaser10is commanded to bring the engine's camshaft to the advanced and retarded angular positions. Referring particularly toFIG. 5, in a specific example, an angular offset □ between the tabs84and lugs80and the tabs86,88,92and spacers90can be thirty degrees (30°). This permits advanced and retarded angular positions that are at greatest thirty degrees (30°) from the normal operating position. Still, other examples of angular offsets are possible, and may depend on the placement of the different tabs and lugs, and on the desired amount of angular displacement when advancing and retarding the engine's camshaft.

Still, other embodiments of the phaser10are possible. For instance, two of the three ring gears could be connected to the sprocket while only one of the three ring gears is connected to the plate; this is unlike the embodiments presented in the figures in which one ring gear is connected to the sprocket and two ring gears are connected to the plate.

The foregoing description is considered illustrative only. The terminology that is used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations will readily occur to those skilled in the art in view of the description. Thus, the foregoing description is not intended to limit the invention to the embodiments described above. Accordingly the scope of the invention as defined by the appended claims.