US20140261265A1

US20140261265A1 - Low friction camshaft with electric phaser

Info

Publication number: US20140261265A1
Application number: US13/829,985
Authority: US
Inventors: Daniel M. Lonowski
Original assignee: Mahle Engine Components USA Inc
Current assignee: Mahle Engine Components USA Inc
Priority date: 2013-03-14
Filing date: 2013-03-14
Publication date: 2014-09-18
Also published as: DE102014204738A1

Abstract

An exemplary engine assembly includes a crankshaft, and a camshaft having cam lobes mounted thereon. The cam lobes are configured to provide lift to respective devices as a function of a rotation of the camshaft. The cam lobes are circumferentially offset from one another such that a timing of operation of the lift is different for each of the at least two cam lobes. The assembly includes at least one roller bearing coupled to the camshaft, and an electric cam phaser configured to alter the timing of the camshaft with respect to the crankshaft as a function of engine operation.

Description

BACKGROUND

Engine manufacturers are constantly seeking to increase power output and fuel efficiency of their products. One method of generally increasing efficiency and power is to reduce the friction within a camshaft of the engine.
Camshafts are typically used to control valve motion and other important timing events in internal combustion engines. The camshaft is a shaft having axially spaced cams or cam lobes, which project outwardly from the surface of the shaft. The shaft and cams can be machined from a single part and may also be assembled from separate parts. The camshaft is typically supported by bearings, such as journal bearings that are positioned between the cams along the axial direction of the camshaft. The journal bearings (or fluid film or sleeve bearings) operate by means of a fluid film of oil, typically fed to the bearings via a pressurized feed through drillings in the bearing housing or other routes.
The engine includes a crankshaft that can be directly coupled to the camshaft using gears, belts, chains, and the like. Thus, the crankshaft is a reference shaft from which timing events are determined for other engine operations. The camshaft may be independently controlled relative to the crankshaft to improve engine efficiency. One known device for independently controlling the camshaft relative to the crankshaft is a cam phaser. A cam phaser on a camshaft provides variable camshaft rotation to improve engine timing and lift events, leading to improved engine efficiency. Overall efficiency is improved at least in part because it may be desirable to alter the relative timing between the camshaft and the crankshaft, depending on the condition of operation of the engine. For instance, at idle the relative timing between the two shafts may have one desired timing, which may differ when the engine is a high speed operation.
Various cam phasing technologies are used to accomplish variable cam phasing, including helical spline phasers, hydraulic vane rotor phasers, and cam torque actuated phasers. Variable cam phasing or timing accommodates the divergent needs for power and torque output, idle stability, fuel economy, and emissions control, as examples. These cam phasing technologies require a pressurized oil feed from the engine hydraulic pump for their operation. Because the engine includes hydraulic feed for the bearings, oil from the hydraulic system is typically thereby fed to the cam phaser as well.
The demands on the hydraulic pump for supplying oil to bearings divert power output away from other engine operations. These parasitic power losses reduce the engine's efficiency. The parasitic losses are increased with the presence of a cam phaser because of its oil feed. Thus, despite improved engine efficiency with the use of variable camshaft/crankshaft timing, parasitic losses from the cam phaser and the bearings prevent the engine from operating at its peak efficiency.
Accordingly, there is a need for an improved camshaft for an internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, illustrative examples are shown in detail. Although the drawings represent the exemplary illustrations described herein, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an exemplary illustration. Further, the exemplary illustrations described herein are not intended to be exhaustive or otherwise limiting or restricting to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings as follows:

FIG. 1 is an exemplary engine assembly;

FIGS. 2A and 2B illustrate exemplary cam lobe profiles that can be incorporated into the engine assembly of FIG. 1; and

FIGS. 3A-3D illustrate exemplary bearing arrangements that can be incorporated into the engine assembly of FIG. 1.

DETAILED DESCRIPTION

Reference in the specification to “an exemplary illustration”, an “example” or similar language means that a particular feature, structure, or characteristic described in connection with the exemplary approach is included in at least one illustration. The appearances of the phrase “in an illustration” or similar type language in various places in the specification are not necessarily all referring to the same illustration or example.
In some exemplary illustrations, components of an engine are shown that includes a camshaft that is coupled to a crankshaft. The camshaft includes at least two cam lobes mounted thereon, and the two cam lobes are configured to provide lift to respective devices as a function of a rotation of the camshaft. The cam lobes may be circumferentially offset from one another such that a timing of operation of the lift is different for the cam lobes. The camshaft includes at least one roller bearing coupled to the camshaft. An electric cam phaser is configured to alter the timing of the camshaft with respect to the crankshaft as a function of engine operation.
Turning now to FIG. 1, an exemplary engine assembly 100 is shown. Engine assembly 100 is an internal combustion (IC) engine according to one embodiment and a compression ignition (CI) engine according to another embodiment. Engine assembly 100 provides motive power to a vehicle such as a car, truck, bus, etc. However, the applications are not limited to those listed and may be applicable to any device that may derive motive power from an engine assembly such as engine assembly 100.
Engine assembly 100 includes a timing input or crankshaft 102 and a camshaft 104 that are coupled to one another via an electric cam phaser 106. Crankshaft 102 is configured to rotate in a crankshaft rotation direction 108 and about a crankshaft rotation axis 110. Crankshaft 102 includes a number of elements, not shown, that include but are not limited to crank throws or crank pins that are radially offset from crankshaft rotation axis 110. During rotation, the crankshaft throws provide a reciprocating motion to, as one example, pistons within cylinders. The angular orientation of the crankshaft throws, with respect to one another, controls motion of the pistons with respect to one another. The relative rotation is of the crankshaft throws is coupled to timing of the combustion events within the cylinders. According to one example, element 102 is simply a timing reference device from which timing events in the are determined.
Camshaft 104 includes, in the illustrated example, two cam lobes 112, and camshaft 104 is configured to rotate about a rotational axis 114, independent of rotation 108 of crankshaft 102. Rotational axis 114 is shown to be collinear with rotational axis 110; however, in other exemplary approaches the two axes 110, 114 are offset from one another. Cam lobes 112 provide mechanical action to devices within engine assembly 100, including but not limited to a valve, an injection pump, a vacuum pump, and a fuel pump, as examples. That is, cam lobes 112 are eccentrically shaped or oblong devices that are positioned having a profile that determines a timing and extent of operation that derives therefrom and is controllable via the profile.
FIGS. 2A and 2B illustrate exemplary profiles of cam lobes. FIG. 2A shows a cam assembly 200 having a generally circular cam lobe 202 that is eccentrically mounted on a rotatable shaft 204. Rotatable shaft 204 corresponds to rotational axis 114 of engine assembly 100. Circular cam lobe 202 is offset an eccentric distance 206 from a center 208 of circular cam lobe 202. As such, when circular cam lobe 202 is caused to rotate 210 about rotatable shaft 204 a cam follower 212 is caused to move axially 214, which causes the mechanical action to the devices as described above.
FIG. 2B shows another example of a cam assembly 250 having an oblong lobe or profile 252 that is mounted to rotatable shaft 204. As such, when oblong lobe 252 is caused to rotate 210 about rotatable shaft 204, a cam follower 254 is caused to move axially 256, which again causes the mechanical action to the devices as described above, however commensurate with the profile of oblong lobe 252.
As such, referring back to FIG. 1, cam lobes 112 are configured to provide lift to respective devices as a function of rotation of camshaft 104, and cam lobes 112 are circumferentially offset from one another such that a timing of operation of the lift is different for each of the at least two cam lobes. Engine assembly 100 includes bearings 116 that support camshaft 104. And, although two cams 112 and two bearings 116 are illustrated, it is contemplated that more cams and bearings may be included along camshaft 104.
One or more of bearings 116 coupled to camshaft 104 are roller bearings and may be, according to illustrative embodiments, a conical roller bearing, a ball bearing, a needle bearing, and a cylindrical bearing. In one embodiment, all of bearings 116 on camshaft 102 are roller bearings. The bearings selected typically provide an ability to carry a radial load, but one or more bearings may also be included to also limit axial motion of the shaft. Roller bearings, as is commonly known, may be lightly lubricated with a residual amount of lubricant, but do not have pressurized or replenished oil supply, and there is not pumped oil for lubrication to operate. That is, the roller bearings do not have a lubricating oil feed. Contrary to bearings that are typically used for a camshaft, one or all of bearings 116 are roller bearings that operate in an operation that does not include a pressurized oil supply. Further, as illustrated and as discussed, electric cam phaser 106 couples crankshaft 102 with camshaft 104.
Electric cam phaser 106 is configured to alter the timing of the camshaft with respect to the crankshaft as a function of engine operation. That is, electric cam phaser 106 may be an electric or electronic device that uses brushless DC electric motors to actuate a gear mechanism to effect cam phasing with low power consumption. As such, cam phaser 106 does not include an oil feed and thus operates in an oil free mode.
Various bearing and cam phaser arrangements may be incorporated into the camshaft and in conjunction with an electric cam phaser. FIGS. 3A-3D illustrate bearing/electric cam phaser arrangements that can be incorporated into engine assembly 100 illustrated in FIG. 1.
Referring to FIG. 3A, bearing/cam phaser assembly 300 includes an electric cam phaser 302 that is coupled to a camshaft 304, and coupleable to a crankshaft, such as crankshaft 102 of engine assembly 100. Assembly 300 includes cam lobes 306 and roller bearings 308, 310, 312, and 314 that operate without an oil feed for lubrication. In the illustrated example, roller bearing 308 is a ball bearing that includes inner and outer races and balls that transmit load on camshaft 304 to a support structure (not shown) via support frame 316. Roller bearings 310-314 are needle bearings that include a relatively large contact surface compared to ball bearing 308. Needle bearings 310-314 also tend to have a lower profile relative to ball bearing 308 so are more compact. Needle bearings 310-314 include a needle cage and needle rollers that contact and support camshaft 304 and carry the load of camshaft 304 to the support structure via support frames 318. Cam phaser 302 may be positioned at a first end 320 of camshaft 304, or may alternatively be positioned at a second end 322 and coupled to the crankshaft. Thus, because cam phaser 302 is electric and because all the bearings are roller bearings, there is no need to feed oil to the region of the cam shaft. This reduces parasitic losses, thereby providing an overall simpler and more compact engine design as compared to approaches previously utilized at least in part because the engine oil pump can be smaller, and because there are no oil feed lines to the area of the cam shaft.
FIG. 3B illustrates another exemplary bearing/cam phaser assembly 340 that includes cam phaser 302 coupled to camshaft 304, cam lobes 306, ball bearing 308, and needle bearing 310. However, in this example two journal bearings 342 are included that do not include roller elements such as in roller bearings 308, 310. Journal bearings 342 include contact surfaces 344 that slide over camshaft 304. Because of the increased surface area compared to roller bearings 308, 310, there is an increased propensity for frictional heating as well during rotation of camshaft 304. Accordingly, journal bearings 342 include oil feed lines 346 that pass through their respective support frames 348. Thus, although in this embodiment oil feed lines 346 are included to some of the bearings (342), the parasitic losses are nevertheless reduced when compared to a design in which all bearings are journal bearings. Thus, with the combination of the electric cam phaser and some roller bearings, parasitic losses to the engine are reduced and overall engine design is simplified because of a reduced need to provide oil feed to all of the bearings and to the cam phaser.
FIG. 3C illustrates another exemplary bearing/cam phaser assembly 360. A cam phaser assembly 362 provides dual independent control to two shafts of a camshaft via a first cam phaser 364 and a second cam phaser 366. First cam phaser 364 is coupled to an inner shaft or inner camshaft 368. Second cam phaser 366 is coupled to first cam phaser 364 as well as to an outer shaft or outer camshaft 370 that is radially or concentrically positioned outside inner shaft 368. Either first cam phaser 364 or second cam phaser 366 is also coupleable to a crankshaft (not shown).
Assembly 360 includes cam lobes that are coupled to either inner shaft 368 or outer shaft 370. In this example, a cam lobe 372 is mounted or coupled to inner shaft 368 via a pin 374, and cam lobes 376 are mounted or coupled directly to outer shaft 370. Outer shaft 370 is supported, in this exemplary approach, by a mix of roller bearings and journal bearings, and inner shaft 368 is supported by first cam phaser 364 on a first end 378 and a bearing (not shown) on a second end 380. Inner shaft 368 and outer shaft 370 are therefore rotatable relative to one another by independently controlling each cam phaser 364, 366, relative to each other. Cam lobe 372 can thereby be rotationally controlled relative to cam lobes 376. Thus, having separate cam phasers enables an additional dimension of control to the operation of assembly 360.
That is, both cam phasers 364, 366 may be coupled to one another and coupled to the crankshaft, which directly couples both shafts 368, 370 (and their respective cam lobes 372, 376) together and to the crankshaft. However, cam phasers 364, 366 may be rotated relative to one another such that a cam profile of cam lobe 372 can be altered circumferentially with respect to cam lobes 376. In such fashion, timing of lift events within assembly 360 may be further controlled by altering rotation of both shafts 368, 370 relative to the crankshaft, and by altering rotation of both shafts 368, 370 relative to each other.
As stated, referring still to FIG. 3C, outer shaft 370 is supported by a mix of roller bearings and journal bearings. Thus, in the example shown ball bearing 382 and needle bearing 384 are included, while oil-fed bearings 386 are shown having oil feed lines 388.
Similarly, FIG. 3D shows an exemplary assembly 394 having cam phaser assembly 362 that enables relative motion between shafts 368, 370 and with respect to the crankshaft. However, in this example all bearings operate without an oil feed for lubrication. As shown in FIG. 3C, roller bearing 382 and needle bearing 384 are shown, but assembly 394 of FIG. 3D includes needle bearings 396 as well. Thus, because cam phaser assembly 362 is electric and because all the bearings are roller bearings, there is no need to feed oil to the region of the cam shaft. This reduces parasitic losses and providing an overall simpler and more compact engine design because the engine oil pump can be smaller, and because there are no oil feed lines to the area of the cam shaft.
Thus, in the examples illustrated, cam shaft operation may be controlled with respect to the crankshaft operation, and lobes within the camshaft may be controlled with respect to one another via an electric phaser assembly having one phaser coupled to one shaft, and another phaser coupled to another shaft (cam-in-cam). Further, both operations are possible and in the concentric camshaft arrangement shafts may be controlled with respect to one another and operation of both is controlled with respect to the crankshaft. As such, the amount of oil fed to the engine is reduced and there is no need for oil or hydraulic fluid for a phaser. In addition, aside from the reduced parasitic losses, there is no need for a rotating coupler for putting oil into the camshaft (such as, for a slide or journal bearing). As a result, fewer engine components are required along with the lack of need for phaser activation. Moreover, the engine oil pump may be reduced in size.
With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claimed invention.
Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation and is limited only by the following claims.
All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary in made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.

Claims

What is claimed is:

1. An engine assembly comprising:

a crankshaft;

a camshaft having at least two cam lobes mounted thereon, the at least two cam lobes configured to provide lift to respective devices as a function of a rotation of the camshaft, wherein the at least two cam lobes are circumferentially offset from one another such that a timing of operation of the lift is different for each of the at least two cam lobes;

at least one roller bearing coupled to the camshaft; and

an electric cam phaser configured to alter the timing of the camshaft with respect to the crankshaft as a function of engine operation.

2. The engine assembly of claim 1, wherein the at least one roller bearing is one of a conical roller bearing, a ball bearing, a needle bearing, and a cylindrical bearing.

3. The engine assembly of claim 1, wherein at least one of the roller bearings coupled to the camshaft operates without a lubricating oil feed.

4. The engine assembly of claim 3, wherein all of the roller bearings coupled to the camshaft do not have a lubricating oil feed.

5. The engine assembly of claim 1, wherein:

the camshaft is comprised of an inner shaft and an outer shaft that is outside the inner shaft;

one of the at least two cam lobes is mounted to the inner shaft;

another of the at least two cam lobes is mounted to the outer shaft; and

the electric cam phaser is a cam phaser assembly that provides dual independent control and is configured to rotate the inner shaft with respect to the outer shaft.

6. The engine assembly of claim 1, wherein the respective devices are one of a valve, an injection pump, a vacuum pump, a fuel pump, or other actuated device.

7. The engine assembly of claim 1, wherein the engine assembly is one of a spark ignition (SI) engine and a compression ignition (CI) engine.

8. A method of manufacturing an engine, comprising:

providing a crankshaft;

providing a camshaft having multiple lobes configured to provide mechanical action to respective devices as a function of a rotation of the camshaft, wherein the at least two cam lobes are circumferentially offset from one another such that a timing of operation of the mechanical action is different for at least two of the multiple cam lobes;

coupling at least one roller bearing to the camshaft;

coupling an electric cam phaser between the camshaft and the crankshaft; and

configuring the electric cam phaser to alter the timing of the camshaft with respect to the crankshaft as a function of engine operation.

9. The method of claim 8, wherein coupling at least one roller bearing to the camshaft comprises coupling one of a conical roller bearing, a ball bearing, a needle bearing, and a cylindrical bearing.

10. The method of claim 8, wherein coupling the at least one roller bearing to the camshaft comprises coupling at least one of the roller bearings to the camshaft that does not have a lubricating feed.

11. The method of claim 8, wherein coupling the at least one roller bearing to the camshaft comprises coupling roller bearings to the camshaft that are all without a lubricating feed.

12. The method of claim 8, wherein:

providing the camshaft comprises providing an inner shaft concentrically placed within an outer shaft such that both inner and outer shafts rotate with respect to a central rotation axis; and further comprising:

mounting one of the at least two cam lobes to the inner shaft;

mounting one of the at least two cam lobes to the outer shaft; and

wherein configuring the electric cam phaser further comprises configuring the electric cam phaser assembly to provide dual acting control and to rotate the inner shaft with respect to the outer shaft.

13. The method of claim 8, wherein providing the camshaft to provide the mechanical action further comprises providing the camshaft to provide the mechanical action to the respective devices that are one of a valve, an injection pump, a vacuum pump, and a fuel pump or other actuated device.

14. The method of claim 8, wherein the engine is one of a spark ignition (SI) engine and a compression ignition (CI) engine.

15. A camshaft assembly comprising:

a camshaft having at least two cam profiles positioned along respective axial locations, the at least two cam profiles configured to provide lift to respective devices of an engine, wherein the at least two cam profiles are circumferentially offset from one another such that a timing of operation of the lift is different for each of the at least two cam profiles; and

at least one roller bearing coupled to the camshaft;

an electric cam phaser coupled to the camshaft and coupleable to a crankshaft, the electric cam phaser configured to alter the timing of the camshaft with respect to the crankshaft as a function of engine operation.

16. The camshaft assembly of claim 15, wherein the at least one roller bearing is one of a conical roller bearing, a ball bearing, a needle bearing, and a cylindrical bearing.

17. The camshaft assembly of claim 15, wherein at least one of the roller bearings coupled to the camshaft does not have a lubricating oil feed.

18. The camshaft assembly of claim 17, wherein all of the roller bearings coupled to the camshaft do not have a lubricating oil feed.

19. The camshaft assembly of claim 15, wherein:

one of the at least two cam profiles is mounted to the inner shaft;

another of the at least two cam profiles is mounted to the outer shaft; and

the electric cam phaser is an electric cam phaser assembly that provides dual independent control and is configured to rotate the inner shaft with respect to the outer shaft.

20. The camshaft assembly of claim 15, wherein the respective devices are one of a valve, an injection pump, a vacuum pump, and a fuel pump or other actuated device.