Patent Application
20140261265
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.
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:
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
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.
As such, referring back to
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.
Referring to
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
Similarly,
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.
