Patent Application
20240077004
This application claims the priority, under 35 U.S.C. §§ 119, 120, 172, 363, and 365, of Great Britain patent application No. GB2212751.8, filed Sep. 1, 2022; the prior application is herewith incorporated by reference in its entirety.
Not Applicable
The invention relates to camshaft phasing systems, and particularly camshaft phasing systems for use with concentric camshafts.
A concentric camshaft has an inner shaft with an outer tube. The camshaft has two groups of cam lobes, one group connected for rotation with the outer tube and the other connected for rotation with the inner shaft. Such a configuration allows the two groups of cam lobes to be phased relative to each other when combined with a camshaft phasing system. The concentric camshaft allows the phase of one, or both, of the two groups of lobes to be controlled independently relative to the phase of the engine crankshaft. In a single camshaft engine, for example, this could allow independent control of intake and/or exhaust valve timing.
Camshaft phasing systems are known to include locking systems, employing locking pins, that act to ensure that the two groups of lobes remain in known positions when unable to be controlled by the phasing system during certain engine operating conditions, for example due to low engine oil pressures such as engine start-up/shut-down, or to act as a failsafe in case of component/software failure.
Dual independent camshaft phasing systems, such as that known from U.S. Pat. No. 6,725,817, are well known for ‘light duty’ applications. These allow independent control of both sets of cam lobes in a concentric camshaft. A typical light duty application comprises either radially or axially stacked hydraulic, mechanical or electric phasers or hybrids combining more than one type, as disclosed in EP 2,456,961 and U.S. Pat. No. 11,041,413. The phasers are arranged to drive the inner shaft or the outer tube of the concentric camshaft.
Being light duty applications, the camshaft's drive arrangement is usually via a drive sprocket utilizing a belt or chain, but rarely a gear drive. Due to the restrictive packaging requirements in an automotive engine bay, drive sprockets are typically limited in diameter because, for example, increasing the diameter of the drive sprocket usually results in increased overall engine height. As such, in order to package within the engine, dual independent phasing systems of increased axial length are most common.
In a ‘heavy duty’ application, the camshaft drive arrangement is almost exclusively gear-type, and these gears are often of much greater diameter than in light duty applications. In addition, the multitude of machines with which heavy duty engines are designed to interface impose strict limits on the axial packaging space available for a cam phasing system. This naturally limits the design of a dual independent camshaft phasing system to those which minimize axial length whilst making use of the increased radial space offered by the large gears. The minimum axial length of a hydraulic phasing system is physically limited by: a) the turning effort (torque) required of the phaser, as reducing the length of the phasing system's hydraulic cavities reduces the area upon which the hydraulic fluid acts, reducing the torque output; and b) engagement lengths for mechanical features such as locking pins and threaded fasteners, which for a robust design require minimum engagement lengths; among other requirements. Therefore, a hydraulic phasing system with a reduced axial length requires novel solutions put forward in this application.
Gear-type drive arrangements, compared to belt or chain driven sprocket types (which make use of a flexible intermediary belt/chain to transmit drive), impose much stricter requirements on the positional accuracy and runout of each gear, as such, any camshaft phasing system which mounts a gear must accurately position this gear relative to the camshaft's support bearings, which further complicates the design of the phasing system.
The systems, apparatuses, and methods described provide a dual independent camshaft phasing system which is applicable to heavy duty internal combustion engines, being capable of incorporation with a drive gear whilst minimising axial length.
According to the present invention, there is provided a phasing system as hereinafter set forth in claim 1 of the appended claims.
Preferred features of the phasing system are set forth in claims 2 to 13 of the appended claims.
With the foregoing and other objects in view, there is provided, a phasing system for an internal combustion engine having a concentric camshaft comprising an annular stator, rotatable by the crankshaft of the internal combustion engine, having an inner circumference, an outer circumference, and two groups of arcuate cavities, at least a first group of the cavities interrupting the inner circumference of the stator, a first phaser having an output member in the form of a hub to be concentrically located relative to the camshaft and mounted within the centre of the stator, the outer circumference of the output member being in contact with the inner circumference of the stator to serve as a bearing for the stator, the first phaser further having a plurality of vanes connected to the output member and extending radially into the first group of cavities to divide the cavities into opposed working chambers, and a second phaser comprising a first end plate and a second end plate located on opposite sides of the stator and fastened to one another in order to axially seal the cavities in the stator, the end plates serving as the output member of the second phaser and being connected to vanes that extend axially through the second group of cavities to divide the cavities into opposed working chambers.
In accordance with another feature, the second group of cavities also interrupts the inner circumference of the stator.
In accordance with a further feature, the output member of the first phaser features oil passageways for both groups of cavities.
In accordance with an added feature, the second phaser comprises stiffening elements extending between the end plates that serve as the output member of the second phaser, the stiffening elements extending through arcuate slots formed in the stator.
In accordance with an additional feature, there is provided at least one locking pin assembly disposed within the stator, for locking the stator relative to the output member of at least one of the phasers.
In accordance with yet another feature, the locking pin assembly comprises a pin, a spring having one end received within a hole in the pin, and a spring seat abutting the opposite end of the spring, and wherein the seat has a plurality of axially extending protrusions about its perimeter, aligned with matching slots in the side wall of the pin.
In accordance with yet a further feature, the locking pin assembly is disposed axially with respect to the camshaft.
In accordance with yet an added feature, the locking pin assembly is located within a through hole in the stator.
In accordance with yet an additional feature, locking pin assemblies disposed within the stator, for locking the stator relative to the output member of the two phasers.
In accordance with again another feature, one of the locking pin assemblies is disposed radially with respect to the camshaft.
In accordance with again a further feature, the radially disposed locking pin assembly is arranged within a housing.
In accordance with again an added feature, the first phaser output member features a through slot on its outer circumference configured to receive the pin of the radially disposed locking pin assembly.
In accordance with a concomitant feature, there is provided a spiral spring for applying a balancing torque to the output member of at least one of the two phasers.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:
The camshaft 10 may further comprise a target wheel 20 for a sensor, the sensor being mounted to the engine (not shown). The sensor and target wheel 20 serve to detect the phase of the cam lobes relative to a part of the engine which is coupled to the crankshaft, such as a camshaft drive gear 22. In embodiments of the invention described below, the camshaft drive gear 22 serves as the stator of the phasing system.
The axial ends of inner shaft 24 and the outer tube 26 of the camshaft 10 are shown in
The first phaser output member 28 is configured for rotation with the outer tube 26, and therefore the first group of cam lobes 12, by mounting its inner circumference directly to the outer tube 26 and fastening the first phaser output member 28 to a bearing 38 at the drive end of the camshaft 10. The bearing 38 is rigidly mounted to, and rotatable with, the outer tube 26 and has threaded holes therein to enable it to be secured to the first phaser output member 28 by means of fasteners 37 passing through arcuate slots 39 in the end plate 30b.
The second phaser is connected for rotation with the inner shaft 24 by means of a slot 40 located in the second end plate 30b. The slot 40 is of a shape complimentary to protrusions 42 on the inner camshaft 24, so that any rotational movement of the second end plate 30b results in corresponding rotation of the inner camshaft 24. The first end plate 30a and the second end plate 30b sandwich the stator 22 between them and are connected to one another by fasteners 41 clamping through a plurality of vanes 52.
As known in the art, the cam lobes 14 of the second group are connected to the inner camshaft 24 by means of pins passing through circumferential slots in the outer tube 26, and into the lobes 14, the latter being free to rotate about the outer tube 26.
The stator 22, as most clearly shown in
The stator 22 is mounted onto the outer diameter of the first phaser output member 28. As the output member 28 is mounted directly onto the outer tube 26, and the stator 22 is mounted to the outer diameter of the first phaser output member 28, the stator is thereby accurately positioned having its drive gear mounted concentrically to the camshaft 10. This is crucial to maximize component durability and reduce the running noise of the drive gear in operation. The accurate location of the stator 22 is more important in engines utilizing gear-driven cams because there is no flexible element, such as a belt or chain, to accommodate any minor misalignment.
The number of cavities 44, 46 and their positions relative to each other are chosen such that the area of contact (the bearing area) between the inner circumference of the stator 22 and the outer circumference of the first phaser output member 28 is maximized. Maximizing the bearing area helps to position the stator 22 accurately during assembly of the engine, and also reduces wear due to less pressure at the interface.
The first cam phaser output member 28 features radial slots extending inwards from its outer circumference. These slots allow the first phaser output member 28 to make use of vanes 48 which extend into the cavities 44 and act as a sealing wall, splitting each cavity 44 into two sections. As such, there will be as many slots and vanes 48 as there are cavities 44 for the first phaser output member 28. When hydraulic pressure is increased on one side of the vane 48, it will cause the vanes 48 to move within the cavities 44, thereby causing the phaser output member 28 to rotate. This ultimately leads to the first group of cam lobes 12 changing phase. The vanes 48 may be radially sprung such that their outer extremities will remain in light contact with their cavities 44, thereby providing a suitable hydraulic seal.
Oil passageways 50 may be formed from axial and radial drillings in the first phaser output member 28 and serve to direct pressurized oil from oil control valves, located elsewhere in the engine, through the phaser output member 28 and to the hydraulic cavities 44, 46 of the first and second phasers 28, 30 as required by a control module (such as an ECU) of the engine.
The second cam phaser, as earlier mentioned, has a different construction from the first in order to maximize the aforementioned bearing area. The two end plates 30a, 30b are positioned one on each side of the stator 22 and are fastened together through the vanes 52. The cavities 46 associated with the second phaser 30 do not interrupt the internal circumference of the stator 22 and are instead radially and circumferentially enclosed by the stator 22. The first end plate 30a of the second phaser 30 includes vanes 52. The vanes 52 may be located on the face of the first end plate 30a by dowel pins 54, or alternatively formed as part of the end plate 30a. The vanes 52 associated with the second group of cavities 46 serve a similar purpose to the vanes 48 associated with the first group of cavities 44 in that they split each cavity 46 into two working chambers. The vanes 52 may comprise sprung sealing elements 56 to seal the cavity 46.
The inner circumference of the stator 22 features circumferential slots 62 so that hydraulic fluid can enter and exit the second group of cavities 46, and thereby control the phase of the second group of cam lobes 14, irrespective of the angular position of the first phaser output member 28 in relation to the stator 22.
The first end plate 30a of the second phaser 30 may further feature stiffening elements 58. The stiffening elements 58 may be fastened to the first end plate 30a in the same manner as the vanes 52 and serve to reduce the distance between fastenings holding the first and second end plates 30a, 30b together. The stiffening elements 58 have the same axial length as the vanes 52 and therefore together act to reduce the deflection of the end plates 30a, 30b when the system is under hydraulic pressure. Consequently, the level of leakage of hydraulic fluid is reduced. Further, the addition of stiffening elements 58 and fastenings reduces the stress placed on the fastenings located in the vanes 52. Arcuate slots 60 are provided within the stator 22 to allow clearance of the stiffening elements 58 throughout their range of motion.
An alternative embodiment of a phasing system is shown in
In order to lock the rotational position of phasers 28 and 30 relative to the stator 22, locking pins as known in the art may be used. Optionally, an intermeshing locking pin as shown in
The compression spring 68 acts on the spring seat 70 to urge the pin 66 away from the spring seat 70 into an extended position, thereby advancing the pin 66 as shown in
The locking pin assembly 64 may be used in an axial or radial orientation. Therefore a locking pin assembly of this design may be used to lock rotation of one or both of the first phaser output member 28 and the second phaser output member 30. The advantage of using a locking pin assembly with matching protrusions and slots is that the overall length of the pin assembly 64 can be reduced, whilst still maintaining the pin length required for adequate engagement in a phaser. This reduction in length is particularly useful when the assembly 64 is disposed axially in relation to the camshaft 10, as it allows the axial length of the phaser, and therefore the engine as a whole, to be reduced. This is critical for heavy duty applications as explained above, where the axial dimension needs to be minimized due to the engine being used across multiple machines.
In use, a locking pin assembly device is housed within a member. When disposed axially, the member may be the stator 22 having an axial through bore 78 (as shown in
During operation, hydraulic pressure acts on the end of the pin 66. If the hydraulic pressure is under a specified threshold, the spring force is sufficient such that the locking pin 66 remains in a hole, slot, indentation or similar 82, 84 provided in the first and second phaser output members 28, 30, as shown in
In some embodiments, the hub constituting the first phaser output member 28 is formed using a process of sintering from powdered metal as shown in
The above-described phaser system 18 may also make use of a spiral spring 32 in order to improve the performance balance of the system. As shown in
It should be noted that the above description describes only a small number of possible embodiments and should not be interpreted as limiting. Various modifications or adaptations may be made by the skilled person without departing from the scope of the appended claims. For example, the inner shaft of the concentric camshaft may be tubular. In another example, the slot 40 and protrusion interface between the second end plate 30b of the second phaser 30 and the inner shaft 24 may be switched, meaning that the inner shaft features a slot into which protrusions of the second phaser fit. Further, the vanes 48 of the first phaser output member 28 may be integrally formed with the main hub of the phaser.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2212751.8 | Sep 2022 | GB | national |
