FOR AN INTERNAL COMBUSTION ENGINE

Field of the invention

The invention relates to a phaser assembly for an internal combustion engine for changing the timing of two sets of cam lobes in relation to the engine crankshaft. Background of the invention

There is an increasing emphasis upon the fuel economy and emissions of motor vehicles, and in recent years this has led to both improvements in the operation of engines and the introduction of alternative power train configurations. Hybrid cars are becoming more commonplace, in which an electric motor is used in conjunction with an IC engine, and an increasing number of vehicles incorporate an automatic stop/start function for reducing engine fuel consumption. The ability to achieve a 'hot' restart with a minimum of noise and vibration is therefore becoming an increasingly important requirement. This is particularly true for diesel engines, which typically use significantly higher

compression ratios than gasoline engines and as a result tend to suffer from high levels of noise/vibration when they are started or stopped.

It is well known that the opening duration of the intake and exhaust valve events can have a significant effect upon engine performance. In particular, the closing timing of the intake valves can be used to control the air mass trapped in the cylinder and the effective compression ratio, while the exhaust valve opening timing can be used to control the expansion ratio. Many systems have been proposed for controlling the opening duration of an engine valve, such as that shown in US 5,787,849 (esp. Fig.15), which superimposes a cyclic angular velocity variation onto the cam lobe rotation. The problem with systems of this type is that they add significant complexity and therefore cost to the engine valve train system. 'Dual-equal' cam phasing systems are also well known, in which an identical phase shift is applied to both the intake and exhaust valves of an engine relative to the crankshaft. A dual equal phasing system is described in US 6,321,731 for providing part load fuel economy and emissions improvements.

Object of the invention

The invention seeks to provide a phaser assembly for use in an engine, the phaser assembly enabling improved fuel economy and emissions and allowing hot restart and shut-off operations to be carried out with reduced levels of

noise/vibration. Summary of the invention

According to the present invention, there is provided a phaser assembly for mounting on one end of a camshaft of an engine, the engine having two groups of cam lobes that are capable of being varied in phase relative to one another and relative to a crankshaft of the engine, the phaser assembly comprising two phasers each having an input member and at least one output member, wherein the first phaser of the assembly has an input member adapted to be driven directly by the engine crankshaft and an output member connectible to a first of the two groups of cam lobes, and the second phaser has an input member connected to, or formed

integrally with, the output member of the first phaser and an output member connectible to drive the second of the two groups of cam lobes. A "phaser" or phase change mechanism is any coupling having an input and an output member that rotate together but whose relative angular position can be varied. In the present invention, a phaser assembly comprises two separately controllable phasers acting on two groups of cam lobes. The first phaser acts to vary the phase of both groups of cam lobes relative to the engine crankshaft without varying the relative phase between the two groups and the second phaser acts to vary the phase of the second group relative to the first group and the engine crankshaft.

The invention in this way provides within a single unitary phaser assembly, designed to be mounted on the end of an engine camshaft, two series connected phasers, in which the first phaser drives both second phaser and one of the two groups of cam lobes while the second phaser drives the second group of cam lobes. The phasers are preferably hydraulically operated vane- type phasers. A vane-type phaser is one having a rotor with radial vanes that divide arcuate recesses in a stator into circumferentially opposed hydraulic working chambers. As oil is pumped into one of the chambers and drawn from the other, the vanes move circumferentially to change the phase of the rotor relative to the stator. The term "stator" is used only to refer to the member defining the arcuate recesses and gives no indication of whether the member in question acts as the input or the output member of the phaser.

In some embodiments of the invention the phasers may be arranged axially in line with one another while in other embodiments they may be arranged in the same axial plane but one radially within the other. The preferred configuration will be determined for any engine by the space available within the engine compartment. The cam lobes can be arranged on two separate solid camshafts, as can be found in DOHC engines with dual overhead camshafts, or they may be formed by the lobes of a concentric assembled camshaft, sometimes referred to as an SCP (single cam phaser) camshaft. Such an SCP camshaft comprises an inner shaft rotatably mounted within an outer tube. A first of the two groups of lobes is fast in rotation with the outer tube while the other group is free to rotate relative to the outer tube but is connected for rotation with the inner shaft by means of pins that pass with

clearance through circumferentially elongated slots in the outer tube.

The invention is applicable to different engine

configurations in which different purposes are served by the two groups of cam lobes. It is possible, for example, for one group to act only on intake valves and the other group to act only on exhaust valves but this need not necessarily always be the case.

It is also possible for some or all of the lobes of the two groups to act on valves of the same type (intake or exhaust) while other lobes in the same group could act on valves of a different type. When these lobes are phased relative to one another, it has the effect of increasing the duration of the valve event for that particular group.

Improvements in engine fuel economy performance can then be gained from optimising the valve lift event duration over the full engine operating range.

Valve trains are also known where the cam follower is a switching cam follower, where the follower is able to switch between two sets of cam lobe profiles on the same camshaft. Such a follower is outlined in EP0620360 and US6668779. It is also possible to use the invention in an engine that uses such a switching follower system, where further benefits in performance could be obtained. Valve trains are also known in which two cam lobes act on the same valve through a summation lever to enable the valve lift and/or duration to be varied by appropriately setting the relative phase of the two cam lobes. Camshafts for such valve trains are termed variable lift and duration camshafts and will be referred to below by the acronym VLD. These camshafts also have two groups of cam lobes that are phased relative to one another to effect a change in the resulting valve lift event.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which :

Figs. IA to IE show different valve train

configurations in which an phaser assembly of the present invention may be used,

Fig. 2A is a perspective view of a first embodiment of a dual phase assembly of the present invention mounted on one end of a concentric camshaft,

Fig. 2B is a side view of the assembly in Fig. 2A, Fig. 2C is a section taken through the axial plane C-C in Fig. 2B,

Fig. 3 is a view similar to than of Fig. 2C showing a section through a second embodiment of the invention,

Fig. 4A is a side view of a third embodiment of the invention,

Figs. 4B and 4C are sections taken through the axial planes B-B and C-C in Fig. 4A, respectively,

Fig. 5A is a perspective view of a fourth embodiment of the invention,

Fig. 5B is a side view of the embodiment of Fig. 5A, Figs. 5C and 5D are sections taken through the axial planes C-C and D-D in Fig. 5B, respectively, and Fig. 5E is an axial section taken through the plane E-E in Fig. 5C.

Detailed description of the preferred embodiment (s)

Fig. IA shows a valve train configuration in which the first and second lobe groups are formed on two solid camshafts. In such a configuration the group of cam lobes may operate the intake valves and the second group the exhaust valves of an engine. A twin phaser driving two cams is known, for example from Figures 9 and 10 of EP1234954.

Fig. IB shows a valve train configuration having a phaser assembly of the invention mounted on a concentric camshaft. This camshaft and phaser configuration would suit DOHC engines as well as three-valve per cylinder engines. In this configuration, both lobe groups operate on the same type of valve (intake or exhaust) , with the first lobe group controlling the first of a pair of identical valves within each cylinder and the second the other.

When the phase of Phaser 1 is changed, both valves of the pair will change their timing relative to the

crankshaft, but when the phase of Phaser 2 is changed only the second lobe group will change its timing. This has the effect of extending the opening duration for a pair of valves within a particular cylinder.

The resulting system therefore makes whole camshaft phasing as well as adjacent lobe phasing possible.

The valve train configuration of Figure 1C is generally similar to that of Fig IB save that it uses a VLD camshaft, as described for example in EP 1417399. In this

configuration, two groups of cam lobes act via a summation lever on pairs of intake or exhaust valves of the same type. This makes it possible to change the actual (rather than effective) opening and closing points of the pair of intake or exhaust valves relative to each other or the crankshaft.

Fig. ID shows a configuration having two lobe groups on separate camshafts, one concentric and the other solid.

Such an arrangement may be required to produce Dual Equal as well as effective duration control on intake, for instance, on a DOHC engine. Though not shown, it would alternatively be possible to link the output from the second phaser to the solid camshaft rather than linking the camshaft to the output of the first phaser. This embodiment is not

depicted.

The configuration shown in Fig. IE is similar to that of Figure ID and is suitable for DOHC engines, where the four valve pattern is rotated through 90°, so the lobes operating each pair of intake/exhaust valves are located on different camshafts. Here, it is necessary to change the phase of lobe groups on adjacent camshafts to achieve Dual Equal with a change in duration control.

It should be mentioned that the configurations of Fig. ID and Fig. IE can be modified to incorporate VLD camshafts .

The remaining drawings all show different embodiments of a dual phaser assembly of the present invention, which is represented schematically in each of Figs. IA to IE by the box in-between the crankshaft drive and the camshaft (s) . The dual phaser assembly in each case comprises two separately controllable phasers arranged to act in series such that the first phaser changes the phase of both of two lobe groups relative to the engine crankshaft while the second changes the phase of the two lobe groups relative to one another. Figs. 2A and 2B shows a dual phaser assembly 100 mounted on one end of a concentric camshaft 102 having an inner shaft driving one of the two groups of lobes and an outer tube driving the other group of lobes. The phaser assembly 100 is hydraulically operated and controlled by oil fed into it by a supply spigot 104 that is stationary and mounted, for example, on an engine cover. The internal design of the phaser assembly 100 is such that one pair of control lines change the phase of the entire camshaft 102 relative to the crankshaft while a second pair of control lines rotate the inner shaft of the concentric camshaft relative to its outer tube.

As the construction of vane-type phasers is well known and documented, the following description will not include a detailed explanation of the construction of the vanes nor of the manner in which control oil is channelled from the supply spigot 104 to the individual working chambers of the phasers .

The two phasers in Fig. 2C share a common stator 114 that defines six circumferentially spaced recesses. Three of the recesses, designated 116a, form the working chambers of a first phaser of which the rotor 112 carries radially inwards projecting vanes and is driven directly by a

sprocket 110 coupled to the engine crankshaft. The other three of the recesses, designated 116b, form the working chambers of a second phaser of which the rotor 118 is a central hub carrying radially outwards projecting vanes.

The rotor 112 serves as the input member of the first phaser and the stator 114 as its output member. The stator 114 doubles as the input member of the second phaser and is directly coupled to the outer tube of the concentric

camshaft 102. The rotor 118 of the second phaser is coupled to the inner shaft of the concentric camshaft 102. When the first phaser is operated by controlling the oil supply to the opposed arcuate working chambers in the recesses 116a, the stator 114 rotates relative to the sprocket 110. If at the same time no oil is transferred between the working chambers in the recesses 116b the stator 114 and the rotor 118 of the second phaser will be locked relative to one another. Therefore both the inner shaft as well as the outer tube of the concentric camshaft will be rotated relative to the crankshaft. Controlling the oil supply to the chambers in the recesses 116b on the other hand will not affect the phase of the stator 114 and the outer tube of the camshaft 102 and will only change the phase of the inner shaft relative to both the outer tube and the engine crankshaft.

Fig. 2C also shows one of two hydraulically operated locks 120 and 122, which are also known and need not be described here in detail. The locks are used to dictated the positions of the phaser during starting when the

hydraulic pressure is not sufficient to bring about any phase changes. The lock 120 locates the rotor 112 relative the stator 114 while the lock 122 locates the stator 114 relative to the rotor 118. Similar locks are present in all the illustrated embodiments of the invention.

Whereas the recesses in the embodiment of Figs 2A to 2C are arranged on a common radius, Fig.3 shows an alternative embodiment in which one phaser is contained radially within the other. This construction offers the advantage that each phaser has six working chambers rather than three, allowing the torque to be spread over a larger number of vanes. In Fig. 3, the stator 212 of the first phaser is connected to the drive sprocket 210. The rotor 214 of the first phaser is connected to the outer tube of the camshaft and doubles as the stator of the second phaser. The rotor 218 of the second phaser is once again constructed as a central hub connected to the inner shaft of the camshaft. The third embodiment, shown in Figures 4A to 4C differs from the embodiments of Figures 2 and 3 in that the two phasers are axially spaced instead of being radially spaced, stator 312 of the first phaser is formed integrally with the drive sprocket 310. The rotor 314A of the first phaser is coupled to the outer shaft of the concentric camshaft and is directly connected to the stator 314B of the second phaser. The rotor 318 of the second phaser is coupled to the inner shaft of the concentric camshaft.

In all the previously described embodiments, the vanes have been retained by means of radial slots in their

respective rotors. The embodiment of Figures 5A to 5E shows an alternate design in which the vanes are axially clamped in position.

As in all the previously described embodiments, the dual phaser assembly 500 is mounted on the end of a

concentric camshaft 502 and containes two phasers. As with the embodiment of Figures 4A to 4C, the two phasers are axially spaced from one another, one lying in the plane C-C of Fig. 5B and shown in the section of Fig. 5C and the other lying in the plane D-D and shown in Fig. 5D. As is best seen in Fig. 5E the two sets of vanes 530 and 532 are axially clamped to a thin plate 534 which doubles as the rotor of the two phasers. The vanes 530 are clamped by bolts 536 to the rear plate 538 of the phaser assembly 500, which is in turn secured by means of bolts to the outer tube 502A of the concentric camshaft 502. The front plate 540 of the phaser assembly is secured by means bolts 539 to the vanes 530, the bolts passing through aligned but unthreaded holes in the vanes 532. The stator 512 of the first phaser is thus formed by sprocket wheel 510 and serves as the input member of the first phaser. The rotor of the first phaser is formed by the vanes 530 which are coupled to the outer tube 502a of the concentric camshaft 502 through the back bolts 536 and the rear plate 538. This serves as the output member of the first phaser.

The rotor of the second phaser is formed by the vanes 532 and front plate 540 which are coupled to the output of the first phaser via front bolts 539. This serves as the input member of the second phaser.

The plate 534 acts as both the rotor and output member of the first phaser and the rotor and input member of the second phaser, of which the stator 542 is coupled to the inner shaft 502b by the hub 544 on which the stator 542 is a driving fit.

An important advantage of the embodiment shown in

Fig. 5A is that timing markers 550 and 552 can be formed on the front plate 540 and on the circumference of the stator 542 of the second phaser so that the phase of both groups of lobes can be measured at all times from in front of the cam drive