Abstract:
A variable phase drive coupling is described for providing drive from an engine crankshaft to two sets of cams. The drive coupling comprising a drive member  12  connectable for rotation with the engine crankshaft and two driven members  18, 20  each connectable with a respective one of the two sets of cams. In the invention, the angular relationship of each of the driven members  18, 20  is independently variable relative to the drive member  12  under the action of camshaft torque reversals.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a variable phase drive coupling, also herein termed a phaser, for providing drive from an engine crankshaft to two sets of cams, the drive coupling comprising a drive member connectable for rotation with the engine crankshaft and two driven members each connectable with a respective one of the two sets of cams.  
       SUMMARY OF THE INVENTION  
       [0002]     According to the present invention, there is provided a phaser as set forth above wherein the angular relationship of each of the driven members is independently variable relative to the drive member under the action of camshaft torque reversals.  
         [0003]     Preferably, the driven members are hydraulically coupled for rotation with the drive member and the phase of the driven members is controlled by selectively permitting the flow of hydraulic fluid between the hydraulic chambers.  
         [0004]     Conventionally, hydraulically operated phasers use an engine generated hydraulic oil pressure in order to alter the timing of the camshafts, but the phaser of the preferred embodiments of the present invention relies instead on the pressure generated by the reaction torque reversals of the cams.  
         [0005]     The invention is particularly applicable to engines using an assembled camshaft having two groups of cam lobes mounted on the same shaft, the timing of the two groups of cam lobes being variable in relation to one another. The invention is however alternatively applicable to an engine having one camshaft driven directly from the engine crankshaft and using a secondary drive to operate the second camshaft from the first.  
         [0006]     Preferably, the phaser is a ‘vane-type’ phaser having a number of oil-filled arcuate cavities, each cavity being divided into two parts by a moveable radial vane. Allowing oil to flow from one side of the vane to the other through one-way valves changes the position of the vane in the cavity, thus actuating the phaser.  
         [0007]     Advantageously, the flow of the hydraulic fluid is controlled via two spool valves mounted concentrically.  
         [0008]     It is possible for each of the driven members to be controlled via two oil passages, each of which is fitted with a one-way valve that may be selectively bypassed.  
         [0009]     Alternatively, each of the driven members may be controlled via two oil passages connected to a single one-way valve that controls the direction of flow between the two passages.  
         [0010]     In order to achieve a compact implementation, it is desirable to integrate one or more of the one-way valves into a spool valve.  
         [0011]     As a further possibility, the two driven members may be controlled via three oil passages, the flow through each of which is controlled via the two spool valves. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:  
         [0013]      FIG. 1  is an exploded perspective view of a first embodiment of the invention,  
         [0014]      FIG. 2  is a front view of the phaser of  FIG. 1 ,  
         [0015]      FIG. 3  is a longitudinal section through an assembled camshaft fitted with the phaser of  FIG. 1  taken in the plane A-A in  FIG. 2 ,  
         [0016]      FIG. 4  is a detail of  FIG. 3  drawn to an enlarged scale,  
         [0017]      FIG. 5  is an exploded perspective view of the solenoid operated control valve of the phaser in  FIG. 1 ,  
         [0018]      FIG. 6  is a plan view of cylinder head using two separate camshafts and a having a phaser of the invention to enable the phase of each of the camshafts to be varied independently relative to the crankshaft, and  
         [0019]     FIGS.  7  to  11  are schematic diagrams showing the design of different hydraulic circuits that may be used for controlling the phaser. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     The following description will assume a basic understanding of the construction and operation of vane-type phasers which are well documented in the prior art, for example in U.S. Pat. No. 6,725,817.  
         [0021]     A phaser  10  shown in FIGS.  1  to  5  has two pairs of cavities  11  and  13  in its drive sprocket  12 , one diametrically opposed pair of cavities for each of two phased outputs. Vanes  14  and  16  are fixed to front and rear plates  18  and  20 , respectively, of the phaser  10  and are fitted with rubber seals  22  to reduce leakage. The rear plate  20  is integral with the front bearing  32  of an assembled camshaft  30 .  
         [0022]     The camshaft  30 , as shown in  FIG. 3 , has an inner shaft  50  rotatable relative to an outer tube  52 . The outer tube is fast in rotation with one set of cams  54 . A second set of cams  56  that are free to rotate about the cuter tube is coupled for rotation with the inner shaft  50  by means of pins  58  that pass through tangentially elongated slots in the outer tube  52 . Such an assembled camshaft is itself well known and is referred to as an SCP (single cam phaser) camshaft.  
         [0023]     The bearing  32  is connected to the inner shaft  50  of the SCP camshaft and drives the cam lobes  56  that can rotate relative to the outer tube of the camshaft. The front plate  18  on the other hand is clamped to the front of the camshaft outer tube  52  via a nut  34  (see  FIG. 4 ) and drives all of the cam lobes  54  fixed to the outer tube  52 .  
         [0024]     Two locking pins  40  and  42  are provided to prevent the front and rear plates  18 ,  20  from moving under low oil pressure conditions when the engine is starting or stopping. The locking pins  40  and  42  are disengaged by an oil pressure feed from the camshaft front bearing, as shown in  FIG. 4 . The oil pressure supply from the front bearing  32  is also used to top-up the oil inside the phaser, to compensate for any leakage, and is connected to the oil circuit inside the phaser by a conventional one-way valve system  60 .  
         [0025]     Each of the phaser outputs is controlled via two one-way valves  70  and  72 , the valves allowing oil to flow into the pair of cavities on opposite sides of their respective vanes, thus allowing the phase of the front/rear plate to be controlled. The flow through the one-way valves  70  and  72  is controlled by a spool valve  80 , shown in exploded view in  FIG. 5 .  
         [0026]     The spool valve  80  comprises an inner spool  82  biased by a spring  84  and an outer spool  86  biased by a spring  88 . The two spools  82  and  86  are separated by a stationary separator sleeve  90  and a spool retainer  92  engages both the front end of the outer spool  86  and the front plate  18  of the phaser to ensure that the spool valve  80  does not rotate within the outer tube of the camshaft. A solenoid  93  having two separate coils  91 ,  95  operates two concentric actuators each displacing a respective one of the two spools  82 ,  86  against the action of its associated spring.  
         [0027]     The operation of the spool valve  80  and the one-way valves  70  and  72  will be better understood by referring to the system diagrams in  FIGS. 7 and 8 .  
         [0028]      FIG. 7 , which is in three parts shows the operation of the outer spool  86  of the spool valve that is connected to one set of vanes. The three views in each of FIGS.  7  to  10  show different positions of the valve spools and the way in which they affect the flow in the hydraulic circuit and the effect on the phase of the outputs of the phaser.  
         [0029]     Oil feeds  100  and  102  are provided in  FIG. 7  to both sides of the vane  16 , which are each connected via a one-way valve  70 ,  72  to a connecting oil gallery  104 . The one-way valves  70  and  72  are arranged such that oil may flow from the oil gallery  104  to either section of the cavity, but oil cannot flow from the cavity into the oil gallery  104 . In its central position, the outer spool  86  blocks the end of both oil feeds  102  and  104  from the cavity  13  and so the vane  16  is unable to move.  
         [0030]     Moving the outer spool  86  to the left (see the second view of  FIG. 7 ) will connect the left hand oil feed  100  to the central oil gallery  104 , opening a path for oil to flow out of the working chamber on left side of the vane  16  and back into the chamber on the right side of the vane  16  via the one-way valve  72  in the right hand oil feed  102 . The phaser can therefore only provide torque in an anti-clockwise direction and any torque from the camshaft in the opposite direction will cause the vane to move in an anti-clockwise direction by pushing oil from one side of the cavity to the other.  
         [0031]     Moving the outer spool  86  in the opposite direction as illustrated in the right hand view of  FIG. 7  allows the vane  16  to move in a clockwise direction as shown.  
         [0032]     The operation of the inner spool  82  is similar in principle to that of the outer spool  86 , but it controls the other output of the phaser via a second set of vanes  14 . The three views of  FIG. 8  illustrate the movement of the inner spool  82  and the associated movement of the vane  14  that will be permitted.  
         [0033]     In order to reach the inner spool  82 , the oil connections need to pass through slots in the outer spool  86  and the stationary spool separator  90 . The slots in the outer spool  86  are designed to ensure that oil flow to the inner spool  82  is not affected by the position of the outer spool.  
         [0034]     Both oil circuits are fed with oil from the engine oil pump in order to replace any leakage, and the feed is connected to the central oil galleries via one-way valves. Two separate valves are required in order to prevent any communication between the two control systems.  
         [0035]     The orientation of the outer spool  86  needs to be controlled in order to ensure that its slots and its drillings for transferring oil to the inner spool are correctly aligned to the holes in the front of the camshaft tube  52 . This is achieved by the spool retainer  92  which both retains the outer spool  86  inside the phaser and prevents it from rotating.  
         [0036]     It would be possible to apply the same type of phasing system to an engine having conventional twin camshafts, using a secondary gear or chain connection to drive the second camshaft from the first. Such an embodiment is illustrated in  FIG. 6  in which two solid camshafts  200  and  202  are mounted parallel to one another in the engine cylinder head. The camshaft  200  is connected to the front plate of the phaser  204  and instead of driving the inner shaft of an assembled camshaft, the rear plate of the phaser  204  drives a sprocket  206  connected to drive the second camshaft  202 .  
         [0037]     It will be appreciated that the invention is not restricted to the hydraulic circuit described above and that various alternative designs may be adopted, examples of such alternative hydraulic circuits being shown in FIGS.  9  to  11 . Most of the components of these circuits operate in analogous manner to that already described and the ensuing description will therefore be restricted to the points of difference.  
         [0038]     The embodiment of  FIG. 9  uses a single one-way valve  250  to replace the valves  70  and  72  in  FIG. 7 . The single one-way valve  250  is positioned at the intersection of the central oil gallery  104  with the two oil feeds from the vane cavity. The valve  250  needs to be designed to isolate the two oil feeds from each other when it is closed, hence it has a long parallel section.  
         [0039]     The top up oil feed from the engine oil pump is fed into the system through the middle of the one-way valve  250  via a simple ball valve. This arrangement causes the one way valve to be forced onto its seat by the engine oil pressure and the valve will only open when the pressure in the central gallery exceeds the engine oil pressure.  
         [0040]     The operation of the system is identical in all other respects as illustrated in  FIG. 7 . Moving the spool to the left connects the left hand oil feed to the central gallery  104 , allowing the vane  16  to push oil out of the left hand side of the cavity and move in an anti-clockwise direction. Moving the spool  86  to the right connects the right hand oil feed to the central gallery, allowing the vane  16  to push oil out of the right hand side of the cavity and move in a clockwise direction.  
         [0041]     The embodiments of  FIGS. 10 and 11  have one-way valves  170 ,  172  positioned within the inner valve spool instead of being mounted in the main body of the phaser.  
         [0042]     These figures also show how the two phaser outputs may be controlled using three oil feeds  300 ,  302 ,  304  rather than four (two each of oil feeds  100  and  102 ) to control both the outputs of the phaser. The embodiments of  FIGS. 10 and 11  operate in essentially the same manner and differ only in that in  FIG. 10  the vanes  14  and  16  driving the two outputs share a common cavity whereas in  FIG. 11  two separate cavities are used as in the previously described embodiments but two of the chambers of the cavities are directly connected to one another.  
         [0043]     In these embodiments, the outer spool is used to determine which of the three feeds is connected to the inner spool. The inner spool is used to control the direction of oil flow between the two oil feed paths that are connected to it. Moving the inner spool to the left allows oil from the left hand feed to flow into the bore of the spool, pass through to the right hand of the bore via a one way valve  170 ,  172  and out into the right hand feed. Moving the inner spool to the right allows oil from the right hand feed to flow into the bore of the spool, pass through to the left hand end of the bore via the one way valve and out into the left hand oil feed.  
         [0044]     Two separate top-up oil feeds  306 ,  308  from the engine oil supply are shown in  FIG. 11  at the bottom of each view.  
         [0045]     The left hand view of  FIG. 10  shows the outer spool in its central position where the two outer oil feeds are connected to the inner spool and the centre oil feed is blocked. This will allow oil to be transferred between the two outer sections of the cavity whilst the middle section remains the same.  
         [0046]     The middle view of  FIG. 10  shows the outer spool moved to the left, such that the right hand oil way is blocked and the inner spool is connected to the left hand and central oil ways. This will allow oil to be transferred between the left hand and the central sections of the cavity whilst the right hand section remains the same.  
         [0047]     The right hand view of  FIG. 10  shows the outer spool moved to the right, such that the left hand oil way is blocked and the inner spool is connected to the central and right hand oil ways. This will allow oil to be transferred between the central and the right hand sections of the cavity whilst the left hand section remains the same.  
         [0048]     Intermediate positions of the outer spool will allow all three sections of the cavity to be controlled at the same time. However, there is no position of the outer spool that will allow oil to flow out of the central section and into both outer sections, or allow oil to flow out of both outer sections and into the central section.  
         [0049]     The oil feeds can be designed to permit this type of variation if required, but there will be a different flow regime that becomes precluded instead.  
         [0050]     The different embodiments of the invention offer the following advantages when compared to existing vane-type phaser designs: 
        The phaser requires only a ‘top up’ oil feed, hence reducing oil consumption.     The response speed of the phaser is not dependent upon oil supply pressure.     No complex oil control drillings are required in the cylinder head or block.     No oil drainage problems result from large quantities of ‘waste’ oil.