Abstract:
A hub is secured to a camshaft for rotation synchronous with the camshaft, and a housing circumscribes the hub and is rotatable with the hub and the camshaft and is further oscillatable with respect to the hub and the camshaft within a predetennined angle of rotation. Driving vanes are radially disposed within the housing and cooperate with an external surface on the hub, while driven vanes are radially disposed in the hub and cooperate with an internal surface of the housing. A locking device, reactive to oil pressure, prevents relative motion between the housing and the hub. A controlling device controls the oscillation of the housing relative to the hub.

Description:
CROSS-REFERENCES 
     The present application is related to pending application Ser. No. 09/450,456 filed Nov. 29, 1999, and entitled “Variable Valve Timing with Actuator Locking for Internal Combustion Engine”, by inventor Roger T. Simpson Additionally, the present application is related to copending application Ser. No. 09/488,903 filed on the same date herewith, and entitled “Multi-Position Variable Cam Timing System Having a Vane-Mounted Locking-Piston Device”, by inventors Roger T. Simpson, and Michael Duffield, and thus is incorporated by reference herein. Finally, the present application is related to copending application Ser. No. 9/592,624 also filed on the same date herewith, and entitled “Control Valve Strategy for Vane-Typc Variable Camshaft Timing System”, by inventors Roger T. Simpson and Michael Duffield and thus is also incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an internal combustion engine having a hydraulic control system for controlling the operation of a variable camshaft timing (VCT) system of the type in which the position of the camshaft is circumferentially varied relative to the position of a crankshaft in reaction to engine oil pressure. In such a VCT system, an electro-hydraulic control system is provided to effect the repositioning of the camshaft and a locking system is provided to selectively permit or prevent the electrohydraulic control system from effecting such repositioning. 
     More specifically, this invention relates to a multi-position VCT system actuated by engine oil pressure and having a large number of thin, spring-biased vanes defining alternating fluid chambers therein. 
     2. Description of the Prior Art 
     It is known that the performance of an internal combustion engine can be improved by the use of dual camshafts, one to operate the intake valves of the various cylinders of the engine and the other to operate the exhaust valves. Typically, one of such camshafts is driven by the crankshaft of the engine, through a sprocket and chain drive or a belt drive, and the other of such camshafts is driven by the first, through a second sprocket and chain drive or a second belt drive. Alternatively, both of the camshafts can be driven by a single crankshaft-powered chain drive or belt drive. It is also known that the performance of an internal combustion engine having dual camshafts, or but a single camshaft, can be improved by changing the positional relationship of a camshaft relative to the crankshaft. 
     It is also known that engine performance in an engine having one or more camshafts can be improved, specifically in terms of idle quality, fuel economy, reduced emissions, or increased torque. For example, the camshaft can be “retarded” for delayed closing of intake valves at idle for stability purposes and at high engine speed for enhanced output. Likewise, the camshaft can be “advanced” for premature closing of intake valves during mid-range operation to achieve higher volumetric efficiency with correspondingly higher levels of torque. In a dual-camshaft engine, retarding or advancing the camshaft is accomplished by changing the positional relationship of one of the camshafts, usually the camshaft that operates the intake valves of the engine, relative to the other camshaft and the crankshaft. Accordingly, retarding or advancing the camshaft varies the timing of the engine in tenes of the operation of the intake valves relative to the exhaust valves, or in terms of the operation of the valves relative to the position of the crankshaft. 
     Heretofore, many VCT systems incorporated hydraulics including an oscillatable vane having opposed lobes and being secured to a camshaft within an enclosed housing. Such a VCT system often includes fluid circuits having check valves, a spool valve and springs, and electromechanical valves to transfer fluid within the housing from one side of a vane lobe to the other, or vice versa, to thereby oscillate the vane with respect to the housing in one direction or the other. Such oscillation is effective to advance or retard the position of the camshaft relative to the crankshaft. These VCT systems are typically “self-powered” and have a hydraulic system actuated in response to torque pulses flowing through the camshaft. 
     Unfortunately, the above VCT systems may have several drawbacks. One drawback with such VCT systems is the requirement of the set of check valves and the spool valve. The check valves are necessary to prevent back flow of oil pressure during periods of torque pulses from the camshaft. The spool valve is necessary to redirect flow from one fluid chamber to another within the housing. Using these valves involves many expensive high precision parts that further necessitate expensive precision machining of the camshaft. 
     Additionally, these precision parts may be easily fouled or jammed by contamination inherent in hydraulic systems. Relatively large contamination particles often lodge between lands on the spool valve and lands on a valve housing to jam the valve and render the VCT inoperative. Likewise, relatively small contamination particles may lodge between the outer diameter of the check or spool valve and the inner diameter of the valve housing to similarly jam the valve. Such contamination problems are typically approached by targeting a “zero contamination” level in the engine or by strategically placing independent screen filters in the hydraulic circuitry of the engine. Such approaches are known to be relatively expensive and only moderately effective to reduce contamination. 
     Another problem with such VCT systems is the inability to properly control the position of the spool during the initial start-up phase of the engine. When the engine first starts, it takes several seconds for oil pressure to develop. During that time, the position of the spool valve is unknown. Because the system logic has no known quantity in terms of position with which to perform the necessary calculations, the control system is prevented from effectively controlling the spool valve position until the engine reaches normal operating speed. Finally, it has been discovered that this type of VCT system is not optimized for use with all engine styles and sizes. Larger, higher-torque engines such as V-8&#39;s produce torque pulses sufficient to actuate the hydraulic system of Such VCT systems. Regrettably however, smaller, lower-torque engines such as four and six cylinder&#39;s may not produce torque pulses sufficient to actuate the VCT hydraulic system. 
     Other VCT systems incorporate system hydraulics including a hub having multiple circumferentially spaced vanes cooperating within an enclosed housing having multiple circumferentially opposed walls. The vanes and the walls cooperate to define multiple fluid chambers, and the vanes divide the chambers into first and second sections. For example Shirai et al., U.S. Pat. No. 4,858,572, teaches use of such a system for adjusting an angular phase difference between an engine crankshaft and an engine camshaft. Shirai et al. further teaches that the circumferentially opposed walls of the housing limit the circumferential travel of each of the vanes within each chamber. 
     Shirai et al. discloses fluid circuits having check valves, a spool valve and springs, and electromechanical valves to transfer fluid within the housing from the first section to the second section, or vice versa, to thereby oscillate the vanes and hub with respect to the housing in one direction or the other. Shirai et al. Further discloses a first connecting means for locking the hub and housing together when each vane is in abutment with one of the circumferentially opposed walls of each chamber. A second connecting means is provided for locking the hub and housing together when each vane is in abutment with the other of the circumferentially opposed walls of each chamber. Such connecting means are effective to keep the camshaft position either fully advanced or fully retarded relative to the crankshaft. 
     Unfortunately, Shirai et al. has several shortcomings. First, the previously mentioned problems involved with using a spool valve and check valve configurations are applicable to Shirai et al. Second, this arrangement appears to be limited to a total of only 15 degrees of phase adjustment between crankshaft position and camshaft position. The more angle of cam rotation, the more opportunity for efficiency and performance gains. Thus, only 15 degrees of adjustment severely limits the efficiency and performance gains compared to other systems that typically achieve 30 degrees of cam rotation. Third, this arrangement is only a two-position configuration, being positionable only in either the fully advanced or fully retarded positions with no positioning in-between whatsoever. Likewise, this configuration limits the efficiency and performance gains compared to other systems that allow for continuously variable angular adjustment within the phase limits. 
     Therefore, what is needed is a VCT system that is designed to overcome the problems associated with prior art variable camshaft timing arrangements by providing a variable camshaft timing system that performs well with all engine styles and sizes, packages at least as tightly as prior art VCT hardware, eliminates the need for check valves and spool valves, provides for continuously variable camshaft to crankshaft phase adjustment within its operating limits, and provides substantially more than 15 degrees of phase adjustment between the crankshaft position and the camshaft position. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a Variable Camshaft Timing (VCT) system that is designed to overcome the problems associated with prior art variable camshaft timing arrangements. The present invention provides a variable camshaft timing system that performs well with all engine styles and sizes, packages at least as tightly as prior art VCT hardware, eliminates the need for check valves and spool valves, provides for continuously variable camshaft to crankshaft phase adjustment within its operating limits, and provides substantially more than 15 degrees of phase adjustment between the crankshaft position and the camshaft position. 
     In one form of the invention, there is provided a camshaft and a hub secured to the camshaft for rotation synchronous with the camshaft. A housing circumscribes the hub and is rotatable with the hub and the camshaft and is further oscillatable with respect to the hub and the camshaft within a predetermined angle of rotation. A plurality of driving vanes is radially disposed in the housing and cooperates with an external surface on the hub. Likewise, a plurality of driven vanes is radially disposed in the hub and cooperates with an internal surface of the housing. A locking arrangement reactive to oil pressure is provided for preventing relative motion between the housing and the hub at any of a multitude of circumferential positions of the housing and the hub relative to one another. Finally, a configuration for controlling the oscillation of the housing relative to the hub is provided. 
     Accordingly, it is an object of the present invention to provide an improved variable camshaft timing arrangement for an internal combustion engine. 
     It is another object to provide a variable camshaft timing arrangement in which the position of a camshaft is continuously variable relative to the position of the crankshaft within its operating limits. 
     It is still another object to provide a hydraulically operated variable camshaft timing arrangement of relatively simplified mechanical and hydraulic construction in contrast to an arrangement that requires check valves and spool valves. 
     It is yet another object to provide an improved VCT system that performs with all engine styles and sizes. 
     It is a further object to provide a VCT system that packages as tightly as previous VCT systems and eliminates the need for check valves and spool valves, 
     It is still a further object to provide a VCT that provides for continuously variable camshaft to crankshaft phase adjustment within its operating limits, and that provides at least approximately 30 degrees of phase adjustment between the crankshaft position and the camshaft position. 
     These objects and other features, aspects, and advantages of this invention i. 0  will be more apparent after a reading of the following detailed description, appended claims, and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a camshaft and vane phaser according to the present invention; 
     FIG. 2 is an end view ol the camshaft and vane phaser of FIG. 1; 
     FIG. 3 is an end view of another camshaft having a vane phaser according to the present invention; 
     FIG. 4 is a schematic view of the hydraulic equipment of the camshaft and vane phaser arrangement according to the preferred embodiment of the present invention and illustrates a phase shift where the position of the camshaft is changing from neutral position to a retard position; 
     FIG. 5 is a cross-sectional view of components of the variable camshaft timing system of the present invention in the position of such components as illustrated in FIGS. 4 and 6; 
     FIG. 6 is a schematic view of the hydraulic equipment of the variable cam timing arrangement according to the preferred embodiment of the present invention and illustrates a phase shift where the position of the camshaft is changing from neutral position to an advance position; 
     FIG. 7 is a schematic view of the hydraulic equipment of the variable camshaft timing arrangement according to the preferred embodiment of the present invention and illustrates a locked condition where the position of the camshaft is neutral and the housing is locked to the camshaft; 
     FIG. 8 is a cross-sectional view of components of the variable camshaft timing system of the present invention in the position of such components as illustrated in FIG. 7; 
     FIG. 9 is a schematic view of the hydraulic equipment of the variable camshaft timing arrangement according to an alternative embodiment of the present invention and illustrates a phase shift where the position of the camshaft is changing from neutral position to an advance position, and further illustrates use of a three-way solenoid to unlock the housing from the camshaft; 
     FIG. 9A is an end view of another camshaft and vane phaser according to the present invention; and 
     FIG. 10 is a schematic view of the hydraulic equipment of the variable camshaft timing arrangement according to another alternative embodiment of the present invention and illustrates a phase shift where the position of the camshaft is changing from neutral position to an advance position, and further illustrates oil pressure flowing directly to a locking piston to unlock the housing from the camshaft. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In general, a hydraulic timing system is provided for varying the phase of one rotary member relative to another rotary member. More particularly, the present invention provides a multi-position Variable camshaft Timing (VCT) system powered by engine oil for varying the timing of a camshaft of an engine relative to a crankshaft of an engine to improve one or more of the operating characteristics of the engine. While the present invention will be described in detail with respect to internal combustion engines, the VCT system is also well suited to other environments using hydraulic timing devices. Accordingly, the present invention is not limited to only internal combustion engines. 
     Referring now in detail to the Figures, there is shown in FIGS. 1 and 2 a vane phaser  10  according to the preferred embodiment of the present invention. The vane phaser  10  includes a housing  24  or sprocket circumscribing a hub  40 . The housing  24  includes sprocket teeth  26  disposed about its periphery and an annular array of locking teeth  30  disposed about a locking diameter  28 . The housing  24  further includes an internal  20  surface  32  and internal lobes  34  circumferentially spaced apart with a radial slot  34   a  in each lobe. Each radial slot  34   a  extends outwardly and is open to the internal surface  32 . The housing  24  includes a driving vane  36  radially and slidably disposed in each radial slot  34   a . Each driving vane  36  has an inner edge  36   a  that engages an external surface  42  of the hub  40 . Each driving vane  36  is spring-loaded by a bias member or spring  38  radially inwardly to ensure constant contact with the external surface  42  of the hub  40 . 
     The hub  40  includes external lobes  44  circumferentially spaced apart, around an external surface  42 , and a radial slot  44   a  in each external lobe  44 . The hub  40  includes a driven vane  46  radially and slidably disposed in each radial slot  44 a. Each driven vane  46  has an outer edge  46   a  that engages the internal surface  32  of the housing  24 . Each driven vane  46  is biased radially outwardly by a bias member or spring  48  to ensure constant contact with the internal surface  32  of the housing  24 . In that regard, each outer edge  46 A of each driven vane  46  of the hub  40  slidably cooperates with the internal surface  32  of the housing  24 . Likewise, each inner edge  36 A of each driving vane  36  of the housing  24  slidably cooperates with the external surface  42  of the hub  40  to permit limited relative movement between the hub  40  and the housing  24 . 
     The driving and driven vanes  36  and  46  are alternately circumferentially interspersed to define advance chambers  12  and retard chambers  14 . Therefore, the advance and retard chambers  12  and  14  are also alternately circumferentially interspersed between the hub  40  and the housing  24 . In addition, the advance and retard chambers  12  and  14  are fluid tightly separated from one another. 
     FIG. 3 illustrates another vane phaser  110  according to an alternative  20  embodiment of the present invention. Here the vane phaser  110  design is more similar to ordinary vane pump design and includes a rotor or hub  140  and housing  124 . In contrast to the vane phaser  10  of FIGS. 1 and 2, this vane phaser  110  has no lobes. Rather, a driven vane  146  is disposed in each radial slot  144  in the hub  140  and a driving vane  136  is disposed in each radial slot  134  in the housing  124 . 
     Referring now to FIGS. 4,  6 , and  7 , the vane phaser  10  of the variable camshaft timing system according to the preferred embodiment of the present invention is provided in schematic form. The vane phaser  1   0  includes the housing  24  having the driving vanes  36  extending inwardly therefrom. The hub  40  includes the driven vanes  46  extending outwardly therefrom. The hub  40  is keyed or otherwise secured to a camshaft  50  to be rotatable therewith, but not oscillatable with respect thereto. The assembly that includes the camshaft  50  with the hub  40  and housing  24  is caused to rotate by torque applied to the housing  24  by an endless chain (not shown) that engages the sprocket teeth  26 , so that motion is impacted to the endless chain by a rotating crankshaft (not shown). The housing  24 , rotates with the camshaft  50  and is oscillatable with respect to the camshaft  50  to change the phase of the camshaft  50  relative to the crankshaft. 
     A locking arrangement is enabled using pressurized engine oil that flows into the camshaft  50  by way of a supply passage  54  in a camshaft bearing  52  (as indicated by the directional arrows). The engine oil flows first to a 3-way on/off flow control valve  16  whose operation is controlled by an electronic engine control unit (ECU)  18 . As shown in FIGS. 4 and 6, when the 3-way valve  16  is on, oil flows through the 3-way valve  16  into a locking passage  56  in the camshaft  50  against a locking plate  70 . The oil pressure thereby urges the locking plate  70 , against the force of a return spring  72 , to a position where the locking plate  70  maintains the vane phaser  10  in an unlocked condition by structure that will hereinafter be described in greater detail. In FIG. 7, however, the 3-way valve  16  is off and no engine oil, therefore, will flow into the locking passage  56 , whereupon the return spring  72  will return the locking plate  70  to its locked position. 
     Referring now to FIGS. 5 and 8, the locking plate  70  is in the form of an annular member that is coaxially positioned relative to the longitudinal central axis of the camshaft  50 . A locking ring  66  is provided with an annular array of locking teeth  68  that is positioned to engage the locking teeth  30  on the housing  24  when the locking plate  70  moves along the longitudinal central axis of the camshaft  50  from the unlocked position shown in FIG. 5 to the locked position shown in FIG.  8 . As heretofore explained in connection with FIGS. 4,  6 , and  7 , the locking plate  70  is biased toward its locked position of FIG. 8 by the return spring  72 , which bears against an axial surface  70 A of the locking plate  70  to which the locking ring  66  is secured by a snap ring  78 . The locking plate  70  is urged to its unlocked position of FIG. 5 by hydraulic pressure through the locking passage  56  shown in FIGS. 4,  6 , and  7 . The hydraulic pressure bears against an axial surface  70 B of the locking plate  70  that is opposed to the axial surface  70 A acted upon by the return spring  72 . 
     As heretofore explained, the locking plate  70  is incapable of circumferential movement relative to the camshaft  50 , whereas the housing  24  is capable of circumferential movement relative to the camshaft  50 . For this reason, and because of the multitude of intercommunicating locking teeth  30  and  68 , the locking plate  70  and locking ring  66  are capable of locking the housing  24  in a fixed circumferential position relative to the camshaft  50  at a multitude of relative circumferential positions therebetweeni. This occurs whenever hydraulic pressure in the locking passage (not shown) falls below a predetermined value needed to overcome the force of the return spring  72 . 
     As shown in FIGS. 5 and 8, the housing  24  is open at either axial end but is closed off by separate spaced apart end plates  80   a  and  80   b .The assembly that includes the locking plate  70 , the end plates  80   a  and  80   b , the housing  24 , and the hub  40  is secured to an annular flange  58  of the camshaft  50  by bolts  82  each of which passes through each of the external lobes  44  of the hub  40 . In that regard, the locking plate  70  is slidable relative to a head  84  of each bolt  82 , as can be seen by comparing the relative unlocked and locked positions of FIGS. 5 and 8. 
     As shown in FIGS. 4 and 6, a control configuration is enabled using pressurized engine oil from the supply passage  54  that flows through the 3-way valve into a 4-way pulse width modulation control valve  20  for closed-loop control. The 4-way valve  20  is in fluid communication with an advancing fluid passage  60  and a retarding fluid passage  62  in the camshaft  50  that communicate through aligned apertures  76  in a sleeve portion  74  of the locking plate  70  to the advance and retard chambers  12  and  14  between the hub  40  and housing  24 . When the locking plate  70  is in the unlocked position, oil may flow to and from the advance and retard chambers  12  and  14  with respect to the 4-way valve  20 . 
     As shown in FIG. 7, however, when the locking plate  70  is in the locked position, the aligned apertures  76  of the slidable annular member do not align with the advancing fluid passage  60  and retarding fluid passage  62 , and therefore block flow of engine oil to and from the 4-way valve  20  with respect to the advance and retard chambers  12  and  14 . 
     In operation, as shown in FIG. 4, when the engine is started the pressurized oil begins to flow through the camshaft bearing  52  and into the 3-way valve  16  and through the 3-way valve  16  into the 4-way valve  20 . The engine control unit  18  processes input information from sources within the engine and elsewhere, then sends output information to various sources including the 3-way valve  16 . The 3-way valve  16  directs engine oil to the locking passage  56  based upon output from the engine control unit  18  to unlock the locking plate  70 , which then allows the vane phaser  10  to shift phase. The engine control unit may then signal the 4-way valve  20  to direct oil from a supply port  20 S to a retard port  20 R through to the retarding fluid passage  62  and into the retard chambers  14 . Simultaneously, engine oil is allowed to exhaust from the advance chambers  12  through the advancing fluid passage  60  into an advance port  20 A of the 4-way valve  20  and out an exhaust port  20 E. Attentively, as shown in FIG. 6, the engine control unit  18  may signal the 4-way valve  20  to direct oil from the supply port  20 S to the advance port  20 A through the advancing fluid passage  60  and into the advance chambers  12 . Simultaneously, engine oil is allowed to exhaust from the retard chambers  14  through the retarding fluid passage  62  into the retard port  20 R of the 4-way valve  20  and out the exhaust port  20 E. 
     As shown in FIG. 7, once the desired phase shift has been achieved, the engine control unit  18  will signal the 3-way valve  16  to permit the oil to exhaust from the locking plate  70  through the locking passage  56  through a locking port  16 L of the 3-way valve  16  and out an exhaust port  16 E. Simultaneously, all engine oil flow to and from the advance and retard chambers  12  and  14  with respect to the 4-way valve  20  will cease since the locking plate  70  slides to a locked position to block oil flow and lock the vane phaser  10  in position. 
     FIGS. 9 and 9A illustrate a vane phaser  210  according to an alternative embodiment of the present invention. FIG. 9 illustrates how the 3-way valve  16 , an advancing fluid passage  260  in a camshaft  250 , and bias members  290  in each of the retard chambers  14  perform the phase shift of the camshaft  250  under closed-loop control. Ilere, the bias members  290  act upon the driven vanes  46  to bias the hub  40  and driven vanes  46  in a fully retarded position under 0% duty cycle. Accordingly, in order to counterbalance the spring force of the bias members  290 , oil pressure under 100% duty cycle flows from the supply passage  254  through the 3-way valve  16  and advancing fluid passage  260  into each of the advance chambers  12 . Therefore, the phase shift is achieved simply by controlling flow of oil pressure into each advance chamber  12 . 
     FIG. 9A illustrates that the vane phaser  210  incorporates compression springs for the bias members  290 . Other springs, however, may be employed such as torsional springs, accordion springs, and beehive compression spriings. It is contemplated that the bias on the hub  40  may also be achieved using a single spring member configuration (not shown). Additionally, the hub  40  may instead be normally biased toward the fully advanced position (not shown), whereby phase shift would be achieved by controlling flow into the retard chambers  14 . 
     Finally, FIG. 10 also illustrates a vane phaser  310  according to an alternative embodiment of the present invention in which the locking plate  70  is always disengaged while oil flows through the camshaft bearing  52  mounted around a camshaft  350 . In this configuration, once oil pressure is high enough to overcome the force of the return spring  72  the locking plate  70  will disengage. Therefore, the locking plate  70  will be disengaged all the time that the engine is running and supplying oil pressure. Accordingly, the vane phaser  310  will be able to move to any position within the accuracy of the phaser control scheme. 
     From the above, it can be appreciated that a significant advantage of the present invention is that no check valves or spool valves are required, and thus the VCT will likely be less susceptible to contamination problems. 
     An additional advantage is that the VCT of the present invention maintains a similar dimensional size as current self-powered VCT phaser mechanisms, yet operates effectively from engine oil pressure and does not require actuation from torque pulses from the camshaft. In order to reduce the size of the vane phaser, the present invention includes a vane phase configuration of less cross-sectional area and having more vane chambers to achieve comparable volume with respect to prior art vane phases. Accordingly, the phaser can achieve 30 degrees of cam phase rotation yet maintain a cross-sectional width of less than 15 mm. 
     Another advantage is that the VCT of the present invention shares many characteristics with traditional vane-style pumps and therefore may share vane pump componentry and the benefit of long established vane pump design and manufacturing principles. 
     Yet another advantage is that no additional seal system is required to seal the alleviating advance and retard chambers since the driving and driven vanes are spring loaded into constant contact with the hub and housing respectively. 
     While the present invention has been described in terms of a preferred embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, an open-loop control strategy could be employed to achieve the phase shift of the camshaft. Likewise, alternative control valve devices may be employed to control fluid flow. Additionally, the reader&#39;s attention is directed to all papers and documents filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. Accordingly, the scope of the present invention is to be limited only by the following claims.