Abstract:
A variable cam timing phaser for adjusting phase between a first shaft and a second shaft using oil pressure from an oil pressure source including a housing assembly and a rotor assembly together defining a plurality of segments. The segments include at least one operating segment including an advance chamber and a retard chamber, the advance chamber and the retard chamber being oppositely switchable between at least a source of oil pressure and a drain, the vane being movable by oil pressure from the oil source applied to either the advance chamber or the retard chamber with the other of the advance chamber and the retard chamber being coupled to the drain and at least one assist segment including an assist chamber and a vent chamber, the vent chamber being vented to atmosphere; such that oil supplied to the assist chamber assists the motion of the vane in a direction.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims one or more inventions which were disclosed in Provisional Application No. 61/291,992 filed Jan. 4, 2010, entitled “OPA VCT PHASER WITH OIL PRESSURE BIAS”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention pertains to the field of variable cam timing. More particularly, the invention pertains to an oil pressure actuated variable cam timing phaser with oil pressure assist. 
         [0004]    2. Description of Related Art 
         [0005]    Apart from the cam torque actuated (CTA) variable camshaft timing (VCT) systems, the majority of hydraulic VCT systems operate under two principles—oil pressure actuation (OPA) or torsional assist (TA). In the oil pressure actuated VCT phaser, one or more operating segments  30  each include a vane  4  defining the operating segments  30  into first working chambers  2  and second working chambers  3  in fluid communication with an oil control valve (OCV)  9 . In the OPA VCT phaser, the OCV directs engine oil pressure to the first working chamber  2  while simultaneously venting the second opposing working chamber  3  defined by the housing  1 , the rotor  5 , and the vane  4 . This creates a pressure differential across one or more of the vanes  4  to hydraulically push the VCT phaser in one direction or the other. Neutralizing or moving the OCV  9  to a null position in which the OCV  9  blocks fluid flow into and out of the first and second working chambers puts equal pressure on opposite sides of the vane  9  and holds the phaser in position. If the phaser is moving in a direction such that valves will open or close sooner, the phaser is said to be advancing and if the phaser is moving in a direction such that valves will open or close later, the phaser is said to be retarding. 
         [0006]    Conventional phasers have three, four, or five operating segments  30 . Within each of the operating segments is a vane  4  separating the chamber  17  formed between the housing  1  and the rotor  5  into first working chambers  2  and second opposing working chambers  3 , commonly referred to as advance chambers and retard chambers. In conventional phasers, supply oil pressure is provided to each side of all of the vanes  4 , designated V 1  V 2 , V 3 , V 4 . 
         [0007]    Referring to  FIG. 1 , the housing assembly  1  of the phaser has an outer circumference  7  for accepting drive force. The rotor assembly  5  is connected to the camshaft and is coaxially located within the housing assembly  1 . The rotor assembly  5  has a vane(s)  4  separating chamber(s)  17  formed between the housing assembly  1  and the rotor assembly  5  into an advance chambers  2 , designated A 1 , A 2 , A 3 , A 4  and a retard chambers  3 , designated R 1 , R 2 , R 3 , R 4 . The vanes  4  are capable of rotation to shift the relative angular position of the housing assembly  1  and the rotor assembly  5 . 
         [0008]    An oil control valve  9  is in fluid communication with all of the advance chambers  2  and the retard chambers  3  through advance passages  12  and retard passages  13 . The oil control valve  9  controls the flow fluid from supply pump  18  to all of the advance chambers  2  and retard chambers  3  and from the advance chambers  2  and retard chambers  3  to exhaust  19 . The oil control valve  9  may be biased in a first direction by a spring  40  and a second direction by an actuator  42 . 
         [0009]    If the phaser were to be moving toward an advance position, supply oil pressure  18  would be provided to all of the advance chambers  2 , designated A 1 , A 2 , A 3 , A 4  of the phaser e.g. all three, four or any number of the advance chambers present in the phaser, and any oil pressure in the retard chambers  3 , designated R 1 , R 2 , R 3 , R 4  e.g. all three, four or any number of the retard chambers present in the phaser, would all be exhausted or vented  19 . 
         [0010]    Additionally, if the phaser were to moving towards a retard position, supply oil pressure  18  would be provided to all of the retard chambers  3  of the phaser, designated R 1 , R 2 , R 3 , R 4  e.g. all three, four or any number of the retard chambers present in the phaser, and any oil pressure in the advance chambers  2 , designated A 1 , A 2 , A 3 , A 4  e.g. all three, four or any number of the advance chambers present in the phaser, would be exhausted or vented  19 . 
         [0011]    Additionally, the phaser may be held in a null position in which the supply oil pressure  18  to advance chambers  2  and the retard chambers  3  is blocked and oil within the chambers is prevented from exhausting. 
         [0012]    The torsional assist (TA) systems operates under a similar principle as the OPA systems, with the exception that it has one or more check valves to prevent the VCT phaser from moving in a direction opposite than being commanded, should it incur an opposing force such as torque. 
         [0013]    In some applications of oil pressure actuated phasers and torsional assist phasers in engines, a bias towards the advance position is necessary. The bias is usually achieved with a bias spring or set of bias springs. The bias springs may be present within the advance or retard chambers themselves or between the between the housing and the rotor to bias the phaser towards an advance position. 
       SUMMARY OF THE INVENTION 
       [0014]    A variable cam timing phaser for adjusting phase between a first shaft and a second shaft using oil pressure from an oil pressure source including a housing assembly and a rotor assembly together defining a plurality of segments. The segments include at least one operating segment comprising an advance chamber and a retard chamber, the advance chamber and the retard chamber being oppositely switchable between at least a source of oil pressure and a drain, the vane being movable by oil pressure from the oil source applied to either the advance chamber or the retard chamber with the other of the advance chamber and the retard chamber being coupled to the drain, the moving of the vane acting to shift the relative angular phase of the rotor assembly and the housing; and at least one assist segment comprising an assist chamber and a vent chamber, the vent chamber being vented to atmosphere; such that oil supplied to the assist chamber assists the motion of the vane in a direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0015]      FIG. 1  shows a conventional oil pressure actuated phaser. 
           [0016]      FIG. 2  shows a schematic of a phaser of a first embodiment of the present invention. 
           [0017]      FIG. 3  shows a schematic of a phaser of a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanisms use “vane phasers” on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers have a rotor  105  with one or more vanes  104  mounted to the end of the camshaft (not shown), surrounded by a housing assembly  101  with the vane chambers  117  into which the vanes  104  are received. It is possible to have the vanes  104  mounted to the housing assembly  101 , and the chambers in the rotor assembly  105 , as well. The housing&#39;s outer circumference  107  forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine. End plates (not shown) are present on either side of the phaser. 
         [0019]    Referring to  FIG. 2 , the housing assembly  101  of the phaser has an outer circumference  107  for accepting drive force. The rotor assembly  105  is connected to the camshaft (not shown) and is coaxially located within the housing assembly  100 . The phaser has at least one assist segment  132  and one or more operating segments  130 . In one embodiment, the phaser preferably has a greater number of operating segments  130  than assist segments  132 . 
         [0020]    The operating segments  130  are each defined by the chamber  117  formed between the housing assembly  101  and the rotor assembly  105  and separated into advance fluid chambers  102 , designated as A 2 , A 3 , A 4  and retard fluid chambers  103  designated as R 2 , R 3 , R 4  by a vane  104  designated V 2 , V 2 , V 4 . The one or more vanes  104 , designated V 2 , V 3 , V 4  are capable of rotation to bi-directionally shift the relative angular position of the housing assembly  101  and the rotor assembly  105  within the operating segments  130  of the phaser. 
         [0021]    The assist segment  132  is defined by the chamber  117  formed between the housing assembly  101  and the rotor assembly  105  and a vane  104  separating the chamber into a fluid assist chamber  134  in fluid communication with an oil pressure supply  118  through an oil control valve and a vent chamber  133  vented to atmosphere or exhaust  119  at all times. The vane  104 , designated V 1  is capable of rotation to uni-directionally shift the relative angular position of the housing assembly  101  and the rotor assembly  105  and therefore, the assist segment  132  assists in shifting the relative angular position of the housing assembly relative to the rotor assembly in one direction only. While the figures only show the assist toward advancing the phaser, a person skilled in the art may apply the invention such that the assist would be toward retarding the phaser. 
         [0022]    A pump  118  supplies supply oil pressure through the oil control valve  109  in fluid communication with the advance chambers  102 , the retard chambers  103 , and assist chamber  134  through advance passages  112  and retard passages  113 . An exhaust or vent  119  is in fluid communication with the oil control valve  109  and the vent chamber  133 . 
         [0023]    A locking mechanism (not shown) may be present to lock the rotor assembly  105  relative to the housing assembly  101 . The locking mechanism may be slidably housed in a bore in the rotor assembly  105  and have an end portion assisted towards and fits into a recess in the housing assembly  101  by a spring. Alternatively, the locking mechanism may be housed in the housing assembly  101  and spring assisted towards a recess in the rotor assembly  105 . 
         [0024]    An oil control valve  109  is in fluid communication with the operating segments  130  through advance passages  112  and retard passages  113  and the assist chamber  134  through the advance passages  112 . The oil pressure to the operating segments  130  and the assist chamber  134  of the assist segment  132  is actively controlled by the oil control valve  109 . The oil control valve  109  in  FIG. 2  is shown to be biased in a first direction by a spring  140  and a second direction by an actuator  142 , however any control in which the position of the oil control valve  109  is controlled may be used. The actuator  142  may be an on/off solenoid, variable force solenoid, electromechanical, motor driven, hydraulic, or any other type of actuator. 
         [0025]    For example, in a four vane system as shown in  FIG. 2 , when the phaser is moving towards the advance position, oil pressure flows from supply pump  118 , through the oil control valve  109  and through the advance passages  112  to all the advance chambers  102  designated A 2 , A 3 , A 4  of the operating segments  130  and to the assist chamber  134  of the assist segment  132 . At the same time, fluid is exhausting from all the retard chambers  103 , designated R 2 , R 3 , R 4  of the operating segments  130 , exhausting fluid through the retard passages  113  and through the oil control valve  109  to exhaust  119 . Any fluid that may leak into the vent chamber  133  is immediately exhausted to atmosphere or exhaust  119 . The oil pressure in the advance chambers  102 , designated A 2 , A 3 , A 4  move the vanes  104  clockwise in the figure with the oil pressure in the assist chamber  134  assist the movement in the advance direction. 
         [0026]    When the phaser is moving towards the retard position, oil pressure flows from supply pump  118 , through the oil control valve  109  and through the retard passages  113  to the retard chambers  103 , designated R 2 , R 3 , and R 4 , and fluid is exhausted from all of the advance chambers  102  designated A 2 , A 3 , A 4  through the advance passages  112 . At the same time, fluid is exhausted from the vent chamber  133  to atmosphere or exhaust  119  and from the assist chamber  134  through the advance passages  112 . The oil pressure in the retard chambers  103 , designated R 2 , R 3 , R 4  move the vanes  104  counterclockwise in the figure. 
         [0027]    When the phaser is in a null position, fluid from the supply pump  118  is restricted by the oil control valve  109  to the advance chambers  102 , designated A 2 , A 3 , A 4 , the retard chambers  103 , designated R 2 , R 3 , R 4  and the assist chamber  134 . Any fluid in the advance chambers  102 , the three retard chambers  103 , and the assist chamber  134  is blocked from exhausting from the chambers. Any fluid in vent chamber  133  is free to vent to atmosphere or exhaust  119 . In an alternate embodiment, fluid from the supply pump  118  may be blocked by the oil control valve  109  from entering the advance chambers  102 , designated A 2 , A 3 , A 4 , the retard chambers  103 , designated R 2 , R 3 , R 4  and the assist chamber  134 . 
         [0028]    By applying supply oil pressure  118  to an increased number of operating segments  130  than assist segments  132 , with one of the chambers of the assist segment not being connected to the supply oil pressure  118 , a higher torque in the advance direction for any given oil pressure is present causing an assist toward the advance direction, which is desirable to offset friction in the camshaft and valvetrain. Furthermore, by providing a vent chamber  133  within the assist segment  132 , the oil pressure actuated phaser has the significant benefits of better balancing of the advance and retard actuation rates, simplifying control strategies; providing much the same function as a bias spring, allowing the elimination of the bias spring, saving cost, weight, and package space; and in the case of a phaser that locks in the advanced direction using a locking mechanism, providing stronger torque to return to the base (locking) position. 
         [0029]    Bias springs provide a constant torque offset, regardless of engine operating condition, while in the present invention, a variable torque offset, based on the available oil pressure is provided. This is advantageous because under the engine operating conditions where the camshaft friction torque is high, the oil pressure also tends to be high (such as cold temperature), the present invention gives a more consistent phaser response than conventional bias springs. The use of oil pressure assist also eliminates the phase angle sensitivity of mechanical bias springs, such as spring torque changes with phase angle, which is undesirable. 
         [0030]      FIG. 3  shows an illustrative example of a second embodiment of the present invention. In this embodiment, an assist towards an advance direction is passively controlled. As in the previous embodiment, the phaser has at least one assist segment  132  and one or more operating segments  130 . In one embodiment, the phaser preferably has a greater number of operating segments  130  than assist segments  132 . 
         [0031]    The housing assembly  101  of the phaser has an outer circumference  107  for accepting drive force. The rotor assembly  105  is connected to a shaft (not shown) and is coaxially located within the housing assembly  100 . The operating segments  130  are each defined by the chamber  117  formed between the housing assembly  101  and the rotor assembly  105  and separated into advance fluid chambers  102 , designated as A 2 , A 3 , A 4  and retard fluid chambers  103  designated as R 2 , R 3 , R 4  by a vane  104  designated V 2 , V 2 , V 4 . The one or more vanes  104 , designated V 2 , V 2 , V 4  are capable of rotation to bi-directionally shift the relative angular position of the housing assembly  101  and the rotor assembly  105  within the operating segments  130  of the phaser. 
         [0032]    The assist segment  132  is defined by the chamber  117  formed between the housing assembly  101  and the rotor assembly  105  and a vane  104  separating the chamber into a fluid assist chamber  134  in fluid communication with an oil pressure supply pump  118  that supplies a constant feed of oil pressure and a vent chamber  133  vented to atmosphere or exhaust  119  at all times. The vane  104 , designated V 1  is capable of rotation to uni-directionally shift the relative angular position of the housing assembly  101  and the rotor assembly  105  and therefore, the assist segment  132  assists in shifting the relative angular position of the housing assembly relative to the rotor assembly in one direction only. While the figures only show the assist toward advancing the phaser, a person skilled in the art may apply the invention such that the assist would be toward retarding the phaser. It should be noted that while the supply pump  118  is shown as providing the supply oil pressure to the assist chamber  134 , a separate pump may also provide the supply oil pressure. 
         [0033]    A locking mechanism (not shown) may be present to lock the rotor assembly  105  relative to the housing assembly  101 . The locking mechanism may be slidably housed in a bore in the rotor assembly  105  and have an end portion assisted towards and fits into a recess in the housing assembly  101  by a spring. Alternatively, the locking mechanism may be housed in the housing assembly  101  and spring biased towards a recess in the rotor assembly  105 . 
         [0034]    An oil control valve  109  is in fluid communication with the operating segments  130  through advance passages  112  and retard passages  113 . The oil pressure to the operating segments  130  is actively controlled by the oil control valve  109 . The oil control valve  109  in  FIG. 3  is shown to be biased in a first direction by a spring  140  and a second direction by an actuator  142 , however any control in which the position of the oil control valve  109  is controlled may be used. The actuator  142  may an on/off solenoid, variable force solenoid, electromechanical, motor driven, hydraulic, or any other type of actuator. It should be noted that in this embodiment, the oil control valve  109  does not control the fluid to the assist chamber  134  of the assist segment  132 . 
         [0035]    For example, in a four vane system as shown in  FIG. 3 , when the phaser is moving towards the advance position, oil pressure flows from supply pump  118 , through the oil control valve  109  and through the advance passages  112  to all the advance chambers  102  designated A 2 , A 3 , A 4  of the operating segments  130 . Fluid is also constantly being supplied to the assist chamber  134  of the assist segment  132  by a supply pump  118 . At the same time, fluid is exhausting from all the retard chambers  103 , designated R 2 , R 3 , R 4  of the operating segments  130 , exhausting fluid through the retard passages  113  and through the oil control valve  109  to exhaust  119 . Any fluid that may leak into the vent chamber  133  is immediately exhausted to atmosphere or exhaust  119 . The oil pressure in the advance chambers  102 , designated A 2 , A 3 , A 4  move the vanes  104  clockwise in the figure with the oil pressure in the assist chamber  134  assist the movement in the advance direction. 
         [0036]    When the phaser is moving towards the retard position, oil pressure flows from supply pump  118 , through the oil control valve  109  and through the retard passages  113  to the retard chambers  103 , designated R 2 , R 3 , and R 4 , and fluid is exhausted from all of the advance chambers  102  designated A 2 , A 3 , A 4  through the advance passages  112 . At the same time, fluid is exhausted from the vent chamber  133  to atmosphere or exhaust  119 . Fluid is also being constantly supplied to the assist chamber  134  by the supply pump  118 . The oil pressure in the retard chambers  103 , designated R 2 , R 3 , R 4  move the vanes  104  counterclockwise in the figure. 
         [0037]    When the phaser is in a null position, fluid from the supply pump  118  is restricted by the oil control valve  109  to the advance chambers  102 , designated A 2 , A 3 , A 4 , the retard chambers  103 , designated R 2 , R 3 , R 4 . Fluid is constantly being supplied to the assist chamber  134  from the supply pump  118  unrestricted. Any fluid in the advance chambers  102 , the three retard chambers  103  is blocked from exhausting from the chambers. Any fluid that may leak into the vent chamber  133  is immediately vented to atmosphere or exhaust  119 . In an alternate embodiment, fluid from the supply pump  118  may be blocked by the oil control valve  109  from entering the advance chambers  102 , designated A 2 , A 3 , A 4 , and the retard chambers  103 , designated R 2 , R 3 , R 4 . 
         [0038]    By applying supply oil pressure  118  to an increased number of operating segments  130  than assist segments  132 , with one of the chambers of the assist segment not being connected to the supply oil pressure  118 , a higher torque in the advance direction for any given oil pressure is present causing an assist toward the advance direction, which is desirable to offset friction in the camshaft and valvetrain. Furthermore, by providing a vent chamber  133  within the assist segment  132 , the oil pressure actuated phaser has the significant benefits of better balancing of the advance and retard actuation rates, simplifying control strategies; providing much the same function as a bias spring, allowing the elimination of the bias spring, saving cost, weight, and package space; and in the case of a phaser that locks in the advanced direction using a locking mechanism, providing stronger torque to return to the base (locking) position. 
         [0039]    Bias springs provide a constant torque offset, regardless of engine operating condition, while in the present invention, a variable torque offset, based on the available oil pressure is provided. This is advantageous because under the engine operating conditions where the camshaft friction torque is high, the oil pressure also tends to be high (such as cold temperature), the present invention gives a more consistent phaser response than conventional bias springs. The use of oil pressure assist also eliminates the phase angle sensitivity of mechanical bias springs, such as spring torque changes with phase angle, which is undesirable. 
         [0040]    An advantage of the passive assist system over the active assist system is that less oil flows through the oil control valve at the same actuation and the oil does not have to flow through the oil control valve and restrictions, overall resulting in an increasingly responsive system. 
         [0041]    In the above embodiments and examples, the vent chamber corresponding to being a retard chamber was always vented to atmosphere to cause an assist of the phaser in the advance direction, however a person skilled in the art may apply the vent chamber to an advance chamber and vent the advance chamber to atmosphere to cause a assist of the phaser in the retard direction. 
         [0042]    In any of the above embodiments, the oil control valve may be located within the phaser or remotely from the phaser. 
         [0043]    The number of segments, vanes, and corresponding advance and retard chambers are provided as illustrative examples only and does not limit the number of vanes or chambers that may be present within the phaser. 
         [0044]    While all embodiments are shown without an inlet check valve, and therefore are oil pressure actuated phasers, a person skilled in the art would be able to apply all of the above embodiments to a torsional assist phaser in which a check valve is present. 
         [0045]    In all of the above embodiments, it is understood that the oil control valve has an infinite number of intermediate positions, so that the control valve not only controls the direction the VCT phaser moves but, depending on the discrete spool position, controls the rate at which the VCT phaser changes positions. Therefore, it is understood that the oil control valve can also operate in infinite intermediate positions and is not limited to the positions shown in the Figures. 
         [0046]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.