Abstract:
The present invention provides a control system and method of controlling a supercharger having an input and a pair of rotors. The method comprises providing a magnetic particle clutch having an input member, an output member and a source of magnetic flux. In the presence of a magnetic field, a magnetically reactive medium disposed between the input and output members is transformed into a torque transmitting coupling that causes the clutch to transition from a disengaged state to an engaged state. The method includes sensing a vehicle parameter and generating a signal operable to engage the clutch in response to the sensed vehicle parameter, so that the transition to the engaged state may be controlled as a function of the sensed vehicle parameter.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a magnetic particle clutch and more particularly, to a method of controlling operation of a magnetic particle clutch drivingly connected to a rotary blower, such as a supercharger, for supercharging an internal combustion engine.  
         BACKGROUND OF THE INVENTION  
         [0002]    As is well known to those skilled in the art, the use of a supercharger to increase or “boost” the air pressure in an intake manifold of an internal combustion engine results in an engine having a greater horsepower output capability than would occur if the engine were normally aspirated (i.e., if the piston drew air into the cylinder during the intake stroke of the piston). Conventional superchargers are normally driven by an engine, and therefore, represent a drain on engine horsepower when engine boost is not required. For at least this reason, it is known to provide an engageable/disengageable device, such as a clutch, in series between an input (e.g., a belt driven pulley) and a supercharger.  
           [0003]    By way of example only, a typical engagement time of a clutch driven supercharger, as specified by a vehicle manufacturer, is about 0.10 seconds. A substantially longer response time would result in the well known “turbo lag” feeling characterized by a time lag between depression of a vehicle accelerator and a point when supercharger boost becomes noticeable, as is inherent in a turbo charger type of engine boost system. On the other hand, response time should not be so fast (when engaging) and so sudden as to result in a large torque spike being imposed upon the engine.  
           [0004]    It is well known in the art to provide a supercharger driven by a clutch assembly that operates electromagnetically. Although a supercharger with such a clutch arrangement can operate in a generally satisfactory manner once the clutch is in either the engaged or disengaged state, the known arrangement exhibits certain limitations during “transient” conditions, i.e., as the clutch assembly changes from the disengaged to the engaged state, or vice versa. Electromagnetic clutch driven superchargers are typically ON-OFF type devices that engage abruptly with little or no slipping of the clutch, which results in an undesirable transient load torque on the engine during engagement of the clutch. Depending on the engine speed, as a conventional electromagnetic clutch is engaged, a resulting “droop” in engine speed may be perceived by a driver of the vehicle and may be manifested as an undesirable slowing of the vehicle.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention overcomes the limitations of conventional electromagnetic clutch driven superchargers by providing an improved method and control system for controlling a rotary blower having an input and a pair of blower rotors adapted to be driven by the input.  
           [0006]    In accordance with an embodiment of the present invention, the method comprises providing a magnetic particle clutch in series driving relationship between the input and the blower rotors. The magnetic particle clutch includes an input member, an output member and a source of magnetic flux. In the presence of a magnetic field, a magnetically reactive medium disposed between the input and output members is transformed into a torque transmitting coupling that causes the clutch to transition from a disengaged state to an engaged state. The method includes sensing a vehicle parameter and generating a signal operable to engage the clutch in response to the sensed vehicle parameter so that the transition from the disengaged state to the engaged state may be controlled as a function of the sensed vehicle parameter.  
           [0007]    A control system is also provided comprising a magnetic particle clutch as described above, at least one sensor for sensing a vehicle parameter, such as a rate of change in throttle position, and a control unit operable to selectively communicate a signal to the source of magnetic flux in response to the sensed vehicle operating parameter.  
           [0008]    The present invention advantageously provides an improved supercharger and clutch assembly that exhibits both a variable and controllable engagement and disengagement response time, thus avoiding the ON-OFF characteristics of conventional electromagnetic clutch driven superchargers and the resulting transient overloading of the engine.  
           [0009]    Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description:  
         [0011]    [0011]FIG. 1 is a schematic illustration of an intake manifold assembly having disposed therein a supercharger of a type that may be utilized in the present invention.  
         [0012]    [0012]FIG. 2 is a plan view of the supercharger assembly shown schematically in FIG. 1.  
         [0013]    [0013]FIG. 3 is an enlarged, fragmentary, cross-sectional view of a magnetic particle clutch assembly to be controlled by the method of the present invention.  
         [0014]    [0014]FIGS. 4A and 4B are schematic illustrations of a magnetically reactive medium during disengagement and engagement, respectively, of the magnetic particle clutch.  
         [0015]    [0015]FIG. 5 is an enlarged cross-sectional view of the clutch of FIG. 3, showing lines of magnetic flux.  
         [0016]    [0016]FIG. 6 is a graph of clutch output torque versus current for the clutch assembly shown in FIG. 3, according to a preferred embodiment of the present invention.  
         [0017]    [0017]FIG. 7 is a graph of current versus time illustrating exemplary control strategies for engaging the clutch assembly shown in FIG. 3, according to a preferred embodiment of the present invention.  
         [0018]    [0018]FIG. 8 is a flow diagram showing the control logic according to a preferred embodiment of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Referring now to the drawings, which are not intended to limit the invention, the preferred embodiments of the present invention are described in detail. FIG. 1 is a schematic illustration of an intake manifold assembly, including a supercharger and bypass valve arrangement. An engine, generally designated  10 , includes a plurality of cylinders  12 , and a reciprocating piston  14  disposed within each cylinder, thereby defining an expandable combustion chamber  16 . The engine  10  includes intake and exhaust manifold assemblies  18  and  20 , respectively, for directing combustion air to and from the combustion chamber  16 , by way of intake and exhaust valves  22  and  24 , respectively.  
         [0020]    The intake manifold assembly  18  includes a positive displacement rotary blower  26  that may be of the Roots type, as illustrated and described in U.S. Pat. Nos. 5,078,583 and 5,893,355, which is owned by the assignee of the present invention and hereby incorporated by reference in their entirety, but is not necessarily limited thereto. Accordingly, the present invention may be used advantageously with superchargers having various rotor types and configurations, such as the male and female rotors found in screw compressors.  
         [0021]    The blower  26  includes a pair of rotors  28  and  29 , each of which includes a plurality of meshed lobes. The rotors  28  and  29  are disposed in a pair of parallel, transversely overlapping cylinder chambers  28   c  and  29   c,  respectively. The rotors  28 ,  29  may be driven mechanically by engine crankshaft torque transmitted thereto in a known manner, such as by means of a drive belt (not illustrated herein). In conventional supercharger assemblies, the mechanical drive rotates the blower rotors  28 ,  29  at a fixed ratio, relative to the crankshaft speed, such that the displacement of blower  26  is greater than the engine displacement, thereby boosting or supercharging the air flowing into combustion chamber  16 .  
         [0022]    The supercharger or blower  26  includes an inlet port  30 , which receives air or an air-fuel mixture from an inlet duct or passage  32 , and further includes a discharge or outlet port  34 , directing the charged air to the intake valves  22  by means of a duct  36 . The inlet duct  32  and the discharge duct  36  are interconnected by means of a bypass passage, shown schematically at  38 . If the engine  10  is of the Otto-cycle type, a throttle valve  40  preferably controls air or air-fuel mixture flowing into the intake duct  32  from a source, such as ambient or atmospheric air. Alternatively, the throttle valve  40  may be disposed downstream of the supercharger  26 .  
         [0023]    Disposed within the bypass passage  38  is a bypass valve  42 , which is moved between an open position and a closed position by means of an actuator assembly, generally designated  44 . The actuator assembly  44  is responsive to fluid pressure in the inlet duct  32  by means of a vacuum line  46 . Actuator assembly  44  is operative to control the supercharging pressure in the discharge duct  36  as a function of engine power demand. When bypass valve  42  is in the fully open position, air pressure in the duct  36  is relatively low, but when the bypass valve  42  is fully closed, the air pressure in the duct  36  is relatively high. Typically, the actuator assembly  44  controls the position of the bypass valve  42  by means of suitable linkage. Those skilled in the art will understand that the illustration herein of the bypass valve  42  is by way of generic explanation and example only, and that, within the scope of this invention, other bypass configurations and arrangements could be used, such as a modular (integral) bypass or an electronically operated bypass, or in some cases, no bypass at all.  
         [0024]    Referring to FIGS. 2 and 3, blower  26  includes a housing assembly generally designated  48 , which includes a main housing  50 , which defines the chambers  28   c  and  29   c.  The housing assembly  48  also includes an input housing  52 , also referred to hereinafter as a clutch housing, upon which rests a portion of a clutch assembly  54 . As illustrated in FIG. 3, housing  52  rotatably supports an input shaft  56  upon which another portion of the clutch assembly  54  rests.  
         [0025]    As will be become apparent from the description herein below, operation of magnetic particle clutch  54  is based on electromagnetic and mechanical forces that act on a magnetically reactive medium disposed between multiple working surfaces of an input member and output member. The magnetic forces operate to increase the viscosity of the medium to interlock the driven and driving members. The magnetic particle clutch  54  offers many advantages, such as, inter alia, smooth engagement, the ability to operate in the slip condition, and the controllability of torque transfer over a relatively wide range of electrical input.  
         [0026]    An exemplary magnetic particle clutch  54  for use with the present invention will be described with reference to FIGS.  3 - 5 . Referring to FIG. 3, clutch housing  52  includes a duct  58  therethrough for receiving shaft  56 . Shaft  56  is preferably supported within duct  58  by a plurality of bearings  60  that are positioned within duct  58  by shoulders  62  and  64  extending from housing  52  and shoulder  66  extending from shaft  56 . At least one of bearings  60  may be further biased axially by an annular sealing member  68 , as shown adjacent the leftward most bearing  60  in FIG. 3.  
         [0027]    A first rotatable or output member  70  of known magnetic properties is fixedly secured to shaft  56 . First rotatable member  70  includes a cylindrical portion  72 , located radially outwardly of shaft  56 , which includes an inner surface  74  and an outer surface  76 . Outer surface  76  preferably includes a plurality of features  78  having non-magnetic properties. As will be described in further detail below, the non-magnetic properties of features  78  prevent lines of magnetic flux from travelling through features  78  in the presence of a magnetic field.  
         [0028]    In the illustrated embodiment of FIG. 3, features  78  are depicted as grooves having a generally trapezoidal cross-section, but are not intended to be limited thereto. Alternatively, features  78  may comprise, for example, non-magnetic rings or slots disposed substantially or completely through cylindrical portion  72 . Moreover, features  76  may be disposed on inner surface  74  or may be disposed substantially or completely through cylindrical portion  72 .  
         [0029]    A second rotatable or driving member  80  of known magnetic properties is supported on shaft  56  by a bearing  81 , the position of which is determined by a shoulder  82  located on a distal end  84  of shaft  56 . Disposed about a forward end of second rotatable member  80  is an integrally formed input pulley  86 , by means of which torque is transmitted from an engine crankshaft (not illustrated) to the input shaft  56  during engagement of clutch  54 .  
         [0030]    Second rotatable member  80  further includes a cylindrical portion  90  located radially outwardly of cylindrical portion  72  of first rotatable member  70  and substantially parallel to shaft  56 . Cylindrical portion  90  includes an inner surface  92  and an outer surface  94 . Inner surface  92  preferably includes a plurality of non-magnetic features  96  substantially similar to features  78  in first rotatable member  70 , but is not intended to be limited thereto. Features  96  are positioned in inner surface  92  such that features  96  are located radially outwardly of a point equidistantly between features  78  in first rotatable member  70 , for reasons that will be described herein below. Features  78  on cylindrical portion  72  and features  96  on cylindrical portion  90  define therebetween a plurality of opposing working surfaces  98 ,  100 ,  102  and  104 .  
         [0031]    First rotatable member  70  and second rotatable member  80  are not in contact, but define therebetween a substantially uniform gap  106 . Gap  106  exhibits a predetermined width that permits a thin layer of magnetically reactive medium  105  (as shown in FIG. 4A), such as a magnetically reactive powder, to reside therein. While a magnetically reactive powder is the preferred magnetically reactive medium due to its ability to resistant temperatures that would degrade oil based magnetorheological fluids, it is not intended to be so limited.  
         [0032]    The non-magnetic properties of features  78  and  96  aid in concentrating lines of magnetic flux  108  across gap  106  and substantially through working surfaces  98 ,  100 ,  102  and  104 , as illustrated in FIGS. 4B and 5, thereby advantageously increasing the working surface area of the clutch without substantially increasing clutch weight. Additionally, as illustrated in FIG. 4A, features  78  and  96  provide physical volume for receiving magnetically reactive medium  105  when no magnetic field is applied. Removing magnetically reactive medium  105  from gap  106  when no magnetic field is applied decreases friction, thereby reducing drag between first rotatable member  70  and second rotatable member  80 . While the illustrative magnetic particle clutch  54  is described as having features  78  and  96 , it is not intended to be so limited. Accordingly, first and second rotatable members  70 ,  80  may contain no non-magnetic features when additional working surface area is not required.  
         [0033]    Clutch  54  further includes a source of magnetic flux, which is depicted in FIGS. 3 and 5 as an electromagnet  110  mounted on the outside of housing member  52  between first rotatable member  70  and housing member  52 . In the illustrated embodiment, electromagnet  110  comprises a wire-wound coil  112  surrounded by a generally toroidal shell  114 . As is well known, an electrical current applied to coil  112  generates a magnetic field in the vicinity of electromagnet  110 , the intensity of which is proportional to the level of current provided. Alternatively, the source of magnetic flux may comprise other arrangements, such as, for example, a permanent magnet supplemented by a counteracting electromagnet so that clutch  54  will default to being engaged should the electromagnet fail.  
         [0034]    Electromagnet  110  is controlled by an electronic control unit (ECU) (not illustrated) that provides an electrical signal to coil  112  via wires  115 . The ECU processes input, such as, for example, sensor readings corresponding to vehicle parameters, and processes the input according to logic rules to determine the appropriate electrical signal to provide electromagnet  110 . The ECU is preferably microprocessor based having sufficient memory to store the logic rules, generally in the form of a computer program, for controlling operation of clutch  54 . It will be appreciated by those skilled in the art that the present invention is not limited to any particular type or configuration of ECU or to any specific control logic. What is essential to the present invention is that the clutch  54  communicate with some sort of control unit capable of modulating the electrical signal applied to electromagnet  110  to achieve engagement and disengagement of clutch  54  at a predetermined rate, and that the control unit include some sort of control logic capable of achieving engagement of clutch  54  at a controllable rate representative of some predetermined vehicle parameter, such as throttle position.  
         [0035]    It is well known in the art that lines of magnetic flux  108  travel a path substantially through structures with known magnetic properties. As illustrated in FIG. 5, upon application of a magnetic field in the vicinity of electromagnet  110 , lines of magnetic flux  108  exit rigid shell  114  in electromagnet  110  and traverse a gap  120 , whereby flux  108  saturates areas  122  located radially inwardly of features  78  in first rotatable member  70 . Upon saturation of areas  122 , lines of magnetic flux  108  follow a path of least resistance and traverse gap  106 , through working surfaces  124 , into second rotatable member  80 . The narrowest width of features  78  is best designed to be greater than the width of gap  106 , thus preventing flux  108  from traversing features  78 . Upon entry into second rotatable member  80 , flux  108  saturates areas  126  located radially outwardly of features  96 . Upon saturation of areas  126 , flux  108  traverses gap  106  through working surfaces  98 , into first rotatable member  70 . The process of weaving across gap  106  between features  78  and  96  is repeated until the number of features  78  and  96  is exhausted. The flux path is completed as flux  108  traverses gap  106  and gap  120  reentering rigid shell  114  of electromagnet  110 .  
         [0036]    As shown in FIG. 4B, magnetically reactive particles  128  in magnetically reactive medium  105  change formation, in relation to the intensity of the magnetic field, by aligning with the lines of magnetic flux  108  as flux  108  traverses gap  106  through working surfaces  100 . Magnetically reactive particles  128  under the influence of a magnetic field will lock into chains  130  increasing the shear force and creating a mechanical friction against the working surfaces  100  facing gap  106 . The increased shear force and mechanical friction result in a transfer of torque between first member  70  and second member  80 .  
         [0037]    When it is desired to operate blower  26  by engaging clutch  54 , an appropriate electrical signal is transmitted to electromagnet  110  to create a magnetic field, which as described above, alters the properties of medium  105  causing a transfer of torque between second rotatable member  80  and first rotatable member  70 . Referring to FIG. 6, the output torque of clutch  54  is plotted versus the current applied to electromagnet  110 . As illustrated in FIG. 6, clutch  54  exhibits a nearly linear relationship between its output torque and the current applied to electromagnet  110 , up to the magnetic saturation point of the clutch  54 . The clutch output torque and coil current values illustrated in FIG. 6 are by way of example only, and may vary depending on factors, such as, for example, the size and number of working surfaces between rotatable members  70 ,  80  and operating speed of the clutch  54 .  
         [0038]    Accordingly, the amount of torque transferred between the second rotatable member  80  and the first rotatable member  70  may be selectively controlled by varying the current applied to electromagnet  110 , such that a “soft engagement” may be achieved when it is desirable, or a more rapid engagement may be achieved when it is needed and acceptable. For example, when the engine is operating under a “part throttle” condition, it may be desirable to achieve a slow engagement, whereas when the engine is operating under a “full throttle” condition, it may desirable to engage the clutch more quickly. Those skilled in the art will appreciate that in most supercharger installations, it is the engagement response time that is more critical than the disengagement response time.  
         [0039]    Referring primarily to FIGS. 7 and 8, a method of controlling the engagement of the supercharger will be described in detail. By way of example only, engagement of the supercharger will be described as a function of a sensed rate of change in engine throttle position, but is not intended to be limited thereto. Alternatively, engagement of the supercharger may be controlled as a function of other sensed vehicle parameters, such as, for example, engine speed or simply throttle position.  
         [0040]    When it is desired to operate the supercharger by engaging clutch  54 , the control logic shown in FIG. 8 is initiated by proceeding to “Start”. Referring to step  200 , the ECU senses a rate of change in position of the throttle pedal, which is generally representative of the rate of acceleration of the vehicle. The ECU then compares the sensed rate of change in throttle position to a predetermined engagement threshold, as shown in step  202 . If the engine operating parameter is less than the threshold (“No”), the logic merely loops back, upstream of step  200 . If the operating parameter is greater than the threshold (“Yes”), the logic proceeds to step  204 .  
         [0041]    Referring to step  204 , a command signal, representing the input current applied to electromagnet  110 , is then calculated as a function of the rate of change in throttle position, as read in step  200 . By way of example, the input current associated with each command signal may be applied in two parts: (1) an engagement current (I1) required to fully engage the clutch; and (2) a steady state current (I2) representing a predetermined current required to maintain the clutch  54  fully engaged.  
         [0042]    An unlimited number of strategies for controlling engagement of clutch  54  may be generated, for example, by varying at least one of (i) the level of engagement current (I1), (ii) the rate of application of engagement current (I1) and (iii) the rate of reduction of engagement current (I1). The graph of FIG. 7 shows several exemplary control strategies for engagement of clutch  54 , each control strategy corresponding to a different rate of change in throttle position, the rates of change in throttle position being labeled T1 through T4, with T1 representing a rate of change in throttle position just above a predetermined threshold value.  
         [0043]    As illustrated in FIG. 7, the parameter T1, which corresponds to a relatively small rate of change in throttle position, results in an engagement current (I1) slowly ramping to approximately 2 amps. By contrast, the parameter T4, which corresponds to a relatively large rate of change in throttle deflection, results in the engagement current (I1) quickly increasing to approximately 6 amps. The current values illustrated in FIG. 7 are by way of example only, and will vary depending on factors, such as, for example, the type of magnetically reactive medium  105  used in clutch  54  and the magnetic saturation point of clutch  54 .  
         [0044]    As may be appreciated by the graphs of FIG. 7, the greater the magnitude and application rate of engagement current (I1), the faster the engagement of clutch  54 . As was described previously, the engagement of clutch  54  is a function of the strength of the magnetic field generated by the electromagnet  110 , which in turn is a function of the current applied to the coil  112 . When relatively fast engagement of clutch  54  is required, the engagement current (I1) may be higher than the steady state current (I2), as illustrated in FIG. 7 for parameters T2 through T4, to overcome the inertial effects of the rotating members  70 ,  80  coming up to speed. When a relatively slow engagement of clutch  54  is required, the engagement current (I1) may slowly ramp toward the steady state current (I2), as illustrated in FIG. 7 for parameter T1, allowing for a smooth engagement without transient overloading of the engine  10 . As will be appreciated, the signals associated with parameters T2 and T3 represent examples of a compromise between the signals associated with parameters T1 and T4.  
         [0045]    The application rate of the input current may be controlled regardless of the level of engagement current (I1), as illustrated in FIG. 7 for parameters T2′ and T2″. The rate at which the input current is increased and decreased may be linear, as illustrated for parameter T2′, or may exhibit other characteristics, such as, for example, an exponential increase to the engagement current (I1) and a subsequent exponential decrease to the steady state current (I2), depicted in FIG. 7 as command signal T2″.  
         [0046]    The application of input current to electromagnet  110  may also be accomplished by pulse width modulating (PWM) the electrical signal provided by the ECU. According to this method, an electrical signal having a predetermined current, for example the current corresponding to the magnetic saturation point of clutch  54 , is pulsed at a predetermined frequency, which results in a lower overall mean input current being applied to the coil  112 . For example, an electrical signal with a current value of 6 amps could be pulsed 50% of the time resulting in approximately one-half of the input power associated with 6 amps being applied to coil  112 . As will be appreciated, pulse width modulating the engagement current (I1) reduces the maximum power input to the coil  112  resulting in a more efficient operation of clutch  54 .  
         [0047]    Under certain operating conditions, it may be desirable for the supercharger to produce a slight amount of boost that is less than the level of boost produced by the supercharger at that particular engine speed when clutch  54  is fully engaged. Because of the substantially linear relationship between the application of current and output torque of the clutch, it is possible to apply an input current to the coil  112  that permits the second rotatable member  80  to slip relative to the first rotatable member  70  resulting in clutch  54  being only partially engaged. When partially engaged, a lessor amount of torque is transferred from the second rotatable member  80  to the first rotatable member  70  than would be transferred if clutch  54  were fully engaged.  
         [0048]    It should be understood by those skilled in the art that the particular current values and control strategies illustrated and described herein are by way of example only, and not by way of limitation. Furthermore, the engagement time, i.e., the time between application of currents (I1) and (I2), is not significant to the invention and is illustrated only as an example engagement time, the length of which may be dependent on factors, such as, for example, vehicle weight, engine horsepower, and supercharger output. By way of example only, it was found during the development of the present invention that for a rate of change in throttle position T2 (I1 equal to 4.0 amps), the result was an engagement time in the range of about 0.5 to 1.5 seconds whereas, at the other extreme, for a rate of change in throttle position T4 (I1 equal to 6.0 amps), the engagement time was in the range of about 200 to 500 milliseconds.  
         [0049]    Although certain preferred embodiments of the present invention have been described, the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention. A person of ordinary skill in the art will realize that certain modifications and variations will come within the teachings of this invention and that such variations and modifications are within its spirit and the scope as defined by the claims.