Patent Publication Number: US-2013228040-A1

Title: Variable mass flywheel

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to flywheels. More particularly, it relates to flywheels with mass that is variable, including mass that varies as a function of the angular frequency of a flywheel. More purposively, the present invention relates to flywheels having mass that varies in amount and/or distribution so as to vary their moment of inertia. 
     2. Description of Related Art 
     A variable mass flywheel is useful for assisting an engine differently at different engine speeds, different vehicle speeds and different road traction conditions. 
     For example, at lower engine speeds, a heavier flywheel can contribute to improved traction, lower idle fuel consumption, and better absorption of fluctuations in engine torque. In contrast, at higher engine speeds, a lighter flywheel can contribute to better throttle response, better acceleration, and improved higher engine torque response characteristics. The tendency to lose traction decreases in higher gears and higher speeds. 
     While variable mass flywheels are known, they suffer from a number of disadvantages. In general, such flywheels have been large and bulky yet delicate and overly complicated. Some, for example, vary their mass using hazardous ferro fluid and electromagnets, which must be provided with electrical power. 
     Accordingly, what is needed is a better way to provide a variable mass flywheel. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to this need. 
     According to one aspect of the present invention, there is provided a variable mass flywheel having: a primary flywheel having an axis of rotation; a secondary flywheel coaxial with the primary flywheel and having a mating portion that one of circumscribes the primary flywheel and inscribes the primary flywheel; a friction disc radiating from the primary flywheel; a drive plate radiating from the mating portion of the secondary flywheel and lapping a portion of the friction disc; a coupler urging the friction disc and the drive plate into abutment whereby the primary flywheel and the secondary flywheel are coupled for unified rotation; a detector for detecting a condition that correlates with the desirability of the primary flywheel and the secondary flywheel being one of coupled and decoupled, the detector being operable to assume a first state when the condition is within a first range and assume a second state when the condition is within a second range; and a decoupler responsive to the state of the detector, operable when the detector is in the second state to overcome the coupler and urge the friction disc and the drive plate out of abutment whereby the primary flywheel and the secondary flywheel are decoupled for separate rotation. 
     The condition might be the angular frequency of the primary flywheel, such that the detector is operable to assume the first state when the angular frequency is less than a predetermined angular frequency and assume the second state when the angular frequency is greater than the predetermined angular frequency. 
     The friction disc and the drive plate might be an interleaved plurality of friction discs and plurality of drive plates. 
     The coupler might include a spring compressed between the primary flywheel and the friction disc. 
     The flywheel might include a pressure plate between the spring and the friction disc. 
     The detector might include: a ramp radiating outward on the primary flywheel, the ramp having a base and an apex, the apex being radially farther than the base from the axis of rotation; and a mass captive on the ramp and operable to move along the ramp between the base and the apex, wherein the mass moves proximate the base when the angular frequency of the primary flywheel is less than the predetermined angular frequency, whereby the detector assumes the first state and moves proximate the apex when the angular frequency of the primary flywheel is greater than the predetermined angular frequency whereby the detector assumes the second state. 
     The decoupler might include: a wedge radiating outward on the pressure plate and opposing the ramp, the wedge having a toe and a heel, the heel being radially farther than the toe from the axis of rotation, the wedge sloping toward the ramp from toe to heel; and a bearing circumscribing the mass and operable to move along the wedge between the toe and the heel as the mass moves along the ramp between the base and the apex, wherein the bearing moves proximate the toe when the detector assumes the first state and moves proximate the heel when the detector assumes the second state, thereby bearing on the pressure plate to overcome the coupler and urge the friction disc and the drive plate out of abutment whereby the primary flywheel and the secondary flywheel are decoupled for separate rotation. 
     The mass may be an axle having a first end and a second end. The ramp may be bifurcated by a channel into a first ramp and a second ramp, wherein the first end of the axle is captive on the first ramp and the second end of the axle is captive on the second ramp. The channel may receive the bearing. The bearing may be a rolling-element bearing. 
     The ramp may slope from the base to the apex toward the wedge. 
     The flywheel may further include a plurality of the detector and a plurality of the decoupler distributed about the primary flywheel. 
     According to another aspect of the present invention, there is provided an actuator having: a body having an axis of rotation; a pressure plate coaxial with the body; a coupler urging the pressure plate toward the body; a ramp radiating outward on the body, the ramp having a base and an apex, the apex being radially farther than the base from the axis of rotation; a mass captive on the ramp and operable to move along the ramp between the base and the apex, wherein the mass moves proximate the base when the angular frequency of the body is less than a predetermined angular frequency and moves proximate the apex when the angular frequency of the body is greater than the predetermined angular frequency; a wedge radiating outward on the pressure plate and opposing the ramp, the wedge having a toe and a heel, the heel being radially farther than the toe from the axis of rotation, the wedge sloping toward the ramp from toe to heel; and a bearing circumscribing the mass and operable to move along the wedge between the toe and the heel as the mass moves along the ramp between the base and the apex, wherein the bearing at the heel bears upon the pressure plate to overcome the coupler and urge the pressure plate away from the body. 
     The mass may be an axle having a first end and a second end. 
     The ramp may be bifurcated by a channel into a first ramp and a second ramp, wherein the first end of the axle is captive on the first ramp and the second end of the axle is captive on the second ramp. The channel may receive the bearing. The bearing may be a rolling-element bearing. 
     The ramp may slope from the base to the apex toward the wedge. 
     Further aspects and advantages of the present invention will become apparent upon considering the following drawings, description, and claims. 
     DESCRIPTION OF THE INVENTION 
     The invention will be more fully illustrated by the following detailed description of non-limiting specific embodiments in conjunction with the accompanying drawing figures. In the figures, similar elements and/or features may have the same reference label. Further, various elements of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar elements. If only the first reference label is identified in a particular passage of the detailed description, then that passage describes any one of the similar elements having the same first reference label irrespective of the second reference label. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section view of a first embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel (not shown in this view for clarity). 
         FIG. 2  is a radial-section view of the variable mass flywheel of  FIG. 1 , along the cutting plane  2 - 2 ,  FIG. 2   a  with the primary flywheel at low angular frequency and  FIG. 2   b  with the primary flywheel at high angular frequency, the top half of the view depicting a decoupler and the bottom half of the view suppressing a decoupler to better depict surrounding elements. 
         FIG. 3  is a radial-section view of the variable mass flywheel of  FIG. 1 , along the cutting plane  3 - 3 ,  FIG. 3   a  with the primary flywheel at low angular frequency and  FIG. 3   b  with the primary flywheel at high angular frequency. 
         FIG. 4  is a radial-section view of a second embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel,  FIG. 4   a  with the primary flywheel at low angular frequency and  FIG. 4   b  with the primary flywheel at high angular frequency, the top half of the view depicting a detector/decoupler and the bottom half of the view suppressing a detector/decoupler to better depict surrounding elements. 
         FIG. 5  is a cross-section view of a third embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel (not shown in this view for clarity). 
         FIG. 6  is a radial-section view of the variable mass flywheel of  FIG. 5 , along the cutting plane  6 - 6 ,  FIG. 6   a  with the primary flywheel at low angular frequency and  FIG. 6   b  with the primary flywheel at high angular frequency. 
         FIG. 7  is a radial-section view of the variable mass flywheel of  FIG. 5 , along the cutting plane  7 - 7 ,  FIG. 7   a  with the primary flywheel at low angular frequency and  FIG. 7   b  with the primary flywheel at high angular frequency. 
         FIG. 8  is a radial-section view of a fourth embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel,  FIG. 8   a  depicting high hydraulic pressure and  FIG. 8   b  depicting low hydraulic pressure. 
         FIG. 9  is a radial-section view of a fifth embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel,  FIG. 9   a  depicting low hydraulic pressure and  FIG. 9   b  depicting high hydraulic pressure. 
         FIG. 10  is a radial-section view of a sixth embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel,  FIG. 10   a  depicting low hydraulic pressure and  FIG. 10   b  depicting high hydraulic pressure. 
         FIG. 11  is a radial-section view of a seventh embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel,  FIG. 11   a  depicting high vacuum (or low pneumatic pressure) and  FIG. 11   b  depicting low vacuum (or high pneumatic pressure). 
         FIG. 12  is a radial-section view of a eighth embodiment of a variable mass flywheel according to aspects of the present invention, the variable mass flywheel including a primary flywheel and a secondary flywheel,  FIG. 12   a  with the primary flywheel at low angular frequency and  FIG. 12   b  with the primary flywheel at high angular frequency. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     The structure and operation of aspects of the invention will now be illustrated by explanation of one general approach and descriptions of eight specific embodiments shown in the drawing figures and described in greater detail herein. These illustrations, explanations and descriptions are only exemplary and are not to be interpreted as limiting the scope of the invention, which is defined in the claims. 
     A General Approach 
     Referring to all of the Figures, a variable mass flywheel  100  can be provided according to aspects of the present invention, as a combination of: a primary flywheel  102  having an axis of rotation; a secondary flywheel  104  coaxial with the primary flywheel  102  and having a mating portion  106  that one of: circumscribes the primary flywheel  102 , and inscribes the primary flywheel  102 ; a friction disc  108  radiating from the primary flywheel  102 ; a drive plate  110  radiating from the mating portion  106  of the secondary flywheel  104  and lapping a portion of the friction disc  108 ; a coupler  112  urging the friction disc  108  and the drive plate  110  into abutment whereby the primary flywheel  102  and the secondary flywheel  104  are coupled for unified rotation; a detector  114  for detecting the angular frequency of the primary flywheel  102 , the detector  114  being operable to: assume a first state when the angular frequency is less than a predetermined angular frequency, and assume a second state when the angular frequency is greater than the predetermined angular frequency; and a decoupler  116  responsive to the state of the detector  114 , operable when the detector  114  is in the second state to overcome the coupler  112  and urge the friction disc  108  and the drive plate  110  out of abutment whereby the primary flywheel  102  and the secondary flywheel  104  are decoupled for separate rotation. 
     Teachings of the present invention can be applied more generally to provide an actuator  101  as a combination of: a body  102  having an axis of rotation; a pressure plate  118  coaxial with the body  102 ; a coupler  112  urging the pressure plate  118  toward the body  102 ; a ramp  120  radiating outward on the body  102 , the ramp  120  having a base  122  and an apex  124 , the apex  124  being radially farther than the base  122  from the axis of rotation; a mass  126  captive on the ramp  120  and operable to move along the ramp  120  between the base  122  and the apex  124 , such that the mass  126  moves proximate the base  122  when the angular frequency of the body  102  is less than a predetermined angular frequency and moves proximate the apex  124  when the angular frequency of the body is greater than the predetermined angular frequency; a wedge  128  radiating outward on the pressure plate  118  and opposing the ramp  120 , the wedge  128  having a toe  130  and a heel  132 , the heel  132  being radially farther than the toe  130  from the axis of rotation, the wedge  128  sloping toward the ramp  120  from toe  130  to heel  132 ; and a bearing  134  circumscribing the mass  126  and operable to move along the wedge  128  between the toe  130  and the heel  132  as the mass  126  moves along the ramp  120  between the base  122  and the apex  124 , such that the bearing  134  at the heel  132  bears upon the pressure plate  118  to overcome the coupler  112  and urge the pressure plate  118  away from the body  102 . 
     In general terms, when the variable mass flywheel  100  rotates within a higher range of angular frequencies it has the mass of only the primary flywheel  102  and when the variable mass flywheel  100  rotates within a lower range of angular frequencies it has the combined mass of both the primary flywheel  102  and the secondary flywheel  104 . 
     More particularly, the coupler  112  urges the friction disc  108  and the drive plate  110  into abutment when the variable mass flywheel  100  rotates at an angular frequency below a predetermined angular frequency, whereby the primary flywheel  102  and the secondary flywheel  104  are coupled for unified rotation. In opposition, the decoupler  116  overcomes the coupler  112  and urges the friction disc  108  and the drive plate  110  out of abutment when the variable mass flywheel  100  rotates at an angular frequency above the predetermined angular frequency, whereby the primary flywheel  102  and the secondary flywheel  104  are decoupled for separate rotation. 
     Thus it will be seen that the coupler  112  acts continuously to couple the primary flywheel  102  and the secondary flywheel  104 , but the decoupler  116  acts and overcomes the coupler  112  only when the variable mass flywheel  100  rotates at an angular frequency above the predetermined angular frequency. 
     In this regard, the decoupler  116  is responsive to the detector  114  for detecting the angular frequency of the primary flywheel  102 , the detector  114  being operable to: assume a first state when the angular frequency is less than a predetermined angular frequency, and assume a second state when the angular frequency is greater than the predetermined angular frequency. The decoupler  116  is responsive to the state of the detector  114 , operable when the detector  114  is in the second state to overcome the coupler  112  and urge the friction disc  108  and the drive plate  110  out of abutment whereby the primary flywheel  102  and the secondary flywheel  104  are decoupled for separate rotation. 
     The predetermined angular frequency can be adjusted by adjusting any of the detector  114 , the coupler  112  and the decoupler  116 . For example, the detector  114  could be adjusted to change state at a different predetermined angular frequency. As another example, the strength of the coupler  112  and the decoupler  116  could be adjusted to change respectively the force at which the decoupler  116  overcomes the coupler  112  and the force which the decoupler applies to overcome the coupler  112 . 
     (i) First Embodiment (Roller Bearing on Axle) 
       FIGS. 1-3  show a first embodiment of the variable mass flywheel  100  and the actuator  101  in accordance with aspects of the present invention. 
     The friction disc  108  and the drive plate  110  are embodied as an interleaved plurality of friction discs  108  and plurality of drive plates  110  to provided further abutment surfaces. The coupler  112  is embodied as a spring  136  compressed between the primary flywheel  102  and the friction disc  108 , and more specifically, there is a pressure plate  118  between the spring  136  and the friction disc  108  to distribute the pressure. 
     The detector  114  is embodied by combining the ramp  120  (which radiates outward on the primary flywheel  102  and spans the base  122  and the apex  124 , the apex  124  being radially farther than the base  122  from the axis of rotation) and the mass  126 , which is captive on the ramp  120  to move along the ramp  120  between the base  122  and the apex  124 , so that the mass  126  moves proximate the base  122  when the angular frequency of the primary flywheel  102  is less than the predetermined angular frequency, such that the detector  114  assumes the first state, and moves proximate the apex  124  when the angular frequency of the primary flywheel  102  is greater than the predetermined angular frequency such that the detector  114  assumes the second state. 
     The decoupler  116  is embodied by combining the wedge  128  (which radiates outward on the pressure plate  118  opposing the ramp  120  and spans the toe  130  and the heel  132 , the heel  132  being radially farther than the toe  130  from the axis of rotation, the wedge  128  sloping toward the ramp  120  from toe  130  to heel  132 ) and the bearing  134 , which circumscribes the mass  126  and is operable to move along the wedge  128  between the toe  130  and the heel  132  as the mass  126  moves along the ramp  120  between the base  122  and the apex  124 , so that the bearing  134  moves proximate the toe  130  when the detector  114  assumes the first state, and moves proximate the heel  132  when the detector  114  assumes the second state, in this way bearing on the pressure plate  118  to overcome the coupler  112  and urge the friction disc  108  and the drive plate  110  out of abutment whereby the primary flywheel  102  and the secondary flywheel  104  are decoupled for separate rotation. 
     In this embodiment, the mass  126  is an axle  138  having an axle first end  140  and an axle second end  142 . The ramp  120  slopes from the base  122  to the apex  124  toward the wedge  128  and is bifurcated by a channel  144  into a first ramp  146  and a second ramp  148 , such that the axle first end  140  is captive on the first ramp  146  and the axle second end  142  is captive on the second ramp  148 . In this way, the channel  144  can receive the bearing  134 , which in this embodiment is a rolling-element bearing. 
     It will be seen that this embodiment of the variable mass flywheel has a plurality of the detectors  114  and a plurality of the decouplers  116  distributed about the primary flywheel  102  for more dispersed and balanced operation. 
     In steady state (when the primary flywheel  102  has less than the predetermined angular frequency and thus the detector  114  is in the first state), the spring  136  of the coupler  112  is compressed between the primary flywheel  102  and the pressure plate  118  to couple the friction disc  108  and the drive plate  110  and hence the primary flywheel  102  and the secondary flywheel  104 . 
     The mass  126  of the detector  114  moves along the ramp  120  between the base  122  and the apex  124 , so that the mass  126  moves proximate the base  122  when the angular frequency of the primary flywheel  102  is less than the predetermined angular frequency, such that the detector  114  assumes the first state, and moves proximate the apex  124  when the angular frequency of the primary flywheel  102  is greater than the predetermined angular frequency such that the detector  114  assumes the second state. 
     The bearing  134  of the decoupler  116  moves along the wedge  128  between the toe  130  and the heel  132  as the mass  126  moves along the ramp  120  between the base  122  and the apex  124 , so that the bearing  134  moves proximate the toe  130  when the detector  114  assumes the first state, and moves proximate the heel  132  when the detector  114  assumes the second state, in this way bearing on the pressure plate  118  to overcome the coupler  112  and urge the friction disc  108  and the drive plate  110  out of abutment whereby the primary flywheel  102  and the secondary flywheel  104  are decoupled for separate rotation. 
     The predetermined angular frequency can be adjusted in a number of ways, some by way of design choices and some by way of tuning. The force of the coupler  112  that must be overcome for decoupling can be adjusted, for example, by increasing or decreasing the number of couplers  112  (either during design and manufacture, or ad hoc during operation by using less than the manufactured number of couplers  112 ). The force of the coupler  112  can also be adjusted by using weaker or stronger springs or adjusting the tension of the springs. The force that the decoupler  116  can apply can be adjusted by increasing or decreasing the number of decouplers  116  (either during design and manufacture, or ad hoc during operation by using less than the manufactured number of decouplers  116 ). The force of the decoupler  116  can also be adjusted by changing its mass, radius and spatial relation to the mass  126  of the detector  114 . The responsiveness of the detector  114  to angular frequency can be adjusted by adjusting the mass of the mass  126  and the incline of the ramp  120 . 
     Those skilled in the art will recognize that hysteresis is usually desirable in a system such as this, so that the detector  114  doesn&#39;t oscillate between the first state and the second state when the angular frequency of the primary flywheel  102  is at or near the predetermined angular frequency. Hysteresis can be increased by increasing the length of the ramp  120  and decreased by decreasing the length of the ramp  120 . Changing the length of the ramp  120  leads to a change in angle for the ramp  120 , which must be balanced, for example by adjusting the strength of the springs  136  or adjusting the number of or spacing between the friction discs  108  and the drive plates  110 . 
     (ii) Second Embodiment (Ball Bearing and Square Wedge) 
       FIG. 4  shows a second embodiment of the variable mass flywheel  100  in accordance with aspects of the present invention. 
     In this embodiment, the detector  114  and the decoupler  116  are combined, more particularly, the mass  126  and the bearing  134  are embodied jointly as a single ball bearing  126 / 134 ; however, otherwise the second embodiment operates similarly to the first. 
     The ball bearing  126 / 134  moves along the ramp  120  between the base  122  and the apex  124 , so that the ball bearing  126 / 134  moves proximate the base  122  when the angular frequency of the primary flywheel  102  is less than the predetermined angular frequency, such that the detector  114  assumes the first state, and moves proximate the apex  124  when the angular frequency of the primary flywheel  102  is greater than the predetermined angular frequency such that the detector  114  assumes the second state. 
     As a result, the ball bearing  126 / 134  simultaneously moves along the wedge  128  between the toe  130  and the heel  132 , so that the bearing  134  moves proximate the toe  130  when the detector  114  assumes the first state, and moves proximate the heel  132  when the detector  114  assumes the second state, in this way bearing on the pressure plate  118  to overcome the coupler  112  and urge the friction disc  108  and the drive plate  110  out of abutment whereby the primary flywheel  102  and the secondary flywheel  104  are decoupled for separate rotation. 
     Advantageously, this second embodiment is structurally simpler than the first embodiment; however, one benefit of the first embodiment is that the distinct mass  126  and bearing  134  tested less prone to becoming lodged at the apex  124  of the ramp  120  and the heel  132  of the wedge  128  respectively, than did the combined mass  126  and bearing  134 . 
     (iii) Third Embodiment (Ball Bearing and Sloped Wedge) 
       FIG. 5-7  show a third embodiment of the variable mass flywheel  100  in accordance with aspects of the present invention. 
     In this embodiment, the detector  114  and the decoupler  116  are combined. More particularly, the mass  126  and the bearing  134  are embodied jointly as a single ball bearing. 
     The third embodiment is structurally and operationally similar to the second embodiment except that in the third embodiment the wedge  128  slopes toward the ramp  120  from toe  130  to heel  132  instead of being square as in the second embodiment. Sloping the wedge  128  is yet another way to adjust the predetermined angular frequency. 
     (iv) Fourth Embodiment (Hydraulic Piston—High Pressure Coupling) 
       FIG. 8  shows a fourth embodiment of the variable mass flywheel  100  in accordance with aspects of the present invention. 
     In this embodiment, the decoupler  116  is hydraulic and the detector (not shown) is embodied so as to drive the hydraulic decoupler  116 . The detector (not shown) might detect a condition that correlates with the desirability of the primary flywheel  102  and the secondary flywheel  104  being one of coupled and decoupled, the detector (not shown) assuming a first state when the condition is within a first range and assuming a second state when the condition is within a second range. For example the detector (not shown) might include a sensor (not shown) for detecting ambient temperature, precipitation, pavement condition, gear selection or wheel slip (for example as measured by comparing wheel speed to vehicle speed). Alternatively, the detector (not shown) might include a simple manual control by which a user could indicate which of the first state and the second state the detector (not shown) should assume in response to the user&#39;s assessment of such conditions. 
     In this regard, the detector (not shown) might include a rotary encoder (not shown) and related circuitry (not shown) to detect the angular frequency of the primary flywheel  102  and whether angular frequency of the primary flywheel  102  is greater than or less than the predetermined angular frequency. The hydraulic decoupler  116  might include a piston  150  slidable within a housing  152  within the primary flywheel  102 , in this embodiment a spring-biased piston  150 , actuated by a hydraulic pressure controller, for example implemented with a hydraulic pump (not shown) or a valve (not shown) for controlling access with a hydraulic fluid source/sink (not shown), which is responsive to the detector (not shown). Those skilled in the art will appreciate that this spring-biased piston  150  also forms part of the coupler  112 . 
     In steady state (when the primary flywheel  102  has less than the predetermined angular frequency and thus the detector (not shown) is in the first state), the hydraulic pressure controller (not shown) pressurizes the hydraulic fluid in the spring-biased piston  150  to urge against the spring-bias and urge the friction disc  108  and the drive plate  110  together. When the primary flywheel  102  has more than the predetermined angular frequency and the detector (not shown) is in the second state, the hydraulic pressure controller (not shown) depressurizes the hydraulic fluid in the spring-biased piston  150  such that the spring-bias urges the friction disc  108  and the drive plate  110  apart. 
     In this embodiment, the predetermined angular frequency can be adjusted by calibrating the detector (not shown), for example a rotary encoder (not shown) and related circuitry (not shown). The force of the coupler  112  can be adjusted by adjusting the hydraulic properties of the spring-biased piston  150  and the hydraulic pressure controller (not shown). The force of the decoupler  116  can be adjusted by adjusting the spring-biasing of the spring-biased piston  150 . 
     (v) Fifth Embodiment (Hydraulic Piston—Low Pressure Coupling) 
       FIG. 9  shows a fifth embodiment of the variable mass flywheel  100  in accordance with aspects of the present invention. 
     The fifth embodiment is similar to the fourth, except that the biasing of the piston  150  is reversed. 
     In steady state (when the primary flywheel  102  has less than the predetermined angular frequency and thus the detector (not shown) is in the first state), the hydraulic pressure controller (not shown) depressurizes the hydraulic fluid in the spring-biased piston  150  such that the spring-bias urges the friction disc  108  and the drive plate  110  together. When the primary flywheel  102  has more than the predetermined angular frequency and the detector (not shown) is in the second state, the hydraulic pressure controller (not shown) pressurizes the hydraulic fluid in the spring-biased piston  150  to urge against the spring-bias and urge the friction disc  108  and the drive plate  110  apart. 
     An advantage of the fifth embodiment is that in steady state, with the primary flywheel  102  having an angular frequency below the predetermined angular frequency (including zero angular frequency), the friction disc  108  and the drive plate  110  are urged together by the spring-bias of the spring-biased piston  150 , without the need for the hydraulic fluid to be maintained pressurized. 
     In this embodiment, the predetermined angular frequency can be adjusted by calibrating the detector (not shown), for example a rotary encoder (not shown) and related circuitry (not shown). The force of the coupler  112  can be adjusted by adjusting the hydraulic properties of the spring-biased piston  150  and the hydraulic pressure controller (not shown). The force of the decoupler  116  can be adjusted by adjusting the spring-biasing of the spring-biased piston  150 . 
     (vi) Sixth Embodiment (Annular Hydraulic Piston) 
       FIG. 10  shows a sixth embodiment of the variable mass flywheel  100  in accordance with aspects of the present invention. 
     In this embodiment, the decoupler  116  is hydraulic and the detector (not shown) is embodied so as to drive the hydraulic decoupler  116 . However, unlike the fourth and fifth embodiments, in this sixth embodiment the spring-biased piston  150  is annular and integrated with the pressure plate  118 . 
     In steady state (when the primary flywheel  102  has less than the predetermined angular frequency and thus the detector (not shown) is in the first state), the hydraulic pressure controller (not shown) depressurizes the hydraulic fluid in the spring-biased piston  150  such that the spring-bias urges the friction disc  108  and the drive plate  110  together. When the primary flywheel  102  has more than the predetermined angular frequency and the detector (not shown) is in the second state, the hydraulic pressure controller (not shown) pressurizes the hydraulic fluid in the spring-biased piston  150  to urge against the spring-bias and urge the friction disc  108  and the drive plate  110  apart. 
     This sixth embodiment operates quite similarly to the fifth embodiment; however, the hydraulic pressure is distributed fully annularly about the pressure plate instead of at multiple discrete pistons  150  as in the fifth embodiment. 
     (vii) Seventh Embodiment (Pneumatic Piston) 
       FIG. 11  shows a seventh embodiment of the variable mass flywheel  100  in accordance with aspects of the present invention. 
     In this embodiment, the decoupler  116  is pneumatic and the detector (not shown) is embodied so as to drive the pneumatic decoupler  116 . The detector (not shown) might detect a condition that correlates with the desirability of the primary flywheel  102  and the secondary flywheel  104  being one of coupled and decoupled, the detector (not shown) assuming a first state when the condition is within a first range and assuming a second state when the condition is within a second range. For example the detector (not shown) might include a sensor (not shown) for detecting ambient temperature, precipitation, pavement condition, gear selection or wheel slip (for example as measured by comparing wheel speed to vehicle speed). Alternatively, the detector (not shown) might include a simple manual control by which a user could indicate which of the first state and the second state the detector (not shown) should assume in response to the user&#39;s assessment of such conditions. 
     In this regard, the detector (not shown) might include a rotary encoder (not shown) and related circuitry (not shown) to detect the angular frequency of the primary flywheel  102  and whether angular frequency of the primary flywheel  102  is greater than or less than the predetermined angular frequency. 
     The pneumatic decoupler  116  might include a piston  150  slidable within a housing  152  within the primary flywheel  102 , in this embodiment a spring-biased annular piston  150  slidable within an annular housing  152  and actuated by a vacuum controller, for example implemented with a vacuum pump (not shown) or a valve (not shown) for controlling access with a vacuum source/sink (not shown) such as an engine intake, that is responsive to the detector (not shown). Those skilled in the art will appreciate that this spring-biased piston  150  also forms part of the coupler  112 . 
     In steady state (when the primary flywheel  102  has less than the predetermined angular frequency and thus the detector (not shown) is in the first state), the vacuum controller (not shown) evacuates the housing  152  around the spring-biased piston  150  to urge the piston  150  against the spring-bias and urge the friction disc  108  and the drive plate  110  together. 
     When the primary flywheel  102  has more than the predetermined angular frequency and the detector (not shown) is in the second state, the vacuum controller (not shown) allows the housing  152  to repressurize to atmospheric pressure such that the spring-bias on the piston  150  urges the friction disc  108  and the drive plate  110  apart. 
     (viii) Eighth Embodiment (Lever) 
       FIG. 12  shows an eighth embodiment of the variable mass flywheel  100  in accordance with aspects of the present invention. 
     In this embodiment, the coupler  112  includes an annular combination pressure-plate  118  and spring  136 . The decoupler  116  includes a lever  154 , as illustrated a class 1 lever, having a fulcrum  156  and pivotally mounted within a pocket  158  in the primary flywheel  102 . The lever  154  has a load end  160  abutting the coupler  112  and an opposite weighted force end  162 . As illustrated, the load end  160  is significantly closer to the fulcrum  156  than is the force end  162 . 
     As the angular frequency of the variable mass flywheel  100  increases, the force end  162  of the lever  154  is urged radially outward from the axis of rotation of the variable mass flywheel  100 . As the force end  162  of the lever  154  moves radially outward, the lever  154  pivots on the fulcrum  156  such that the load end  160  is urged against the combination pressure-plate  118  and spring  136 . When the angular frequency of the variable mass flywheel  100  increases beyond the predetermined angular frequency, the lever  154  overcomes the combination pressure-plate  118  and spring  136 , thereby allowing the friction disc  108  and the drive plate  110  to disengage and thus the primary flywheel  102  and the secondary flywheel to disengage. When the angular frequency of the variable mass flywheel  100  decreases below the predetermined angular frequency, the combination pressure-plate  118  and spring  136  overcomes the lever  154 , thereby forcing the friction disc  108  and the drive plate  110  back into engagement and thus the primary flywheel  102  and the secondary flywheel back into engagement. 
     The predetermined angular frequency can be adjusted by adjusting the spatial and weight relationships in the lever  154  between the load end  160 , the force end  162  and the fulcrum  156 . Further adjustment can be effected by adjusting the spatial relationships between the lever  154  and the pocket  158  and the lever  154  and the combination pressure-plate  118  and spring  136 . Additional adjustment can be effected by adjusting the strength of the combination pressure-plate  118  and spring  136 . 
     (c) Description Summary 
     Thus, it will be seen from the foregoing embodiments and examples that there has been described a way to provide a flywheel having mass that is a function of its angular frequency. 
     While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims. In particular, any quantities described have been determined empirically and those skilled in the art might well expect a wide range of values surrounding those described to provide similarly beneficial results. 
     It will be understood by those skilled in the art that various changes, modifications and substitutions can be made to the foregoing embodiments without departing from the principle and scope of the invention expressed in the claims made herein.