Patent Publication Number: US-2012031719-A1

Title: Self-powered and self-sensing magnetorheological dampers

Description:
TECHNICAL FIELD 
     The application relates to a self-powered and self-sensing MR damping device and an electrical circuit applicable to devices that have electrical power generation, velocity sensing and MR damping capabilities. 
     BACKGROUND 
     Vibration controls are crucial to today&#39;s increasingly high-speed dynamic systems. In an application of a magnetic field, magnetorheological (MR) fluids are one kind of smart materials that exhibit fast, reversible and tunable transition from a free-flowing state to a semi-solid state in a few milliseconds. MR fluids are very promising for semi-active vibration control because they provide a simple and fast response interface between electronic controls and mechanical devices/systems. MR dampers have attractive advantages such as controllable damping force, broad operational temperature range, fast response, and low power consumption. 
     The schematic of the typical MR damper based semi-active control system is illustrated in  FIG. 1 . As shown in  FIG. 1 , in the current MR damper system, a separate power supply  60  and a dynamic sensor  64  are required. The power supply  60  is used for activating electromagnetic coils inside an MR damper  62  to provide a magnetic field for the MR fluids. The sensor  64  is used to measure a dynamic response, which may comprise a displacement or velocity of a plant  61  or components in the MR damper  62 . A system controller  66  uses measured signals representing the velocity in determining the control action. The current MR damper system also comprises a damper controller  67  to generate a command of voltage based on the measured signals from the system controller  66 . The generated command is then applied to a current driver  68 . 
     In the current MR damper system, as two ends of the MR damper  67  move relative to each other under an external excitation, the mechanical energy from the MR damper will be converted into heat and the converted heart will be dissipated. For example, during the everyday usage of an automobile, only 10-16% of the fuel energy is used to drive the car to overcome a resistance from a road friction and an air drag. A fair amount of fuel power is wasted when the car is running under an irregular road. In addition, the separate power supply (battery) needs to be recharged or replaced due to its limited lifetime. It also increases the installation space, weight and cost of MR damper systems. 
     Also, to fully take advantages of the controllable damping characteristics of the MR damper, an extra velocity/displacement sensor that measures the relative velocity/displacement of two ends of MR damper is necessary in the current MR damper system. In general, the extra sensor is separately paralleled with the MR damper. The extra dynamic sensor increases the installation space, weight and cost of MR damper systems. Besides, the connectors between the separate sensor and MR damper system lower the system reliability. 
     SUMMARY 
     The present application provides an ideal solution for vibration mitigation systems. Under vibration excitations, a self-powered and self-sensing MR damper according to embodiments of the application will generates a required damping force automatically without the extra power supply and sensor. 
     In one aspect, there is provided a self-powered and self-sensing MR damping device, comprising: 
     an MR damper part having a damper piston assembly and a damper cylinder, the damper piston assembly being movable relative to the damper cylinder under an external excitation; 
     a power generator configured to generate electrical power according to the relative movement between the damper piston and the cylinder assembly; and 
     an electrical circuit configured to estimate said relative movement to output a damper driving current based on the estimated velocity,
         wherein the MR damper part is further configured to generate a damper force according to the damper driving current.       

     In another aspect, there is provided a self-powered and self-sensing MR damping device, which may comprise: 
     an MR damper part having a damper piston assembly and a damper cylinder, the damper piston assembly being movable relative to the damper cylinder under an external excitation; 
     a power generator configured to generate electrical power according to the relative movement between the damper piston and said cylinder assembly; and 
     a sensing part configured to sense the relative movement of the damper piston assembly and the damper cylinder. 
     According to the above MR damping device, a part of mechanical energy from the MR damper may be converted to electricity for the usage of MR damping system itself, rather than just wasting it as heat. Also, it could measure relative velocity/displacements between two ends of MR damper without an extra sensor. Therefore, separate power supply and dynamic sensor in the current MR damping system are not needed any more. Great benefits such as energy saving, size and weight reduction, lower cost, and less maintenance could be obtained for the MR damper systems. Moreover, the reliability of MR damper system could be improved by eliminating two separate devices and their connectors. 
     In addition, the present application could provide system dynamic information by utilizing a sensing function. The dynamic information could be used to provide a controlling function in the MR damper system. This sensing function is applicable to different control algorithms. By using different control algorithms, the above mentioned device could have good performances for broad applications, for instances, vehicle suspensions, buildings, and prostheses. 
     The MR damper part, the power generator and the sensing part is not a simple combination. Instead, the three parts share some common space and components. Motion and magnetic-field interactions among three parts are also considered. In addition, some special components are designed for magnetic-field interactions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a typical MR damper based semi-active control system. 
         FIG. 2  illustrates a self-powered and self-sensing MR damper according to one embodiment of the application. 
         FIG. 3  illustrates an enlarged view of a portion of  FIG. 2  showing details of the mechanical structure thereof. 
         FIG. 4  illustrates a self-powered and self-sensing MR damper according to another embodiment of the application. 
         FIG. 5A  illustrates an enlarged view of a portion of  FIG. 3  showing greater details of a multi-pole slotted power generator thereof. 
         FIG. 5B  illustrates a multi-pole slotless power generator according to one embodiment of the application. 
         FIG. 6  illustrates an electrical part of a self-powered and self-sensing MR damper according to one embodiment of the application. 
         FIG. 7  illustrates a velocity-extraction sensing mechanism according to one embodiment of the application. 
         FIG. 8  illustrates distributions of magnetic fields of MR damper part and the power generator according to one embodiment of the application. 
         FIG. 9A  illustrates a spring-based multi-pole slotted power generator according to one embodiment of the application. 
         FIG. 9B  illustrates a spring-based multi-pole slotless power generator according to one embodiment of the application. 
         FIG. 10  illustrates a mechanical part having spring-based multi-pole slotless power generator and moving-spacer velocity-sensing part according to one embodiment of the application. 
         FIG. 11A  illustrates an enlarged view of a portion of  FIG. 10  showing greater details of moving-spacer velocity-sensing part thereof according to one embodiment of the application. 
         FIG. 11B  illustrates the moving-magnet velocity-sensing part according to one embodiment of the application. 
         FIG. 12  illustrates the distributions of magnetic fields of a MR damper part and a moving-spacer velocity-sensing part according to one embodiment of the application. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, some embodiments of the application will be described in reference to the accompanying drawings. 
       FIG. 2  illustrates a self-powered and self-sensing MR damper  79  according to one embodiment of the application. The MR damper  79  shown in  FIG. 2  has a single-ended MR damper structure with multi-pole slotted power generator. The MR damper  79  carries out sensing functions by extracting velocity information from signals of power generations. This means that sensing parts of the MR damper  79  shares the same mechanical components with a power generator  86  of the MR damper  79 . 
     As shown in  FIG. 2 , the MR damper  79  comprises an electrical part  76  and a mechanical part  78 . Hereinafter, the mechanical part  78  will be discussed first. 
     Referring to  FIG. 3 , the mechanical part  78  according to one embodiment of the application is illustrated. The mechanical part  78  may comprise a MR damper part  84  and a power generator  86 . The power generator  86  may be of a multi-pole slotted linear generator. As shown, the power generator  86  is concentric with the MR damper part  84 , and is radially outside of the MR damper part  84 . That is, the MR damper part  84  is inside the power generator  86 . In one aspect, this arrangement has a smaller axial size (length) than the conventional axial and outside arrangement, so that it could be very useful when an axial installment space (length) is limited. In the other aspect, the most useful part of the mechanical part  78  is the exterior part for generating the magnetic field and electricity; and the interior part of the mechanical part  78  is usually used for mounting and less important than the exterior part. Since the MR damper part  84  is used as the interior part, the interior space of the mechanical part  78  is better utilized than the conventional axial and outside arrangement. The space and components of MR damper part  84  are fully utilized. The power generation ability of the power generator  86  may increase significantly while the size (diameter) only increases slightly. 
     The MR damper part  84  may comprise a hydraulic cylinder  106  normally made from a high-permeability material, such as low-carbon steel. In this embodiment, the cylinder  106  provides a cylindrical hollow  116  to house fluids, e.g., MR fluids, air, oil, and/or other liquids or materials/components. The cylinder  106  is closed by two non-magnetic covers  100  and  114  at its two ends. They are assembled together to form a partially closed assembly. 
     The MR damper part  84  may also comprise at least one piston rod  96 . The piston rod  96  is in sliding fit with the hydraulic cylinder  106  through two central holes in the covers  100  and  114 . The piston rod  96  is non-magnetic. Seal components  98 A, which may be bushings, O rings, lubricants, bearings and/or combined sealers, centralize and provide supports to the rod  96 . Additionally, the piston rods  96  is configured as axially slidable without touching covers  110  and  114 , and is further configured to seal the MR fluids inside the hollow  116 . 
     The MR damper part  84  may also comprise a piston assembly  104  connected to the piston rod  96  by screws or welding. The piston assembly  104  is axially slidable within the cylinder  106  by guiding of the seal components  98 A, and keeps centralizing or to be aligned within the cylinder  106 . The piston assembly  104  is preferably manufactured by a high-permeability material with at least one spool and coil winding. In this embodiment, one coil winding  108  is shown. The MR damper part  84  may also comprise one rod-volume compensator. In this embodiment, an accumulator  160  is used, which has a floating piston  158 . 
     A gap between the inner wall (diameter) of the hydraulic cylinder  106  and the outer wall (diameter) of the piston  104  forms a working portion of MR fluids, i.e. an annular fluid orifice  109 . The coil winding  108  may be configured to create a magnetic field that affects the MR fluids in the fluid orifice  109 . As the piston rod  96  moves under an external excitation, the MR fluids will flow through the annular orifice  109 . 
     The coil winding  108  may be formed as a solenoid in this embodiment to generate magnetic fields. The coil winding  108  is interconnected to the electrical part  76  by wires  92 . The wires  92  exit through the damper part by wire holes in the piston  104  and the piston rod  96 . When an electrical current is applied to the coil winding  108 , a magnetic field is generated to solidify the MR fluids in the annular orifice  109 . Then the yield strength of MR fluids in the annular orifice  109  is increased, and thus the damping force of MR damper part  84  is increased. By adjusting input currents of coil winding  108 , the damping force of MR damper part  84  could be controlled. The piston rod  96  has a threaded rod end mated with an upper connector  90 A. 
       FIG. 4  illustrates a self-powered and self-sensing MR damper according to another embodiment of the application. In this embodiment, the MR damper is configured with a double-ended MR damper structure with a multi-pole slotted power generator. Different from the single-ended MR damper structure as shown in  FIGS. 2 and 3 , the double-ended structure has two piston rods  70  and  71 . As an example, the piston rods  70  and  71  have the same diameter, so there is no volume change of a hollow  72  containing the MR fluids. The rod-volume compensator, the accumulator or other similar devices are not required in this embodiment. 
     There are at least four different configurations for the power generator  86 . A multi-pole slotted linear generator  86  is shown in  FIG. 5A , which illustrates an enlarged view of a portion of  FIG. 3 . In general, the generator  86  is concentric with and radially outside the MR damper part  84  as mentioned in the above. The term “multi-pole” means the power generator  86  has multiple groups of permanent magnets and coils arranged specially. In one aspect, the special arrangement of the multiple groups is configured such that the generated power in every coil could be fully utilized. In the other aspect, this arrangement could be configured such that the magnetic flux runs in a controlled path, which could reduce the flux leakage sand enhance the strength of the magnetic field. These two aspects make the multi-pole power generator  86  have high power generation efficiency. 
     As shown in  FIG. 5A , the power generator  86  comprises an inner part  86 A and an outer part  86 B. The inner part  86 A comprises at least one pole piece and permanent magnet. Four permanent magnets and five pole pieces are shown in  FIG. 5A . The inner part  86 A may also comprise a magnetic-flux shield layer  154  formed by non-magnetic materials, a high-permeability magnetic-flux guided layer  140 , and a supporting plate  138 . The assembly of inner part  86 A is attached to the piston rod  96  by the screws or pins  93  through the connective cap  94 . Therefore, the assembly of inner part  86 A is movable with the piston rod  96 . 
     In this embodiment, ring permanent magnets  150 A˜C made from rare earth may be radially magnetized or axially magnetized. The polarities of the adjacent magnets  150 A˜C are opposite. As shown, the magnets  150 A˜C are axially magnetized for illustrative purpose. The magnets  150 A˜C are stacked in pairs so that opposing magnetomotive forces drive the flux through spacers  142  segmented in the outer part  86 B. The magnets  150 A˜C are interspersed with high-permeability pole pieces  152  mounted on the magnetic-flux shield layer  154 . When the ring magnets are radially magnetized, the materials of the pole pieces  152 , the magnetic-flux shield layer  154  and the magnetic-flux guided layer  140  should accordingly be changed to non-magnetic, high-permeability and non-magnetic. 
     The outer part  86 B may comprise at least one winding coil and at lest one spacer. Eleven winding coils  144  and twelve spacers  142  are shown in  FIG. 5 . The winding coils  144  are interspersed with the high-permeability spacers  142 . The winding coils  144  and the spacers  142  form a slotted structure in the outer part  86 B. A gap between the inner wall of the outer part  86 B and the outer wall of the inner part  86 A forms a working gap  151  of the power generator  86 . The spacers  142  are used to increase the magnetic flux density of the working gap  151 , so that high electrical power could be generated. 
     The outer part  86 B is attached to the cylinder cover  114  of MR damper part  84  by the screws  135 . Therefore, the assembly of outer part  86 B is movable with the cylinder  106 . In one embodiment, the outer part  86 B may also comprise a high-permeability shell  136  and a locker  156 . 
     A specially designed magnetic-flux shield layer  154  and a magnetic-flux guided layer  140  are used to minimize the mutual interferences of the magnetic fields of the power generator  86  and the damper part  84 , to solve the integration problem between the power generator  86  and the damper part  84 . 
     A guide rail  112  is connected to the cover  114 , and has a relatively low surface finish. The guide rail  112  is in slide fit with the inner part assembly  86 A, and insures a proper centralizing of the inner part assembly  86 A when it moves with piston rod  96 . 
     Magnetic flux paths are depicted by dashed lines in  FIG. 5A . Because the inner part assembly  86 A and the outer part assembly  86 B are connected to the piston rod  96  and the cylinder  106  of the MR damper part  84 , respectively, under vibration excitation, the relative motion between piston rod  96  and the cylinder  106  could also cause the relative linear motion between the inner part assembly  86 A and the outer part assembly  86 B. The relative movement between the coils  144  and the magnets  150 A˜C in the outer part assembly  86 B will provide a changing magnetic flux linkage through the coils  144 , thus the electrical power is generated therein. Different kind or shape of coils may be interconnected according to the voltage direction of each coil to get a maximum electrical power. The electrical power is output to the electrical part  76  through wires  102 . 
       FIG. 5B  illustrates another configuration of power generator-the multi-pole slotless power generator  180 . The difference between multi-pole slotless linear generator  180  and multi-pole slotted linear generator  86  as shown in  FIG. 5A  lies in that, there is no spacer  142  between two adjacent coils in the slotless configuration. For multi-pole slotless linear generator  180 , coils  182  and  184  are arranged one by one without being separated by the spacer that has high magnetic permeability. The magnetic flux will go through the coil  182  directly. For the slotted generator  86  as shown in  FIG. 5A , the magnetic flux will go through the spacer  142 . This slotless generator  180  has lower power generation ability, simpler structure and smaller cogging force than the slotted generator  86 . 
     Hereinafter, the electrical part  76  will be discussed in references to  FIGS. 6 and 7 . 
       FIG. 6  illustrates the electrical part  76  of the self-powered and self-sensing MR damper  79  according to one embodiment of the application. The input of the electrical part  76  is generated AC voltages from a mechanical part  78 , and the output thereof may be the driving current for the damper coil  108  to activate the magnetic field for solidifying the MR fluid. The electrical part  76  comprises an energy harvesting circuit  482 , a sensing estimator  484 , a controller  486 , and current driver  488 , which will be discussed below. 
     The energy harvesting circuit  482  may comprise a power conditioning circuit  4821 , an energy storage device  4822 , and a voltage regulator  482323 . The power conditioning circuit  4821  is coupled to the energy storage device  4822 . The power conditioning circuit  4821  receives the AC voltage from the mechanical part  78  and rectifies the AC voltage to DC voltage so as to provide charging voltages to the energy storage device  4822 . The power conditioning circuit  4821  may include a bridge rectifier and/or voltage multiplier such as a tripler. 
     The energy storage device  4822  may be rechargeable batteries, capacitors or ultracapacitors. The device  4822  receives the charging voltages of power conditioning circuit  4821 . The device  4822  is used to store and accumulate the harvested energy for intermittent use. In many cases, the output of harvested electrical energy of storage device  4822  may be not appropriate for load use directly (e.g., the required working power supply of the controller  486  may be 3.3 Volt, while the output voltage of storage device  4822  may be 12 Volt). Therefore, the voltage regulator  4823  is utilized to adjust the voltage received from the energy storage device  4822  to appropriate values that could be used for loads. The voltage regulator  4823  will output the electrical power to the sensing estimator  484 , the controller  486  and current driver  488 . The majority of the electrical power is for the current driver  488 , because this branch of power is used for driving the MR damper coil  108  finally. According to one embodiment, the physical circuits in the voltage regulator  4823  may be DC-DC circuits. The voltage regulator  4823  is designed to regulate the output voltages to appropriate values (e.g. the power supply voltages for the controller  486 , the sensing estimator  484 , and the current driver  488  may be ±3.3 V, ±5 V, and 12 V, respectively). 
     A sensing estimator  484  receives the AC power signals from the power generator  86  or the sensing voltages from the sensing part  82 , and outputs the relative velocity of the two ends of MR damper. The sensing estimator  484  may comprise an analog amplifier if it receives a sensing voltage from the moving-spacer velocity-sensing part  82  of the mechanical part  220 , which is proportional to the relative velocity. The moving-spacer velocity-sensing part  82  will be discussed in reference to  FIG. 11A  latter. Alternatively, it may comprise a digital processor that runs the estimation algorithm  242  and has A/D and/or D/A conversions, if it receives AC power signal from the power generator  86 . 
       FIG. 7  illustrates a velocity-sensing process  242  deployed in the sensing estimator  484  according to one embodiment of the application. The process  242  utilizes a portion of the power voltage from the generator as the original sensing voltage, and then the voltage is processed by the sensing estimator  484 . According to one embodiment of the application, the power voltage from the generator may be the voltage from the multi-pole slotted generator  86  or the multi-pole slotless generator  180 . For an illustrative purpose, the multi-pole slotted linear generator  86  as shown in  FIG. 5A  is used herein. 
     The relative velocity between the two ends of self-powered and self-sensing MR damper is identical with the relative velocity between the inner part  86 A and the outer part  86 B. The generated voltages of two adjacent coils  141  and  144  (as shown in  FIG. 5A ) may be used for velocity extracting so as to obtain the relative velocity between the inner part  86 A and the outer part  86 B from following equations: 
     
       
         
           
             
               
                 
                   
                     E 
                     1 
                   
                   = 
                   
                     
                       - 
                       N 
                     
                      
                     
                         
                     
                      
                     
                       φ 
                       g 
                     
                      
                     
                         
                     
                      
                     
                       π 
                       τ 
                     
                      
                     
                       sin 
                        
                       
                         ( 
                         
                           
                             π 
                             τ 
                           
                            
                           z 
                         
                         ) 
                       
                     
                      
                     
                       
                          
                         z 
                       
                       
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                         t 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                      
                     
                       
                          
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                   = 
                   
                     
                       
                         
                           E 
                           1 
                           2 
                         
                         + 
                         
                           E 
                           2 
                           2 
                         
                       
                       
                         
                           ( 
                           
                             N 
                              
                             
                                 
                             
                              
                             
                               φ 
                               g 
                             
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                         2 
                       
                     
                   
                 
               
               
                 
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     where E 1  and E 2  are the generated voltages of the coils  141  and  144 , respectively, N is the number of turns of the coils, φ g  is an air-gap magnetic flux, r is a magnet pole pitch, z is a relative displacement, and dz/dt is a relative velocity. 
     The sensing algorithm  242  provides a method to extract the accurate velocity information. Firstly, the structural parameters (that is, N, φ g , τ and z) are input to the sensing estimator  484 , and then E 1  and E 2  are computed according to equation (2) to obtain the absolute value of velocity |dz/dt(t)|. Next, the absolute value is assumed to have two different signs to obtain two possible velocities, i.e. dz/dt=|dz/dt(t)|, and dz/dt=−|dz/dt(t)|. And then, the obtained two possible velocities are summed up by a common integral transform to get two computed relative displacements z 1  and z 2 . Two calculated voltages E 11 (t) and E 12 (t) are determined by rule of equation (1). Then, it is determined whether |E 11 (t)−E 1 (t)| is less than |E 12 (t)−E 1 (t)|. If yes, dz/dt=|dz/dt(t)|; otherwise, dz/dt=−|dz/dt(t)|. 
     The relative velocity dz/dt could be obtained from the algorithm  242  by online processing of sensing estimator  484 . Although this method requires online signal processing, the separate mechanical part  78  is not needed and the size of self-powered, self-sensing MR damper would be decreased. This method is applicable to the muti-pole linear electromagnetic power generators, and could be used for various applications, not only for MR damper systems shown in this embodiment. 
     The controller  486  is an essential component of the electrical part  76 . It receives the velocity sensor signal from the sensing estimator  484 . For some complex applications, the controller  486  may also receive some external sensing signals. The physical circuits for the controller  486  may comprise MCU, DSP et al. The controller  486  uses some readily available measurements to run certain control algorithms, and generates a command of voltage that could instruct the current driver  488  to induce a desired damping force of MR damper. The command of voltage output from the controller  486  is received by a current driver  488 . The current driver  488  operates to convert input commands from the controller  486 , which are in form of analog voltage, into the driving current accordingly. As mentioned in the above, the power supply of the current driver  488  is provided by the voltage regulator  4823 . The physical circuits for the current driver  488  may be composed of operational amplifiers and MOS transistors. The output current of current driver  488  is applied to the MR damper coil  108  for activating MR fluids. 
       FIG. 8  illustrates distributions of magnetic fields of MR damper part  84  and the power generator  86 . These magnetic-field distributions are obtained from finite element analysis. Since the power generator  86  and MR damper part  84  have their own magnetic fields while sharing some common space, the magnetic flux interferences between the power generator  86  and the MR damper part  84  should be minimized. In some embodiments, some special components are designed for magnetic-field interactions. The magnetic flux shield layer  154  and the flux guided layer  140  would be used to minimize the mutual interferences of the magnetic fields of the power generator  86  and the MR damper part  84 . A magnetic field  170  from the power-generator  86  and a magnetic field  172  from the MR-damper part  84  are shown in  FIG. 8 . As shown, the mutual magnetic-field interferences from the fields  170  and  172  are effectively prevented. 
       FIG. 9A  illustrates a spring-based multi-pole slotted power generator  190  according to another embodiment of the application. The generator  190  may be used with a particular excitation frequency. The difference between the spring-based multi-pole slotted linear generator  190  and the multi-pole slotted linear generator  86  is that, the inner part  190 A of spring-based generator  190  is attached to a spring  194 , which in turn is attached to a cover  196  by welding or pressing. So, the inner part  190 A is also movable with the cover  196  through the spring  194 . A guide rail  192  is connected to the cover  196 , and in slide fit with the inner part  190 A, to insure proper centralizing of the inner part  190 A as it moves. An outer part  190 B of spring-based generator  190  is also attached to the cover  196 . The stiffness of spring  194  is designed particularly for a vibration frequency. When the cover  196  moves under an external excitation, the external excitation would make the relative movement occur between the inner part  190 A and the outer part  190 B. Similar to the slotted generator  86 , the term “slotted” means that there is a spacer  198  between two adjacent coils  197  and  199 . 
       FIG. 9B  illustrates a spring-based multi-pole slotless linear generator  200  according to another embodiment of the application. The generator  200  may be used with a particular excitation frequency. The difference between the spring-based multi-pole slotless linear generator  200  and the spring-based multi-pole slotted linear generator  190  is that, there is no spacer  198  between two adjacent coils  204  and  206  in a slotless configuration. For the spring-based slotless generator  200 , the coils  204  and  206  are arranged one by one without being separated by a spacer that has high magnetic permeability. 
     The configurations of spring-based generators  190  and  200  could not work together with the velocity-extraction configuration  240 . Therefore, when the self-powered and self-sensing MR damper uses the spring based power generator  190  or  200 , it needs other sensing methods. Two other sensing methods could be used and require separate mechanical components, i.e. a moving-magnet velocity-sensing part and a moving-spacer velocity-sensing part.  FIG. 10  illustrates these two sensing methods. 
       FIG. 10  illustrates a mechanical part having spring-based multi-pole slotless power generator  200  and a moving-spacer velocity-sensing part  82 . For a purpose of illustration, the mechanical part  220  comprises a multi-pole slotless power generator  200  and a moving-spacer velocity-sensing part  82 . A base excitation of a cover  114  would make the multi-pole slotless power generator  200  generate an electrical power. 
       FIG. 11A  is an enlarged view of a portion of  FIG. 10  showing greater details of the moving-spacer velocity-sensing part. In general, the sensing principle is based on the electromagnetic induction. As shown in  FIG. 11A , a high-permeability outer cylinder  118  is attached to the cover  114  by screws  115 , thus is movable with a lower connector  223 B. The connectors  223 A and  223 B may be coupled to the piston rod and the damper cylinder of the MR damper part, such that the relative movement of the piston rod and the damper cylinder of the MR damper part may cause the connectors  223 A and  223 B to move accordingly. A multi-layer coil  130  is wound on a bobbin  128  inside the outer cylinder  118 . A non-magnetic plate  126  is arranged for assembly convenience. 
     A radially magnetized ring magnet  134  is fixed on the top of the outer cylinder  118 . There is also provided a non-magnetic steel piece  132  that is attached to the outer cylinder  118  by interference fit for locating the ring magnet  134 . The polarity of the magnet  134  may be opposite with that shown in  FIG. 11A . 
     A high-permeability piston rod  120  that is slidable through a central hole of the magnet  134  is kept centralized by seal components  98 B. The piston rod  120  is also attached to the non-magnetic magnetic-flux shield segment  110 . The specially designed magnetic-flux shield segment  110  is used to minimize the mutual interferences of the magnetic fields of the velocity-sensing part  82  and the MR damper part  222 , to solve the integration problem between the velocity-sensing part  82  and the MR damper part  222 . The other end of the piston rod  120  is attached by a high-permeability washer  122 . 
     A gap  129  between the inner wall (diameter) of the bobbin  128  and the outer wall (diameter) of the washer  122  forms a working portion  129  of the velocity-sensing part  82 . The primary magnetic flux path is depicted by the dashed line in  FIG. 11A . As shown, the primary magnetic flux path is a closed magnetic circuit, which may be traced from the magnet  134 , through the outer cylinder  118 , the coil  130 , the bobbin  128  and the gap  129 , the washer  122 , the piston rod  120  to magnet  134 . Another leakage flux path is also indicated by dashed line, but the leakage flux has little effect on the sensing. If the magnetic reluctance of steel components in the primary flux path is neglectable, the total reluctance of the primary magnetic circuit is independent of its position, but dominated by the air gap. So when the relative linear movement between the piston rod  120  and the outer cylinder  118  happens, the magnetic flux through the coil  130  keeps constant. And the number of turns of the coil  130  enclosed by the flux path will change with this movement. The coil  130  is uniformly wounded. Therefore, the total magnetic flux leakage through the coil  130  is proportional to the moving displacement. According to the Faraday&#39;s law of electromagnetic induction, the generated voltage in coil  130  is proportional to the relative velocity between piston rod  120  and the outer cylinder  118 , so the sensing voltage is proportional to the relative velocity between connectors  223 A and  223 B. The sensing voltage is output to the electrical part  76  by wire  124 . 
     Specifically, when the damper piston assembly  96  and the damper cylinder  106  move relative to each other under an external excitation, there will be a corresponding relative velocity between connectors  223 A and  223 B, which may in turn result a relative linear movement between the piston rod  120  and the outer cylinder  118  such that the number of turns of the coil  130  enclosed by the flux path through the coil  130  will change with this movement so as to generate a voltage in coil  130  that is proportional to the relative velocity between piston rod  120  and the outer cylinder  118 . Hereinabove, it is described that the piston rod  120  and the outer cylinder  118  may be moved according to the movement of the damper piston assembly  96  and the damper cylinder  106 , respectively. It shall be understood that the moving-spacer velocity-sensing part may be configured such that the piston rod  120  is movable according to the movement of the damper cylinder  106 , and the outer cylinder  118  may be moved according to the movement of the damper piston assembly  96 . 
       FIG. 11B  illustrates another configuration of velocity-sensing part-moving-magnet configuration  210 . In general, the principle of moving-magnet configuration  210  is similar to the moving-spacer configuration  82 . The main difference between the moving-spacer configuration  82  and the moving-magnet configuration  210  is that, the radially magnetized ring magnet  216  moves with the piston rod  212  in the moving-magnet configuration  210 , while the high-permeability spacer  122  moves with the piston rod  120  in the moving-spacer configuration  82 . The magnet  216  is attached to a ring washer  214  that is mounted to the piston rod  212  by screws. The piston rod  212  moves linearly through a central hole of the outer cylinder  218 . The primary magnetic flux is depicted by dashed line, and the induction voltage in coil  220  is proportional to the relative velocity between the piston rod  212  and the outer cylinder  218 . 
       FIG. 12  illustrates distributions of magnetic fields of the MR damper part and moving-spacer velocity-sensing part. When the moving-spacer configuration  82  and the moving-magnet configuration  210  are used in the embodiments as described in the present application, the magnetic-field interferences between velocity-sensing part and the MR damper part should be considered for different applications. 
     Features, integers, characteristics, compounds, compositions, or combinations described in conjunction with a particular aspect, embodiment, implementation or example disclosed herein are to be understood to be applicable to any other aspect, embodiment, implementation or example described herein unless incompatible therewith. All of the features disclosed in this application (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments and extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.