Abstract:
Several embodiments of electric power assisted manually operated devices wherein the manual input force is sensed by a sensor that does not require lost motion connections and significant movement in order to determine the force applied. Also a compact drive is disclosed that permits the application to winding drums such as fishing reels. In addition a simplified temperature compensation system for the sensor is employed. Thus, the arrangements can be easily utilized with conventional structures with minimum change.

Description:
BACKGROUND OF INVENTION 
     This invention relates to an improved electric motor power assist system and more particularly to an improved method and device for detecting the manually inputted drive force to the system. 
     A wide variety of types of systems have been proposed wherein a manual force is assisted by an electric motor. In many of these types of systems, the amount of electric motor assist provided is related to the degree of manual force applied, among other things. Therefore, the mechanisms that operate on this principal generally require some form of manual force measuring device. 
     This is normally done by providing some form of lost motion connection in the connection between the element to which the manual force is applied and the thing to be operated. The manual force application is measured by determining the amount of lost motion that occurs. Thus, the sensors that operate on this principal require the addition of the lost motion connection to the mechanical transmission for coupling at least the manual force applying device to the load which is driven. This makes it difficult to embody the electric power assist in conventional mechanisms merely through the use of an added electric motor or the assist. 
     It is, therefore, a principal object to this invention to provide an improved force sensor arrangement for an electrically assisted, manually operated device and more particularly to an improved sensor for sensing the manual force applied without necessitating a lost motion connection. 
     For example, in one type of device, there is employed a planetary transmission which produces relative movement in response to the lost motion and this planetary transmission then drives a force sensor. Obviously, this not only complicates the system and adds to its costs, but also makes it difficult to apply the system to conventional non-assisted mechanisms. 
     In another type of arrangement, the lost motion is measured by a pair of cylindrical cams which are held in contact with each other by a spring and relative movement occurs when the manual force is applied. The degree of manual force is measured by measuring the degree of relative movement. Again, this type of device adds to the costs and complexity of the system and makes it difficult to incorporate into conventional non-assisted mechanisms. In addition, the accuracy of these devices is dependent upon maintaining a consistent degree of lost motion for a given force input which requires bearings and lubrication and also which can be adversely effected by temperature changes. 
     It is, therefore, a still further object to this invention to provide an improved force sensor for an electric power assisted system wherein lost motion is not necessary in order to measure the applied force. 
     As noted above, temperature variations can result in variations in the amount of assist provided in response to a given input force. Even if lost motion is eliminated, this can still present some problems. It is, therefore, a further object of this invention to provide an electric power assisted system in which temperature variations will not adversely effect the performance. 
     The type of power assist mechanisms previously employed have not lent themselves to applications where such assist is desirable. For example in winding drums such as fishing reels power assist is desirable, but not possible with the power assist mechanisms previously employed. It is, therefore, a still further object of this invention/n to provide a compact power assist mechanism that is compact enough for such applications. 
     SUMMARY OF INVENTION 
     A first feature of this invention is adapted to be embodied in an electrically assisted, manually powered unit. The unit includes a manual drive element receiving a manual input force from an operator, an electric motor for providing an assist force, a transmission arrangement for receiving a driving force from the manual drive element and the electric motor and driving the unit. A force sensor senses the manual force applied to the manual drive element and delivers an output signal indicative of the manual force. A control controls the operation of the electric motor. The control has a sensor input stage receiving the signal from the force sensor and a logic for determining the operation of the electric motor from at least the signal from the force sensor. The force sensor provides the force signal without necessitating any significant displacement of a component thereof. 
     Another feature of the invention is adapted to be embodied in an electrically assisted, manually powered unit. The invention in accordance with this feature includes a manual drive element receiving a manual input force from an operator. An electric motor for providing an assist force is also used. A transmission arrangement receives a driving force from the manual drive element and the electric motor for driving said unit. A force sensor senses the manual force applied to the manual drive element and delivers an output signal indicative of the manual force. A control controls the operation of the electric motor. The control has a sensor input stage receiving the signal from the force sensor and a logic for determining the operation of the electric motor from at least the signal from the force sensor. The force sensor includes a first electrical device providing a signal indicative of applied force. A second electrical device capable of providing a signal indicative of applied force is also employed. The manual force is applied only to the first electrical device. The first and the second electrical devices are positioned in proximity to each other so as to experience the same temperature. Finally, a circuit connects the first and the second electrical devices to provide a temperature compensated signal to the sensor input stage of the control. 
     A third feature of the invention is adapted to be embodied in a an electrically assisted, manually powered reel. The reel includes a manual drive element receiving a manual input force from an operator, an electric motor for providing an assist force, a transmission arrangement for receiving a driving force from the manual drive element and the electric motor and driving the reel. A force sensor senses the manual force applied to the manual drive element and delivers an output signal indicative of the manual force. A control controls the operation of the electric motor. The control has a sensor input stage receiving the signal from the force sensor and a logic for determining the operation of the electric motor from at least the signal from the force sensor. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side elevational view of an electric power assisted bicycle constructed in accordance with a first embodiment of the invention. 
     FIG. 2 is a partially schematic block diagram showing the components of the drive and power assist system. 
     FIG. 3 is an enlarged cross sectional view taken though the axis of rotation of the driving wheel and shows the force sensor arrangement as well as the assist motor. 
     FIG. 4 is an exploded perspective view showing the force sensor and its actuating mechanism. 
     FIG. 5 is a schematic electrical diagram of the force sensor and shows how temperature compensation is effected. 
     FIG. 6 is a cross sectional view taken through the crank mechanism of a power assisted bicycle constructed in accordance with a second embodiment of the invention and shows the force sensor associated therewith. 
     FIG. 7 is a cross sectional view taken through a manually rotated electric motor assisted winding drum constructed in accordance with a third embodiment of the invention. 
     FIG. 8 is a cross sectional view taken through the axle of a wheel of a wheelchair having an electric motor assist in accordance with a fourth embodiment of the invention. 
     FIG. 9 is a cross sectional view taken through the steering shaft of an electric motor power assisted steering mechanism in accordance with a fifth embodiment of the invention. 
     FIG. 10 is a cross sectional view taken along the line  10 — 10  of FIG.  9 . 
     FIG. 11 is an enlarged view looking in the direction of the arrow  11  in FIG.  10  and shows the connection for loading the sensor. 
    
    
     DETAILED DESCRIPTION 
     Referring now in details to the drawings and initially to the embodiment of FIGS. 1 through 5 and initially primarily to FIG. 1, a manually operated electric power assisted unit in the form of a vehicle is shown and indicated generally by the reference numeral  21 . In this embodiment, the vehicle is in the form of a bicycle having a tubular frame assembly, indicated generally by the reference numeral  22 . 
     A front wheel  23  is dirigibly supported by a head pipe  24  of the frame assembly  22  and is steered by a handle bar assembly  25  in a well known manner. 
     A seat  26  is adjustably supported by a seat pipe  27  of the frame  22  for accommodating a seated rider in a well known manner. At the bottom of the seat pipe  27 , is provided a bracket  28  on which a crankshaft  29  is rotatably journaled in a well known manner. Pedals  31  at the ends of the crank arms of the crankshaft  29  are operated by a rider seated on the seat  26  to drive a driving sprocket  32 . 
     The driving sprocket  32 , in turn, drives a chain  33  which, in turn, drives a driven sprocket  34  (FIG.  3 ). The driven sprocket  34  transmit the drive to a rear wheel  35  that is journeyed at the rear end of the frame assembly  22  via a drive arrangement, indicated generally by the reference numeral  36  and which is shown in most detail in FIG.  3 . 
     Still referring to FIG. 1, the drive assembly  36  includes an electric assist motor which receives electrical power from a battery  37  that is carried by a battery box  38  at a rear portion of the frame assembly  22  forwardly of the rear wheel  35 . 
     Before describing the drive assembly  36  in detail by reference to FIG. 3, the general relationship will be described first by reference to the schematic view of FIG.  2 . As seen in this figure, the drive assembly  36  is comprised of a one-way clutch  39  which, in this specific embodiment, is interposed in the connection between the driven sprocket  34  and the rear wheel  35 . This one-way clutch in turn transfers the drive to the rear wheel through a hub case  41 . A pedal force detector  42  is interposed in this transmission relationship in a manner to be described. It should be noted, however, that unlike the prior art constructions, the pedal force detection device  42  does not require lost motion for its operation. Hence, a much simpler detector can be employed and the basic driving arrangement and hub construction can be generally conventional and embodied in a conventional housing. 
     In addition to the manual force transmitted to the rear wheel  35  there is also provided a selective power assist from an electric motor, indicated schematically at  43  in FIG.  2 . This electric motor  43  assists the drive of the hub case  41  in a manner which will be described in more detail by reference to FIG.  3 . 
     The electric motor  43  has electrical power supplied to it from the battery  37  via a controller  44 . The controller  44  may of any type well known in this art and basically operates on the principal that the amount of electric motor assist is proportional to the force applied by the rider applied to the pedals  31  as determined by the pedal force detector  42 . The controller  44  may also operate so as to provide a varying power assist that is greater at lower speeds and decreases as speed of the vehicle and specifically the rear wheel drive  35  increases. Of course, those skilled in the art will readily understand how the invention can be utilized in conjunction with various types of control arrangements. Also to state again, although this embodiment describes the invention in connection with a vehicle such as a bicycle, but as will become apparently from the following description the invention can be utilized with a wide variety of types of manually operated units in which electric power assist is desirable. 
     Referring now in detail to FIG. 3, the hub case  41  is comprised of a first generally cup-shape portion  45  that defines a cavity in which the electric motor  43  is positioned in a manner to be described. This cavity is closed by a cover plate  46  of the hub case  41  which completes its assembly. These pieces define flanges  47  and  48  on which the spokes of the rear wheel  43  are joined in a manner well known in the art. 
     This hub case  41  is rotatably journalled on the frame assembly  22 . This journaling is provided by a first bearing  40  that cooperates with an extension  49  that is formed of an outer housing  51  of the motor  43 . The extension  49  terminates in an axle  52  that is fixed in a known manner to the bicycle frame  22 . At the opposite side thereof, the hub case  41  is journaled on a stub axle shaft  53 . This journaling is provided by a ball bearing assembly  54  contained within a cylindrical extension  50  of the hub case end closure  46 . 
     The driven sprocket  34  is connected via the one-way clutch  39  to an outer member  55  of a helical spline connection provided by balls  56  trapped in the helical splines formed in the inner portion of the member  55  and the outer surface of the projection  50  of the hub case closure plate  46 . This helical connection provided by the balls  56  has a slight skew so as to create an axial force on the hub case  41  and specifically the end plate  46  thereof under the influence of driving forces. As will become apparent later, this force is measured and provides the signal to the pedal force detector  42  which, in this embodiment, is comprised of a magneto-strictive sensor  42  mounted in manner to be described. 
     The electric power assist from the electric motor  43  is transmitted to the hub case  41  via a planetary transmission, indicated generally by the reference numeral  57 . This transmission includes a sun gear  58  which is affixed to the output shaft of the electric motor  43 . This sun gear  58  is enmeshed with the larger diameter gear portions  59  of three planet gears (only one of which is shown in FIG. 3) that are circumferentially spaced and are journalled on a planet carrier  61 . Smaller diameter portions  62  of these planet gears are enmeshed with a ring gear  63  which is associated with the cover plate  46  and is mounted to the cover plate. To this end, the ring gear  63  is connected to a mounting member  64  via a one-way clutch  65 . The mounting member  64  is connected to the hub case cover  46  via an overload release connection  66  which will release upon excessive loading to prevent damage. Of course, the described transmission is only one of many types that may be utilized to transmit drive from the electric motor  43  to the rear wheel  35 . 
     The arrangement for transmitting the degree of manual driving force to the pedal force detector  42  will now be described by primary reference to FIGS. 3 and 4. It has been noted that the helical spline connection provided by the balls  56  causes an axial force on the hub case  41  in response to the driving force. A water tight seal  67  is provided between the end of the hub case cover  46  and the member  55 . The member  55  is abutingly engaged with a force taking ring  68 , as best seen in FIG. 4, and specifically with three outwardly extending tab portions  69  thereof. These tabs portions  69  are received in slots  71  formed in an opening of the hub case cover plate  46  so as to hold them against rotation. 
     The force taking ring  68 , in turn, bears against a thrust bearing  72  which, in turn, engages a retainer  73 . This, in turn, engages a cross piece  74  that has a pair of arm portions that are also retained in the opening  71  and thus held against rotation. This cross piece  74  is engaged with a detector portion  75  of the magneto-strictive sensor  42 . The sensor  42  is, in turn, mounted on an extension  76  of the cover of the motor  43 . It should be noted that driving thrust in one direction is resisted by the connection to the sensor  42 . Driving thrust in the event the pedal rotation is reversed, is taken by end portions  77  of the extension  50  of end cap  46  with a thrust member  78  that is fixed relative to the axle shaft  53 . 
     In accordance with temperature compensating features of the invention, a dummy sensor  42   a  is mounted at one side of the sensor assembly  42  and is provided in the electrical circuit as will be described by reference to FIG. 5 to provide temperature compensation. Referring now to FIG. 5, the electrical connection for the pedal force detector  42  will be described along with this temperature compensation. 
     A bridge circuit is formed between the sensor  42  and the dummy sensor  42   a  and a pair of resistors R 1  and R 2 . These the outputs are connected to an amplifier  79  that outputs a temperature compensated signal because of the unbalance voltage between the output terminals of the sensor  42  and the dummy sensor  42   a , that receives no load. The amplifier  79  outputs its signal to the controller  44  as seen in FIG. 2 so as to provide the pedal force signal without necessitating any significant movement of the components and thus, avoids the lost motion connections of the prior art. 
     Thus, from the foregoing description, it should be readily apparent that the utilization of the structure shown in this embodiment necessitates no changes in the basic structure of the bicycle frame and merely requires the incorporation of the assist mechanism within the hub case of the driven wheel. Although the pedal force detector is positioned at the connection of pedal force to the driven sprocket, a similar arrangement could also be employed at the driving sprocket  32  adjacent the frame bracket  28  without any other change to the basic frame assembly of the vehicle  21 . Such an embodiment is shown in FIG.  6  and will now be described by reference to that figure. The crankshaft, indicated by the reference numeral  101  in this embodiment, is supported in the frame bracket  28  by means of a pair of transversely spaced ball bearings  102 . 
     The driving sprocket, indicated here at  103 , is connected by means of fasteners  104  to an outer element  105  of a helical spline connection to the crankshaft  101 . This helical spline connection includes a plurality of balls  106 . When a rotational force is exerted on the driving sprocket  103  this force is transmitted to the spline outer element  105  and the balls  106  in the helical spline place an axial force on the outer element  105  tending to move it toward the left. 
     A series of circumferentially spaced coil springs  107  press against a thrust plate  108 , which in turn, acts against a force transmitter  109  that is engaged with the contact arm  111  of a magnostrictive sensor  112 . As with the previously described embodiment, the magnostrictive sensor  112  is in a circuit with a dummy sensor  112   a  that is mounted in proximity to it and which is in a bridging circuit to provide the force signal to the controller as with the previously described embodiment. 
     The thrust exerted on the drive sprocket  103  by rotational movement of the crankshaft  101  in the opposite direction is resisted by a thrust plate  113  fixed on the opposite side of the crankshaft  101  and adjacent the drive sprocket  103 . 
     In the two embodiments as thus far described, the invention has been described in conjunction with an electric power assist for a manually powered bicycle. FIG. 7 shows another embodiment of the invention that is embodied in a manually powered reel or drum such as a fishing reel that is provided with an electric power assist. This reel mechanism is indicated generally by the reference numeral  151 . 
     The reel includes an outer housing that is comprised of a central member  152  closed at its opposite sides by end closures  153  and  154 . A reel drum  155  is affixed, by means of a fastener  156  to one end of a reel shaft  157 . This reel shaft  157  is journalled in the housing member  152  by means of a pair of spaced ball bearings A crank arm  159  is fixed to the opposite end of the crankshaft  157  from the drum  155  for rotating the drum  155  manually so as to wind a line or the like on it. 
     An electric assist motor, indicated generally by the reference numeral  160 , is mounted within the housing. The electric motor  160  has an output shaft  161  that is journalled by a pair of ball bearings  162  carried by the end plate  153  and main housing member  152 . One end of the electric motor output shaft  161  is formed with an integral pinion  163  which drives a reduction gear  164 . The reduction gear  164  is engaged with a further reduction gear  165  that is fixed by means of threaded fasteners  166  to an outer member  167  of a helical spline connection to the crankshaft  157 . This connection with the crankshaft  157  includes balls  168 . 
     When a manual force is exerted on the crank handle  159  to turn the crankshaft  158 , to take up a line on the drum  155 , a axial force will be exerted because the spline connection of the outer member  167 . This places a force on a thrust member  168 , which is in turn, engaged with a thrust plate  169 . The thrust plate  169  is engaged with the contact  171  of a magnostrictive sensor  172 . 
     This sensor  172  is provided in a bridged resistor circuit with a controller as with the first described embodiment along with a dummy sensor  172   a  to provide temperature compensation. Thus, again the force is sensed without necessitating a lost motion connection and without requiring any significant movement for actuating the sensor. 
     When the crank handle  1159  is turned in the opposite direction, the thrust in this direction is taken by a thrust washer  173  affixed to the crankshaft  157  on the opposite side from the sensors  172  and  172   a.    
     A one-way clutch, not shown, may be interposed in the connection between the electric motor driven gear  165  and the member  167  of spline connection so as to permit rotation in the opposite direction without driving the electric motor shaft  161  under this condition. 
     FIG. 8 shows another embodiment of the invention that utilizes an electric power assist mechanism similar to those shown in FIG. 7 but, in this instance, applied to drive a wheel of a wheelchair which is shown only partially and indicated generally by the reference numeral  201 . The wheelchair wheel is indicated at  202  and has associated with it a passenger operated hand wheel  203  with which the operator may rotate the wheelchair wheel  202 . Threaded fasteners  204  connect the hand wheel  203  to the wheelchair wheel  202 . 
     The wheelchair wheel  202  is affixed to one end of a shaft, which shaft is indicated by the same reference numeral  157  as the crankshaft in the embodiment of FIG. 7 since the electric motor assist and the sensor arrangement for it are the same as that shown in that figure. For this reason, like components have been identified by the same reference numerals as applied in FIG. 7 and a further description of them in this embodiment is not believed to be necessary to permit those skilled in the art to practice the invention. However the housing assembly comprising the housing member  152  and its end closures  153  and  154  are affixed in any desired manner to the frame of the wheelchair  201 , thus simplifying the addition of the electric motor assist to conventional wheelchair constructions. 
     FIGS. 9 through 11 show a still further embodiment of the invention that is adapted to be employed in an electrically assisted, manually operated, steering system for a vehicle, shown partially and indicated generally by the reference numeral  251 . This steering mechanism  251  includes a manually operated steering shaft  252  that is journalled within a housing assembly  253  by means of spaced apart ball bearings  254 . 
     At the lower end of the steering shaft  252 , there is provided a short stub shaft  255  to which the steering shaft  252  is connected by means of a pin connection embodying a pin  256 . The lower end of this shaft  255  has a pin connection provided by a pin  257  to a steering shaft  258  of the vehicle which is connected to the dirigible vehicle wheels in any known type manner. 
     For power assist of the steering, there is provided an electric steering assist motor, indicated generally by the reference numeral  259 , which has an output shaft on which a worm gear  261  is affixed. This worm gear  261  is engagement with a worm wheel  262  fixed to the steering shaft  258  for providing power assist. 
     In this embodiment, the electric assist motor  259  is a reversible electric motor and power assist is given when the steering shaft  252  is rotated in either direction and an appropriate force applied thereto. The steering force sensor arrangement, indicated generally by the reference numeral  263 , includes an outer spline connection member  264  which has a helical spline connection with the lower end of the steering shaft  252  by means that include a plurality of balls  265 . 
     As may be seen in FIGS. 10 and 11, the pin  256  passes through an opening  266  in the lower end of the steering shaft  252  that is elongated so as to provide some clearance in the direction of the rotational axis of the steering shaft  252  for roller members  267  that are carried on the ends of the pin  256 . Coil compression springs  268  are carried in the member  264  and bear against upper and lower thrust members  269  and  271 , respectively. These members  269  and  271 , in turn, act upon bearing plates  272  and  273  which are engaged with the contact elements  274  of upper and lower magnostrictive sensors  275  and  276 . 
     Since power assist is required in both directions, the sensors  275  or  276  will be activated in response to the steering force inputted to the steering shaft  252  depending upon the direction of rotation. These sensors  275  and  276  are placed in circuits that include a dummy sensor  277  for temperature compensation as with the previously described embodiment. Thus, a compensated output will be outputted to the controller for providing the desired degree of power assist in accordance with any desired strategy. 
     Thus, from the forgoing description it should be readily apparent that the number of embodiments disclosed each provides very effective force sensors for sensing the manual input force for control of electric power assist in a wide variety of devices. Since the sensors require no significant movement, no lost motion is present in the system and incorporation of the device in the desired unit is simplified with out changing the basic construction of the device which is to be power assisted. Although all of the embodiments illustrated employ magneto-strictive sensors for sensing force, other types of force rather than motion detecting sensors such as strain gauges can be employed for sensing the force generated through the helical spline connection. Of course, the foregoing description is that of preferred embodiments of the invention and various changes and modifications may be made without departing from the sprit and scope of the invention, as defined by the appended claims.