Abstract:
A lock cylinder opening system comprising: a lock cylinder body housing with a direction of elongation defining an axial direction for the system, having a first and a second end, and having a first and a second axial bores; a rotatable first cylindrical plug in the first bore, the first plug having an axially extending key slot from the first end of the lock cylinder; a rotatable second cylindrical plug in the first bore, the second plug extending to the second end; a rotatable opening shaft in the second bore, the opening shaft extending at the first and second ends of the lock cylinder; and a selector unit positioned at the second end, having a mechanical connection with the second plug and receiving the opening shaft, the selector unit adapted to selectively enable and disable rotation of the second plug by rotation of the opening shaft.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a lock cylinder opening system and method and, in particular, it concerns a retrofittable system that can be operated to electrically open a cylinder lock, such as used in doors, with minimal power utilization and one which may also be operated conventionally with a key. 
         [0002]    In a conventional mechanical cylinder lock, when an appropriate matching key is inserted into the cylinder lock, the key serves to mechanically align tumbler pins (“unlocked” or “opened” state), allowing the cylindrical plug to be rotated freely to retract a bolt which is typically mechanically connected the cylindrical plug and is driven by the rotated cylindrical plug. Retraction of the bolt is typically referred to as “unbolting” the lock. Conversely, when the cylindrical plug is rotated (usually in a direction opposite that used for unbolting) and the bolt is extended in such a way as to inhibit movement of a door or window, etc. the action is referred to as “bolting” the lock. Following bolting, the key is typically withdrawn from the key slot, the tumbler pins are not aligned, which inhibits free rotation of the cylindrical plug, and the lock is then in a “locked” or “closed” state. 
         [0003]    In a conventional mechanical cylinder lock, when an appropriate matching key is inserted into the cylinder lock, the key serves to mechanically align tumbler pins, and thereby allowing the cylindrical plug to be rotated freely to open the lock. Referring now to  FIGS. 1A and 1B , which are representations of a prior art cylinder lock  10 , with a key  12  inserted into the cylinder lock, and a door lock  15 . Door lock  15  includes, inter alia, a shaped slot  16  for receiving cylinder lock  10  and a door lock hole  17  through which a bolt (not shown) is inserted to secure the cylinder lock inside the door lock. Typically, door lock  15  is inserted into a hollowed-out edge of the door (not shown) and cylinder lock  10  is inserted through prepared holes in the door (not shown in the figure) and perpendicularly into and through shaped slot  16 , substantially along axis  18 . Door lock further includes a bolt  19 . Typically, cylinder lock  10 , when unlocked, serves to translate bolt  19  into the door lock, so that bolt  19  is substantially flush and the door lock is referred to as “unbolted”. When bolt  19  translated out of door lock  15 , the door lock is “bolted”. Typically, other cylinder locks having a cross-sectional profile and length substantially matching cylinder lock  10  may be replaced or retrofitted instead of cylinder lock  10 . Typical names/manufacturers of such cylinder locks include, but are not limited to: Euro Cylinders; Oval Cylinders; Asec 6-pin Euro profile; and Chubb M3. Overall lengths of such cylinders typically vary from approximately 60-110 mm. 
         [0004]    Reference is now made to  FIG. 2 , which is a cross sectional side view of the cylinder lock shown in  FIG. 1A . The cylinder lock has a body housing  20 , which is bored from one end to the other end and a cylindrical plug  22 , which is fitted into the bore, and which may be rotated, as described hereinbelow. A set hole  23  is located approximately in the middle of cylinder lock  10  to typically receive a threaded bolt (not shown in the figure) which is inserted into lock hole  17 , to secure the cylinder lock within door lock  15 , as described hereinabove in  FIG. 1B . Cylindrical plug  22  has a key slot  25  formed axially in cylindrical plug. Key  12  is inserted into slot  25 . A pin-tumbler set  30  is located in body housing  20  and in cylindrical plug  22  to serve to lock and unlock rotational movement of cylindrical plug  22 . Cylindrical plug  22  and a second cylindrical plug  31  may be mechanically coupled and uncoupled to a rotating tongue  35  by means of a clutch unit (not shown in the figure), which allows either of the two cylindrical plugs to rotate the rotating tongue, which in turn serves to move the bolt of the door lock (refer to  FIG. 1B ). The cylinder lock shown in  FIG. 2  is called a “blind cylinder”, in that a key can be inserted into only one side of the lock. However, cylinder lock  10  may also comprise pin-tumbler sets and key slots in respective cylindrical plugs at both ends. 
         [0005]    A number of prior art electronic or combination electrical/mechanical lock systems allow a user to open a locked cylinder in a number of ways. In U.S. Pat. No. 3,889,501 by Fort, whose disclosure is incorporated herein by reference, a combination electrical and mechanical system is described. The system includes a lock having a fixed lock cylinder and a rotatable key slug. A first solenoid is employed in the current system to drive a lock pin, which is normally extended to lock the key slug. Upon insertion of an appropriately aperture-encoded key, light sources and detectors mounted in the lock are used in concert with appropriate circuitry to operate to the first solenoid to unlock key slug. A second solenoid is operable, in response to an electrical power failure, to extend a bolt pin. When the bolt pin is extended a proper mechanical key is inserted and rotated, extension of the lock pin is prevented. A proper mechanical key can be inserted to move a plurality of spring loaded pin tumblers in the lock to enable rotation of the key slug during an electrical power failure. 
         [0006]    Fonea, in U.S. Pat. No. 6,147,622, whose disclosure is incorporated herein by reference, discloses an electronic lock system which is also manually operable to drive a lock cylinder to move a lock mechanism which includes at least one bolt. The system includes a bidirectional motor engagable with the lock cylinder At least one sensor in the lock system is used in conjunction with an angular measurement device and/or stepper motor feedback to provide a level of lock self diagnostics and self testing. The system may also be operated in a mechanical manner. Additional features of the lock system, not related to the capabilities noted hereinabove are also disclosed. 
         [0007]    While the prior art includes an array of combination electrical/mechanical lock systems of varying complexity and systems that employ motorized opening of a cylindrical lock, the problem of relatively high power necessary to open the cylinder lock and to bolt and unbolt the door remains. Attempts to solve this problem necessitate employing systems with limited reliability, especially when onboard power is necessary to power motors. There is therefore a need for a combination electrical/mechanical lock cylinder opening system that has the capability to be operated with high reliability over time, utilizing little power, and which can easily be retrofitted to an existing lock installation. The system should be remotely operated to allow unbolting and bolting of the lock and to allow the same operations to be performed in a conventional manual manner in case of an electrical power failure. Furthermore, such a system should be integrated with capabilities of electrically and manually locking and unlocking the lock. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is a lock cylinder opening system and method and, in particular, it concerns a retrofittable system that can be operated to electrically open a cylinder lock, such as used in doors, with minimal power utilization and one which may also be operated conventionally. 
         [0009]    According to the teachings of the present invention there is provided, a lock cylinder opening system comprising: a lock cylinder body housing with a direction of elongation defining an axial direction for the system, having a first and a second end, and having a first and a second axial bores; a rotatable first cylindrical plug in the first bore, the first plug having an axially extending key slot from the first end of the lock cylinder; a rotatable second cylindrical plug in the first bore, the second plug extending to the second end; a rotatable opening shaft in the second bore, the opening shaft extending at the first and second ends of the lock cylinder; and a selector unit positioned at the second end, having a mechanical connection with the second plug and receiving the opening shaft, the selector unit adapted to selectively enable and disable rotation of the second plug by rotation of the opening shaft. Preferably, the selector unit is adapted to allow manual rotation of the second plug from the second end of the lock cylinder. Most preferably, the selector unit includes a control and communications unit; a clutch unit; and a power subassembly. 
         [0010]    Typically, the control and communications unit is adapted to receive command signals, to transmit telemetry signals, and to control the clutch unit. Most typically, the clutch unit includes a motor. Preferably, the motor is adapted to operate the clutch unit and to mechanically engage and disengage the rotatable shaft and the second plug. Most preferably, the control and communications unit is further adapted to sense the status of the motor and of the clutch unit and to include information indicative of system status in the telemetry signals. Typically the power assembly is adapted to provide power to the system, the power assembly including at least one chosen from a list including: batteries, mains power, and battery and mains power. 
         [0011]    Preferably, a matching key is insertable in the key slot to open and rotate the first plug. Most preferably, the lock cylinder body housing is retrofittable in place of a conventional lock cylinder. Typically, the selector unit is retrofittable along with the body housing. Most typically, the selector unit is retrofittable modularly to the body housing. 
         [0012]    According to the teachings of the present invention there is provided a method of opening a lock system comprising the steps of: taking a lock cylinder body housing with a direction of elongation defining an axial direction for the system, having a first and a second end, and having a first and a second axial bores; configuring a rotatable first cylindrical plug in the first bore, the first plug having an axially extending key slot from the first end of the lock cylinder; placing a rotatable second cylindrical plug in the first bore, the second plug extending to the second end; configuring a rotatable opening shaft in the second bore, the opening shaft extending at the first and second ends of the lock cylinder; and positioning a selector unit at the second end, having a mechanical connection with the second plug and receiving the opening shaft, the selector unit selectively enabling and disabling rotation of the second plug by rotation of the opening shaft. Preferably, the selector unit allows manual rotation of the second plug from the second end of the lock cylinder. Most preferably, the selector unit includes a control and communications unit; a clutch unit; and a power subassembly. Typically, the control and communications unit receives command signals, transmits telemetry signals and controls the clutch unit. 
         [0013]    Most typically, the clutch unit includes a motor. Preferably, the motor operates the clutch unit and mechanically engages and disengages the rotatable shaft and the second plug. Most preferably, the control and communications unit is further senses the status of the motor and of the clutch unit and includes information indicative of system status in the telemetry signals. Typically, the power assembly provides power to the system, the power assembly including at least one chosen from a list including: batteries, mains power, and battery and mains power. 
         [0014]    Preferably, a matching key is inserted in the key slot to open and rotate the first plug. Most preferably, the lock cylinder body housing is retrofitted in place of a conventional lock cylinder. Typically, the selector unit is retrofitted along with the body housing. Most typically, the selector unit is retrofitted modularly to the body housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: 
           [0016]      FIGS. 1A and 1B  are representations of a prior art cylinder lock and a door lock, respectively; 
           [0017]      FIG. 2  is a cross sectional side view of the prior art cylinder lock shown in  FIG. 1A ; 
           [0018]      FIG. 3  is a side view of a lock cylinder opening system, in accordance with an embodiment of the present invention; 
           [0019]      FIGS. 4A and 4B  are isometric views of the lock cylinder opening system of  FIG. 3 , respectively with and without an integral cylinder lock module; 
           [0020]      FIG. 5  is an isometric view of the lock cylinder opening system of  FIGS. 3 ,  4 A, and  4 B with covers removed; and 
           [0021]      FIG. 6  is an isometric detailed view of a selector unit in accordance with an embodiment of the present invention; 
           [0022]      FIGS. 7A and 7B  are isometric views of a lock cylinder opening system, in accordance with an embodiment of the present invention; and 
           [0023]      FIGS. 8A to 8D  are isometric detailed views of a selector unit, in accordance with an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    The present invention includes a lock cylinder opening system and method. 
         [0025]    Reference is now made to  FIGS. 3 ,  4 A, and  4 B which are, respectively, a side view of a lock cylinder opening system  110  and pictorial representations of the cylinder opening system  110  shown with and without an integral cylinder lock module  120 , in accordance with an embodiment of the present invention. System  110  includes integral cylinder lock module  120 , which is connected to a selector unit  130 —the functioning of both modules described hereinbelow. Apart from differences described below, cylinder lock module  120  is generally similar to operation of cylinder lock  10  as shown in  FIGS. 1A ,  1 B, and  2 , so that elements indicated by the same reference numerals are generally identical in configuration and operation. The general orientation of system  110  relative to a typical door is indicated by the dotted lines and the “Door” indication in the figure, indicating a cross section or “thickness” of the door. Cylinder lock module  120  is show in the present figures without cylinder plug  22  (refer to  FIG. 2 ). Cylinder lock module  120  is mechanically connected to selector unit  130  and at the “blind end” of the cylinder lock module. 
         [0026]    At the “key end” of cylinder lock module  120 , a hinged handle  121 , having a general shape allowing it to be grasped similarly to a key, is connected to a generally cylindrical fitting  122 , which is mechanically connected to opening shaft  123 . (Opening shaft  123  is shown in  FIG. 4B .) Opening shaft  123  has a generally elongated cylindrical shape and passes through a bore (not shown in the figures) in the lower part of cylinder lock module  120 . Opening shaft is typically fabricated from a rigid metal, allowing the shaft to transfer torque sufficient to activate selector unit  130 , as described hereinbelow. Hinged handle  121  is connected to cylindrical fitting  122  by means of axis  125 , which may be a set pin or other suitable hinge device, allowing hinged handle  121  to be oriented generally parallel to opening shaft  123  (so that the hinged handle may be grasped to rotated the opening shaft) and allowing hinged handle  121  to be stowed generally parallel to the end of cylinder lock module  120  when the hinged handle is not in use. Hinged handle  121  and cylindrical fitting  125  may be removed from and later reattached to opening shaft  123  to allow cylinder  120  to be inserted into the door, when, for example, system  110  is retrofitted in the door, by sliding cylinder  120  from the secured side into shaped slot  17  (see  FIG. 1B ). Alternatively or optionally, hinged handle  121  and cylindrical fitting  125  may be shaped sufficiently compactly to allow them to remain fixed to opening shaft  123  when retrofitting system  110  in the door. 
         [0027]    Typically, although not obligatorily, selector unit  130  is configured “inside” or on the side of the door which is considered secured; and hinged handle  121  is configured “outside”, or on the side of the door which is considered unsecured. The unsecured side of the door is typically the side of the door from where a key may be used to open cylinder lock module  120 . Selector unit  130  is oriented substantially parallel and close to the door. A cylinder rotation knob  132  serves to freely rotate a blind cylinder (not shown) in cylinder lock module  120 . An outer cover  134 , a lateral cover  136 , and a door-side cover  137  serve to cover and protect the selector unit, as well as supporting some components of the selector unit, as described hereinbelow. Covers  134 ,  136 , and  137  are typically made of a sturdy and lightweight plastic material, but may also be fabricated from a metallic material. Support  138 , fabricated from a rigid metallic material, serves to support and hold components of the selector unit as described hereinbelow and to mate with cylinder lock module  120  as shown in the figures, including a blind cylinder shaft  144 , which at one end is connected to cylinder rotation knob  132  and which is connected at a second end with the blind cylinder (not shown in the figures) of cylinder lock module  120 , thereby allowing the blind cylinder to be rotated by rotating the cylinder rotation knob. A stabilizing pin  146 , located beneath the blind cylinder shaft, protrudes from selector unit  130  as shown to mate with a matching hole (not shown) in the blind cylinder and thereby support and stabilize the blind cylinder while also ensuring minimal or no lateral forces are applied to opening shaft  123 . Opening shaft  123  is connected to components within Selector unit  130  as described hereinbelow. 
         [0028]    Reference is now made to  FIG. 5 , which is an isometric view of the lock cylinder opening system of  FIG. 4B  with covers  136 , and  137  removed, and to  FIG. 6 , which is an isometric view of a clutch unit  150 , in accordance with an embodiment of the current invention. Apart from differences described below, elements indicated by the same reference numerals in the present figures are generally identical in configuration and operation as noted in previous figures. Selector unit  130  further includes a clutch unit  150 , a control and communications unit  152 , and a power assembly  154 . In one embodiment of the present invention, power assembly  154  includes typical rechargeable or one-time batteries. Alternatively or optionally, power assembly  154  may use mains power or a combination of mains power and batteries, such as with rechargeable batteries that maintain a charge when normally supplied mains power is discontinued. Power assembly  154  supplies power to operate selector unit  130  and specifically the clutch unit, as described hereinbelow, and to power control and communications unit  152 , which is responsible for command and telemetry communications for selector unit  130  and for sensing, controlling, and reporting the status of components of the selector unit, including the status of clutch unit  150 . Command and telemetry communications are effected primarily by wireless means but they may alternatively or optionally be effected by wired means. 
         [0029]    The clutch unit includes motor  156 , eccentric driver  158 , gears  160 ,  162 , and  164  (represented as truncated cylindrical shapes in the figure), and clutch wheel  166 , further described hereinbelow. Gears  160 ,  162 , and  164  are supported from support  138 . Gear  160  is mechanically connected to blind cylinder shaft  144  (shown previously in  FIG. 4B ) which passes axially through gear  160  and which rotates with gear  160 . Gears  160 ,  162 , and  164  are configured and engaged so that rotation of gear  164  provides rotation of gear  160  and of blind cylinder shaft  144 . Motor  156  is configured and fixed substantially perpendicular to opening shaft  123 . The opening shaft enters clutch unit  150  from the side of support  138  and exits clutch unit  150  from the side of clutch wheel  166 . Gear  164  and clutch wheel  166  are configured coaxially with opening shaft  123 . Opening shaft  123  is mechanically attached to clutch wheel  166  so that rotation of opening shaft rotates the clutch wheel; however clutch wheel  166  is free to move axially along opening shaft  123 , towards and away from gear  164 , through which opening shaft passes. Examples of suitable attachment means of opening shaft  123  to clutch wheel  166  may be a matching regular geometric cross-section (square, hexagonal, etc) or other matching cross-sectional shapes (keyed or slotted, for example) of the end of shaft  123  fitted within the central opening of clutch wheel  166 . 
         [0030]    Operation of clutch unit  150  is described hereinbelow. Clutch wheel  166  is typically not engaged, meaning that upon rotation of opening shaft  123 , because there is no mechanical connection between the clutch wheel and gear  164 , only clutch wheel  166  rotates. Clutch wheel  166  is formed in a shape similar to a typical automobile wheel, meaning a generally truncated cylindrical shape having a lateral surface having a continuous peripheral depression  167 , thereby leaving two lateral ridges. Eccentric driver  158  is mechanically and substantially coaxially fixed onto the shaft of motor  156  and motor  156  is mechanically fixed within selector unit  130 . The eccentric driver has a pin (not shown in the figure) configured eccentrically from the eccentric driver axis of rotation and protruding from the edge of the driver facing the clutch wheel. The pin mates with peripheral depression  167  so that when motor  156  is commanded to operate, and eccentric driver  158  rotates, clutch wheel  166  is urged towards and away from gear  164 . 
         [0031]    One example of the movement of clutch wheel  166  towards and away from gear  164  could be that when the motor is commanded to rotate  180  degrees, the clutch wheel is moved a maximal distance towards gear  164  and that when the motor is further commanded to rotate 180 degrees more (i.e. to a 0 or 360 degree position), the clutch wheel is moved a maximal distance away from gear  164 . 
         [0032]    A plurality of engaging pins  168 , typically 3 or more, are located on the surface of clutch wheel  166  facing gear  164  and are configured to mate with matching depressions (not shown in the figure) on the surface of gear  164  facing clutch wheel  166 . When the clutch wheel is urged towards gear  164  and as the clutch wheel is rotated, engaging pins  168  engage the matching depressions, thereby mechanically connecting the clutch wheel and gear  164 . When clutch wheel  166  is engaged, rotation of opening shaft  123  rotates gear  164 , which serves to rotate gears  162  and  160 , thereby rotates blind cylinder shaft  144  and the blind cylinder of the cylinder lock. Sensors located within components of clutch unit  150  provide feedback information to the communications unit. 
         [0033]    In one embodiment of the current invention, opening shaft  123  has a diameter of 3.5 mm and is fabricated from 4340 Steel. In general, the diameter and material of opening shaft  123  are chosen to allow sufficient shaft strength while minimizing the diameter to pass through the bore (described hereinabove) in the lower part of cylinder lock module  120 . 
         [0034]    Typical operation of system  110  to open cylinder  120  from the unsecured side of the door, when no key is used includes: 
         [0035]    Commanding selector unit  130  to activate clutch unit  150  to engage clutch wheel  166 ; 
         [0036]    Turning hinged handle  121  to turn opening shaft  123  and thereby turn blind cylinder shaft  144 , thereby opening the blind cylinder. 
         [0037]    Note that commanding selector unit  130  to activate clutch unit  150  may be accomplished by wireless or wired means and commanding may be done in close proximity to system  110  or remotely, by the individual turning hinged handle  121 , or by another person or device working with him, respectively. Examples of close proximity commanding include, but are not limited to: using a wireless RF device (key fob, for example) from the unsecured side; using a similar RF device to command from the secured side; and issuing a wired command. Examples of remote commanding include, but are not limited to wired or wireless commands from a control center or another remote location. 
         [0038]    Reference is now made to  FIG. 7A , which is an isometric view of a modular lock cylinder opening system  210 , and to  FIG. 7B , which is an isometric view of the modular lock opening system with modular cylinder unit  220  removed, in accordance with an embodiment of the present invention. Apart from differences described below, system  210  is generally identical in configuration and operation to system  110  as shown in  FIGS. 3 and 4A  and elements indicated by the same reference numerals in the present figures are generally identical in configuration and operation as noted in previous figures. 
         [0039]    System  210  has features that allow for modular and more flexible retrofitablity in comparison to system  110 . Opening shaft  223  is formed to allow it to be slid into modular cylinder unit  220  before or after the cylinder is retrofitted into slot  17  of the door. The shape of the unsecured-side end of the opening shaft allows for a variety of handles to be attached. The shape of the secured-side of the opening shaft allows for it to be easily inserted into selector unit  230  before or after modular cylinder unit  220  is retrofitted into slot  17  of the door. Additionally, as seen in  FIGS. 7A and 7B , modular cylinder unit  220  may be readily attached to selector unit  230  by means of set screws (not shown) inserted into eyelets  232  formed into support  138  on either side of located on either side of where the modular cylinder abuts selector unit  230 . Other elements that aid in easier retrofittablity and modularity of system  210  include blind cylinder shaft  244 , which extends from selector unit  230  to dock with a matching socket in the blind cylinder (not shown) of modular cylinder unit  220 . Blind cylinder shaft  244  may have a variety of cross sectional shapes, including, among others, hexagonal, square, and octagonal. 
         [0040]    Because opening shaft is configured to pass through the lower part of the cylinder, as noted hereinabove, set hole  23  of units  120  and  220  must have a reduced diameter, when compared to the diameter of set hole  23  of the prior art (FIG  1 B). Retention bolt  235 , which is inserted into lock hole  17  ( FIG. 1B ) and into set hole  23  ( FIGS. 2 and 3 ) to retain the cylinder, has a tapered end  236  to allow it to be inserted into the reduced diameter of set hole  23  of units  120  and  220 . 
         [0041]    Reference is now made to  FIG. 8A , which is an isometric detailed view of a selector unit  250 , and to and  FIGS. 8B  and C, which are isometric details of the selector unit with some parts removed and others added, and to  FIG. 8D , which is an isometric detail of the selector unit viewed from the reverse side of the views of  FIGS. 8A-C , all in accordance with an embodiment of the present invention. Apart from differences described below, selector unit  250  is generally similar to operation of selector unit  150  as shown in  FIG. 6 , so that elements indicated by the same reference numerals in the present figures are generally identical in configuration and operation as noted in previous figures. Selector unit includes a clutch arm  255 , secured in position by bracket  258  (refer to  FIG. 8D ) and a clutch unit  267 . Bracket  258  serves to rotationally fix clutch arm  255  about axis  259  (indicated as a hole in bracket  258  and corresponding to a similar hole in clutch arm  255 ) so that the clutch arm rotates when it is driven and in turn drives other elements of selector unit  250  as described hereinbelow. Bracket  258  may be positioned with respect to clutch arm  255  to increase or decrease rotational movement of the clutch arm, depending on the relative position of axis  259 , as may be apparent to one skilled in the art. 
         [0042]    Clutch unit  267  further comprises a clutch wheel  268 , a preload spring  271 , and a clutch plate  273 . Clutch arm  255  has a general “U” shape, with two arms and a base, and its base is connected to and driven by eccentric driver  158 . Protrusions  256  on the inner surface near the end of each arm fit into the peripheral depression of clutch wheel  269 , which has a general shape substantially identical to clutch wheel  166 . Eccentric driver  158  drives the clutch arm which, in turn, urges the clutch wheel towards gear  164 . In the present configuration, preload spring  271  is located between the clutch arm and clutch plate  273  and clutch plate  273  has a plurality of engaging pins (not shown in the present figure), which are located on the surface of clutch plate  273  facing gear  164  and are configured to mate with matching depressions (not shown in the figure) on the surface of gear  164  facing clutch plate  273 . When selector unit  250  is commanded to engage the clutch plate with gear  164 , preload spring  271  allows for efficient engagement of engaging pins with the matching depressions by providing a preload force, which acts to engage respective pins as they pass over matching depressions. 
         [0043]    In one embodiment of the current invention selector unit  250  may be integrated into system  110 , in place of selector unit  150 . 
         [0044]    It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.