Patent Publication Number: US-2013240274-A1

Title: Expandable vehicle systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 13/421,923, filed Mar. 16, 2012 and U.S. patent application Ser. No. 13/467,521, filed May 9, 2012, both of which are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present teachings generally include a drivable vehicle that can be selectively expanded. 
     BACKGROUND 
     An individual may have different mobility needs on different occasions. For example, the individual may work in an urban area and need to commute to work on a daily basis. For these commuting needs, a fuel efficient vehicle that seats at least the driver and is of a small size that is easy to maneuver and park in a congested area is ideal. On other occasions, the driver may need to transport one or more additional passengers or cargo, may need or desire a higher performance vehicle, or may need to travel a further distance than the typical commute to and from work. Heretofore, the driver would need to use a different vehicle for these occasions. 
     SUMMARY 
     An expandable vehicle system includes a base unit having a frame, a first wheel rotatably mounted with respect to the frame, and a battery-electric propulsion system mounted with respect to the frame. The expandable vehicle system also includes a first extension module having a first vehicle body portion and an auxiliary power unit mounted with respect to the first vehicle body portion. The base unit has a first attachment interface mounted with respect to the frame and the first extension module has a second attachment interface mounted with respect to the first vehicle body portion. The first and second attachment interfaces are configured to selectively and releasably engage one another such that the first extension module and the base unit form a single drivable unit when the first and second attachment interfaces are engaged with one another. 
     The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view illustration of a first embodiment of an expandable vehicle system including a base unit with a first extension module connected thereto; 
         FIG. 2  is a schematic side view illustration of the base unit of  FIG. 1  with a second extension module connected thereto; 
         FIG. 3  is a schematic side view illustration of a second embodiment of an expandable vehicle system including a base unit having a frame in a retracted position; 
         FIG. 4  is a schematic side view illustration of the base unit of  FIG. 3  with the frame in an extended position and an extension module connected thereto; 
         FIG. 5  is a schematic side view illustration of a base unit of a third embodiment of an expandable vehicle system; 
         FIG. 6  is a schematic side view illustration of an extension module of the third embodiment of an expandable vehicle system; 
         FIG. 7  is a schematic side view illustration of the extension module of  FIG. 6  connected to the base unit of  FIG. 5 ; 
         FIG. 8  is a schematic side view illustration of a fourth embodiment of an expandable vehicle system including a base unit with a first extension module connected thereto.; 
         FIG. 9  is a schematic side view illustration of the base unit of  FIG. 8  with a second extension module connected thereto; 
         FIG. 10  is a schematic side view illustration of a fifth embodiment of an expandable vehicle system including a base unit with an extension module connected thereto; 
         FIG. 11  is a schematic illustration of the base unit and extension module of  FIG. 10  including respective steering and braking systems; 
         FIG. 12  is a schematic side view illustration of a sixth embodiment of an expandable vehicle system including a base unit with an extension module connected thereto; and 
         FIG. 13  is a schematic illustration of the base unit and extension module of  FIG. 12  including respective steering and braking systems. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , an expandable vehicle system  10  includes a base unit  12 , which includes a vehicle body portion  14 . The body portion  14  includes structure that functions as a frame  16 . As used herein, a “frame” may include structure that provides structural integrity, and may be part of a vehicle body. The base unit  12  includes two front wheels  18  (only one of which is shown in  FIG. 1 ) rotatably mounted with respect to the frame  16 . The body portion  14  of the base unit  12  partially defines an interior compartment  22  having an opening  26  at the rearward end of the body portion  14 . The base unit  12  includes a driver&#39;s seat  28  disposed within the interior compartment  22  and mounted to the body portion  14 . The base unit  12  also includes other systems (not shown) to enable drivability, such as a steering system and a braking system. 
     The base unit  12  also includes a first attachment interface  30  mounted with respect to the frame  16  adjacent the opening  26  at the rearward end of the body portion  14 ; the first attachment interface  30  in the embodiment depicted includes at least one mechanical fastening element  32 . 
     The expandable vehicle system  10  also includes two rear modules, or extension modules, that are selectively and releasably engageable at the first attachment interface  30 . More specifically, the expandable vehicle system  10  includes a first extension module, shown at  34  in  FIG. 2 , and a second extension module, shown at  34 A in  FIG. 1 . Referring specifically to  FIG. 2 , the first extension module  34  includes a vehicle body portion  42 . The first extension module  34  also includes a second attachment interface  36  that is mounted to the body portion  42 ; in the embodiment depicted, the second attachment interface  36  includes mechanical fastening elements  38  that are selectively and releasably engageable with the fastening elements  32  of the first attachment interface  30  to connect the first extension module  34  to the base unit  12  such that the first extension module  34  and the base unit  12  form a single drivable unit  40 , as shown in  FIG. 2 . In the embodiment depicted, fastening elements  32 ,  38  rigidly interconnect the base unit  12  with the first extension module  34 . 
     The mechanical fastening elements  32 ,  38  may have many different configurations within the scope of the claimed invention. For example, mechanical fastening elements  32  may be latches and fastening elements  38  may be strikers that releasably engage the latches, fastening elements  32  may be threaded fasteners and fastening elements  38  may be tabs with holes through which the threaded fasteners extend (a nut would then engage the threaded fasteners to secure the tabs), etc. 
     The first extension module  34  includes a body portion  42  that defines an interior compartment  46  having an opening  50  at the forward end of the body portion  42  adjacent fastening elements  38 . The opening  26  of interior compartment  22  is adjacent the opening  50  of interior compartment  46  when extension module  34  is mounted to the body portion  14  via the fastening elements  32 ,  38  (i.e., the first and second attachment interfaces  30 ,  36 ), and the interior compartments  22 ,  46  cooperate to form one contiguous compartment  54 . The extension module  34  has two wheels  58  (only one of which is shown in  FIG. 2 ) rotatably connected thereto. The wheels  58  of the extension module  34  form the rear wheels of the drivable unit  40 . 
     The base unit  12  in the embodiment depicted includes a battery-electric powertrain or propulsion system  62  mounted with respect to the frame  16 . The battery-electric propulsion system includes an electric motor  66  operatively connected to an energy storage device, such as a battery  70 . As used herein, a “battery electric propulsion system” or a “battery-electric powertrain” includes a battery or other electrical energy storage device and an electric motor operatively connected to the battery to receive electrical energy therefrom; the motor is operatively connected to at least one of the vehicle wheels  18 ,  58  to transmit torque thereto and thereby propel the vehicle system  10 . 
     The first extension module  34  also includes an auxiliary power unit  78  mounted with respect to the first vehicle body portion  42 . As used herein, an “auxiliary power unit” is any device that produces power to propel the vehicle system  10 ; examples of auxiliary power units  78  include torque-producing devices, such as internal combustion engines, that transmit torque to at least one of the wheels  18 ,  54 . Other auxiliary power units  78  within the scope of the claimed invention may generate electrical energy to power the electric motor  66  or recharge the battery  70 , such as an internal combustion engine in combination with a generator, or a fuel cell. Accordingly, the interfaces  30 ,  36  may include an electrical interface (not shown) to transmit control signals to the auxiliary power unit  78  or to transmit electrical energy from the auxiliary power unit  78  to the battery  70  and/or the motor  66 . 
     Referring specifically to  FIG. 1 , the second extension module  34 A includes a body portion  42 A. The second extension module  34 A also includes a third attachment interface  36 A that is mounted with respect to the body portion  42 A; in the embodiment depicted, the third attachment interface  36 A includes mechanical fastening elements  38  that are selectively and releasably engageable with the fastening elements  32  of the first attachment interface  30  to rigidly connect the second extension module  34 A to the base unit  12  such that the base unit  12  and the second extension module  34 A form a single, drivable unit  40 A. 
     The second extension module  34 A includes a body portion  42 A that defines an interior compartment  46 A having an opening  50 A at the forward end of the body portion  42 A adjacent fastening elements  38 . The opening  26  of interior compartment  22  is adjacent the opening  50 A of interior compartment  46 A when the second extension module  34 A is mounted to the base unit  12  via the fastening elements  30 ,  38 , and the interior compartments  22 ,  46 A cooperate to form one contiguous compartment  54 A. The second extension module  34 A has two wheels  58  rotatably connected thereto. The wheels  58  of the second extension module  34 A form the rear wheels of the drivable unit  40 A when the second extension module  34 A is attached to the body portion  14 . 
     Referring to  FIGS. 1 and 2 , the interior compartment  46 A of the second extension module  34 A is shorter and smaller than the interior compartment  46  of the first extension module  34 , and thus the interior compartment  54 A formed when the second extension module  34 A is attached to the base unit  12  is shorter and smaller than the interior compartment  54  formed when the first extension module  34  is attached to the base unit  12 . The second extension module  34 A is characterized by the absence of an auxiliary power unit  78 , and thus drivable unit  40 A is a compact, electric vehicle. Accordingly, the second extension module  34 A may be used, for example, for one or two people commuting short distances. 
     When a user of the vehicle system  10  desires additional cargo space, passenger capacity, and/or driving range before recharging the battery  70 , the user may remove the second extension module  34 A from the base unit  12  (by disengaging the fastening elements  38  of the third attachment interface  36 A from the fastening elements  32  of the first attachment interface  30 ) and then engage the fastening elements  38  of the second attachment interface  36  with the fastening elements  32  of the first attachment interface  30  to attach the first extension module  34  to the base unit  12 . The first extension module  34  provides increased cargo space and/or passenger capacity compared to the second extension module  34 A, and the auxiliary power unit  78  provides additional power and or/driving range to the vehicle system  10 . When a user of the vehicle system  10  desires a compact, electric-only vehicle, then the user may disconnect the first extension module  34  from the base unit  12  and then connect the second extension module  34 A to the base unit  12 . In the embodiment depicted, the first extension module  34  has at least one passenger seat  74  mounted to the body portion  42  and disposed within the interior compartment  46 . 
     Thus, the expandable vehicle system  10  includes a base unit  12  having a frame  16 , a first wheel  18  rotatably mounted with respect to the frame  16 , and a battery-electric propulsion system  62  mounted with respect to the frame  16 . A first extension module  34  has a first vehicle body portion  42  and an auxiliary power unit  78  mounted with respect to the first vehicle body portion  42 . The base unit  12  has a first attachment interface  30  mounted with respect to the frame  16  and the first extension module  34  has a second attachment interface  36  mounted with respect to the first vehicle body portion  42 . The first and second attachment interfaces  30 ,  36  are configured to selectively and releasably engage one another such that the first extension module  34  and the base unit  12  form a single drivable unit  40  when the first and second attachment interfaces are engaged with one another. 
     The base unit  12  includes a second vehicle body portion  14  mounted with respect to the frame  16 . The first vehicle body portion  42  defines a first interior compartment  46  having a first opening  50 . The second vehicle body portion  14  defines a second interior compartment  22  having a second opening  26 . The first attachment interface  30  is positioned with respect to the second body portion  14 , and the second attachment interface  36  is positioned with respect to the first body portion  42  such that the first and second interior compartments  46 ,  22  are contiguous when the first and second attachment interfaces  30 ,  36  are engaged with each other. 
     The vehicle system  10  also includes a second extension module  34 A having a third vehicle body portion  42 A and a third attachment interface  36 A mounted with respect to the third vehicle body portion  42 A. The first and third attachment interfaces  30 ,  36 A are configured to selectively and releasably engage one another such that the second extension module  34 A and the base unit  12  form a single drivable unit  40 A when the first and third attachment interfaces  30 ,  36 A are engaged with one another. 
     The third vehicle body portion  42 A defines a third interior compartment  46 A having a third opening  50 A. The first attachment interface  30  is positioned with respect to the second body portion  14 , and the third attachment interface  36 A is positioned with respect to the third body portion  42 A such that the third and second interior compartments  46 A,  22  are contiguous when the first and third attachment interfaces  30 ,  36 A are engaged with each other. The third interior compartment  46 A is smaller than the first interior compartment  46 . 
     Referring to  FIGS. 3 and 4 , wherein like reference numbers refer to like components from  FIGS. 1 and 2 , an expandable vehicle system  110  includes a base unit  112  having a frame  116 , a first wheel (front wheel  120 ) and a second wheel (rear wheel  124 ) rotatably mounted with respect to the frame  116 , and a battery-electric propulsion system  62  mounted with respect to the frame  116 . Only one front wheel  120  and one rear wheel  124  is shown in  FIGS. 3 and 4 ; the base unit may include at least one other front wheel and rear wheel. 
     The battery-electric propulsion system  62  includes a motor  66  operatively connected to at least one of the wheels  120 ,  124  to transmit torque thereto. A battery  70  is operatively connected to the motor  66  to transmit electrical energy thereto. The base unit  112  in the embodiment depicted includes a body portion  114  that defines an interior compartment  122  having an opening  126  at the rearward end of the body portion  114 . The base unit  112  also includes a vehicle body closure  127  that is configured to selectively obstruct the opening  126 . In the embodiment depicted, the closure  127  is a rear liftgate that is selectively movable between a closed position, as shown in  FIG. 3 , in which the liftgate is generally vertical and obstructs the opening  126 , and an open position, as shown in  FIG. 4 , in which the liftgate is generally horizontal and does not obstruct the opening  126 . In the embodiment depicted, the closure  127  is pivotable about a hinge  129  that interconnects the closure  127  and the body portion  114 . The base unit  112  includes a driver&#39;s seat  128  disposed within the interior compartment  122  and mounted to the body portion  114 . The base unit  112  also includes other systems (not shown) to enable drivability, such as a steering system and a braking system. 
     The base unit  112  also includes a first attachment interface  130  mounted with respect to the frame  116  adjacent the opening  126  at the rearward end of the body portion  114 ; the first attachment interface  130  in the embodiment depicted includes at least one mechanical fastening element  132 . In the embodiment depicted, one of the fastening elements  132  is mounted to the body  114  and one of the fastening elements  132  is mounted to the frame  116 . 
     The frame  116  includes a first frame portion  180  and a second frame portion  184 . The second frame portion  184  is selectively movable with respect to the first frame portion  180  to change the length of the frame  116 . In the embodiment depicted, the first frame portion  180  is a first rail, and the second frame portion is a second rail. The first rail  180  defines a channel (not shown) in which the second rail  184  is selectively slidable with respect to the first rail  180 . The second rail  184  is shown in a retracted position in  FIG. 3  and an extended position in  FIG. 4 . In the retracted position, the second rail  184  does not extend outward from the first rail  180  as far as it does in the extended position. As seen in  FIGS. 3 and 4 , the length of the frame  116  is thus dependent upon the position of the second rail  184  with respect to the first rail  180 . The frame  116  in the embodiment depicted includes a duplicate set of rails (not shown) that are parallel to the first and second rails  180 ,  184  and that are connected to the first and second rails by cross members (not shown). 
     The front wheel  120  is mounted with respect to the first rail  180 , and the rear wheel  124  is mounted with respect to the second rail  184 . Accordingly, movement of the second rail  184  with respect to the first rail  180  alters the wheelbase of the base unit  112 , as seen in  FIGS. 3 and 4 . 
     When the second rail  184  is in the retracted position, the base unit  112  is a compact, battery-electric vehicle. When the second rail  184  is in the extended position, an extension module  134  may be attached to the base unit  112  to provide additional cargo space, passenger capacity, power, and/or driving range, as shown in  FIG. 4 . More specifically, the extension module  134  includes a vehicle body portion  142 . The extension module  134  also includes a second attachment interface  136  that is mounted to the body portion  142 ; in the embodiment depicted, the second attachment interface  136  includes mechanical fastening elements  138  that are selectively and releasably engageable with the fastening elements  132  of the first attachment interface  130  to connect the extension module  134  to the base unit  112  such that the extension module  134  and the base unit  112  form a single drivable unit  140 , as shown in  FIG. 4 . In the embodiment depicted, fastening elements  132 ,  138  rigidly interconnect the base unit  112  with the extension module  134 . 
     The mechanical fastening elements  132 ,  138  may have many different configurations within the scope of the claimed invention. For example, mechanical fastening elements  132  may be latches and fastening elements  138  may be strikers that releasably engage the latches, fastening elements  132  may be threaded fasteners and fastening elements  138  may be tabs with holes through which the threaded fasteners extend (a nut would then engage the threaded fasteners to secure the tabs), etc. 
     The body portion  142  of the extension module  134  defines an interior compartment  146  having an opening  150  at the forward end of the body portion  142 . The opening  126  of interior compartment  122  is adjacent the opening  150  of interior compartment  146 , and when extension module  134  is mounted to the body portion  114  of the base unit  112  via the fastening elements  132 ,  138  (i.e., the first and second attachment interfaces  130 ,  136 ), the interior compartments  122 ,  146  cooperate to form one contiguous compartment  154 . Thus, the first attachment interface  130  is positioned with respect to body portion  114 , and the second attachment interface  136  is positioned with respect to body portion  142  such that the first and second interior compartments  146 ,  122  are contiguous when the first and second attachment interfaces  130 ,  136  are engaged with each other. It should be noted that the closure  127  is in the open position, and therefore not obstructing opening  126 , when the extension module  134  is connected to the base unit  112 . The closure  127  in the open position may be supported by, or connected to, the roof of body portion  142 , as shown in  FIG. 4 . 
     The extension module  134  also includes an auxiliary power unit  78  mounted with respect to the first vehicle body portion  142 . The auxiliary power unit  78  may be an internal combustion engine that transmits torque to at least one of the wheels  120 ,  124 . The auxiliary power unit  78  may also generate electrical energy to power the electric motor  66  or recharge the battery  70 , such as an internal combustion engine in combination with a generator, or a fuel cell. Accordingly, the interfaces  130 ,  136  may include an electrical interface to transmit control signals to the auxiliary power unit  78  from the base unit  112 , or to transmit electrical energy from the auxiliary power unit  78  to the battery  70  and/or the motor  66  in the base unit  112 . 
     When a user of the vehicle system  110  desires additional cargo space, passenger capacity, and/or driving range before recharging the battery  70 , the user may extend the frame  116  of the base unit  112  (by sliding the second rail  184  rearward with respect to the first rail  180 ), open the closure  127 , and then engage the fastening elements  138  of the second attachment interface  136  with the fastening elements  132  of the first attachment interface  130  to attach the extension module  134  to the base unit  112 . The extension module  134  provides increased cargo space and/or passenger capacity to the base unit  112 , and the auxiliary power unit  78  provides additional power and or/driving range to the vehicle system  110 . When a user of the vehicle system  110  desires a compact, electric-only vehicle, then the user may disconnect the extension module  134  from the base unit  112 , and then move the second rail  184  forward with respect to the first rail  180  (to the retracted position). The base unit  112  is then drivable as a compact, battery-electric vehicle. In the embodiment depicted, the extension module  134  has at least one passenger seat  174  mounted to the body portion  142  and disposed within the interior compartment  146 . 
     Referring to  FIG. 5 , wherein like reference numbers refer to like components from  FIGS. 1-4 , an expandable vehicle system  210  includes a base unit  212  having a frame  216 , a first wheel (front wheel  220 ) and a second wheel (rear wheel  224 ) rotatably mounted with respect to the frame  216 , and a battery-electric propulsion system  62  mounted with respect to the frame  216 . Only one front wheel  220  and one rear wheel  224  is shown in  FIG. 5 ; the base unit  212  may include at least one other front wheel and rear wheel. 
     The battery-electric propulsion system  62  includes a motor  66  operatively connected to at least one of the wheels  220 ,  224  to transmit torque thereto. A battery  70  is operatively connected to the motor  66  to transmit electrical energy thereto. The base unit  212  includes a body portion  214  that defines an interior compartment  222  having an opening  226  at the rearward end of the body portion  214 . The base unit  212  also includes a vehicle body closure  227  that is configured to selectively obstruct the opening  226 . In the embodiment depicted, the closure  227  is a rear liftgate that is selectively movable between a closed position, as shown in  FIG. 5 , in which the liftgate is generally vertical and obstructs the opening  226 , and an open position, as shown in  FIG. 7 , in which the liftgate is generally horizontal and does not obstruct the opening  226 . In the embodiment depicted, the closure  227  is pivotable about a hinge  229  that interconnects the closure  227  and the body portion  214 . The base unit  212  includes a driver&#39;s seat  228  disposed within the interior compartment  222  and mounted to the body portion  214 . The base unit  212  also includes other systems (not shown) to enable drivability, such as a steering system and a braking system. 
     The base unit  212  also includes a first attachment interface  230  mounted with respect to the frame  216  adjacent the opening  226  at the rearward end of the body portion  214 ; the first attachment interface  230  in the embodiment depicted includes at least one mechanical fastening element  232 . 
     The base unit  212  is a compact, battery-electric vehicle. An extension module (shown at  234  in  FIGS. 6 and 7 ) may be attached to the base unit  212  to provide additional cargo space, passenger capacity, power, and/or driving range, as shown in  FIG. 7 . Referring specifically to  FIG. 6 , wherein like reference numbers refer to like components from  FIGS. 1-5 , the extension module  234  includes a vehicle body portion  242 . The extension module  234  also includes a second attachment interface  236  that is mounted to the body portion  242 ; in the embodiment depicted, the second attachment interface  236  includes mechanical fastening elements  238  that are selectively and releasably engageable with the fastening elements  232  of the first attachment interface  230  to connect the extension module  234  to the base unit  212  such that the extension module  234  and the base unit  212  form a single drivable unit  240 , as shown in  FIG. 7 . In the embodiment depicted, fastening elements  232 ,  238  rigidly interconnect the base unit  212  with the extension module  234 . 
     The mechanical fastening elements  232 ,  238  may have many different configurations within the scope of the claimed invention. For example, mechanical fastening elements  232  may be latches and fastening elements  238  may be strikers that releasably engage the latches, fastening elements  232  may be threaded fasteners and fastening elements  238  may be tabs with holes through which the threaded fasteners extend (a nut would then engage the threaded fasteners to secure the tabs), etc. 
     The body portion  242  of the extension module  234  defines an interior compartment  246  having an opening  250  at the forward end of the body portion  242 . The opening  226  of interior compartment  222  is adjacent the opening  250  of interior compartment  246  when extension module  234  is mounted to the body portion  214  of the base unit  212  via the fastening elements  232 ,  238  (i.e., the first and second attachment interfaces  230 ,  136 ), and the interior compartments  222 ,  246  cooperate to form one contiguous compartment  254 . Thus, the first attachment interface  230  is positioned with respect to body portion  214 , and the second attachment interface  236  is positioned with respect to body portion  242  such that the first and second interior compartments  246 ,  222  are contiguous when the first and second attachment interfaces  230 ,  236  are engaged with each other. It should be noted that the closure  227  is in the open position, and therefore not obstructing opening  226 , when the extension module  234  is connected to the base unit  212 . The closure  227  in the open position may be supported by, or connected to, the roof of body portion  242 , as shown in  FIG. 7 . 
     The extension module  234  includes at least one wheel  280  mounted with respect to the body portion  242 . The rear wheel  224  of the base unit is selectively retractable; in  FIG. 5  the wheel  224  is shown in an extended position in which the wheel  224  rotatably supports the base unit  212  on the ground, and in which the wheel  224  enables the base unit  212  to operate as a fully functional vehicle without the extension module  234 . In  FIG. 7 , the wheel  224  is shown in a retracted position relative to the frame  216 , in which the wheel  224  does not contact the ground. Wheels  280  of the extension module  234  then form the rear wheels of the drivable unit  240 . 
     The extension module  234  also includes an auxiliary power unit  78  mounted with respect to the vehicle body portion  242 . The auxiliary power unit  78  may be an internal combustion engine that transmits torque to at least one of the wheels  220 ,  280 . The auxiliary power unit  78  may also generate electrical energy to power the electric motor  66  or recharge the battery  70 , such as an internal combustion engine in combination with a generator, or a fuel cell. Accordingly, the interfaces  230 ,  236  may include an electrical interface (not shown) to transmit control signals to the auxiliary power unit  78  from the base unit  212 , or to transmit electrical energy from the auxiliary power unit  78  to the battery  70  and/or the motor  66  in the base unit  212 . 
     When a user of the vehicle system  210  desires additional cargo space, passenger capacity, and/or driving range before recharging the battery  70 , the user may open the closure  227 , and then engage the fastening elements  238  of the second attachment interface  236  with the fastening elements  232  of the first attachment interface  230  to attach the extension module  234  to the base unit  212 . After the extension module  234  is connected to the base unit  212 , the wheel  224  may then be retracted. The extension module  234  provides increased cargo space and/or passenger capacity to the base unit  212 , and the auxiliary power unit  78  provides additional power and or/driving range to the vehicle system  210 . When a user of the vehicle system  210  desires a compact, electric-only vehicle, then the user may extend wheel  224  to the position shown in  FIG. 5 , disconnect the extension module  234  from the base unit  212 , and then move the closure  227  to the closed position. The base unit  212  is then drivable as a compact, battery-electric vehicle. In the embodiment depicted, the extension module  234  has at least one passenger seat  274  mounted to the body portion  242  and disposed within the interior compartment  246 . 
     Referring to  FIGS. 8 and 9 , wherein like reference numbers refer to like components from  FIGS. 1-7 , an expandable vehicle system  310  includes a base unit  312  having a frame  316 , front wheels  318  rotatably mounted with respect to the frame  316 , rear wheels  320  rotatably mounted with respect to the frame  316 , and a battery-electric propulsion system  62  mounted with respect to the frame  316 . The frame  316  is a chassis frame configured for body-on-frame vehicle architecture. The base unit  312  in the embodiment depicted does not include a vehicle body or body portion defining an interior compartment. The base unit  312  also includes a steering system (not shown) and a braking system (not shown). 
     The base unit  312  has a first attachment interface  330  mounted with respect to the frame  316 . In the embodiment depicted, the first attachment interface  330  includes mechanical fasteners, and, more specifically, the mechanical fasteners are vehicle body mounts  332 . The expandable vehicle system  310  also includes two rear modules, or extension modules, that are selectively, releasably engageable at the first attachment interface  330 . More specifically, the expandable vehicle system  310  includes a first extension module, shown at  334  in  FIG. 9 , and a second extension module, shown at  334 A in  FIG. 8 . 
     Referring specifically to  FIG. 9 , the first extension module  334  includes a vehicle body portion  342 . It should be noted that, as used herein, a “body portion” may include an entire body or a smaller portion thereof. Body portion  342  is an entire, or substantially entire, vehicle body. The first extension module  334  also includes a second attachment interface  336  that is mounted to the body portion  342 ; in the embodiment depicted, the second attachment interface  336  includes mechanical fastening elements  338  that are selectively and releasably engageable with the body mounts  332  of the first attachment interface  330  to connect the first extension module  334  to the base unit  312  such that the first extension module  334  and the base unit  312  form a single drivable unit  340 , as shown in  FIG. 9 . 
     The body portion  342  of the first extension module  334  defines an interior compartment  346 . The battery-electric powertrain or propulsion system  62  mounted with respect to the frame  16  includes an electric motor  66  operatively connected to an energy storage device, such as a battery  70 . The motor  66  is operatively connected to at least one of the vehicle wheels  318 ,  320  to transmit torque thereto and thereby propel the vehicle system  310 . 
     The first extension module  334  also includes an auxiliary power unit  78  mounted with respect to the first vehicle body portion  342 . As used herein, an “auxiliary power unit” is any device that produces power to propel the vehicle system  310 ; examples of auxiliary power units  78  include torque-producing devices, such as internal combustion engines, that transmit torque to at least one of the wheels  318 ,  320 . Other auxiliary power units  78  within the scope of the claimed invention may generate electrical energy to power the electric motor  66  or recharge the battery  70 , such as an internal combustion engine in combination with a generator, or a fuel cell. Accordingly, the interfaces  330 ,  336  may include an electrical interface to transmit control signals to the auxiliary power unit  78  or to transmit electrical energy from the auxiliary power unit  78  to the battery  70  and/or the motor  66 . 
     Referring again to  FIG. 8 , the second extension module  334 A includes a body portion  342 A. The second extension module  334 A also includes a third attachment interface  336 A that is mounted with respect to the body portion  342 A; in the embodiment depicted, the third attachment interface  336 A includes mechanical fastening elements  338  that are selectively and releasably engageable with the body mounts  332  of the first attachment interface  330  to rigidly connect the second extension module  334 A to the base unit  312  such that the base unit  312  and the second extension module  334 A form a single, drivable unit  340 A. Body portion  342 A is an entire, or substantially entire, vehicle body. 
     The body portion  342 A defines an interior compartment  346 A. Referring to  FIGS. 8 and 9 , the interior compartment  346 A of the second extension module  334 A is shorter and smaller than the interior compartment  346  of the first extension module  334 . The second extension module  334 A is characterized by the absence of an auxiliary power unit  78 , and thus drivable unit  340 A is a compact electric vehicle. Accordingly, the second extension module  334 A may be used, for example, for one or two people commuting short distances. The second extension module  334 A includes a driver&#39;s seat  328 . 
     When a user of the vehicle system  310  desires additional cargo space, passenger capacity, and/or driving range before recharging the battery  70 , the user may remove the second extension module  334 A from the base unit  312  (by disengaging the fastening elements  338  of the third attachment interface  336 A from the fastening elements  332  of the first attachment interface  330 ) and then engage the fastening elements  338  of the second attachment interface  336  with the fastening elements  332  of the first attachment interface  330  to attach the first extension module  334  to the base unit  312 . The first extension module  334  provides increased cargo space and/or passenger capacity compared to the second extension module  334 A, and the auxiliary power unit  78  provides additional power and or/driving range to the vehicle system  310 . When a user of the vehicle system  310  desires a compact, electric-only vehicle, then the user may disconnect the first extension module  334  from the base unit  312  and then connect the second extension module  334 A to the base unit  312 . In the embodiment depicted, the first extension module  334  has both a driver&#39;s seat  328  and at least one passenger seat  374  mounted to the body portion  342  and disposed within the interior compartment  346 . 
     Accordingly, the base unit  312  is a chassis including at least three wheels  318 ,  320  mounted with respect to the frame  316 . The frame  316  is characterized by an upper face  380 . The first attachment interface  330  includes body mounts  332  exposed at the upper face  380 , and the first vehicle body portion  342  is an entire vehicle body. The second extension module  334 A has a second vehicle body portion  342 A and a third attachment interface  336 A mounted with respect to the third vehicle body portion  342 A. The first and third attachment interfaces  330 ,  336 A are configured to selectively and releasably engage one another such that the second extension module  334 A and the base unit  312  form a single drivable unit  340 A when the first and third attachment interfaces  330 ,  336 A are engaged with one another. The second extension module  334 A is characterized by the absence of an auxiliary power unit  78 . 
     Referring to  FIGS. 10 and 11 , wherein like reference numbers refer to like components from  FIGS. 1-9 , an expandable vehicle system  410  includes a base unit  412  having a frame  416 , front wheels  418  rotatably mounted with respect to the frame  416 , rear wheels  420  rotatably mounted with respect to the frame  416 , and a battery-electric propulsion system (shown at  462  in  FIG. 11 ) mounted with respect to the frame  416 . The base unit  412  includes a body portion  414  mounted with respect to the frame  416 . The body portion  414  defines an interior compartment  422 . A seat  428  is mounted with respect to the body portion  414  and is disposed within the interior compartment  422 . 
     The base unit  412  includes a steering system  430  and a braking system  432 . Accordingly, with a vehicle body, propulsion system  462 , steering system  430 , and braking system  432 , the base unit  412  forms a compact, electric vehicle that is independently drivable without and extension module. The steering system  430  and the braking system  432  are “by wire,” i.e., they are controllable via electronic or other non-mechanical control signals. Referring specifically to  FIG. 11 , the steering system  430  includes a steering input device  436 , such as a steering wheel, which is manipulatable by a human vehicle driver to control the steering system  430 . For example, the human vehicle driver inputs mechanical steering signals into the steering system  430  by changing the angular position of the steering wheel and the angular velocity of the steering wheel. A steering transducer  438  detects the angular position of the steering wheel and the angular velocity of the steering wheel and converts these mechanical steering signals to electronic or other non-mechanical steering input signals  440 . The steering transducer  438  is operatively connected to a control unit  442  and transmits the steering input signals  440  to the control unit  442 . A control unit typically includes a microprocessor, ROM and RAM and appropriate input and output circuits of a known type for receiving the various input signals and for outputting various control commands to the actuators. 
     The control unit  442  processes the steering input signals  440  in combination with various sensor signals and in accordance with a predetermined algorithm to generate steering actuator control signals  446 . The control unit  442  is operatively connected to a steering actuator  448  and transmits the steering actuator control signals  446  thereto. The steering actuator  448  is operably connected to the front wheels  418  and configured to adjust the steering angle of the front wheels  418  in response to the control signals  446  from the control unit  442 . Actuators in a by-wire system transform electronic (or other non-mechanical) control signals into a mechanical action or otherwise influence a system&#39;s behavior in response to the control signals. Examples of actuators that may be used in a by-wire system include electromechanical actuators such as electric servomotors, translational and rotational solenoids, magnetorheological actuators, electrohydraulic actuators, and electrorheological actuators. Those skilled in the art will recognize and understand mechanisms by which the steering angle may adjusted. In one embodiment, the steering actuator  448  is an electric drive motor configured to adjust a mechanical steering rack. 
     Similarly, the braking system  432  includes a braking input device  450 , such as a brake pedal, which is manipulatable by a human vehicle driver to control the braking system  432 . For example, the human vehicle driver inputs mechanical braking signals into the braking system  432  by changing the position of the brake pedal relative to the body portion  414  and the velocity of the brake pedal relative to the body portion  414 . A braking transducer  452  detects the position of the brake pedal relative to the body portion  414  and the velocity of the brake pedal relative to the body portion  414 , and converts these mechanical braking signals to electronic or other non-mechanical braking input signals  454 . The braking transducer  452  is operatively connected to the control unit  442  and transmits the braking input signals  454  to the control unit  442 . 
     The control unit  442  processes the braking input signals  454  in combination with various sensor signals and in accordance with a predetermined algorithm to generate braking actuator control signals  456 . The control unit  442  is operatively connected to a braking actuator  458  and transmits the braking actuator control signals  456  thereto. The braking actuator  458  is configured to reduce the angular velocity of the wheels  418 ,  420  in response to the braking actuator control signals  456 . Those skilled in the art will recognize the manner in which the braking actuator  458  acts on the wheels  418 ,  420 . Typically, actuators cause contact between friction elements, such as pads and disc rotors. Optionally, an electric motor may function as a braking actuator in a regenerative braking system. 
     The propulsion system  462  in the embodiment of  FIGS. 10 and 11  includes by-wire control. The propulsion system  462  includes a propulsion system input device  464 , such as an accelerator pedal, which is manipulatable by a human vehicle driver to control the propulsion system  462 . For example, the human vehicle driver inputs mechanical propulsion signals into the propulsion system  462  by changing the position of the accelerator pedal relative to the body portion  414  and the velocity of the accelerator pedal relative to the body portion  414 . A propulsion transducer  466  detects the position of the accelerator pedal relative to the body portion  414  and the velocity of the accelerator pedal relative to the body portion  414 , and converts these mechanical propulsion signals to electronic or other non-mechanical propulsion input signals  468 . The propulsion transducer  466  is operatively connected to the control unit  442  and transmits the propulsion input signals  468  to the control unit  442 . 
     The control unit  442  processes the propulsion input signals  468  in combination with various sensor signals and in accordance with a predetermined algorithm to generate propulsion control signals  470 . The control unit  442  is operatively connected to the motor  66  and transmits the propulsion control signals  470  thereto. The motor  66  is responsive to the propulsion control signals  470  to vary to the amount of torque and power applied by the motor  66  to the wheels  418 ,  420 . The motor  66  is operatively connected to the battery  70  to receive electrical energy therefrom. 
     The expandable vehicle system  410  also includes an extension module  434  having a body portion  474 , front wheels  478  rotatably mounted with respect to body portion  474 , and rear wheels  482  rotatably mounted with respect to body portion  474 . The body portion  474  defines an interior compartment  484 . A seat  486  is mounted with respect to the body portion  474  and is disposed within the interior compartment  484 . 
     The extension module  434  includes a steering system  530 , a braking system  532 , and a propulsion system  562 . Accordingly, with a vehicle body  474 , propulsion system  562 , steering system  530 , and braking system  532 , the extension module  434  forms a vehicle that is independently drivable without the base unit  412 . 
     The steering system  530  and the braking system  532  are “by wire,” i.e., they are controllable via electronic or other non-mechanical control signals. Referring specifically to  FIG. 11 , the steering system  530  includes a steering input device  536 , such as a steering wheel, which is manipulatable by a human vehicle driver to control the steering system  530 . For example, the human vehicle driver inputs mechanical steering signals into the steering system  530  by changing the angular position of the steering wheel and the angular velocity of the steering wheel. A steering transducer  538  detects the angular position of the steering wheel and the angular velocity of the steering wheel and converts these mechanical steering signals to electronic or other non-mechanical steering input signals  540 . The steering transducer  538  is operatively connected to a control unit  542  and transmits the steering input signals  540  to the control unit  542 . A control unit typically includes a microprocessor, ROM and RAM and appropriate input and output circuits of a known type for receiving the various input signals and for outputting various control commands to the actuators. 
     The control unit  542  processes the steering input signals  540  in combination with various sensor signals and in accordance with a predetermined algorithm to generate steering actuator control signals  546 . The control unit  542  is operatively connected to a steering actuator  548  and transmits the steering actuator control signals  546  thereto. The steering actuator  548  is operably connected to the front wheels  478  and configured to adjust the steering angle of the front wheels  478  in response to the control signals  546  from the control unit  542 . 
     Similarly, the braking system  532  includes a braking input device  550 , such as a brake pedal, which is manipulatable by a human vehicle driver to control the braking system  532 . For example, the human vehicle driver inputs mechanical braking signals into the braking system  532  by changing the position of the brake pedal relative to the body portion  474  and the velocity of the brake pedal relative to the body portion  474 . A braking transducer  552  detects the position of the brake pedal relative to the body portion  474  and the velocity of the brake pedal relative to the body portion  474 , and converts these mechanical braking signals to electronic or other non-mechanical braking input signals  554 . The braking transducer  552  is operatively connected to the control unit  542  and transmits the braking input signals  554  to the control unit  542 . 
     The control unit  542  processes the braking input signals  554  in combination with various sensor signals and in accordance with a predetermined algorithm to generate braking actuator control signals  556 . The control unit  542  is operatively connected to a braking actuator  558  and transmits the braking actuator control signals  556  thereto. The braking actuator  558  is configured to reduce the angular velocity of the wheels  478 ,  482  in response to the braking actuator control signals  556 . 
     The propulsion system  562  in the embodiment of  FIGS. 10 and 11  includes by-wire control. The propulsion system  562  includes a propulsion system input device  564 , such as an accelerator pedal, which is manipulatable by a human vehicle driver to control the propulsion system  562 . For example, the human vehicle driver inputs mechanical propulsion signals into the propulsion system  562  by changing the position of the accelerator pedal relative to the body portion  414  and the velocity of the accelerator pedal relative to the body portion  474 . A propulsion transducer  566  detects the position of the accelerator pedal relative to the body portion  474  and the velocity of the accelerator pedal relative to the body portion  474 , and converts these mechanical propulsion signals to electronic or other non-mechanical propulsion input signals  568 . The propulsion transducer  566  is operatively connected to the control unit  542  and transmits the propulsion input signals  568  to the control unit  542 . 
     The control unit  542  processes the propulsion input signals  568  in combination with various sensor signals and in accordance with a predetermined algorithm to generate propulsion control signals  570 . The control unit  542  is operatively connected to an electric motor  572  and transmits the propulsion control signals  570  thereto. The motor  572  is responsive to the propulsion control signals  570  to vary to the amount of torque and power applied by the motor  572  to the wheels  478 ,  482 . The motor  572  is operatively connected to a battery  574  to receive electrical energy therefrom. 
     The propulsion system  562  also includes an electrical generation subsystem, which, in the embodiment depicted, is an engine  576  operatively connected to an electrical generator  578 . The electrical generator  578  is operatively connected to the battery  574  and the motor  572  to selectively transmit electrical energy thereto. 
     The base unit  412  includes a first attachment interface  630  mounted with respect to the frame  416 . The extension module  434  includes a second attachment interface  636  mounted with respect to the body portion  474 . The first and second attachment interfaces  630 ,  636  are configured to selectively and releasably engage one another such that the extension module  474  and the base unit  412  form a single drivable unit  580  when the first and second attachment interfaces  630 ,  636  are engaged with one another. 
     In the embodiment of  FIGS. 10 and 11 , the first interface  630  is at least one electrical connector  638  operatively connected to the control unit  442 , the battery  70 , and the motor  66 , such as by wires. The second interface  636  is at least one electrical connector  640  that is operatively connected to the control unit  542  and the generator  578 , such as by wires. When electrical connector  638  is engaged with electrical connector  640 , control signals  642  from control unit  442  are transmittable to control unit  542  through the connectors  638 ,  640 . Similarly, when electrical connector  638  is engaged with electrical connector  640 , electrical energy  644  is transmittable from the generator  578  to the battery  70  and the motor  66  through the electrical connectors  638 ,  640 . 
     The propulsion system  562  is thus an auxiliary power unit that can supplement the energy requirements of the base unit  412 . Control signals  642  from the base unit  412  control the steering system  530 , braking system  532 , and propulsion system  562  of the extension unit  434 . The control unit  442  is configured to generate the control signals  642  in response to the inputs from input devices  436 ,  450 ,  464  such that the extension unit  434  follows the base unit  412  and remains within a predetermined range of the base unit  412  (determined in part by the length of the flexible wires  646  connecting electrical connector  640  and the body  474 . In this manner, the base unit  412  and the extension module  434  form a single, drivable unit  580 . It should be noted that the interfaces  630 ,  636  do not transmit significant mechanical forces between the base unit  412  and the extension unit  434 ; instead, only electrical energy and non-mechanical (electrical) control signals are transmitted between the base unit  412  and the extension module  434  when the interfaces  630 ,  636  are engaged with one another. 
     Referring to  FIGS. 12 and 13 , wherein like reference numbers refer to like components from  FIGS. 1-11 , the expandable vehicle system  710  is substantially identical to the expandable vehicle system  410  of  FIGS. 10 and 11 , except for interfaces  730 ,  736 . Interface  730  of the base unit  412  is mounted with respect to the frame  416  and includes a wireless transceiver  740  (transmitter/receiver) configured to send wireless control signals  742  from the base unit  412  to the extension module  434 . The interface  736  of the extension module  434  is mounted with respect to the body portion  474 , and includes a transceiver  744  configured to receive the wireless signals  742 . The transceiver  740  is operatively connected to the control unit  442  to receive control signals  642  therefrom, and convert the control signals  642  to wireless form  742 . The transceiver  744  is operatively connected to control unit  542 , and converts the wireless control signals  742  back to electronic control signals  642 , which are transmitted to the control unit  542 . 
     Interface  736  and interface  730  also include respective inductive couplings  750 . The inductive coupling  750  of interface  730  is operatively connected to the motor  66  and the battery  70 . The inductive coupling  750  interface  736  is operatively connected to the generator  578 . Accordingly, the interfaces  730 ,  736  provide wireless power transmission from the generator  578  of the extension module  434  to the propulsion system  462  of the base unit  412 . 
     It should be noted that, in the embodiment of  FIGS. 12 and 13 , the interfaces  730 ,  736  are characterized by the absence of any physical connections between the base unit  412  and the extension module  434  when the interfaces  730 ,  736  are engaged with each other to form the single, drivable unit  780 . 
     While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.