Abstract:
Improvements using a door sensors or monitoring the vehicle CAN bus to determine when a door is opened or closed to simplify installation of a retractable door step to send a wireless or wired command to a step. Upon door movement the transmitter sends an open status message to a receiver where the message data is stored and the controller determines the correct responses. The step remains lowered until the receiver stops receiving messages indicating a door is closed or the transmitter on an open door has timed out ceasing transmissions. The step extension mechanism is a two-bar link that transfers rotation from a sealed waterproof motor and transmission to extend and retract the step.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
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     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
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     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
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     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a retractable/extendable step. More particularly, the present retractable step interfaces with the CAN bus in modern vehicles to signal when to extend and retract a vehicle step to assist entry into the vehicle. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     High ground clearance vehicle such as trucks, SUV&#39;s and four wheel drive vehicle typically create a problem for people to get into because the distance between the ground and the floorboard of the vehicle can be great. To reduce the height of the step, fixed running boards are often installed. While the fixed running board makes entry into the vehicle easier the fixed running board defeats the purpose of the vehicle having high ground clearance. Another solution is to provide an extendable/retractable step. These steps are usually wired to the door switch of the vehicle to extend and retract the step based upon the status of the door switch. Wiring the step into the vehicle usually requires removal of door or interior panels to gain access to the switch wiring. Car dealers and new vehicle owners are often apprehensive to have modifications made to the interior of their new vehicles and possibly voiding the new car warranty. There is a need to provide a step signaling mechanism that minimizes disassembly of the interior of a vehicle. Some patents have been published and issued on systems that describe signaling systems to extend and retract a truck step. Exemplary examples of patents covering these products are disclosed herein. 
     U.S. Pat. Nos. 6,942,233, 7,398,985, 7,413,204 and 7,584,975 issued to Horst Leitner disclose Retractable Vehicle Steps. These retractable vehicle steps require the installer to cut into the electrical system of a vehicle to obtain power for the retractable step and also require the installer to connect into the door switch on all the doors where the step will be extended. This requires running a significant amount of wiring to each door, to a controller and to the extension mechanism. Some of these patents also disclose using the key fob that unlocks the door to extend a step. While these patents disclose an extendable and retractable step, they either rely upon wiring the system into a door switch or the key fob that can leave a step extended until some signal that retracts the step(s). 
     U.S. Pat. No. 7,081,816 issued Jul. 25, 2006 to Dean David Schebal et al., discloses a Compact Wireless Sensor. The sensor is for placement in a door or window and sends a signal when the door or window is opened. The signal does not activate a step to extend or retract and further does not send a complimentary signal to indicate when the door or window has been closed. The device uses a timer to sample the state of the sensor and send updated information only when the timer initiates a reading and the status changes. This sensor is configured for installation within a wood doorjamb and is not configured for installation into an automotive door. 
     U.S. Pat. No. 7,692,542 issued Apr. 6, 2010 to Allan Outzs discloses a Door Position Monitor that couples a magnetic field through the door to determine the status of the door. The sensor uses a wired connection to a magnetic reed switch to determine the status of the door. While this patent determines the status of the door it does not transmit a wireless signal to activate a step for entry or exit from a vehicle. 
     Modern vehicles have an integrated CAN bus (controller area network). The CAN bus is a vehicle bus standard that is designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer. The protocol was released in 1986, came to market in 1987 and was mandatory on cars and light trucks sold in the US since 1996. This specification has two parts; part A is for the standard format with an 11-bit identifier, and part B is for the extended format with a 29-bit identifier. A CAN device that uses 11-bit identifiers is commonly called CAN 2.0A and a CAN device that uses 29-bit identifiers is commonly called CAN 2.0B. 
     What is needed is a wireless sensor that can be glued, bonded or otherwise secured to or near a door of a vehicle to determine when a door is opened or closed to signal a step to extend or retract the step based upon the status of the door. Accordingly, a wireless sensor and transmitter to operate a vehicle step which overcomes the above-stated problems is desired. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the retractable truck step with CAN bus interface to signal a motor to extend and retract a step on an elevated vehicle. The automatic vehicle entrance and exit step lowers for use when a vehicle door is opened and retracted when the door is closed. The step is placed at an intermediary height between the ground and the floorboard of the elevated vehicle. A typical installation hardwires the motion of the step with the door switch. 
     It is an object of the retractable truck step with CAN bus interface to use a wireless signal to trigger the drive motor to extend or retract the step. The wireless system makes installation of the retractable truck step easier by eliminating opening door, side or door sill panels to gain access to the door switch. Each door switch must be connected to move the steps separately on each side of a vehicle. 
     It is an object of the retractable truck step with CAN bus interface for the sensor to operate in a sleep mode while it is not transmitting a signal. The sleep mode reduces power consumption and the wireless transmitter only turns on when the door is opened to extend the step. A cyclic redundancy check (CRC) eliminates the need to send redundant transmission. 
     It is another object of the retractable truck step with CAN bus interface for the door sensors to be positioned at any location within the vehicle where the CAN bus is available. This can be performed in less than a minute instead of the up to an hour to locate and install on a vehicle with multiple door sensors. 
     It is another object of the retractable truck step with CAN bus interface for the foot pad extension mechanism to be sealed from moisture and water intrusion. The water can enter as humidity from ambient conditions, rain or fording the vehicle. Water can cause corrosion and rust within the mechanism. Over an extended period of time rust and corrosion degrades the motor, connectors, gears and bearings. The sealing prevents premature failure of the mechanism. The motor and gear case are designed to prevent water from entering the motor or gear case. This is possible due to the short duty cycle of the motor. By not allowing water to enter the gear case or motor, the life of the actuator is greatly extended. 
     It is another object of the retractable truck step with CAN bus interface to utilize a torsion bar between the drive motor and an idler. The addition of a torsion bar that is attached to the drive shaft of the motor directly to the pivot point of the idler shaft serves several functions. By driving the idler with the torsion bar, both linkages pull up together. This keeps the board from hanging down and presenting an uneven appearance on the idler side. It also pulls up evenly thus removing any misalignment between the motor linkage and the idler linkage. This prevents corner loading of the bushings and keeps the any noise from occurring because of the uneven bushing contact. Because of a better load distribution on the motor, the torsion bar will extend the life of the motor. 
     It is still another object of the retractable truck step with CAN bus interface to use multiple command identifiers to differentiate one vehicle from another. The use of multiple ID codes reduces the potential of opening a door on a first vehicle and having the step of a second vehicle extend unexpectedly. 
     It is still another object of the retractable truck step with CAN bus interface to use the CAN bus to signal the step to extend and retract based upon the door being opened. The CAN bus interface can send a wired or wireless command to the retractable step. 
     Various objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  shows four wireless door sensors. 
         FIG. 2  shows a detailed view of the wireless door transmitter. 
         FIG. 3A  shows a block diagram of the code flow chart in the transmitter. 
         FIG. 3B  shows a block diagram of the CAN bus flow chart. 
         FIG. 4  shows a common connection for a CAN bus in a vehicle. 
         FIG. 5  shows a connection for a CAN Node. 
         FIG. 6  shows a communications protocol over a CAN bus. 
         FIG. 7  shows detailed information regarding the CAN bus protocal. 
         FIG. 8A  shows the wireless data transmission from a transmitter. 
         FIG. 8B  shows the wireless data transmission from a transmitter when using the CAN bus. 
         FIG. 9  shows block diagram of the receiver unit and the step controller motors. 
         FIG. 10  shows a block diagram of the code flow chart in the receiver. 
         FIG. 11  is a front perspective view of a retracted step. 
         FIG. 12  is a front perspective view of an extended step. 
         FIG. 13  is a top view of the retracted step. 
         FIG. 14  is a front view of the retracted step. 
         FIG. 15  is a front view of the extended step. 
         FIG. 16  is a sectional view of the retracted step cut from section  16 - 16  from  FIG. 14 . 
         FIG. 17  is a sectional view of the extended step cut from section  17 - 17  from  FIG. 15 . 
         FIG. 18  is a perspective detail view of a portion of the motor mechanism from  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This document discloses three different approaches to signaling a step to be extended and retracted. The two different approaches are outlined herein. 
     Door Transmitter Approach 
     This system consists of four Sensor/Transmitters mounted in the vehicle door frames. Through the use of magnets and reed switches an open door is sensed and on that event “open door” messages are transmitted to a vehicle mounted Receiver. The Receiver signals the step Controller through a wired interface to actuate the motors to extend or retract the automatic step(s). Since only “open door” messages are transmitted to the receiver it is a function of the receiver to determine the closing of a door from the cessation of “open door” messages transmitted by the door Sensor/Transmitters. 
     CAN Bus Approach 
     This system consists of one CAN Monitor/Transmitter mounted anywhere in the vehicle where the CAN Bus wiring is accessible. The CAN Monitor/Transmitter monitors the data on the CAN bus and detects messages that contain data indicating the position of the doors. Upon detecting the door condition messages the CAN Monitor/Transmitter will transmit “door open” or “door closed” messages to the vehicle mounted Receiver. The receiver will act on the messages and signal the step Controller to extend or retract the step(s). Since “door open” and “door closed” messages are transmitted to the Receiver the receiver only acts on the message data and performs no timed action on the cessation of received messages. 
     Common System Components 
     Both systems incorporate identical Step Controllers. The Receivers of both systems are identical in hardware design, the only differences lie in the message processing software of the receivers. Both Receivers utilize identical message protocols, patent document  FIG. 8B  describes the message content. 
     The Power Board is an automatic vehicle entrance and exit step that lowers for use when a vehicle door is opened and retracted when the door is closed. Traditional installation of the board requires modification of the vehicle to gain access to the door light switch wiring to sense door movement. Wiring is installed that accesses the vehicle wiring and is routed to a controller in the vehicle engine compartment. The controller engages the step motors to lower and retract the step. 
       FIG. 1  shows four wireless door sensors. A wireless car door sensor system eliminates the need to modify the vehicle wiring and simplify the installation of the power board is comprised of door sensors  21 - 24  installed on each door. For vehicles with only two doors, only a single left and right door sensor will be used.  FIG. 2  shows a more detailed view of the internal and external components used in the sensor/transmitter. 
       FIG. 2  shows a detailed view of the wireless door transmitter on vehicles that do not have a CAN bus. Each door sensor  20  consist of transmitter  30  coupled with reed switch  33 , or a proximity switch, having contacts that are effected by the presence or absence of a magnetic field caused by a magnet  41  or a ferric material near the magnetic field. The magnet  41  or the magnetic sensor  20  is mounted on the edge of each door  42  opposing the doorjamb  40 . A magnet  41  is mounted in the doorjamb  40  that comes in close proximity to the transmitter&#39;s magnetic sensor  33  when the door  42  is closed. The effective range of most reed switches  33  is one inch or less and is based upon the strength of the magnetic field that is created or coupled by the magnet  41 . This figure and the description show and describe a preferred embodiment for orientation, location and placement. Other embodiments are also contemplated that will provide the equivalent result of signaling when a car door has been opened and closed. The method of securing the transmitter  20  and or the magnet  41  can be as simple as tucking the components under body panels to gluing, bonding or screwing the components to a vehicle. 
     A battery  32  is included with the transmitter  20  along with an antenna  31  that transmits  50  a signal based upon the status of the sensor  33 . The transmitter  20  operates in a low power sleep mode until the magnetic sensor  33  senses a movement of the magnet  41 .  FIG. 3  shows a flow chart of the general operations within the microcontroller-transmitter  40 . 
       FIG. 3A  shows a block diagram of the code flow chart in the transmitter on vehicles that do not have a CAN bus or on vehicles that are not connected into the CAN bus. The transmitter operates in a low power sleep mode until a door is moved  43 . Since the sensing distance of the preferred reed switch sensor is limited, the detection of movement of the door is generally limited to motion when a door is just being opened and when the door latches shut. The opening and closing of the door  43  changes the status of the sensor and wakes up  60  the microcontroller from sleep. After the microcontroller wakes up  60  it will detect the status of the door and determine if the door is opened or closed. If the door is opened  43  the microcontroller will initiate the transmission of door open messages  64 . 
     If the door is now closed  62  the microcontroller will cease open door message transmissions. After the opened  64  command has been transmitted the microcontroller will repeat open door messages on a 0.5 second interval  61  until either the door is closed or a five minute time out period is reached after which the microcontroller will re-enter the sleep mode. While in the preferred embodiment a 5 five minute time out period is used it is contemplated that the time out period can be between one minute and 15 minutes. Various methods and frequencies of data transmission are contemplated including but not limited to frequencies that are utilized by car locking devices and garage door remote controls. While a 0.5 interval is preferred as a dead man type device to ensure that the door is still open an interval as small as 0.1 seconds to as long as 5 seconds between transmissions is contemplated. These frequencies are typically 315˜930 MHz but can be lower or higher in carrier wave frequency. One contemplated transmission protocol is shown and described with  FIG. 8 . 
       FIG. 3B  shows a block diagram of the CAN bus flow chart. When a vehicle has a CAN bus, a CAN node monitors  44  the bus to determine is a door related message is detected  45 . The message is decoded  46  as a driver side front door, a driver side rear door, a passenger side front door and a passenger side rear door. The message is parced  47  and the transmitter generates a message  48 . The message is the transmitted  49 . The node can be connected to the motor(s) that control the step or can be in wireless communication to the motor(s) that operate the step. It is also contemplated that the CAN node can transmit a signal on said CAN bus to indicate the status of the step(s). 
       FIG. 4  shows a common connection for a CAN bus in a vehicle, and  FIG. 5  shows a connection for a CAN Node. In a vehicle multiple CAN nodes  25 ,  26 ,  29  and more exist in different locations in a vehicle. The CAN nodes can listed to the bus lines  27  and  28  as well as communicate over the CAN bus. In the preferred embodiment the CAN node that controls the step(s) just listen to the CAN bus, but can communicate to indicate the status of the step. 
     In  FIG. 5  there is a CAN Transceiver  36  that operates with Medium Access Unit Electrical Levels per ISO 11898-2, 3. The CAN Controller  35  is a Data Link Layer that operates under ISO 11898-1. The microcontroller is shown with an integrated wireless transmitter, but the transmitter can be a separate unit or can be performed with a wired connection to the step(s). The wireless communication was previously described with  FIGS. 1-3  and  8 - 10  herein. 
       FIG. 6  shows a communications protocol over a CAN bus, and  FIG. 7  shows detailed information regarding the CAN bus protocal. The CAN bus protocal shown is a current standard, but can change in the future. Regardless of the protocol, detection of commands from a Controller Area Network (CAN) in a vehicle that identify a door open, door lock status, seatbelt status, manual switch or other desired change to the CAN bus can be used to operate a step or other ingress or egress feature. The CAN bus protocol operates in a Normal Bit Time  51 . Each Normal Bit Time  51  has a start of the frame followed with Sync bits. The status of some of the bits are fixed based upon the vehicle or the vehicle configuration. Following the Sync  52  are Prop bits  53 . Again, some bits can be fixed based upon the vehicle or the vehicle configuration. After the Prop bits  53  is phase  1  and includes Data bits and is then followed with Phase  2  for the CRC Field. An End of Frame follows the data bits. 
     Each vehicle can have different bits that are set or cleared based upon the features and functions of the vehicle. To determine the commands that will operate the step an oscilloscope or protocol analyzer can be connected to the CAN bus and the bits are monitored to determine what bits change based upon operation of different parts of the vehicle, like a door opening. 
       FIG. 8A  shows the wireless data transmission from a transmitter. While this data transmission protocol shows a particular order for the transmission various other baud rates, start bit(s), stop bit(s), command orders and redundant commands are contemplated. In one preferred embodiment the opening  70  or closing  71  of a door will change the status of the sensor and trigger  72  the microcontroller to awaken  74 . The microcontroller will determine the status of the door sensor switch and turn on the transmitter to begin  73  transmission of the signal. The sine wave  87  of the transmission frequency is shown for reference, but the preferred embodiment uses a transmission frequency is 915 MHz Other frequencies are contemplated but these frequencies are generally preferred for transmissions of short bursts of data and have a range of several hundred feet or less. 
     The transmission of the data begins with an attention or start bit(s) signal  81 . The data then includes a vehicle ID  82 . It is contemplated that the vehicle ID will include options of 100 to 256 vehicles to reduce the possibility that opening the door of a first vehicle will inadvertently extend the step of both the desired first vehicle and an undesirable second vehicle. The data also includes a status indicator of the door and the status of the door  83 . To reduce the possibility of a step extending or retracting with a stray signal from a car door being unlocked or a garage door being opened a redundant vehicle ID  84  and door status  85  is transmitted. The order of these commands as well as the second set of commands being inverted are contemplated to reduce the possibility of a step extending or retracting at an undesirable time. It is also contemplated that the transmitted signal includes a check sum. After the transmission of command data has been sent the transmitter will send a stop command  86  or will remain silent for some period of time while the transmitter is turned off  75  and the microcontroller ensures the status of the door is unchanged ( 67  from  FIG. 3 ). The microcontroller will then return to a low power sleep mode  76 . 
       FIG. 8B  shows the wireless data transmission from a transmitter when using the CAN bus. When the CAN bus is being used the transmitter and the receiver both receive power from the battery system of the vehicle. Redundancy of transmission is not required because a cyclic redundancy check (CRC) is used. The block of the transmission include a preamble, an address, door status bits and the cyclic redundancy check (CRC). 
       FIG. 9  shows block diagram of the receiver unit and the step controller motors. The receiver  91  receives the wireless command  50  from an antenna  92  and communicates the decoded command to a controller  90 . In one contemplated embodiment the receiver  91  includes one or a plurality of contacts that simulate the car door sensors opening and closing using solid state or mechanical relays. In this contemplated embodiment an existing controller  90  receives and acts upon equivalent contact closures that would be detected from the closures being hard wired to the door switches or a vehicle. The receiver  91 /controller  90  is typically installed in the vehicle engine compartment or underneath the vehicle where it is wired to the electrical system and battery  96  to power lights  95 , the left  93  and or right  94  motors. 
       FIG. 10  shows a block diagram of the code flow chart in the receiver. The receiver/controller listens to receive the messages  100  and determines if the received signal and the ID is good and or valid  101 . If the data is found to be invalid the microcontroller will not take any action and end  120  or return to a listen state. If the data is valid the microcontroller will further check to ensure that the command was sent twice  102 . Again if this check shows that the data is not valid the process will end  120 . Since that command is now considered valid the receiver will determine which door changed state  103  and will branch to either the driver  104  or passenger  107  door to determine the status of the door to command the controller to retract or extend  105 ,  106  the appropriate step. The four door transmitters, stores the message data, and determines the correct responses and end  120  or wait for an additional command. If a door on either side of the vehicle is open the receiver asserts the proper signal to the controller to engage the appropriate step motor and lower the step. A step will remain lowered until the receiver/controller receives messages indicating that both doors on a vehicle side are closed. 
       FIG. 11  is a front perspective view of a retracted step  200  and  FIG. 12  is a front perspective view of an extended step  200 . The step extends from an elevated position, as shown in  FIG. 11 , to a deployed position, as shown in  FIG. 12 . In the retracted position the bottom  210  of the step covers the majority of the mechanism to provide some protection from debris, water or other contamination from harming the mechanism. The motor  220  is arranged in a position to reduce fluid and moisture from entering into the motor or the gear transmission  221 . The motor  220  and the gear transmission  221  is sealed to prevent intrusion of moisture and water. The sealing prevents water from entering into the mechanism when the vehicle is exposed to rain, drives through a pool or water or the vehicle is fording a stream or other water way. The motor  220  is energized when the controller  90  receives a signal from one or more of the wireless transmitters  21 - 24  (previously shown and described). 
     As the motor  220  turns a gear reduction transmission  221  reduces the rotational speed and alters the rotational direction. The altered rotational directions enters into housing  230 . A portion of the rotational energy is transmitted along torsion shaft  250  to a second housing  240 . 
     The torsion bar  251  that is attached between the drive shaft of the motor  220  directly to the pivot point of the idler shaft that serves several functions. By driving the idler with the torsion bar  251 , both linkages  232  and  242  pull up together. This keeps the board  211  from hanging down and presenting an uneven appearance on the idler side. Twist  251  of the torsion bar  251  pulls up both linkages  232  and  242  evenly thus removing any misalignment between the motor linkage  221  and the idler  240  linkage. This prevents corner loading of the bushings and keeps the any noise from occurring because of the uneven bushing contact. Because of a better load distribution on the motor  220 , the torsion bar  251  will extend the life of the motor  220 . While the drawings show a motor linkage  221  and a single idler  240 , it is contemplated that more than one idler  240  could be incorporated to provide stability to a longer board  211 . 
     Both housing  230  and  240  have internal gears that convert the rotation to rotate rear tension members  232 ,  242  and front tension members  231 ,  241 . The rear tension members  232 ,  242  and the front tension members  231 ,  241  are connected to arms  233  and  243  respectively. These two sets of tension members are unequal length and as they rotate they move the step between the elevated position of  FIG. 11  and the deployed position of  FIG. 12 . Front and top views in  FIGS. 13-15  provide additional clarity of the deployment. 
       FIG. 13  is a top view of the retracted step  211 ,  FIG. 14  is a front view of the retracted step  211  and  FIG. 15  is a front view of the extended step  210 . In the retracted position, the step is brought under the vehicle. In the extended position the step allows a person to step onto the elongated platform  211  to essentially split the height from the ground to the floorboard to the vehicle where the extendable step is mounted. The motor  220  is shown connected to the transmission  221 . The transmission is mounted to the left housing  230 . A coupling  252  is connected to a transmission shaft  250  to a coupling  251  and then to the right housing  240 . The left housing  230  and the right housing  240  are bolted or otherwise secured to the underside or the frame of the vehicle. From the front view of  FIG. 15  the front tension members  231  and  241  are visible and connected to arms  233  and  243  respectively. Arms  233  and  243  are connected to the step platform  210  at  239  and  249 . 
       FIG. 16  is a sectional view of the retracted step cut from section  16 - 16  from  FIG. 14  and  FIG. 17  is a sectional view of the extended step cut from section  17 - 17  from  FIG. 15 . The gear transmission (not shown in this figure) connects to shaft  222  that is connected to the rear articulating arm  232 . 
     Shaft  222  is connected to the torsion bar  250  (not shown in this figure). In  FIG. 17 , counter-clockwise rotation  253  of the shaft extends the board  211 . This rotation of the shaft is transmitted down the torsion bar to the idler linkage. Driving the idler with the torsion bar, both linkages pull up together. In  FIG. 16 , clockwise rotation  252  of the shaft  222  is transmitted through the torsion bar  250  and raises the board  211  on both sides evenly. 
     As the rear articulating arm  232  rotates, the rotation applies forces to the arm  233  through the pivot pin  234 . The arm  233  is connected to the foot pad and also through pivot  235 . Pivot  235  is connected to the front arm  231  that is connected through pivot  236  on the housing  230 . This two-link of rotating arms  231  and  232  allows the foot pad to retract and rotate from the retracted to the extended position to expose the foot tread surface  211  or the back of the footpad platform  210 . The foot pad is connected with a fastener  209  to the arm  233 . In the retracted position a cushion  261  prevents vibration of the mechanism and the foot pad. In the extended position, a cushion  262  prevents vibration and provides some cushion as a person steps onto the platform  211 . 
       FIG. 18  is a perspective detail view of a portion of the motor mechanism from  FIG. 12 . In this figure the motor  220  is shown connected to the transmission  221 . The transmission  221  is connected to the housing  230 . From the other side of the housing  230  a coupling connector  252  is shown connected to the torsion arm shaft  250 . The rear articulating arm  232  and the front articulating arm  231  are connected to arm  233  with pins  234  and  235 . One end of the front arm  231  is connected with pivot pin  236 . The arm  233  is shown passing under the foot pad rail  211 . 
     Thus, specific embodiments of a retractable truck step with CAN bus interface have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims.