Patent Publication Number: US-2022219612-A1

Title: Vehicle and vehicle step apparatus with multiple drive motors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of and claims priority to and all benefits of U.S. patent application Ser. No. 15/931,474, filed May 13, 2020, which is a continuation of and claims priority to and all benefits of U.S. patent application Ser. No. 16/826,094, filed Mar. 20, 2020, now U.S. Pat. No. 11,021,108, which is a continuation of and claims priority to and all benefits of U.S. patent application Ser. No. 16/655,149, filed Oct. 16, 2019, now U.S. Pat. No. 10,618,472 B2, which is a continuation-in-part of and claims priority to and all benefits of U.S. patent application Ser. No. 15/200,940, filed Jul. 1, 2016, now U.S. Pat. No. 10,479,278, which claims priority to and all benefits of Chinese Patent Application 201510731518.7 filed on Oct. 30, 2015, Chinese Patent Application 201520860004.7 filed on Oct. 30, 2015, Chinese Patent Application 201510468824.6 filed on Aug. 4, 2015, Chinese Patent Application 201520576675.0 filed on Aug. 4, 2015, Chinese Patent Application 201510469324.4 filed on Aug. 4, 2015, and Chinese Patent Application 201520580148.7 filed on Aug. 4, 2015, all of which are hereby expressly incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present technology generally relate to the field of vehicle accessories, and more particularly, to a vehicle and a vehicle step apparatus with multiple drive motors. 
     BACKGROUND 
     In relative art, a vehicle step apparatus of a vehicle uses a driving mechanism (with motor) and a driven mechanism (without motor) to drive a step to move. That is to say, the vehicle step apparatus uses one motor to drive the step to move. Thus, all of load is borne by the one motor, such that the load of the one motor is very high. Thus, a requirement for performance of the one motor is very high, a manufacturing difficulty, a manufacturing cost and a failure rate of the one motor are increased and a working life of the one motor is shortened. 
     Moreover, because the driving mechanism has a function of self-lock and the driven mechanism does not have a function of self-lock, the driven mechanism is easy to droop, especially when the step is very long. 
     SUMMARY 
     The present technology seeks to solve at least one of the technical problems existing in the related art. Accordingly, a first aspect of the present technology provides a vehicle step apparatus. 
     A second aspect of the present technology provides a vehicle, which includes the above vehicle step apparatus. 
     Embodiments of a first aspect of the present technology provide a vehicle step apparatus, including: a first extending and retracting device comprising a first mounting bracket, a first step bracket, and a first arm assembly coupled between the first mounting bracket and the first step bracket and configured to drive the first step bracket to move between a first extended position and a first retracted position; a second extending and retracting device comprising a second mounting bracket, a second step bracket, and a second arm assembly coupled between the second mounting bracket and the second step bracket and configured to drive the second step bracket to move between a second extended position and a second retracted position; a step mounted on the first step bracket and the second step bracket; a first permanent magnet direct current motor mounted on the first mounting bracket and coupled with the first arm assembly to drive the first arm assembly; and a second permanent magnet direct current motor mounted on the second mounting bracket and coupled with the second arm assembly to drive the second arm assembly. 
     With the vehicle step apparatus according to embodiments of the first aspect of the present technology, the vehicle step apparatus is low in manufacturing cost, low in failure rate, and long in working life, has good synchronization, and drooping of the vehicle step apparatus can be prevented. 
     Embodiments of a second aspect of the present technology provide a vehicle, including: a first extending and retracting device comprising a first mounting bracket, a first step bracket, and a first arm assembly coupled between the first mounting bracket and the first step bracket and configured to drive the first step bracket to move between a first extended position and a first retracted position; a second extending and retracting device comprising a second mounting bracket, a second step bracket, and a second arm assembly coupled between the second mounting bracket and the second step bracket and configured to drive the second step bracket to move between a second extended position and a second retracted position; a step mounted on the first step bracket and the second step bracket; a first permanent magnet direct current motor mounted on the first mounting bracket and having a first motor shaft coupled with the first arm assembly; and a second permanent magnet direct current motor mounted on the second mounting bracket and having a second motor shaft coupled with the second arm assembly. 
     The vehicle is low in manufacturing cost, low in failure rate, and long in working life. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial exploded view of a vehicle according to an example embodiment of the present technology; 
         FIG. 2  is a schematic view of a first extending and retracting device and a second extending and retracting device of a vehicle step apparatus according to an example embodiment of the present technology, in which both the first extending and retracting device and the second extending and retracting device are in the form of four-link mechanism; 
         FIG. 3  is a schematic view of a first extending and retracting device and a second extending and retracting device of a vehicle step apparatus according to an example embodiment of the present technology, in which both the first extending and retracting device and the second extending and retracting device are in the form of five-link mechanism; 
         FIG. 4  is a schematic view of a first extending and retracting device and a second extending and retracting device of a vehicle step apparatus according to an example embodiment of the present technology, in which both the first extending and retracting device and the second extending and retracting device are in the form of six-link mechanism; 
         FIG. 5  is a schematic view of a vehicle step apparatus according to an example embodiment of the present technology; 
         FIG. 6  is an exploded view of a vehicle step apparatus according to an example embodiment of the present technology; 
         FIG. 7  is a partial exploded view of a vehicle step apparatus according to an example embodiment of the present technology; 
         FIG. 8  is a partial exploded view of a vehicle step apparatus according to an example embodiment of the present technology. 
         FIG. 9  is a schematic view of a vehicle step apparatus according to an example embodiment of the present technology. 
         FIG. 10  is a schematic diagram of a self-locking motor assembly according to an example embodiment of the present technology. 
         FIG. 11  is an exploded view of a self-locking motor assembly according to an example embodiment of the present technology. 
         FIG. 12  is a partial sectional view of a self-locking motor assembly according to an example embodiment of the present technology, which shows the interface between a worm reduction mechanism and a worm gear. 
         FIG. 13  is another partial sectional view of a self-locking motor assembly according to an example embodiment of the present technology, which shows the interface between a worm reduction mechanism and a worm gear. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will be made in detail to embodiments of the present technology. Embodiments of the present technology will be shown in drawings, in which the same or similar members and the members having same or similar functions are denoted by like reference numerals throughout the descriptions. The embodiments described herein according to drawings are explanatory and illustrative, not construed to limit the present technology. 
     The following description provides a plurality of embodiments or examples configured to achieve different structures of the present technology. In order to simplify the publication of the present technology, components and dispositions of the particular embodiment are described in the following, which are only explanatory and not construed to limit the present technology. In addition, the present technology may repeat the reference number and/or letter in different embodiments for the purpose of simplicity and clarity, and the repetition does not indicate the relationship of the plurality of embodiments and/or dispositions. Moreover, in description of the embodiments, the structure of the second characteristic “above” the first characteristic may include an embodiment formed by the first and second characteristic contacted directly, and also may include another embodiment formed between the first and the second characteristic, in which the first characteristic and the second characteristic may not contact directly. 
     In the description of the present technology, unless specified or limitation otherwise, it should be noted that, terms “mounted,” “coupled,” “coupled to,” and “coupled with” may be understood broadly, such as electronic connection or mechanical connection, inner communication between two members, direct connection or indirect connection via intermediary. Those having ordinary skills in the art should understand the specific meanings in the present technology according to specific situations. 
     At present, the vehicle industry is increasingly developing, and vehicle design is becoming more and more detailed and humanized. For some vehicles with high chassis, it is quite difficult for passengers to get on and off, especially for the elderly, the weak, the sick and pregnant passengers, who have difficulty getting on and off high chassis vehicles by themselves. 
     In order to address these challenges and problems, conventional methods in existing applications is to add a step (also referred to as a pedal or running board) to each passenger entry side of the vehicle. Some examples include a fixed (non-moveable) pedal, whereas other conventional methods include providing a moveable pedal, such as a manually retractable pedal or an electrically retractable pedal. Today, mainstream electric retractable steps in the market are driven by a one-sided single motor. Yet, a single drive motor requires high motor performance, which results in high manufacturing difficulty and high cost. 
     In some aspects, a vehicle step apparatus and a vehicle having a vehicle step apparatus in accordance with the disclosed embodiments are described. A vehicle  1000  according to embodiments of the present technology will be described with reference to the drawings. 
     As shown in  FIGS. 1-6 , the vehicle  1000  according to embodiments of the present technology includes a chassis  40  and a vehicle step apparatus  100 . The vehicle step apparatus  100  includes a first extending and retracting device  10   a , a second extending and retracting device  10   b , a step  20 , a first permanent magnet direct current motor  30   a  and a second permanent magnet direct current motor  30   b.    
     The first extending and retracting device  10   a  includes a first mounting bracket  11   a , a first step bracket  12   a  and a first arm assembly  13   a . The first arm assembly  13   a  is coupled between the first mounting bracket  11   a  and the first step bracket  12   a  and configured to drive the first step bracket  12   a  to move between a first extended position and a first retracted position. The first mounting bracket  11   a  is mounted on the chassis  40 . 
     The second extending and retracting device  10   b  includes a second mounting bracket  11   b , a second step bracket  12   b  and a second arm assembly  13   b . The second arm assembly  13   b  is coupled between the second mounting bracket  11   b  and the second step bracket  12   b  and configured to drive the second step bracket  12   b  to move between a second extended position and a second retracted position. The second mounting bracket  11   b  is mounted on the chassis  40 . 
     The step  20  is mounted on the first step bracket  12   a  and the second step bracket  12   b . The first permanent magnet direct current motor  30   a  is mounted on the first mounting bracket  11   a  and coupled with the first arm assembly  13   a  to drive the first arm assembly  13   a . The second permanent magnet direct current motor  30   b  is mounted on the second mounting bracket  11   b  and coupled with the second arm assembly  13   b  to drive the second arm assembly  13   b.    
     In some embodiments, the first permanent magnet direct current motor  30   a  has a first motor shaft  32   a  coupled with the first arm assembly  13   a . The second permanent magnet direct current motor  30   b  has a second motor shaft  32   b  coupled with the second arm assembly  13   b.    
     Thus, the first step bracket  12   a  is driven to move between the first extended position and the first retracted position by the first permanent magnet direct current motor  30   a  via the first arm assembly  13   a , and the second step bracket  12   b  is driven to move between the second extended position and the second retracted position by the second permanent magnet direct current motor  30   b  via the second arm assembly  13   b . In other words, the vehicle  1000  uses the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b  to drive the step  20  to extend and retract. 
     The vehicle  1000  uses two motors, i.e. the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b , to drive the step  20  to extend and retract, thus a load applied to the vehicle step apparatus  100  is distributed to the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b.    
     Thus, comparing to the vehicle step apparatus  100  employing only one motor, the load of the first permanent magnet direct current motor  30   a  is decreased so as to decrease a failure rate of the first permanent magnet direct current motor  30   a , and the load of the second permanent magnet direct current motor  30   b  is decreased so as to decrease a failure rate of the second permanent magnet direct current motor  30   b , thus prolonging a working life of the first permanent magnet direct current motor  30   a  and a working life of the second permanent magnet direct current motor  30   b.    
     Because the load of the first permanent magnet direct current motor  30   a  is low, a requirement for performance of the first permanent magnet direct current motor  30   a  is decreased so as to lower a manufacturing difficulty and a manufacturing cost of the first permanent magnet direct current motor  30   a.    
     Similarly, the load of the second permanent magnet direct current motor  30   b  is low, a requirement for performance of the second permanent magnet direct current motor  30   b  is decreased so as to lower a manufacturing difficulty and a manufacturing cost of the second permanent magnet direct current motor  30   b.    
     Because both the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b  have a function of self-lock, even the step  20  is very long, both the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b  can be prevented from drooping. 
     Additionally, for the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b , a rotational speed is related to a load. Thus, a rotational speed of a motor will be decreased due to an increasing load, and a rotational speed of a motor will be increased due to a decreasing load. 
     Thus, a rotational speed of the first permanent magnet direct current motor  30   a  is dynamically balanced with a rotational speed of the second permanent magnet direct current motor  30   b , so as to realize a synchronized motion of the first extending and retracting device  10   a  and the second extending and retracting device  10   b.    
     Thus, the vehicle step apparatus  100  according to embodiments of the present technology is low in manufacturing cost, low in failure rate, long in working life, and has good synchronization, and the vehicle step apparatus  100  can be prevented from drooping. 
     As shown in  FIG. 1 , in some embodiments, the vehicle  1000  includes the chassis  40  and the vehicle step apparatus  100 . The vehicle step apparatus  100  includes the first extending and retracting device  10   a , the second extending and retracting device  10   b , the step  20 , the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b.    
     The first extending and retracting device  10   a  includes the first mounting bracket  11   a , the first step bracket  12   a  and the first arm assembly  13   a . The first mounting bracket  11   a  is mounted on the chassis  40 . The first step bracket  12   a  is used to mount the step  20 . The first arm assembly  13   a  is coupled between the first mounting bracket  11   a  and the first step bracket  12   a  and configured to drive the first step bracket  12   a  to move between the first extended position and the first retracted position. 
     The second extending and retracting device  10   b  includes the second mounting bracket  11   b , the second step bracket  12   b  and the second arm assembly  13   b . The second mounting bracket  11   b  is mounted on the chassis  40 . The second step bracket  12   b  is used to mount the step  20 . The second arm assembly  13   b  is coupled between the second mounting bracket  11   b  and the second step bracket  12   b  and configured to drive the second step bracket  12   b  to move between the second extended position and the second retracted position. 
     Both the first mounting bracket  11   a  and the second mounting bracket  11   b  may be mounted on the chassis  40  in well-known manner. The step  20  is mounted on the first step bracket  12   a  and the second step bracket  12   b  by known means. 
     As shown in  FIG. 1 , the first arm assembly  13   a  includes a plurality of arms pivotally connected together. At least one arm of the first arm assembly  13   a  is coupled with the first mounting bracket  11   a , and at least one arm of the first arm assembly  13   a  is coupled with the first step bracket  12   a.    
     As shown in  FIG. 1 , the second arm assembly  13   b  includes a plurality of arms pivotally connected together. At least one arm of the second arm assembly  13   b  is coupled with the second mounting bracket  11   b , and at least one arm of the second arm assembly  13   b  is coupled with the second step bracket  12   b.    
     The first permanent magnet direct current motor  30   a  is mounted on the first mounting bracket  11   a , and the second permanent magnet direct current motor  30   b  is mounted on the second mounting bracket  11   b . As shown in  FIG. 5 , the first permanent magnet direct current motor  30   a  has the first motor shaft  32   a , and the second permanent magnet direct current motor  30   b  has the second motor shaft  32   b . The first motor shaft  32   a  of the first permanent magnet direct current motor  30   a  is coupled with an arm of the first arm assembly  13   a , and the second motor shaft  32   b  of the second permanent magnet direct current motor  30   b  is coupled with an arm of the second arm assembly  13   b.    
     As shown in  FIG. 6 , the vehicle step apparatus  100  further includes a first connection shaft  80   a  and a second connection shaft  80   b . The first connection shaft  80   a  is coupled with both the first motor shaft  32   a  and the first arm assembly  13   a , and the second connection shaft  80   b  is coupled with the second motor shaft  32   b  and the second arm assembly  13   b . In other words, first motor shaft  32   a  is coupled with the first arm assembly  13   a  via a first connection shaft  80   a , and the second motor shaft  32   b  is coupled with the second arm assembly  13   b  via a second connection shaft  80   b.    
     Alternatively, the first extending and retracting device  10   a  is configured in the form of four-link mechanism  10   al , five-link mechanism  10   a   2  or six-link mechanism  10   a   3 , and the second extending and retracting device  10   b  is configured in the form of the four-link mechanism  10   al , five-link mechanism  10   a   2  or six-link mechanism  10   a   3 . 
     It can be understood that a structure of the second extending and retracting device  10   b  may be the same as that of the first extending and retracting device  10   a . Thus, the first extending and retracting device  10   a  will be described below, and the second extending and retracting device  10   b  will be omitted here. 
     In an embodiment shown in  FIG. 2 , the first extending and retracting device  10   a  is in the form of four-link mechanism  10   al , and includes the first mounting bracket  11   a , the first step bracket  12   a  and the first arm assembly  13   a . The first arm assembly  13   a  is coupled between the first mounting bracket  11   a  and the first step bracket  12   a , and includes a first arm  131  and a second arm  132 . 
     A first end (an upper end) of the first arm  131  is pivotally coupled with the first mounting bracket  11   a  via a first connection pin  136 , and a second end (a lower end) of the first arm  131  is pivotally coupled with the first step bracket  12   a  via a second connection pin  137 . A first end (an upper end) of the second arm  132  is pivotally coupled with the first mounting bracket  11   a  via a third connection pin  138 , and a second end (a lower end) of the second arm  132  is pivotally coupled with the first step bracket  12   a  via a fourth connection pin  139 . 
     The first motor shaft  32   a  of the first permanent magnet direct current motor  30   a  is coupled with one of the first arm  131  and the second arm  132 . Thus, the first motor shaft  32   a  drives the one of the first arm  131  and the second arm  132  to rotate, thereby drives the first step bracket  12   a  to extend and retract. 
     In an embodiment shown in  FIG. 3 , the first extending and retracting device  10   a  is in the form of five-link mechanism  10   a   2 , and includes the first mounting bracket  11   a , the first step bracket  12   a  and the first arm assembly  13   a . The first arm assembly  13   a  is coupled between the first mounting bracket  11   a  and the first step bracket  12   a , and includes a first arm  131 , a second arm  132  and a third arm  133 . 
     A first end (an upper end) of the first arm  131  is pivotally coupled with the first mounting bracket  11   a  via a first connection pin  136 , and a second end (a lower end) of the first arm  131  is pivotally coupled with the first step bracket  12   a  via a second connection pin  137 . A first end (an upper end) of the second arm  132  is pivotally coupled with the first mounting bracket  11   a  via a third connection pin  138 , and a second end (a lower end) of the second arm  132  is pivotally coupled with a first end (an upper end) of the third arm  133  via a fifth connection pin  140 . A second end (a lower end) of the third arm  133  is pivotally coupled with the first step bracket  12   a  via a fourth connection pin  139 . 
     The first motor shaft  32   a  of the first permanent magnet direct current motor  30   a  is coupled with one of the first arm  131  and the second arm  132 . Thus, the first motor shaft  32   a  drives the one of the first arm  131  and the second arm  132  to rotate, thereby drives the first step bracket  12   a  to extend and retract. 
     In an embodiment shown in  FIG. 4 , the first extending and retracting device  10   a  is in the form of six-link mechanism  10   a   3 , and includes the first mounting bracket  11   a , the first step bracket  12   a  and the first arm assembly  13   a . The first arm assembly  13   a  is coupled between the first mounting bracket  11   a  and the first step bracket  12   a , and includes a first arm  131 , a second arm  132 , a third arm  133  and a fourth arm  134 . 
     A first end (an upper end) of the first arm  131  is pivotally coupled with the first mounting bracket  11   a  via a first connection pin  136 , and a second end (a lower end) of the first arm  131  is pivotally coupled with the first step bracket  12   a  via a second connection pin  137 . A first end (an upper end) of the second arm  132  is pivotally coupled with the first mounting bracket  11   a  via a third connection pin  138 . 
     A first end (an upper end) of the third arm  133  is pivotally coupled with a second end (a lower end) of the second arm  132  via a fifth connection pin  140 , and a second end (a lower end) of the third arm  133  is pivotally coupled with the first step bracket  12   a  via a fourth connection pin  139 . A first end of the fourth arm  134  is pivotally coupled with both of the second end of the second arm  132  and the first end of the third arm  133 , and a second end of the fourth arm  134  is pivotally coupled with a middle portion of the first arm  131  via a sixth connection pin  141 . 
     The first motor shaft  32   a  of the first permanent magnet direct current motor  30   a  is coupled with one of the first arm  131  and the second arm  132 . Thus, the first motor shaft  32   a  drives the one of the first arm  131  and the second arm  132  to rotate, thereby drives the first step bracket  12   a  to extend and retract. 
     The vehicle step apparatus according to other embodiments of the present technology will be described with reference to  FIG. 7  and  FIG. 8 . The difference between the vehicle step apparatus according to other embodiments and the above-mentioned vehicle step apparatus  100  will be described in detail. 
     In some other embodiments, the vehicle step apparatus  100  includes the first extending and retracting device  10   a , the second extending and retracting device  10   b , the step  20 , the first permanent magnet direct current motor  30   a , the second permanent magnet direct current motor  30   b , a first elastic member  50   a  and a second elastic member  50   b.    
     The first elastic member  50   a  is configured to elastically deform so as to store energy when the first permanent magnet direct current motor  30   a  drives the first step bracket  12   a  to move towards the first extended position, and to release energy so as to assist the first permanent magnet direct current motor  30   a  to drive the first extending and retracting device  10   a , i.e., to drive the first step bracket  12   a , when the first permanent magnet direct current motor  30   a  drives the first step bracket  12   a  to move towards the first retracted position. 
     The second elastic member  50   b  is configured to elastically deform so as to store energy when the second permanent magnet direct current motor  30   b  drives the second step bracket  12   b  to move towards the second extended position, and to release energy so as to assist the second permanent magnet direct current motor  30   b  to drive the second extending and retracting device  10   b , i.e., to drive the second step bracket  12   b , when the second permanent magnet direct current motor  30   b  drives the second step bracket  12   b  to move towards the second retracted position. 
     The load of the first permanent magnet direct current motor  30   a  during driving the step  20  to retract is bigger than that of the first permanent magnet direct current motor  30   a  during driving the step  20  to extend, so that the working current of the first permanent magnet direct current motor  30   a  during driving the step  20  to retract is larger than that of the first permanent magnet direct current motor  30   a  during driving the step  20  to extend. 
     The load of the second permanent magnet direct current motor  30   b  during driving the step  20  to retract is bigger than that of the second permanent magnet direct current motor  30   b  during driving the step  20  to extend, so that the working current of the second permanent magnet direct current motor  30   b  during driving the step  20  to retract is larger than that of the second permanent magnet direct current motor  30   b  during driving the step  20  to extend. 
     For the vehicle step apparatus, when the step  20  is extending, the first motor shaft  32   a  drives the first elastic member  50   a  to move and the second motor shaft  32   b  drives the second elastic member  50   b  to move. Thus, both the first elastic member  50   a  and the second elastic member  50   b  are caused to be elastically deformed so as to store energy. 
     When the step  20  is retracting, the first elastic member  50   a  releases energy to assist the first permanent magnet direct current motor  30   a  in driving the first extending and retracting device  10   a , so that the load and the working current of the first permanent magnet direct current motor  30   a  are decreased during driving the step  20  to retract. The second elastic member  50   b  releases energy to assist the second permanent magnet direct current motor  30   b  in driving the second extending and retracting device  10   b , so that the load and the working current of the second permanent magnet direct current motor  30   b  are decreased during driving the step  20  to retract. 
     Thus, the working current of the first permanent magnet direct current motor  30   a  in the processes of driving the step  20  to retract is generally consistent with that of the first permanent magnet direct current motor  30   a  in the processes of driving the step  20  to extend; and the working current of the second permanent magnet direct current motor  30   b  in the processes of driving the step  20  to retract is generally consistent with that of the second permanent magnet direct current motor  30   b  in the processes of driving the step  20  to extend. Thus, the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b  are protected effectively, and the working life of the first permanent magnet direct current motor  30   a  and that of the second permanent magnet direct current motor  30   b  are prolonged. 
     In some embodiments, the first elastic member  50   a  includes a first scroll spring, and the second elastic member  50   b  includes a second scroll spring. A first end  51   a  of the first scroll spring is fixed, and a second end  52   a  of the first scroll spring is driven by the first motor shaft  32   a  of the first permanent magnet direct current motor  30   a  so as to twist. A first end  51   b  of the second scroll spring is fixed, and a second end  52   b  of the second scroll spring is driven by the second motor shaft  32   b  of the second permanent magnet direct current motor  30   b  so as to twist. 
     As shown in  FIG. 7  and  FIG. 8 , an end of the outermost ring of the first scroll spring is bent outwards to form the first end  51   a , and an end of an innermost ring of the first scroll spring is bent inwards to form the second end  52   a . The first end  51   a  includes the end of the outermost ring of the first scroll spring and a portion of the outermost ring coupled with the end of the outermost ring. The second end  52   a  includes the end of the innermost ring of the first scroll spring and a portion of the innermost ring coupled with the end of the innermost ring. 
     An end of the outermost ring of the second scroll spring is bent outwards to form the first end  51   b , and an end of an innermost ring of the second scroll spring is bent inwards to form the second end  52   b . The first end  51   b  includes the end of the outermost ring of the second scroll spring and a portion of the outermost ring coupled with the end of the outermost ring. The second end  52   b  includes the end of the innermost ring of the second scroll spring and a portion of the innermost ring coupled with the end of the innermost ring. 
     The first end  51   a  of the first scroll spring and the first end  51   b  of the second scroll spring are fixed with respect to the bracket  11   a  and the bracket  11   b , respectively. When the step  20  is extending, the second end  52   a  of the first scroll spring rotates along with the first motor shaft  32   a  and is twisted tightly to store energy, and the second end  52   b  of the second scroll spring rotates along with the second motor shaft  32   b  and is twisted tightly to store energy. 
     When the step  20  is retracting, the second end  52   a  of the first scroll spring rotates along with the first motor shaft  32   a  and releases energy so as to assist the first permanent magnet direct current motor  30   a  to drive the first extending and retracting device  10   a  to retract, and the second end  52   b  of the second scroll spring rotates along with the second motor shaft  32   b  and releases energy so as to assist the second permanent magnet direct current motor  30   b  to drive the second extending and retracting device  10   b  to retract. 
     However, the present technology is not limited to this, both the first elastic member  50   a  and the second elastic member  50   b  may be a spring leaf, a disk spring or other units or parts easy to be deformed elastically. 
     As shown in  FIG. 7  and  FIG. 8 , the vehicle step apparatus  100  further includes a first cover  70   a , a first connection plate  60   a , a second cover  70   b  and a second connection plate  60   b.    
     A first recess  312   a  is formed in a first motor casing  31   a  of the first permanent magnet direct current motor  30   a , and the first cover  70   a  covers the first recess  312   a  to define a first cavity. The first connection plate  60   a  is mounted within the first cavity and driven by the first motor shaft  32   a  of the first permanent magnet direct current motor  30   a  to rotate. The first scroll spring is mounted within the first cavity, the first end  51   a  of the first scroll spring is fixed in the first cover  70   a , and the second end  52   a  of the first scroll spring is coupled with the first connection plate  60   a.    
     A second recess  312   b  is formed in a second motor casing  31   b  of the second permanent magnet direct current motor  30   b , and the second cover  70   b  covers the second recess  312   b  to define a second cavity. The second connection plate  60   b  is mounted within the second cavity and driven by the second motor shaft  32   b  of the second permanent magnet direct current motor  30   b  to rotate. The second scroll spring is mounted within the second cavity, the first end  51   b  of the second scroll spring is fixed in the second cover  70   b , and the second end  52   b  of the second scroll spring is coupled with the second connection plate  60   b.    
     As shown in  FIG. 7  and  FIG. 8 , the first cover  70   a  is detachably fastened to the first motor casing  31   a  of the first permanent magnet direct current motor  30   a . A first limitation notch  71   a  is formed in the first cover  70   a , a first limitation column  111   a  is formed on the first mounting bracket  11   a , the first limitation column  111   a  is fitted within the first limitation notch  71   a  to mount the first cover  70   a  on the first mounting bracket  11   a . The first end  51   a  of the first scroll spring is fitted over the first limitation column  111   a.    
     The second cover  70   b  is detachably fastened to the second motor casing  31   b  of the second permanent magnet direct current motor  30   b . A second limitation notch  71   b  is formed in the second cover  70   b , a second limitation column  111   b  is formed on the second mounting bracket  11   b , the second limitation column  111   b  is fitted within the second limitation notch  71   b  to mount the second cover  70   b  on the second mounting bracket  11   b . The first end  51   b  of the second scroll spring is fitted over the second limitation column  111   b.    
     Specifically, the first connection plate  60   a  is configured as a substantially circular plate. The first connection plate  60   a  is disposed within the first cavity, and the first connection plate  60   a  defines a first surface opposing to the first recess  312   a  and a second surface opposing to the first cover  70   a . The first connection plate  60   a  is coupled with the first motor shaft  32   a  directly or indirectly, so that the first connection plate  60   a  can rotate under the drive of the first motor shaft  32   a . The first scroll spring is fitted over the first connection plate  60   a , and the second end  52   a  of the first scroll spring is connected to the first connection plate  60   a  and rotates along with the first connection plate  60   a  in a same direction. 
     The second connection plate  60   b  is configured as a substantially circular plate. The second connection plate  60   b  is disposed within the second cavity, and the second connection plate  60   b  defines a first surface opposing to the second recess  312   b  and a second surface opposing to the second cover  70   b . The second connection plate  60   b  is coupled with the second motor shaft  32   b  directly or indirectly, so that the second connection plate  60   b  can rotate under the drive of the second motor shaft  32   b . The second scroll spring is fitted over the second connection plate  60   b , and the second end  52   b  of the second scroll spring is connected to the second connection plate  60   b  and rotates along with the second connection plate  60   b  in a same direction. 
     Therefore, the first scroll spring and the second scroll spring can be integrated in the first permanent magnet direct current motor  30   a  and the second permanent magnet direct current motor  30   b  respectively so as to decrease transmission loss and make the structure of the vehicle step apparatus  100  more compactly. 
     The first connection plate  60   a , the second connection plate  60   b , the first cover  70   a , the second cover  70   b , the first recess  312   a  and the second recess  312   b  may have a circular shape or an oval shape. 
     A number of each of the first limitation notch  71   a , the first limitation column  111   a , the second limitation notch  71   b  and the second limitation column  111   b  is not limited to two, and when there are more than two first limitation notches  71   a  and two second limitation notches  71   b , the first limitation notches  71   a  are provided and evenly spaced apart from each other along a circumferential direction of the first cover  70   a , and the second limitation notches  71   b  are provided and evenly spaced apart from each other along a circumferential direction of the second cover  70   b.    
     A first catch groove  61   a  is formed in an outer circumferential surface of the first connection plate  60   a , and the second end  52   a  of the first scroll spring is inserted into and fitted within the first catch groove  61   a . The first connection plate  60   a  is fitted over the first connection shaft  80   a  and coupled with the first connection shaft  80   a  via spline coupling. 
     A second catch groove  61   b  is formed in an outer circumferential surface of the second connection plate  60   b , and the second end  52   b  of the second scroll spring is inserted into and fitted within the second catch groove  61   b . The second connection plate  60   b  is fitted over the second connection shaft  80   b  and coupled with the second connection shaft  80   b  via spline coupling. 
     As shown in  FIG. 7 , the first catch groove  61   a  extends along a radial direction of the first connection plate  60   a , and the second catch groove  61   b  extends along a radial direction of the second connection plate  60   b . A center of each of the first connection plate  60   a , the first motor shaft  32   a , the second connection plate  60   b  and the second motor shaft  32   b  has a spline hole. Each of the first connection shaft  80   a  and the second connection shaft  80   b  has an external spline. 
     The first motor shaft  32   a  drives the first connection shaft  80   a  and the first connection plate  60   a  to rotate, and the second end  52   a  of the first scroll spring fixed on the first connection plate  60   a  rotates along with the first connection plate  60   a . The second motor shaft  32   b  drives the second connection shaft  80   b  and the second connection plate  60   b  to rotate, and the second end  52   b  of the second scroll spring fixed on the second connection plate  60   b  rotates along with the second connection plate  60   b.    
     Thus, the first scroll spring and the second scroll spring are gradually rolled up tightly, thus resulting in a simple and compact structure. In addition, the first connection shaft  80   a  is coupled with the first motor shaft  32   a  and the first connection plate  60   a  via spline connection so as to ensure driving force transmission and make installation and disassembly to be easy, and the second connection shaft  80   b  is coupled with the second motor shaft  32   b  and the second connection plate  60   b  via spline connection so as to ensure driving force transmission and make installation and disassembly to be easy. 
     As shown in  FIG. 7 , a first mounting hole  311   a  is formed in the first motor casing  31   a , and the first limitation column  111   a  is passed through the first mounting hole  311   a . A first threaded hole  1111   a  is formed in the first limitation column  111   a , and the first permanent magnet direct current motor  30   a  is mounted on the first mounting bracket  11   a  via a first bolt  90   a  fitted within the first threaded hole  1111   a.    
     A second mounting hole  311   b  is formed in the second motor casing  31   b , and the second limitation column  111   b  is passed through the second mounting hole  311   b . A second threaded hole  1111   b  is formed in the second limitation column  111   b , and the second permanent magnet direct current motor  30   b  is mounted on the second mounting bracket  11   b  via a second bolt  90   b  fitted within the second threaded hole  1111   b.    
     The first limitation column  111   a  is passed through the first limitation notch  71   a  and bears against the first motor casing  31   a . The first mounting hole  311   a  of the first motor casing  31   a  is opposite to the first threaded hole  1111   a  of the first limitation column  111   a . The first bolt  90   a  is passed through the first mounting hole  311   a  and is fitted within the first threaded hole  1111   a  so as to mount the first motor casing  31   a  to the first mounting bracket  11   a.    
     The second limitation column  111   b  is passed through the second limitation notch  71   b  and bears against the second motor casing  31   b . The second mounting hole  311   b  of the second motor casing  31   b  is opposite to the second threaded hole  1111   b  of the second limitation column  111   b . The second bolt  90   b  is passed through the second mounting hole  311   b  and is fitted within the second threaded hole  1111   b  so as to mount the second motor casing  31   b  to the second mounting bracket  11   b.    
     Some example embodiments in accordance with the disclosed vehicle step apparatus are described below. 
     In an example embodiment in accordance with the present technology (example A1), a motorized step for a vehicle includes a first extending and retracting device comprising a first mounting bracket attachable to a chassis of a vehicle, a first step bracket, and a first arm assembly coupled to the first mounting bracket and the first step bracket and configured to drive the first step bracket to move between a first extended position and a first retracted position; a second extending and retracting device comprising a second mounting bracket attachable to the chassis of the vehicle, a second step bracket, and a second arm assembly coupled to the second mounting bracket and the second step bracket and configured to drive the second step bracket to move between a second extended position and a second retracted position, wherein the second extended position is aligned with the first extended position, and wherein the second retracted position is aligned with the first retracted position; a step coupled to the first step bracket and the second step bracket; a first permanent magnet direct current motor coupled with the first arm assembly to drive the first arm assembly; and a second permanent magnet direct current motor coupled with the second arm assembly to drive the second arm assembly, wherein the first permanent magnet direct current motor and the second permanent magnet direct current motor are configured to drive the first arm assembly and the second arm assembly, respectively, in unison and with synchronized motion as the step extends and retracts. 
     Example A2 includes the motorized vehicle step of example A1, wherein the first permanent magnet direct current motor comprises a first motor shaft that is coupled with a first connection shaft of the first arm assembly, and wherein the second permanent magnet direct current motor comprises a second motor shaft that is coupled with a second connection shaft of the second arm assembly. 
     Example A3 includes the motorized vehicle step of example A2, including a first elastic member configured to elastically deform so as to store energy when the first permanent magnet direct current motor drives the first step bracket to move towards the first extended position, and to release energy so as to assist the first permanent magnet direct current motor to drive the first extending and retracting device when the first permanent magnet direct current motor drives the first step bracket to move towards the first retracted position; and a second elastic member configured to elastically deform so as to store energy when the second permanent magnet direct current motor drives the second step bracket to move towards the second extended position, and to release energy so as to assist the second permanent magnet direct current motor to drive the second extending and retracting device when the second permanent magnet direct current motor drives the second step bracket to move towards the second retracted position. 
     Example A4 includes the motorized vehicle step of example A3, wherein the first elastic member comprises a first spring defining a fixed first end and a second end driven by the first motor shaft of the first permanent magnet direct current motor so as to change shape; wherein the second elastic member comprises a second spring defining a fixed first end and a second end driven by the second motor shaft of the second permanent magnet direct current motor so as to change shape. 
     Example A5 includes the motorized vehicle step of example A4, wherein the first spring and the second spring each include one of a scroll spring, a spring leaf, or a disk spring. 
     Example A6 includes the motorized vehicle step of example A4, wherein the first spring includes a first scroll spring, and the second spring includes a second scroll spring, the motorized vehicle step further including a first cover and a first connection plate, wherein a first recess is formed in a casing of the first permanent magnet direct current motor, and the first cover covers the first recess to define a first cavity, the first connection plate is mounted within the first cavity and driven by the first motor shaft of the first permanent magnet direct current motor to rotate, wherein the first scroll spring is mounted within the first cavity, the first end of the first scroll spring is fixed in the first cover, and the second end of the first scroll spring is coupled with the first connection plate; and a second cover and a second connection plate, wherein a second recess is formed in a casing of the second permanent magnet direct current motor, and the second cover covers the second recess to define a second cavity, the second connection plate is mounted within the second cavity and driven by the second motor shaft of the second permanent magnet direct current motor to rotate, wherein the second scroll spring is mounted within the second cavity, the first end of the second scroll spring is fixed in the second cover, and the second end of the second scroll spring is coupled with the second connection plate. 
     Example A7 includes the motorized vehicle step of example A1, wherein the first extending and retracting device includes a four-link mechanism, where the first arm assembly includes a first arm defining a first end pivotally coupled with the first mounting bracket, and a second end pivotally coupled with the first step bracket; and a second arm defining a first end pivotally coupled with the first mounting bracket, and a second end pivotally coupled with the first step bracket, wherein the first permanent magnet direct current motor is coupled with one of the first arm or the second arm. 
     Example A8 includes the motorized vehicle step of example A1, wherein the first extending and retracting device includes a five-link mechanism, where the first arm assembly includes a first arm defining a first end pivotally coupled with the first mounting bracket, and a second end pivotally coupled with the first step bracket; a second arm defining a first end pivotally coupled with the first mounting bracket, and a second end; and a third arm defining a first end pivotally coupled with the second end of the second arm, and a second end pivotally coupled with the first step bracket, wherein the first permanent magnet direct current motor is coupled with one of the first arm or the second arm. 
     Example A9 includes the motorized vehicle step of example A1, wherein the first extending and retracting device includes a six-link mechanism, where the first arm assembly includes a first arm defining a first end pivotally coupled with the first mounting bracket, and a second end pivotally coupled with the first step bracket; a second arm defining a first end pivotally coupled with the first mounting bracket, and a second end; a third arm defining a first end pivotally coupled with the second end of the second arm, and a second end pivotally coupled with the first step bracket; and a fourth arm defining a first end pivotally coupled with both of the second end of the second arm and the first end of the third arm, and a second end pivotally coupled with a middle portion of the first arm, wherein the first permanent magnet direct current motor is coupled with one of the first arm or the second arm. 
     Example A10 includes the motorized vehicle step of example A1, wherein the first permanent magnet direct current motor is coupled to the first mounting bracket, and the second permanent magnet direct current motor is coupled to the second mounting bracket. 
     Example A11 includes the motorized vehicle step of example A1, wherein the first permanent magnet direct current motor and the second permanent magnet direct current motor are operable to self-lock. 
     Example A12 includes the motorized vehicle step of example A1, wherein the first permanent magnet direct current motor and the second permanent magnet direct current motor are operable to drive the first arm assembly and the second arm assembly, respectively, at rotational speed that is related to a load, such that the rotational speed will be decreased due to an increasing load and the rotational speed will be increased due to a decreasing load. 
     In an example embodiment in accordance with the present technology (example A13), a motorized step for a vehicle includes a dual drive mechanism assembly, comprising a first extending and retracting device and a second extending and retracting device, the first extending and retracting device comprising a first mounting bracket attachable to a chassis of a vehicle, a first step bracket, and a first arm assembly coupled to the first mounting bracket and the first step bracket and configured to drive the first step bracket to move between a first extended position and a first retracted position, the second extending and retracting device comprising a second mounting bracket attachable to the chassis of the vehicle, a second step bracket, and a second arm assembly coupled to the second mounting bracket and the second step bracket and configured to drive the second step bracket to move between a second extended position and a second retracted position, wherein the second extended position is aligned with the first extended position, and wherein the second retracted position is aligned with the first retracted position; a step coupled to the first step bracket and the second step bracket; and a dual motor assembly comprising a first motor and a second motor, the first motor coupled with the first arm assembly to drive the first arm assembly, and the second motor coupled with the second arm assembly to drive the second arm assembly, wherein the dual motor assembly is operable to cause the step to extend and retract in a balanced orientation where neither side of the step is drooping with respect to the other based on the first motor and the second motor configured to drive the first arm assembly and the second arm assembly, respectively, in unison and with synchronized motion. 
     Example A14 includes the motorized vehicle step of example A13, wherein the dual drive mechanism assembly includes a four-link mechanism for one or both of the first extending and retracting device and the second extending and retracting device, wherein the four-link mechanism includes a first arm defining a first end to pivotally couple with a mounting bracket of the dual drive mechanism assembly, and a second end to pivotally couple with a step bracket of the dual drive mechanism assembly; and a second arm defining a first end to pivotally couple with the mounting bracket, and a second end to pivotally couple with the step bracket, wherein one of the first arm or the second arm is coupled with a motor of the dual motor assembly. 
     Example A15 includes the motorized vehicle step of example A13, wherein the dual drive mechanism assembly includes a five-link mechanism for one or both of the first extending and retracting device and the second extending and retracting device, wherein the five-link mechanism includes a first arm defining a first end to pivotally couple with a mounting bracket of the dual drive mechanism assembly, and a second end to pivotally couple with a step bracket of the dual drive mechanism assembly; a second arm defining a first end to pivotally couple with the mounting bracket, and a second end; and a third arm defining a first end pivotally coupled with the second end of the second arm, and a second end to pivotally couple with the step bracket, wherein one of the first arm or the second arm is coupled with a motor of the dual motor assembly. 
     Example A16 includes the motorized vehicle step of example A13, wherein the dual drive mechanism assembly includes a six-link mechanism for one or both of the first extending and retracting device and the second extending and retracting device, wherein the six-link mechanism includes a first arm defining a first end to pivotally couple with a mounting bracket of the dual drive mechanism assembly, and a second end to pivotally couple with a step bracket of the dual drive mechanism assembly; a second arm defining a first end to pivotally couple with the mounting bracket, and a second end; a third arm defining a first end pivotally coupled with the second end of the second arm, and a second end to pivotally couple with the step bracket; and a fourth arm defining a first end pivotally coupled with both of the second end of the second arm and the first end of the third arm, and a second end pivotally coupled with a middle portion of the first arm, wherein one of the first arm or the second arm is coupled with a motor of the dual motor assembly. 
     Example A17 includes the motorized vehicle step of example A13, wherein the first motor includes a first motor shaft that is coupled with a first connection shaft of the first arm assembly, and wherein the second motor comprises a second motor shaft that is coupled with a second connection shaft of the second arm assembly. 
     Example A18 includes the motorized vehicle step of example A17, including a first elastic member configured to elastically deform so as to store energy when the first motor drives the first step bracket to move towards the first extended position, and to release energy so as to assist the first motor to drive the first extending and retracting device when the first motor drives the first step bracket to move towards the first retracted position; and a second elastic member configured to elastically deform so as to store energy when the second motor drives the second step bracket to move towards the second extended position, and to release energy so as to assist the second motor to drive the second extending and retracting device when the second motor drives the second step bracket to move towards the second retracted position. 
     Example A19 includes the motorized vehicle step of example A18, wherein the first elastic member comprises a first spring defining a fixed first end and a second end driven by the first motor shaft of the first motor so as to change shape; wherein the second elastic member comprises a second spring defining a fixed first end and a second end driven by the second motor shaft of the second motor so as to change shape. 
     Example A20 includes the motorized vehicle step of example A19, wherein the first spring and the second spring each include one of a scroll spring, a spring leaf, or a disk spring. 
     In some aspects, a vehicle step apparatus with dual drive motors in accordance with the disclosed embodiments is described. 
     Motorized vehicle steps typically must carry substantial loads and therefore may be made of materials of relatively large weight and size, thereby putting demands on the motor. Conventional motorized vehicle step devices may include multiple extension-retraction devices coupled to the step with one motor driving one of the extension-retraction devices. A single drive motor requires high motor performance, which results in high manufacturing difficulty and high cost. 
     Conventional single motor-driven vehicle step devices do not provide durability and reliability of the motorized vehicle step, particularly after continuous uses. For example, after a conventional single motor-driven vehicle step device is used for a period of time (e.g., hundreds of extensions and retractions), the driven end of the step may sag relative to the motor-driving end of the step, which can create a larger gap between the driven end of the step and the vehicle body than the gap between the driving end of the step and the vehicle body, thus affecting the appearance and performance of the vehicle step device. Furthermore, when the driven end is not locked by the motor assembly, the failure rate of the motor of the motorized vehicle step is increased after the vehicle step vibrates for a long time, and the service life of the product is shortened. Yet it is challenging to provide a motorized vehicle step device that can employ multiple (e.g., two or more) motors to distribute the drive power for extending and retracting the step that sufficiently addresses and solves these problems with conventional systems. 
     Disclosed are devices and methods for driving a vehicle step assembly by multiple (e.g. two or more) motors by a motor assembly capable of self-locking of the of the vehicle step assembly. 
     As shown in  FIGS. 9-13 , a vehicle step apparatus  100 ′ according to embodiments of the present technology includes a step  20 ′ and a first extending and retracting device  10   a ′ and a second extending and retracting device  10   b ′, which are driven by a first motor assembly  900   a  and a second motor assembly  900   b , respectively, each capable of self-locking and sometimes referred to as self-locking motor assemblies. In some embodiments, the first motor assembly  900   a  and the second motor assembly  900   b  each include a worm mechanism including a worm gear and worm to drive the worm gear based on rotation of the worm rotated by a worm shaft coupled to a motor of the respective motor assembly, where the worm is structured to have a lead angle greater than the friction angle to create a self-locking effect of the respective motor assembly, such that only the motor can drive rotation of the shaft in either rotational directions while preventing the shaft from rotation in the other non-driven rotational direction. In this manner, the first motor assembly  900   a  and the second motor assembly  900   b  are each capable of self-locking in reversible directions, e.g., reverse self-locking, depending on which direction the motor is driving the worm mechanism. This is illustrated in greater detail in  FIGS. 9-13 . 
       FIG. 9  shows a schematic view of the vehicle step apparatus  100 ′. The first extending and retracting device  10   a ′ includes a first mounting bracket  11   a ′ that is attachable to the underside of a vehicle (e.g., chassis), a first step bracket  12   a ′ and a first arm assembly  13   a ′, where the first arm assembly  13   a ′ is coupled between the first mounting bracket  11   a ′ and the first step bracket  12   a ′ and configured to drive the first step bracket  12   a ′ to move between a first extended position and a first retracted position. Similarly, the second extending and retracting device  10   b ′ includes a second mounting bracket  11   b ′ that is attachable to the underside of a vehicle (e.g., chassis), a second step bracket  12   b ′ and a second arm assembly  13   b ′, where the second arm assembly  13   b ′ is coupled between the second mounting bracket  11   b ′ and the second step bracket  12   b ′ and configured to drive the second step bracket  12   b ′ to move between a second extended position and a second retracted position. In operations of the vehicle step apparatus  100 ′, the respective arm assemblies  13   a ′ and  13   b ′ of the first extending and retracting device  10   a ′ and the second extending and retracting device  10   b ′ are driven in synchrony such that the respective step brackets  12   a ′ and  12   b ′ are aligned with each other during movement and in the first extended position and the second extended position, respectively. 
     The first self-locking motor assembly  900   a  is coupled with an arm of the first arm assembly  13   a ′ (via a shaft, not shown), and the second self-locking motor assembly  900   b  is coupled with an arm of the second arm assembly  13   b ′ (via a shaft, not shown). The first self-locking motor assembly  900   a  is able to mount on the first mounting bracket  11   a ′, and the second self-locking motor assembly  900   b  is able to mount on the second mounting bracket  11   b′.    
     Each extending and retracting device  10   a ′ and  10   b ′ of the vehicle step apparatus  100 ′ is equipped with a drive motor assembly capable of a reverse self-locking functionality based on configuration of the motor assembly. In implementations, for example, after receiving a movement instruction (e.g., from a controller device), both of the self-locking motor assemblies  900   a  and  900   b  operate synchronously, driving the respective extending and retracting devices  10   a ′ and  10   b ′ to operate according to a predetermined trajectory, thus driving the step  20  to operate between the extended position and the retracted position. When the respective extending and retracting devices  10   a ′ and  10   b ′ are in the retracted state, due to the reverse self-locking function of the motor assembly, the step  20  is located in the retracted position and held into the position without any further movement, e.g., the step  20  does not vibrate or result in sagging or drooping after several usages. For example, the reverse self-locking to maintain the step  20  in the retracted position (without vibrating, sagging or drooping) and the consistency in movement can occur even after thousands of operations of the vehicle step apparatus  100 ′ to move the step  20  between the extended and retracted positions. 
       FIGS. 10 and 11  show diagrams depicting an outside perspective view and an exploded view, respectively, of an example embodiment of the self-locking motor assembly  900 . The self-locking motor assembly  900  includes a motor  911  and a worm gear  915  (both shown in  FIG. 11 ) that collectively are encased in a motor housing  904  and a worm gear casing  909 . In some examples, the motor  911  can include a DC permanent magnet motor, like the permanent magnet direct current motor  30  discussed earlier. The motor  911  includes a stator portion and a rotor portion, which the rotor includes a worm  911 A at the end of a rotor shaft  911 B (shown in  FIG. 12 ), and which the stator of the motor  911  couples to an armature  906 . The worm  911 A engages with the teeth of the worm gear  915  so as to cause rotation of the worm gear  915  to in turn cause a planetary wheel drive assembly  920  to rotate, e.g., via interface between a gear box bearing  917  from the worm gear  915  to a planetary shaft  921  of the planetary wheel drive assembly  920 . The worm gear  915  is encased within the worm gear casing  909 , in which a first opening of the worm gear casing  909  can be partially covered by a cover  910 . The planetary wheel drive assembly  920  is encased within the worm gear casing  909  on the other side, in which a second opening of the worm gear casing  909  can be partially covered by a cover  925 . 
     The motor assembly  900  includes the worm gear  915  and the worm reduction mechanism (e.g., worm  911 A coupled to the stator of the motor  911  via shaft  911 B), which enables the motor assembly to have a reverse self-locking function. In multiple-motorized systems, there is a hidden danger of each motor operating out of synch, which in the case of the two motors in the dual-motor driving mode of vehicle step apparatus  100 ′, could lead to misalignment of the step brackets and result in sagging or drooping of the step. The worm gear  915  and worm reduction mechanism  911 A can provide the motor assembly  900  with a means to synchronize two (or more) permanent magnet direct current motors that drive components (e.g., arm assemblies  13   a ′ and  13   b ′) without having to share a common shaft. 
     For example, a motor having a high rotating speed has an increased load and a decreased rotating speed, whereas a motor having a low rotating speed has a decreased load and an increased rotating speed. Thus, rotating speeds of the two mechanisms reach dynamic balance, thereby realizing the motion synchronization of the two mechanisms. 
     Referring to  FIG. 11 , additional components of the example embodiment of the motor assembly  900  are shown, but it is understood that some of these components are not required for providing a self-locking capability. As shown in  FIG. 11 , the example embodiment of the self-locking motor assembly  900  can include a socket  908  coupled to the armature  906 , e.g., which can be attached by hexagon socket head cap screws  907 . The socket  908  can be connected to the motor housing  904  and/or worm gear casing  909  by a connector  905 . The end of the rotor of motor  911  (with the worm  911 A) can be encased in the worm gear casing  909  at worm casing region  909 A, in which an opening of the worm casing region  909 A can be secured by adjustment screw assembly  914 . The end of the rotor can be coupled to a gear box ball bearing  913  and an elastic ring  912 . The gear box bearing  917  can interface with the planetary shaft  921  via an O-ring  918  and adjusting washer  919 . The planetary wheel drive assembly  920  can include a plurality of planetary gear wheels  920  that interface with the teeth of the planetary output shaft  921 , and a plurality of planetary axels  923  and an output planet carrier component  924 . The planetary shaft  921  can be secured by a shaft circlip  926 . 
       FIGS. 12 and 13  show partial sectional views of the self-locking motor assembly  900 , which shows the interface between a worm reduction mechanism and a worm gear. 
     In some embodiments, the vehicle step apparatus  100 ′ can also include the first elastic member  50   a  and the second elastic member  50   b  to further augment the drive capability of the first motor assembly  900   a  and the second motor assembly  900   b , respectively. For example, similar to that shown in  FIG. 7 , the first elastic member  50   a  can be coupled between the first mounting bracket  11   a ′ and the first motor assembly  900   a ; and the second elastic member  50   b  can be coupled between the second mounting bracket  11   b ′ and the second motor assembly  900   b . Such embodiments of the vehicle step apparatus  100 ′ can include the example embodiments discussed above for the first elastic member  50   a  and the second elastic member  50   b , e.g., such as the embodiments pertaining to a spring leaf, a disk spring or other elastically deformable component and/or to a cover and/or connection plate. 
     The disclosed multi-motorized vehicle step device, such as the example vehicle step apparatus  100 ′, provide several advantages over conventional retractable steps, including but not limited to: (1) long service life of the device, e.g., as the multiple (dual) motor driving mode greatly improves the service life of the product and reduces the motor failure rate; (2) the structure is not prone to sag or droop, e.g., as both motors have a self-locking function (e.g., reversible self-locking) to prevent detrimental movements in the extended and retracted positions; (3) reduced costs of the motor system, e.g., as the dual motor driving mode reduces the requirements for motor performance, thereby allowing a motor that is more simple in manufacturing and lower in cost (such that the comprehensive cost of the double motor driving mode and the single motor driving mode is similar if not equivalent); and (4) the dual motor driving mode is more suitable for vehicles with longer and heavier steps. 
     Reference throughout this specification to “an embodiment,” “some embodiments,” “an example,” “a specific example,” or “some examples,” means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. The appearances of the phrases throughout this specification are not necessarily referring to the same embodiment or example of the present invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples. 
     Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that the above embodiments cannot be construed to limit the present invention, and changes, alternatives, and modifications can be made in the embodiments without departing from spirit, principles and scope of the present invention. 
     While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments. 
     Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.