Patent Publication Number: US-9849900-B2

Title: Driving assist unit of truck

Description:
TECHNICAL FIELD 
     The present invention relates to a driving assist unit of a truck for assisting a driving force to be applied to the truck by a worker. 
     BACKGROUND ART 
     Generally, when a heavy cargo is loaded on a truck used in a factory or the like, the worker needs to push the truck with a large force at start of conveyance, which is a heavy labor. 
     JP2008-126900A discloses an electric truck provided with a driving device for driving the truck through a connecting member. In this electric truck, the driving device is connected to the truck through the connecting member with one end connected to the truck, the connecting member being capable of swing around a horizontal axis. 
     SUMMARY OF INVENTION 
     However, in the electric truck described in JP2008-126900A, one end of the connecting member is fastened to a rear end portion of a deck of the truck with a bolt and a nut, while the other end of the connecting member is fastened to the driving device with a bolt and a nut. Thus, connecting the driving device to the truck requires labor. 
     The present invention has an object to provide a driving assist unit of a truck which can be connected to the truck easily. 
     According to an aspect of the present invention a driving assist unit of a truck, configured to assist a driving force applied to the truck by a worker, includes a unit body connected to the truck, the unit body being turnable with respect to the truck, an operation portion provided on the unit body, the operation portion being configured to input a driving force to the truck through the unit body by being pressed by the worker, a driving wheel provided on the unit body, the driving wheel being rotatable in a longitudinal direction of the unit body, an assist force according to the operation of the operation portion being applied to the driving wheel, a lower engagement mechanism configured to be engaged with the truck by pressing the unit body onto the truck, and an upper engagement mechanism provided above the lower engagement mechanism and configured to be engaged with the truck by fitting of a locking member by the worker. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a driving assist unit of a truck according to an embodiment of the present invention and the truck. 
         FIG. 2  is a side view in  FIG. 1 . 
         FIG. 3  is a rear view in  FIG. 1 . 
         FIG. 4  is a plan view in  FIG. 1 . 
         FIG. 5  is a perspective view of the driving assist unit of the truck according to the embodiment of the present invention. 
         FIG. 6  is a perspective view illustrating an internal structure of the driving assist unit of the truck according to the embodiment of the present invention. 
         FIG. 7  is a side view in  FIG. 5 . 
         FIG. 8  is an enlarged view of a VIII part in  FIG. 5  and illustrates a state in which an upper engagement mechanism is not engaged with a connecting rod. 
         FIG. 9  is a view illustrating a state in which the upper engagement mechanism is engaged with the connecting rod in  FIG. 8 . 
         FIG. 10  is an enlarged view of an X part in  FIG. 5  and illustrates a state in which a lower engagement mechanism is not engaged with the connecting rod. 
         FIG. 11  is a view illustrating a state in which the lower engagement mechanism is engaged with the connecting rod in  FIG. 10 . 
         FIG. 12  is a side view illustrating a state before the driving assist unit of the truck is connected to the truck. 
         FIG. 13A  is a plan view in  FIG. 12 . 
         FIG. 13B  is a XIIIB-XIIIB sectional view in  FIG. 12 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A driving assist unit (hereinafter referred to simply as “assist unit”)  100  of a truck according to an embodiment of the present invention will be described below by referring to the attached drawings. 
     First, by referring to  FIGS. 1 to 4 , a truck  1  to which the assist unit  100  is connected will be explained. 
     The truck  1  is used for conveying a heavy article in a factory or the like, for example. As illustrated in  FIG. 1 , the truck  1  is a cage truck having a deck  2  formed having a rectangular shape, standing portions  3  provided vertically upward from four sides of an outer periphery of the deck  2 , and four wheels  4  supporting four corner parts of the deck  2 , respectively. The truck  1  is movable by rotation of the wheels  4 . 
     Since it is only necessary that the truck  1  can convey a cargo loaded thereon, it is not limited to a cage truck. The truck  1  may be a handcart on which a handle is provided vertically only on one side of the deck  2  or a hand-lift whose deck is elevated up/down by an operation by a worker, for example. 
     On the deck  2 , a cargo is loaded. In this embodiment, the deck  2  is a pair of rectangular plates split right and left. The deck  2  may be a rectangular single plate provided on the whole surface. 
     The wheels  4  are universal wheels directed toward a traveling direction at all times during traveling. All the four wheels  4  do not have to be universal wheels but a pair of wheels  4  away from the assist unit  100  may be fixed wheels, while only the pair of wheels  4  close to the assist unit  100  may be universal wheels. By setting the pair of wheels  4  away from the assist unit as the fixed wheels as above, straight traveling ability of the truck  1  is improved. 
     On the truck  1 , a connecting member  5  for connecting the assist unit  100  is mounted on the standing portion  3  on a side of the deck  2 . 
     The connecting member  5  has a bracket  6  fixed to the standing portion  3  and a connecting rod  7  provided on a free end of the bracket  6 . 
     The bracket  6  is welded to the standing portion  3 . Instead of welding, the bracket  6  may be mounted by bolting. When the bracket  6  is to be bolted to the standing portion  3 , the connecting member  5  can be mounted on the truck  1  easily. Moreover, since it is only necessary that the bracket  6  can be bolted, the assist unit  100  can be connected by mounting the connecting member  5  on an existing truck having various shapes. 
     The connecting rod  7  is a cylindrical rod member provided by protruding to an outside from the truck  1  by a length of the bracket  6 . The connecting rod  7  is provided perpendicularly to the ground surface. The connecting rod  7  is connected to the truck  1  through the bracket  6  between a position where an upper hook mechanism  11  which will be described later is engaged and a position where a lower hook mechanism  12  is engaged. On the connecting rod  7 , the assist unit  100  is mounted. The connecting rod  7  may be a solid round rod having a circular cross section instead of a cylindrical shape. 
     Subsequently, the assist unit  100  will be explained by referring to  FIGS. 5 to 7 . 
     The assist unit  100  is to assist the driving force applied to the truck  1  by the worker. The assist unit  100  has a unit body  10  connected to the truck  1 , capable of turning, an operation handle  20  as an operation portion capable of inputting a driving force to the truck  1  through the unit body  10  by being pressed by the worker, and driving wheels  30  provided on the unit body  10 , rotatably only in a longitudinal direction of the unit body  10  and to which an assist force according to the operation of the operation handle  20  is applied. 
     The unit body  10  is formed having a vertically long box shape and is supported by the driving wheels  30 . The unit body  10  has the upper hook mechanism  11  as an upper engagement mechanism engaged with the connecting rod  7  and the lower hook mechanism  12  as a lower engagement mechanism. Moreover, in the unit body  10 , an auxiliary wheel  13  (see  FIGS. 6 and 7 ) not grounded in a state in which the assist unit  100  is connected to the truck  1  is provided. 
     The upper hook mechanism  11  is engaged with the connecting rod  7  manually by the worker. On the other hand, the lower hook mechanism  12  can be engaged with the connecting rod  7  in a single operation only by pressing the assist unit  100  onto the truck  1 . The assist unit  100  is connected to the truck  1  by holding of the connecting rod  7  by the upper hook mechanism  11  and the lower hook mechanism  12 . The upper hook mechanism  11  and the lower hook mechanism  12  will be explained later in detail by referring to  FIGS. 8 to 11 . 
     The auxiliary wheel  13  is a fixed wheel provided away from the driving wheels  30  in a longitudinal direction and rotatable only in the same direction as that of the driving wheels  30 . The auxiliary wheel  13  is used by being grounded when the assist unit  100  is removed from the truck  1  and moved as a single body. Specifically, the worker can ground the auxiliary wheel  13  by tilting the assist unit  100  having been removed from the truck  1  longitudinally and can move the assist unit  100  in a state in which three wheels, that is, the pair of driving wheels  30  and the auxiliary wheel  13  are grounded. Thus, stable movement of the assist unit  100  as a single body can be realized. 
     If the single driving wheel  30  is provided, a pair of the auxiliary wheels  13  is provided. As a result, similarly to the case in which the pair of driving wheels  30  is provided, the assist unit  100  can be stably moved as a single body with the three wheels being grounded. 
     The operation handle  20  is a handle provided on the unit body  10  and pressed by the worker. The operation handle  20  is a rod material horizontally extended in the right-and-left direction of the unit body  10 . The operation handle  20  is connected to an upper part of the unit body  10  on the right and left thereof. As a result, a driving force inputted by operation of the operation handle  20  by the worker is transmitted to the truck  1  through the unit body  10 . 
     The driving wheels  30  are provided unable of being steered and provided toward the longitudinal direction of the unit body  10 . The driving wheels  30  are provided in a pair spaced from each other on right and left of the unit body  10 . The driving wheels  30  are juxtaposed on right and left by sandwiching a turning center of the unit body  10 . In this embodiment, the driving wheels  30  are provided in a pair but instead, the single driving wheel  30  may be provided. 
     Moreover, as illustrated in  FIG. 6 , the assist unit  100  includes a torque sensor  21  as a torque detection portion for detecting a driving torque inputted from the operation handle  20 , an electric motor  40  for applying an assist force according to the driving torque detected by the torque sensor  21  to the driving wheels  30 , a controller  50  for controlling the electric motor  40  in accordance with the driving torque detected by the torque sensor  21 , and a battery  60  as a power supply device. 
     The torque sensor  21 , the controller  50 , the battery  60 , and the electric motor  40  are arranged by being vertically arranged in order from the top in the unit body  10 . As a result, the assist unit  100  can be formed with a compact shape. 
     The torque sensors  21  are provided in a pair in the unit body  10  and detect a driving torque inputted to each of the right and left two spots of the unit body  10 . The torque sensor  21  is electrically connected to the controller  50  and outputs an electric signal according to the detected driving torque to the controller  50 . 
     The torque sensor  21  includes a torsion bar (not shown) connecting the operation handle  20  to the unit body  10  and twisted by the driving force inputted from the operation handle  20  and also for transmitting the driving force to the unit body  10  and a potentiometer (not shown) for outputting the electric signal according to the torsion of the torsion bar and detects the driving torque on the basis of the torsion of the torsion bar. By changing the torsion bar, operation feeling by the worker can be also changed in accordance with a loaded load of the truck  1  without changing the other members. 
     The electric motor  40  is electrically connected to the controller  50  and rotated in accordance with the electric signal inputted from the controller  50 . The electric motors  40  are provided in a pair and apply an assist force independently to each of the driving wheels  30 . 
     The electric motor  40  is disposed so that its rotating shaft is oriented in a direction perpendicular to the ground. The electric motor  40  is provided outside of each of the pair of driving wheels  30 . As a result, an interval between the pair of driving wheels  30  can be made small. Thus, a rotation radius of the driving wheel  30  is made small, and a moment required for the worker to rotate the assist unit  100  can be made small. Therefore, handling of the assist unit  100  by the worker is facilitated. 
     Between the driving wheel  30  and the electric motor  40 , a warm transmission  41  as a transmission for reducing a speed of the rotation of the electric motor  40  and for changing a rotating direction and transmitting it to the driving wheel  30  is provided. 
     The controller  50  is mounted on the unit body  10 . The controller  50  is for controlling the assist unit  100  and is constituted by a microcomputer provided with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an I/O interface (input/output interface). The RAM stores data in processing of the CPU, the ROM stores a control program of the CPU and the like in advance, and the I/O interface is used for input/output of information with respect to connected devices. By operating the CPU, the RAM and the like in accordance with a program stored in the ROM, control of the assist unit  100  is realized. 
     The controller  50  controls each of the right and left electric motors  40  in accordance with each of the driving torques detected by the right and left torque sensors  21  and applies an assist force to the right and left driving wheels  30 . Specifically, the controller  50  controls the left-side electric motor  40  in accordance with the driving torque detected by the left-side torque sensor  21  and controls the right-side electric motor  40  in accordance with the driving torque detected by the right-side torque sensor  21 . As a result, an assist force for advancing and retreating as well as linearly advancing, turning around or turning the assist unit  100  is applied. 
     The battery  60  is mounted on the unit body  10 . The battery  60  is a battery cell for driving the controller  50  and for supplying a DC power to the electric motor  40  on the basis of control by the controller  50 . 
     Subsequently, the upper hook mechanism  11  and the lower hook mechanism  12  will be explained by referring to  FIGS. 8 to 11 . 
     The upper hook mechanism  11  is provided above the lower hook mechanism  12 . The upper hook mechanism  11  is engaged slidably in an axial direction with respect to the connecting rod  7 . The upper hook mechanism  11  can be engaged with the truck  1  through the connecting rod  7  by a pin  16  as a locking member fitted by the worker. 
     The upper hook mechanism  11  has, as illustrated in  FIG. 8 , a fixed portion  14  fixed to the unit body  10  and with which a side surface of the connecting rod  7  is brought into contact, a movable portion  15  provided rotatably with respect to the fixed portion  14  and fixed to the fixed portion  14  by the pin  16  fitted in a state in which the connecting rod  7  is sandwiched between the fixed portion  14  and the movable portion  15 , and the pin  16  fitted by the worker. 
     The fixed portion  14  is a plate having a base end  14   a  mounted on the unit body  10  and provided protruding from the unit body  10 . The fixed portions  14  are provided in a pair by being juxtaposed vertically in parallel. On a free end  14   b  of the fixed portion  14 , a recess portion  14   c  having an arc portion  14   d  formed having a shape corresponding to an outer shape of the connecting rod  7  is formed. 
     The fixed portion  14  has a through hole  14   e  formed on one end of the recess portion  14   c  and in which the movable portion  15  is mounted rotatably and a through hole  14   f  formed on the other end of the recess portion  14   c  and into which the pin  16  can be inserted in a state in which the movable portion  15  sandwiches the connecting rod  7  between the fixed portion  14  and the movable portion  15 . 
     The movable portion  15  is a plate having a base end  15   a  rotatably mounted on the through hole  14   e  of the fixed portion  14 . The movable portion  15  is located between the pair of fixed portions  14 . In the movable portion  15 , a recess portion  15   c  having an arc portion  15   d  formed to be faced with the recess portion  14   c  of the fixed portion  14  in a state in which the connecting rod  7  is sandwiched between the fixed portion  14  and the movable portion  15  and formed having a shape corresponding to the outer shape of the connecting rod  7 . 
     In a free end  15   b  of the movable portion  15 , a through hole  15   f  coaxial with the through hole  14   e  of the fixed portion  14  in a state in which the connecting rod  7  is sandwiched between the fixed portion  14  and the movable portion  15  is formed. 
     The pin  16  has a shaft part  16   a  inserted into the through hole  14   f  and the through hole  15   f  and a head part  16   b  formed with a diameter larger than that of the shaft part  16   a . The shaft part  16   a  is formed having a diameter smaller than those of the through hole  14   f  and the through hole  15   f , and the head part  16   b  is formed having a diameter larger than those of the through hole  14   f  and the through hole  15   f.    
     Regarding the pin  16 , as illustrated in  FIG. 9 , the shaft part  16   a  is inserted from above the through hole  14   f  and the through hole  15   f  in a state in which the connecting rod  7  is sandwiched between the fixed portion  14  and the movable portion  15 . As a result, the movable portion  15  is fixed unable of rotation with respect to the fixed portion  14 . The position of the pin  16  in an axial direction is defined by the head part  16   b  brought into contact with the upper fixed portion  14 . 
     On the other hand, when the pin  16  is pulled upward out of the through hole  14   f  and the through hole  15   f , as illustrated in  FIG. 8 , the movable portion  15  is made rotatable with respect to the fixed portion  14 . 
     The lower hook mechanism  12  is provided below the upper hook mechanism  11 . The lower hook mechanism  12  is engaged with the connecting rod  7  slidably in the axial direction with respect to the connecting rod  7 . The lower hook mechanism  12  can be engaged with the truck  1  through the connecting rod  7  by pressing the unit body  10  onto the truck  1 . 
     The lower hook mechanism  12  has, as illustrated in  FIG. 10 , a fixed portion  24  fixed to the unit body  10  and having a recess portion  24   c  into which the connecting rod  7  enters, a first movable portion  25  provided rotatably with respect to one end of the recess portion  24   c  in a free end  24   b  of the fixed portion  24 , a second movable portion  26  provided rotatably with respect to the other end of the recess portion  24   c  in the free end  24   b  of the fixed portion  24 , and a release lever  27  provided protruding to an outside from the unit body  10  and operated by the worker. 
     The fixed portion  24  is a plate having a base end  24   a  mounted on the unit body  10  and provided protruding from the unit body  10 . The fixed portions  24  are provided in a pair by being juxtaposed vertically in parallel. On a free end  24   b  of the fixed portion  24 , a recess portion  24   c  having an arc portion  24   d  formed having a shape corresponding to an outer shape of the connecting rod  7  is formed. 
     The fixed portion  24  has a through hole  24   f  formed on one end of the recess portion  24   c  and on which the first movable portion  25  is mounted rotatably and a through hole  24   e  formed on the other end of the recess portion  24   c  and on which the second movable portion  26  is mounted rotatably. 
     The first movable portion  25  is a plate rotatably mounted on the through hole  24   f  of the fixed portion  24 . The first movable portion  25  is located between the pair of fixed portions  24 . The first movable portion  25  is rotated by being pressed by the connecting rod  7  when the connecting rod  7  enters into the recess portion  24   c  and thus the recess portion  24   c  is closed and the connecting rod  7  is sandwiched. 
     On the first movable portion  25 , a recess portion  25   c  having an arc portion  25   d  formed having a shape corresponding to an outer shape of the connecting rod  7  and in sliding contact with the connecting rod  7  when the connecting rod  7  enters into the recess portion  24   c  and an engagement portion  25   a  engaged with the second movable portion  26  are formed. 
     The first movable portion  25  is rotated by being pressed by the connecting rod  7  in a state in which the connecting rod  7  is brought into contact with the recess portion  25   c  when the connecting rod  7  enters into the recess portion  24   c . As a result, the recess portion  25   c  is located coaxially with the recess portion  24   c , and the connecting rod  7  is sandwiched by the fixed portion  24  and the first movable portion  25 . 
     The engagement portion  25   a  is brought into sliding contact with a sandwiching portion  26   c  of the second movable portion  26  when the first movable portion  25  is rotated. The engagement portion  25   a  is locked by an engagement projection portion  26   a  of the second movable portion  26  in a state in which the first movable portion  25  is rotated and the recess portion  25   c  is located coaxially with the recess portion  24   c . As a result, the first movable portion  25  is fixed incapable of rotation. 
     The second movable portion  26  is a plate rotatably mounted on the through hole  24   e  of the fixed portion  24 . The second movable portion  26  is located between the pair of fixed portions  24 . The second movable portion  26  has the engagement projection portion  26   a  engaged with and fixing the first movable portion  25  in the state sandwiching the connecting rod  7  and the sandwiching portion  26   c  for sandwiching the connecting rod  7  between the recess portion  25   c  and the sandwiching portion  26   c.    
     The engagement projection portion  26   a  is pressed by the engagement portion  25   a  of the first movable portion  25  when the connecting rod  7  enters into the recess portion  24   c . Then, when the second movable portion  26  is rotated, the engagement portion  25   a  of the first movable portion  25  rides over the engagement projection portion  26   a . As a result, the engagement projection portion  26   a  locks the engagement portion  25   a  and fixes the first movable portion  25  (state illustrated in  FIG. 11 ). 
     The release lever  27  is provided integrally with the second movable portion  26 . The release lever  27  is operated by the worker when the engagement of the lower hook mechanism  12  with the connecting rod  7  is to be released. 
     When the release lever  27  is operated by the worker in a direction separated away from the unit body  10 , the second movable portion  26  is rotated integrally with the release lever  27 , and the engagement between the engagement projection portion  26   a  and the engagement portion  25   a  is released. As a result, fixing of the first movable portion  25  is released and made rotatable, and the connecting rod  7  can be separated away from the recess portion  24   c  of the fixed portion  24 . 
     Subsequently, an action of the assist unit  100  will be explained by referring to  FIGS. 1 to 4 . 
     First, a case in which the truck  1  is to be advanced or retreated linearly through the assist unit  100  will be explained. Here, an instance in which the assist unit  100  pushes the truck  1  is referred to as advance, while an instance in which the truck  1  is towed is referred to as retreat. 
     When the worker pushes the operating handle  20  with both hands in parallel, the assist unit  100  linearly advances the truck  1 . In this case, the driving force inputted into the unit body  10  as the operation handle  20  is pushed is substantially the same on both right and left ends of the operation handle  20 . Thus, the driving torque detected by the right and left torque sensors  21  are substantially the same. 
     When the right and left torque sensors  21  detect the same driving torque, the controller  50  instructs to apply the same assist force to the right and left driving wheels  30  from the right and left electric motors  40 . As a result, the same assist force is applied to the right and left driving wheels  30 . 
     Therefore, the assist unit  100  can linearly advance the truck  1  while it is faced with the same direction as the truck  1  without turning since the assist force of the electric motor  40  is applied to the driving force applied by the worker. 
     When the truck  1  is to be linearly retreated, the direction in which the operation handle  20  is pushed becomes the opposite, and only the rotating direction of the electric motor  40  becomes opposite, while the other actions are the same as those of the case of linear advancement. 
     Subsequently, a case in which the truck  1  is turned/made to travel through the assist unit  100  will be explained. 
     If the worker wants to differentiate the forces on the right and left used for pushing the operation handle  20 , the assist unit  100  is turned/made to travel to left or right. At this time, the assist force applied to the right and left driving wheels  30  is different between the right and left electric motors  40 . 
     Specifically, when the truck  1  is to be turned in the left direction, for example, the force for pushing the operation handle  20  with the right hand by the worker becomes larger than the force for pushing the operation handle  20  with the left hand. Thus, the driving torque detected by the right-side torque sensor  21  becomes larger than the driving torque detected by the left-side torque sensor  21 . 
     The controller  50  gives an instruction that the assist force to be applied to the driving wheel  30  from the right-side electric motor  40  becomes larger than the assist force to be applied to the driving wheel  30  from the left-side electric motor  40 . As a result, the assist force applied to the right-side driving wheel  30  becomes larger than the assist force applied to the left-side driving wheel  30 . 
     Thus, the assist unit  100  is brought into a state of turning with respect to the truck  1 . As described above, the assist unit  100  can apply not only the assist force for advancing or retreating the truck  1  but also a moment for turning the truck  1 . Therefore, the assist unit  100  can turn/make the truck  1  run as the assist force of the electric motor  40  is applied to the driving force applied by the worker. 
     The unit body  10  is connected to the truck  1 , capable of turning. Moreover, the driving wheels  30  are provided on the unit body  10  rotatably only in the longitudinal direction. Thus, since the driving wheels  30  do not turn with respect to the unit body  10 , a mechanism for turning the driving wheels  30  is not necessary. Therefore, a structure of the assist unit  100  of the truck  1  can be simplified. 
     Moreover, if a heavy article is loaded on the truck  1 , the truck  1  can be moved by applying the assist force from the assist unit  100  on the basis of the operation of the worker. On the other hand, if a cargo mounted on the truck  1  is light or there is no cargo, the truck  1  can be moved only by the driving force by the worker without applying the assist force from the assist unit  100 . 
     The right and left torque sensors  21  can detect a driving torque continuously and thus, magnitude of the assist force can be controlled in accordance with the force for pressing the operation handle  20  by the worker. 
     Subsequently, by referring mainly to  FIGS. 12 and 13 , connection of the assist unit  100  to the truck  1  and removal thereof will be explained. 
     When the assist unit  100  is to be connected to the truck  1 , the worker moves the assist unit  100  toward the truck  1  so that the lower hook mechanism  12  is pressed onto the connecting rod  7 . At this time, the movable portion  15  of the upper hook mechanism  11  is opened so that the connecting rod  7  can enter into the recess portion  14   c  of the fixed portion  14 . 
     When the worker presses the unit body  10  of the assist unit  100  onto the lower hook mechanism  12  so that the connecting rod  7  enters, the first movable portion  25  is rotated until the recess portion  25   c  of the first movable portion  25  and the recess portion  24   c  of the fixed portion  24  are located coaxially. At this time, the engagement portion  25   a  of the first movable portion  25  is brought into sliding contact with the sandwiching portion  26   c  of the second movable portion  26 . 
     Then, after the engagement portion  25   a  rides over the engagement projection portion  26   a , the recess portion  25   c  of the first movable portion  25  and the recess portion  24   c  of the fixed portion  24  come to be located coaxially. As a result, the first movable portion  25  is fixed to the fixed portion  24 , unable to be rotated, since the engagement portion  25   a  is locked by the engagement projection portion  26   a.    
     As described above, the lower hook mechanism  12  can be engaged with the connecting rod  7  in a single operation only by pressing the unit body  10  of the assist unit  100  onto the truck  1 . Therefore, connection between the assist unit  100  and the truck  1  can be made easily. 
     After the lower hook mechanism  12  is engaged with the connecting rod  7 , the worker rotates the movable portion  15  of the upper hook mechanism  11  so that the connecting rod  7  is sandwiched between the movable portion  15  and the fixed portion  14 . Then, the pin  16  is inserted from above into the through hole  14   f  and the through hole  15   f  located coaxially. As a result, the movable portion  15  is fixed to the fixed portion  14 , unable to be rotated, and the upper hook mechanism  11  is engaged with the connecting rod  7 . 
     The upper hook mechanism  11  is provided above the lower hook mechanism  12  and is located at a relatively high position and thus, an operation of fitting the pin  16  by the worker is easy. Therefore, the connection between the assist unit  100  and the truck  1  can be made easily. 
     Moreover, even if the release lever  27  of the lower hook mechanism  12  is operated by contact with an obstacle outside against an intension of the worker and engagement of the lower hook mechanism  12  with the connecting rod  7  is released, for example, the engagement of the upper hook mechanism  11  with the connecting rod  7  is maintained. As described above, since the upper hook mechanism  11  and the lower hook mechanism  12  are given different structures, the connection of the assist unit  100  with the truck  1  can be made reliably. 
     On the other hand, when the assist unit  100  is to be removed from the truck  1 , the worker pulls the pin  16  of the upper hook mechanism  11  upward from the through hole  14   f  and the through hole  15   f . As a result, the movable portion  15  is made rotatable with respect to the fixed portion  14 . Thus, the engagement of the upper hook mechanism  11  with the connecting rod  7  is released. 
     In this case, too, since the upper hook mechanism  11  is provided above the lower hook mechanism  12  and located at a relatively high position, an operation of pulling out the pin  16  by the worker is easy. Therefore, removal of the assist unit  100  from the truck  1  can be made easily. 
     After the engagement of the upper hook mechanism  11  with the connecting rod  7  is released, the worker operates the release lever  27  of the lower hook mechanism  12  in a direction away from the unit body  10 . Then, the second movable portion  26  is rotated integrally with the release lever  27 , and the engagement between the engagement projection portion  26   a  and the engagement portion  25   a  is released. As a result, fixing of the first movable portion  25  is released and is made rotatable, and the connecting rod  7  can be separated away from the recess portion  24   c  of the fixed portion  24 . Thus, the engagement of the lower hook mechanism  12  with the connecting rod  7  is released. 
     As described above, the lower hook mechanism  12  is released from engagement with the connecting rod  7  only by operation of the release lever  27  by the worker. Therefore, the removal of the assist unit  100  from the truck  1  can be made easily. 
     According to the above embodiment, the following effects are exerted. 
     By pressing the unit body  10  of the assist unit  100  onto the truck  1 , the lower hook mechanism  12  is engaged with the truck  1  through the connecting rod  7 . Then, when the pin  16  of the upper hook mechanism  11  is fitted by the worker, the upper hook mechanism  11  is engaged with the truck  1  through the connecting rod  7 . The upper hook mechanism  11  is provided above the lower hook mechanism  12  and is located at a relatively high position. Thus, the operation of fitting the pin  16  by the worker is easy. Therefore, the connection between the assist unit  100  and the truck  1  can be made easily. 
     Moreover, even if the release lever  27  of the lower hook mechanism  12  is operated by contact with an obstacle outside against an intension of the worker and engagement of the lower hook mechanism  12  with the connecting rod  7  is released, for example, the engagement of the upper hook mechanism  11  with the connecting rod  7  is maintained. As described above, since the upper hook mechanism  11  and the lower hook mechanism  12  are given different structures, the connection of the assist unit  100  with the truck  1  can be made reliably. 
     Although an embodiment of the present invention has been described, the embodiment is merely one of application examples of the present invention and by no means limits the technical scope of the present invention to a specific configuration of the above-mentioned embodiment. 
     This application claims priority to Japanese Patent Application No. 2013-064460 filed in the Japanese Patent Office on Mar. 26, 2013, the entire contents of which are incorporated by reference herein.