Patent Publication Number: US-2022219531-A1

Title: Driving assistance device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Application No. 2021-003544, filed Jan. 13, 2021, the entire contents of which are incorporated herein by reference. 
     The present invention relates to a driving assistance device including a manually operable accelerator operation unit in the vicinity of a steering wheel provided in front of a driver seat in a vehicle cabin. 
     BACKGROUND 
     A driving assistance device has been proposed in which as disclosed in Japanese Patent Laid-Open No. 9-277850 (“Patent Literature 1”), an operation unit for performing an accelerator operation of a vehicle is provided in the vicinity of a steering grip portion so that even a physically handicapped person, who is handicapped in a lower limb and has difficulty in a stepping operation of a brake pedal and an accelerator pedal by his/her foot (lower-limb disabled person), is enabled to perform an accelerator operation of a vehicle by a manual operation while performing steering of a steering grip portion in a state where he/she is seated on a driver seat. 
     That is, the driving assistance device disclosed in Patent Literature 1 includes an accelerator operation unit enabling a manual accelerator operation in a steering wheel and adjusts an operation reaction force of the accelerator operation unit in accordance with a vehicle speed and a steering angle. 
     There has been a concern that fatigue of a hand of a driver which accompanies an accelerator operation can be reduced by adjusting the operation reaction force of the accelerator operation unit as in the above related art but the driver has difficulty in retaining an accelerator operation amount in a constant state due to a continuous change in the operation reaction force. 
     Further, there has been a problem that since a driver who manually performs an accelerator operation has to simultaneously perform an operation of a steering wheel and an accelerator operation, the driver has to quickly and largely steer the steering wheel, for example, in a situation where a right or left turn is made at a street corner, an intersection, or the like, which causes a change in an operation force on an accelerator operation unit which is operated by a fingertip in a steering operation and thus results in slight acceleration or deceleration of a vehicle, so that riding comfort is degraded. 
     SUMMARY 
     Accordingly, an object of embodiments of the present disclosure is to provide a driving assistance device that enables a driver who manually performs an accelerator operation and a steering operation to easily retain an accelerator operation state in a constant state. 
     A driving assistance device according to embodiments of the present disclosure is a driving assistance device including a manually operable accelerator operation unit in a vicinity of a steering wheel provided in front of a driver seat in a vehicle cabin, in which the accelerator operation unit is operable in a state where the steering wheel is gripped and an operation reaction force of the accelerator operation unit exhibits an inflection point at which the operation reaction force rapidly becomes large in response to an increase in an operation amount of the accelerator operation unit. 
     With the above configuration, because the inflection point is present, even when the operation force (the force of a finger of a driver) on the accelerator operation unit slightly increases, the operation amount does not change very much as long as the operation amount of the accelerator operation unit does not exceed the inflection point. Thus, retainment of an accelerator operation can easily be performed. 
     In one aspect of embodiments of the present disclosure, at the inflection point of the operation reaction force, target requested acceleration of a vehicle by an accelerator operation is set to approximately zero. 
     The above-described case where the target requested acceleration is approximately zero means a range of ±0.05 G with respect to zero G. Further, G denotes gravitational acceleration (gravity). 
     With the above configuration, because at the inflection point of the operation reaction force, the target requested acceleration of the vehicle by the accelerator operation is set to approximately zero (in other words, approximately zero G), acceleration and deceleration do not occur in a state where the accelerator operation is retained. Thus, a steering operation can safely be performed. 
     In one aspect of embodiments of the present disclosure, the accelerator operation unit includes a first operation reaction force generation unit which generates an operation reaction force in a region where the operation amount is smaller than an operation amount at the inflection point of the operation reaction force and a second operation reaction force generation unit which generates an operation reaction force in a region where the operation amount is larger than the operation amount at the inflection point of the operation reaction force. 
     With the above configuration, the first operation reaction force generation unit and the second operation reaction force generation unit are provided, and different operation reaction forces can thereby be set for the region where the operation amount is smaller than the operation amount at the inflection point (first operation region) and for the region where the operation amount is larger than the operation amount (second operation region). 
     In one aspect of embodiments of the present disclosure, the accelerator operation unit is provided in an arc shape along an inner periphery side of the steering wheel, at least four or more support portions which are capable of a slide operation with respect to the steering wheel are arranged in left-right symmetry, and at least one support portion among the support portions is configured to serve as the second operation reaction force generation unit. 
     With the above configuration, at least four or more support portions capable of a slide operation with respect to the steering wheel are arranged in left-right symmetry, and an operational feeling of the accelerator operation unit with respect to the steering wheel can be made uniform. 
     Embodiments of the present disclosure provide an advantageous effect that a driver who manually performs an accelerator operation and a steering operation can easily retain an accelerator operation state in a constant state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an internal portion of a vehicle including a driving assistance device of the present disclosure. 
         FIG. 2  is a perspective view illustrating an accelerator operation unit provided to a steering wheel. 
         FIG. 3  is a perspective view of the steering wheel in a front view. 
         FIG. 4  is a perspective view of the steering wheel in a back view. 
         FIG. 5  is an arrow cross-sectional view taken along line A-A in  FIG. 2 . 
         FIG. 6  is an arrow cross-sectional view taken along line B-B in  FIG. 2 . 
         FIG. 7  is a characteristic diagram illustrating a change in a reaction force with respect to a stroke amount of the accelerator operation unit. 
     
    
    
     DETAILED DESCRIPTION 
     In some embodiments, a driving assistance device enables a driver to manually perform an accelerator operation and a steering operation at the same time. The driving assistance device may include a manually operable accelerator operation unit in a vicinity of a steering wheel provided in front of a driver seat in a vehicle cabin. The accelerator operation unit is operable in a state where the steering wheel is gripped. An operation reaction force opposes a force applied by the driver&#39;s hand to the accelerator operation unit, which moves downward when pressed. The operation reaction force of the accelerator operation unit may exhibit an inflection point at which the operation reaction force rapidly becomes large in response to an increase in an operation amount of the accelerator operation unit. In some embodiments, this makes it easier for the driver to maintain a state of constant (e.g., zero) acceleration. 
     An embodiment of the present disclosure will hereinafter be described in detail with reference to drawings. 
       FIG. 1  is a perspective view of an internal portion of a vehicle including a driving assistance device,  FIG. 2  is a perspective view illustrating an accelerator operation unit provided to a steering wheel,  FIG. 3  is a perspective view of the steering wheel in a front view, and  FIG. 4  is a perspective view of the steering wheel in a back view. 
     Further,  FIG. 5  is an arrow cross-sectional view taken along line A-A in  FIG. 2 ,  FIG. 6  is an arrow cross-sectional view taken along line B-B in  FIG. 2 , and  FIG. 7  is a characteristic diagram illustrating a change in a reaction force with respect to a stroke amount of the accelerator operation unit. 
     Note that in the drawings, an arrow F indicates a vehicle front region, an arrow R indicates a vehicle rear region, an arrow LE indicates a vehicle left region, and an arrow RI indicates a vehicle right region. 
     Referring to  FIG. 1 , a driver seat  1  and a passenger seat (not illustrated) are mounted on left and right sides of a front portion of a floor in a vehicle cabin in a vehicle, and in front of the driver seat  1 , a steering wheel  2  is provided which is operated in a state where that is gripped by a driver seated on the driver seat  1 . 
     At a front end of the vehicle cabin, an instrument panel  3  is provided throughout the vehicle cabin in a vehicle width direction. A center console  4  is attached between the driver seat  1  and the passenger seat in a floor front portion of the vehicle cabin, and a front portion of the center console  4  may be integrally connected with a vehicle-width-direction center portion of the instrument panel  3 . The center console  4  forms a portion of an interior member of the vehicle cabin, and in a part of the center console  4 , the part being operable by the left hand of the driver seated on the driver seat  1 , a shift knob  5 , a start switch  6 , and so forth may be disposed. 
     On a front side of the driver seat  1  in the instrument panel  3 , a display unit  7  of various kinds of meter instruments such as a tachometer and a speedometer is disposed so as to be visually recognized across the steering wheel  2 . Above a connection portion to the front portion of the center console  4  on a left side of the display unit  7 , a wind outlet  8  of air-conditioning air and various kinds of operation buttons  9  such as setting dials of an audio device and an air-conditioning device are disposed. In addition, above those, a display  10  of a navigation device  10  may be provided. 
     Note that in a position, on which the right foot of the driver seated on the driver seat  1  is placed, on a floor in front of the driver seat  1  in the vehicle cabin, an accelerator pedal (not illustrated) may be provided. On a left side of the accelerator pedal in the vehicle width direction (on a center side in the vehicle width direction), a brake pedal (not illustrated) may be provided. 
     Both of the accelerator pedal and the brake pedal are common pedals which may be included in a base vehicle. 
     Further, as illustrated in  FIG. 2  and  FIG. 3 , the above-described steering wheel  2  may include a base portion  11  which is coupled with a steering shaft (not illustrated), a rim portion  12  which is gripped by the driver and is arranged in a ring shape around the base portion  11  as a center on an outer periphery side of the base portion  11  when seen from the driver side (hereinafter, abbreviated as driver-side view) in an axis direction of the steering shaft (hereinafter, abbreviated as steering axis direction), and plural spoke portions  13  which radially extend from the base portion  11  to the rim portion  12 . 
     In this embodiment, the spoke portions  13  have three spoke portions which are a right-side spoke portion  13 RI extending rightward from the base portion  11  in the driver-side view in the steering axis direction (that is, a front view), a left-side spoke portion  13 LE extending leftward, and a lower-side spoke portion  13 D extending downward. 
     As illustrated in  FIG. 2  and  FIG. 3 , a horn unit  14  which is pressed to sound a horn (warning sound) may be provided on a driver side of the base portion  11  in the steering axis direction. 
     On the driver side of the left and right spoke portions  13 LE and  13 RI in the steering axis direction, plural operation switches (not illustrated) for operating in-vehicle equipment such as the audio device and the navigation device may be disposed. 
     Further, as illustrated in  FIG. 4 , the steering wheel  2  may include paddle shift devices  15  which correspond to up-shifting and down-shifting. 
     In this embodiment, a paddle shift device  15 U for up-shifting is provided to the right-side spoke portion  13 RI, and a paddle shift device  15 D for down-shifting is provided to the left-side spoke portion  13 LE. 
     As illustrated in  FIG. 5  and  FIG. 6 , the steering wheel  2  has a core bar  16  as a frame member, and the core bar  16  may be covered by an outer cover member  17  of urethane or the like. 
     Next, a description will be made about a driving assistance device  20  (acceleration-deceleration manual operation assistance device) of the present embodiment, which is incorporated in a base vehicle. 
     As illustrated in  FIG. 1  to  FIG. 6 , the driving assistance device  20  may include an accelerator operation unit  21  whose slide displacement is performed along the steering axis direction and which thereby performs acceleration and deceleration operations of the vehicle, first support portions  31  and a second support portion  32  which slidably support the accelerator operation unit  21  along the steering axis direction, and transmission means which detects a slide displacement amount (stroke amount) of the accelerator operation unit  21  and transmits the detected slide displacement amount (stroke amount), as a signal, to an ECU controlling an opening of a throttle valve of an engine. 
     The accelerator operation unit  21  may be disposed in the vicinity of the steering wheel  2  and integrally formed with plural operation units  22 , which are operated in a manner such that the driver pushes the plural operation units  22  downward (or the like) in the steering axis direction with the thumb or other portion of his/her hand gripping the steering wheel  2 . Opposed portions  41  and  42  are slide supported portions which are supported by first and second support portions  31  and  32  slidably in the steering axis direction. Connecting portions  23  couple the plural operation units  22  together and couple the operation units  22  and the opposed portions  41  and  42  together. As a result of connecting portions  23 , plural operation units  22  slide together along opposed portions  41  and  42  when any one of plural operation units  22  is pressed downwards by the driver. 
     For example, in some embodiments, plural operation units  22  may be curved levers that can be pressed downward by the diver&#39;s hand while simultaneously gripping the steering wheel. The levers could have other shapes and be arranged differently, provided that the driver can press them with his/her hand while also gripping the steering wheel. In this way, the driver may safely control acceleration of the vehicle through manual operation. 
     As illustrated in  FIG. 2 , the operation unit  22  may be disposed in an arc shape in an inside vicinity with respect to the rim portion  12  of the steering wheel  2  in the driver-side view in the steering axis direction, in other words, an arc shape along an inner periphery side of the steering wheel  2 . An upper surface of the operation unit  22  in the steering axis direction may be formed into a flat shape such that the driver easily presses the upper surface of the operation unit  22  with the pad of the thumb of his/her hand gripping the steering wheel  2 . 
     In addition, as illustrated in  FIG. 2  and  FIG. 3 , the operation units  22  may be divided into sections corresponding to the spoke portions  13  in the driver-side view in the steering axis direction and respectively formed into arc shapes along the rim portion  12 . 
     Specifically, in some embodiments, the operation units  22  may include three operation units as follows: an upper-side operation unit  22 U arranged above both of the left and right spoke portions  13 LE and  13 RI in the driver-side view in the steering axis direction; a lower-right operation unit  22 RI arranged between the right-side spoke portion  13 RI and the lower-side spoke portion  13 D; and a lower-left operation unit  22 LE arranged between the left-side spoke portion  13 LE and the lower-side spoke portion  13 D. 
     As illustrated in  FIG. 2 , as for the above-described opposed portions  41  and  42 , the opposed portions  41  and  41  are disposed on both of upper and lower sides of the right-side spoke portion  13 RI in the driver-side view in the steering axis direction. The opposed portion  41  is disposed on an upper side of the left-side spoke portion  13 LE, and the opposed portion  42  is disposed on a lower side of the left-side spoke portion  13 LE. 
     As illustrated in the embodiment of  FIG. 2 , the connecting portions  23  may include a right-side connecting portion  23 RI which couples the upper-side operation unit  22 U and the lower-right operation unit  22 RI together, a left-side connecting portion  23 LE which couples the upper-side operation unit  22 U and the lower-left operation unit  22 LE together, and a lower-side connecting portion  23 D which couples the right-side operation unit  22 RI and the lower-left operation unit  22 LE together. The right-side connecting portion  23 RI is disposed in the section corresponding to the right-side spoke portion  13 RI, the left-side connecting portion  23 LE is disposed in the section corresponding to the left-side spoke portion  13 LE, and the lower-side connecting portion  23 D is disposed in the section corresponding to the lower-side spoke portion  13 D. 
     Next, because the right-side connecting portion  23 RI and the left-side connecting portion  23 LE are in a left-right symmetrical shape in some embodiments, structures of those connecting portions  23  will be described based on a configuration of the right-side connecting portion  23 RI. 
     As illustrated in the embodiment of  FIG. 2 , the right-side connecting portion  23 RI may be integrally formed with radial-direction coupling sides  24  on both of upper and lower sides, which extend in the radial directions of the steering wheel  2  (rim portion  12 ) in both of upper and lower side vicinities of the right-side spoke portion  13 RI. Axis-direction coupling sides  25  may extend upward in the steering axis direction from those radial-direction coupling sides  24  on both of the upper and lower sides, and a circumferential-direction coupling side  26  may couple the radial-direction coupling sides  24  on both of the upper and lower sides together in the circumferential direction of the steering wheel  2 . 
     The opposed portion  41  may be coupled with a radial-direction inner end portion in an upper portion of the above-described axis-direction coupling side  25 , and a radial-direction outer end portion may be coupled with a lower right side of the upper-side operation unit  22 U. Note that because the left-side connecting portion  23  LE and the above-described right-side connecting portion  23 RI are in a symmetrical structure in this embodiment, the same reference characters as those on the right side are given to the left-side connecting portion  23 LE. 
     Next, a description will be made based on a configuration of the lower-side connecting portion  23 D in some embodiments. 
     As illustrated in  FIG. 2 , the lower-side connecting portion  23 D may be integrally formed with a left-side axis-direction coupling side  27  which extends generally downward in the steering axis direction from an extending-direction end portion of the lower-left operation unit  22 LE in a left-side vicinity of the lower-side spoke portion  13 D, a right-side axis-direction coupling side  28  which extends generally downward in the steering axis direction from an extending-direction end portion of the lower-right operation unit  22 RI in a right-side vicinity of the lower-side spoke portion  13 D, and a circumferential-direction coupling side  29  which couples both of those left-side and right-side axis-direction coupling sides  27  and  28  together in the circumferential direction of the steering wheel  2 . 
     As illustrated in the embodiment of  FIG. 2 , at least four or more support portions may enable a slide operation of the above-described accelerator operation unit  21  with respect to the steering wheel  2 . In this embodiment, four support portions  31  and  32  are arranged in left-right symmetry. 
     As illustrated in the embodiment of  FIG. 2 , the first support portions  31  and  31  are arranged on both of upper and lower sides of the right-side spoke portion  13 RI in the driver-side view in the steering axis direction. The first support portion  31  is arranged on an upper side of the left-side spoke portion  13 LE, the second support portion  32  is arranged on a lower side in addition, and a total of four support portions  31  and  32  are configured to be in left-right symmetry. 
     More specifically, as illustrated in the embodiment of  FIG. 2 , the first support portions  31  may be respectively arranged in an upper left position, an upper right position, and a lower right position across the left and right spoke portions  13 LE and  13 RI, and the second support portion  32  may be arranged in a lower left position across the left and right spoke portions  13 LE and  13 RI. 
       FIG. 7  is a characteristic diagram in which the horizontal axis represents a stroke amount as an operation amount of the accelerator operation unit  21 , the left-side vertical axis represents an operation reaction force, and the right-side vertical axis represents target requested acceleration. 
     In  FIG. 7 , a characteristic (a) indicates the characteristic of a pushing-down side of the accelerator operation unit  21 , a characteristic (b) indicates the characteristic of a returning side (in other words, a direction in which a pushing-down force is weakened) of the accelerator operation unit  21 , and a characteristic (c) indicates the characteristic of the target requested acceleration with respect to the stroke amount of the accelerator operation unit  21 . 
     As illustrated in the embodiment of  FIG. 7 , the operation reaction force of the accelerator operation unit  21  may exhibit an inflection point POI (abbreviation for “point of inflection”) at which the operation reaction force rapidly becomes large in response to an increase in the stroke amount as the operation amount of the accelerator operation unit  21 . 
     That is, as indicated by the characteristic (a) in  FIG. 7 , in a range of a zero stroke amount st 0  at which the stroke amount of the accelerator operation unit  21  is zero to a predetermined stroke amount st 1  at which the stroke amount increases by a predetermined amount, the operation reaction force is generally constant. The operation reaction force rapidly becomes large when the stroke amount exceeds the inflection point POI, and the operation reaction force thereafter becomes large in accordance with an increase in the stroke amount in a range to a maximum stroke amount stmax. 
     Accordingly, in the range of the zero stroke amount st 0  to the predetermined stroke amount st 1 , even when the operation force on the accelerator operation unit  21  slightly increases, the operation amount does not change very much as long as the operation amount of the accelerator operation unit  21  (in other words, a pushing-down stroke amount) does not exceed the inflection point POI. Thus, the accelerator operation is easily performed through manual operation in this embodiment. 
     Further, as illustrated in the embodiment of  FIG. 7 , at the inflection point POI of the operation reaction force, the target requested acceleration (see the characteristic c) of the vehicle by the accelerator operation may be set to approximately zero. Approximately zero denotes a range of ±0.05 G with respect to zero G (G denotes an abbreviation for gravitational acceleration “gravity”). In this embodiment, as illustrated in  FIG. 7 , at the inflection point POI of the operation reaction force, the target requested acceleration of the vehicle by the accelerator operation is set to zero G. 
     Specifically, in this embodiment, a setting is made such that when the stroke amount of the accelerator operation unit  21  is the predetermined stroke amount st 1 , the inflection point POI of the operation reaction force is reached, and at this inflection point POI of the operation reaction force, the target requested acceleration of the vehicle by the accelerator operation becomes zero G. Accordingly, because acceleration and deceleration does not occur in a state where the accelerator operation by the accelerator operation unit  21  is retained at the predetermined stroke amount st 1 , a steering operation may be safely performed by the driver. 
     As illustrated in  FIG. 2  and  FIG. 7 , the accelerator operation unit  21  may include a first operation reaction force generation unit  51 , which generates an operation reaction force in a region where the operation amount is smaller than the operation amount (predetermined stroke amount st 1 ) at the inflection point POI of the operation reaction force in  FIG. 7 . The accelerator operation unit  21  also may include a second operation reaction force generation unit  52 , which generates an operation reaction force in a region where the operation amount is larger than the operation amount (predetermined stroke amount st 1 ) at the inflection point POI of the operation reaction force. 
     The above-described first operation reaction force generation units  51  may be coupled with the first support portions  31 , and the above-described second operation reaction force generation unit  52  may be coupled with the second support portion  32 . 
     As described above, in some embodiments, the first operation reaction force generation units  51  and the second operation reaction force generation unit  52  are provided, and different operation reaction forces may be set for the region where the operation amount is smaller than the operation amount (predetermined stroke amount st 1 ) at the inflection point POI in  FIG. 7  (a first operation region α) and for the region where the operation amount is larger than the operation amount (predetermined stroke amount st 1 ) (a second operation region β). 
     As illustrated in the embodiment of  FIG. 2 , a total of four support portions  31  and  32  may be arranged in left-right symmetry, one support portion positioned in a lower-left part among those support portions  31  and  32 . Thus, the second support portion  32  may serve as the second operation reaction force generation unit  52 , and the three first support portions  31  may serve as the first operation reaction force generation units  51 . 
     As described above, in some embodiments, a configuration is made such that the four support portions  31  and  32  capable of a slide operation with respect to the steering wheel  2  are arranged in left-right symmetry and an operational feeling of the accelerator operation unit  21  with respect to the steering wheel  2  is thereby made uniform. 
     Next, a description will be made about a specific structure of the first operation reaction force generation unit  51  configuring the first support portion  31  with reference to the embodiment of  FIG. 5 . Because each of a total of three first operation reaction force generation units  51  is configured the same, here, a description will be made about the first operation reaction force generation unit  51  positioned in a lower right part in  FIG. 2 . 
     As illustrated in the embodiment  FIG. 5 , the first operation reaction force generation unit  51  may include a support tube  61  which is attached to a rigid member on the steering wheel  2  side, the rigid member integrally rotating with the base portion  11 , a rod  62  which is arranged to pass through a through hole  61   a  of the support tube  61  and to be capable of up-down movement with respect to the through hole  61   a , and an upper-side nut  63  and a lower-side spring retainer  64  which fix a screw portion  62   a  at an upper end of the rod  62  to the opposed portion  41 . 
     Further, between a recessed bottom portion in an upper end recess  61   b  of the above-described support tube  61  and the spring retainer  64 , a first coil spring  65  may be stretched as urging means which urges the lower-right operation unit  22 RI of the operation unit  22  upward. 
     In addition, in a lower end recess  61   c  of the above-described support tube  61 , a fall prevention member  67  may be provided to a lower end of the rod  62  via a spacer  66 . This fall prevention member  67  is configured with a bolt, and the fall prevention member  67  is screwed in the lower end of the rod  62 . 
     A spring force of the above-described first coil spring  65  may be set small compared to a spring force of a second coil spring  76  described later. 
     When the lower-right operation unit  22 RI illustrated in  FIG. 5  is pushed down against the spring force of the first coil spring  65 , the characteristic of the first operation region α illustrated in  FIG. 7  can be obtained. 
     Because the upper-left and upper-right first operation reaction force generation units  51  illustrated in  FIG. 2  are configured the same as the first operation reaction force generation unit  51  illustrated in  FIG. 5 , the characteristic of the first operation region a illustrated in  FIG. 7  can be obtained also by pushing down the upper-side operation unit  22 U against the spring force of the first coil spring  65 . 
     Next, a description will be made about a specific structure of the second operation reaction force generation unit  52  configuring the second support portion  32  with reference to the embodiment of  FIG. 6 . 
     As illustrated in the embodiment of  FIG. 6 , the second operation reaction force generation unit  52  may include a support tube  71  which is attached to a rigid member on the steering wheel  2  side, the rigid member integrally rotating with the base portion  11 , and a rod  72  which is arranged to pass through a through hole  71   a  of the support tube  71  and to be capable of up-down movement with respect to the through hole  71   a.    
     An upper end recess  71   b  may be formed at an upper end of the above-described support tube  71 , and a lower end recess  71   c  may be formed at a lower end of the support tube  71 . 
     Further, while a spring retainer  73  may be fixed by screwing to an upper end of the above-described rod  72 , in the lower end recess  71   c  of the support tube  71 , a fall prevention member  75  may be fixed to a lower end of the rod  72  via a spacer  74 . This fall prevention member  75  may be configured with a bolt, and the fall prevention member  75  may be screwed in the lower end of the rod  72 . 
     In addition, between the spring retainer  73  at the upper end of the rod  72  and a recessed bottom portion in the upper end recess  71   b  of the support tube  71 , a second coil spring  76  may be stretched as urging means which urges the rod  72  upward. 
     A spacer  77  may be provided to a lower surface of the opposed portion  42  of the lower-left operation unit  22 LE which may be opposed to the above-described rod  72 , and a clearance g may be formed between a lower surface of the spacer  77  and an upper surface of the spring retainer  73  when the lower-left operation unit  22 LE is not pushed down. 
     The spring force of the above-described second coil spring  76  may be set large compared to the spring force of the above-described first coil spring  65  (see  FIG. 5 ). 
     An up-down interval of the clearance g, which is illustrated in  FIG. 6 , corresponds to the first operation region α in  FIG. 7 . When the lower-left operation unit  22 LE illustrated in  FIG. 6  is pushed down, the lower surface of the spacer  77  is caused to abut the upper surface of the spring retainer  73 , the clearance g is made zero, and the lower-left operation unit  22 LE is thereafter further pushed down against the spring force of the second coil spring  76 , the characteristic of the second operation region β illustrated in  FIG. 7  can be obtained. 
     As illustrated in the embodiments of  FIG. 3 ,  FIG. 5 , and  FIG. 6 , upper sides of the above-described opposed portions  41  and  42  and axis-direction coupling sides  25  may be covered by covers  80 , the characteristics of the first operation region α and the second operation region β in  FIG. 7  can be obtained also by directly pushing down those covers  80 , and upper surfaces of the covers  80  are formed to be flat for the purpose of intending an improvement in operability. 
     Note that in  FIG. 1  and  FIG. 2 , for convenience of illustration, the above-described covers  80  are not illustrated. 
     As described above, the driving assistance device  20  of the embodiment illustrated in  FIG. 1  to  FIG. 7  is the driving assistance device  20  including the manually operable accelerator operation unit  21  in the vicinity of the steering wheel  2  provided in front of the driver seat  1  in the vehicle cabin. The accelerator operation unit  21  is operable in a state where the steering wheel  2  is gripped and the operation reaction force of the accelerator operation unit  21  exhibits the inflection point POI at which the operation reaction force rapidly becomes large in response to an increase in the operation amount (see the stroke amount in  FIG. 7 ) of the accelerator operation unit  21  (see  FIG. 1 ,  FIG. 2 , and  FIG. 7 ). 
     In this configuration, because the inflection point POI is present, even when the operation force on the accelerator operation unit  21  slightly increases, the operation amount does not change very much as long as the operation amount of the accelerator operation unit  21  does not exceed the inflection point POI. Thus, the accelerator operation can easily be performed through manual operation. 
     Further, in some embodiments of the present disclosure, at the inflection point POI of the operation reaction force, the target requested acceleration (see the characteristic c in  FIG. 7 ) of the vehicle by the accelerator operation is set to approximately zero (see  FIG. 7 ). 
     In this configuration, because at the inflection point POI of the operation reaction force, the target requested acceleration of the vehicle by the accelerator operation is set to approximately zero (in other words, approximately zero G), acceleration and deceleration do not occur in a state where the accelerator operation is retained. Thus, the steering operation can safely be performed. 
     In addition, in some embodiments of the present disclosure, the accelerator operation unit  21  includes the first operation reaction force generation unit  51  which generates the operation reaction force in the region where the operation amount is smaller than the operation amount (stroke amount) at the inflection point POI of the operation reaction force (first operation region α), and the second operation reaction force generation unit  52  which generates the operation reaction force in the region where the operation amount is larger than the operation amount (predetermined stroke amount st 1 ) at the inflection point POI of the operation reaction force (second operation region β). 
     In this configuration, the first operation reaction force generation unit  51  and the second operation reaction force generation unit  52  are provided, and different operation reaction forces can thereby be set for the region where the operation amount is smaller than the operation amount (predetermined stroke amount st 1 ) at the inflection point POI (first operation region α) and for the region where the operation amount is larger than the operation amount (predetermined stroke amount st 1 ) (second operation region β). 
     Moreover, in some embodiments of the present disclosure, the accelerator operation unit  21  is provided in an arc shape along the inner periphery side of the steering wheel  2 , at least four or more support portions  31  and  32  which are capable of a slide operation with respect to the steering wheel  2  are arranged in left-right symmetry, and at least one support portion  32  among the support portions  31  and  32  is configured to serve as the second operation reaction force generation unit  52  (see  FIG. 2  and  FIG. 6 ). 
     In this configuration, because at least four or more support portions  31  and  32  capable of a slide operation with respect to the steering wheel  2  are arranged in left-right symmetry, an operational feeling of the accelerator operation unit  21  with respect to the steering wheel  2  can be made uniform. 
     In embodiments of the disclosure, the operation amount of the accelerator operation unit  21  may correspond to the stroke amount of the accelerator operation unit  21 . Also, the operation amount at the inflection point may correspond to the predetermined stroke amount st 1 , the region where the operation amount is smaller than the operation amount at the inflection point may correspond to the first operation region α, the region where the operation amount is larger than the operation amount at the inflection point may correspond to the second operation region β, the support portions may correspond to the first support portions  31  and the second support portion  32 , and the support portion to serve as the second operation reaction force generation unit may correspond to the second support portion  32 . 
     The present disclosure is not limited only to the configurations of the above-described embodiments but can be used in many embodiments and variations, as would be understood by a person of ordinary skill in the art reading this disclosure. 
     For example, in the above embodiments, the second support portion  32  positioned in the lower-left part is used as the second operation reaction force generation unit  52 , but the position of the second support portion  32  may be any of upper-left, upper-right, and lower-right positions in  FIG. 2 . 
     Further, in the above embodiments, a total of four support portions  31  and  32  are provided, but a structure may be employed in which a total of six (or more) support portions  31  and  32  are arranged in left-right symmetry. Similarly, fewer support structures may be used. 
     In addition, in the above embodiments, a configuration is exemplified in which the accelerator operation is performed in a total of two phases which are a first phase of the zero stroke amount st 0  to the predetermined stroke amount st 1  and a second phase of the predetermined stroke amount st 1  to the maximum stroke amount stmax; however, a structure is possible in which the accelerator operation is performed in three or more phases. Similarly, only one phase could be used. 
     As described in the foregoing, the present disclosure is useful for a driving assistance device including a manually operable accelerator operation unit in the vicinity of a steering wheel provided in front of a driver seat in a vehicle cabin. 
     REFERENCE SIGNS LIST AND NUMERALS 
     
         
           1  driver seat 
           2  steering wheel 
           20  driving assistance device 
           21  accelerator operation unit 
           31  first support portion (support portion) 
           32  second support portion (support portion) 
           51  first operation reaction force generation unit 
           52  second operation reaction force generation unit 
         α first operation region (region where operation amount is smaller than operation amount at inflection point) 
         β second operation region (region where operation amount is larger than operation amount at inflection point) 
         POI inflection point 
         st 1  predetermined stroke amount (operation amount at inflection point)