KR200244032Y1 - A wheel chair - Google Patents

Abstract

The present invention provides a wheelchair that can be freely and stably up and down hills or stairs to improve the productivity, and the seating angle of the chair is changed according to the inclination or shape of the terrain to be driven, thereby improving the stability and convenience of the occupant. The wheelchair includes a body having a chair; A power generator having an actuator and a main shaft for supplying power; A sun gear fixed to the main shaft, a plurality of planetary gears which are geared around the sun gear and rotate and rotate, a ring gear which is geared around each planetary gear, and a carrier which is connected to each planetary gear and rotates when the planetary gear rotates A first power transmission device comprising; A second driving force including a drive shaft engaged with the ring gear of the first power transmission device by the drive gear, an axis frame extrapolated to the drive shaft and connected to the carrier, and acting as a central axis during step operation, and a casing fixed to the axis frame; Delivery device; A plurality of front wheels respectively connected to the drive shafts of the second power transmission device and fixed to respective rotation shafts fixed to the casing; A driven device connected to the drive shaft and the main frame and having a driven shaft to which the vehicle body is fixed; And a rear wheel fixed to the end of the driven shaft of the driven device.

Description

Wheelchair {A WHEEL CHAIR}

The present invention relates to a wheelchair, and more particularly, to a wheelchair that can easily climb or descend obstacles or stairs, the passenger can always maintain a stable posture.

Generally, but not limited to, patients with disabilities, disabled persons, etc., at their own will, use wheelchairs for their mobility or activities. Such a wheelchair basically includes a vehicle body having a seating portion capable of maintaining a sitting position of a passenger generally. This vehicle body is provided with a rear wheel of relatively large diameter capable of actually driving the vehicle body. This rear wheel can be driven manually by the patient or can be driven automatically by a separate actuator. Moreover, the front wheel is provided in front of a vehicle body for maintaining the vehicle body stably with a front wheel.

However, such a conventional wheelchair can move safely in the case of a flat or limited height obstacle by the wheel only rotating the axle shaft or drive shaft, but encounters a sand field, a muddy road or a high obstacle during the movement, in particular, When it reaches the stairs there is a problem that the wheel can not move because it can not move or ride over the obstacles.

In addition, when the inclined area is moved, the occupant is inclined corresponding to the inclination of the area, and thus there is a problem in that a stable posture cannot be maintained and a stable posture cannot be maintained.

On the other hand, in the case of an automatic driving type using an actuator or a motor, when the driver of the power source breaks down manually, the occupant must directly rotate the rear wheel and rotate, so that excessive force is required as well as an inconvenience.

Therefore, the present invention is designed to solve the above problems, and an object of the present invention is to provide a wheelchair that can be easily driven from an obstacle or a staircase.

Another object of the present invention is to provide a wheelchair that can maintain a stable posture when driving a slope.

Another object of the present invention is to provide a wheelchair that can be easily driven manually by the occupant when the power supply is interrupted.

1 is a block diagram showing a half of the overall driving device of the wheelchair according to the present invention.

2 is a cross-sectional view showing in detail the front wheel drive unit of FIG.

3 is a cross-sectional view showing in detail the rear wheel drive of FIG.

4 is a partial cross-sectional view showing an upper portion of a rear wheel drive according to an embodiment.

Figure 5 is a cross-sectional view showing the structure of the gear and the latch of the rear wheel drive.

Figure 6 is a partial cross-sectional view showing the structure of the gear and the latch of the other rear wheel drive.

Figure 7 is a side view showing the top of the rear wheel manual drive of Figure 6;

8 is a block diagram of a chair according to a preferred embodiment of the present invention.

9 is a variable view of the chair of FIG. 8;

Figure 10 is a side view showing the front wheel auxiliary drive means.

Figure 11 is a side view showing a state in which the auxiliary wheel of the auxiliary drive means of Figure 10 deployed.

12 is a partial front view of FIG. 11;

Fig. 13 is a partial front view showing the front wheel body;

Figure 14 is a side view showing the overall structure of a wheelchair according to the present invention.

♣ Explanation of symbols for the main parts of the drawing ♣

10: chair 12: body

16: power generating device 22: first power transmission device

36: second power transmission device 60: casing

78: driven device 84: manual drive device

144: auxiliary drive device

Such objects include: a wheelchair capable of climbing over stairs and climbing stairs; A power generating device installed on the vehicle body and having an actuator for supplying a driving force and a main shaft connected to the actuator; A sun gear fixed to the main shaft, a plurality of planetary gears rotatably and revolving according to an applied load and a ring gear geared around each of the planetary gears according to an applied load, and connected to the respective planetary gears A first power transmission device having a carrier rotated when the planetary gear is processed; A drive shaft meshed with the ring gear of the first power transmission device by a drive gear, a shaft frame externally rotatably coupled to the drive shaft, connected to the carrier, and acting as a central axis during step operation, and fixed to the shaft frame; A second power transmission device having a casing; A plurality of front wheels each connected to a drive shaft of the second power transmission device and fixed to respective rotation shafts rotatably fixed to the casing; A driven device operatively connected to the drive shaft and the main frame and having a driven shaft to which the vehicle body is fixed; And it can be achieved by a wheelchair comprising a rear wheel fixed to the end of the driven shaft of the driven device.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings. In most of the drawings, only half of the driving device is shown in detail for clarity. In addition, the directional terms indicated in the following description are only terms set when the front view of the accompanying drawings showing the present invention by way of example only, and those skilled in the art, the scope of the present invention is limited by such directional terms You will clearly understand that it is not.

First, referring to FIGS. 1 to 3 and 10, the wheelchair according to the present invention basically includes a vehicle body 12 having a chair 10 on which a passenger can board. The vehicle body 12 is equipped with an actuator 14 for supplying a power source, such as a general combustion engine or an electric motor.

As shown in detail in FIG. 2, the actuator 14 is spoken with a power generator 16 for actually driving the wheelchair. The power generating device 16 includes a main shaft 18 such as an axle shaft, and at the end of the main shaft 18 there is a pulley 20 connected to the actuator 14 by a connecting member such as a belt or a chain, for example. It is preferred to be provided.

The main shaft 18 includes a first power transmission device 22 for transmitting power by rotationally driving according to its driving. The first power transmission device 22 is preferably formed of a sun and planet gear, which is basically geared to the sun gear 24 fixed to the main shaft 18 and the sun gear 24 around the gears. A plurality of planetary gears 26 and another sun gear, ie, a ring gear 28, which are geared to the circumference of the planetary gear 26 are provided. Here, the plurality of planetary gears 26 are installed to rotate according to the rotation of the sun gear 24 or to rotate according to the load, and the ring gear 28 is preferably formed on both the inner surface and the outer surface.

The carrier 30 is installed in the first power transmission device 22. The carrier 30 is extrapolated so as not to contact the main shaft 18. The carrier includes a plurality of support shafts 32 to which each planetary gear 26 is idlely connected by a bearing. In particular, the pulley 34 is integrally provided at the end of the carrier 30.

In addition, the second power transmission device 36 is operatively installed in the first power transmission device 22. The second power transmission device 36 includes a drive gear 38 meshed with the outer side of the ring gear 28 of the first power transmission device 22. The drive gear 38 is provided with a drive shaft 40 fixed through the center thereof, one end of the drive shaft 40 is provided with a pulley 44 connected to the rear wheel described later by the belt 42, At the other end, two sprockets 46 and 48 are provided. And, the outer side of the drive shaft 40 is supported by a bearing so as to be rotatable to the drive shaft and the cylindrical base frame 50, which serves as a central axis during the step operation is extrapolated. In addition, the main frame 50 is provided with two pulleys, that is, the first pulley 52 and the second pulley 54. Here, the first pulley 52 is connected to the pulley 34 provided at the end of the carrier 30 by the belt 56, the second pulley 54 is the axle of the rear wheel described later by the belt 58 Is connected to. In addition, the main frame 50 of the second power transmission device 36 is provided with a casing 60 that can have a sufficient accommodation space.

The first front wheel 64 is rotatably installed in the casing 60 by the rotation shaft 62. The rotary shaft 62 is provided with a sprocket 66, which is connected to the sprocket 46 provided at the end of the drive shaft 40 by the chain 68.

In addition, the second front wheels 72 are rotatably installed on the casing 60 by the rotation shaft 70. Similarly, the rotating shaft 70 is provided with a sprocket 74, which is connected to the sprocket 48 provided at the end of the drive shaft 40 by the chain 76.

In addition, the casing 60 is rotatably provided with a third front wheel 73 on the rotation shaft 71 for more stable driving. As described above, the rotating shaft 71 is provided with a sprocket, not shown, which is connected to the sprocket 49 provided on the drive shaft 40 by a chain, not shown.

According to this configuration, the rotational direction of the drive shaft 40 is transmitted to the rotational shaft without conversion, so that each of the front wheels 64, 72, and 73 can be rotationally driven in the same direction. In the present embodiment, but described as having three front wheels, it can be understood that the front wheel may be composed of two or four, this configuration also operates in the same manner as having the three front wheels described above.

In the power generator 16 for driving the front wheels 64, 72 and 73, the driven device 78 for driving the rear wheels is spoken. The driven device 78 has a driven shaft 82 that is rotatably fixed to the bracket 80 for supporting the vehicle body. One end of the driven shaft 82 is provided with a driven pulley 84 connected to the pulley 44 provided in the drive shaft 40 by the main shaft belt 42. The driven pulley 84, as shown in detail in Figure 3, is preferably configured to be loaded only during the forward drive, for this purpose, the driven pulley 84 is preferably provided with a forward clutch bearing 86. .

On the other hand, the other side of the driven shaft 82 of the driven device 78 is provided with another driven pulley 88 connected to the pulley 54 provided in the main frame 50 by the main shaft belt (58). This driven pulley 88 is also preferably provided with a forward clutch bearing 90 so that a load is applied only during the forward drive. In particular, the pivot belt 58 is preferably supported by a tensionpulley 92 mounted to the vehicle body 12 so that it can be manually operated by the occupant to release the load upon reversing.

Of course, the end of the driven shaft 82 of the driven device 78 is provided with a large diameter rear wheel 94 that substantially dominates the drive of the wheelchair. Inside the rear wheel 94, a brake lining 96 is provided for braking the rear wheel.

Optionally, the follower 78 is provided with a manual drive 97 for rotating the rear wheels in the event of a power failure, emergency or manually. The manual drive device 97 has two gears fixed to the driven shaft 82 and, more specifically, to the driven shaft 82 between the respective body brackets 80 provided on the driven shaft 82. The gears may be divided into a first gear 98 used for forward movement of the rear wheel and a second gear 100 used for rearward movement of the rear wheel. In addition, an end portion of the lever 102 that can be manipulated by a passenger is rotatably installed on the driven shaft 82 between the first gear 98 and the second gear 100. The guide 104 is fixed in place of the lever 102, and the support 106 is fixed to the top of the guide 104.

In particular, one end of the guide 104 is actually provided with a first latch (108) for reciprocating up and down the first latch (98) for rotating the first gear forward, the end is actually engaged to the first gear (98). 108 is coalesced into the support 106 by a spring 110. In addition, the first clasp 108 is connected to the first handle 114 by the first connecting member 112. In the same way, the other side of the guide 104 is actually provided with a second latch 116 to be reciprocated up and down in order to actually engage the second gear 100 and rotate the second gear backward. Clasp 116 is coalesced on support 106 by spring 118. Of course, the second clasp 116 is connected to the second handle 122 by the second connecting member 120.

In addition, the upper portion of the lever 102 is provided with a rotating piece 124, the first handle 114 is fixed to one end of the rotating piece 124 and the second handle 122 is fixed to the other end , Each handle is to move up and down in opposite directions.

Of course, as shown in Figure 5, each tooth is formed with teeth in opposite directions for easy rotation of each of them. That is, the first gear 98 is formed with a tooth groove 98a in which the front is vertical and the rear is formed at an acute angle so as to be rotated in the forward direction, while the second gear 100 is rearward to be rotated in the rear direction. This vertical and front tooth groove 100a is formed at an acute angle. In addition, it is preferable that the first clasp 108 and the second clasp 116 correspond to the respective tooth grooves 98a and 100a formed in the first gear 98 and the second gear 100. .

Optionally, the manual drive device 84 'has a first latch 108' and a second latch 116 'mounted horizontally, as shown in Figs. The first handle 114 'and the second handle 122' connected by each other are installed in such a manner as to cross each other with the lever 102 'as an axis, which is different from the manual driving apparatus of FIGS. 4 and 5. The other components 110 ', 112', 106 ', 118', 120 ', etc. are similar to the components corresponding to the respective reference numerals of Figs. Detailed description will be omitted.

As shown in FIG. 8, the chair 10 provided in the main body 12 of the wheelchair according to the present invention automatically changes the seating angle according to the driving inclination degree of the wheelchair and the intention of the occupant so as to maintain a stable posture at all times. It is composed. In more detail, the chair 10 includes a base 126 that may include an upper portion of a vehicle body, and a front member 130 that is pivotably connected to the front of the base 126 by a hinge 128. The rear member 134 is pivotally fixed to the rear of the base 126 by the hinge 132, and one end thereof is fixed to the upper side of the front member 130 by the hinge 136 and is folded in a foldable manner. The upper side of the 134 preferably includes a seating member 140 fixed in a folding manner by a hinge 138, and a backrest 142, one side of which is fixed to the rear of the seating member 140. According to this configuration, as shown in FIG. 9, the center of gravity of the occupant is generally the base 126 when the wheelchair moves on a flat surface, climbs a sloped hill, or descends while being seated on the chair 10. The passengers can always maintain a stable boarding position because they face the center of the board. Of course, the occupant or the user may adjust the inclination angle of each member by using each hinge or a part of the hinge to arbitrarily set the seating angle of the chair 10.

On the other hand, as shown in Figures 10 and 11, the wheelchair according to the present invention is provided with an auxiliary drive device 144 for driving the wheelchair manually in the event of a power supply interruption or emergency. The auxiliary drive device 144 includes a support member 148 that is rotatably fixed to the vehicle body 12 by a hinge 146, and an auxiliary wheel 150 that is rotatably fixed to the support member 148. . In addition, the auxiliary drive device 144 is provided with a hinge 152 that can rotate the support member 148 so that the auxiliary wheel 150 can contact the ground. Of course, the lever 152 preferably includes a handle 154 that is bent and extended to the side of the vehicle body so that the user can easily handle the lever 152.

Optionally, as shown in FIGS. 10 to 13, the vehicle body 12 of the wheelchair according to the present invention is preferably composed of the front wheel body 156 and the rear wheel body 158. In particular, the front wheel body 156 and the rear wheel body 158 are preferably connected by a joint 160. In this way, the front wheel body 156 is connected to the rear wheel body 158 in a joint manner, so that the front wheel body 156 can swing from side to side with respect to the rear wheel body 158, so that a uneven road or curved sidewalk is provided. You can keep your body stable as you pass or climb your chin.

Hereinafter, the operation of the wheelchair and its operation mode according to the present invention will be described in detail with reference to FIGS. 14 and 1 to 13.

First, when a vehicle equipped with a drive device according to the present invention passes through a flat or low obstacle, for example, an actuator 14 such as a motor is operated and the power generated therein rotates the main shaft 18 through the main shaft pulley 20. Then, the sun gear 24 mounted on the main shaft rotates counterclockwise, and the plurality of planetary gears 26 engaged with the sun gear 24 rotate in a clockwise direction, that is, they rotate. 28 rotates clockwise. When the ring gear 28 rotates as described above, the drive shaft 38 of the second power transmission device 36 engaged with the ring gear 28 rotates and the drive shaft 40 rotates. As the drive shaft 40 rotates as described above, the rotational force is directly applied to the respective rotary shafts through the respective sprockets 46 and 48 and 49, the respective chains 68 and 76, and the respective sprockets 66 and 74; 62; 70; 71 to drive wheels 64; 72; 73 to drive the wheelchair forward. In addition, as the drive shaft pulley 44 rotates as the drive shaft 40 rotates, the driven wheel pulley 84 connected to the drive shaft pulley 44 by the main shaft belt 42 rotates so that the rear wheel rotates.

On the other hand, when driving on a steep hill or stairway while driving the wheelchair and driving in a step manner, the pulley 34 of the carrier 30 and the pulley 52 of the main frame 50 are rotated by the belt 56 and the main frame As the 50 is rotated, the casing 60 is rotated so that the step driving is performed in such a manner that one front wheel crosses the other front wheel. At this time, since the driven pulley 88 of the driven shaft 82 is connected to the pulley 54 provided in the base frame 50 by the belt 58, the rear wheel 94 can still be driven to rotate and the entire wheelchair is stable. And can be easily driven. In addition, each driven pulley (84; 88) is capable of driving the rear wheel 94 stably by having a clutch bearing (86; 90) that can be applied to the load only in the forward rotation.

The driving method as described above is disclosed in detail in the pending Korean patent application No. 10-1999-0053982 filed by the applicant under the designation of the driving device on November 30, 1999, the specification of this patent application Is cited entirely for reference.

On the other hand, if the actuator 14 is reversed to reverse the wheelchair, the operation as described above is reversed so that the wheelchair may be reversed and step driving may also be reversed. At this time, it is preferable to manually release the tension pulley 92 from the belt 58 to release the load applied to the belt 58. Accordingly, the backward of the wheelchair can be easily performed.

On the other hand, if the transmission of power is stopped during driving or if you need to manually drive the rear wheel, the occupant may use the manual drive device (97). For example, when the rear wheel is moved forward, that is, the lever 102 is pushed in the state where the end of the first latch 108 is inserted into the tooth groove 98a of the first gear 98 by pulling the second handle 122. By pulling the driven shaft 82 forward with the first gear 98, the wheelchair can be moved forward manually. On the contrary, in the case where the wheelchair is manually retracted, the lever 102 is pushed in the state where the end of the second latch 116 is inserted into the tooth groove 100a of the second gear 100 by pulling the first handle 114. As the driven shaft 82 is rotated backward together with the second gear 100, the wheelchair can be manually reversed. In the above description, the manual driving method has been described with reference to FIGS. 4 to 5, but the manual driving using the manual driving device having the configuration as shown in FIGS. 6 and 7 may also be performed in the same manner.

In addition, the chair 10 of the wheelchair according to the present invention is automatically changed according to the inclination of the road on which the wheelchair is driven can always maintain a stable posture. In particular, the chair 10 according to the present invention is preferably formed in an inverted trapezoidal shape that can maintain the most stable posture as shown in the figure. For example, when the wheelchair climbs a hill or a staircase in a forward direction, each of the hinges 128, 132, 136 and 138 interconnecting the base 126, the front member 130, the rear member 134, and the seating member 140 constituting the chair. By doing so, the respective members are maintained at an appropriate angle so that the occupant can maintain a stable posture. For example, the shape of the chair that can be adjusted and maintained to the maximum when moving forward may be represented by the solid line of FIG. 9. Conversely, the angle of the chair that can be maintained at maximum adjustment when descending a hill or a staircase in the forward direction may be represented by the chain line of FIG. 9. Of course, when moving to the reverse may appear contrary to the above description. In either case, the occupant is always able to maintain a stable boarding posture because the center of gravity of the occupant is always generally toward the center of the base 126.

On the other hand, the wheelchair according to the present invention can temporarily drive the wheelchair by using the auxiliary drive device in the case of stopping the supply of power or emergency. That is, when the lever 152 is rotated by pulling the handle 154 during the emergency stop of the wheelchair, the support member 148 is deployed so that the auxiliary wheel 150 is in contact with the ground and each front wheel is slightly spaced from the ground. Will remain in the state. In this state, the wheelchair can be driven by driving the rear wheel by hand or by using a manual driving device.

In addition, since the vehicle body 12 of the wheelchair according to the present invention is configured in such a way that the front wheel body 156 and the rear wheel body 158 are connected by a joint, a non-uniform road or curved sidewalk during the forward or backward driving of the wheelchair As the front wheel body 156 may swing left and right with respect to the rear wheel body 158 as shown in FIG. 13 when the chin is moved up or down, the vehicle body can be kept stable at all times.

Accordingly, the wheelchair can effectively and reliably move the occupant regardless of the terrain being driven.

According to the wheelchair according to the present invention as described above, it is possible to freely and stably climb hills or stairs as well as flat, there is an effect that the productability is improved.

In addition, the seating angle of the chair is changed according to the inclination or shape of the terrain to be driven, thereby improving the stability and convenience of the occupant.

In addition, when the power supply is stopped, the rear wheel can be driven manually, and the auxiliary wheel can be used to drive the wheelchair with the front wheel spaced from the ground, and the front wheel body swings or rotates relatively to the rear wheel body. There is an advantage that can facilitate the steering and driving of the wheelchair.

Although a preferred embodiment according to the present invention has been described above, it will be understood by those skilled in the art that various modifications and variations can be made without departing from the scope of the appended claims.

Claims (12)

In a wheelchair that can climb stairs and climb stairs, A vehicle body having a chair that can be seated by a passenger; A power generating device installed on the vehicle body and having an actuator for supplying a driving force and a main shaft connected to the actuator; A sun gear fixed to the main shaft, a plurality of planetary gears rotatably and revolving according to an applied load and a ring gear geared around each of the planetary gears according to an applied load, and connected to the respective planetary gears A first power transmission device having a carrier that rotates when the planetary gear revolves; A drive shaft meshed with the ring gear of the first power transmission device by a drive gear, a shaft frame externally rotatably coupled to the drive shaft, connected to the carrier, and acting as a central axis during step operation, and fixed to the shaft frame; A second power transmission device having a casing; A plurality of front wheels each connected to a drive shaft of the second power transmission device and fixed to respective rotation shafts rotatably fixed to the casing; A driven device operatively connected to the drive shaft and the main frame and having a driven shaft to which the vehicle body is fixed; And A wheelchair comprising a rear wheel fixed to the end of the driven shaft of the driven device. According to claim 1, The end of the carrier is provided with a pulley and the main frame is provided with two pulleys, the pulley of the carrier and one of the pulleys of the main frame is operatively connected by a belt Wheelchair characterized in that. According to claim 1 or 2, the end of the drive shaft is provided with a drive shaft pulley, the driven shaft of the driven device is provided with two driven shaft pulley, the other pulley and the driven shaft provided in the base frame One of the two pulleys provided is operably connected by the axis belt, the drive shaft pulley and the other pulley provided on the driven shaft is operably connected to the wheelchair by the main shaft belt. 3. The other end of the drive shaft in the casing is provided with a plurality of sprockets corresponding to the number of front wheels, and the rotating shaft to which each front wheel is fixed is connected to the sprocket corresponding to each sprocket of the drive shaft. A wheelchair, comprising: a sprocket connected by a chain. 4. The wheelchair according to claim 3, wherein each pulley provided in the driven shaft has a clutch bearing to which a load is applied only in the forward direction. 4. The wheelchair according to claim 3, wherein the pivot belt is supported by a tension pulley for releasing the load when reversing. 2. The wheelchair of claim 1 further comprising a manual drive for manually advancing or reversing the rear wheels in the event of power failure. The method of claim 7, wherein the manual drive device is fixed to the driven shaft for forward movement of the rear wheel and a first gear having a plurality of teeth groove, and fixed to the driven shaft for the rear movement of the rear wheel having a plurality of teeth groove A second gear, a lever that a passenger can operate by hand on a driven shaft between the first gear and the second gear, a guide provided on the lever, a support provided on an upper portion of the guide, and a It is reciprocally installed on one side and the end is engaged with the tooth groove of the first gear and is coalesced by a spring and connected to the first latch by a first connecting member to rotate the first gear forward. And a second latch for reciprocatingly installed on the other side of the guide, the end of which is engaged with the tooth groove of the second gear and is driven by a spring and rotates the second gear backward. A wheelchair comprising a second handle connected to the latch by a second connecting member. 9. The wheelchair according to claim 8, wherein a pivoting piece is hingedly fixed to one end of the first handle and hingedly fixed to the other end of the second handle. The chair of claim 1, wherein: the chair is formed in an inverted trapezoid shape; A base that may include an upper portion of the vehicle body, a front member hinged to the front of the base, a rear member hinged to the rear of the base, one end is hinged to the upper side of the front member and the other end Consisting of a seating member hinged to an upper portion of the rear member; Wheelchairs characterized in that. The support member of claim 1, wherein the support member is rotatably fixed to the vehicle body by a hinge, the auxiliary wheel rotatably fixed to the support member, and the support member can be rotated so that the auxiliary wheel can contact the ground. And an auxiliary drive having a lever and a handle extending and bent to the side of the vehicle body so as to operate the lever. 2. The vehicle body of claim 1, wherein the vehicle body includes a rear wheel body in which rear wheels are installed and fixed to a bracket of a driven shaft, and a front wheel body body in which each front wheel is mounted and connected by a joint so as to be able to swing left and right in the rear wheel body. Wheelchairs characterized in that.