NO312535B1 - Wheelchair accessible chassis - Google Patents

Description

This invention relates to a drivable undercarriage for a wheelchair, comprising an undercarriage frame on which is mounted the front wheel, primary, large removable/remountable rear wheels and secondary, smaller additional rear wheels, which are movably mounted on the undercarriage frame so that they can be placed in at least two different positions, one non-driving position and one driving position where they also function as a jack when disassembling/reassembling the large rear wheels whose lowest peripheral point in the secondary rear wheel driving/jacking position is at a level above the ground.

In the case of a wheelchair base of this type, the aforementioned large rear wheels have a greater mutual distance across the wheelchair's longitudinal direction than the frame and other pairs of wheels and are thus decisive for the wheelchair's width.

As examples of the state of the art, reference can be made to DE off. document no. 3239472 and DE off. font 19712453.

Often the width of the wheelchair, corresponding to the distance between the aforementioned large rear wheels, is so large that certain doorways are too narrow for the wheelchair to pass through.

To solve this problem, the large rear wheels are attached rotatably to the undercarriage frame by means of quick-connect pieces known per se, so that the large rear wheels can be temporarily dismantled when the wheelchair is to be used for some time in a building with narrow doorways. When the large rear wheels are removed, the smaller rear so-called anti-tip wheels move down to rest against the ground by a pivoting movement that the undercarriage frame makes with the front wheel axle as the pivot axis. The front wheel axle can be height-adjustable, so that the height of the axle above the ground can be adjusted.

After the two large rear wheels are disconnected, the wheelchair's greatest width is reduced to such an extent that it can pass through narrow doorways.

Dismantling and the subsequent reassembly of the large rear wheels is problematic because when disassembling these wheels rest against the ground with a weight that corresponds to the weight of the wheelchair and the wheelchair patient.

According to the present invention, it has been aimed to remedy this problem and thus enable a very convenient disassembly/reassembly of the large rear wheels when such a wheelchair's greatest width is to be reduced temporarily due to narrow doorways or other narrow passages.

This purpose is achieved by each secondary rear wheel carrier being pivotally mounted to the chassis frame for pivoting at least between the secondary rear wheel main positions, the driving/jacking position and a rearward/swinging non-driving/non-jacking position - where the secondary rear wheels are protected the wheelchair against tipping in the rearward direction and thus assumes an anti-tip position - as each of the aforementioned wheel holders is provided with a hand lever/pedal-equipped, preferably angular locking device for blocking/fixing, respectively releasing, each wheel holder in each of its secondary rear wheel's main positions and possibly other positions.

The storage device for said second, smaller, additional rear wheel is thereby generally designed so that these additional rear wheels can be made to act as a jack for the undercarriage frame, the jacking being made to take place immediately before disassembly of said large rear wheel, which is thus located in the jack, relieved position with its lowest points on the circumference at a distance from the ground before and during disassembly.

More specifically, each of the aforementioned second, rear extra wheels is rotatably supported at the end of a wheel holder which, at its other end, is pivotally arranged to the undercarriage frame about a largely horizontal, first pivot axis. The wheel holder carries a pivotable locking member, which is arranged to lock the wheel holder in each of its two main positions, the inactive, raised standby position as a tip protection and its active, lowered jacking and driving position. The locking member can thereby have a locking and blocking part which, in each of the two main positions of the locking member, engages locking/blocking in a corresponding, for example shaped and force-determined complementary locking and blocking part designed in the undercarriage frame.

In relation to a horizontal longitudinal axis which is assumed to represent the central longitudinal axis L of the undercarriage frame which has a certain height extension H to the ground, this vertical distance from the longitudinal axis L to the ground H will correspond to the distance from a horizontal plane for the longitudinal axis L and the outermost, lowest peripheral point on each of the aforementioned first, large rear wheels.

In order to ensure that a jacking-up operation with respect to the undercarriage frame/wheelchair is carried out before the large rear wheels are dismantled while the aforementioned other, additional, rear, small wheels are swung down into an active position, the distance from a horizontal plane for the aforementioned longitudinal axis L to each of the aforementioned second, small rear wheel's outermost lowermost peripheral point in these wheels' effective driving position exceed the height H with an additional height hi which corresponds to the lifting height that you want each of the large rear wheels' lowermost peripheral point to clear the ground with before dismantling the large rear wheels . When reassembling the large rear wheels, the chassis frame is already in the jacked-up position. When the large rear wheels have been mounted in place again using the aforementioned quick couplings, the wheel holders for the aforementioned other, small extra wheels are swung up into an inactive position, possibly as tip protection, whereby the tires of the large rear wheels are lowered to rest against the ground.

In another embodiment, the extra wheel holder is fixed in position in the form of a pivotable arm in its various pivoting positions, in particular main positions, by means of interlocking/releasable locking devices, for example in the form of a spring-loaded locking pin or similar loose locking device, which is displaceable arranged in a recess in the inner end of the swiveling extra wheel holder arm, the outlet end of which recess is designed so that approximately half of the locking member can protrude and is normally held in a protruding position by means of a compression spring, so that said protruding part of the locking member/- the locking pin can be brought into engagement with one of several corresponding edge recesses formed in a stationary locking part which is rigidly connected to the undercarriage frame.

When the extra wheel holder arm is swung obliquely upwards in its inactive position, its spring-loaded locking device (the locking pin) can be in retaining engagement with a relatively shallow, groove-like edge recess in said stationary locking part. The engagement is thereby maintained as long as the engagement connection is not exposed to external forces. If, on the other hand, this pivoting arm is subjected to a downward force by deliberately placing the foot on the arm, the spring-actuated locking pin will, against the action of the compression spring, be pressed completely into the recess at the inner end of the pivoting extra wheel holder arm, whereby the intervention is canceled so that the extra wheel holder arm can be swung to its next swing position where the holder arm is directed backwards in a direction from top to bottom. In order to fix the arm in this swing position which corresponds to the aforementioned second, additional rear wheel tipping protection position where they are to prevent the wheelchair from tipping backwards in a manner known per se, and where the large rear wheels are in active positions, the additional wheel holder arm's locking pin engages in another , groove-like edge recess which has a greater depth than the first edge recess, and which can receive the entire protruding part of the locking pin to ensure a stronger engagement than with the shallower, groove-like edge recess.

The extra rear wheel holder arm can be brought out of this anti-tip position by its spring-loaded locking pin again being pressed completely into the recess at an inner end of the extra rear wheel holder arm, whereby the blocking effect of the locking pin is canceled as it no longer simultaneously engages in said deeper

edge recess in the stationary locking part which is rigidly fixed

done in the chassis frame. For these locking pin pressing-in operations, a pivotably arranged cam disc is used in the area of the locking device which is designed with cam sections along the edge, with one of several different convex between concave cam sections being brought to press against said spring-actuated locking pin when the cam disc is rotated about the pivot point of the extra rear wheel holder arm on the stationary undercarriage frame. This cam disc is also used when the blocking effect is to be canceled while the small extra rear wheels are in the jacking/driving position after the large rear wheels have been fitted again.

These other, extra, small rear wheels can be assigned to a braking device which, for example, is brought into operation opposite the respective extra wheels when these are to be moved into the jacking position. The braking device can optionally be looped, as one can, for example, put one's foot against one of the extra wheels or against a transverse bar that connects the two extra rear wheels.

Non-limiting examples of preferred embodiments of a drivable wheelchair chassis according to the invention are explained in more detail below with reference to the drawings, where fig. 1 and 2 show a first embodiment, while fig. 3-9 shows a second embodiment, and where: Fig. 1 shows in partial side view the drive wheels of the drivable wheelchair chassis in the positions they take when the wheelchair's primary front and rear wheels are in their active position, and the rear, small additional wheels are in their upturned positions as tip protection; Fig. 2 shows a partial side view of the drivable wheelchair undercarriage with the wheels in the positions they take when the small rear wheels have been swung down into the working position and thereby the jack has raised the undercarriage, so that the normal, large rear wheels are in a favorable, pressure-relieved disassembly position ; Fig. 3 shows a partial view, seen from the side, of a drivable wheel-undercarriage, where the additional, small rear wheels are pivotably suspended in accordance with a second embodiment of the invention, the additional rear wheels being shown in their fully inflated, inactive position; Fig. 4 is an enlarged section of fig. 3 and shows a small spare rear wheel, its pivotable wheel holder arm and its associated locking mechanism for locking and fixing the wheel holder arm in the spare rear wheels' various main positions, the spare rear wheel's braking device being in an inactive position, at a distance from the wheel circumference; Fig. 5 corresponds to fig. 3, but shows the extra rear wheel holder arm in a pivoting position where it is directed obliquely backwards in a top-down direction, corresponding to the extra rear wheels' tip protection position where they should be able to prevent the wheelchair from tipping backwards, with the large ordinary rear wheel's axis of rotation as the tipping axis; Fig. 6 shows an enlarged section of fig. 5, but where the braking device is in the active braking position; Fig. 7 corresponds to fig. 3 and 5, but shows the spare rear wheel's pivoting holding arm in the jack position which corresponds to the active driving position when the large ordinary rear wheels have been dismantled, and where the small spare rear wheel's braking device has been brought into an effective braking position in contact with the spare rear wheel's circumference, to prevent it from turning while being brought in the jack position; Fig. 8 shows an enlarged section of fig. 7; Fig. 9 shows a side view similar to fig. 8, but with the brake device in an inactive position and with the pivoting pair of arms' locking pin (locking device) in engagement with the recess in the stationary locking part which corresponds to the driving position of the extra wheels; Fig. 10 shows a perspective view of the small pair of extra rear wheels in a connected state, with the extra rear wheels and their swiveling holding arms in the driving position, essentially corresponding to fig. 9; Fig. 11 corresponds to fig. 9, but here the outer pivoting arm of the pair of arms (see fig. 10) has not been removed as in, for example, fig. 8 and 9, to show a longitudinally elongated guide, stop and storage slot for the transverse locking pin.

In the two embodiments, identical or functionally identical parts are denoted by the same reference number.

In what follows, the embodiment shown in fig. will first be described. 1 and 2: The wheelchair chassis has a horizontal frame 10 which carries a storage part 12 for a first pair of large rear wheels 14, the front of which hides the rear in the drawings. The cross-axle 16 for the large rear wheels 14 has several different storage holes 18 which are offset in relation to each other both in the longitudinal and height directions of the wheelchair.

The undercarriage frame 10 has a horizontally extending central longitudinal axis 20 which one imagines lies in an imaginary, horizontal plane, to which one returns later in connection with the dimensions of the two pairs of rear wheels, namely the large rear wheels 14 which are used if the wheelchair gets through relatively narrow door openings, and a second set, small extra rear wheels 22, which normally occupy the one in fig. 1 shown, boosted, inactive standby position and can then serve as tip protection.

A pair of front wheels 24 are mounted on wheel holders 26 directed obliquely forward/downwards from above which are designed with several storage holes 28 distributed in their longitudinal direction for the front wheel axle 30 to enable mounting of the latter at different levels.

The undercarriage frame 10 has, at its rear end, an attached vertically hanging bracket 32, which at its upper end forms pivotable storage for an elongated, angled wheel holder 34. There is one wheel holder 34 with a pivot shaft 36 for every other, small rear wheel 22. The wheel holders 34 and their locking devices are identical and only one such device will be described in the following: Each wheel holder 34 is provided with a pivotable locking and blocking device 38 which is essentially angled.

The locking and blocking member 38 thus has a rounded locking part 38' which, in both positions for the wheel holder 34 and the rear wheel 22, grips firmly into a downwardly open recess 40 in the end fitting 32, the locking part 38' of the locking and blocking member 38 being retained in a shape and force-determined manner the locking recess 40 in both positions for said second back-

wheel 22.

In the unloaded state, the engagement of the locking part 38' in the locking recess 40 is sufficiently deep that the locking and blocking member 38 is not swung out of this engagement.

The second angular part 38'' of the locking and blocking member 38 is an operating arm (operating pedal) which is pushed down with the foot from the one in fig. 1 shown position during swinging of the member 38 in the anti-clockwise direction to that in fig. 2 shown position where said second, small rear wheel 22 is in active driving position.

Thereby, the locking part 38' of the locking and blocking member 38 is pressed up and further into the locking recess 40 of the fitting 32, until the upper, outer rounded flat bottom of the locking part 38' in the top end part of the fitting recess 40, which has a complementary design.

In order to secure the wheel holders 34 in this effective, inherently blocked and blocked driving position, the blocking and blocking member 38 can be provided with a through transverse hole 42 as in fig. 2, the position corresponds to a spring-loaded locking pin 44 on the locking bracket 32. A safeguard is thereby achieved against the extra rear wheels 22 coming out of the driving position.

One now returns to the aforementioned imaginary horizontal plane through the central longitudinal axis 20 of the wheelchair base frame 10.

In fig. 1, the height H represents the vertical distance from said horizontal plane for the longitudinal axis 20 to the outermost, lowest peripheral point 14' and 24' of the rotation path of the large rear wheels 14 and the small front wheels 24 respectively.

In order for the undercarriage frame portion carrying the large, removable rear wheels 14 to be jacked up sufficiently, for example in the order of 1.0 cm (hi) from the ground to the bottom peripheral point 14' of the rotat ion track, the small rear wheels 22 plus their wheel holders each have such a longitudinal extent that the distance from said horizontal plane through the longitudinal axis 20 of the undercarriage frame 10 to the outermost, lowermost peripheral point 22', fig. 2, is greater than H, i.e. equal to H + hi.

The one in fig. The embodiment shown in 3-11 has many similarities with the embodiment described above, and structurally and/or functionally identical parts are here assigned the same reference numbers as in fig. 1 and 2.

The parts included in the drivable wheelchair chassis such as the front wheel 24, large, ordinary rear wheel 14 and small, extra rear wheel 22 with pivotable wheel holder arms 34 generally will not be described again in connection with this second embodiment; nor will the problems or the general solutions be repeated. However, the outer pivotable arm of the pair of arms 34 is only shown in fig. 10 and 11 to show a special guide, stop and storage gap for a locking device described later, and new features of the outer pivoting arm will be discussed later in connection with fig. 11.

Each of the small additional rear wheels 22 is rotatably supported between two in a pair of included plate-shaped wheel holder arms 34 which are pivotably suspended on a pivot pin 36; everything as with the previous implementation. In contrast to the angled wheel holder arm 34 in the first embodiment, the wheel holder arm 34 in this embodiment, fig. 3 - 11, right.

Each of the aforementioned second, small, additional rear wheels 22 is assigned a braking device 46 in the form of a two-armed lever which can be pivoted about a midpoint between each pair of wheel holder arms 34, its one free end being assigned to a brake cable 48 which, at the opposite end of known manner is attached to a handbrake handle (not shown). The handbrake handle is attached to the wheelchair's push handle located above the backrest, and the brake is operated by the helper pushing the wheelchair.

Instead of using a braking device, one can put the foot on the extra rear wheel 22 to prevent it from turning during the swing of the wheel holder arms 34 about the stationary axis 36 from the one in fig. 5 and 6 showed the anti-tip position to that in fig. 7 and 8 showed jack position. Braking is canceled when the extra rear wheels have taken up the locked position.

In fig. 3 and 4 are the little extras on Jul 22 and their swivels

wheel holder arms 34 shown in an inactive position where the arms 34 from their pivot points 36 point obliquely upwards-backwards. This position can be used when the wheelchair is pushed by a helper. In fig. 5 and 6 show the anti-tip position which can be used when the wheelchair user drives the chair alone by turning the wheels

14 with the hands.

The small extra rear wheels 22 and their pivoting wheel support arms

34 thus have several different positions.

These different swing positions for the small extra rear wheels

22 pivotable wheel holder arms 34 must be able to be blocked and position-fixed, just as respective blocked position fixation must be able to be canceled when the small extra rear wheels are to be placed in one of their other main positions. A locking mechanism and a release mechanism are therefore required for each small extra rear wheel.

The locking mechanism consists of a stationary (fixed to the frame) locking part 52 provided with a pin 53 which is pushed into and attached to the undercarriage frame 10. The locking mechanism 52 is designed with a circular arc-shaped peripheral edge part 52' with its center in the pivot point 36 of the wheel holder arm 34, which is designed with wood above the peripheral part distributed edge recesses 54, 54', 54'', fig. 3 and 4; the shape of one edge recess 54'' can best be seen from fig. 6 and 8.

One of these edge recesses 54, 54', 54'' at a time acts as a locking recess for a cooperating locking member 56, preferably in the form of a locking pin which is displaceably arranged in a spring chamber 58 formed near the end part of the respective extra rear wheel holder arm 34, in a certain distance from its pivot point 36. This spring chamber 58 accommodates a pressure spring 60 for the locking pin 56, possibly two pressure springs 60 at a certain distance from each other.

In fig. 11 shows a possible embodiment for the locking pin 56 storage, control and movement limitation. The spring chamber 58 accommodates the compression spring 60 and can also accommodate the entire locking pin 56, so that this can be brought completely out of engagement with the respective edge recess 54, 54' or 54''.

For storing, guiding and restricting the movement of the locking pin 56, the latter can be assigned to an elongated slot 74 extending in the longitudinal direction of the respective pivotable arm 34, which an outer end part of the locking pin 56 grips displaceably

into.

Cancellation of a created engagement between a stationary locking recess 54, 54' or 54'' and the locking pin 56 is implemented by means of a cam disc-based, engagement canceling release mechanism 62 which is pivotable about the pivot pin 36 of the adjacent wheel holder arm 34.

The cam disc 62 of the release mechanism has, along a certain part of the circumferential edge, two successive convex cam surfaces 66, 66' facing the locking pin 56 with an intermediate concave transition part 68. The convex cam surfaces 66, 66' are delimited by stops 70 and 70 respectively '. The frame discs 62, 64 are mutually connected by a cross bar 72, fig. 10.

When the locking pin 56 engages with one of the edge recesses 54'', 54', 54, the concave transition part 68 of the cam disc 62 is located directly opposite the locking pin 56. When the extra rear wheels 22 and their wheel holder arms 34 swing from the one in fig. 4 to that in fig. 5 position, which usually happens by applying pressure on the cross pin 50 with the foot for anti-clockwise rotation, the cam disc 62 follows with its laterally projecting fastening part 64 for the cross bar 72 and respective wheel holder arm 34. There is therefore no relative oscillation between these parts. When the wheel holder arms 34 arrive in the small extra rear wheel's anti-tip position, fig. 5 and 6, the locking pin 56 snaps into the deep central recess 54'.

When this deep engagement is to be cancelled, the cam-based, engagement canceling release mechanism 62 must be used.

From the one in fig. 5 showed the position of the wheel holder arm 34 and the cam disc 62, to that in fig. position shown in 6, only the cam disc 62 has changed its rotational position, as it has been rotated clockwise in relation to the position of the locking pin 56 such that the convex cam surface 66 has been guided over the locking pin 56 and thereby pushed it out of the edge recess 54' and into in the mouth part of the spring chamber 58, which constitutes a locking pin receiving chamber area, during compression of the spring 60.

From the one in fig. 5 showed the anti-tip position to that in fig. 7 shown jack position, the swing of the wheel holder arm 34 takes place jointly with the cam disc 62 about the pivot point 36. As previously mentioned, the braking device for the small additional rear wheels 22 can be activated immediately before the jack position is established. When the wheelchair is then pulled backwards, the lower part of the wheel holder arm 34 will be at rest while its upper part will move backwards until the locking pin 56 engages with the edge recess 54. In fig. 7, the lifting height is indicated here.

In fig. 8 shows a situation where the small additional rear wheels 22 have been in the driving position, but are now to be transferred to either the anti-tip position, fig. 5, or to inactive position, fig. 3 and 4, the locking pin 56 being moved out of its engagement with the edge recess 54 by means of the cam disc 62. The wheel holder arms 34 are swung from the one in fig. 8 shown position, together with associated cam discs 62, clockwise until the locking pin 56 has come just opposite the edge recess 54' or the shallow edge recess 54''. To create a new engagement as mentioned, the cam disc 62 is swung in relation to the adjacent wheel holder arm 34 so that the concave transition part 68 between the two convex cam surfaces 66, 66' comes into position just opposite the locking pin 56.

In fig. 8, the brake member 46 is shown in an active position. This only applies to the transition movement to the jack position. In the transition position shown from the small additional rear wheel driving position and back to the anti-tip or inactive position, the braking device 46 will not be activated.

In fig. 9 - 11, the brake member 46 is shown in an inactive position and with the locking pin 56 in engagement with the edge recess 54 in the stationary locking part 52, which corresponds to the driving position of the rear extra wheels 22.

Claims (11)

1. Movable undercarriage for a wheelchair, comprising an undercarriage frame (10) on which is mounted a front wheel (24), primary, large removable/remountable rear wheels (14) and secondary, smaller additional rear wheels (22), which are movably mounted on the undercarriage frame (10 ) so that they can be placed in at least two different positions, one non-driving position and one driving position where they also function as a jack when disassembling/reassembling the large rear wheels (14) if the lowest peripheral point (14') in the secondary rear wheels (22) driving/jacking position is at a level above the ground, characterized in that each secondary rear wheel (22) wheel holder (34) is pivotally mounted to the undercarriage frame (10) for swinging at least between the secondary rear wheel (22) main positions, driving/ the jacking position and a backwards/upturned non-driving/non-jacking position - where the secondary rear wheels (22) protect the wheelchair from tipping in the rearward direction and thus assume an anti-tip position - as each of the aforementioned wheel holders (34) are provided with a hand lever/pedal equipped, preferably angular locking member (38, 62, 68) for locking/fixing, respectively releasing, each wheel holder (34) in each of its secondary rear wheel (22) main positions and possibly other positions. 2. Movable undercarriage for a wheelchair according to claim 1, characterized in that the locking part (38') of the locking member (38) consists of a preferably rounded end which cooperates with a downwardly open recess (40) which forms the stationary locking part connected to the undercarriage frame (10), and that the locking recess (40)'s upper end is designed complementary to the preferably rounded, pivotable locking part (38') which in the respective secondary rear wheel's (22) inactive standby position engages with a lower part near the locking recess's (40) opening, and which in respective secondary rear wheel (22) active driving position engages with the upper end of the recess (40), respectively with the edge parts of a fitting part (32) which delimits said parts of the recess (40). 3. Movable undercarriage for a wheelchair according to claim 1 or 2, characterized in that said wheel holder/wheel holder pair (34) has an additional securing means (44), for example a spring-loaded locking pin, which is brought into alignment and engagement with a corresponding additional securing means (42) on the locking member (38), for example in the form of a transverse hole, when the locking parts (38', 40) are engaged in the active driving position of the secondary rear wheels (22). 4. Movable undercarriage for a wheelchair according to claim 1 or 2, characterized in that the wheel holder arm/wheel holder arm pair (34) and a stationary locking part (52) which is rigidly connected to the undercarriage frame (10) are provided with releasably cooperating locking members (56 and 54, 54' , 54'') which engage with each other in the main positions of the secondary, small, rear wheel (22) (idle position, tilt action position, combined jacking and driving position) and hold the wheel holder arm/pair of arms (34) in these positions until they in engagement blocking means (56 and 54, 54', 54'') are intentionally acted upon by an engagement canceling release device (62). 5. Movable undercarriage for a wheelchair according to claim 4, characterized in that the locking device of the wheel holder arm/pair of arms (34) consists of a spring-loaded locking pin (56) in the direction towards the stationary locking part (52)/ and that the stationary locking part (52) is designed with edge recesses (54, 54', 54'') which are spaced apart along a peripheral edge portion of said locking part (52), said spring-loaded locking pin (56) being arranged to snap into respective edge recesses (54, 54', 54 '') and keep the respective wheel holder arm/arm pair (34) locked in the respective main position, as there is a cam disc-based engagement canceling release device (62) which is designed to be able to press the spring-loaded locking pin (56) in in a recess (58) formed in the adjacent wheel holder arm (34) or in a part attached to it, so that the engagement between said locking pin (56) and respective locking recess (54, 54', 54'') is cancelled, whereby the wheel holder arm/arm pair (34) can swung to another position. 6. Movable undercarriage for a wheelchair according to claims 4 and 5, characterized in that the cam disc-based, engagement canceling release device (62) is pivotally supported on the swivel pin (36) of the wheel holder arm (34) and, at the peripheral edge portion facing the wheel holder arm/arm pair ( 34) spring-loaded locking pin (56), exhibits two convex peripheral edge portions (66, 66') with an intermediate, concave transition portion (68) against which said locking pin (56) is oriented and partially engages when the secondary, small, additional rear wheels ( 22) is in one of its main positions and said spring-loaded locking pin (56) engages with one of the edge recesses (54, 54', 54'') of the stationary locking part (52). 7. Movable undercarriage for a wheelchair according to claim 6, characterized in that said cam disc-based, swiveling release device (62) in the circumferential direction at opposite outer ends of said two convex circumferential edge parts (66, 66') has protruding stops (70, 70'). 8. Movable undercarriage for a wheelchair according to claims 1 and 4, characterized in that at least one of the secondary, small, additional rear wheels (22) is assigned a braking device (46,48), with the help of which the small additional wheels can be braked (22) for example immediately before they are to be transferred to the jack position. 9. Movable undercarriage for a wheelchair according to any one of claims 4-8, characterized in that said engagement canceling release devices (62) which are assigned to the two secondary, small, extra rear wheel (22) wheel holder arms (34) are connected by means of a transverse rod (72). 10. Movable undercarriage for a wheelchair according to any one of claims 8 and 9, characterized in that the active members (46) of the two braking devices (46,48) are rotatable about a horizontal axis which can be constituted by a transverse rod (50). 11. Movable undercarriage for a wheelchair according to any one of claims 4-6, characterized in that the spring-loaded locking pin (56) is oriented across the longitudinal direction of said pivotable arms (34) and displaceably arranged in this longitudinal direction in elongated guide slots 74 into which the end parts of the locking pin (56) engage displaceably.