Abstract:
A device for transporting a child in a child seat includes a main frame for supporting the child seat, a swivable push bar for pushing the main frame from different sides, and pivotable wheels or wheel sets for supporting the main frame whereby the wheels or wheel sets are provided with pivot locks and brakes. The push bar has a brake handle for activating the brakes and the device includes a mechanism for activating the pivot locks of the wheels or wheel sets under the push bar and for simultaneously coupling only the brakes on these wheels or wheel sets with the brake handle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from European patent application no. 07104252, filed Mar. 15, 2007, the content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention concerns a device for transporting a child in a child seat ( 1 ) comprising a main frame ( 16 ) for supporting the child seat, a swivable push bar ( 2 ) for pushing the main frame from different sides, pivotable wheels or wheel sets ( 13 , 15 ) for supporting the main frame whereby the wheels or wheel sets are provided with pivot locks ( 69 ) characterized in that the push bar ( 2 ) comprises a brake handle for activating the brakes ( 88 , 93 ) in the wheels or wheel sets ( 13 , 15 ) and that the device comprises a mechanism ( 32 , 35 , 38 , 40 , 42 , 58 , 61 ) for activating the pivot locks ( 69 ) of the wheels or wheel sets under the push bar and for simultaneously coupling only the brakes on these wheels or wheel sets with the brake handle. 
     BACKGROUND OF THE INVENTION 
     Such devices are known, for instance from publication EP 0260056. The disadvantage of the known device is that the wheels have no brakes. From WO 9307039 brakes for each wheel are known but these brakes have to be actuated for each wheel separately which is a disadvantage. 
     SUMMARY OF THE INVENTION 
     In order to overcome this disadvantage the device for transporting a child in a child seat ( 1 ) comprises a main frame ( 16 ) for supporting the child seat, a swivable push bar ( 2 ) for pushing the main frame from different sides, pivotable wheels or wheel sets ( 13 , 15 ) for supporting the main frame whereby the wheels or wheel sets are provided with pivot locks ( 69 ) characterized in that the push bar ( 2 ) comprises a brake handle for activating the brakes ( 88 , 93 ) in the wheels or wheel sets ( 13 , 15 ) and that the device comprises a mechanism ( 32 , 35 , 38 , 40 , 42 , 58 , 61 ) for activating the pivot locks ( 69 ) of the wheels or wheel sets under the push bar and for simultaneously coupling only the brakes on these wheels or wheel sets with the brake handle. 
     In this way the device can be pushed in two directions whereby in each direction the brakes are activated in those wheels for which the pivot locks are activated as well so that when the brakes are activated the pivot locks are activated as well and the wheels or wheel sets are in a stable position relative to the device and can brake properly. 
     In accordance with an embodiment the device comprises a push bar ( 2 ) that is coupled to a push bar axis ( 21 ) swivellable in bearings ( 25 ) mounted on the main frame ( 16 ), which push bar axis has cams ( 32 , 38 ) activating cable pulling means connected to cables ( 47 ) which actuate the pivot locks ( 69 ). In this way changing the activation of the swivel locks is combined in an easy way with changing the position of the push bar. 
     In accordance with an embodiment the device comprises a push bar ( 2 ) that is coupled with a slide ( 22 ) to a push bar axis ( 21 ) swivellable in bearings ( 25 ) mounted on the main frame, which slide can be positioned along the length of the push bar for changing its longest distance from the push bar axis. In this way the height of the push bar can be adapted to the length of the person using the device. 
     In accordance with an embodiment the device comprises a push bar ( 2 ) that is U-shaped and at both ends connected by the slides ( 22 ) to the push bar axis ( 21 ). In this way there is a strong and stable connected push bar. 
     In accordance with an embodiment the device comprises a horizontal axes ( 83 ) of the wheels or wheel sets ( 13 , 15 ) that are mounted in a spring arm ( 77 ) that can resiliently move relative to the main frame ( 16 ) against a spring ( 82 ). In this embodiment the device means has springs that reduce the jolts as a result of an uneven pavement and the child transported in the device is more comfortable. 
     In accordance with an embodiment the device comprises a spring arm ( 77 ) that has a brake lever ( 85 ) for activating a brake ( 88 ,  93 ), which brake lever has a arc shaped cam surface ( 91 ) on which a cable activated pin ( 73 ) can push for activating the brake. In this embodiment the activation of the brake is independent from the position of the spring arm. This means that the weight of the child or the condition of the pavement has no influence on the braking. 
     In accordance with an embodiment, the rotation of the wheel ( 84 ) can be stopped by moving a brake lever ( 85 ) coupled to a brake pin ( 104 ) so that the brake pin is pushed between brake notches ( 88 ) on the inside of the hub ( 87 ) of the wheel and whereby the brake pin can move against a spring ( 106 ) in a slot ( 103 ) in the brake lever when the brake pin is pushed against a brake notch. In this way activation of the brake does not lead to unacceptable deformations when the brake notch prevents moving of the brake pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained below with reference to one or more exemplary embodiments with the aid of a drawing, in which: 
         FIG. 1  shows a perspective view of a stroller with a child seat, 
         FIG. 2  shows a perspective view of the stroller of  FIG. 1  adapted for pushing the stroller in the opposite direction, 
         FIG. 3  shows the stroller of  FIG. 1  in side view without child seat, 
         FIG. 4  shows the stroller of  FIG. 2  in side view without child seat, 
         FIG. 5  shows the stroller of  FIG. 1  in side view without child seat and with reduced height of a push bar, 
         FIG. 6   a  shows a schematic section of a first embodiment of a push bar rotation axis and a mechanism activated by the push bar rotation axis for controlling the wheel pivots, 
         FIG. 6   b  shows a top view of a second embodiment of the push bar rotation axis and the mechanism for controlling wheel pivots, 
         FIG. 6   c  shows a top view of a third embodiment of the push bar rotation axis and the mechanism for controlling wheel pivots, 
         FIGS. 7   a - c  show a rendering of cam surfaces used in the mechanism shown in  FIG. 6 , 
         FIGS. 8   a - c  show schematic sections of a part of a wheel pivot under three control conditions, 
         FIG. 9  shows a schematic section of a wheel pivot with wheel, 
         FIGS. 10   a - c  show schematic sections of the wheel pivot as shown in  FIG. 9  under three control conditions, 
         FIG. 11  shows a top view of the lower part of the wheel pivot and partly a section of the wheel, 
         FIGS. 12   a - b  show side views of the wheel pivot with wheel, 
         FIG. 13   a  shows a second embodiment of the wheel in side view whereby the wheels are free to rotate, 
         FIG. 13   b  shows a detail of the side view of the embodiment of  FIG. 13   a  whereby the brake is activated, and 
         FIG. 13   c  shows a section and view XIV-XIV of a hub with a brake pin. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a child seat  1  mounted on a stroller  4 . The child seat  1  has a seat frame  19 , which encompasses the child seat  1 . A carrying handle  20  for carrying the child seat  1  is fastened to the seat frame  19  and can be used for lifting the child seat  1  off the stroller  4 . The stroller  4  has a support bracket  3 , which connects to the seat frame  19 . The support bracket  3  is connected with a lower support bar  6  via a lower support bearing  9  to a lower frame  10  and also with an upper support bar  7  via an upper support bearing  8  to an upper frame  16 . The C-shaped support bracket  3  is reinforced at its open end with a bar  5 . In  FIG. 1  the shown child seat  1  is an infant carrier type, suitable for very young children. The C-shaped support bracket  3  has a design that is also suitable for connecting to other child seat types, such as a conventional stroller seat for older children and/or a carry cot type for new born children. In this way the stroller  4  is suitable for use with children of different age groups. 
     The upper frame  16  and the lower frame  10  are coupled by a rail  18 , which is fastened in the lower frame  10  and which can slide in the upper frame  16 . This relative movement of the upper frame  16  and the lower frame  10  arranges that the stroller  4  can fold to a smaller size when not in use. For this reason the first wheel arms  12  can slide through an opening in the lower frame  10  and are connected with their ends to the upper frame  16  and the second wheel arms  14  are coupled with their ends to the lower frame  10  and are coupled with a connecting bar  17  to the upper frame  16 . When folded out in the position of use of the stroller  4  the first wheel arms  12  have at their lower ends a wheel pivot  11  with a first wheel set  13 , whereby the wheel pivot  11  has a vertical pivot axis so that the wheel set  13  can pivot around this axis. In that position the second wheel arms  14  have at their lower ends wheel pivots  11  in the same position so that a second wheel set  15  can pivot around the vertical pivot axis. 
     For pushing the stroller  4  there is a push bar  2  fastened on the upper frame  16 . In the position shown in  FIG. 1 , the push bar  2  is behind the head of the child in the child seat  1  and the child is facing forward in the same direction as the direction of travel of the stroller  4 . At each end of its U shaped legs the push bar  2  has a push bar slide  22 , which push bar slides  22  are connected by a push bar axis  21 . The push bar axis  21  can rotate in push bar bearings  25  (see  FIGS. 3-6 ) which is fastened on the upper frame  16 . The wheel pivots  11  are designed such that the pivot movements of the wheel sets  13 , 15  can be locked so that for the two wheel sets that are located on the side of the push bar  2 , hereafter described as underneath the push bar  2 , have a common rotation axis c which is perpendicular to the general direction of travel. In  FIG. 1  the wheels of the first wheel sets  13 , which are nearest to the person pushing the stroller  4 , rotate around a common rotation axis c and cannot pivot and the second wheel sets  15  are free to pivot in the wheel pivots  11 . This makes maneuvering the stroller easier. 
       FIG. 2  shows the stroller  4  of  FIG. 1 , whereby the push bar axis  22  has been rotated in the push bar bearing  25  to the other side of the stroller  4 . In this position, the child looks to the person pushing the stroller  4 , and the first wheel sets  13  are now free to pivot while the wheels of the second wheel sets  15 , which are under the push bar  2 , are in a locked pivot position with a common rotation axis c. 
       FIG. 3  shows the stroller  4  with the push bar  2  in the position as shown in  FIG. 1 , whereby the push bar  2  makes an angle of approximately 10 to 15 degrees with the plane of the upper frame  16  and lower frame  10 . In  FIG. 3  the stroller  4  is shown without child seat  1 . It is schematically shown that for positioning the child seat  1  the support bracket  3  has a positioning pin  23 . For coupling the child seat  1  to the stroller  4  there is a strong construction, which is not shown here. Interrupted lines show a first slide  94  connected to the lower support bar  6 , the position of the first slide  94  is lockable in the support bracket  3  and can be changed by activating the release button  24 . 
     The upper support bar  7  is coupled in the support bracket  3  to the first slide  94  by a second slide movable relative to the first slide  94 , the position of the second slide is determined by the distance between the upper support bearing  8  and the lower support bearing  9  and thereby changes during folding of the stroller  4 . The slides in the support bracket  3  create a stable connection between the support bracket  3  and the stroller  4  so that there is a stable coupling between the child seat  1  and the stroller  4 . In a different embodiment the upper support bar  7  is directly coupled to the first slide  94  by a pivot (not shown). 
       FIG. 4  shows the stroller  4  with the push bar  2  in the position as shown in  FIG. 2 , whereby the push bar  2  is rotated a further 85-90 degrees in the push bar bearing  25 . This further rotation of the push bar axis  21  changes the settings of the wheel pivots  11  so that the pivoting of the wheel sets  13  under the push bar  2  is locked and the wheels will have a common rotation axis c. The forward wheel sets  15  can pivot freely. 
       FIG. 5  shows the stroller  4  as shown in  FIG. 3  with a reduced height of the push bar  2 . This is achieved by releasing the movement of the push bar slide  22  with a height setting release button on the push bar  2  (not shown). The push bar slide  22  can slide over a distance a along the push bar  2 , whereby the distance a can be approximately 200 mm. In this way, the height of the push bar  2  can be adapted to the height of the person pushing the stroller  4 . 
       FIG. 6   a  shows in a schematic section the mechanism used for changing the settings of the wheel pivots  11  by rotating the push bar axis  21  and the connection of the push bar axis  21  to the push bar  2 . The push bar axis  21  is a hollow pipe  21 , which can rotate in the two push bar bearings  25 . The hollow pipe  21  is inserted in a groove  49  of the push bar slides  22  are fastened thereto in a fixed position in a known way. The push bar slide  22  can slide over the distance a that can be 200-250 mm along the push bar  2 . The push bar  2  shown in  FIG. 6  is shown to have a partly open profile in which the push bar slide  22  can be positioned. 
     For positioning the push bar slide  22  relative to the push bar  2  a notched plate  27  of this distance is mounted on the push bar  2  and a spring loaded catch  28  mounted in the push bar slide  22  can click in openings of the notched plate  27 . In the push bar the height setting release button pushes in each push bar slide  22  a release bar  95  downwards. The release bar  95  is provided with wedges  96  for pushing the catches  28  out of the openings in the notched plate  22 , so that the push bar slide  22  can slide in the push bar  2  till the catch  28  clicks in the next opening. 
     Near one of the push bar bearings  25  a pin  44  rotationally positions a toothed ring  45  on the outside of the push bar axis  21 . The hollow pipe  21  has two slots  54  for positioning the pin  44  so that the toothed ring  45 , with teeth  53  on its outside circumference, can move in axial direction along the push bar axis  21  and rotates with this axis  21 . A positioning ring  46 , with teeth  53  on its inside circumference, is fastened to the push bar bearing  25 . The teeth  53  on the toothed ring  45  and the positioning ring  46  make it possible that in at least two positions the toothed ring  45  can slide inside the positioning ring  46  for blocking the rotation of the push bar axis  21 . These blocked positions of the rotation of the push bar axis  21  coincide with the positions of the push bar  2  as indicated in the  FIGS. 1 and 3  and  2  and  4 . 
     In an embodiment that is not shown here there is a further lever that is activated by the axial movement of the toothed ring  45 . This lever unlocks the axial movement of the rail  18  in the upper frame  16  so that the movement of the rail  18  is locked when the toothed ring  45  is positioned inside the positioning ring  46  and the stroller  4  is ready for use and the stroller  4  can be folded when the toothed ring  45  is outside the positioning ring  46  and the push bar  2  is free to rotate. 
     The pin  44  is fixed in and moves in axial direction with a swivel release sleeve  56 , which is mounted inside the hollow pipe of the push bar axis  21 . A spring  57  between the swivel release sleeve  56  and the push bar slide  22  pushes the toothed ring  45  in the positioning ring  46  when the push bar axis  21  is in the right rotational position. A swivel release cable  26  can pull the toothed ring  45  out of the positioning ring  46 . The swivel release cable  26  is activated by a swivel release handle (not shown) mounted on the push bar  2 , and is guided along the sheaves  59  on the push bar slide  22  and sheave  60  on the swivel release sleeve  56  and its end is fastened on the push bar  2  with a clamp  52 . By guiding the swivel release cable  26  in this way the push bar slide  22  can move along the push bar  2  without influencing the position of the swivel release sleeve  56 . 
     For locking the wheel pivots  11  of the first wheel sets  13  the wheel pivots  11  of the wheel sets  13  are connected with levers  61  by a cable  47 , which is part of a Bowden cable between the upper frame  16  and a wheel pivot  11 . For locking the wheel pivots of the second wheel sets  15  the wheel pivots  11  are connected by cables  47  with levers  58 . The position of the levers  58  and  61  determines whether the wheel pivot  11  is locked or free and whether a brake is applied to the wheels or not. When the lever  58  or  61  is in position P the wheel pivot  11  can rotate and there is no brake applied to the wheels. With the lever  58  or  61  in position Q the wheel pivot  11  will lock in a fixed position and the brake is not applied to the wheels either. With the lever  58  or  61  in position R the wheel pivot  11  will lock in a fixed position and the brake will be applied to the wheels. In the wheel pivots  11  the cables  47  that are connected to the first wheel sets  13  are subjected to a pulling force F 1  and in the wheel pivots  11  the cables  47  that are connected to the second wheel sets  15  are subjected to a pulling force F 2 . It has been found that it is sufficient for keeping the stroller  4  located at one position to brake only those two wheel sets that have locked wheel pivots  11 . 
     The levers  58  and  61  rotate around a pivot pin  36  and are moved by a pin  29  which is fixed in a lever actuating slide  42 . For coupling the movement of the levers  58  and  61  with the movement of the lever actuating slide  42  the levers  58  and  61  are provided with a slotted hole  30 . For guiding the lever actuating slide  42  it is provided with a slot  43  which can move along a guide pin  41 . 
     The lever actuating slide  42  that positions the levers  58  is connected to a fourth cam ring  40 . This fourth cam ring  40  is pushed by the pulling force F 2  in axial direction against a third cam ring  38  and can be moved by it. The rotation of the third cam ring  38  is coupled to the rotation of the push bar axis  21  by a pin  39 . The pin  39  can move in axial direction in the slots  31  and  34  and is fixed in a wheel braking bar  37 . The surface between the third cam ring  38  and the fourth cam ring  40  is profiled as indicated in  FIG. 7 . As the rotation of the push bar axis  21  and the third cam ring  38  are coupled and the fourth cam ring  40  does not rotate this rotation creates an axial movement positioning the levers  58  in the positions P and Q. For bringing the levers  58  in the position R, where by the wheels of the second wheel set  15  are braked, a brake handle on the push bar  2  (not shown) is activated whereby the brake cable  48  is pulled. The brake cable  48  is guided along sheaves  51 , which are mounted in the push bar slide  22 , and a sheave  50 , which is mounted on the wheel braking bar  37  and the end of the brake cable  48  is fastened to the push bar  2  by a clamp  52 . By pulling the brake cable  48  the wheel braking bar  37  pushes the third cam ring  38  and the fourth cam ring  40  to the right so that the levers  58  are brought in position R. In order that the axial movement of the wheel braking bar  37  is not hindered by the pin  44 , this pin is guided through a slot  55 . By limiting the length of the slot  55  braking can be prevented in situations when the push bar  2  is free to rotate. 
     For actuating the levers  61  the lever actuating slide  42  coupled to the levers  61  is coupled to a second cam ring  35  which is pulled by the pulling force F 1  in axial direction against a first cam ring  32  which is connected in the same way as previous described for the third cam ring  38  by a pin  33  to the wheel braking bar  37  and rotated by the push bar axis  21 . When the push bar axis  21  rotates, the first cam ring  32  moves the second cam ring  35  in axial direction and so adjusts the setting of the lever  61 . The wheel braking bar  37  activates the braking of the first wheel sets  13  in the same way as described above for the second wheel sets  15 . 
       FIG. 6   b  shows a top view of a second embodiment of the mechanism used for changing the settings of the wheel pivots  11  by rotating the push bar axis  21 . In this embodiment the cables  47  are directly connected with their cable ends  99  to the second cam ring  35 ′ and the fourth cam ring  40 ′, thereby avoiding backlash and resistance in the various levers. The load on the cam rings  35 ′,  40 ′ is equally divided over the circumference which improves the contact between the first cam ring  32  and the second cam ring  35 ′ and respectively the third cam ring  38  and the fourth cam ring  40 ′ and improves their movements in longitudinal direction along the push bar axis  21 . For guiding the cables  47  to either both first wheel sets or both second wheel sets both cables  47  are guided around a first capstan  97 , after passing the capstan  97  one of the cables is connected to the cam ring  35 ′ or  40 ′ and the other is looped around a second capstan  98  and then connected to the cam ring  35 ′ or  40 ′. The Bowden cables have cable shields  101  that end in a cable shield stop  102 . The cable shield stops  102  are fastened in a known way on the upper frame  16 . In the embodiment shown the four cables  47  pull the cam rings  35 ′,  40 ′ in the same direction so pushing the push bar axis  21  in a stable position. In a further embodiment, the cables  47  could have opposite directions so reducing the axial load on the push bar axis  21 . 
       FIG. 6   c  shows a top view of a third embodiment of the mechanism used for changing the settings of the wheel pivots  11  by rotating the push bar axis  21 . In this embodiment, a second cam ring  35 ″ is directly coupled to the cable end  99  and/or the cable shield stop  102  of both Bowden cables to the second wheel sets  15 . A fourth cam ring  40 ″ is also directly coupled to the cable end  99  and/or the cable shield stop  102  of both Bowden cables to the first wheel sets  13 . In this embodiment, the cables  47  follow a straight line from the cable shield stops  102  to the cable end  99  and if required are guided through an opening  100  in either the second cam ring  35 ″ or the fourth cam ring  40 ″. 
       FIG. 7  shows a rendering of the cam surfaces and the interaction between the first cam ring  32  and the second cam ring  35  (or  35 ′ and  35 ″ respectively) and respectively the third cam ring  38  and the fourth cam ring  40  (or  40 ′ and  40 ″ respectively) as a result of the rotation of the push bar axis  21  which is illustrated by the differing positions of the pins  33  and  39 .  FIG. 7   a  shows the situation of  FIG. 1  whereby only the wheel pivots  11  of the first wheel sets  13  are locked,  FIG. 7   b  shows the situation of  FIG. 2  whereby only the wheel pivots  11  of the second wheel sets  15  are locked and  FIG. 7   c  shows the situation whereby all wheel pivots  11  are free to rotate for instance in a situation during folding of the stroller  4 . 
       FIG. 8  shows an upper pivot housing  65  of the wheel pivot  11 , whereby  FIG. 8   a  shows the situation when the lever  58  or  61  connected to the wheel pivot  11  is in the position P whereby the wheel pivot  11  can pivot freely.  FIG. 8   b  shows the situation whereby the lever  58 , 61  is in the position Q whereby the pivoting is locked and  FIG. 8   c  shows the situation whereby the lever  58 , 61  is in the position R and the pivoting is locked and the wheel is braked. The cable  47  is attached to a control lever  62  which pushes on a control rod  67  that is movable in axial direction in a pivot axis  68 . The control rod  67  extends below the pivot axis  68  in the situation whereby the wheels must be braked. The outside of the pivot axis  68  has a groove  66  for positioning the pivot axis  68  in a lower pivot housing  76 , see  FIG. 9 . A brace  63  is connected to and moves with the control rod  67 . A pin  64  is connected to the brace  63  and the pin  64  actuates a pivot lock  69 . 
       FIG. 9  shows a wheel pivot  11  together with a wheel  84  of the wheel set  13 , 15 .  FIGS. 10   a ,  10   b  and  10   c  show the wheel pivot  11  in more detail respectively in the positions P, Q and R of the cable  47 , the control lever  62  and the control rod  67 . The lower pivot housing  76  can rotate around the pivot axis  68 . A lock is clicked in the groove  66  of the pivot axis  68  to fixate the pivot axis  68  in the lower pivot housing  76 . For removing the wheel set  13 , 15  from the wheel pivot  11   a  wheel remove button  71  can be pushed so that the lock is free from the groove  66 . 
     The lower pivot housing  76  has a socket  70  in which the pivot lock  69  can be inserted. If the pivot lock  69  extends into the socket  70 , rotation of the lower pivot housing  76  relative to the upper pivot housing  65  is locked. As the control rod  67  and the brace  63  with pin  64  can be lowered by the cable  47  while the socket  70  is not under the pivot lock  69  the pin  64  and the pivot lock  69  are coupled in such a way that their total length can be reduced under a spring load. With a lowered pin  64  as soon as the pivot lock  69  is above the socket  70  this spring load pushes the pivot lock  69  into the socket  70 . The pivot lock  69  and the pin  64  are coupled in such a way that when the pin  64  moves upwards with the control rod  67  it pulls the pivot lock  69  upwards out of the socket  70 . 
     In the lower pivot housing  76  immediately under the control rod  69  there is a slide piece  72  which is pressed by a spring  74  against the control rod  67  and which slide piece  72  follows the axial movement of the control rod  67 . The spring  74  causes the tension in the cable  47 . Perpendicular to the pivot axis  68  there is a swivel axis  75  that connects the lower pivot housing  76  to a swivel arm  77 . The swivel arm  77  holds a wheel axis  83  on which a hub  87  is mounted, which hub  87  is connected to a wheel rim  81  around which there is a tire. At the side of the lower pivot housing  76  there is a spring bracket  78 . Between an axis  79  through the spring bracket  78  and the wheel axis  83  a spring holder  80  with a spring  82  is mounted. This spring  82  absorbs the bumpiness in a pavement on which the stroller  4  rides. For limiting the stroke of the spring  82  the rotation of the swivel arm  77  is limited by a toggle  89  which can rotate around a pin  90  and which toggle  89  interacts with the lower pivot. housing  76 . For detecting axial movement of the slide piece  72  the slide piece  72  is coupled to a brake control rod  73  which controls the movement of a brake lever  85  (see  FIGS. 11 and 12 ) and which is movable in a slot  92 . 
       FIG. 11  shows a top view of the lower pivot housing  76  and partly a section of the wheel with the hub  87 . The hub  87  rotates using a bearing  86  around the wheel axis  83 , whereby the wheel axis  83  is fastened in the swivel arm  77 . The brake levers  85  are mounted on both sides of the swivel arm  77  near the wheel hubs  87  and can rotate around the pin  90 . On the inside circumference of the hub  87  there are brake notches  88  that can interact with a resilient brake nib  93  (see  FIG. 12 ) for stopping the rotation of a wheel. The brake nib  93  is elastic and made of for instance rubber, so that no damage occurs when the brake lever  85  pushes the brake nib  93  on a brake notch  88  instead of between two brake notches  88 . 
       FIG. 12  shows in two views a wheel set  13 , 15  with a wheel  84  in side view with one of the wheels  84  removed so that the brake lever  85  can be seen in side view.  FIG. 12   a  shows the situation whereby the wheel can rotate freely and  FIG. 12   b  shows the situation whereby the brake control rod  73  is moved downwards by the slide piece  72  (see  FIGS. 9 and 10 ) in the slot  92 . The brake control rod  73  runs through an arcuate slot  91  of the brake lever  85  and by moving the brake control rod  73  downwards the brake lever  85  is pushed to rotate around pin  90 . If this is possible, the brake nib  93  then moves upwards, is inserted between the brake notches  88  and so stops the rotation of the wheel. If the brake nib  93  cannot move upwards the brake control rod  73  will bend until the brake nib  93  can slip between two brake notches  88 . The slot  91  through which the brake control rod  73  runs is arcuate so that the swivel arm  77  with the brake lever  85  can rotate around the swivel axis  75  and so follow the bumpiness in the pavement. 
       FIGS. 13   a - 13   c  show a further embodiment of the wheel sets. In this embodiment a bearing  109  is mounted in the swivel arm  77 . The wheel axis  83  rotates in the bearing  109  and is fixed in the hub  87 . The spring  82  is directly coupled to the spring bracket  78  and the swivel arm  77 . The coupling between the brake lever  85  and the hub  87  is with a brake pin  104 . The brake pin  104  extends through slots  103  in the brake lever  85  to within the hub  87 . Each brake lever  85  has a spring  106  that is located in a holder  105  at the side and one end of the spring  106  extends through a hole  105 . The spring  106  pushes the brake pin  104  towards the brake notches  88 . 
     In  FIG. 13   a  the brake control rod  73  is in its upward position in the slot  92  and the wheel  84  is not braked and the brake notches  88  can rotate past the brake pin  104 . In  FIG. 13   b  the brake control rod  73  has moved downwards in the slot  92  and the brake lever  85  rotates around pin  90 . For braking the wheel  84 , the brake pin  104  has to move between the brake notches  88  in a gap  108 . As is shown in  FIG. 13   b  and in  FIG. 13   c  on the left side of the figure, a brake notch  88  sometimes prevents this. In that situation the brake pin  104  can move in the slot  103  so that no damage occurs. After the wheel  84  has rotated slightly the brake pin  104  slides into the gap  108  and rotation of the wheel  84  is stopped, see  FIG. 13   c  on the right side.