WO2008146136A2

WO2008146136A2 - Wheelchair

Info

Publication number: WO2008146136A2
Application number: PCT/IB2008/001338
Authority: WO
Inventors: Aniello Langella
Original assignee: Stabilimento Ortopedico Variolo Srl
Priority date: 2007-05-31
Filing date: 2008-05-28
Publication date: 2008-12-04
Also published as: EP2157960B1; EP2157960A2; ITUD20070101A1; WO2008146136A3

Abstract

Wheelchair (10) comprising at least a seat (12) for the user, two rear wheels (13, 113) disposed lateral to the seat (12), at least a front wheel (15), and thrust means (16, 116) associated coaxially with an external side of each of the first wheels (13, 113). The wheelchair (10) also comprises means to invert the motion (20, 120) mounted on each of the rear wheels (13, 113) in an intermediate position between each of the wheels (13, 113) and the relative thrust means (16, 116). The means to invert the motion (20, 120) are selectively configurable with respect to the thrust means (16, 116) and the wheels (13, 113) so as to define at least a first position of concordant thrust, in which the thrust means (16, 116) are associated with the wheels (13, 113) so that a rotation thereof in a first direction determines a rotation of the wheels (13, 113) in the same first direction, and a second position of discordant thrust, in which the thrust means (16, 116) cooperate with the means to invert the motion (20, 120) so that a rotation thereof in the first direction determines a rotation of the wheels (13, 113) in a second direction, opposite the first direction.

Description

"WHEELCHAIR"

* * * * *

FIELD OF THE INVENTION

The present invention concerns a wheelchair. The present invention also concerns a wheel for a wheelchair or similar means of locomotion.

In particular, the invention concerns a wheelchair in which the wheels are equipped with a mechanism to invert the motion, permanently or selectively activated, which allows the motion of the thrust system to be inverted while keeping the direction of movement of the wheelchair unchanged. BACKGROUND OF THE INVENTION

Wheelchairs are known, used as an instrument of locomotion by persons deprived of the total or partial use of the lower limbs, since birth or due to subsequent traumas.

In order to move, forward or backward, traditional wheelchairs use the propulsion generated by the user himself, acting on a thrust rim mounted coaxial to and outside each wheel. Traditional wheelchairs are conformed in such a manner that the thrust exerted by the user with his arms is directed in the same direction in which he wants to move the wheelchair.

In other words, if the user sitting in the wheelchair wants to move forward, he must act on the thrust rims so as to put the wheels in rotation in a clockwise direction, moving his arms backward with respect to his body and then moving them from behind to forward, so as to exert a thrust on the wheels.

This movement from back to forward is very unnatural, however, and needs an unfavorable biomechanical disposition of the user's arms and the upper part of his trunk, entailing a thrust which is not very effective in proportion to the force exerted. In other words, the bone levers and the muscular masses involved in the thrust movement are not used in an optimum manner, and especially they exploit only a limited thrust angle.

This movement often causes motor and clinical complications for the user, due to muscular stress on some joints and to correlated pathologies, thus making periodic sessions to rehabilitate the patient necessary and possibly the prescription of drugs.

These disadvantages also entail an increase in health expenses both with regard to the rehabilitation and medical programs, and also with regard to the use of drugs.

One purpose of the present invention is to achieve a wheelchair that allows the user to make an ergonomic and effective thrust in order to determine movement.

Another purpose of the present invention is to achieve a wheelchair which guarantees a rehabilitative and therapeutic action for the patient, and allows to reduce health expenses as much as possible, both with regard to the rehabilitation and medical programs, and also with regard to the use of drugs.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purpose, a wheelchair according to the present invention comprises a seat on which the user sits, two rear wheels disposed^ lateral to the seat, and at least a front wheel, possibly pirouetting. The wheelchair according to the invention also comprises means used for thrust, for example a thrust rim associated coaxially to the external side of each of the rear wheels.

In the following description we shall refer to a traditional wheelchair, in which the thrust means are manual and are directly associated with both rear wheels of the chair. However, the invention is equally applicable, with the suitable adaptations, to chairs of different types, for example with traction exerted by a single rear wheel, or by one or two front wheels, or again to chairs in which the thrust means are associated with the wheels not directly but by means of suitable transmission elements.

According to a characteristic feature of the present invention, the wheelchair comprises means to invert the motion, mounted on the respective rear wheels in an intermediate position between each of them and the relative thrust rim. Moreover, the inversion means are able to be selectively configured, with respect to the thrust rim and the relative rear wheel, so as to define at least a first position of concordant thrust, in which the rim is angularly attached to the relative wheel, so that a movement thereof in one direction, for example clockwise, determines a corresponding rotation of the rear wheels in the same first direction, and a second position of discordant thrust, in which the rim is angularly released from the relative wheel and cooperates with the inversion means, so that a movement thereof in the first direction determines a corresponding rotation of the relative rear wheels in a second direction, for example anti-clockwise, opposite the first.

With the present invention, therefore, by selectively configuring the inversion means in their second position, it is possible to determine the advance of the wheelchair, exerting a thrust directed in the direction opposite the direction of advance; that is, if we want to move the wheelchair forward, the arms are taken forward with respect to the body and moved exerting a thrust from forward to back.

In this way, it is possible to use favorable biomechanical levers of the user's arms and the upper part of his trunk, correctly and harmoniously stimulating the joints concerned in the movement, considerably reducing fatigue and muscular mechanical stress.

The solution according to the invention thus allows to increase the efficiency of the thrust in proportion to the force exerted, also allowing to extend the angle of thrust. Furthermore, by effecting a thrust from forward back, improvements are obtained both in correlated and secondary pathologies, and also in systemic breathing pathologies (thanks to a more correct stimulus on the diaphragm), cardiovascular pathologies and others.

Thanks to this, we have a reduced need to provide frequent rehabilitation sessions, or the administration of drugs, consequently reducing health expenses.

The possibility of selectively configuring the inversion means allow the user to use the traditional thrust system, moving his arms from back to forward, in those situations where that may be preferable, for example, for small or minimum movements, or if the user has particular pathologies, for example of the arms and/or the upper part of the trunk.

In a preferential form of embodiment, for each rear wheel, the means to invert the motion comprise a kinematic mechanism to invert the motion, in which an idler member is provided.

According to a variant, the idler member comprises at least an idler wheel disposed with its axis of rotation substantially perpendicular to the axis of rotation of the relative wheel, and in such a manner as to rotate on an external surface of said wheel. In this variant, the selective configuration of the inversion means determine the axial displacement of the thrust rim. The rim, in the first position, is angularly constrained due to direct contact with the rear wheel and, in the second position, contacts the idler wheel so that the idler wheel contacts, on one side, the rear wheel and, on the other side, the thrust rim, making the direction of rotation of one discordant with respect to that of the other.

According to another variant, the idler member is part of a kinematic transmission mechanism, for example consisting of toothed crowns and chains, toothed wheels engaging with each other, pulleys with toothed belts, or combinations of such mechanisms, so as to determine, apart from the inversion of the motion, also a desired transmission ratio between the thrust rim and the rear wheel and vice versa.

In particular, in this last variant, the selective configuration of the inversion means in the second position determine the axial displacement of a friction flange which angularly constrains/releases the idler member and the rim, deactivating/activating the inversion effect determined by the kinematic transmission mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 shows a first form of embodiment of a wheelchair according to the present invention;

- fig. 2 shows the wheelchair in fig. 1 with a sectioned detail;

- fig. 3 shows an enlarged detail, partly sectioned, of the wheelchair in fig. 1, in a first operating condition;

- fig. 4 shows an enlarged detail, partly sectioned, of the wheelchair in fig. 1, in a second operating condition;

- fig. 5 shows an enlarged sectioned detail of a second form of embodiment of the wheelchair according to the present invention, in a first operating condition; - fig. 6 shows the detail in fig. 5 in a second operating condition;

- fig. 7 is a schematic front view, partly sectioned, of fig. 5.

DETAILED DESCRIPTION OF SOME PREFERENTIAL FORMS OF

EMBODIMENT

With reference to figs. 1 and 2, a wheelchair 10 is shown in its entirety, comprising as essential elements a frame 11, a seat 12, two rear wheels 13, mounted rotary on the frame 11 by means of respective hubs 19, and two front pirouetting wheels 15.

The wheelchair 10 according to the present invention also comprises two thrust rims 16, mounted coaxial on the hubs 19 of the rear wheels 13, and each provided with a thrust ring 17, which allows the user, sitting in the seat 10, to grip so as to exert the movement thrust.

The wheelchair 10 according to the present invention also comprises two members to invert the motion 20, each mounted in an intermediate position between a relative rear wheel 13 and the associated thrust rim 16.

In particular, each member to invert the motion 20 comprises a radial support 21 with three spokes 22, attached to the relative hub 19, and able to support rotatably, on each spoke 22, a respective idler wheel 23.

Each idler wheel 23 is normally in contact with an external surface of the relative rear wheel 13 and has its axis of rotation substantially perpendicular to the axis of rotation of the relative rear wheel 13. Advantageously, each idler wheel 23 has an external crown made of material with high friction coefficient, so as to slip as little as possible with respect to the external surface of the relative rear wheel 13.

According to the invention, each thrust rim 16 is mounted on the relative hub 19 so as to be able to be selectively moved in an axial direction in order to assume two operating positions, respectively in contact with or detached from the relative rear wheel 13.

The thrust rim 16 is selectively positionable between a first concordant thrust position (fig. 3), in contact with the respective rear wheel 13, in which the direction of rotation imparted by the user to the thrust rims 16 is transmitted concordantly to the rear wheels 13, and a second discordant thrust position (fig. 4), distanced from the relative rear wheel 13, in which the direction of rotation imparted by the user to the thrust rims 16 is transmitted discordantly to the rear wheels 13, through the action of the member to invert the motion 20.

The selective movement between the first thrust position and the second thrust position is made by the user sitting on the wheelchair 10, by means of a cam lever 27, kinematically connected to the thrust rim 16 in correspondence with the zone where it is mounted on the hub 19.

In this case, the cam lever 27 is configured so that its rotation of about 180° determines the movement between the two positions.

In particular, by rotating the lever 27 from its "concordant" position in fig. 3 to its "discordant" position in fig. 4, the cam element 30 associated with the end of the lever 27 thrusts on a rigid element 31, elastically contrasted, inserted coaxially to the hub 19 of the wheel.

Thanks to this thrust, the thrust rim 16 is taken into contact with the idler wheels 23.

In particular, each thrust rim 16 comprises an annular seating 25, and an external transmission crown 26. In particular, the annular seating 25 allows, in the "discordant" thrust position (fig. 4), a double contact of the idler wheels 23, on one side, against the external surface of the relative rear wheel 13 and, on the other side, inside the annular seating 25 of the thrust rim 16. The contact between idler wheels 23 and thrust rim 16 determines the transmission of the motion with opposite directions of rotation, that is, the clockwise rotation of the thrust rim 16 is translated into an anti-clockwise rotation of the wheel 13, and vice versa, thus allowing the user to advance with the chair 10 by executing a movement from forward to back with his arms.

Advantageously, the annular seating 25 is conformed so that the thrust rim 16 does not contact the relative rear wheel 13, while still allowing double contact of the idler wheels 23.

The external crown 26 is conformed to cooperate with a corresponding radial clamping seating 29 of the rear wheel 13, so as to transmit directly to the latter the motion and the direction of rotation imparted by the user on the thrust rim 16.

Therefore, when the lever 27 is returned to the position in fig. 3, the rigid element 31 is thrust toward the outside by the elastic means with which it is associated, the detachment is determined of the wheel 23 and the thrust rim 16, so that there is no longer any inversion of motion. The anti-clockwise rotation of the thrust rim 16, that is, with traditional traction from back to forward, determines the anti-clockwise rotation of the rear wheels 13 and therefore the wheelchair 10 advances.

With reference to figs. 5, 6 and 7, a vertical section is shown of a rear wheel 113 of a second form of embodiment of the wheelchair 10 according to the invention.

In this case, the member to invert the motion 120 comprises a mixed kinematic mechanism of chains and gears mounted in an intermediate position between the rear wheel 113 and the associated thrust rim 116.

In particular, each member to invert the motion 120 comprises a first toothed crown 121, axially and angularly attached to the rear wheel 113, a second toothed crown 125 axially and angularly attached to the thrust rim 116, and an idler member 123 with gears, kinematically connected to the two toothed crowns 121 and 125 by means of a first chain 132 and a second chain 133.

The idler member 123 comprises a rotary flange 134 mounted rotatable with respect to the hub 119 and provided with a radial arm 135, of adjustable length.

The radial arm 135 rotatably supports, at its end, two transmission shafts, respectively a first 136 and a second 137, substantially parallel to each other.

The first shaft 136 comprises, at one end, a third toothed crown 138 mechanically engaging with the first chain 132 and, at the other end, a first toothed wheel 139.

The second shaft 137 comprises, at one end, a fourth toothed crown 140, mechanically engaging with the second chain 133 and, at the other end, a second toothed wheel 141 engaging with the first toothed wheel 139 of the first shaft 136.

In this way, in the second operating position shown in fig. 6, the clockwise rotation imparted by the user through the thrust rim 116 is transmitted coherently in a clockwise direction by ^J the second crown 125 to t Che fourth crown 140 through the second chain 133.

From here, through the second shaft 137, the clockwise rotation is transmitted directly to the second toothed wheel 141 which, due to reciprocal engagement, transmits it to the first toothed wheel 139. The transmission by engagement between the two toothed wheels 14 land 139 determines an inversion of the direction of rotation which thus, from clockwise as it was in the second toothed wheel 141, becomes anti-clockwise in the first toothed wheel 139.

The rotation, now anti-clockwise, is then transmitted from the first shaft 136 to the third crown 138, from which, through the first chain 132, it is transmitted in an anti-clockwise direction to the first crown 121 and from here directly to the rear wheel 113.

In this configuration we therefore have a rotation imparted in a clockwise direction on the thrust rim 116 which becomes anti-clockwise on the rear wheel 113.

In this case, the two toothed wheels 139 and 141 have an equal transmission ratio, but it cannot be excluded that this ratio can be different, substantially functioning as a derailleur, for example in order to reduce the thrust force on the rim 16 with respect to the actual advance of the wheelchair 10.

The member to invert the motion 120 also comprises a selection member 130 which, moved by a lever 127 outside the thrust rim 116, allows the selective passage between the first and second position.

The lever 127 comprises a command head 157 disposed inside an axial cavity 153 and provided with an inclined front surface, the functions of which will be explained in detail hereafter.

In particular, the selection member 130 comprises a friction flange 142 mounted able to slide axially with respect to the hub 119, and interposed between the hub 119 and the rotary flange 134.

The friction flange 142 is provided with jointing pins 143, directed substantially parallel to the axis of rotation of the wheel 113, and comprises a central part 145 directly mounted sliding on the hub 119, and a ring 146 mounted rotary with respect to the central part 145 and on which the pins 143 are mounted protruding, in positions angularly offset with respect to each other.

In particular, each pin 143 has a flared front end and cooperates at the rear with a helical spring 147, so as to be able to be selectively inserted into relative holes 156 made angularly offset on the second crown 125.

The central part 145 is angularly constrained to the hub 119 by means of a pin 150, which is disposed transversely through the hub 119 through an eyelet 151. The eyelet 151 is directed so as to allow a movement of the pin 150, and therefore of the central part 145, in a direction substantially parallel to the axis of rotation of the rear wheel 113.

Furthermore, the central part 145 comprises a slider 152 disposed able to slide axially inside the axial cavity 153 of the hub 119.

The slider 152 is constrained to the pin 150, cooperates at the rear with a helical spring 154 and has at the front an inclined surface 155 able to cooperate selectively with the front surface 158 of the command head 157 of the lever 127.

The ring 146 of the friction flange 142 is associated peripherally with one or more keys 148, which are disposed slidingly in relative seatings 149 made inside the rotary flange 134.

The disposition of the keys 148 and the conformation of the relative seatings 149 are such as to allow the keys 148 to slide in a direction substantially parallel to the axis of rotation of the rear wheel 113.

In this way, the ring 146 of the friction flange 142 is angularly constrained to the rotary flange 134, but able to slide with respect thereto.

In this way, by rotating the lever 127 by 180° around the axis of rotation of the rear wheel 113, a rotation is determined of the front surface 158, so as to allow the slider 152 to move axially due to the effect of the thrust of the helical spring 154, so far as to make the inclined surface 155 abut with the front surface 158.

This axial movement of the slider 152 determines a corresponding movement of the friction flange 142 both with respect to the hub 119 and also with respect to the rotary flange 134, towards the second crown 125.

As shown in fig. 5, the pins 143 are inserted inside the relative holes 156, thus angularly constraining the ring 146 to the second crown 125.

In this way, in the first operating position, the clockwise rotation imparted by the user through the thrust rim 116 is transmitted coherently in a clockwise direction from the second crown 125 to the ring 146 of the friction flange 142.

From here, through the angular coupling of the keys 148 and the relative seatings 149, the clockwise rotation is transmitted directly to the rotary flange 134.

The rotation of the rotary flange 134 around the axis of rotation of the rear wheel 113 determines a coordinated movement of revolution of the group consisting of the two shafts 136, 137, the two toothed wheels 139, 141, and the third and fourth crown 138, 140.

This kinematic condition of revolution entails a relative clamping of the chains

132 and 133 with respect to the corresponding crowns 121 and 125, so that the clockwise rotation of the rotary flange 134 is directly transmitted to the first crown 121 and hence to the rear wheel 113.

In other words, the mechanical system consisting of the two chains 132 and

133 and the idler member 123 in this kinematic condition substantially functions as a crank and transmits the clockwise rotation of the second crown 125 directly and concordantly to the first crown 121.

In this configuration, therefore, a rotation imparted in a clockwise direction on the thrust rim 116 becomes a concordant direction on the rear wheel 113.

In the embodiment shown in figs. 5, 6 and 7, it can be seen that the hub 119 is also mounted on the frame 11, with a bayonet type rapid attachment 18.

In this case, a clamping of the coupling between the hub 119 and the frame 1 1 is also provided, by means of an eccentric lever 24 able to be actuated selectively and manually by the user.

It is clear, however, that modifications and/or additions of parts may be made to the wheelchair 10 as described heretofore, without departing from the field and scope of the present invention.

For example, it comes within the field of the present invention to provide that instead of manual action by means of the cam levers 27, the selective movement of the thrust rims 16 can be made by means of electronic, electro pneumatic or other apparatuses, commanded by the user by means of a pushbutton panel, for example positioned on an arm of the wheelchair.

It is also clear that, although the present invention has been described with reference to specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of wheelchair, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Wheelchair comprising at least a seat (12) for the user, two rear wheels (13, 113) disposed lateral to said seat (12), at least a front wheel (15), and thrust means (16, 116) associated coaxially with an external side of each of said first wheels (13, 113), characterized in that it also comprises means to invert the motion (20, 120) mounted on each of said rear wheels (13, 113) in an intermediate position between each of said wheels (13, 113) and the relative thrust means (16, 116), and in that said means to invert the motion (20, 120) are selectively configurable with respect to said thrust means (16, 116) and said wheels (13, 113), so as to define at least a first position of concordant thrust, in which said thrust means (16, 116) are associated with said wheels (13, 113) so that a rotation thereof in a first direction determines a rotation of said wheels (13, 113) in the same first direction, and a second position of discordant thrust, in which said thrust means (16, 116) cooperate with said means to invert the motion (20, 120) so that a rotation thereof in said first direction determines a rotation of said wheels (13, 113) in a second direction, opposite said first direction.

2. Wheelchair as in claim 1, characterized in that said means to invert the motion (20, 120) comprise, for each of said wheels (13, 113), a kinematic mechanism to invert the motion in which at least an idler member (23, 123) is provided.

3. Wheelchair as in claim 2, characterized in that said idler member comprises at least an idler wheel (23) normally in contact with an external surface of the relative wheel (13) and having its axis of rotation substantially perpendicular to an axis of rotation of the relative wheel (13).

4. Wheelchair as in claim 3, characterized in that said means to invert the motion (20) comprise, for each of said wheels (13), a radial support (21) with spokes (22), attached to a hub (19) of the relative first wheel (13), and able to rotatably support a respective idler wheel (23).

5. Wheelchair as in claim 3 or 4, characterized in that said idler wheel (23) has an external crown made of material of high friction coefficient.

6. Wheelchair as in any claim hereinbefore, characterized in that each of said thrust means (16) comprises an external transmission crown (26) able to be attached angularly to the relative wheel (13) in said first position, and an annular seating (25) able to contact said means to invert the motion (20) in said second position.

7. Wheelchair as in claim 2, characterized in that said idler member (123) comprises at least a rotary flange (134) mounted rotatable around a hub (119) of said rear wheel (113) and kinematically connected both to said thrust means (116) and also to said rear wheel (113).

8. Wheelchair as in claim 7, characterized in that said member to invert the motion (120) comprises a first toothed crown (121), axially and angularly attached to said rear wheel (113), and a second toothed crown (125) axially and angularly attached to said thrust means (116), said first toothed crown (121) and said second toothed crown (125) being kinematically connected to said idler member (123), respectively, by means of a first chain (132) and a second chain (133).

9. Wheelchair as in claim 8, characterized in that said rotary flange (134) comprises a radial arm (135) rotatably supporting two transmission shafts (136, 137), each provided with a respectively toothed crown (138, 140) mechanically engaging with a relative one of the first and second chains (132, 133), and a toothed wheel (139, 141), reciprocally engaging with the toothed wheel (141, 139) of the other transmission shaft (137, 136).

10. Wheelchair as in any claim from 7 to 9, characterized in that said member to invert the motion (120) comprises a selection member (130) comprising at least a friction flange (142) able to be selectively moved to define said first and said second position, and respectively constrain/release angularly said idler member (123) and said thrust means (116).

11. Wheelchair as in claim 10, characterized in that said selection member (130) also comprises a lever (127) having a command head (157) and cooperating with an elastic element (154), to determine the selective movement of said friction flange (142).

12. Wheelchair as in claim 10 or 11, characterized in that said friction flange (142) is provided with a plurality of jointing pins (143), directed substantially parallel to the axis of rotation of said rear wheel (113), and able to be selectively inserted into relative holes (156) made angularly offset on said second toothed crown (125).

13. Wheelchair as in claim 12, characterized in that said friction flange (142) comprises a central part (145) mounted angularly constrained and able to slide axially on said hub (119), and a ring (146) mounted rotary with respect to said central part (145) and on which said pins (143) are mounted protruding, in angularly offset positions with respect to each other.

14. Wheelchair as in claim 12 or 13, characterized in that said central part (145) comprises a slider (152) disposed able to slide axially inside the axial cavity (153) of the hub (119), and able to cooperate with said selection member (130) to command the movement of said friction flange (142).

15. Wheelchair as in claim 12, 13 or 14, characterized in that each pin (143) has a flared front end and cooperates at the rear with a helical spring (147).

16. Wheelchair as in claim 13, characterized in that said ring (146) is angularly constrained to said rotary flange (134).

17. Wheelchair as in any claim hereinbefore, characterized in that a hub (119) of said rear wheel (113) is mounted on a frame (11) of said wheelchair, with a bayonet-type rapid connection (18).

18. Wheelchair as in claim 17, characterized in that an eccentric lever (24) is provided, able to be actuated selectively and able to determine the clamping of the coupling of said hub (119) and said frame (11).

19. Wheelchair as in any claim hereinbefore, characterized in that said thrust means comprise, for each of said wheels (13, 113), a thrust rim (16, 116) mounted on a relative hub (19, 119) of the relative first wheel (13, 113), so as to be able to be selectively moved between said first position and said second position.

20. Wheelchair as in any claim hereinbefore, characterized in that it comprises, for each first wheel (13, 113), at least a command lever (27, 127), kinematically connected to said means to invert the motion (20, 120), in order to determine the selective movement thereof between said first position and said second position.

21. Wheel for a wheelchair or similar means of locomotion, characterized in that it comprises means to invert the motion (20, 120) suitable to cooperate with a thrust means ( 16, 1 16) so that the action exerted on said thrust means ( 16, 1 16) determines a movement of the rear wheel concordant with said action on the thrust means ( 16, 1 16) when the inversion means (20, 120) are in a first thrust position, and discordant with said action on the thrust means ( 16, 1 16) when the inversion means (20, 120) are in a second thrust position.