The invention relates to a drive system for a tooth rack lift comprising a tooth rack, a gear journalled in a member, fixedly connected to a lift cage, and engaged with the teeth of the tooth rack for driving the lift cage along the tooth rack and a counter force means located in vicinity of the gear and bearing against the back of the tooth rack.

Such drive systems for driving tooth rack lifts are well known. Thereby, the counteracting means, generally in the form of a steel roll rolling on the back of the tooth rack, is arranged to counteract deflection of the tooth rack which else would occur by the engagment of the gear, if the gear alone would act against the tooth rack. As an alternative, for preventing deflection and by that caused incorrect mesh of teeth, the tooth rack might be made more rigid and thus thicker. However, this is not an attractive solution with respect to weight and cost. Previously the counter roll has been disposed on a specific machinery plate, the gear then being journalled in the gear box of the lift cage, the gear box being flanged to said plate.

This solution has caused a lot of inconveniencies, among other the things the machinery plate has to be made rather large and thick to withstand those rather big forces and moments it will be affected by, e.g. in the flange coupling between the gear box and the plate. Further it has been difficult to accomplish the required tolerances between the gear and the counter roll due to rather long force transmission paths and the occuring big forces and resulting deformations and the fact that a plurality of members are involved in the transmission chain, leading to a long chain of tolerances and in the end to a big total tolerance error due to the fact that the tolerance error of the plurality of individual members are added to each other.

Because of these circumstances large vibrations will be obtained, resulting in a high noise level and an exaggerated rate of wear and finally in a reduced life.

The object of the invention is to avoid the above indicated deficiencies in a drive system as initially defined by a new and different disposition of the counteracting means than that has been used up to now.

The above object is solved in accordance with the invention by the features defined

in the characterizing part of claim 1

Preferably the safety means, which always must be present and which are activated in case of the counteracting means would become worn out or even would break down, are located at the same member as the counteracting means and the gear Conveniently, the gear is journalled m the gear box casing of the drive unit, the counteracting means, and preferably the safety means as well, being formed at the same gear box wall, which receives the bearing for the gear

In a preferable construction the counteracting means is in the form of a roll bearing against the back of the tooth rack The invention will now be described in detail by means of a preferred embodiment with reference to the annexed drawings, wherem the only fig 1 is a side elevational view, showing a gear, a counteracting roll and safety stop shoulders located on a gear box casing in accordance with the invention In the figure a portion 1 of a vertically movable lift cage is shown, which amongst other thmgs carries a drive unit, compnsmg a drive motor (not shown) and a gear box 3 connected to the drive motor in a conventional manner Neither the connection of these members to Lhe lift cage nor the manner of control of the lift cage will be described, smce this is throughout conventional art m the field of lifts and thus, do not constitute pan of the invention An output gear 7, journalled in a wall 5 of the gear box casing, engages a vertical tooth rack 9, shown with dashed lines in the sole figure When the gear 7 rotates in engaement with the teeth 11 of the tooth rack 9, the lift cage will move along the tooth rack 9, upwardly or downwardly in dependence of rotary direction

If only the gear 7 and the tooth rack 9 were provided for the transmission of forces the tooth rack would be untolerably deformed due to the strong forces of engagement, resulting in an incorrect gear mesh with exaggerated wear as a consequence In order to solve this problem some kind of counteracting means is required, generally a counteracting roll, bearing against the back 13 of the tooth rack 9 in the gear mesh area As initially mentioned the previous solutions have lead to problems in respect of tolerances, deformations and vibrations

By, according to the invention, providing the counteracting roll 15 on the same member, l e in this case on the wall 5 of the gear box casing, as the gear 7, shorter

paths of force and deformation are achieved as well as the absolute tolerances can be made significantly closer than previously due to the considerably shorter distance between the gear 7 and the counteracting roll 15.

Preferably, the safety stop shoulders 17a and 17b, which will act, if the counteracting roll 15 of any reason should fail, are disposed on the same member, i.e. the gear box wall 5. The shoulders 17a and 17b generally protrude the same height from the wall 5 as the counteracting roll 15, but their engagement surfaces 19a and 19b respectively are somewhat displaced behind the surface of contact 16 of the counteracting roll 15 with the back 13 of the tooth rack 9, so they will act only after the counteracting roll has been worn out or been damaged.

Thanks to the structure of the invention the fitting of the counteracting roll 15, the safety stop shoulders 17a, 17b and the bearing of the gear 7 e.g. can be moulded and machined in one piece, allowing a high precision and significant gain of time at the assembly in relation to the previously necessary time-consuming fitting in of members. The improved structure provided by the invention results in a significantly improved noise level, less vibrations, smoother operation and a considerably reduced rate of wear. Moreover, the number of required members is reduced in addition to a rational and considerably quicker assembly, which altogether provides for a substantially lower production cost. Even if in this embodiment the member common to the gear 7, the counteracting roll 15 and safety stop shoulders 17a, 17b is a wall 5 of the gear box, this must not always be the case, but the gear 7 may be journalled in another member, e. g. in the wall of a catch device, the fitting means for the counteracting means 15 and the safety stop shoulders then, of course, being provided in the same wall.