Background of the Invention Such passenger conveyors find much use in the form of escalators or moving sidewalks. The present invention concerns especially escalators with high elevations and moving sidewalks with long paths, i. e. applications wherein very large forces must be transmitted between the sprocket wheel teeth and the engaged chain bushings. An installation usually includes a chain moving around a sprocket wheel drive and a reversing sprocket wheel on both sides and under the tread surface area called a step or pallet band in the landing areas, i. e. the access and exit areas of the passenger conveyor. The individual steps or pallets of the passenger conveyor are usually attached on both sides to chain link pins and are thus carried along by the chain. The chain is frequently supported by support wheels between the sprocket wheels, which are attached to chain link pins on the side that extends over the chain.

Among other things such passenger conveyors have the problem of high maintenance costs which to a considerable degree are due to the required regular lubrication of the contact areas between chain and sprocket wheel. Insufficiently lubricated chain/ sprocket wheel drives wear very quickly and have clearly increased power requirement.

Beyond that they tend to run more unevenly, particularly in jerks, and produce disturbing noises during the operation. The pairing of two equally hard metals in the contact area

between chain and sprocket wheel has low elasticity by nature, and furthermore has the tendency to run unevenly and create noise even in new and well maintained installations.

Disclosure of the Invention It is therefore a goal of the present invention to provide a passenger conveyor which has better running and noise developing characteristics, and whose chain/sprocket wheel drive arrangement can operate in a lubricant-free manner. The invention achieves this by providing plastic in at least one of the contact areas where chain and sprocket wheel engage each other.

The invention furthermore concerns a chain and a sprocket wheel for driving the circulating tread surface area of a passenger conveyor.

The plastic is preferably provided on the force-transmitting surfaces of the sprocket wheel teeth. This is in particular the side of the gear wheel which moves the chain bushing, or the base of the tooth which transmits a considerable part of the chain supporting force. It is especially preferred to provide plastic basically over the entire circumference of the sprocket wheel along the contour of the teeth.

Plastic is preferably provided laterally on at least one side of the sprocket wheel.

It should be noted that when the chain engages the sprocket wheel in the same way as when the tread enters the tread comb in the landing area, the gap between the sprocket wheel tooth and the internal tread chain link plates must be about 0.5 mm (0.02 inch). The link plates often touch the sprocket wheel during engagement, which leads to wear on the link plates and the sprocket wheel. This wear takes place on one side of the sprocket wheel, depending on where the passengers stand on the tread surface area, i. e. on the left or the right side of the tread band. The use of plastic on that side of the sprocket wheel, or on both sides if necessary, considerably reduces the wear due to metal-to-metal contact. It is advantageous to provide this plastic on the side, basically in the overlap area between chain link plates and sprocket wheel, and if necessary provide a piece that extends beyond them. It is particularly advantageous to provide the plastic on the force-transmitting surfaces of the teeth and laterally on the sprocket wheel.

Plastic is preferably provided on the circumferential surface of the chain bushings.

The chain bushings are entirely made of plastic. The chain bushings, whose circumferential surface engages the teeth of the sprocket wheel and works with them, can have plastic as an alternative or in addition to the sprocket wheel. Chain bushings have special relevance because when existing passenger conveyors are overhauled, conventional metal chain bushings can easily be replaced with those made of plastic This also allows existing installations to be retrofitted in accordance with the invention at a defensible cost. The chain bushings can have a cylindrical metal body and a plastic body placed around it. The possibility of retrofitting existing passenger conveyors has very special commercial value, notably in view of the large number of already operating passenger conveyors and because it is relatively simple to realize.

Plastic is preferably provided on the side of the chain link plates facing the sprocket wheel. It is possible to provide this as an alternative or in addition to the plastic on the side of the sprocket wheel. The plastic in this part of the chain fulfills essentially the same purpose as the plastic on the side of the sprocket wheel. In addition these link plates can also be retrofitted when the plastic chain bushings are retrofitted.

It should be noted that preferably only the internal chain link plates are provided with plastic and possibly only the internal chain link plates on one side of the sprocket wheel. Because of the large forces to be transmitted, it is preferable to install plastic on a link plate body that is made of metal, so that the metal body essentially transmits the tensile forces.

Preferably a very high grade, wear-resistant plastic is provided. Polyamide is especially suitable, particularly PA12G or PA6.6, or polyethylene terephthalate, polyacrylate or polytetra-fluoroethylene.

The plastic is preferably applied in the form of a layer on a basic body. The application can take place especially by casting over the basic body. A very close connection between metal and plastic can be achieved with basic metal bodies and PA12G as the plastic, which is particularly preferred from the service life point of view. The final form of the plastic applied by casting can be obtained through machining, for example

milling, sawing, grinding. Worn components can also be reworked accordingly, by partially or entirely removing the worn plastic from the basic body, for example by machining, and replacing it by means of casting.

However the plastic can also be secured to the basic body with the usual fastening devices such as screws, rivets, etc., or by cementing or welding. In that case plastic parts which are preformed to their final shape are preferred.

For fire prevention reasons it is especially preferred not to manufacture the sprocket wheel or the chain link plates entirely of plastic, but of a combination of metal and plastic, so that in case of a fire the escalators maintain their structure as much as possible and can be used as conventional stationary stairways. Especially a sprocket wheel made entirely of plastic would melt in the high heat or burn, thus eliminating all the support provided by the tread chains.

Plastic in at least one of the contact areas leads to improved sound absorption when the chain and the sprocket wheel are combed, thereby providing a quietly running passenger conveyor. It leads to improved vibration and shock absorption which increases travel comfort on the passenger conveyor. Furthermore it leads to improved emergency operating characteristics of the passenger conveyor due to the metal-to-plastic pairing and thereby in effect to a lubricant-free operation of the passenger conveyor. In addition it has the advantage of clearly reducing the tendency toward corrosion, especially in the vulnerable contact areas.

Brief Description of the Drawings The invention will be explained in greater detail in the following by means of illustrated configuration examples, where: Fig. 1 is section of a chain and sprocket wheel in a first configuration of a passenger conveyor of the invention; Fig. 2 is a side view of the sprocket wheel in the configuration of Fig. 1 ; Fig. 3 is a section of a chain and sprocket wheel of a passenger conveyor of the invention, in a lateral configuration crosswise to the running direction of the

chain ; Fig. 4 is a section of the chain and sprocket wheel in Fig. 3 in the plane indicated by the arrows IV-IV in Fig. 3; Fig. 5 is another configuration of the sprocket wheel of the invention; Fig. 6 is a lateral view of the sprocket wheel in Fig. 5; and Fig. 7 is a section of a detailed enlarged view of Fig. 6.

Best Mode for Carrying Out the Invention Fig. 1 shows a chain 2 and a sprocket wheel 4 according to the first configuration of the invention. The chain 2 is a so-called"roller chain"comprising internal chain link plates 6, external chain link plates 8, a chain link pin 10, a chain tube 12 and chain bushings 14. The chain tube 12 can rotate around the chain link pin 10. The external chain link plates 8 are attached to the chain link pin 10 and the internal chain link plates 6 are attached to the chain tube 12. Adjacent chain link pins 10 along the chain 2 are interconnected by internal chain link plates 6 or by external chain link plates 8. Internal chain link plates 6 and external chain link plates 8 alternate along the course of the chain 2. A chain bushing 14 can rotate between the internal chain link plates 6 and outside over the chain tube 12. When the sprocket wheel 4 engages the chain 2, the chain bushing 14 rolls along the sprocket wheel 4 toothing and the chain tube 12 does not slide off the sprocket wheel 4 toothing which would cause wear. Plastic 18 is provided in the contact area 16 between chain 2 and sprocket wheel 4, especially in the contact area 16 on the outer circumference of the chain bushing 14 and the force-transmitting surfaces of the teeth on the sprocket wheel 4. In particular the plastic 18 is applied in the form of a layer on the basic body 20 of the sprocket wheel. The plastic layer generally has a thickness of 3-20 mm (0.1-0.8 inch) and preferably 5-15 mm (0.2-0.6 inch). In the configuration of Fig. 1 the layer can also be provided laterally on the sprocket wheel 4, so that it can contact the internal chain link plates 6 during operation. The entire force-transmitting surface shown in Fig. 1 is covered with plastic 18. The chain link pin 10 shown in Fig. 1 is extended on the left side of the figure where it carries a support wheel 22 which is attached to the extension 26 of the link pin 10 by a bearing 24. The

support wheel 22 is used to support the chain 2 at least along a part of its run along a support path.

Like Fig. 1, Fig. 2 shows the sprocket wheel in a lateral view. The basic sprocket wheel body 20 can be seen, and the plastic layer 18 which is formed over the toothing contour along the entire circumference. Plastic 18 is provided on the plateau area 28 of the teeth 30, on the base 32 of the teeth 30 and on the sides 34 and 36 of the teeth 30. It can also be seen that the plastic 18 is essentially applied to the basic body 20 as a layer of uniform thickness, and that the basic body 20 itself is also equipped with toothing. This is an advantage, particularly in case of a fire, because it ensures that the chain 2 remains securely in its position even after the plastic 18 has burned or melted away. This ensures for example that an escalator can be used as a"normal"stairway even during or after a fire.

Fig. 3 shows the second configuration of the invention which in general is relatively similar to the configuration in Fig. 1. Again the chain 2 and sprocket wheel 4 are shown, as well as internal chain link plates 6, external chain link plates 8, chain link pins 10, chain tube 12, the extension 26 of the chain link pin 10, the bearing 24 and the support wheel 22. It can further be seen that the sprocket wheel 4 is a conventional metal part. By contrast, the chain bushing 14 is made entirely of plastic 18. This also avoids the metal-to- metal pairing in the contact area 16 between the chain and the sprocket wheel on the circumference of the chain bushing 14, and a plastic-to-metal contact is provided like in the first configuration, and brings about in the mentioned advantages.

The sectional view in the IV-IV plane of Fig. 3 which is illustrated in Fig. 4, shows more clearly the combing of the chain 2 with the sprocket wheel 4. The chain 2 is only illustrated schematically. The upper left part of the figure shows the internal chain link plates 6 drawn by solid lines, while the one illustrated external chain link plate 8 is basically only shown by broken lines. For reasons of simplification the chain tube 12 in Fig. 4 has been omitted in the illustration of the chain link pin 10, the chain bushing 14 or the plastic 18.

Fig. 5 shows a sprocket wheel according to a third configuration of the present invention. This sprocket wheel 4 again shows the sprocket wheel teeth 30, the raised area or

the plateau 28 of the teeth 30, the tooth base 32 and the tooth sides 34 and 36. Along the toothing contour and offset toward the inside is a line running essentially parallel thereto, and represents a laterally applied plastic layer. The circular line shown in conjunction therewith further on the inside represents the internal limit of the laterally applied plastic 18.

Typically such a sprocket wheel has a diameter on the order of 800 mm (31 inch) of which about 50 mm (2 inch) as measured from the circumference have plastic 18 applied on the side. The exact measurement of the area covered by plastic 18 depends on the depth of the toothing, the size of the overlap area between the internal chain link plates 6 and the sprocket wheel 4, and possibly also on other factors, for example the attachment of the plastic 18 to the basic sprocket wheel body 20. In the illustrated configuration plastic 18 is essentially provided separately for each tooth, i. e. the plastic 18 is not applied in a solid layer over the circumference of the sprocket wheel. However in some applications it is preferred to give the plastic a deeper inside limit, for example inside the openings 38 in sprocket wheel 4, in order to obtain as large a contact surface as possible and thereby as large a fastening surface as possible between the basic the sprocket wheel body 20 and the plastic 18. This is especially preferred when the plastic 18 is cast or cemented to the basic sprocket wheel body 20, where a larger fastening surface produces a plastic-to-metal combination which can support more loads. Continuous plastic is furthermore easier to machine as a rule than separate tooth by tooth plastic. The machining tools for example have a significantly longer service life if they only contact plastic material during the machining, and not plastic and metal.

Fig. 6 shows another view of the sprocket wheel in Fig. 5. The circle 40 drawn by broken lines in Fig. 5 shows the section which is shown as an enlarged detail in Fig. 7. It shows the plastic 18 which is only applied to one side of the tooth area on the basic body 20 of sprocket wheel 4. It can also be seen that the plastic 18 is applied as a layer with a thickness d of about 2-8 mm (0.08-0.3 inch).

Fig. 7 further shows that the plastic 18 essentially extends over the height of a tooth 20 and downward over the tooth base 32 into the disk 42 of the sprocket wheel 4. This also provides a better and larger surface for fastening the plastic 18 to the basic sprocket

wheel body 20. A cutout or recess can be made in the sprocket wheel, into which the plastic extends for better attachment of the plastic 18 to the basic sprocket wheel body, particularly in the area of tooth 20 where the greatest forces take place. This produces a positive connection in the manner of a rivet. It also enables an improved force transmission in the fastening plane. Fig. 7 shows such a configuration in the form of cutout 44 and the plastic 46 which extends into it. In that case the cutout 44 has a diameter of about 15 mm (0.6 inch) while the outside diameter of the countersink is about 25 mm (1 inch).

It should be pointed out that the configuration in Figs. 5 to 7 can also be used for chain/sprocket wheel drives where the support wheel 22 instead of the chain bushing 14 is located between the internal chain link plates 6, and engages the corresponding cutouts in the sprocket wheel 4 during the operation.

As an alternative or in addition to the lateral plastic 18 on the sprocket wheel 4, plastic 18 can be applied to the internal link plates 6 of the chain 2. Whether applied to the lateral area of the sprocket wheel 4 or to the corresponding insides of the internal link plates 6, the plastic 18 also has the advantage of vibration and shock absorption when the sprocket wheel 4 with the chain 2 are combed, and thus provides noise reduction. This is especially preferred in this area since the required play between chain 2 and sprocket wheel 4 often causes the side of the chain 2 to strike heavily against the sprocket wheel 4. In an extreme case and with a worn sprocket wheel 4, it can happen that the chain 2 already engages the tooth 20 of sprocket wheel 4 at a very early moment and hangs there for a certain time, after which it is released and jerks heavily until it finds the correct engagement on the tooth base between the chain 2 and the sprocket wheel 4. Since lubricant is unable to stay in this lateral area, the adverse emergency running characteristics of a metal-to-metal pairing become especially negative in this area. Here the favorable emergency running characteristics of the plastic 18 are especially advantageous.

It must be pointed out that the different special features of configurations 1 to 3 can be combined with each other in any desired manner, so that in an extreme case all contact areas between the chain 2 and the sprocket wheel 4 are equipped with plastic. When plastic is cast onto a basic body 20 it is particularly advantageous to use a basic body 20

made of cast iron, for example GG 25. The fastening surface between the basic body 20 and the plastic 18 can be preprocessed before the casting, for example by roughing or by special mechanical or chemical procedures for better adhesion of the plastic to the basic body 20. It is also possible to provide cutouts in the basic body for better adhesion, for example in the form of notches or undercut recesses to produce a positive connection. It is possible to cast the plastic 18 over the basic body 20 in a mold. The mold can be designed so that excess plastic 18 is cast which is removed by machining, or it can be molded to its final size.