The object of the invention is a transfer device that grips one or more wheels, which is intended to move an aircraft or other wheeled device over a base, which transfer device includes two rollers that are placed on opposite sides of the wheel and press against it, at least one of which rollers is a friction roller rotated by means of a motor, compression devices to create the aforementioned pressure, and three or more support wheels and drive devices for the independent movement of the device. There may be several pressure and friction rollers for each wheel to be driven.

The weight of a transfer device can be substantially reduced when the rotational force is transferred to the aircraft's own wheel from the drive wheel i.e. friction roller belonging to the transfer device. A light construction for an entirely general purpose transfer device is shown in Finnish Patent Application FI 833275 (partly corresponding to W085/ 01265) . This does not require any contact with the bogie of the air¬ craft in order to press the drive wheel against the aircraft wheel. The pressure is created by means of the mutual movement of pressure rollers placed around the wheel of the aircraft and connected by an intermediate device.

In its most general form the intermediate device draws the two pressure rollers connected by it towards one another, when the are pressed against the wheel between them. At least one of the pressed wheels is now the friction roller, i.e. drive wheel, which transmits the rotational force to the wheel of the air¬ craft. Other transfer devices that belong to the field of the invention are shown in Finnish Patent Applications FI861714, FI870313, and FI870710, as well as in Swedish Patent Publication SE 437 137.

In practice nearly all aircraft are equipped with either double wheels or even larger bogie wheels. It is thus natural to make the transfer device such that it grips double wheels, because in that case the greatest force applied to the tyre can be reduced. In this sense transfer devices equipped with so-called self-

wedging friction rollers are not. advantageous, because they stress the wheel of the aircraft considerably more than a transfer device that grips each wheel with two or more friction rollers.

A transfer device that grips a double wheel, especially the nose bogie wheels, is shown in US Patent Publication 3,005,510. In it the wheels beside each other are.driven by means of a friction roller mat, which is wedged between the in line bogie wheels.

Most typically the transfer device's own drive is implemented by means of rotating devices connected to the support wheels, or else the transfer device is intended to be moved manually. During the transfer stage the transfer device is moved by the wheel of the aircraft or other device. In this case the trans¬ fer device's own support wheels must be freely turnable so that the transfer device can turn when the wheel being transferred turns. This causes difficulties especially in the case of support wheels connected to the power transmission, because the power transmission makes difficulties for the arrangements for the turning of the wheel. On the other hand, in order to make the independent steering of the transfer device possible, the wheels, which are not steered, must be locked into the straight position for the duration of independent driving. This has been typically solved by adding separate locking devices to such wheels.

The intention of this invention is to create a transfer device, in which the power transmission required for independent move- ment is both simple and reliable. The characteristics of the invention appear in the accompanying Patent Claim 1.

The form of application in accordance with Patent Claim 2 solves in a simple manner the locking of the transfer device's own wheels during independent movement and their release in the transfer stage. By means of the friction roller it possible to advantageously transmit the drive and to lock the direct of certain support wheels straight forward. In particular a trans-

fer device gripping double or bogie wheels can be realized advantageously in accordance with Patent Claim 3.

In what follows the invention is illustrated by reference to the accompanying Figures, which show one form of application of the invention.

Figure 1 shows the transfer device being driven around the double wheel of an aircraft Figure 2 shows the transfer device in the operating posi¬ tion seen from above and in partial cross-section Figure 3 shows the transfer device seen from the side Figure 4 shows the hydraulic scheme of the transfer device

In Figures 1-3 the aircraft 1 is represented by only a part of the undercarriage and the wheels 6. The transfer device runs on its support wheels 7 and 8. The front friction rollers 3 are located on a guide 11 that moves laterally and the rear friction rollers 4 on a slide member 12, which is arranged to move along longitudinal guides 13 that are welded to the frame 2. The rear friction rollers 4 rotate alternatively either the wheel 6 of the aircraft 1 or the transfer device's own rear wheels 8. The slides 12 of the rear friction rollers are moved by means of the hydraulic cylinder 14, by means of which the pressure that is essential in friction transmission is also created. When the transfer device is driven away, the rear friction rollers 4 turn the rear wheels 8 of the transfer device straight ahead and steering takes placed by turning the front wheels 7 with the aid of a cable mechanism 9. When the transfer device is attached to the double wheel 6 of the aircraft 1, the transfer device's own wheels 7 and 8 both in front and at the rear are free to turn when the wheel 6 of the aircraft 1 turns.

In Figure 3 the wheel 6 of the aircraft is shown by broken lines. The rear friction roller 4 is shown in alternative positions 4 and 4• , in the former of which it rotates the transfer device's own rear wheels 8 and in the latter of which the wheel 6 of the aircraft 1. The rear friction rollers 4 are

rotated by hydraulic motors 20, which do not appear separately in Figures 1-3.

The frame 2 of the transfer device includes side tubes, which are connected to the rear section 5. The sliding members 3 and 4 of the friction rollers and their moving devices are located in these side tubes. A diesel motor and a hydraulic pump driven by it together with control devices are located in the rear section. In addition other necessary control and adjustment devices are located in the rear section 5.

Figure 4 shows a schematic diagram of the hydraulic circuit of the transfer device. Only features of the right-hand side pressure cylinders 14 drive motors 20, 19 are shown as they are symmetrical.

The diesel motor drives a pump unit, which includes an auxil- liary pump 23 and normal loss oil pump in addition to the high-pressure pump 22. The high-pressure pump 22 in the drive oil circuit drives the motors 19 and 20 of the friction rollers 3 and 4. The motors 19 of the from friction rollers 3 can be shut off during independent movement by means of the electric direction valve 21. Another possibility is to use here a mechanical connection to lock rollers 3.

Oil is led to the pressure cylinders 14 is such a way that if drive pressure is insufficient they receive pressurized oil feed from the auxilliary oil pump 23 through the counter pressure valve 25, otherwise they are fed from the high-pressure pump 22 through two counter pressure valves 24 and 25. The pressure cylinder 14 is used to move the rear friction rollers 4 alter¬ natively either against the transfer device's own support wheel 8 or against the wheel 6 of the aircraft 1. Selection of direc¬ tion takes place by means of valve 27.

The lateral movement cylinders 18 receive their feed continuous¬ ly from the auxilliary oil pump 23 and changes in their direc¬ tion are carried out with the aid of valve 26. Return oil from

the lateral movement and pressure cylinders 18 is led to the loss oil reservoir 28.

The front friction rollers equipped with lateral movement make it possible to use the transfer device not only with normal double wheels but also with sets of bogie wheels, because the front friction rollers 3 can be placed between wheels that are in line.