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The present invention concerns a variable transmission which auto¬ matically changes its transmission ratio in accordance with the resistance to propagation of the vehicle and in which the power- transmitting transmission link is a V-belt or equivalent, and wherein at least the secondary pulley consists of cup disks urged against each other and interconnected with a multiple-end thread and a torsion spring- of conical spiral shape which in addition to its torsion action presses against the external cup disk with an axial force.

An automatic variable transmission for a bicycle is known in the art for instance through the reference DE PS 93896, the principle of the transmission therein disclosed being that the pulleys for the flat belt serving as transmission link are made of helical leaf springs which in the secondary pulley are curved in the direction of rotation and in the primary pulley, against it. This principle has later been applied in several references, for instance by supplementing or replacing the springs with levers moving in heli¬ cal grooves. A drawback of transmissions of this type are pulley designs which are complex and involve friction and are sensitive to dust and dirt.

A torque-sensing V-belt pulley is known in the art for instance through the reference DE PS 224180, where admittedly the pressure effect of the cup disk rotating with reference to the other half ture only serves to boost the lever control acting on both belt pulleys. V-belt pulleys consisting of cup disks which are non-ro- tatable in relation to each other have been tried out in the first place in drives for auxiliary apparatus of internal combustion engines, such as charging generators and fans, where compression or torsion springs also occur in addition to threads. A design of this kind is for instance disclosed in the reference USP 2,478,289.

The object of the present invention is to eliminate the above draw¬ backs. The variable transmission of the invention automatically changing transmission ratio in accordance with the resistance to propagation of the vehicle is characterized in that the torsion spring is at least a two-ended spring. The object of the invention is to provide a variable transmission which in all circumstances automatically and steplessly changes its transmission ratio and which is competitive in efficiency with a chain transmission, and which has not been achieved so far in spite of endeavours.

An advantageous embodiment of the variable transmission of the invention is characterized in that the outer ring of the torsion spring is provided with knobs which fit in recesses in the outer cup disk, thus enabling the torque to be adjusted with steps deter¬ mined by the recess spacing.

An advantageous embodiment of the variable transmission of the invention is also characterized in that with the thread intecon- necting the cup disks is associated a pressurized oil cylinder pushes the cup disks apart with the aid of oil pressure and with adjustable force.

An advantageouss embodiment of the variable transmission of the invention is also characterized in that the flow passage of the pressurized oil cylinde is provided with an adjustable resistance check valve with which the inflow of the oil into the cylinder, and as a. esult thereof, the changing of the transmission ratio of the transmission towards higher speed, can be retarded.

An advantageous embodiment of the variable transmission of the invention is also characterized in that the thread interconnecting the cup disks is completely enclosed in the pressurized oil cylind¬ er, lubricated on all sides by the oil.

An advantageous embodiment of the variable transmission of the

invention is also characterized in that the cup disks and control members of the secondary pulley are connected to a conventional wheel hub containing a roller idling clutch and a brake inside the cover so that only the shaft and the inner ring of the hub clutch with its bearing are replaced with special parts.

An advantageous embodiment of the variable transmission of the invention is also characterized in that pressure increase in the cylinder pushing the cup disks of the secondary pulley apart in¬ creases the tension of the V-belt with the aid of a cylinder acting on the jockey pulley.

An advantageous embodiment of a variable transmission according to the invention in which also the primary pulley is variable is also characterized in that the same pressurized fluid which pushes apart the cup disks of the secondary pulley urges together the cup disks in the primary pulley.

An advantageous embodiment of the variable transmission of the in¬ vention is also characterized in that the means controlling the pressure of the pressurized fluid has been mounted on the handle¬ bar αf the bicycle and provided with a pressure gauge.

An advantageous embodiment of the variable transmission of the invention for a motor-driven vehicle, in which the cup disks of the primary pulley are urged together by action of springs and of a cylinder containing pressurized fluid is also characterized in that the pressure control of the pressurized fluid has been connected to the control system of the engine.

An advantageous embodiment of the variable transmission of the invention is also characterized in that at least one surface in contact with a side of the belt on the pulleys transmitting power is grooved in a manner known in itself in the art,

An advantageous embodiment of the variable transmission of the

invention is also characte ized in that the curved shape of the grooving approximates an evolvent.

Although the present invention primarily concerns the secondary pulley, of which the retardation is in general, and in bicycles in particular, advantageously accomplished in that a rotation is as¬ sociated with the axial control movement of the cup disks, the throttling of the flow of the fluid just mentioned and its control aid in the first place in making the movement of the cup disks of the secondary pulley away from each other suitably fast and smooth when the resistance to propagation of the vehicle decreases.

The object of the present invention is to provide a variable trans¬ mission in which the control members of the secondary pulley are appropriate to be connected to wheel hubs of standard design com¬ prising a roller idling clutch and a drum or lamella brake inside the cover, of which there are commercially available several brands which are similar in design but different in quality level. With some modifications, the control members are also applicable in connection with wheel hubs in which a conical sleeve tightened by a screw serves as idling clutch.

The invention is described in the following more in detail with the aid of an example, referring to the drawing attached, i n which: -

Fig. 1 presents a section of a wheel hub in which all other members, in addition to the control members, are visible at least in half-section;

Fig. 2 presents an embodiment which is particularly advantageous of its friction conditions and in which the control thread is totally accomodated within the the control cylinder and lubricated on all sides by the control oil;

Fig. 3 presents in partial projection a four-ended conical spiral interconnecting the cup disks over a threaded sleeve, viewed from

the right hand shaft end;

Fig. 4 presents schematically, in both extreme positions, a trans¬ mission of which the primary pulley is fixed and round in shape;

Fig. 5 presents likewise schematically, and in both extreme posi¬ tions, a transmission wherein the primary pulley is fixed and oval in shape;

Fig. 6 presents a transmission wherein the primary pulley is a variable pulley round in shape; and

Fig. 7 presents a transmission wherein the primary pulley is a variable pulley oval in shape.

Let us next consider, referring to Fig. 1, a variable transmission according to the invention which automatically changes its trans¬ mission ratio in accordance with the resistance to propagation of the vehicle, in which the pαwerransmitting transmission link is a V-belt 1 or equivalent and in which at least the secondary pulley consists of cup disks 2 and 3 urged against each other. In Fig. 1 is presented, in section, a wheel hub operating with a roller idling clutch and in which half of the peripheral force of the belt 1 acting as the transmission link goes to the inner cup disk 3 and whence over the hub 6 and the rollers 9 of the roller clutch to the cover 13 of the wheel hub. The other half of the peripheral force of the belt 1 goes from the outer cup disk 2 to the nut sleeve 4, and whence over the adjusting thread and the threaded sleeve 5 to the idling clutch, where the partial torques are combined. The con¬ necting thread between the threaded sleeve 5 and the hub of the idling clutch is preferably secured with an anaerobic locking seal which also acts as oil seal and is detachable by heating.

The cup disks 2 and 3 are interconnected with a multiple-end thread 4 and 5 and with a torsion spring 7 which is a conical spiral spring with at least two ends and which in addition to torque

action presses against the cup disk 2 with an axial force. The outer ring of the torsion spring 7 is provided with knobs which fit into the recesses in the outer cup disk 2 and which enable adjust- ment of torque with steps defined by the recess spacing. In order that the adjustment position of the outer ring of the spring might be maintained even, in spite of jolts and vibration, the axial pre¬ loading has to be high enough and the spring must have at least two ends.

The torque with which the cup disks 2 and 3 are urged together and and by effect of which the belt 1 rises up to its largest contact ring, is determined by four factors: the pitch of the control thread, the rigidity and initial position of the torsion spring 7, and the pressure in the control cylinder. With the thread 4 and 5 interconnecting the cup disks 2 and 3 is associated a pressurized oil cylinder, which pushes the cup disks 2 and 3 apart with a force adjustable with the aid of the oil pressure. In Fig. 2 is shown an embodiment which is particularly advantageous as to its friction properties, in which the control thread is totally accomocated within the control cylinder and lubricated on all sides by the control oil. If the pitch of the control thread is made low, the cup disks 2 and 3 are already urged together at a very small peri¬ pheral force and the torsion spring 7 has to be preloaded so that it tends to rotate the cup disk 2 counter-clockwise, that is, against the peripheral force. In the designs of Figs 1 and 2, the effect of the control cylinder has the same direction, that is, it increases the peripheral force of the belt 1. The flow passage of the pressurized oil cylinder may be provided with an adjustable resistance check valve, with the aid of which the inflow of oil into the cylinder, and as its result, the changing of the transmission ratio towards higher speed, can be retarded.

In Fig. 3 is presented, in partial projection, the conical spiral spring with four ends interconnecting the cup disks 2 and 3 over the threaded sleeve 5, viewed from the right-hand shaft end. The cup disks 2 and 3 of the secondary pulley as well as the control

members can be connected to a wheel hub comprising a standard roller idling clutch and a brake within the cover so that only the shaft and the inner ring of the hub clutch with its bearings are replaced with special parts.

In Fig. 4 is presented schematically a transmission, in both extreme control positions, in which the primary pulley is fixed and round in shape. In Fig. 5, the primary pulley is fixed and oval in shape. In the design of Fig. 6 the primary pulley is a variable pulley round in shape, and in Fig. 7, it is a variable pulley oval in shape. In bicycles, and in vehicles operated by muscular force in general, the primary pulley may be fixed, or a variable pulley changing the radius of its contact ring in likeness with the se¬ condary pulley but inversely, and it may in both cases also be oval in shape. In a variable transmission comprising an oval pri¬ mary pulley, a jockey pulley equalizing the belt length is required also in the case that both power-transmitting pulleys are variable pulleys. Straight arrows indicate the direction of the pedal force and curved arrows, the direction of rotation. In an embodiment of the invention, the primary pulley is fixed and pressure increase in the cylinder pushing the cup disks 2 and 3 of the secondary pulley apart increases the tension of the V-belt 1 with the aid of a cylinder acting on the jockey pulley. If also the primary pulley is variable, the same pressurized fluid which pushes apart the cup disks 2 and 3 in the secondary pulley will urge the cup disks of the primary pulley together. The pressure control means for the pressurized fluid may be mounted on the handle-bar of a bicycle and be provided with a pressure gauge.

In a variable transmission of a motor-driven vehicle in which the cup disks of the primary pulley are urged together by effect of springs and of a cylinder containing pressurized fluid, the pressure control of the pressurized fluid may be connected to the control system of the engine.

In an advantageous embodiment of the invention, the variable spring

suspension system is a liquid or air spring suspension or a com¬ bination of both, whereby excessively rapid control movements can be prevented by throttling the liquid flow.

The effect of the axial force of the conical spiral spring is ad¬ vantageous, as it reduces friction, but it is small in magnitude. The greatest benefit from the axial force is in fact that the outer ring of the torsion spring is kept pressed against the cup disk and is easy to adjust in different positions within the graduation de¬ fined by the recess spacing of the cup disk. The torsion spring 7 may, within the scope of the invention, be manufactured in a number of ways. For instance, instead of a ring disk and spring wire spirals welded thereon, a structure is conceivable which is cut from spring steel sheet in its entirety. Laser cutting, for instance, may be carried out as the last work step after hardening.

When a small control thread pitch and comparatively high control oil pressure is used, it is useful to be able to retard the inflow of the control oil with a resistance check valve.

The properties and control facilities described in the foregoing are sufficient to guarantee reliable operation and good efficiency, provided that the belt is flexible and has sufficient rigidity against tension and lateral compression and that it has been manu¬ factured to be uniform enough in quality and dimensionally accurate.

In very dirty conditions or in rain some slipping may still occur, and such is best counteracted by providing one of the contact sur¬ faces of the secondary pulley with spiral grooves. Such grooving may also be used for higher efficiency and in order to reduce the belt wear if the spiral configuration is made to approximate an evolvent, as disclosed in the Finnish patent application No. 853430.

The reliability and precision in operation of the variable trans-

mission may also be improved by further developing the control system. Modern electronics, pick-up technique and hydraulics offer opportunities which are becoming better, and developing, all the time.

The variable transmission of the invention is provided with a thread sensing the torque of the shaft, but the design differs known in the art in that here are at least two active spring systems, and both are either settable or adjustable.

It is obvious to a person skilled in the art that various embodi¬ ments of the invention are not exclusively confined to the example presented in the foregoing and that they may vary within the scope of the claims stated below.