DESCRIPTION

Field of the invention

[001] The present invention relates to stepless belt transmissions.

Background of the invention

[002] The prior art discloses various stepless belt transmissions. Typical stepless belt transmissions are disclosed in US patent publications Nos. US 4541821 and US4717368, European patent application publication No. EP2487386, and Chinese patent application publication No. CN101245851. Aforementioned publications discloses a stepless belt transmission comprising a first shaft, an adjustable belt pulley comprising two sheaves mounted on the first shaft, wherein at least one sheave is axially adjustable along the first shaft, a second shaft arranged in parallel to the first shaft, a driven pulley fixed on the second shaft, and an endless belt arranged on the adjustable belt pulley and the driven pulley to transmit a power from the adjustable belt pulley to the driven pulley. Some additional stepless transmissions are disclosed in US patent publications Nos. US2516821 and US4941863, and in Japanese patent publication No. JPS57186655.

[003] In order to provide efficient grip between the pulleys, the tensioning pulley may be arranged in the stepless belt transmission as disclosed in the Japanese patent application publication No. JPS5926654.

[004] Another variable tension pulley system is disclosed in the US patent application publication No. US5938551. The publication describes the variable tension pulley system including a drive pulley, a slave pulley, a belt interconnecting the drive pulley and slave, a tensioner assembly positioned between the drive pulley and the slave pulley and in engagement with the belt. The tensioner assembly includes an elongated rack, a drive rod rotatably positioned on the rack, the drive rod having opposing ends and being selectively rotatable in a positive rotation or a negative rotation. The tensioner assembly also includes a drive block positioned on each end of the rod and in moveable engagement with the rack, each of the drive blocks being moveable along the length of the rod upon rotation of the rod, the drive blocks moving toward each other when the rod is rotated in the positive direction, and the drive blocks moving away from each other when the rod is rotated in the negative direction, a slide block slidably positioned on the rod adjacent to, inside of and in selective engagement with each drive block, and in slidable engagement with the rack, each slide block being moved toward the other slide block by the associated drive block when the drive blocks are moved toward each other, and a tensioner pulley attached to each slide block, each tensioner pulley in engagement with one of the opposing belt spans. The tensioner pulleys displace the opposing belt spans closer together upon positive actuation of the tensioner system in the positive direction. This system can be used for exercise equipment, but is not suitable for higher torque solutions like micro transportation solutions.

[005] German utility model registration publication No. DE9304846U discloses a steplessly- adjustable take-down device for flexible goods e.g. in a circular knitting machine comprises at least one take-down roller, a drive source and a V-belt transmission. The transmission includes a V-belt pulley with two conical flanges at least one of which is mounted so as to be axially movable against spring force to alter the effective diameter of the pulley. The transmission further includes a device for adjusting the tension of the V-belt, changes in belt tension resulting automatically in changes in the effective diameter of pulley, which in turn changes the take-down speed and tension. The adjusting device suitably comprises two screw-adjusted tensioning pulleys. The following transmission requires various mechanism making it very complex machine.

[006] Aim of the invention is to design a stepless belt transmission which provides the best possible grip between the drive pulley and driven pulley as well as improve operational characteristics of the belt compared to the prior art. Additional aim of the invention is to simplify the transmission without compromising on it effectiveness and is very suitable for micro transportation or mobility.

Summary of the invention

[007] The aim is reached by a design of a stepless belt transmission that comprises a first shaft, a second shaft arranged in parallel to the first shaft, an adjustable V-belt pulley comprising two sheaves mounted on the first shaft and a driven toothed pulley fixed to the second shaft. At least one of the two sheaves of the adjustable V-belt pulley is axially adjustable along the first shaft. The sheave can be mechanically, hydraulically, pneumatically, or electronically axially adjusted by sheave adjustment unit thus, during adjustment, the diameter of the V- belt pulley changes at the arc of contact of the endless toothed V- belt. The endless toothed V-belt itself is arranged on the adjustable V-belt pulley and the driven toothed pulley to transmit a power from the adjustable V-belt pulley to the driven toothed pulley.

[008] The stepless belt transmission further comprises a belt tensioner arranged between the adjustable V-belt pulley and the driven toothed pulley. The belt tensioner comprises a guide and two tensioning pulleys mounted on the guide in a slidable manner and disposed to each other and on the outside periphery of the endless toothed V-belt so that the tensioning pulleys apply a force from both sides of the endless toothed V-belt in the direction to each of the tensioning pulleys or tensioning said V-belt from both its sides.

[009] The present invention comprises mechanically, hydraulically, pneumatically, electronically or otherwise adjustable V-belt pulley. The adjustment is perfomed by the sheave adjustment unit and this adjustment is made by moving its sheaves further or closer from each other (axial movement), thereby the diameter of the V-belt pulley decreases or increases at the arc of contact of the V-belt, where angle of the V-belt corresponds to the angle of V-belt pulley groove. The toothed pulley tooth profile corresponds to the toothed V- belt. The changes in toothed V-belt tension in the transmission device, resulting from adjusting the diameter of the V-belt pulley at the arc of contact of the toothed V-belt, are compensated by the aforementioned belt tensioner.

[010] During a use the guide is configured to move both tensioning pulleys towards each other only when at least one sheave by means of the sheave adjustment unit is axially moved away from another sheave along the first shaft and to move both tensioning pulleys away from each other when at least one sheave by means of the sheave adjustment unit is axially moved towards another sheave along the first shaft.

[Oil] In a preferred embodiment of the present invention, the guide comprises a trapezoidal lead screw with a right-hand thread on a one side and with a left-hand thread on another side. One tensioning pulley is arranged on the right-hand thread of the trapezoidal lead screw and another tensioning pulley is arranged on the left-hand thread of the trapezoidal lead screw so that upon rotation of the trapezoidal lead screw in one direction both tensioning pulleys are retracted to each other and upon rotation of the trapezoidal lead screw in opposite direction both tensioning pulleys are moved away from each other.

[012] The following invention allows effective transmission while maintaining the ability to adjust the gear ratio by acting on only one of the members (driven or driving). Moreover, a use of two tensioning pulleys provides more grip surface between the V-belt and adjustable V-belt pulley and the toothed pulley. In addition, a use of two tensioning pulleys allows to tension the V-belt under wider angle than it would be with only one tensioning pulley. Moreover, on the toothed pulley the V-belt works with its teeth, but on the adjustable V-belt pulley the V-belt works with its side surfaces. Hence, the load is divided between the teeth and the side surface of the V-belt and lifetime of the V-belt is increased.

[013] In one embodiment of the invention a belt drive ratio can be set to 2.3:1, which means that rotation of the first shaft in amount of 1000 rpm is transferred to the second shaft in amount of 2300 rpm. The aforementioned ratio is maintained until the first shaft reaches 2500 rpm. Starting from the 2500 rpm the ratio is linearly decreased from 2.3:1 until 1.5:1. This linear decrease is followed according to the linear increase of rotation of the first shaft from 2500 rpm to 4000 rpm. The ratio is decreased by means of the guide and the sheave adjustment unit. The guide moves both tensioning pulleys away each other and simultaneously the sheave adjustment unit axially moves one sheave towards another sheave. In opposite way the ratio is again increased by means of the guide and the sheave adjustment unit - the guide moves both tensioning pulleys towards each other and simultaneously the sheave adjustment unit axially moves away one sheave from another sheave.

[014] The distinguishing features of the present invention, which are endless toothed V-belt in combination with adjustable tensioning pulleys and adjustable sheaves, provide efficient, adjustable, and high torque transmission in micro mobility solutions.

Brief description of the drawings

[015] The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments of the invention. [016] Fig. 1 is a front perspective view of a go-kart (30) equipped with a stepless belt transmission (20).

[017] Fig. 2 is a close up view of the stepless belt transmission (20) as seen in Fig. 1.

[018] Fig. 3 is top view of the stepless belt transmission (20) as seen in Figs. 1 and 2, where one sheave (4) is axially moved away from another sheave (5) along the first shaft (1) by means of a sheave adjustment unit (41).

[019] Fig. 4 is a front perspective view of the stepless belt transmission (20) as seen in Figs. 1 to 3 equipped with a toothed V-belt (7).

[020] Fig. 5 is a front view of the stepless belt transmission (20) as seen in Fig. 1 to 5 where two tensioning pulleys (10; 11) are position in closest position or moved towards each other by means of a guide (9).

[021] Fig. 6 is a front view of the stepless belt transmission (20), where two tensioning pulleys (10; 11) are retracted in farthest position or moved away from each other.

[022] Fig. 7 is a top view of the stepless belt transmission (20) as seen in Fig. 6, but without the toothed V-belt (7), where two tensioning pulleys (10; 11) are retracted in farthest position or moved away from each other and one sheave (4) is axially moved towards another sheave (5) along the first shaft (1).

Detailed description of the embodiments

[023] The preferred embodiments of the invention are now described with reference to the figures to illustrate objectives, advantages, and efficiency of the present invention.

[024] Fig. 1 illustrates a go-kart (30) equipped with a stepless belt transmission (20). The stepless belt transmission (20) is mounted to the frame (31) of the go-kart (30). [025] Fig. 2 to 6 illustrates the stepless belt transmission (20) comprising a first shaft (1). The first shaft (1) is a shaft of an electric motor (32) which in turn is mounted onto the frame (31) of the go-kart (30). The stepless belt transmission (20) comprises an adjustable V-belt pulley (3) comprising two sheaves (4; 5) mounted on the first shaft (1). One sheave (4) is axially adjustable along the first shaft (1) by means of sheave adjustment unit (41). Axial adjustment of one sheave (4) in relation to another sheave (5) is accomplished by means of mechanical actuator (12). The stepless belt transmission (20) comprises a second shaft (2) arranged in parallel to the first shaft (1). In the present embodiment, the second shaft (2) is the driven shaft (2) with the wheels (33) of the go-kart (30) attached thereto. A driven toothed pulley (6) is fixed on the second shaft (2). The stepless belt transmission (20) comprises an endless toothed V-belt (7) arranged on the adjustable V-belt pulley (3) and the driven toothed pulley (6) to transmit a power from the adjustable V-belt pulley (3) to the driven toothed pulley (6). The guide (9) is configured to move both tensioning pulleys (10; 11) towards each other only when at least one sheave (4) axially moves away from another sheave (5) along the first shaft (1) by means of the sheave adjustment unit (41) and to move both tensioning pulleys (10; 11) away from each other when at least one sheave (4) axially moves towards another sheave (4) along the first shaft (1) by means of the sheave adjustment unit (41).

[026] The stepless belt transmission (20) is characterized in that the stepless belt transmission (20) comprises a belt tensioner (8) arranged between the adjustable V-belt pulley (3) and the driven toothed pulley (6) so that the belt tensioner (8) can automatically tension the endless toothed V-belt (7) arranged therebetween. The belt tensioner (8) comprises a guide (9) and two tensioning pulleys (10; 11) mounted on the guide (9) in a slidable manner and disposed to each other and on the outside periphery of the endless toothed V-belt (7) so that the tensioning pulleys (10; 11) apply a force to both sides of the endless toothed V-belt (7) in the direction to each other (see Figs. 2 to 6).

[027] In the preferred embodiment of the present invention as seen in Figs. 1 to 6, the guide (9) of the belt tensioner (8) comprises a trapezoidal lead screw (91) with a right-hand thread on a one side and with a left-hand thread on another side. One tensioning pulley (10; 11) is arranged on the right-hand thread of the trapezoidal lead screw (91) and another tensioning pulley (10; 11) is arranged on the left-hand thread of the trapezoidal lead screw (91) so that upon rotation of the trapezoidal lead screw (91) in one direction both tensioning pulleys (10; 11) are retracted to each other and upon rotation of the trapezoidal lead screw (91) in opposite direction both tensioning pulleys (10; 11) are moved away from each other. The rotation of the trapezoidal lead screw (91) is provided by the means of the electric motor - stepper (92) connected to said lead screw (91).

[028] Fig. 4 illustrates the stepless belt transmission (20) comprising the endless toothed V- belt (7). Figs. 3, 5 and7 illustrate the stepless belt transmission (20) without the endless toothed V-belt (7) for ease of understanding in more detail other members of the stepless belt transmission (20). The adjustable V-belt pulley (3) with its two sheaves (4; 5) and the toothed pulley (6) may be seen more clearly without the endless toothed V-belt (7).

[029] Figs. 4 to 5 illustrate an operation of the stepless belt transmission (20), especially an operation of the belt tensioner (8) and its tensioning pulleys (10; 11). Figs. 4 and 5 illustrates a situation when both tensioning pulleys (10; 11) are moved in the closest possible position to each other and the endless toothed V-belt (7), as seen in Fig. 4, is tensioned in its maximum.

[030] Fig. 6 and 7 illustrates a situation when both tensioning pulleys (10; 11) are moved retracted from each other to its farthest positions and the endless toothed V-belt (7), as seen in Fig. 4, would not be tensioned at all. The sheaves (4; 5) are moved towards each other.

[031] While the invention may be susceptible to various modifications and alternative forms, specific embodiments of which have been shown by way of example in the figures and have been described in detail herein, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the following claims.