WO2020221379A1

WO2020221379A1 - Bicycle drivetrain system with variable angular velocity of pedals

Info

Publication number: WO2020221379A1
Application number: PCT/CZ2019/000020
Authority: WO
Inventors: Petr HAVELKA
Original assignee: Havelka Petr
Priority date: 2019-04-29
Filing date: 2019-04-29
Publication date: 2020-11-05

Abstract

A bicycle drivetrain system with a variable angular velocity of pedals includes two cranks (1) with the pedals (3), the chain (8), the sprocket (7), further new parts for gear mechanism, that determines the variable angular velocity relations among the cranks (1) mutually and the sprocket (7) during the pedaling cycle, the external housing of the central assembly fixed to the bicycle frame and also firmly fixed with an eccentric hub, inside which the right shaft (2) and the left shaft (9) are mounted. The right shaft (2) is placed in the hollow of the left shaft (9), whereas their common axis is eccentrically shifted towards axis of the sprocket hub (4). The shafts (2, 9) are fixed to the cranks (1) and they fit by means of their nose between the rollers (5), which are placed inside the sprocket hub (4).

Description

BICYCLE DRIVETRA1N SYSTEM WITH VARIABLE ANGULAR VELOCITY OF PEDALS

Technical Field

The presented invention relates to a power transmission system used for bicycles. The system includes two cranks, at least one sprocket wheel and a chain.

Background Art

Nowadays a bicycle drive is realized by means of two cranks firmly connected to each other by a shaft in most cases. The cranks are equipped with pedals at the ends. The drive force developed on the pedals is transmitted via a crank and a shaft to a sprocket of a circular or non-circular shape. From the sprocket, the force is further transmitted to the rear wheel by means of a chain. The bicycle drive system defined in this way is characterized by the same left and right pedal angular velocities. The angular velocity varies over the pedaling cycle due to the speed of the crank rotation and the shape of the sprocket, but the variation is the same for both pedals. The same angular velocity of both pedals does not seem to be the most efficient use of the applied force.

The bicycle drive with independent movement of the cranks has been patented for example in: US006840136B1, US 2005/0022626 A1 , US 2004/0045401A1, US006085613A.

Disclosure of Invention

An object of the presented invention of a bicycle drivetrain system with a variable angular velocity of pedals is to increase the efficiency of the transmission of the force that is generated by a bicyclist during cycling considering the entire chain of the power transmission from the pedals to the point of the contact of the rear wheel with the ground in comparison with a classical bicycle. The presented bicycle drivetrain system causes a periodic change in the power ratio due to the different periodically varying angular velocities of the left and the right pedal, while maintaining the circular motion trajectory of the pedals. The angular velocities of the left and the right pedal are reduced in the forward active phase of the pedaling cycle and at the same time they are increased in the backward inactive phase, thereby is achieved the extension of the time period in the active phase of the pedaling cycle, when the crank is in more advantageous position to the force vector acting on the pedal.

Another aspect of the presented invention in comparison with a classical bicycle is the increase in the force transmission efficiency in the phase around the top and bottom parts of the pedaling cycle. The better efficiency is achieved by higher angular velocity in these dead points in which both legs are in the active pushing stroke at the same time.

Another main advantage of the presented invention in comparison with a classical bicycle is that the maximum transmitted force by the chain at the same average cadence at one pedaling cycle is lower and the minimum transmitted force is higher. The decrease of difference between maximum and minimum force during one pedaling cycle causes reduction of the value of ineffective elastic

deformations, which are proportional to the transmitted force and mainly occurring in a bicycle frame, a chain and a rear wheel. This decrease of the transmitted force difference results in more balanced power transmission and also in lower variation of bicycle speed.

The presented invention of the bicycle drivetrain system that comprises two cranks with two pedals, a chain, at least one sprocket of circular or non-circular shape and furthermore, a central assembly. An external housing of the central assembly is mechanically connected to the bicycle frame by at least one locking screw and, further, by means of dowel pins is permanently jointed with an eccentric hub. The eccentric hub supports right and left shafts. The shafts are in the rolling contact with the rollers by means of the shaft noses, that have shape of thumb. The rollers are placed inside the sprocket hub. The right shaft is in the rolling contact with two rollers. One roller is used for power transmission in the forward direction. The second one serves as backlash eliminator and eventually for power transmission in opposite direction. The layout is identical for the left shaft. The sprocket hub is mounted on a needle bearing and on a ball bearing that are housed in the external housing of the central assembly. Further, the sprocket hub is supported by a support bearing placed on the eccentric hub, so that this arrangement prevents its radial motion. The sprocket hub is fixed to the ball bearing by a check nut, which eliminates the hub axial motion.

Furthermore, the essence is that the right shaft is placed by means of the bearings in the hollow of the left shaft, which is mounted by means of the bearings inside of the eccentric hub. The common axis of rotation of the right shaft and the left shaft is eccentrically displaced relative to the axis of rotation of the sprocket hub. The sprocket hub with the rollers, the sprocket together with the right shaft and the left shaft create the base of the gear mechanism. This gear mechanism determines variable angular velocity relations among the sprocket hub, the right shaft and the left shaft. It also determines the cyclic rotation of the right crank and the left crank in the active phase of the pedaling cycle accompanied by periodic variations of the angular velocity. The difference in the gear ratio is based on the variation of the distance between the common axis of the shafts and the positions of the rolling contacts on the shaft noses. The average gear ratio of the gear mechanism between the sprocket and the cranks for one revolution is equal one.

Another feature of the presented invention is that the right crank is firmly

mechanically jointed and positioned with the right shaft according to the position of its nose. The position, in which the right shaft is fixed with the right crank, is determined thereby that the thread axis for mounting of the right pedal is part of the symmetry plane of the right shaft. The symmetry plane of the right shaft includes the axis of the right shaft and splits the shaft nose into two identical halves. The left crank is mechanically jointed and positioned with the left shaft in the same way as in the case of the right crank.

Another aspect is that the four rollers for the rolling contact with the noses are radially mounted on the pins and axially fitted in the slot of the sprocket hub. The one pair of the rollers is for the right shaft; another pair is for the left shaft. The rollers belonging to the right shaft are arranged in order to be in contact with the left and the right nose side of the right shaft. The pair of the rollers for the right shaft and the pair of the rollers for the left shaft are arranged in axial symmetry according to the axis of the sprocket hub.

Furthermore, the essence is that the sprocket hub is firmly mechanically jointed with at least one sprocket of circular or non-circular shape. The non-circular shape sprocket varies the pedal angular velocity during the pedaling cycle, while the relationship of the instantaneous angular velocities of the right and the left pedals remains independent on a sprocket shape. The sprocket hub could be composed from several parts, which could simplify its production and mounting to the central assembly.

The essence of the presented invention is that the noses of the right shaft and of the left shaft have the shape of thumb. The contact areas of the thumbs, fitted between the rollers, have curve profile allowing the pendulous and linear motion of the thumbs between the rollers.

Another aspect is that the right shaft and the left shaft are axially fixed by the sliding contact in the slots of the sprocket hub by the means of the noses. There are two slots in the sprocket hub, one for the right shaft and one for the left shaft. The slots are arranged in the axial symmetry according to the axis of the sprocket hub.

The essence of the presented invention is, that the sliding contacts areas of the rollers and also of the right shaft and of the left shaft are equipped with oil grooves. The oil grooves are arranged so that the effective lubrication was secured during the relative motion of the rollers and the shafts.

Furthermore, the essence of the presented invention is that at least two lock holes are made out in the external housing of the central assembly. These holes are angularly graduated in the perpendicular plane to the axis of the external housing of the central assembly. There is at least one row of holes. The holes are used for fixation and rotary setting of the central assembly to the bicycle frame in the position, which is the best for a specific pedaling technique.

Significant feature is, that the bearings for one side of the supports of the right shaft, the left shaft and the sprocket hub are placed one above the other which improves the toughness of the central assembly. The second side is arranged in the similar way.

Another advantage of the presented invention is, that all the components causing the angular velocity variation are integrated in one unit inside of the central assembly. This arrangement is advantageous for mounting into the frame and also for maintenance-free operation.

Disadvantage of the presented invention, in comparison with a classical bicycle, is slightly higher weight, the more robust design of the central assembly, whose diameter is not quite normal for mounting to the frame of a classical bicycle.

Further, for full usage of the system, some cyclists has to be adapted to the change of pedaling speed during the pedaling cycle.

Brief Description of Drawings

Fig. 1 shows the bicycle drivetrain system with the variable angular velocity of the pedals in a cross section.

Fig. 2 shows the bicycle drivetrain system with the variable angular velocity of the pedals in a longitudinal section.

Fig. 3 shows the graph of the relative angular velocity of the right crank for one revolution.

Best Mode for Carrying Out the Invention

Fig. 1 shows the bicycle drivetrain system with the variable angular velocity of the pedals in a cross section through the integrated gear mechanism. The right crank 1 is shown in the position over the dead point. In this position the crank determines an angle a from the left side and an angle b from the right side. The angles a and b are shown in the perpendicular plane to the axis of the sprocket hub 4 and determined from the plane A. The plane A is defined by means of the axis of the sprocket hub 4 and of the common axis of the right and the left shafts 2, 9.

The force developed during pedaling on the right pedal 3 is transmitted via the right crank 1, in which the right pedal 3 is mounted, to the right shaft 2. The right shaft 2 is firmly mechanically connected and positioned with the right crank 1. The right shaft 2 has a nose, which has shape of thumb, via which the force is transmitted to the sprocket hub 4 by means of one from four rollers. The rollers 5_are radially mounted on the pins 6 and axially mounted in the slot of the sprocket hub 4.

Further, the force is transmitted to the at least one sprocket 7, which is fixed to the sprocket hub 4. The force transmission from the sprocket 7 is carried out by means of a chain 8. The left shaft 9 has also a nose that has shape of thumb, which is fitted between the two rollers 5. This arrangement defines the relations between the left shaft 9, the right shaft 2 and the sprocket hub 4. The left shaft 9 is shown at Fig. 1 in the position, where it forms with the plane A an angle a'. The angle arm for the left shaft 9 is determined by its symmetry plane, that splits its nose to two identical halves. The value of the angle a^' is the same as the angle a. In the case of this gear mechanism design, displayed at Fig. 1 , the cranks do not move the uniform angular velocity. The time of the cranks movement in the section defined by the angle a or, alternatively, by the angle a^', is equal to the time of the crank movement in the section defined by the angle b.

Particular components of the bicycle drivetrain system are shown at Fig. 2. The longitudinal section is taken on the plane A, whereas compared to the drawing at Fig. 1 the right crank 1 and the left crank 20 are indexed so that the thread axis of the right pedal 3 and the thread axis of the left pedal are included in the plane A.

To improve a lucidity the drawing at Fig. 2 is displayed without seal.

The external housing 10 of the central assembly serves for two basic purposes. Firstly it serves for mounting to the bicycle frame H, where its external shape is suitable for fixation and rotary setting of the whole drivetrain system in the position, which is the best for the specific pedaling technique. The rotary setting is made by means of the locking screw 12, which is screwed into the bicycle frame V\ and fits into one of the holes made on the circumference of the external housing I of the central assembly. The holes are angularly graduated in the perpendicular plane to the axis of the external housing 10 of the central assembly.

Second main purpose of the external housing 10 of the central assembly is to support the bearings 13 and 14. The needle bearing 13 serves to support the sprocket hub 4 in radial direction. Further, the sprocket hub 4 is mounted in the ball bearing 14, to which it is fixed by the check nut 15, which eliminates its radial and axial motion. The external housing IQ of the central assembly is firmly joined to the eccentric hub 16 by means of the dowel pins 17. Inside the eccentric hub 16, the bearing 18 and 19 are mounted so, that their common axis is eccentrically shifted towards axis of rotation of the sprocket hub 4 by the value e. The bearing 18 and 19 support the left shaft 9 in radial direction. The left shaft 9 is firmly fixed and positioned with the left crank 20. In the hole of the left shaft 9, the bearing 22 and 23 are mounted so, that they prevent the radial motion of the right shaft 2. To prevent the axial motion of the right shaft 2 and the left shaft 9, the both shafts are equipped with the noses, which are fitted in the slots of the sprocket hub 4 in a sliding contact. The nose areas, which are in a rolling contact with the rollers 5, have curve profile allowing the pendulous and linear motion between the rollers 5. To improve the toughness of the central assembly, the support bearing 21 is placed between the eccentric hub 16 and the sprocket hub 4.

Fig. 3 shows the graph of the relative angular velocity of the right crank 1 for one revolution at the constant angular velocity of the circular sprocket 7. The beginning of curve 0° corresponds to the position in the forward phase of the pedaling cycle, when the right crank 1 comes through the plane A. The displayed values of angular velocity are derived from ratio e/I that equals 0.1 , where e is eccentric shift of the common axis of the right and the left shaft 2, 9.

The distance I is shown at Fig. 1 and is defined as perpendicular distance between the sprocket hub axis and the join of the rollers axes. In the case of the circular sprocket with 44 teeth the relative change of angular velocity of the right crank 1 between maximum and minimum value corresponds to the gear ratio change as though the sprocket with 48.4 teeth was replaced by the sprocket with 39.6 teeth during one pedaling cycle.

It is to be understood that the above described embodiment is provided for purpose of the illustration and the invention itself is not limited by this embodiment.

However, the various features of the invention may be implemented in a different manner than the specific illustration in the accompanying drawings. Industrial Applicability

The invention of the bicycle drivetrain system with the variable pedals angular velocity is applicable to all types of bicycles including electric bikes, both racing and recreational.

List of reference marks:

1 - right crank

2 - right shaft

3 - right pedal

4 - sprocket hub

5 - roller

6 - pin

7 - sprocket

8 - chain

9 - left shaft

10 - external housing of the central assembly

1 1 - bicycle frame

12 - locking screw

13 - bearing

14 - ball bearing

15 - check nut

16 - eccentric hub

17 - dowel pin

18 - bearing

19 - bearing

20 - left crank

21 - support bearing

22 - bearing

23 - bearing

Claims

1. A bicycle drivetrain system with a variable angular velocity of pedals that comprises two cranks (1 , 20), with two pedals (3), a chain (8), at least one sprocket (7) of circular or non-circular shape, characterized in that, an external housing (10) of the central assembly is mechanically connected to a bicycle frame (1 1) by at least one locking screw (12) and further by means of dowel pins (17) is

permanently jointed with an eccentric hub (16), in which the right and the left shafts (2, 9) are placed, so that the shafts (2, 9) by means of their nose are in a rolling contact with the rollers (5) placed inside the sprocket hub (4), that is mounted on the support bearing (21), further on the bearing (13) and on the ball bearing (14), in which the sprocket hub (4) is locked by a check nut (15).

2. The bicycle drivetrain system according to claim 1 , characterized in that, the right shaft (2) is placed by means of the bearings (22, 23) in the hollow of the left shaft (9), which is mounted on the bearings (18, 19), where the common axis of the right shaft (2) and the left shaft (9) is eccentrically displaced relative to the axis of the sprocket hub (4).

3.The bicycle drivetrain system according to one of claims 1 or 2, characterized in that, the right shaft (2) is firmly mechanically jointed and positioned according to its nose with the right crank (1) in the position, where the symmetry plane of the right shaft (2) includes the thread axis of the right pedal (3), further the left shaft (9) is firmly mechanically jointed and positioned with the left crank (20) in the same way as in the case of the right shaft (2).

4. The bicycle drivetrain system according to claim 1 , characterized in that, four rollers (5) for the rolling contact with nose are radially mounted on the pins (6) and axially fitted in the slot of the sprocket hub (4), where the pair of the rollers (5) for the right shaft (2) are arranged according to the pair of the rollers (5) for the left shaft (9) in axial symmetry according to the axis of the sprocket hub (4).

5. The bicycle drivetrain system according to claim 1 , characterized in that, the sprocket hub (4) composed of at least one part is firmly mechanically jointed with at least one sprocket (7) of circular or non-circular shape.

6. The bicycle drivetrain system according to one of claims 1 , 2 or 3, characterized in that, the noses of the right shaft (2) and of the left shaft (9) have the shape of thumb, where its contact areas with the rollers (5) have curve profile.

7. The bicycle drivetrain system according to one of claims 1 , 2, 3 or 6,

characterized in that, the right shaft (2) and the left shaft (9) are axially fixed by sliding contact in the slots of the sprocket hub (4) by the means of the noses, where the slots are arranged in the axial symmetry according to the axis of the sprocket hub (4).

8. The bicycle drivetrain system according to one of claims 1 , 2, 3, 6 or 7, characterized in that, sliding contact areas of the rollers (5), of the right shaft (2) and of the left shaft (9) are equipped with oil grooves.

9. The bicycle drivetrain system according to claim 1 , characterized in that, in the external housing (10) of the central assembly at least two lock holes, which are angularly graduated in the perpendicular plane to the axis of the external housing (10) of the central assembly, are made, whereas the holes are placed at least in one row.

10. The bicycle drivetrain system according to one of claims 1 or 2, characterized in that, the bearings (4, 19, 21 and 23) are placed one above the other and the bearings (18 and 22) are placed one above the other too.

1 1. The bicycle drivetrain system according to one of the preceding claims, characterized in that, all the components causing the angular velocity variation are integrated in one unit inside of the central assembly.