Description - Main Applications - Frequently Asked Questions
Rack transmissions are a brand new concept that allows for all kinds of automatic gearboxes with infinite variation.
The basic principle
A linear reciprocating movement is converted into a rotary motion with a rack and pinion gear transmission. The output shaft rotates in one direction only because these pinions are connected to the output shaft through freewheels.
The advantage is that the rack stroke may vary without inverting the rotation direction of the output shaft. A long stroke leads to a fast rotation while a short one leads to a slower one.
Although it is extremely simple, it may transfer a very high torque, because it uses only perfectly conjugated gears. There is no friction and no possible slipping.
You will find below many possible options that can be combined to build a transmission that fits perfectly any specific need.
View the video posted June 12. 2018 on LinkedIn and the very first presentation posted March 21. 2018, also on LinkedIn
The "infinite" variation
The reciprocating linear movement may be obtained from a rotary motion by a classical crank/rod mechanism. The amplitude of this linear reciprocating movement is therefore fixed, but the amplitude of this movement is varied before turning into rotary motion again with a rack and pinion gear transmission, these pinions being connected to the output shaft through freewheels.
They include not only a continuously variable gear ratio, but an "infinite" range as well, as it includes a "zero ratio". This "zero ratio" is a very innovative characteristic and means this transmission also works as a clutch. The RANGE of the transmission is freely chosen by the designer.
The gear selector may be activated manually or by a computer driven engine.
The automatic adaptation or the gear ratio to the resistive torque
This adaptation may be obtained automatically, instantly, using only mechanical means.
A spring (purple), is compressed when the resistive torque increases, and decreases the amplitude of oscillation of the oscillating lever (brown), which simultaneously causes a decrease in the stroke of the rack (green).
This adaptation can go as far as to confuse the axis of rotation of the point of attachment of the connecting rod with the axis of the motor shaft. The system can therefore completely disengage the output shaft of the motor shaft, and this also makes it possible to create an Infinitely Variable Transmission (IVT).
The direct drive option
This option eliminates any movement that could emit noise or vibration, and provides a 100% efficiency. It may be selected automatically, depending on the speed of rotation of the input or of the output shaft.
It is of course possible to combine several rack devices in order to obtain a smoother output motion.
The piston engines synchronization
When used in conjunction with a piston motor, the movement of the oscillating rack may be synchronized with the one of the pistons, and regulated by a flywheel which is located at the output of the gearbox.
Reciprocating engines produce an irregular torque, which is due to the pressure variation in the cylinders during the cycle.
Instead of regulating this acyclism by a flywheel located between the engine and the gearbox, the irregularity of the movement during the cycle is transmitted further.
Each engine stroke is then converted into a rotation of the output shaft, and it is only at this stage that the movement is regulated by a flywheel.
This method allows the engine to operate at a rate that uses better the pressure variation in the cylinders.
It is of course possible to combine several rack devices in order to obtain a smoother output motion.
View the video posted July 17. 2018 on LinkedIn
The reverse continuous variation of the gear ratio
This option is obtained by allowing the rack to cooperate either with different sets of gears, either the two green ones or the two blue ones in the diagram below.
Each of these green or blue gears cooperates with the axis of the relevant red gear by a freewheel, which is in its center. These free wheels allow the blue gears to rotate in the clockwise direction and the green ones in the opposite direction.
This enables to have two different rules operations, for example forward and backward. To simplify the diagram, the fork that allows to move the rack to the left or right is not shown. The change from one rule to another may happen only when the rack is stationary, at the ZERO point.
The rack may also be placed astride blue and green gears. The transmission is then a native a parking pawl that locks the output shaft of the transmission to keep the vehicle from rolling either forward or backward
The homokinetik conversion of a rotation movement to a linear reciprocating one
With this option, the speed of the output shaft is permanently proportional to the one of the primary shaft, which means there is no possible acyclism.
The movement is transmitted alternately by two similar transmissions turning the rotary motion into a back and forth motion. The cycle of one of these transmissions is shifted so that each of them acts only in the parts of its cycle where the movement is transmitted linearly. The other parts of the cycle are used to slow down the racks at the end of the race and gradually re-accelerate them, in order to avoid vibrations.
The absolute regularity of the movement allows running the device at a very slow speed, using gears to slow down the primary shaft and to accelerate the output one.
This diagram shows only one half of the transmission, in order to explain the functioning of each of the very few components.
The primary shaft (yellow) cooperates with the crown (green) whose shape is left to the discretion of the designer. This crown may be similar to the above design to get a constant speed of the output.
A wheel (pink) rotates on the periphery of the fixed guide (orange), so that the gear of the primary shaft remains at all times in contact with the teeth of the crown.
One rack moves in four steps:
- sliding at constant speed from left to right,
- slowing down, reversing its movement and accelerating up to the same constant speed to the left
- sliding at constant speed from right to left,
- and slowing down, reversing its movement and accelerating up to the same constant speed to the right.
The designer designs the crown so that steps 1 and 3 are equal or longer than steps 2 and 4.
The movement of one of the transmissions is shifted by one quarter of a cycle, and due to the presence of the free wheels, the movement is transferred only by the steps 1 and 3 of each rack.
That is why the speed of the output shaft remains permanently proportional to the one of the primary shaft.
Different types of racks and pinions cooperation
Below is the first version of the LiToR, which has been simplified later as shown above for some applications.
When the rack goes from right to left,
- the upper blue wheel rotates clockwise and causes the upper red wheel to turn clockwise, which in turns rotates the yellow wheel clockwise,
- and the lower blue wheel rotates counterclockwise, but it does not drive the lower red wheel because there is a freewheel which does not drive the lower red wheel in that direction.
When the rack goes from left to right,
- the lower blue wheel rotates clockwise and causes the lower red wheel to turn clockwise , which in turns rotates the yellow wheel clockwise,
- and the upper blue wheel rotates counterclockwise, but it does not drive the upper red wheel because there is a freewheel which does not drive the upper red wheel in that direction.
So each movement of the rack rotates the yellow wheel clockwise, and moves the vehicle frontwards.
Or course, it is possible to obtain a specific transmission ratio at each stage of the cycle, by using gears with a non constant radius, as shown below.
In all cases, it remains a very simple mechanism.
The homokinetik conversion of a rotation movement to a linear reciprocating one
With this option, the speed of the output shaft is permanently proportional to the one of the primary shaft, which means there is no possible acyclism.
The movement is transmitted alternately by two similar transmissions turning the rotary motion into a back and forth motion. The cycle of one of these transmissions is shifted so that each of them acts only in the parts of its cycle where the movement is transmitted linearly. The other parts of the cycle are used to slow down the racks at the end of the race and gradually re-accelerate them, in order to avoid vibrations.
The absolute regularity of the movement allows running the device at a very slow speed, using gears to slow down the primary shaft and to accelerate the output one.
This diagram shows only one half of the transmission, in order to explain the functioning of each of the very few components.
The primary shaft (yellow) cooperates with the crown (green) whose shape is left to the discretion of the designer. This crown may be similar to the above design to get a constant speed of the output.
A wheel (pink) rotates on the periphery of the fixed guide (orange), so that the gear of the primary shaft remains at all times in contact with the teeth of the crown.
One rack moves in four steps:
- sliding at constant speed from left to right,
- slowing down, reversing its movement and accelerating up to the same constant speed to the left
- sliding at constant speed from right to left,
- and slowing down, reversing its movement and accelerating up to the same constant speed to the right.
The designer designs the crown so that steps 1 and 3 are equal or longer than steps 2 and 4.
The movement of one of the transmissions is shifted by one quarter of a cycle, and due to the presence of the free wheels, the movement is transferred only by the steps 1 and 3 of each rack.
That is why the speed of the output shaft remains permanently proportional to the one of the primary shaft.
The multi-rack transmissions
It is of course possible to combine several rack devices in order to obtain a smoother output motion.
This may be combined with the direct drive option, and with the piston engines synchronization.
The number of rack devices is chosen freely by the designer.
All these options and improvements can be combined.
Latest videos posted on LinkedIn about our transmissions
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