Raja Rajendran MSME, President, EcoNovaTech LLC
Prashanth Rajendran MSME, PhD Candidate, CEO, EcoNovaTech LLC
- Breakthrough innovation using Geneva mechanism for transmissions
- Multi-speed uninterrupted shifting for EV
- IVT with uniform input-to-output ratio, NOT dependent on friction for HEV
For the last several years, EcoNovaTech has been developing multiple innovative technologies to solve problems that are in the forefront of the automotive industry. With its latest developments, EcoNovaTech provides a paradigm shift in transmission technology with uninterrupted shifting and ALL gear-based transmission.
Multi-Speed Transmission with Uninterrupted Shifting (MSTUS) for EV:
OEMs are continually striving to increase the range per charge for EVs. Some OEMs now recommend not depleting the battery below 25 % capacity, to extend its life. Battery charges relatively fast for the first 80 % but the last 20 % takes about as much time. Therefore, charging the battery up to 100 % could take overnight. However, there are concerns that the battery can catch fire making it difficult for consumers to use the full capacity. Moreover, battery degrades depending on the frequency and number of times it is charged and discharged. A transmission that can improve the range will reduce this frequency thereby extending battery life. So, OEMs are actively looking for a multi-speed transmission in place of a single speed Transmission to increase the range.
OEMs currently use two stage reduction for EVs. They are also actively looking into two speed transmissions with two stage reduction. Ideally, shifting occurs at around 40 − 45 miles per hour at which the wheel spins at about 650 − 750 RPM and the motor spins at about 6,500 − 7,500 RPM, since two stage reduction results in about one tenth the RPM of the electric motor. Current technology takes about 150 milliseconds of interruption for synchronizing and shifting, which causes a delay in achieving 0 − 60. So, a Multi-Speed Transmission with Uninterrupted Shifting (MSTUS) is desirable since it further increases the range, without affecting the time needed for 0 − 60. For electric motors spinning at 7,000 RPM the first reduction results in about 2,200 − 2300 RPM. This allows about 25 − 30 milliseconds for the transmission to shift over a full revolution, during the second reduction.
Smooth shifting occurs when the vehicle speed remains constant during shifting. Since vehicle speed is a product of motor RPM and angular velocity ratio, the change in this ratio should be inversely proportional to the change in motor RPM. Since the rotor of an electric motor has very low inertia when compared to IC engines, the RPM can be rapidly changed without changing the vehicle speed during shifting. As a result, occupants will not experience a jolt during shifting.
Experimental study using chain and sprocket mechanism for uninterrupted shifting shows that when shifting in about 19 milliseconds, most occupants may not experience the abrupt change in vehicle speed. However, use of chain and sprocket mechanism in transmissions is still in developmental stage. Noise and durability issues must be overcome. Chain and sprocket mechanism is not commonly used in transmissions in the industry.
Founded in 2014, EcoNovaTech has been dedicated to its mission of designing custom eco-friendly products through simple, effective engineering solutions and being a leader in Automotive Engineering.
In 2021, EcoNovaTech came up with a break through invention for Multi-Speed Transmission with Uninterrupted Shifting where the motor is continuously powering the wheels, even during shifting. It replaces the synchronizer with custom Geneva mechanism where the Geneva pin wheel has multiple pins and the Geneva slot wheel has multiple custom slots, along with dog clutch. The force required to operate a dog clutch is negligible.
With its latest innovation, EcoNovaTech now has two MSTUS solutions (one using non-circular gears and the other using Geneva mechanism) for EVs that are patent pending in multiple countries.
To briefly explain the operating principles of this innovation, both EcoNovaTech solutions use a transition module for uninterrupted shifting. The transition module transmits power parallel to the transmission gears in the transmission. The transition module can be engaged or disengaged using a dog clutch. The transition module has non-circular gears or Geneva pin and slot wheels cycling smoothly through all the constant angular velocity ratios used in the transmission, ramping up and down as needed. In a two-speed transmission, the transition module has 4 zones, a constant low speed zone, ramp up zone, constant high-speed zone, and a ramp down zone. Thus, it alternates between two constant speed zones sandwiched by a ramp up zone and a ramp down zone.
Use of partial gears for the constant zone makes it economical and less complex, and the number of pins can be reduced to 1 pin for up-shift and 1 pin for down-shift.
Use of helical gears reduces the space required when compared to chain and sprocket with tensioner. Also, helical gears provide a smoother and quieter ride at higher efficiency, when compared to chain and sprocket systems. A pair of Geneva wheels without partial gears and a pair of Geneva wheels with partial gears are shown in the figure.
Unlike in DCT the need for a high-pressure hydraulic system is eliminated resulting in significant savings. Also, the DCT only decreases the duration of interruption while EcoNovaTech innovation COMPLETELY eliminates the interruption. The lower ratio driven gear is placed on a one-way bearing on its shaft eliminating the need for linking it through a dog clutch. During reversing or regenerative breaking this must be connected through a dog clutch.
EcoNovaTech’s first solution is best suited for luxury passenger vehicles. For such vehicles, it is recommended that duration of uninterrupted shifting is extended when compared to current emerging technology, for a perfectly smooth ride. This solution uses a Duration Extender Module (DEM) that extends the duration of uninterrupted shifting to an optimal value of 30 − 50 ms (multiple revolutions) with zero interruption. DEM uses additionally a pair of overdrive gears., however is highly suitable for luxury passenger vehicles.
EcoNovaTech’s second and latest solution uses a DEM and eliminates the shortcomings of the chain and sprocket solution that is currently being developed in the industry. In 2019, EcoNovaTech developed a solution for uninterrupted shifting without a DEM using non-circular gears (patent pending). EcoNovaTech now has a less expensive innovative design (patent pending) that uses Geneva pin and slot mechanism with a customized slot, in lieu of non-circular gears, to transition from one angular velocity ratio to another. Geneva wheels can be mass produced at a lower cost when compared to non-circular gears.
Since the original design, EcoNovaTech has come up with a significant improvement where the Geneva wheel has only one pin for upshift and one pin for downshift, with the addition of two pairs of partial gears.
For EV, since the electric motor has a low inertia and can change the RPM instantaneously, shifting can occur within one revolution of the input from the electric motor. Since EV uses two stage reduction, it is advantageous to have the uninterrupted shifting happen in the second stage so that it spans a longer duration.
Non-friction dependent IVT for HEV:
In a hybrid vehicle, since we have a combination of IC engine and electric motor, a smaller IC engine can be used. An IVT can get maximum power out of a small engine for a quick acceleration.
EcoNovaTech has two innovative IVT solutions, one using non-circular gears (patented in US, China and Japan, and patent pending in Canada and India) and its latest using Geneva wheel mechanism (patent pending), along with other COTS components.
The operating principle involves converting
- uniform rotation from the engine to non-uniform rotation using non-circular gears or Geneva mechanism
- non-uniform rotation from above to linear oscillation (a portion being uniform) of a rack using a Scotch yoke mechanism
- linear oscillation of the rack to rocking motion of a pinion
- rocking motion of the pinion to a unidirectional uniform rotation of the output using a one-way bearing
The location of the pin in the scotch yoke mechanism dictates the angular velocity ratio. With as low as 3 scotch yoke modules, a continuous and steady output can be achieved.
The ratio changing mechanism in EcoNovaTech’s solution uses a unique and simple feature enabling the relocation of the crank pin in a rotating coordinate system from a fixed coordinate system. This is used to change the input-to-Output ratio for the transmission. The crank pin location can be changed purely mechanically at high RPMs so that it can be operated with a lever or cable. Planetary gears, computer controlled clutch or reversible one-way bearing can be used to achieve reverse gear. Use of reversible one-way bearing eliminates torque recirculation thereby reducing the peak load on the one-way bearing. This results in overall size reduction, since the size of the one-way bearing increases with the torque that is transmitted via the one way bearing.
Use of elliptical gears produce close results as non-circular gears, allowing ease of mass production since the driving and driven non-circular gears can be identical. EcoNovaTech’s latest IVT solution using Geneva wheel mechanism instead of non-circular gears will significantly reduce the manufacturing cost associated with non-circular gears.
EcoNovaTech’s eco-friendly innovative technical solutions can help OEMs progress towards the goal of Net-Zero Emissions by 2050 to help stop climate change.
