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First high-efficiency CVT

Advantages of a CVT over an Automatic and a Manual

By adjusting the transmission ratio in infinitesimally small steps, the engine or E-motor can be kept running at the speed of best efficiency; they can also continuously be kept on the speed of maximum power as long as requested.

This property of CVTs offers advantages over stepped transmissions such as Automatics and Manuals that have a limited amount of gears. Over the last decades stepped transmissions got more and more gear ratios (in the seventies 3 to 4 speeds, nowadays up to 10 speeds) to come closer to CVT properties.

However, when stepped transmissions change the ratio, there is a significant efficiency drop and reduction in the transmitted power by slipping clutches or synchronizers, so that a higher number of gears would have a negative effect. Stepped transmissions with a high number of gears are expensive, bulky and heavy. The optimum amount of gears seems to be reached; the stepped transmission has reached its limits of optimization.

The problem with traditional CVTs

Current CVTs such as the belt-CVT have the above mentioned advantage of being continuously variable to keep the engine or E-motor closer to their best efficiency curve. However, a belt-CVT has a lower internal efficiency than an Automatic, a DCT or a Manual transmission. Roughly speaking, the lower internal efficiency counteracts the advantages of being continuously variable.

There are also the experimental full and half toroidal CVTs, the cone ring transmissions and systems with rolling balls. All these systems suffer drill-slip (also called drilling motion). Due to the geometry of all these CVTs the rolling contacts that transmit power do slip, whatever the contact pressure. This drilling motion causes major problems that cannot be solved due to the typical design of these systems:

  • Drill slip is a permanent slip, causing losses of several percentages. This explains why all current CVTs have a low efficiency.
  • Power loss due to drill-slip causes heat dissipation in the tiny oil layer between the rolling contacts. The oil gets hot, its viscosity drops, the layer gets thinner causing steel to steel contact. Due to the slip, wear occurs. Durability of these systems remains an unsolved problem.
  • Drill-slip means that inside the rolling contact surface, there is a region with traction in the wrong direction. The shear forces partially counteract each other. The result is a poor power density or bulky transmissions.
  • The above mentioned problems also make current CVTs unsuitable for the high power and torque levels of trucks and buses.

Problem solved with MAZARO’s transmissions

MAZARO’s transmissions are the only continuously variable systems with a unique solution to eliminate drill-slip for all driving conditions and all ratios.

Major advantages:

  • No drill-slip, leading to high efficiency
  • No heat dissipation in the rolling contacts, thus stable oil film
  • No wear at all, high durability
  • All shear forces in the rolling contacts work in the driving direction, so there is high power density in a compact design
  • MAZARO already has a transmission driving a demo truck

Inattentive readers easily mistake MAZARO’s technology for a toroidal CVT so please note that its innovative design is very distinct from all previous CVTs, containing no toroids, no belt, no cones nor gears.

No toroidal CVT

Another step ahead

Besides the elimination of drill-slip, the construction of the SVT allows for designing high spreads.

The RVT goes a step further by extending the speed ratio down to zero and to reverse. Even for drive-away with an engine driven vehicle, there is not one slipping component: there are no clutches, nor torque converter.

The absence of gears, even not for reverse, eliminates all possible gear noises and back-lash when reversing the load. The rolling surfaces of MAZARO’s traction wheels are always separated by an oil film, which explains the silent operation and the absence of wear.

Efficient actuation system

All automatic transmissions including belt-CVTs have a hydraulic (or sometimes an electro-mechanic) actuation system to change the ratios automatically. In general such an actuation system is a major source of power loss. MAZARO has developed a hydraulic actuation system consuming around 0.9% of the transmitted power which is several times lower than what DCT’s (Dual Clutch Transmissions) or Automatic transmissions consume.

Currently MAZARO is developing an alternative actuation system intended to consume only some 0.1% of the transmitted power.