New traction drive technologies set to boost appeal of variable-speed supercharging and auxiliary drives

Variator developments announced at industry conference further reduce parasitic losses and can scale to larger transmissions

Low carbon vehicle technology company, Torotrak Group, this week presented innovative technologies for low-cost, high efficiency drive systems at the Berlin CTI symposium and exposition.

These developments will allow Torotrak’s V-Charge variable supercharging technology to compete with the latest boosting solutions coming to market, but without their integration challenges.

In a technical paper titled, ‘Low-cost developments in full-toroidal variator technology’, Chris Gaskell, one of the design engineers responsible for new concepts and intellectual property for the Torotrak Group, introduced and described two new proprietary technologies, called PitchSteer™ and DriveDisconnect™.

V-Charge Unit

V-Charge Unit

PitchSteer is a low-cost method of control that reduces the actuation power requirement of the Torotrak variable drive for devices such as superchargers; use of a 10W actuator means that cost, weight and losses are minimised.

DriveDisconnect provides a zero output speed capability within the variator itself to provide the functionality of a disconnect clutch without the cost or weight penalty. Torotrak will continue to develop both technologies to further advance its V-Charge variable speed supercharger system.

“In a main-drive transmission application we typically control variator torque by modulating hydraulic pressure to give exceptional functionality and driveability. Most likely there are other devices requiring hydraulics in the transmission, such as clutches, and so this is no problem. However, for a small auxiliary drive this is not the case and we need to strip out all the cost we can” explained Gaskell. “PitchSteer enables the use of a single, low cost mechanical actuator with very low power consumption. The actuator draws only 10W whilst changing ratio, and negligible actuation power is required to maintain a constant ratio.”

Torotrak has validated PitchSteer in one of its V-Charge supercharger units with a variator ratio range of 10, achieving a rapid rate of ratio change of just 300ms for a full sweep. In addition to minimising the actuation power, the wide ratio range capability allows the driven device to be reduced to a very low speed relative to the input whenever its function is not required, and therefore parasitic losses are greatly reduced.

Chris Gaskell – Design Engineer, Concepts & IP for Torotrak Group

Chris Gaskell – Design Engineer, Concepts & IP for
Torotrak Group

The second new technology, DriveDisconnect, provides the function of a disconnect clutch, further reducing parasitic losses by disconnecting the variator output when the driven device is not required. As an integral function of the variator, DriveDisconnect does not add weight or cost, markedly differentiating it from a typical electromagnetic clutch, which can add 3kg to the mass and around 30 Euros to the cost of an auxiliary drive, even in high volume automotive production.

“DriveDisconnect provides an extra function for free,” commented Gaskell. “Our development work for both technologies has proven that we can offer unique CVT functionality that addresses the needs of our customers, for example in the variable supercharging space.”

The same low power actuator can provide both the PitchSteer and DriveDisconnect functions. Torotrak believes DriveDisconnect could also be used in other applications, citing variable speed flywheel drives and main drive CVTs and IVTs as likely beneficiaries.

Torotrak Group shared exhibition facilities at the CTI Symposium, Berlin 2015 with Univance Corporation, which is productionising the discs and rollers that are the key traction components of full toroidal variator technology, as well as value-engineering complete variator modules. Univance hardware targeting off-highway main drive transmission applications was on display at the Symposium.