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Dayco's James Miller stands next to a Ford F-150 equipped with the supplier's Activac system, shown under hood in blue. (Dayco photo)

Venturi effect powers Dayco's new brake-assist system

A unique twist on a basics physics principle provides a fuel efficiency boost to more than 188,000 full-size pickup trucks fitted with the innovative brake-assist technology, known as Activac, with new applications coming in MY2018.

Engineers at Dayco Products harnessed the Venturi effect to create an engineered system that evacuates air from a vehicle's brake boost canister to provide brake assist without any compromise to fuel economy, according to James Miller, the company's Business Unit Director.

The Activac system debuted on 2017MY Ford F-150s powered by the second-generation 3.5-L EcoBoost V6. The engine's induction air flow creates the required pressure differential across the venturi, a key component within the Activac system.

The 1.82 lb (0.826 kg) vacuum-generation system, including hoses, replaced a 2.27 lb (1.03 kg) cam-driven mechanical pump. “The mechanical pump runs constantly, so it was pulling power from the engine all the time,” Miller said, noting the pump’s 0.3% fuel economy penalty. Dayco’s product is also lighter than the 6.3 lb (2.86 kg) electric pump that pre-dated the F-150’s mechanical pump for brake assist.

The Activac has 13 U.S. granted and pending patents, mostly relating to specific parts within the system. It earned Dayco a 2017 PACE (Premier Automotive Suppliers’ Contribution to Excellence) Award.

Among the system's key components is a 4.96 in (126 mm)-long injection molded thermoplastic part that creates and amplifies the Venturi effect, named after Italian physicist Giovanni Venturi (1746-1822). “The typical venturi is a converging cone, circular throat, and a diverging cone,” said Miller. The basic design increases the speed of a fluid’s flow, while decreasing the air pressure at the point of constriction.

Ford opted to replace the previous cam-driven mechanical pump because "as a vacuum source, a large, thermally efficient aspirator with a shut-off valve was lighter, more fuel efficient, and less expensive," explained Ross Pursifull, Research Specialist in Ford's powertrain controls research & advanced engineering group.

To develop Dayco’s Venturi component, three mechanical engineers, a designer and a testing technician worked with team leader Miller. The team ran thousands of computation fluid dynamic (CFD) iterations and evaluated hundreds of different wall and throat profiles.

The component’s throat geometry is unique. “It’s an ellipse, not a circle,” explained Miller. “We tried all sorts of different things. We even did a throat profile that looks like a daisy,” he quipped. “That didn’t work so well.”

Once the ellipse proved an effective design, the fine-tuning began. “When we saw that an ellipse of a certain height and width worked well, we then went beyond that width and height to see if it got worse or improved,” he noted. “But if you get improvement, you still haven’t gone far enough.”

Striking a win with the Venturi part’s design was only a partial solution as other system components received ample attention, including the gate valves. Miller noted that a tight tolerance is desirable between the gate and the housing to prevent air leak when the gate is closed, but it can't be so overly tight that it’s difficult to move.

The solution was a fluorosilicone spring between the gate plates. The spring keeps the normal force low and consistent, keeps the size of the solenoid small, and maintains a tight fit when the gate is closed. During brake-assist scenarios, boosted air pressure passes through a tiny hole to further expand the fluorosilicone spring and prevent boosted air from leaking.

Activac’s two noise attenuators address the hissing sound that the Venturi part causes. “The challenge was to come up with noise attenuation that would not restrict the flow of air,” Miller said. A stainless steel mesh, packaged within the Venturi assembly, effectively serves as a noise muffler.

The re-launch of the company’s advanced engineering group in 2011 paved the way for the Activac’s design and development.

Although specific vehicle models are not being named at this time, the Activac product will gain new applications in North America for MY2018. The system is produced and assembled at Dayco's Springdale, AR, plant.

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