FEATURE HYDRAULICS & PNEUMATICS
Improving braking
performance
(with reverse polarity) is applied to switch its flow direction. Aside from the momentary pulse, no power is consumed while maintaining each flow state, an important feature when considering range with electric vehicles.
When developing a new drag-free brake design which would significantly
improve braking efficiency, Sussex-based AirBack specified
3-port HDI Solenoid Valves from Lee Products. Here the company looks
into the design and explains how the valves helped towards the system achieving 100% reliability
E
ngineers and machine builders are well aware of the importance of
reducing emissions and improving energy efficiency, and this remains a hot topic in the automotive industry. However, whatever the type of vehicle or the energy used for propulsion, the essential function of braking remains crucial to overall automotive performance. Maximising braking efficiency, how best to retain and reuse energy generated from braking, are also important areas of focus for today’s automotive engineers. AirBack of Sussex has therefore
developed a drag-free brake design which aims to significantly improve braking efficiency. The system was launched in 2015, with the automotive industry impressed by its concept and effectiveness on plain discs. This then led to requests for a design that would work on all types of braking systems. So, in response to demands, the
company developed a design that can be retro-fitted. This has since evolved into what is described as an effective solution to efficient and clean braking.
IMPROVING PERFORMANCE Designed as an add-on system, AirBack reduces the friction between brake pads and discs, improving the overall braking
10 JUNE 2018 | DESIGN SOLUTIONS
The 3-port Lo-Lohm latching design is said to excel in applications like the AirBack brake system where high flow capacity, low power, miniature size and reliability are critical
performance. It operates as a retraction and pre-fill system which utilises positive and negative pressure and vacuum to deliver a minute gap (depending on the actual brake calliper design) between the brake and the disc. This is achieved by applying negative pressure to the brake line during acceleration and then supplying positive pressure when applying the brake. Two variations are available: an
electronically controlled version for road vehicle use; and an accelerator-linked option for motorsport use which has no electronic controls. Both use the principle of differential air pressure between the master cylinder (MC) and that of atmosphere to control and move the calliper pistons. The adjustable air pressure supply imbalance causes the brake fluid to either negatively or positively bring about the effect of brake retraction, or the prefill of the brake system, respectively. To ensure no cross contamination in the MC reservoir, a flexible diaphragm is used to separate the air supply and the brake fluid. The design incorporates miniature
compressors and Lee Products’ plug-in Lo-Lohm Latching 3-port HDI Solenoid Valve, which combines the high flow capabilities of the Lo-Lohm HDI valve with the power savings of the Latching HDI valve. According to the company, the 3-port Lo-Lohm latching design excels in applications like the AirBack brake system where high flow capacity, low power, miniature size and reliability are critical. For example, after supplying only a
momentary (10ms minimum) voltage pulse, the magnetically latched solenoid valve will hold its flow state until follow-on momentary voltage pulse
AN EFFECTIVE DESIGN AirBack is suitable for use with any type of disc or calliper brake design, and both designs are failsafe in use with power interruption or removal from mid-cycle, without compromising normal braking performance. System settings can be optimised for reduced brake pedal travel (safer) or less non- braking drag (economy). During accelerator use, brake drag is
removed by adding negative pressure to the MC. With the accelerator linked system, when the accelerator is released the compressor adds positive air pressure to the MC reservoir, pre-filling the fluid system ready for use. When brake actuation occurs the compressor switches off to ensure that the system does not affect any other brake control system during its use. The compressor otherwise continues to be operational because motorsport applications will require its continual use. With the electronically controlled system, when the accelerator is released, a positive pulse of high pressure air is added for a few tenths of a second (adjustable) from a small reservoir which causes the calliper pistons to return to their former position and be in firmer contact with their respective brake pad. This means that there are no piston gaps remaining and the brake pedal stroke is much reduced, providing a faster acting, safer, brake system. The AirBack system is both highly effective and adjustable without detriment to either brake effect or brake feel, as confirmed by extensive road tests. Furthermore, additional testing conducted at elevated temperatures has seen results which far exceeded expectations. The 3-port HDI Solenoid Valve has
played a key role in the system’s 100% reliability, the company explains.
Lee Products
www.leeproducts.co.uk
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