Lee Lo-Lohm Solenoid Valves Applied to Brake Innovation
Reducing emissions and improving energy efficiency continue to be high on the agenda for today’s engineers and machine builders and they certainly remain as hot topics in the automotive industry. However, whatever the type of vehicle or the energy used for propulsion the essential function of braking also 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.
A good example of an important innovation in braking technology is from Sussex based brake design specialists AirBack Ltd who have developed an innovative drag-free brake design which aims to significantly improve braking efficiency. Reliability is crucial to the success of the braking system and Lee Products supplied their 3-port HDI Solenoid Valve which has played a key role in the 100% reliability being achieved.
The revolutionary AirBack® system was launched in 2015 and many in the automotive industry were impressed by its concept and effectiveness on plain discs, which led to requests for a design that would work on all types of braking systems. AirBack responded with a new, world-first compact design that can be retro-fitted and since then the system has evolved into what the company claims, is an effective solution to efficient and clean braking.
Designed as an add-on system, AirBack reduces the friction between brake pads and discs without compromising the performance of the brakes and consequently improves the overall braking 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. There are 2 variations of the system; an electronically controlled version for road vehicle use, and an accelerator-linked option for motorsport use which has no electronic controls.
Both variations 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’s plug-in Lo-Lohm Latching 3-port HDI Solenoid Valve which combine the high flow capabilities of their Lo-Lohm HDI valve with the power savings of their Latching HDI valve. This 3-port Lo-Lohm latching design excels in applications like the AirBack brake system where high flow capacity, low power and miniature size and 100% reliability are critical. For example, after supplying only a momentary (10 ms minimum) voltage pulse, this magnetically latched solenoid valve will hold its flow state until follow-on momentary voltage pulse (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.
The AirBack system can be used in conjunction with any type of disc or calliper brake design with equal effect 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.
Trevor Mennie, the AirBack developer, who was recognised for his work in the field of dustless brakes by his nomination for the inaugural Queen Elizabeth Award for Engineering Design in 2013 said, “The performance, 100% reliability and small weight and size of Lee’s Magnetically Latching Solenoid Valve perfectly matched our design criteria and to be honest there was very little else available on the market that satisfied our requirements”. He continued, “Since we specified the Lee valve we have never looked back, Lee Products provide a high quality product supported by first class product support”.