A brake-through in electrohydraulics

Though intelligent systems and electronic precision are continuing to be demanded in the heavy-duty equipment arena, hydraulics continue to reign in power density. Electrical and mechanical brake systems cannot, at this time, compete due to their size and weight. And, while pneumatic brake systems can come close to the benefits obtained by full power hydraulic versions, because of their lower operating pressures, the accumulators are larger, which is often difficult to accommodate with vehicle space constraints.

Larger equipment in off-road markets such as construction, agricultural and mining have several benefits to gain from employing an electronic and hydraulic hybrid system (electrohydraulics or EH), building upon the existing hydraulic platform that has been established and enhanced throughout the years. “The full power hydraulic brake system uses the same operating fluid, reservoir and pump. There is no need to add an air compressor, air reservoir, dryer or other items specific to the needs of [a pneumatic] system,” explains Peter Backes, Senior Product Engineer, MICO, Inc.

“The fluid within a full power hydraulic brake system is virtually incompressible in comparison to air in a pneumatic brake system. This allows for very rapid changes in brake control by modulating pressure in the brakes,” Backes continues. The responsiveness of a hydraulic brake system is most apparent when executing control in anti-lock brake systems (ABS), traction control systems (TCS) and electronic stability control (ESC) events.

MICO, Inc. will be launching its MOBEUS^TM electrohydraulic braking system platform at MINExpo 2012 (Booth 7557) in Las Vegas, NV. MOBEUS^TM, which stands for Mobile Braking Electrohydraulic Utilization System, consists of several of MICO’s electronic and hydraulic products contained in a fully optimized system to deliver an integrated braking package that offers advanced operator control through ABS, Traction Control and ESC. The company’s aim is not to sell the change to ABS and EH braking. “The change in the industry is already happening,” says Len Walton, Director of Sales and Marketing for MICO. “Military vehicles are being driven by 18 year old soldiers who are used to ABS, TC and ESC on their personal vehicles at home.” In several off-road industries, the decline in skilled operators has made vehicle operation simplification essential, so drawing similarities in drivability from familiar passenger vehicle brake systems is a step in the right direction to accommodate new operators and keep safety and productivity benefits possible.

The theory for ABS has not changed in nearly 30 years, though its applications are continuing to diversify as heavy equipment operators expect the drivability and responsiveness of automotive passenger vehicles. In an ABS event, the goal is to prevent the wheel from locking up which can improve vehicle control during braking, and reduce stopping distance on slippery (split or low coefficient of friction) road surfaces by limiting wheel slip and minimizing lockup. Reducing wheel slip improves vehicle stability and steerability during braking. Traction control improves vehicle acceleration under low traction conditions by controlling excessive wheel spin. Stability control adds sophisticated sensors which detail the yaw rate, acceleration and other vehicle orientations.

The general theory of operation behind an electrohydraulic brake system has the electronic control unit (ECU) monitoring wheel speed and brake line pressures with sensors added to the machine. When wheel lock-up or wheel slip conditions exist, the ECU’s embedded software algorithms determine the current needed at the electrohydraulic control valves to improve the operator’s control of the vehicle. The traction control algorithm attempts to regain traction by braking the spinning wheels, and sometimes throttling back engine power through the vehicle communication network. System status outputs are provided to light ABS and low traction indicators for operator warning and to meet on-highway regulations (FMVSS 105 and ECE R13).