1991-09-01

Hydraulic Brake Control System for Off-Highway Vehicles 911834

In February of 1987, Dresser introduced a pair of new mechanical drive, off-highway trucks designed to operate in the 35 to 60 ton, rear-dump, classes. These trucks, designated 140M and 210M, replaced three previous models while covering the same payload range. One distinctive feature of these new vehicles was their hydraulic system and in particular the brake control portion of this system.
This new hydraulic brake control system can be described as a closed-center arrangement using a pressure-compensated, variable displacement pump as an energy source with accumulator-based energy reserves for independent and redundant circuits. In the basic version, a pair of pressure regulating valves are used to control system pressure at the brakes. These valves can be actuated in
tandem by a treadle (foot pedal) or separately by hydraulic pilot pressure. A single, filtered hydraulic fluid is used throughout the system and is stored in a single reservoir vented to atmosphere.
The basic system is capable of accommodating multiple-axle (i.e. more than two) arrangements but was originally applied to a two-axle vehicle using dry, disc-type (caliper and rotor) brakes on all wheels. In February of 1990, the Model 140M and 210M trucks were revised to offer rear axle oil-cooled brakes as an option. The brake control system was subsequently modified to provide for this change primarily by the use of an additional pressure regulating valve and redundant circuitry.
Both the original and latest versions of this system are characterized by their use of a unique emergency brake control system. Through the use of logic-type control valves, a loss of hydraulic pressure in one circuit is used to force the remaining high pressure circuits into actuating the brakes. This paper will describe the arrangement and operation of this hydraulic brake control system and its function as an integral part of the overall vehicle hydraulic system.

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