INTRODUCTION TO THE HMMWV - OD1615 - LESSON 3/TASK 1
hydraulic brake fluid used in today's modern vehicles have some important
properties; the most important are discussed in this paragraph. The fluid
must remain a liquid during all operating temperatures. The boiling point
of the fluid must, therefore, be well above the temperatures encountered
during the most severe brake applications on the hottest day. It must also
maintain an even viscosity at extreme cold temperatures.
The brake fluid
must be able to absorb and hold moisture and also act as a lubricant. There
are several types of hydraulic brake fluids in use today.
After 40 years of research and development, a brake fluid that was
acceptable under extreme operating conditions was developed.
This fluid
achieved low water pickup and good corrosion protection.
The fluid also
provides good lubrication qualities and rubber compatibility.
Silicone
brake fluid has been used in all military vehicles since the end of 1982.
This is the only brake fluid used in the HMMWV.
(4) Combination Valve. The combination valve consists of a one-piece
housing containing a rear brake proportioning valve section and a
differential valve and switch. The proportioning section provides balanced
front-to-rear braking action.
The pressure differential valve sections
activate the brake warning lamp, should a pressure loss in the front or rear
hydraulic system occur. The combination valve is just that--a combination
of two different valves often found in brake systems. These two valves are
the proportioning valve and the limiting valve.
The operational
characteristics of these two valves will be discussed in the paragraphs that
follow.
(5) Hydro-Boost.
The hydro-boost is a hydraulically operated power
assist mechanism used to increase fluid pressure in the brake system while
at the same time decreasing the pedal effort.
The hydro-boost is also a
component of the steering system. This unit does the same job as a vacuum
booster and is connected in the brake system in much the same way.
The
major difference between the two is that the hydro-boost unit uses
pressurized power steering fluid to obtain its assist power.
The vacuum
booster depends on manifold vacuum and atmospheric pressure for its assist
power. The unit's smaller size has made it
33
Previous Page
