INTRODUCTION
Vehicles today have two separate brake systems. One is the service brake system and the other is the parking brake system. The service brake system is used to slow or stop a vehicle during normal operation. The parking brake system is usually cable operated and used to hold the vehicle stationary while parked.
Experience has shown that some vehicle applications require more brake holding capacity than provided by properly maintained parking brakes. The MICO 691 Brake Lock System uses the vehicle service brakes to supplement the parking brake. The 691 System provides pressure to the service brake system in the same manner as when the vehicle operator presses on the brake pedal.
The 691 also provides external inputs which can activate the system without direct operator interjection.
The 691 Brake Lock System consists of:
The Control Module and User Interface
(Figure 1)
The control module controls operation of the system through the user interface or remote activation. The user interface incorporates a manually activated switch, audible alarm, and "locked" lamp.
Control Module
User Interface
FIGURE 1
The Power Unit (Figure 2)
The power unit uses a 12 volt DC pump to produce pressure in the vehicle service brake system to lock the brakes. The pump reverses flow to release locking pressure.
Two pressure switches are located on the power unit. The pressure switches sense the pressure that the power unit is producing. The high pressure switch starts and stops the pump while pressurizing the sys- tem. The low pressure switch starts and stops the pump while releasing pressure from the system. Although the power unit contains a built in fluid reservoir, a remote reservoir is available as an option for special applications. Refer to 691 Accessories chart on page 19.
FIGURE 2
The Actuator (Figure 3)
The actuator is a mechanical device that links the hydraulics of the 691 System to the vehicle service brake system. The actuator separates the 691 System fluid from the vehicle service brake system. Various actuators are available for use in different types of service brake systems.
FIGURE 3
PRINCIPLE OF OPERATION
1.When the 691 System is activated, the control module starts the power unit pumping fluid into the actuator(s). As the actuator(s) become pressurized they isolate the vehicle master cylinder and pressurize the service brakes.
When lock pressure is reached, the
While the pump is stopped, locking pressure is held in the brake system. If locking pressure drops, the high pressure switch signals for the power unit to turn "on" and restore locking pressure.
2.When the 691 System is deactivated, the pump reverses and releases pressure. The actuator releases pressure from the brakes and opens the ports to the vehicle master cylinder. When locked pressure returns to zero psi a signal from the
NOTE
Brake System fluid and 691 System fluid always remain isolated from one another.
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