Brake-Pedal Transmitter Unit -Dimensions
Figure 013
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Brake-Pedal Transmitter Unit - Characteristics
Figure 014
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C. Selector Valve and Filter (Ref. Fig. 015) The selector valve is located in the hydraulics compartment. The selector valve is of the 3-way type and isolates the Normal braking system when:
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the solenoid is de-energized,
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the Normal braking is not selected, or
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the pedals are released.
An internal valve progressively opens the supply-to-delivery passage of
the selector valve.
A filter with a filtering capacity of 15 microns absolute is installed on
the delivery port.
The purpose of the filter is to protect the supply to the servovalves
downstream of the selector valve.
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Selector Valve and Filter
Figure 015
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D. Automatic Selector and Throttle Valve (Ref. Fig. 016, 017, 018) The brake automatic selector is located in the hydraulics compartment. The main function of the selector is to automatically supply during braking the Normal or Alternate braking systems depending on the hydraulic system available. The selector ensures the segregation of the two systems and preferential supply of the Normal system. When the pedals are released, the Yellow system positions the slide valve in the automatic selector. Consequently the Yellow pressure is available for the Alternate braking (D to E). When the brake selector valve delivers the Green pressure to A, the automatic selector:
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connects the Alternate system to the return of the Yellow reservoir (I to H),
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connects the Green pressure to the Normal system (A to B), as soon as P is more than or equal to 150 plus or minus 6 bars (2175 plus or minus 87 psi).
The inverse operation occurs when the Green pressure falls below 90 bars.
A throttle valve is installed on the Green supply port (A) of the
automatic selector.
It decreases the speed of movement of the main slide valve of the
selector when the brake selector valve is de-energized.
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Automatic Selector
Figure 016
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Automatic Selector - Schematic
Figure 017
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Throttle Valve
Figure 018
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E. Normal-Brake Pressure Transducers (Ref. Fig. 019) The brake pressure transducers are installed on the manifold of the Normal brake servovalve, one downstream of each servovalve. The integrated-logic transducer supplies a DC voltage between 1 and 5V for a pressure signal between 0 and 200 bars. The zero has been shifted to enable BITE testing.
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Pressure Transducer
Figure 019
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F. Normal Brake Servovalves There are four servovalves; one for each brake. (Ref. Fig. 020, 021, 022) There are also:
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two associated safety valves, with integrated downstream filter,
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two pressure transducers located downstream of the safety valve, - one filter on the supply line of the manifold. The brake servovalve supplies a pressure inversely proportional to the current which passes through the control coil used. The influence of the supply pressure on the pressure/current gain is negligible (unigain-type servovalve). The current moves a flapper located between two jets. Two coils are installed around the core which is mounted in the gap of a permanent magnet. The attraction of the core by the poles of the magnet is function of the current which passes through the coils. The movement of the flapper modifies the sections of the fluid passage at the jets. Consequently the pressure in the control chambers of the slide valve is modified. The differential action of the pressure moves a slide valve. This fills or drains the brake depending on whether the current decreases or increases. The slide valve is in a balanced position under the action of the pressure supplied on one of the opposite faces of the slide valve. With zero current in the coil, the pressure supplied is equal to the pressure supplied to the servovalve. If there is no supply pressure, the servovalve connects the brake to the reservoir return system.
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