Electro-pneumatic control apparatus for an electric/friction brake blending system

A brake blending control system for a vehicle having electric and friction brake apparatus, said control system comprising:

• (a) means for providing a fluid pressure brake command signal representing the desired degree of vehicle braking to be provided by said electric and friction brake apparatus;
• (b) said electric brake apparatus being operative responsive to said brake command signal;
• (c) means for providing a fluid pressure friction brake control signal comprising:
• (i) means for providing an electric feedback signal representing the effective brake effort produced by said electric brake apparatus in response to said brake command signal;
• (ii) first transducer means for converting said fluid pressure brake command signal to a corresponding electrical quantity;
• (iii) comparison means for providing an error signal in accordance with the difference between said electrical quantity representing said brake command signal and said feedback signal representing the effective electric brake effort;
• and
• (iv) second transducer means for converting said error signal to a corresponding fluid pressure signal to provide said friction brake control signal;
• and
• (d) a fluid pressure operated relay valve device having a first control port to which said friction brake control signal is connected, a second control port to which said brake command signal is connected, and a delivery port, said relay valve device being operative responsive to pressurization of said first or said second control port to provide fluid brake pressure via said delivery port to effect operation of said friction brake apparatus;
• and
• (e) valve means for normally cutting off said brake command signal from said second control port and for connecting said brake command signal to said second control port in response to a malfunction of said means providing said friction brake control signal.