| 摘要 |
PURPOSE:To simplify the constitution of the device in the caption by detecting the operating condition on spring brake systems as a parking brake through utilization of pressure in the chamber thereof so as to make an auxiliary brake device for operation operable only at the time of the secure operation of the spring brakes. CONSTITUTION:When a spring brake controlling valve 9 is set in the operating position air in the brake chambers of spring brake systems 11 is exhausted vie a relay valve 10, so as to operate a rear brake 8. In this case, there is provided a brake lock relay valve 12 having a volume variable pilot chamber 14 connected to the brake chambers. The relay valve 12 is constituted in such a way as to connect a feed port 20 to a control port 22 when pressure in the pilot chamber 14 is lower time a predetermined value, while to open the port 22 in the atmosphere and close the port 20 when it is higher than the predetermined value. In addition, a reducing valve 26 is provided on the upstream side from the relay valve 12, while a brake lock controlling valve 25 is provided on the downstream side therefrom.
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