Patent GB-1170050-A (GB)
Title: Motor Vehicle Braking System
Inventor: MCKNIGHT JAMES
IPC: B60T13/10
Filed: 1968-07-16
Abstract: 1,170,050. Trailer air-braking systems. FORD MOTOR CO. Ltd. 16 July, 1968, No. 33739/68. Headings F2E and F2F. A braking system for a motor vehicle includes a dual hydraulic braking system having first and second hydraulic circuits 13, 14 for applying the vehicle brakes and an air-braking system for actuating service and auxiliary brakes on a trailer, the air-braking system comprising: (a) service and auxiliary air reservoirs 41, 43 respectively; (b) a compressor 36 for maintaining air pressure in both reservoirs; (c) a service air supply line 47 for connecting the service reservoir to the trailer service brakes; (d) a valve 48 in the service air supply line 47 arranged to be opened by fluid pressure in the first hydraulic circuit 13; (e) an auxiliary air supply line 49 for connecting the auxiliary reservoir 43 to auxiliary brakes on the trailer; (f) a first valve 52 in the auxiliary air supply line 49 arranged to be opened by fluid pressure in the second hydraulic circuit 14; and (g) an inverted relay valve 50 in the auxiliary air supply line 49 normally held closed by air pressure in the service reservoir 41, whereby air is supplied to the trailer auxiliary brakes in the event of failure in the service braking system on the vehicle or trailer. Operation.-Whenever the vehicle or tractor brakes are applied, valves 48 and 52 are opened by fluid pressure obtaining in the first and second hydraulic circuits 13 and 14 respectively. Because relay valve 50 is normally held closed by the air pressure in service reservoir 41 communicated by pipe 51, and this valveisinseries with valve 52 in line 49, air is normally supplied only along line 47 to the trailer service line connected at 34. If, however, there is a leak or a failure in the trailer service braking system either in the tractor or the trailer, the pressure in the service reservoir 41 falls below working pressure, whereupon valve 50 opens, permitting air to be supplied by the auxiliary reservoir 43 along line 49 to the trailer auxiliary line connected at 35. Preferably a by-pass circuit 55 around valve 50 is provided, including an inverted fluid reaction valve 54 connected to an accumulator 18. The accumulator 18 is provided in the supply line 25 for the first hydraulic circuit 13. Thus, if instead of the air supply 41, 47 failing, the first hydraulic circuit 13 fails, air is again supplied along line 49 to the trailer auxiliary line. Alternatively, the by-pass circuit 55 and valve 54 may be dispensed with. Instead, a by-pass circuit (not shown) may be provided around valve 48, and mould include an ordinary fluid reaction valve arranged to be opened by fluid pressure in the second hydraulic circuit 14. All the above arrangements rely upon there being no failure in the second hydraulic circuit 14. Preferably an emergency air supply line 45 connects the service reservoir 41 to an emergency brake (on the trailer) which is held off by air pressure in the line and is applied when pressure falls in this line. Preferably the hydraulic supply lines 25, 26 have a dual pressure gauge 31 connected to them, and a buzzer 32 rings if the pressure in either accumulator falls below a predetermined value. A load-apportioning valve 15 is connected in each circuit 13 and 14 between the front and rear brakes to control the relative braking effect applied to the front and rear wheels. Accumulators 22 and 23 may be provided for supplying pressurized fluid for actuating a parking brake.