| 摘要 |
In a vacuum-operated brake booster and tandem master cylinder assembly, a jump (increase) of transmission ratio is achieved in the event of failure of the booster in that only a part of the push-rod piston (25) which has a smaller cross-sectional area is effective. For this purpose, the push-rod piston (25) is provided with a stem (26) which is coupled to the output force push-rod (12) of the booster and over which a sleeve (27) is slidable which controls the passage of hydraulic fluid through a duct (36, 36') provided in said stem (26) and which is, to this end, coupled to the control valve housing (7, 7') of the booster through a cap (21). In the event of failure of the booster, only the push-rod piston (25) with its stem (26) will shift, whereas the sleeve (27) will remain in its initial position, as a result whereof the passage of hydraulic fluid through the duct (36, 36') is opened up, which latter duct (36, 36') now links an annular chamber (28) positioned behind the shoulder (29) of the push-rod piston (25) to the pressure chamber (40) positioned before the push-rod piston (25), so that only a reduced cross-sectional area will be effective. Simultaneously the recuperation part (31) is closed by an annular valve member (32). <IMAGE> |
