Title: Dual power brake booster

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Abstract: A vehicle brake booster and master cylinder assembly has a vacuum suspended booster section which is controlled by movement of the vehicle brake pedal. A hydraulic booster section is in series with the vacuum suspended booster section, and a master cylinder unit is in series with the hydraulic booster section. The assembly is so arranged that in normal operation the vehicle operator obtains booster brake actuating pressures by operation of the vacuum suspended booster which acts through the hydraulic booster mechanism without operating the hydraulic booster. When greater brake actuating pressures are required, as indicated by increased brake pedal force exerted by the operator, the vacuum booster reaches its limit or run-out condition and the hydraulic booster is operated so as to continue the increase in master cylinder output pressure. If still further master cylinder output pressure is required when the hydraulic booster has reached its run-out condition, the master cylinder is actuated manually through mechanical force transmitting elements which are parts of the booster sections. The vacuum suspended booster section is connected to the vehicle engine intake manifold as a vacuum source, and the hydraulic booster section is connected in the hydraulic power steering gear system so that hydraulic pressure for its operation is generated by the power steering gear pump. The assembly is so interconnected that the master cylinder can be operated manually when there is no or insufficient power pressure to operate either booster section. It may also be operated by actuating the vacuum suspended booster section, and, when no hydraulic pressure is available to the hydraulic booster section, this operation may be followed by manual actuation. It may be operated by initially actuating the hydraulic booster section when there is no vacuum available for initially operating the vacuum suspended booster section, followed by manual actuation as needed. In one embodiment the assembly utilizes a single hydraulic fluid for the hydraulic booster section and for the master cylinder and brake apply circuitry. In another embodiment the hydraulic booster section is operated by a separate fluid circuit which is fluidly independent of the master cylinder and brake apply pressure circuitry.


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