E147 — Inverted Inlet Valve & Check-Valve-Free BBW

Since the introduction of ABS series production in 1978, brake pressure has been finely regulated during ABS control via PWM-controlled inlet valves (pulse width modulation). Check valves in parallel with the inlet valves ensure that no unintended excess pressure remains trapped in the wheel brake if supply pressure falls below wheel brake pressure and the power supply fails.

Furthermore, conventional check-valve architectures constrain pressure control to one direction: if the supply pressure drops — e.g., to service one wheel at low pressure — the check valve will automatically equalize all other wheel brakes downward. Maintaining asymmetric pressures during a supply-pressure decrease is impossible with check valves.

This solution ideally requires pressure-balanced valves that are resistant to closing under flow forces. Standard inlet valves can also be used, provided that pressure build-up dynamics are limited — either via passive throttling elements or by software-based volume flow limitation (e.g., limiting the drive motor speed of the pressure supply). The trade-off is that PWM pressure control during pressure build-up is eliminated; instead, pressure is regulated purely via volume control through the plunger, while PWM remains available during pressure reduction.

The 3 invention complexes of E147 cover the inverted-valve device architecture, a dual-circuit bypass-valve variant, and the fault-tolerant check-valve-free control method.