How It Works: Notes
Active Steering can generate faster wheel-angle rates (wheels move faster in response to the steering wheel) than a conventional hydraulically power-assisted rack-and-pinion steering systems. The power available in the hydraulic system must be correspondingly higher in order to obtain these faster wheel-angle rates. A conventional vane-cell pump of adequate size and capacity would result in unacceptable power losses. Fuel consumption, too, would be increased to an unnecessary extent. This situation can be alleviated with the aid of a variable-output power-steering pump. The ECO valve in the power-steering pump regulates the volume flow in accordance with demand and reduces the static pressure in the hydraulic system.
The ECO valve therefore affects the power consumption of the power-steering pump. The fuel consumption and carbon dioxide emissions (CO2) for the vehicle's engine are reduced.
When the ECO valve closes, the static pressure in the hydraulic system decreases. The hydraulic fluid delivered by the pump returns through the open pressure-control valve in the bypass to the expansion tank. This means that the power-steering pump does not have to operate against the hydraulic resistance in the hydraulic system (cooler of the power-steering pump, hydraulic hoses).
The power-steering pump needs less power. When the ECO valve opens, the pressure in the hydraulic system increases. The pressure-control valve closes the return to the expansion tank in the bypass. The pressure limiting valve limits system pressure to 135 bar.