German patent application No. 43 37 133 discloses a hydraulic automotive vehicle brake system with wheel slip control which is equipped with additional non-return valves between the primary and secondary circuits to let the air in the secondary circuit escape to the primary circuit during bleeding of the brake system. The additional arrangement of non-return valves necessitates special structural modifications to the brake system which automatically increase manufacturing costs.
Generic EP patent 0 543 187 describes a method of repeated vacuum charging of the primary circuit of an anti-lock automotive vehicle brake system after the brake fluid has been removed from the primary circuit for the purpose of installation into an automotive vehicle. To this end, the primary circuit includes a filter element downstream of a damping chamber which is adapted to the surface stress of the brake fluid so that the brake fluid under vacuum cannot escape from the damping chamber.
Further, European patent application No. 275 351 discloses an undersaturated brake fluid which has only a low solubility of gases and which exhibits a certain ability to take up the residual air in the brake system under vacuum.
An object of the present invention is to simplify a hydraulic automotive vehicle brake system of the above-mentioned type as regards the bubble-free filling process to such an effect that the design necessary for the hydraulic automotive vehicle brake system is maintained, and the need for additional structural modifications for the purpose of bleeding and bubble-free filling of the secondary circuit of the brake system is eliminated. Also, it is desirable to absorb the air disposed in the secondary circuit in the brake fluid in a fashion as good as possible.