Braking system with selective braking backup system

A vehicle, comprising:

• a plurality of wheels;
• and
• a brake system, comprising:
• a primary braking system configured to apply braking energy to the wheels;
• a backup braking system comprising a master cylinder configured to supply braking energy to one or more of the wheels;
• a parking brake system;
• and
• a braking system controller configured to select a mode of backup braking based on a functional state of the primary braking system;
• wherein the master cylinder supplies the braking energy to wheels of a single axle of the vehicle and only the parking brake system applies braking energy to wheels of a single axle of the vehicle that differs from the single axle to which the master cylinder supplies braking energy in a first mode of backup braking, and the master cylinder supplies the braking energy to all of the wheels in a second mode of backup braking;
• and
• wherein brake lines configured to supply braking energy via the primary and backup braking systems have a diagonal split configuration.

A method of braking a vehicle, the method comprising:

• determining an operational state of a primary braking system of the vehicle;
• selecting a first mode of backup braking when the primary braking system is non-functional or selecting a second mode of backup braking when the primary braking system is partially functional;
• and
• when the first mode of backup braking has been selected, commanding a backup braking system to supply braking energy to all wheels of the vehicle using a master cylinder;
• and
• when the second mode of backup braking has been selected, commanding the backup braking system to supply braking energy to wheels of a single axle of the vehicle using the master cylinder and commanding a parking brake system to apply braking energy to wheels of a single axle of the vehicle that differs from the single axle to which the master cylinder supplies braking energy in an amount proportional to an amount of brake pedal travel, wherein in the second mode of backup braking, only the parking brake system provides braking energy to the wheels of the single axle of the vehicle that differs from the single axle to which the master cylinder supplies braking energy.