use of its increased performance, recuperation ability, increased comfort and its compact shape, our MK C1 can also be used in hybrid and electric vehicles without any modifications, thus offering the ideal basis for vehicle platforms that contain these various drive concepts. At the same time, the reduced weight due to the integration, as well as the need-based energy consumption, improves our CO2 balance sheet,” said Frank Jourdan, Head of the Business Unit Electronic Brake Systems in the Continental Chassis & Safety Division. The new braking unit is already in development for series production. The start of production (SOP) is planned for 2015.
Fast actuation without a pressure-accumulator
Instead of the vacuum brake booster commonly used today, the MK C1 uses a highly dynamic electric motor that drives a cylinder piston in a linear way, thus combining the functioning of the brake booster during driver braking with the active pressure modulation of a slip control system. When pressure is actively being built-up, as within a normal braking process, only the brake fluid already in the cylinder needs to be pressurized. In this process, the braking pressure builds up much faster – a decisive advantage that could also be seen during trials at the Continental testing site in Frankfurt, Germany. During a two-year preliminary development process, among other tests, one vehicle type was equipped with MK C1 and another with a conventional braking system, and both were tested. In comparison to the conventionally equipped vehicle, the test vehicle fitted with the new MK C1 showed a significantly shorter braking distance during electronically initiated emergency braking.
No vacuum required
In addition to the actuation, the compact system also includes the electronic control unit (ECU) and the braking pressure modulator, which are normally part of a separate slip control system. Since the MK C1 does not require a vacuum brake booster, the vacuum pump required in many vehicles today can be eliminated.
In addition to vehicles with diesel and electric drives, vacuum pumps can now also be used for modern gasoline engines, where minimized throttling in the intake system means that sufficient vacuum is not available. When the driver steps on the brake pedal, the MK C1 system utilizes pressure, travel and speed measurement to monitor the braking force required by the driver. This decelerating requirement is then performed by the electric drive without any implications to the brake pedal. The pedal feel is created by a spring/damper unit that is also integrated into the actuation module. The characteristics of the brake pedal in terms of its deceleration allocation can also be individually adapted to the vehicle. Furthermore, this allocation can be modified during operations, according to the driving situation (e.g. emergency braking) or the operating mode (e.g. sport).
In contrast to a purely electro-mechanical braking system, this system has a hydraulic fallback solution that allows the driver to bring the vehicle to a stop with moderate pedal force even in the event of a complete system failure.
An especially efficient use of energy
Since the modulation is integrated into the system, only that pressure needed for the individual wheels is built up in each case. This saves energy compared to systems with accumulators: if you reduce the pressure in a hydraulic accumulator by 5 percent, the pump must first collect the 95 percent filling pressure in the accumulator before it can be filled. This is not the case for electro-hydraulic actuation. If the MK C1 only needs 5 percent of the possible braking pressure, the braking cylinder delivers exactly this level and no more. This means that “power on demand” now exists for the braking system, too. Another way of avoiding energy losses is utilizing the pedal simulator. “Zero drag” wheel brake calipers reduce the losses caused by friction on the brake disks if the brake is not actuated. The use of these calipers with conventional braking actuation, however, leads to a tangible decline in response time and pedal travel for the driver. With the MK C1, the driver always feels the same force-path characteristics in the pedal, while the braking pressure modulator balances out the various operating conditions in the wheel brakes.
Braking effectively but quietly is a requirement for driving electric vehicles
The elimination of the vacuum pump and the hydraulic ESC multi-piston pump also eliminates the main noise sources in the electronic braking system. This allows for almost soundless braking, which provides a significant gain in comfort, especially for hybrid and electric vehicles.