Regenerative and hydraulic brake mode, function - GF42.22-P-1001FLM
MODEL 212.095/098/298 as of model year 2014
Diagram of operating principle
Function requirements for regenerative and hydraulic brake mode, general
- Hybrid system "READY"
- Selector lever position "D"
- Vehicle speed > 8 km/h
Regenerative and hydraulic brake mode, general
The driver's braking request is recorded by the pedal angle sensor and sent to the regenerative braking system control unit. Via chassis CAN 1 (CAN E1), the regenerative braking system control unit continuously sends the value of the currently available regenerative braking torque, the requested regenerative braking torque and the implemented regenerative braking torque to the CDI control unit (N3/9) (on diesel engine) or ME-SFI control unit (N3/10) (on gasoline engine).
The regenerative braking system control unit divides the overall braking torque moment requested by the driver according to the driving condition into a regenerative (to be implemented by the drivetrain) part and a hydraulic (to be implemented over the wheel brake) braking torque moment.
As soon as a brake application drops below a speed of 1 0 km/h, a switchover takes place from regenerative braking to hydraulic braking. Regenerative braking is not possible at speeds lower than 3 km/h.
The three-phase AC voltage generated during regenerative braking by the electrical machine is converted by the power electronics control unit into high-voltage DC voltage and supplied to the high-voltage battery (A100g1).
Regenerative and hydraulic brake mode, function sequence
On the regenerative braking system control unit the brake pedal connection to the push rod of the BAS brake booster has free travel (3) integrated into it. This is used to display the regenerative braking system control unit's functionality. When in normal operation the driver's braking request is recorded by the pedal angle sensor using the pedal travel (1) and read in and processed by the regenerative braking system control unit. At the same time the brake pressure simulator valve generates a simulated pedal resistance each time the brakes are actuated. If regenerative braking is used, it increasingly reduces the free travel (3) between the brake pedal and push rod as the regenerative braking torque increases. The regenerative braking system is activated during the first brake actuation. While doing so, the brake pressure simulator is deactivated resulting in a somewhat longer pedal travel than in normal operation during the first brake actuation. Once the brake pedal has been completely released again, the regenerative braking system is activated again.
As a matter of principle, the brake pedal feeling on a regenerative braking system is perceived differently from that on a conventional brake system. In the event of an emergency braking, a fault in the hybrid system or an antilock brake system (ABS) activation, the braking torque is generated hydraulically only.
Regenerative braking is switched off for the ignition sequence, when:
- The requested regenerative braking torque is not provided correctly
or
- The hybrid system is malfunctioning.
The braking torque actually implemented is sent by the power electronics control unit via the hybrid CAN (CAN L) and chassis CAN 1 back to the regenerative braking system control unit. For the brake-power fraction to be realized hydraulically, the regenerative braking system control unit actuates the BAS solenoid valve to generate the brake pressure for the hydraulic brakes. The free travel (3) is not further reduced here.
Distribution of the brake pressure to the front axle and rear axle is specified by the installed brake pressure distribution system.
| Overview of system components for regenerative braking system | GF42.22-P-9999FLM |