Deceleration mode, function - GF08.30-P-2004FLM

ENGINE 276.952 in MODEL 212.095 as of model year 2014 

ENGINE 651.924 in MODEL 212.098/298 as of model year 2014 

The subfunction "decel mode function" is considered and described from the point of view of the hybrid system. We will not go into more detail here about internal signals and function sequences of the internal combustion engine. This is described in the following document:

• Deceleration fuel shutoff, function 

• Function requirements for deceleration mode - general points 
• Hybrid drive "READY" (green or yellow)
• Accelerator pedal not operated
• Service brakes not operated
• Vehicle rolling
• Gear range "D"

Deceleration mode - general points 

If the brake and accelerator pedal is not actuated for a rolling vehicle, then:

• Kinetic energy is taken up over the electrical machine (A79/1) and converted into electrical energy (regenerative braking) for a low charge level of the high-voltage battery (A100g1)
• A deceleration fuel shutoff of the internal combustion engine can also take place

For a slightly actuated accelerator pedal, the electrical machine supports the drive for an adequately high charge level of the high-voltage battery in order to counteract the falling vehicle speed.

Precise information about deceleration fuel shutoff of the internal combustion engine is described in the following document:

• Deceleration fuel shutoff, function 

If the brake pedal is actuated regenerative braking occurs. Precise information is described in the follow document:

• Recuperative braking, function 

The CDI control unit (N3/9) (for a diesel engine) or ME-SFI [ME] control unit (N3/10) (for a gasoline engine) reads in the following signals in decel mode:

• Accelerator pedal sensor (B37), accelerator pedal position
• Fully integrated transmission control unit (Y3/8n4) via the drive train CAN (CAN C)
• Gear range status
• Transmission oil temperature
• Status of the electric transmission oil pump (M42)
• Regenerative braking system control unit (N30/6), via chassis CAN 1 (CAN E1)
• Wheel speed
• Service brake status
• Battery management system control unit (N82/2) via hybrid CAN (CAN L)
• Voltage of high-voltage battery
• Temperature of high-voltage battery
• Power electronics control unit (N129/1) via hybrid CAN
• Status of electrical machine
• Torque of electrical machine
• Rotational speed of electrical machine

Function sequence for deceleration mode 

The CDI control unit or the ME-SFI [ME] control unit calculates a nominal deceleration torque dependent on the charge level of the high-voltage battery and the selected transmission mode which the CDI control unit or the ME-SFI [ME] control unit implements with deceleration fuel shutoff and / or deceleration recuperation.

Sailing mode without actuating the accelerator pedal 

If the brake and accelerator pedal are not actuated for a rolling vehicle and recuperation can take place, the internal combustion engine is disconnected from the engine in the transmission mode Economy (E) up to a speed < 160 km/h through opening the wet clutch of the drive and switched off. If it is not possible for recuperation to take then the deceleration fuel shutoff of the internal combustion engine can also be activated.

Deceleration recuperation 

Kinetic energy is taken up over the electrical machine and converted into electrical energy (regenerative braking) for a low charge level of the high-voltage battery. To do this the CDI control unit or the ME-SFI [ME] control unit requests a generative torque from the power electronics control unit via the hybrid CAN. This actuates according to the request from the electrical machine. Regenerative actuation of electrical machines and generates an AC voltage. This is converted by the power electronics control unit into a direct voltage and fed to the high-voltage battery. In decel mode > 160 km/h or in transmission mode Sport (S) or manual (M) the wet clutch remains closed and the internal combustion engine goes over into deceleration fuel shutoff and therefore generates a deceleration torque. The electrical machine supports this deceleration torque if necessary by a generative torque. In deceleration mode and active deceleration fuel shutoff the internal combustion engine generates a boost torque which can be greater together with the recuperative boost torque than the calculated specified boost torque. In this case the deceleration fuel shutoff is not activated and the internal combustion engine generates a minimum actuatable torque. This concept ensures that the drive always remains the same for the driver as much as possible, with and without deceleration fuel shutoff.

The decel mode with deceleration fuel shutoff is more effective from an energy usage point of view. At a low charge level for the high-voltage battery and a low nominal deceleration torque is the higher deceleration recuperation with deceleration fuel shutoff is actually more meaningful.