Energy management for engine start/stop function - GF54.10-P-1040CE

MODEL 204.0/2 with CODE (B03) ECO start/stop function as of model year 2011 YoM 10 

MODEL 204.3 with CODE (B03) ECO start/stop function fuse box 

MODEL 204.9 as of 1.12.10 with CODE (B03) ECO start/stop function as of model year 2011 YoM 10 

The "energy management for engine start/stop function" subfunction is viewed from an energy management point-of-view. Information on the "engine timing Start-Stop function" subfunction is contained in the "Common-Rail Diesel Injection (CDI) function" description (with diesel engine) or "gasoline injection and ignition system with direct-injection function" (with gasoline engine).

Function requirements, general 

• Engine running and at operating temperature
• Engine hood closed
• One-time overspeeding of v = 15 km/h in forward travel
• System diagnosis completed
• Outside temperature T = -10 to 40 °C
• Battery temperature T = 0 to 60 °C
• A/C regulated

Energy management for engine start/stop, general 

For a stationary vehicle, the engine Start-Stop function switches the engine off automatically and starts it again, as soon as the driver wishes to drive off.

Switching of the engine during standstill periods of the vehicle reduces the fuel consumption and therefore the carbon dioxide emissions.

The master control unit for the engine start/stop function is the CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) that records and evaluates all influencing factors.

The conventional switching off and starting the engine with the transmitter key (A8/1) or via the KEYLESS-GO start-stop button (S2/3) (with code (889) Keyless-Go) continues to be possible.

Through the use of an additional battery (G1/7) with a capacity of 12 Ah the voltage dip perceived by vehicle occupants when the engine is started (e.g. during radio or ventilation operation) is prevented.

The additional battery then assumes the power supply for the active consumers in the process while the on-board electrical system battery (G1) is isolated from the on-board electrical system (at engine start). Active comfort functions are not switched off.

Immediately after the cold start of the engine the CDI control unit or the ME-SFI [ME] control unit runs a system diagnosis [SD] and evaluates the functional capability of the start/stop function. The front SAM control unit with fuse and relay module (N10/1) also checks the function of all affected components for isolating the on-board electrical system battery and connecting the additional battery.

The additional battery is activated by actuating the additional battery relay (K57/2).

The on-board electrical system battery is decoupled from the on-board electrical system by actuating the decoupling relay (F32k1). For model 204.0/2/3 with manual transmission both relays are mechanical relays. For model 204.9 and model 204.0/2/3 with automatic transmission both relays are electronic relays.

The engine start/stop function encompasses the following subfunctions:

• Function sequence for engine stop 
• Function sequence for engine start 
• Function sequence for a forced engine start 
• Determine function sequence of status of additional battery 
• Function sequence of charge additional battery 

Additional function requirement for engine stop 

• Stop enable issued by the CDI control unit or the ME-SFI [ME] control unit

Function sequence for engine stop 

As the master control unit for the engine start/stop function, the CDI control unit or the ME-SFI [ME] control unit checks the various influencing factors for the stop enable:

The on-board electrical system management provides information, which describes the on-board electrical system management status or the requirements for the on-board electrical system.

The following on-board electrical system management information is provided by the rear SAM control unit with fuse and relay module (N10/2):

• State of on-board electrical system battery
• Condition of additional battery
• On-board electrical system status
• Requirements for load-intensive consumers (e.g. A/C)

The CDI control unit or the ME-SFI [ME] control unit evaluates all the relevant data and then issues the stop enable. The engine is switched off as a result of this.

While the vehicle is at a standstill the brake pedal must remain pressed or the "Hold" function be active. The blower output is reduced when the automatic blower system of the A/C is active. In high ambient temperatures the system changes into air circulation mode depending on the specified temperature adjusted.

After an engine stop a maximum of three engine starts is permitted without exceeding the speed threshold of v = 8 km/h.

Function sequence for engine start 

The engine is started automatically when the accelerator pedal (A/T) or clutch pedal (manual transmission) is pressed.

During the starting procedure the on-board electrical system battery is isolated from the on-board electrical system. Active consumers are now powered through the additional battery.

This serves to prevent any voltage dip as perceived by vehicle occupants when starting the engine (e.g. during radio or ventilation operation).

The CDI control unit or the ME-SFI [ME] control unit evaluates all relevant influencing factors and then issues the start enable (hot start signal). The front SAM control unit reads in this warm-start signal over a direct line and actuates the decoupling relay in the front prefuse box (F32) and the additional battery relay on the additional battery.

The additional battery is switched through to the on-board electrical system. Shortly after this, the decoupling relay isolates the on-board electrical system battery from the on-board electrical system for the duration of the starting process.

Power is now supplied by the additional battery.

The on-board electrical system battery now supplies the energy required for the engine starting process.

As soon as the ME-SFI [ME] control unit or CDI control unit detects an engine rpm of n = 400 to 700 rpm, it stops the starting process and transmits a corresponding signal over the chassis CAN (CAN-E) to the front SAM control unit

The front SAM control unit then actuates the decoupling relay and the additional battery relay. The decoupling relay connects the on-board electrical system battery to the on-board electrical system. The additional battery relay then disconnects the additional battery from the on-board electrical system. The energy requirement of the on-board electrical system is now supplied again by the on-board electrical system battery.

Function sequence for a forced engine start 

To ensure that the on-board electrical system stability is also given during engine OFF, the CDI control unit or the ME-SFI [ME] control unit can also force the engine to start.

A forced engine start is also conducted if, as a consequence of load-intensive consumers, the on-board electrical system stability can no longer be assured.

Load-intensive consumers can be requested by the following systems:

• PRE-SAFE (with code (299) PRE-SAFE)
• Brake assist and adaptive cruise control systems
• Air conditioning
• Steering

As soon as the on-board electrical system management is no longer able to ensure on-board electrical system stability, the rear SAM control unit sends an engine start request over the interior CAN (CAN B), front SAM control unit and the chassis CAN to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit receives this and starts the engine. If, following this, the on-board electrical system stability can still not be assured, the engine is no longer switched off.

The Start-Stop function is switched off.

Illustration of power supply at engine start principle 

Illustration of power supply when engine running principle 

Determine function sequence of status of additional battery 

The front SAM control unit runs a battery state recognition immediately after the engine is started. This provides information on the availability of the additional battery's electrical output.

If the engine is switched off during the battery state recognition, the SAM control unit switches this off and discards the previous results. In addition to battery state recognition, the voltage of the additional battery in the start-stop function mode is tested after every engine start.

The battery state recognition can be started by means of a diagnosis tester.

The additional battery relay is no longer actuated under the following conditions:

• Deep discharge of additional battery
• Internal short circuit of additional battery
• Short circuit of positive line in additional battery

To determine this, the additional battery voltage is compared against an internal value.

A corresponding fault message is shown on the travel distance display (A1p7) (model 204.0/2/3/9 (except 204.077/277/377) without code (442) Comfort multifunction steering wheel) or in multifunction display (A1p13) (with code (442) Comfort multifunction steering wheel, model 204.077/277/377) of the instrument cluster (A1).

The front SAM control unit transmits the data required for this to the IC via the interior CAN.

Function sequence of charge additional battery 

The charge strategy for the additional battery must take two requirements into consideration:

• The additional battery must be sufficiently charged.
• The number of additional battery relay actuations and the related load on the additional battery must be keep to a minimum.

If the open circuit voltage (U > 12.5 V) of the additional battery is too low, then the alternator's output limitation (alternator management) is deactivated so that the additional battery can be charged.

If the voltage dip (U < 11 V) at the engine start is too large, then the engine is stopped for t = 5 minutes to enable the additional battery to be recharged.

The additional battery is only switched-in, when the alternator's output limitation is not active and when the on-board electrical system voltage (U > 13 V) is high enough.

It is cleared again when the alternator's power limit is active or the on-board electrical system is severely overloaded.

	Electrical function schematic for energy management for engine start/stop		PE54.10-P-2070-97FAA
	Overview of system components for energy management		GF54.10-P-9990CE