ECO start/stop function energy management, function - GF54.10-P-1040CAM

MODEL 207.3/4 as of model year 2014 

The function "Engine start/stop energy management, function" is viewed from an energy management point-of-view. Information on the function "Engine timing start/stop function" is information in the description "Common rail diesel injection (CDI), function" (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
• On-board electrical system battery temperature (G1) T = 0 to 60°C
• A/C regulated

As the master control unit for the engine start/stop function, the CDI control unit (N3/9) (with diesel engine) or the ME-SFI control unit (N3/10) (with gasoline engine) checks various influencing factors and then enables the function accordingly.

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.

It is still possible to stop and start the engine in the conventional way.

Use of the additional battery (G1/7) with a capacity of 12 Ah prevents the dip in starting voltage which occurs when the engine is started (e.g. when the radio or ventilation system is in operation). The additional battery supplies the power for the active consumers while the on-board electrical system battery used for starting the engine is disconnected from the on-board electrical system. Active comfort functions are not switched off. Immediately after cold start of the engine, the CDI control unit or the ME-SFI control unit performs a system diagnosis and evaluates the functional capability of the engine start/stop function. In addition, the front SAM control unit with fuse and relay module (N10/1) checks that all components involved in isolating the on-board electrical system battery and connecting the additional battery are functioning correctly.

The additional battery is connected by means of actuation of the additional battery relay (K57/2) at the additional battery. The on-board electrical system battery is decoupled from the on-board electrical system by actuation of the decoupling relay (F32k1) in the front prefuse box (F32).

On model 207.3 with transmission 711, 716, both relays are mechanical relays. On model 207.3 with transmission 722 or 725 and on model 207.4, 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 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 rear SAM control unit with fuse and relay module (N10/2) reads in the data from the battery sensor (B95) via the on-board electrical system LIN (LIN B7), evaluates this data and sends information which describes the on-board electrical system status or the requirements with regard to the on-board electrical system, via the interior CAN (CAN B), front SAM control unit and chassis CAN 1 (CAN E1) to the CDI control unit or the ME-SFI control unit.

The following information is included in it:

• State of on-board electrical system battery
• Condition of additional battery
• Energy state of on-board electrical system
• 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, issues the stop enable and switches the engine off. The CDI control unit or the ME-SFI control unit then sends the "Drive train operational" signal to the rear SAM control unit via chassis CAN 1, the front SAM control unit and interior CAN. This prevents the energy management system from reducing or switching off consumers if the "Engine running" signal is not sent.

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 with the actuation of the accelerator pedal. During the starting procedure the on-board electrical system battery is isolated from the on-board electrical system. The active consumers are then supplied with power from 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 hot-start signal via a direct line and actuates the decoupling relay and the additional battery relay.

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. The energy requirement of the on-board electrical system is now covered by the additional battery alone. The on-board electrical system battery now supplies the energy required for the engine starting process.

As soon as the CDI control unit or the ME-SFI control unit detects an engine speed of n = 400 to 700 RPM, it terminates the starting procedure and sends the "Engine running" signal to the front SAM control unit via the chassis CAN and to the rear SAM control unit via the chassis CAN, front SAM control unit and interior CAN. 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 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, for example, the following systems:

• PRE-SAFE®
• Brake assist and adaptive cruise control systems
• Air conditioning
• Steering

As soon as the energy management is no longer able to ensure the stability of the on-board electrical system, the rear SAM control unit sends the "Start engine" request to the CDI control unit or to the ME-SFI [ME] control unit over the interior CAN, front SAM control unit and chassis CAN 1. The CDI control unit or the ME-SFI control unit then 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 engine start/stop function is deactivated.

On the basis of the data from the battery sensor, the rear SAM control unit calculates the required alternator specified voltage and sends it to the CDI control unit or to the ME-SFI control unit via the interior CAN, front SAM control unit and chassis CAN 1. This makes the CDI control unit or the ME-SFI control unit start the alternator regulation (alternator management). For this purpose, the CDI control unit or the ME-SFI control unit evaluates the operating rate of the alternator (G2) and requests the corresponding specified voltage. The alternator and the CDI control unit or the ME-SFI control unit communicate with each other via the drive train LIN (LIN C1). The CDI control unit or the ME-SFI control unit additionally sends information about the operating rate of the alternator to the rear SAM control unit via chassis CAN 1, front SAM control unit and interior CAN.

Detailed information about the alternator regulation can be found in the subfunction "engine ON energy management function".

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 at the additional battery in engine start/stop function mode is measured after every engine start.

Battery state recognition can be started using the diagnostic tester. The additional battery relay is no longer actuated under the following conditions:

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

To determine this, the additional battery voltage is compared against an internal value. A corresponding fault message is shown in the multifunction display (A1p13) of the IC (A1). The front SAM control unit transmits the data required for this to the instrument cluster 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 of the additional battery is too low (U > 12.5 V), 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 engine start is too great, an engine stop is suppressed for t = 5 min in order to recharge the additional battery. 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-2070-97EAB
	Overview of energy management system components		GF54.10-P-9990CAM