Working speed control, function

W07.16-1144-79

General

The electronic working speed control takes place as soon as a power take-off is switched in. To do this up to three power take-offs can be parameterized differently according to the vehicle equipment. This means that for every power take-off difference control specifications can be established according to the area of use of the vehicle and according to how the parameters for the power take-off functions are set in the SCA (SCA) control unit (A7) or in the parameterizable special module (PSM) control unit (A22). Along with a range of other parameters it is possible, for example, to set the entry requirements such as "parking brake tightened" or "transmission in neutral", or the engine speed range (min. engine speed, max. engine speed) as well as a torque limitation. It is furthermore possible to set the working speed during operation of a power take-off over the accelerator pedal or the keys on the multifunction steering wheel individually to a rotational speed between 550 rpm and 750 rpm or to raise it over the idle speed switch (S900) to a parameterizable value.

 The working speed is only regulated if the appropriate power take-off is fully engaged.

Control of the working speed

Upon switching on of a power take-off its parameters for working speed control are transmitted by the SCA (SCA) control unit (A7) and the parameterizable special module (PSM) control unit (A22) via the CAN data bus system to the drive control (CPC) control unit (A3). The drive control (CPC) control unit (A3) passes on the parameter via the drive train CAN (CAN 4) to the engine management (MCM) control unit (A4) whereby it initially takes account of the parameters set in the parameterizable special module (PSM) control unit (A22) since these are super-imposed over the parameters set in the SCA (SCA) control unit (A7). E3YE3ZThis means: for vehicles with code (PSM, body and trailer CAN ISO 11992) and for vehicles with code (PSM, body CAN ISO 11898 instead of 11992) only the parameters in the parameterizable special module (PSM) control unit (A22) are taken into account, independently of which parameters are set in the SCA (SCA) control unit (A7).

A4Y608Y613Upon receipt of the appropriate information and while taking account of the current operating condition of the engine, the parameterizable special module (PSM) control unit () computes the now required actuation begin of the fuel injectors as well as the necessary period of actuation (injection quantity) and ensures that the fuel is injected at the correct point in time and in the correct quantities into the respective combustion chamber through appropriate actuation of the quantity control valve () and the fuel injectors for cylinders 1 to 6 ( to ). Through appropriate actuation of the quantity control valve (Y643) one ensures that an adequate amount of fuel is available at the fuel system high pressure pump. The pressure regulating valve (Y634) is actuated in such a way that the pressure in the rail is about 900 bar. This ensures smooth engine running.

The injection quantity is constantly adjusted during operation of the power take-off - e.g. if the load condition of the engine changes or a higher fuel requirement exists (due to a low outside temperature). To calculate the injection quantity, the engine management (MCM) control unit (A4) mainly takes account of the following input factors:

 Engine speed

 Coolant temperature

 Fuel temperature

 Load request (specified torque)

Smoke limitation, smooth running control and altitude correction in the engine management (MCM) control unit (A4) can also influence the injection quantity (period of actuation) as well as the start of actuation for the fuel injectors.

Smoke limit

The fuel quantity is limited via the smoke limitation characteristics so that virtually no output of smoke occurs.

Smooth running control

The smooth running control compensates for all of the differences in injection quantity in the individual fuel injectors. Development of torque on the various cylinders can differ due to tolerances and wear on the individual fuel injectors. This leads to irregular running of the engine, that is the rotational speed of the crankshaft is slightly faster and slower. One particularly feels this when idling. The smooth running control can respond to rough running because it actuates every injection nozzle individually. It balances out the rotational speed fluctuations through slightly different injection quantities for the individual cylinder until all cylinders develop the same torque.

Altitude correction

The altitude correction is primarily designed so that the limits established for the air/fuel ratio λ (lambda) are not exceeded or gone below. To do this, the exhaust gas recirculation rate (AGR rate), the actuation begin as well as the actuation period (injection quantity) for fuel injectors for cylinder 1 to 6 (Y608 to Y613) are adapted.

Exhaust gas recirculation (EGR)

In order to reduce nitrous oxide emissions, the exhaust gas recirculation (AGR) is active for a certain period of time during idling mode (the AGR is switched off for longer periods of operation so that the exhaust gas recirculation cooler is not sooted up).

In the case of the exhaust gas recirculation (AGR), the suctioned out or supercharged fresh air is mixed with exhaust gas. This leads to the situation where the oxygen content of the suctioned out or supercharged air drops and its specific heat increases. One can therefore achieve a lower combustion temperature and thus reduced output of nitrogen oxides (NOx), whose proportion increases with increasing combustion temperatures. The amount of exhaust gases produced is also reduced.

Fan control

During the whole operation of the engine, that is also when operating power take-offs, the fan speed is controlled dependent on the coolant temperature. The fan speed is determined from the input signals (A) of the fan rpm sensor (Y616 b1). Control takes place through appropriate actuation of the fan clutch solenoid valve (Y616).

Exhaust aftertreatment

The EATS is active immediately after the engine start during the whole operation of the engine. It ensures that the emissions in the exhaust are reduced down to the limits established for the respective emissions standard. Thus different measures are taken according to the emissions standard. For the engine version EURO VI exhaust aftertreatment takes place, for example, through:

 Selective Catalytic Reduction (SCR) with an ammonia locking CAT

 Diesel oxidation catalytic converter (DOC)

 Diesel particulate filter (DPF)

Camshaft adjustment

Through shifting the timing of the exhaust camshaft for low engine rpm one can ensure that the temperature of the exhaust is increased, which improves regeneration of the diesel particulate filter.

Changing the working speed

Changing the working speed it is possible, dependent on the vehicle equipment and parameterization of the power take-off functions, to set the working speed during operation of a power take-off over the accelerator pedal or the keys on the multifunction steering wheel individually to a rotational speed between 550 rpm and 750 rpm or to raise it over the idle speed switch (S900) to a parameterizable value in as far as the max. working speed is not exceeded and the min. working speed is always reached.

1 Changing the working speed using the accelerator pedal

If the accelerator pedal is actuated and thus the position of the accelerator pedal sensor (B44) alters then the drive control (CPC) control unit (A3) alters the control specification for the working speed and transmits this via the drive train CAN (CAN 4) to the engine management (MCM) control unit (A4). It takes account at the same time of the parameters prescribed by the SCA (SCA) control unit (A7) or by the parameterizable special module (PSM) control unit (A22), according to the vehicle equipment as well as the current actual rotational speed. The engine management (MCM) control unit (A4) increases the working speed through appropriate actuation of the injection quantity to the desired value and holds this constant.

2 Changing the working speed over the multifunctional steering wheel

The working speed can be altered step by step in steps of 20 with the aid of buttons on the multifunction steering wheel. The buttons on the multifunction steering wheel are connected via the button group LIN (LIN 7) with the modular switch panel (MSF) control unit (A43) which transmits the entries via the interior CAN (CAN 2) to the central gateway (CGW) control unit (A2) which, in turn, passes this on via the frame-CAN (CAN 3) to the drive control (CPC) control unit (A3). The drive control (CPC) control unit (A3) compares the desired working speed with the current one, the max. permissible as well as the min. permissible working speed (if these were parameterized), adapts the control specification and transmits this to the engine management (MCM) control unit (A4). The engine management (MCM) control unit (A4) alters the working speed through appropriate actuation of the injection quantity to the desired value and holds this constant.

3 Changing the working speed with the idle speed switch (S900)

One special task in controlling the working speed is taken on by the idle speed control switch (S900). This allows one to switch in the constant engine speed facility which means that the engine management (MCM) control unit (A4) sets a single engine speed which has been parameterized and maintains this constant, quite independently of the loading conditions.