Driving mode, basic function

Overview

This document contains information on:

 General

 Function requirements

 Transmission modes

 Controlling the drive torque of the electric machine

 Distributing the total drive torque among the front and rear axle

 Activating the sound generator (vehicles with an acoustic presence indicator)

General

In the drive mode the electrical power from the high-voltage battery system is converted to mechanical drive energy. The electric machine works in engine mode.

Function requirements

 Circuit 15 ON

 Drive train operational

Transmission modes

The user can switch between the drive programs with the DYNAMIC SELECT switch on the lower control panel. The powertrain control unit implements the selected drive program. The letter of the selected drive program is displayed in the multimedia display. After the ignition is switched on, the drive program Comfort is active.

Depending on the transmission mode selected, the following vehicle characteristics are changed:

 Drive

 Chassis

 Steering

 Driving dynamics control

Controlling the drive torque of the electric machine

 In vehicles with two electric machines, the following explanations apply per machine.

The power electronics control unit constantly reads in the engine speed of the electric machine via the rpm sensors. Furthermore the power electronics control unit monitors the status of the integral power inverter in the power electronics control unit. It evaluates the performance of the electric drive system and transmits the currently available torque to the powertrain control unit.

The powertrain control unit reads in the accelerator pedal's position.

On the basis of the accelerator pedal position and the operating state of the electric drive system, the powertrain control unit calculates a torque value.

After taking different power output limitation criteria into consideration, the powertrain control unit requests a suitable torque from the power electronics control unit.

The power inverter integrated in the power electronics control unit converts the high voltage direct voltage into a 3-phase alternating voltage and supplies this to the electric machine. The power electronics control unit regulates the frequency and amplitude of the alternating stress and therefore directly the generated drive torque dependent on the performance specifications.

Distributing the total drive torque among the front and rear axle

The powertrain control unit reads in the accelerator pedal's position.

The accelerator pedal position corresponds to an entire specified torque. In vehicles with two electric machines, the drive control distributes this among a specified torque for the front axle and a specified torque for the rear axle. The distribution of the entire specified torque takes place in accordance with the axle load distribution and the acceleration skid control criteria. Depending on the situation, only the front or only the rear axle can be activated or the drive is distributed steplessly among both axles. In the case of low torque requests, the machine that is not required is switched off completely in order to reduce the base load.

The powertrain control unit requests the partial torques from the power electronics control unit.

Activating the sound generator (vehicles with an acoustic presence indicator)

The electric drive system is very quiet at low speed. Since pedestrians and bike riders are used to the noise of conventional drives, they can easily not hear electrically driven vehicles. To reduce the risks associated with this, the sound generator generate an artificial warning noise.

Depending on the accelerator pedal position, a speed-dependent noise is emitted via the sound generator and the sound generator rear end at a speed between 0 to 30 km/h. At speeds greater than 30 km/h, the sound generators are deactivated as the rolling and wind noises are loud enough.