Method for controlling a starter-generator

Abstract

A method for controlling a starter-generator for an internal combustion engine in motor vehicles by means of an electronic control unit that acquires operating parameters of the starter-generator and / or the internal combustion engine as input signals, characterized in that the starter-generator is controlled in a starter mode with maximum excitation with a view to reaching a predetermined target speed, that during the starter mode at least one operating parameter is evaluated in the control unit to detect a started state of the internal combustion engine, and that when the started state of the internal combustion engine is reached, the system switches from starter mode to generator mode by reducing the excitation current, even if the predetermined target speed has not yet been reached.

Description

[0001] The invention relates to a method for controlling a starter-generator according to the preamble of claim 1.

[0002] Such a method is known, for example, from DE 10 2004 056 187 A1. Starter-generators are generally known (see, for example, www.motorlexikon.de).

[0003] Furthermore, a device for improving the start-stop operation of a vehicle is known from DE 103 17 090 A1.

[0004] The purpose of the invention is to improve the control of a starter-generator with regard to driving comfort.

[0005] This problem is solved according to the invention by the subject matter of claim 1. The dependent claims are advantageous embodiments of the invention.

[0006] The invention is based on the following findings: When using externally excited synchronous motors as starter-generators in motor vehicles, the transition from starter to generator operation presents a challenge. A high excitation is required for starter operation to achieve high torques, while a lower excitation is desired for generator operation. With current starter-generator control concepts, this transition is often abrupt, resulting in an unmatched excitation during the initial generator operation and consequently, over- or undervoltage. Furthermore, the starting system can generate a strong counter-torque during this transition phase, which can significantly reduce the service life of a belt-driven motor.

[0007] Therefore, according to the invention, in starter mode, the starter-generator is controlled as a motor with speed or rotational speed control to achieve a target speed. Initially, the excitation is fully applied. The target speed of the starter-generator and the controller characteristics are selected to generate maximum torque at low speeds. Once it is apparent that the internal combustion engine has started, the excitation current is reduced even before the end of starter mode, i.e., before the target speed is reached. The starter-generator is then switched to generator mode in the so-called zero-current transition (change from positive to negative current flow). This transition can also occur later, depending on the target speed setting or the behavior of the internal combustion engine. The setpoint of the excitation current control is set to the desired setpoint at this switching point.

[0008] The main advantages of the invention are: 1. Protection of the vehicle electrical system by selecting suitable controller parameters to avoid overvoltage during the transition to generator operation. 2. Protection of the belt drive: If a controlled transition according to the invention does not take place, a very high counter-torque can be generated on the belt drive by the starting system, which leads to damage to the belt. 3. The automated transition ensures that generator operation is achieved in the shortest possible time (no signal delay due to the bus system, the calculation cycle or the function run in the motor control).

[0009] The core of the invention is therefore the control of the motor or starter-generator as a motor in starter mode with speed control and subsequently with a reduction of the excitation current before the end of the control as a drive (in starter mode) in order to achieve a smooth transition to generator mode.

[0010] The invention will now be explained in more detail using a specific embodiment as an example: In starter mode, the engine is controlled by a speed control system. Initially, the excitation is fully applied. The target speed for the starter-generator is, for example, 1000 rpm. The controller characteristic is selected to generate maximum torque at low speeds. When the starter-generator speed reaches, for example, approximately 600 rpm, it is assumed that the internal combustion engine has started. Other parameters, such as engine current, engine speed, the change in speed over time, or the torque of the starter-generator, can also be used to detect this state. Crucially, when detecting that the engine has started, the starter-generator no longer drives the engine but begins to brake it.The excitation current is then reduced by activating the excitation control and setting the setpoint to a predetermined lower value. Alternatively, a fixed low excitation current could be set, or a fixed pulse width modulation could be used for excitation control. The motor control, or the control of the starter-generator as a motor, initially remains active as speed or rotational speed control.

[0011] As the engine and starter-generator speeds increase, the phase currents are reduced by the speed control system. The starter / motor operation is then terminated at a suitable point. This could be implemented, for example, as follows: If the engine continues to gain speed and the starter-generator reaches its target speed, the phase current is set to values ​​close to zero. In this state, the starter-generator's motor operation for starting the engine is terminated, and regular generator operation begins.

[0012] Regular generator operation (generator mode) can be implemented either as diode rectification, active diode rectification, or active generator control.

[0013] The setpoint of the excitation current control is set to the desired setpoint at a defined time.

Claims

[1] Method for controlling a starter-generator for an internal combustion engine in motor vehicles by means of an electronic control unit which acquires operating parameters of the starter-generator and / or the internal combustion engine as input signals, characterized by , that the starter-generator is controlled in a starter mode with maximum excitation with a view to reaching a predetermined target speed, that during the starter mode at least one operating parameter is evaluated in the control unit to detect a started state of the internal combustion engine, and that when the started state of the internal combustion engine is reached, the starter mode is switched to generator mode by reducing the excitation current, even if the predetermined target speed has not yet been reached. [2] Method according to claim 1, characterized by, that the control unit evaluates operating parameters by which the started state of the internal combustion engine is recognized by the fact that the internal combustion engine is being braked by the starter-generator.