This application claims the priority of International Application No. PCT/EP01/09947, filed Aug. 29, 2001, and German Patent Document No. 100 46 631.1, filed Sep. 20, 2000, the disclosures of which are both incorporated by reference herein.
The invention relates to a method for regulating the generator voltage in a motor vehicle and to a generator controller for carrying out the method.
In modern vehicles with an internal combustion engine, a generator is driven by an internal combustion engine and produces electrical power for the vehicle power supply system. In order to buffer the amount of electrical power available, the vehicle power supply system has a battery which acts as an energy store and, after being partially discharged, is recharged by means of the generator. The generator voltage governs the direction and magnitude of the charge flow at the battery, that is to say the charging and discharging cycles. The generator is normally regulated such that the voltage which is produced corresponds as closely as possible to the final charge voltage on the battery, so that the battery is always completely charged if the charge balance is positive.
A method for regulating the generator voltage in a motor vehicle as a function of operating states is known from German Patent DE 43 07 907 A1. This proposes that the generator voltage be reduced during acceleration, in order to reduce the load on the vehicle engine, and that the generator voltage be increased during braking, in order that the generator can absorb more power in order to charge the battery by recuperation of braking energy. The power flow between the battery, the generator and the loads is controlled by presetting the nominal value of the generator voltage such that it is matched to the driving state. A similar method is also known from U.S. Pat. No. 4,659,977.
Finally, U.S. Pat. No. 6,118,237 discloses a hybrid propulsion system with battery management. This battery management provides input and output power for a battery when the battery temperature is low. On detecting a low battery temperature, the state of charge of the battery is determined, and is compared with a predetermined value. This comparison result is used in order to determine whether the battery can be discharged further or whether the battery must be charged. If the state of charge is greater than or equal to the predetermined value, a control device discharges the battery to a greater extent, in order to drive an electric motor of a hybrid propulsion system in the power mode. This increased discharging causes an increase in the battery temperature, thus resulting in the input power and output power of the battery being produced once again. If, on the other hand, the state of charge is less than or equal to the predetermined value and the battery temperature of the battery is less than or equal to the predetermined temperature value, the battery is charged to an increased extent by supplying electrical power from the electric motor.
The object of the invention is to lengthen the life of the battery in motor vehicles with a recuperation mode.
The method according to the invention extends the known methods for regulating a generator by introducing an operating mode which partially reverses the consequences of stress on the battery resulting from recuperation. During recuperation of braking energy, increased stress is placed on the motor vehicle battery by the frequency changes between battery discharging and charging processes. In order to carry out regeneration of the battery regularly, a generator controller regularly switches from a recuperation readiness mode to a recovery mode, and regularly back again to the recuperation readiness mode. In the recuperation readiness mode, recuperation operation can be selected when required by presetting a suitable nominal value voltage. In the recovery mode, the nominal value voltage is preset by the generator controller such that the battery is regenerated from the increased stress on the basis of the recuperation charged changes. This method has the advantage that it prevents premature ageing of the battery.
In one advantageous development of the invention, a recuperation characteristic variable, which is a characteristic measure of the battery stress resulting from the recuperation operation, is continuously assessed as a criterion for switching to the recovery mode. This development of the method has the advantage that the battery is regenerated as required, so that a greater time is thus available for recuperation, without the life of the battery being adversely affected.
In one advantageous refinement, the charge throughput of the battery, which takes place after a specific start time, is used as a recuperation characteristic variable. One advantageous choice for the start time is, for example, the time when switching last took place from the recovery mode to the recuperation readiness mode.
A further advantageous development of the method for regulating the generator voltage proposes that, in the recuperation readiness mode, an intermediate stage, in which the loads are supplied in a mixed manner from the battery and from the generator, is provided during a change from a charging process for the battery to charge being drawn from the battery. This extension to the method has the advantage that the power losses which occur in the battery, when changing from a charging process, to a discharging process are reduced. In another advantageous development, the battery is kept in a partial state of charge in the recuperation readiness mode. In the partial state of the charge, the battery can absorb a particularly large amount of the charge which is produced by recuperation, thus receiving a particularly large proportion of the energy obtained from recuperation. This method has the advantage that it reduces the fuel consumption since the electrical power, which is required in the motor vehicle, is produced to a greater extent than before by recuperation. The disadvantage of increased stress on the battery is kept in check by controlled switching to the recovery mode.