METHOD AND CONTROL DEVICE FOR ENERGY RECOVERY IN A HYBRID VEHICLE

Description

[0001] The invention relates to a method for energy recuperation in a hybrid vehicle comprising an internal combustion engine and an electric motor, and having an on-board electrical system with an energy storage device that can be charged with electrical energy by the electric motor during recuperation. The invention further relates to a device for controlling recuperation operation in a hybrid vehicle.

[0002] Due to increasingly strict emissions regulations and vehicle owner demands for reduced operating costs, motor vehicles are subject to increasingly stringent demands regarding their fuel consumption and pollutant emissions, while simultaneously maintaining a high level of driving comfort. To achieve this goal, it is common practice to equip motor vehicles with an automatic stop-start system that allows the internal combustion engine to be automatically switched off and started under predetermined conditions. For example, the combustion engine is automatically switched off when no driving power is required, such as when stopped at a traffic light. As soon as driving power is required again, for example, when the traffic light turns green and the driver presses the accelerator, the electric motor restarts the vehicle. This can reduce the vehicle's fuel consumption.

[0003] Furthermore, it is known in practice to equip motor vehicles with recuperation systems. In addition to the combustion engine, such hybrid vehicles usually comprise an electric motor which, depending on the driving situation, operates either in motor mode or in generator mode. In motor mode, the electric motor generates additional drive torque, which supports the combustion engine, for example, during an acceleration phase. In generator mode, however, the kinetic energy released during deceleration of the vehicle is converted into electrical energy (recuperation). The electrical energy thus generated is stored in at least one energy storage device, such as an UltraCap storage device, and can be used in other driving situations, for example to drive the vehicle or to supply electrical consumers. The vehicle's efficiency can be significantly increased as a result.

[0004] In such vehicles, it is a common approach to try to use the generator to exert as high a proportion as possible of the desired overall deceleration, which the driver sets, for example, by pressing the foot brake pedal, and thus recover as much energy as possible. In such vehicles, it is therefore a common operating strategy to recuperate with maximum generator power in recuperation mode until at least one energy storage device in the vehicle is full. The amount of electrical energy that can be generated by the generator depends on the state of charge and the absorption capacity of the energy storage device. When the energy storage device is fully charged, very little or no electrical energy can be fed into the on-board electrical system, as otherwise the energy storage device could be overloaded or voltage-sensitive consumers could be damaged.The power output of the generator is adjusted accordingly by a regulator. This means that the generator (including the inverter) and energy storage system operate with high power losses, and the energy storage system usually has a high energy level, although there are energy windows that are optimal for the service life depending on the type of energy storage system. For ultracapacitors in particular, a fully charged state significantly reduces the service life of the energy storage system.

[0005] Document US 2011 / 0276243 A1 discloses, among other things, a regenerative braking system and an energy storage system. A value is determined for a variable that relates to a state that reflects the energy consumption of the energy storage system. This value is used to determine a regenerative braking torque capacity for the regenerative braking system. Regenerative braking is controlled by the regenerative braking system based at least in part on the regenerative braking torque capacity.

[0006] It is therefore an object of the invention to provide an improved method for recuperating energy in a hybrid vehicle, with which disadvantages of conventional techniques can be avoided. The object of the invention is, in particular, to provide a method for recuperating energy in a hybrid vehicle, with which power losses in the recuperation system, in particular in the electric motor, inverter, energy storage device and / or the wiring, can be reduced during recuperation operation and which enables component-saving operation. A further object is to provide a device for controlling recuperation operation in a hybrid vehicle, with which disadvantages of conventional devices can be avoided.

[0007] These objects are achieved by devices and methods having the features of the independent claims. Advantageous embodiments and applications of the invention emerge from the dependent claims and are explained in more detail in the following description, with partial reference to the figures.

[0008] According to a first aspect of the invention, a method for recuperating energy in a hybrid vehicle is provided. The hybrid vehicle comprises an internal combustion engine, an electric motor, and preferably an automatic stop-start device by means of which the internal combustion engine can be automatically switched off and started under predetermined conditions. The hybrid vehicle also has an on-board electrical system with an energy storage device that can be charged with electrical energy from the electric motor during recuperation mode.

[0009] According to a first measure, a recuperation power for a recuperation operation of the electric machine is set to a first value, hereinafter also referred to as P_max, which enables a recuperation operation with a maximum generator capacity of the electric machine if a current energy level of the energy storage device is less than or equal to a threshold value, hereinafter referred to as E_3. The recuperation power for a recuperation operation of the electric machine, on the other hand, is set to a second value, hereinafter also referred to as P_lim, which is less than the first value P_max and enables or defines a recuperation operation with a reduced generator capacity of the electric machine if the current energy level of the energy storage device is greater than the threshold value E_3, ie E_ist > E_3.

[0010] The value P_lim can be set to a fixed value or to a variable value below P_max. If the value of P_lim is set to be variable, the value P_lim can be calculated such that the energy storage device is fully charged at the end of recuperation, i.e., after the vehicle speed falls below the minimum speed at which recuperation is possible. The recuperation power is specified by a device controlling the electric motor, so that during recuperation mode, the electric motor recovers power equal to the specified recuperation power.

[0011] According to the first measure, the power output by the electric machine in generator mode is reduced to the value P_lim below the maximum power P_max if the energy level or the state of charge of the energy storage device exceeds a predetermined level. This significantly reduces the operating phases in which the energy storage device, used to absorb recuperation energy, and the electric machine operate with high power losses, thus enabling a more component-friendly operation.

[0012] According to a first measure, a recuperation energy E_rek is predicted, i.e., predicted or estimated, for a current operating state of the motor vehicle. This energy indicates how much energy could be recuperated if the motor vehicle, starting from the current driving state, were to decelerate to at least a speed threshold. The speed threshold preferably indicates a speed limit above which energy can be recuperated in recuperation mode and below which no recuperation mode is possible. The recuperation energy E_rek thus estimates how much energy can be recuperated on average from the kinetic energy of the motor vehicle if the motor vehicle is decelerated to a standstill and, for example, transitions into a stop phase of stop-start operation.Estimating this recuperation energy E_rek offers the advantage that, taking into account the current energy storage level of the energy storage device, it can be estimated more precisely whether an "overcharging" of the energy storage device or the associated power losses are imminent during the next recuperation process and whether sufficient energy will be available in the energy storage device at the beginning of a coming stop phase of the stop-start operation.

[0013] In an advantageous variant of this embodiment, the threshold value E_3 is defined as the difference between a maximum energy level E_max of the energy storage device, i.e., a state in which the energy storage device is fully charged within the specified operating limits, and the predicted recuperation energy E_rek, i.e., E_3 = E_max minus E_rek. If the current energy level E_actual corresponds precisely to the threshold value E_3, the storage device can be fully charged to the maximum level E_max through recuperation operation if the vehicle is braked to a standstill.If the current energy level at the start of recuperation operation were above the threshold value E_3, a conventional recuperation operation with maximum power of the generator would lead to a power loss, which is, however, avoided or at least reduced according to the invention by reducing the power of the generator to P_lim in this case.

[0014] The predicted recuperation energy E_rek can be determined depending on the current vehicle speed, average vehicle deceleration, on-board electrical system load, and maximum generator capacity P_max of the recuperation operation. This allows an estimated recuperation or braking duration to be estimated from the current vehicle speed and an assumed average vehicle deceleration. Based on the estimated braking duration, the expected recuperation power, e.g., assuming maximum generator capacity P_max of the generator, minus the current on-board electrical system load, results in the expected recuperable energy if the vehicle is brought to a standstill. In this way, the expected recuperable energy can be precisely predicted or estimated based on the vehicle's current driving state.

[0015] It is also particularly advantageous if the predicted recuperation energy E_rek and / or the threshold value E_3 are continuously recalculated during driving, so that the values ​​for the predicted recuperation energy E_rek and / or the threshold value E_3 are adjusted as soon as the vehicle state, in particular the vehicle speed, changes. The average vehicle deceleration can indicate the average deceleration with which the motor vehicle is decelerated during a recuperation process and can be stored in advance in the vehicle. For the value of the on-board electrical system load, a current value of the on-board electrical system load is preferably determined. Alternatively, a previously stored value for an average on-board electrical system load can also be used.

[0016] If the hybrid vehicle comprises an automatic stop-start device by means of which the internal combustion engine can be automatically switched off and started under predetermined conditions, a further measure can be used to determine a minimum threshold value E_min for an energy level of the energy storage device as a function of the predicted recuperation energy E_rek and a minimum energy E_Stopp which is required on average for an engine stop phase of a stop-start operation.

[0017] The minimum energy E_Stopp, which is required on average for an engine stop phase of a stop-start operation, can be determined as the sum of an engine start energy E_1 for the start-stop operation and an energy requirement E_2 for an on-board power supply during a stop phase of the stop-start operation. The engine start energy E_1 indicates how much electrical energy is required from the energy storage device for the warm start of the combustion engine during stop-start operation, with the electric machine serving as the starter motor. The energy requirement E_2 for the on-board power supply can be determined depending on the average vehicle downtime during the stop phase and the average on-board power supply load. The minimum threshold value E_min is preferably continuously recalculated during driving.

[0018] In this way, it can be ensured that when the vehicle is stationary, sufficient energy is available for the basic functions, such as engine start and on-board power supply, during the stop phase.

[0019] An advantageous variant of this measure provides that the minimum threshold value E_min is set to a value below the minimum energy E_Stopp required on average for an engine stop phase of a stop-start operation if the sum of the current energy level E_actual of the energy storage system and the predicted recuperation energy E_rek is greater than the minimum energy E_Stopp. This allows energy storage management to be further optimized. If the sum of the current energy level E_actual of the energy storage system and the predicted recuperation energy E_rek is less than or equal to the minimum energy E_Stopp, E_min is set to the value of E_Stopp.

[0020] If the energy storage device's minimum threshold value E_min is undershot during driving, the energy storage device's energy level E_actual can be increased by increasing the engine's load point. Furthermore, the engine can be started during a stop phase if the energy storage device's energy level E_actual falls to a value corresponding to the engine starting energy E_1 during a stop phase.

[0021] The energy level of the energy storage device corresponds to a specific state of charge of the energy storage device. Therefore, for the purposes of this document, the corresponding state of charge threshold values ​​can be used instead of the energy level values ​​used. The term "energy level of the energy storage device" also refers to the state of charge of the energy storage device. For example, the current energy level E_actual can also be determined as the current state of charge (SOC) of the energy storage device, and the threshold value E_3 can then be set as the corresponding state of charge threshold value.

[0022] It has already been mentioned above that the second value P_lim for the recuperation power of the recuperation operation of the electric machine is set variably.

[0023] P_lim is set in such a way that the energy storage device would be fully charged at the end of a subsequent recuperation process if the motor vehicle were to be braked from the current driving state to at least a speed threshold value, wherein the speed threshold value, already referred to above as v_min, preferably indicates a speed limit above which energy can be recuperated in recuperation mode and below which no recuperation mode is possible.For example, P_lim can be calculated according to the formula P_lim = ((E_max - E_actual) + P_board*t_rec)) / t_rec, where E_max is the maximum and E_actual the current energy level of the energy storage device, P_board is an average assumed or instantaneous on-board network load, and t_rec is an estimate for the duration of a recuperation process, which can be estimated from the difference between the current vehicle speed v_actual and the speed threshold v_min divided by the assumed average vehicle deceleration a_brake, i.e. t_rec = (v_actual - v_min) / a_brake. The value t_rec corresponds to the aforementioned average braking duration during which energy can be recuperated in a recuperation mode.

[0024] According to a second aspect of the invention, a device is provided for controlling recuperation operation in a hybrid vehicle, which comprises an internal combustion engine, an electric machine, and preferably an automatic stop-start device by means of which the internal combustion engine can be automatically switched off and started under predetermined conditions, and which has an on-board electrical system with an energy storage device that can be charged with electrical energy by the electric machine during recuperation operation. The device is configured according to the invention to carry out the method as described in this document. To avoid repetition, features disclosed purely according to the method should also be considered as disclosed according to the device and should be claimable. The aforementioned aspects and features according to the invention therefore also apply to the device.

[0025] The invention further relates to a motor vehicle, in particular a commercial vehicle, comprising such a device for controlling the recuperation operation.

[0026] Further details and advantages of the invention are described below with reference to the accompanying drawings. They illustrate: Figure 1 shows an electrical system of a hybrid vehicle; and Figures 2 to 4 show the variation of the recuperation power as a function of the current operating state of the hybrid vehicle according to an embodiment of the invention.

[0027] Figure 1shows a schematic example of an on-board electrical system 1 of a hybrid vehicle, in particular a commercial vehicle, known per se from the prior art. The on-board electrical system 1 has two sub-networks 2, 3: a first sub-network 2, in which a first mains voltage U1 is applied and which comprises a first energy storage device 5 and a load resistor 6. The load resistor 6 is formed by at least one, preferably several, consumers. Furthermore, a conventional starter 7 for the internal combustion engine is provided in the first sub-network 2.

[0028] Furthermore, a second sub-network 3, in which a second mains voltage U2 is applied and in which an electric machine 10 is provided. The electric machine 10 is designed to start an internal combustion engine (not shown) of the motor vehicle and for generator operation or recuperation operation and can be designed, for example, as a crankshaft starter generator. Furthermore, a second energy storage device 9 is provided in the second sub-network 3, e.g., a high-capacity storage device (ultracap storage device), which can be connected to the electric machine 10 via an inverter 11. The second energy storage device 9 is designed to store electrical charge generated by the electric machine 10 in generator operation or recuperation operation. The first energy storage device 5 can also be designed as a capacitor storage device or as a conventional lead-acid battery. The power lines 12 are in Figure 1 marked with solid black lines.

[0029] The vehicle electrical system 1 further comprises a DC / DC converter 4, which bidirectionally connects the first sub-network 2 to the second sub-network 3. The DC / DC converter 4 is configured to receive a DC voltage from one of the sub-networks 2, 3, for example, a DC voltage with which the first sub-network 2 is operated, and to generate an output voltage that differs from the voltage received on the input side.

[0030] The on-board electrical system 1 or 21 further comprises a control unit (not shown) which is connected via corresponding signal lines (not shown) to the corresponding components of the on-board electrical system 1, 21, in particular the voltage converter 4, the energy storage devices 5 and 9 and the electric machine 10.

[0031] The control unit receives data about the charge state of the energy storage devices 5, 9 from the energy storage devices 5, 9 or the charge state sensor 8, and from a storage management system (not shown) of the energy storage device 9. The control unit is further configured to output corresponding control signals to the voltage converter 4 depending on the received charge states. Depending on the control signals received by the control unit, the voltage converter 4 is configured to transfer energy from the first sub-network 2 to the second sub-network 3 and vice versa.

[0032] It is emphasized that the Figure 1 The on-board network topology shown is merely exemplary and a large number of other variants of on-board network topologies for integrating an electric machine and an electrical energy storage device for hybrid operation are known from the prior art, with which the method according to the invention can also be carried out.

[0033] According to the invention, the control unit is particularly configured to carry out the method for controlling a recuperation operation and, in doing so, to vary the recuperation power of the electric machine 10 via the inverter 11, which will be described below with reference to the Figures 2 to 4 is illustrated by example.

[0034] Figure 2 The upper diagram illustrates the current values ​​for the energy storage energy level E_actual and the threshold value E_3 for a specific vehicle operating state. The lower diagram shows the corresponding value of the specified recuperation power P_actual.

[0035] The Figures 3 and 4 show corresponding values ​​for the energy level E_actual, the threshold value E_3 and the currently set recuperation power P_actual in other operating states of the vehicle. Values ​​with the same reference symbols correspond to the values ​​of the Figure 1and are not described separately.

[0036] In Figure 2 Axis 8 indicates the level of energy storage 9. The energy level E_max indicates the energy level of a fully charged energy storage device. The dashed line indicates the current energy level E_actual, corresponding to the current state of charge (SOC) of energy storage 9, which is continuously determined and monitored.

[0037] The length of the arrow marked with the reference symbol E_rek indicates the amount of currently predicted recuperation energy. E_rek indicates how much energy could be recuperated if the vehicle were to decelerate from the current driving state to at least a speed threshold value v_min. The speed threshold value v_min indicates the speed limit up to which energy can be recuperated in recuperation mode. At a driving speed below v_min, no more energy is recuperated.

[0038] E_rek is continuously calculated during driving operation. For this purpose, an average braking duration during which energy can be recuperated in a recuperation mode is calculated from the current vehicle speed and a stored average vehicle deceleration. The faster the vehicle travels, the longer the average braking duration and thus the average duration of a recuperation phase. Assuming a set maximum generator power P_max of the electric machine 10 in recuperation mode, subtracting the average on-board network load results in an average recuperation power, which, when multiplied by the average braking duration, yields the predicted recuperation energy E_rek.

[0039] Depending on the determined recuperation energy E_rek, the energy threshold E_3 is continuously determined as E_3 = E_max minus E_rek.

[0040] If the current energy level E_ist of the energy storage device 9 is less than or equal to the threshold value E_3, the current recuperation power P_ist for a recuperation operation of the electric machine 10 is set to the maximum power P_max, so that the recuperation operation takes place with a maximum generator power of the electric machine.

[0041] However, if the current energy level E_ist of the energy storage device is greater than the threshold value E_3, the recuperation power P_ist for a recuperation operation of the electric machine 10 is set to a value P_lim which is smaller than the first value P_max and enables or specifies a recuperation operation with a reduced generator capacity of the electric machine 10.

[0042] In the example of Figure 2the current energy storage level E_ist is less than E_3, so P_ist is set to the value P_max, which is shown in the lower diagram of the Figure 2 is shown. If recuperation were to begin, it would occur with the maximum recuperation power P_max.

[0043] Figure 3 corresponds to a vehicle operating state in which the current energy storage level E_actual is above the energy threshold E_3, so that in this case, the recuperation power P_actual is set to a reduced value P_lim. If recuperation were to begin in this case, it would only occur with the reduced recuperation power P_lim.

[0044] It has already been mentioned above that the recuperation energy E_rek is continuously predicted and the energy threshold value E_3 is also continuously adjusted accordingly. Figure 4shows an example where E_3 was set to the value E_max. This corresponds, for example, to a vehicle operating state where the current vehicle speed is below the threshold v_min, so that the value for the predicted recuperation energy E_rek is zero. Consequently, a value of E_max results for E_3.

[0045] In the Figures 2 to 4The energy levels E_1, E_2, E_Stopp, and E_min are also shown. The energy level labeled E_Stopp indicates the minimum energy level that must be contained in memory 9 at the beginning of a stop phase. The energy level E_Stopp is composed of an engine start energy E_1, which is required for the warm start of the combustion engine during stop-start operation, and an energy requirement E_2 for the on-board power supply. The energy requirement E_2 results from a stored average vehicle downtime during the stop phase, i.e., an assumed average duration of the stop phase, and an average on-board power supply load during the stop phase.

[0046] If the electric machine 10 cannot generate any energy during an engine stop phase, the energy in the storage device 9 is used up to the threshold E_1 and then the combustion engine is forced to start. The stop phase of the combustion engine is thus terminated prematurely. One possibility here is to subsequently recharge the energy storage device 9 using the electric motor so that the combustion engine can then be stopped again if the vehicle is still stationary, i.e., the driver has not yet signaled the end of the stop-start operation, for example by pressing the accelerator pedal. Alternatively, after the forced start of the combustion engine, the combustion engine can operate in idle mode until the driver signals the end of the stop phase.

[0047] E_min specifies a threshold value for the energy level below which, when driving, a load point increase of the combustion engine is started in order to charge the energy storage device to at least the value E_min using the excess energy generated. In the exemplary embodiments of the Figures 2 to 4 E_min is set to the value of E_Stopp = E1 plus E2.

[0048] According to a further embodiment, E_min can be continuously recalculated depending on the average vehicle electrical system load, the required engine start energy E_1, the average vehicle deceleration, the vehicle speed, and the expected vehicle standstill time. In particular, E_min can be determined depending on the predicted recuperation energy E_rek and the minimum energy E_stop required on average for an engine stop phase of a stop-start operation.

[0049] For example, according to this variant, the minimum threshold value E_min can be set to a value below the minimum energy E_Stopp (not shown) if the sum of the current energy level E_actual of the energy storage device and the predicted recuperation energy E_rec is greater than the minimum energy E_Stopp. This takes into account that sufficient energy can still be recuperated from the vehicle's current kinetic energy to charge the energy storage device 9 to at least the value E_Stopp at the beginning of the next stop phase. If the sum of the current energy level E_actual of the energy storage device and the predicted recuperation energy E_rec is less than or equal to the minimum energy E_Stopp, E_min is set to the value of E_Stopp.

[0050] Although the invention has been described with reference to specific embodiments, it will be apparent to one skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made without departing from the spirit and scope of the invention. Consequently, the invention is not intended to be limited to the disclosed embodiments, but is intended to include all embodiments falling within the scope of the appended claims. In particular, the invention also claims protection for the subject matter and features of the dependent claims, independent of the referenced claims. List of reference symbols

[0051] 1On-board electrical system 2First sub-network 3Second sub-network 4Voltage converter 5First energy storage device 6Load resistor 7Starter 8Energy level of the energy storage device 9Second energy storage device 10Electric machine 11Inverter 12Power lines E_1Engine starting energy E_2Energy reserve for on-board electrical system supply during vehicle stop E_3Threshold value E_maxMaximum energy level of the energy storage device E_actualCurrent energy level of the energy storage device E_StoppRequired minimum energy during vehicle stop E_minRequired minimum energy during vehicle stop taking into account E_rek E_rekCurrently recuperable energy P_maxMaximum recuperation power for recuperation mode P_limLimited recuperation power for recuperation mode

Claims

1. Method for recuperating energy in a hybrid vehicle, which hybrid vehicle comprises an internal combustion engine, an electrical machine (10) and preferably an automatic stop / start apparatus by means of which the internal combustion engine can be automatically turned off and started under predetermined conditions, and which hybrid vehicle has an on-board electrical system (1) comprising an energy store (9) which can be charged with electrical energy by the electrical machine (10) during the recuperation operation, wherein a recuperation power (P_act) for a recuperation operation of the electrical machine (10) (a) is set to a first value (P_max) which allows a recuperation operation with a maximum generator capacity of the electrical machine if an actual energy level (E_act) of the energy store (9) is lower than or equal to a threshold value (E_3); and (b) is set to a second value (P_lim) which is lower than the first value (P_max) and allows a recuperation operation with a reduced generator capacity of the electrical machine (10) if the actual energy level (E_act) of the energy store (9) is greater than the threshold value (E_3), characterized that the second value (P_lim) for the recuperation power (P_act) of the recuperation operation of the electrical machine (10) (a) is in each case set such that the energy store would be fully charged at the end of a subsequent recuperation process if the motor vehicle were to be braked from the current driving state at least to a speed threshold value (v_min), wherein the speed threshold value preferably indicates a speed limit above which energy can be recuperated during the recuperation operation and below which a recuperation operation is not possible; and / or (b) is calculated in accordance with the formula P_lim = ((E_max - E_act) + P_on-board*t_rec)) / t_rec, where E_max indicates a maximum energy level and E_act indicates an actual energy level of the energy store (9) and P_on-board indicates an average on-board electrical system load and t_rec indicates an estimate for a duration of a recuperation process which can be estimated from the difference between the actual vehicle speed (v_act) and the speed threshold value (v_min) divided by an assumed average vehicle deceleration.

2. Method according to Claim 1, characterized in that a recuperation energy (E_rek) is predicted for an actual operating state of the motor vehicle, the said recuperation energy indicating how much energy would be able to be recuperated if the motor vehicle were to be braked starting from the current driving state at least to a speed threshold value (v_min), wherein the speed threshold value preferably indicates a speed limit above which energy can be recuperated during the recuperation operation and below which a recuperation operation is not possible.

3. Method according to Claim 2, characterized in that the threshold value (E_3) is defined as the difference between a maximum energy level (E_max) of the energy store (9) and the predicted recuperation energy (E_rek) .

4. Method according to Claim 2 or 3, characterized in that the predicted recuperation energy (E_rek) is determined depending on an actual vehicle speed, an average vehicle deceleration, an on-board electrical system load and a maximum generator capacity (P_max) of the recuperation operation.

5. Method according to one of the preceding claims, characterized in that the threshold value (E_3) is continuously recalculated during driving.

6. Method according to one of the preceding Claims 2 to 5, characterized in that a minimum threshold value (E_min) for an energy level of the energy store (9) is determined depending on the predicted recuperation energy (E_rec) and a minimum energy (E_stop) which is required on average for a motor stop phase of a stop / start operation.

7. Method according to Claim 6, characterized in that the minimum energy (E_stop) which is required on average for a motor stop phase of a stop / start operation is determined as a sum of a motor start energy (E_1) for the start / stop operation and an energy requirement (E_2) for an on-board electrical system supply during a stop phase of the stop / start operation, wherein the energy requirement (E_2) for the on-board electrical system supply is determined depending on an average stationary time for the vehicle in the stop phase and an average on-board electrical system load.

8. Method according to either of Claims 6 and 7, characterized in that the minimum threshold value (E_min) is set to a value below the minimum energy (E_stop) which is required on average for a motor stop phase of a stop / start operation if the sum of the actual energy level (E_act) of the energy store and the predicted recuperation energy (E_rec) is greater than the minimum energy (E_stop).

9. Method according to Claims 6 to 8, characterized (a) in that the minimum threshold value (E_min) is continuously recalculated during driving; and / or (b) in that the energy level (E_act) of the energy store is increased by means of raising the load point of the internal combustion engine when the minimum threshold value (E_min) of the energy store is undershot during driving; and / or (c) in that the internal combustion engine is started in a stop phase if the energy level (E_act) in the energy store drops to a value which corresponds to the motor start energy (E_1) during a stop phase.

10. Apparatus for controlling a recuperation operation in a hybrid vehicle, which hybrid vehicle comprises an internal combustion engine, an electrical machine (10) and an automatic stop / start apparatus by means of which the internal combustion engine can be automatically turned off and started under predetermined conditions, and which hybrid vehicle has an on-board electrical system (1) comprising an energy store (9) which can be charged with electrical energy by the electrical machine (10) during the recuperation operation, characterized in that the apparatus is designed to carry out the method according to one of Claims 1 to 9.

11. Motor vehicle, in particular utility vehicle, having an apparatus according to Claim 10.