DE102014203852B4 - Starting a combustion engine serving as a range extender in an electric vehicle - Google Patents

Abstract

Method for starting an internal combustion engine serving as a range extender in an electric vehicle, the electric vehicle having an electric drive machine for generating a drive torque to drive the motor vehicle, an electric energy store for supplying the electric drive machine with electric energy, the range extender serving Combustion engine and- a generator coupled to the combustion engine for generating electrical energy, with the steps:- detecting uphill driving by- determining a speed-dependent comparison value (MFW, MFW,s2,vakt) as a function of the current vehicle speed (v, vakt). , and- a drive torque signal (MEM,actual,f) corresponding to the current actual drive torque or the target drive torque of the electric drive machine after filtering the drive torque signal or without filtering the drive torque signal with the comparison value (MFW, MFW.s 2,vakt) is compared; and- starting the internal combustion engine after recognizing the uphill drive.

Description

The invention relates to a method for starting an internal combustion engine serving as a range extender in an electric vehicle. In this case, the electric vehicle comprises an electric drive machine for generating a drive torque and an electric energy store (in particular a battery) for supplying the electric drive machine with electric energy. Furthermore, an internal combustion engine serving as a range extender is provided, which is coupled to an electrical generator for generating electrical energy

As for example in the pamphlets DE 10 2010 034 444 A1 and DE 10 2010 016 188 A1 described, the internal combustion engine serving as a range extender in known electric vehicles is started when the electric energy storage device reaches or falls below a specific threshold value for the state of charge (SOC), for example when the state of charge is SOC=10%. With the generator driven by the range extender, the electrical energy storage device of the electric vehicle can be charged, thus increasing the range of the vehicle. Ideally, the electrical power consumed by the drive motor should be less than the electrical power generated by operating the range extender on average over time.

In driving situations in which the vehicle is driving uphill or in which the vehicle is heavily accelerated due to a sporty driving style or is being driven at high speed, the electrical power consumed by the electric drive motor is significantly greater than the electrical power generated by operating the range extender. As a result, the state of charge (SOC) of the electrical energy storage unit continues to decrease despite the combustion engine running.

In order to counteract the further decrease in the state of charge despite the running range extender, the power consumed by the electric motor can be reduced or limited, which, however, significantly restricts the driving characteristics of the electric vehicle.

From the DE 103 09 854 A1 There is known a vehicle control device that charges a battery by driving the internal combustion engine when the amount of electric power stored in the battery that supplies electric power to the electric motor becomes equal to or smaller than a predetermined lower limit value. The vehicle control device preheats the internal combustion engine, a catalyst, and the like when the stored electric energy amount in the battery falls to or below a value set as a stored electric energy amount larger than the lower limit value.

From the DE 10 2004 038 919 A1 there is known a system for driving a vehicle, comprising: a primary power source for driving the vehicle in a period after initial driving of the vehicle; a secondary power source for initially propelling and accelerating the vehicle prior to activation of the primary power source; and a controller for determining a weight of the vehicle based on an initial acceleration of the vehicle, determining a driver torque request, and activating the primary power source when the weight of the vehicle exceeds a predetermined vehicle weight threshold and the driver torque request exceeds a predetermined torque threshold exceeds.

From the CA 2 794 707 A1 a controller for a series hybrid vehicle is known, comprising a basic required power calculator for calculating a basic required power for running the vehicle based on a vehicle speed and an accelerator pedal opening, a grade calculator for calculating an increasing grade of a road surface on which the vehicle is running. A correction power calculator for calculating a correction power added to the base demand moment based on the increasing gradient, and a target power calculator for calculating when a target power resulting from the addition of the correction power to the base demand power is greater than a predetermined value based on of required power, a battery target electric power by which the battery is required to deliver part of the required power, and a motor target power by which the motor is required to deliver the remainder of the required power.

From the U.S. 2013/0 218 383 A1 a hybrid drive for a motor vehicle and a method for its control is known, the hybrid drive comprising an internal combustion engine; and a control unit that is configured to determine an actual power requirement required by the internal combustion engine during a current driving situation of the motor vehicle; a predetermined power requirement model of the internal combustion engine and the determined actual power requirement, and control the internal combustion engine as a function of the speed of the motor vehicle based on the determined difference.

It is therefore the object of the invention to avoid, as far as possible, a reduction in the power consumed by the electric motor in such driving situations.

The object is solved by the features of the independent patent claims. Advantageous embodiments are described in the dependent patent claims.

A first aspect of the invention relates to a method for starting an internal combustion engine serving as a range extender in an electric vehicle. The electric vehicle includes an electric drive machine for generating a drive torque and an electric energy store for supplying the electric drive machine with electric energy. Furthermore, the internal combustion engine serving as a range extender and a generator mechanically coupled to the internal combustion engine for generating electrical energy are provided, with the electrical energy being supplied to the electrical energy store or directly to the drive motor. According to the invention, driving uphill is detected. For this purpose, a comparison value is determined as a function of the current driving speed; the comparison value preferably increases with increasing vehicle speed. The comparison value is preferably a driving resistance value that is dependent on the current vehicle speed and is based on an incline of the roadway (e.g. 7% incline). The gradient taken as a basis generally does not correspond to the actual gradient and is preferably in the range of 2-15% gradient. Rather, the underlying incline represents a threshold for the incline, when the range extender is started when it is reached or exceeded. In addition to the gradient-dependent gradient resistance, the driving resistance preferably also includes the air resistance and optionally the rolling resistance.

Furthermore, a drive torque signal from the electric drive machine is compared with the driving resistance value. After recognizing the uphill drive, the combustion engine is started.

So if driving uphill is detected by comparing the drive torque of the electric drive motor with the speed-dependent comparison value, in particular the value of the driving resistance characteristic at the current speed, the range extender can be started earlier and it is not necessary to wait until the range extender has completed the Threshold for the state of charge reached at which the range extender is started in previously known electric vehicles. Therefore, the decrease in the state of charge by operating the range extender is counteracted at an early stage, so that a power limitation of the electric drive machine can be avoided in most cases.

A drive torque signal is preferably filtered with a filter, in particular a low-pass filter, and the filtered drive torque signal is compared with the comparison value, in particular the driving resistance value. By filtering the drive torque using the filter, the signal can be smoothed in order to avoid a nervous switching on or off of the range extender when the incline increases or decreases briefly uphill.

In order to recognize when driving uphill, it can be checked, for example, whether the drive torque signal from the electric drive machine is greater than or greater than or equal to the comparison value, in particular the driving resistance value.

Preferably, however, a driving situation is not recognized as uphill driving and the internal combustion engine is then started if the comparison value is exceeded for a very short time, but rather a driving situation is only evaluated as uphill driving if the drive torque signal of the electric drive machine is greater than or greater than or equal to the comparison value for a predetermined period of time . In this case, the predetermined time period is preferably a continuous time period, preferably in the range from 10 seconds to 3 minutes, for example a time period of 40 seconds. In this period of time, the drive torque signal must then continuously meet the above criterion.

After the internal combustion engine has started, it is preferably checked whether the drive torque signal from the electric drive machine is no longer greater than or no longer greater than or equal to the comparison value. It is preferably provided here that a switch-off signal for switching off the internal combustion engine is only triggered after a predetermined second period of time has elapsed, after it has been determined that the drive torque signal of the electric drive machine is no longer greater than or greater than or equal to the comparison value. The switch-off signal is therefore delayed by the second period of time in order to cause the range extender to overrun. The background for the after-run is the delayed activation of the range extender due to any low-pass filtering and/or waiting for the first period of time.

The second time period is in the range from 10 seconds to 2 minutes, for example, the second time period is 40 seconds long. It is advantageous if the second period of time in corresponds approximately to the delay by waiting the first period of time. Provision can also be made for the second period of time to correspond approximately to the delay caused by any low-pass filter used and by waiting for the first period of time.

However, the range extender is preferably only started if the state of charge of the energy store is less than or less than or equal to a specific threshold value. In this case, it is not sufficient for starting the range extender that driving uphill is detected, but that the state of charge is actually less than or less than or equal to a specific threshold value. This threshold value SOC _TH,1 is preferably greater than another threshold value SOC _TH,2 , when it is reached or fallen below, the range extender is started anyway (ie even without detecting uphill driving), for example SOC _TH,1 =20% in comparison to SOC _TH,2 = 10%. Provision can therefore be made, for example, for the state of charge to be less than or less than or equal to the threshold value SOC _TH,1 in addition to the positive detection of the uphill driving situation in order to trigger the range extenders to start; in this case, the two criteria for activating the range extender are ANDed.

Alternatively, it can be provided that it is first checked that the state of charge of the energy store is less than or less than or equal to a specific threshold value and only after a positive check is the detection of the uphill situation started.

A second aspect of the invention relates to an alternative method for starting an internal combustion engine serving as a range extender in an electric vehicle. In this case, a rate of change of the state of charge of the electrical energy store is determined. The rate of change is preferably an instantaneous rate of change and can be determined, for example, by forming the gradient of the state of charge by differentiating the state of charge over time t. However, it would also be conceivable to use an average rate of change, which takes into account the change within the last 5 minutes, for example.

The internal combustion engine, which serves as a range extender, is then started as a function of the rate of change. If, for example, the rate of change shows that the state of charge of the energy storage device is rapidly decreasing (e.g. due to a sporty driving style with high driving speed or high acceleration or due to driving uphill), the range extender can be switched on immediately.

Preferably, not only the rate of change of the state of charge, but also the current value of the state of charge is taken into account when deciding whether to start the range extender. Depending on the state of charge and its rate of change over time, the range extender can be switched on as required.

It is advantageous if a characteristic field over the state of charge and the rate of change of the state of charge is used, which indicates whether the range extender should be started or not depending on the current state of charge and the rate of change.

A third aspect of the invention is directed to a control device for starting an internal combustion engine serving as a range extender in an electric vehicle. The control device is set up to carry out the method according to the first aspect of the invention and/or the method according to the second aspect of the invention.

The above statements on the method according to the invention according to the first and second aspect of the invention also apply in a corresponding manner to the control device according to the invention according to the third aspect of the invention.

• 1 eine beispielhafte Signalverarbeitung eines Ausführungsbeispiels für ein Verfahren nach dem ersten Aspekt der Erfindung;
• 2 Fahrwiderstandskennlinien bei verschiedenen Steigungen s;
• 3 beispielhafte Zeitverläufe der Antriebsmomentsignale M_EM,ist und M_EM,ist,f; und
• 4 ein beispielhaftes Kennfeld zum Aktivieren des Range-Extenders über dem Ladezustand SOC und dessen Gradienten ∂SOC/∂t gemäß dem zweiten Aspekt der Erfindung.

The invention is described below with the aid of the accompanying drawings based on two exemplary embodiments. In these show:

• 1 an exemplary signal processing of an embodiment of a method according to the first aspect of the invention;
• 2 Driving resistance characteristics at different gradients s;
• 3 exemplary time curves of the drive torque signals M _EM,actual and M _EM,actual,f ; and
• 4 an exemplary map for activating the range extender over the state of charge SOC and its gradient ∂SOC / ∂t according to the second aspect of the invention.

1 shows an exemplary signal processing of an embodiment of a method according to the first aspect of the invention. In this case, the current actual drive torque M _{EM,actual of the electric drive machine of the electric vehicle is} filtered in a low-pass filter F. The actual drive torque M _EM, act can be calculated as a function of the currents of the electric drive machine. Instead of the actual drive torque M _EM,actual, a target drive torque could also be used in the sense of a torque specification.

Furthermore, a driving resistance value M _FW at the current driving speed is calculated as a function of the current driving speed v from a driving resistance characteristic curve KL, which indicates the driving resistance over the driving speed v with an underlying incline (e.g. 7% incline uphill). The gradient used as a basis does not correspond to the actual gradient; the calculated driving resistance value M _FW serves as a kind of driving resistance threshold value. The driving resistance value M _FW and the drive torque M _{EM are} each a torque value.

The filtered drive torque signal M _EM,actual,f and the driving resistance value M _FW are compared. It is checked whether the filtered drive torque signal M _EM,ist,f is greater than the driving resistance value M _FW . If the drive torque signal M _{EM,actual,f is} greater than the driving resistance value M _FW , the binary comparison result signal vs corresponds to a logical 1. In block TOn, it is checked whether the binary comparison result signal vs after switching to 1 for a period of time Δt (e.g . Δt = 40 s) keeps this state. As soon as this is the case, the binary signal vs' switches from the value 0 to the value 1 at the output of the block TOn.

The edge change of the signal vs' from 0 to 1 is transferred essentially without delay to the signal b_e at the output of the block TOf; for an edge change from 0 to 1, the block TOf represents a through connection.

If the signal b_e switches to 1, driving uphill was detected. If the state of charge SOC of the energy store feeding the drive machine is less than or equal to a first threshold value SOC _TH,1 (e.g. SOC _TH,1 = 20%) and uphill travel has been detected (b_e = 1), the activation signal a switches after the AND operation AND to 1 and the range extender is started. The OR linkage causes the activation signal a to switch to 1 regardless of whether the vehicle is driving uphill and the range extender is started if the state of charge SOC is less than or equal to a second threshold value SOC _TH,2 (e.g. SOC _TH,2 = 5%). becomes.

The two threshold value comparisons with the state of charge SOC have a hysteresis function (not shown) in order to prevent the activation signal a from switching back and forth.

The delay block TOf is used to delay an edge change from 1 to 0 of the signal vs' in the signal b_e by the time period Δt. An edge change from 1 to 0 in signal vs′ indicates that filtered drive torque M _{EM,actual,f is} now no longer greater than driving resistance value M _FW . The signal b_e, which is used to control the range extender, but is delayed by the time period Δt, switches from 1 to 0 as a result of the delay block TOf, in order to cause the range extender to overrun. The reason for the lag is the delay in activating the range extender by the time Δt that is required until the signal vs' switches from 0 to 1 at the output of the block TOn.

In 2 Various exemplary driving resistance characteristics KL ₁ , KI ₂ , KL ₃ are shown schematically for three different predefined values s ₁ , s ₂ and s ₃ for the gradient s of the roadway over the driving speed v, for example with s ₁ = 0% gradient, s ₂ = 7% gradient and s ₃ > 7% gradient. The driving resistance includes, for example, the air resistance dependent on the driving speed v, the rolling resistance and the gradient resistance dependent on the incline s. For example, the characteristic curve KL ₂ with the underlying gradient s ₂ for detecting uphill travel in block KL in 1 used. A driving resistance value M _FW =M _FW,s2,vakt is determined for a current speed v=v _akt at the underlying gradient s ₂ .

An acceleration resistance is shown in the driving resistance characteristics in 1 and 2 not considered; it is therefore based on a constant speed v. Brief increases in the drive torque due to acceleration are filtered out by the low-pass filter F anyway. However, it would also be possible to 1 to consider the acceleration resistance by evaluating the current acceleration, for example by differentiating the driving speed v over time t.

In 3 An exemplary curve of the drive torque M _EM,actual and the filtered drive torque M _{EM,actual,f is} shown over time t. At time t = 0, the incline of the road increases and the drive torque M _EM,actual,f increases. At time t=t ₁ the drive torque M _EM,actual exceeds the driving resistance value M _FW,s2,vakt serving as a threshold value at the current speed and the underlying (but not current) roadway gradient s=s ₂ . The filtered drive torque M _EM,actualf exceeds the driving resistance value M _FW =M _FW,s2,vakt at time t=t ₂ and the comparison result signal vs switches to the value 1. From time t=t ₂ it is checked for the period Δt in block TOn whether the comparison result signal vs remains continuously at the value 1 and thus the filtered drive torque M _{EM,actual,f is} greater than the driving resistance value M _FW =M _{FW,s2 ,vakt} remains. If this is the case and the state of charge SOC is less than or equal to the threshold value SOC _TH,1 , the range extender is started.

4 shows an exemplary map of the state of charge SOC and the time gradient ∂SOC / ∂t of the state of charge SOC according to the second aspect of the invention, which indicates whether the range extender started depending on the current state of charge SOC and the gradient ∂SOC / ∂t should be or not. The map is divided into individual areas (see the dashed lines that delimit the individual areas) and each area is assigned a value of 1 or 0. The value 1 of a range indicates that the range extender should be started if the current state of charge SOC and the current gradient ∂SOC/∂t are within the respective range, and the value 0 indicates that the range extender should not be started if the current state of charge SOC and the current gradient ∂SOC/∂t are within the range. A hysteresis (not shown) is provided for switching off a range extender that is already switched on, in order to avoid switching back and forth.

For negative gradients ∂SOC/∂t of high magnitude, i. H. in the case of a sharply decreasing SOC, the range extender is already started at higher values of the state of charge SOC than in the case of negative gradients ∂SOC/∂t with a small magnitude or positive gradients ∂SOC/∂t.

Claims (12)

Method for starting an internal combustion engine serving as a range extender in an electric vehicle, the electric vehicle having - an electric drive machine for generating a drive torque for driving the motor vehicle, - an electric energy store for supplying the electric drive machine with electric energy, - the one serving as a range extender internal combustion engine and - a generator coupled to the internal combustion engine for generating electrical energy, with the steps: - detecting uphill driving by - a speed-dependent comparison value (M _FW , M _FW,s2,vakt ) depending on the current vehicle speed (v, v _act ) is determined, and - a drive torque signal (M _EM,actual,f ) corresponding to the current actual drive torque or the target drive torque of the electric drive machine after filtering the drive torque signal or without filtering the drive torque signal with the comparison serving as a threshold value value (M _FW , M _FW.s2,vakt ) is compared; and - starting the internal combustion engine after recognizing the uphill drive. procedure after claim 1 , wherein the speed-dependent comparison value (M _FW , M _FW,s2,vakt ) serving as a threshold value is a speed-dependent driving resistance value for an underlying incline of the roadway, the incline being in the range of 2-15% in particular. Method according to one of the preceding claims, wherein a drive torque signal (M _EM, actual ) is filtered with a filter (F), in particular a low-pass filter, and the filtered drive torque signal (M _{EM,actual, f} ) with the comparison value (M _FW , M _FW,s2,vakt ) is compared. Method according to one of the preceding claims, wherein, to detect uphill driving, it is checked whether the drive torque signal (M _{EM,actual,f ) of the electric drive machine is} greater than or greater than or equal to the comparison value (M _FW , M _FW,s2,vakt ). procedure after claim 4 , wherein to detect uphill driving, it is checked whether the drive torque signal (M _{EM,actual,f) of the electric drive machine is} greater than or greater than or equal to the comparison value (M _FW , M _FW,s2,vakt ) for a predetermined first period of time (Δt). , and in the event that the drive torque signal (M _EM,actual,f ) of the electric drive machine is greater than or greater than or equal to the comparison value (M _FW , M _FW,s2,vakt ) for the predetermined first period of time (Δt), the combustion engine is started. procedure after claim 5 After starting the internal combustion engine, it is checked whether the drive torque signal (M _{EM,actual,f) of the electric drive machine is} no longer greater than or greater than or equal to the comparison value (M _FW , MFw,s2,vakt), and a switch-off signal to switch off the internal combustion engine after a predetermined second period of time (Δt) has elapsed, after it has been determined that the drive torque signal (M _{EM,actual,f) of the electric drive machine is} no longer greater than or greater than or equal to the comparison value (M _FW , M _FW,s2,vakt ) is, is triggered. Method according to one of the preceding claims, in which the internal combustion engine is only started when driving uphill if the state of charge (SOC) of the energy store is less than or less than a specific threshold value (SOC _TH,1 ). Method for starting an internal combustion engine serving as a range extender in an electric vehicle, the electric vehicle - an electric drive unit for generating a drive torque for driving the motor vehicle, - an electrical energy store for supplying the electric drive unit with electrical energy, - the internal combustion engine serving as a range extender and - a generator coupled to the internal combustion engine for generating electrical energy, with the Steps: - determining a rate of change (∂SOC/∂t) of the state of charge (SOC) of the electrical energy store; and - starting the internal combustion engine depending on the rate of change (∂SOC/∂t). procedure after claim 8 , the starting of the internal combustion engine being dependent on - the state of charge (SOC) of the electrical energy store and - the rate of change (∂SOC/∂t) of the state of charge (SOC). procedure after claim 9 , whereby a map of the state of charge and the rate of change of the state of charge is used, which indicates whether the range extender should be started depending on the current state of charge (SOC) and the rate of change (∂SOC/∂t). Procedure according to one of Claims 8 - 10 , where the rate of change (∂SOC/∂t) corresponds to the time gradient of the state of charge (SOC). Control device for starting an internal combustion engine serving as a range extender in an electric vehicle, wherein the control device is set up to carry out the method according to one of the preceding claims.

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