KR100461273B1 - Method of determining performance index of fuel consumption for a hybrid electric vehicle - Google Patents

Abstract

Disclosed is a method for determining fuel economy performance index of a hybrid electric vehicle. The method for determining a fuel economy performance index of the disclosed hybrid electric vehicle includes: (a) setting an SOC lower limit criterion (con_lo_soc) and an SOC upper limit criterion (con_hi_soc) of the hybrid electric vehicle battery; (b) A coefficient (a_charge, b_charge / a_discharge, b_discharge) determined by a minimum value (best E-BSFC) and a maximum value (worst E-BSFC) for the brake fuel consumption rate of the hybrid electric vehicle engine according to charging or discharging is calculated. Setting; (c) setting a slope according to a predefined control algorithm; (d) determining whether the electric system of the hybrid electric vehicle has been charged; (e) When the condition in step (d) is satisfied, the charging function equation of the brake fuel consumption rate of the hybrid electric vehicle engine for SOC is obtained by the following equation (1).

[Equation 1]

Description

METHOD OF DETERMINING PERFORMANCE INDEX OF FUEL CONSUMPTION FOR A HYBRID ELECTRIC VEHICLE}

The present invention relates to a method for determining a fuel efficiency index of a hybrid electric vehicle, and more particularly, to a method for determining a fuel efficiency index of a hybrid electric vehicle for facilitating the charging level of a battery while driving an electric vehicle.

As shown in FIG. 1, when a shift map or a driving algorithm for minimizing fuel economy in a general internal combustion engine vehicle, an engine fuel consumption is determined as an objective function and an algorithm for minimizing the fuel consumption is generally used.

However, as shown in FIG. 2, the hybrid electric vehicle uses two energy sources, such as fuel and electric energy, and thus, it is impossible to minimize fuel economy of the entire vehicle based solely on the fuel consumption of the engine.

In addition, when only the fuel consumption is used as the objective function, the driving of the vehicle proceeds in the direction of maximizing the electric energy consumption. In this case, there is a problem in that the battery is discharged in the end without providing a separate charging algorithm or a discharge restriction condition.

In addition, since hybrid electric vehicles use two energy sources, fuel and electric energy, in order to develop a driving strategy that minimizes the fuel consumption of the entire vehicle, the fuel economy performance index that can be expressed as one index (hereinafter, Performance index).

The method of determining performance index by preparing fuel efficiency minimization algorithm of hybrid electric vehicle is well known as follows.

First, the fuel consumption of the engine is determined as a figure of merit and a minimum algorithm is applied. When the battery charge level is low, only the engine is charged using the engine power when driving or stopping.

Second, the fuel consumption of the engine is determined as a figure of merit and a minimum algorithm is applied. When the battery charge level falls below a certain level, the engine is charged while driving.

Third, the consumption of electrical energy is defined as equivalent fuel consumption, or conversely, the fuel consumption of the engine is expressed as equivalent electrical energy consumption, and the equivalent index is added to the fuel consumption of the engine or the electrical energy consumption of the motor, and the performance of the entire vehicle. Determine by index and finally create a driving strategy to minimize this figure of merit.

The first method described above has been adopted by the present applicant, but the battery may discharge below a dangerous level while driving, and since the strategy for charging is not defined, it is possible to minimize the actual vehicle fuel consumption considering the energy consumption of the electrical system. none.

The second method is adopted by HONDA in Japan, but since the output of the motor is determined solely by the driver's accelerator opening, it is not guaranteed that discharge and charging will actually be directed at improving the overall efficiency of the system.

In addition, the third method is the equivalent fuel economy concept, also known as the NREL method proposed by the US RICARDO and NREL (National Renewable Energy Lab.), But the battery charge level is not included in the determination of the performance index. The charging algorithm of must be included.

In the third method, the battery charging level is taken into consideration, but there is a disadvantage in that only the driving strategy applicable to the driving mode tested after the test driving in the specific driving mode is presented.

The present invention was created in order to solve the above problems, and in the determination of the performance index of the hybrid electric vehicle defined by the equivalent fuel efficiency concept (NREL method), instead of the conventional index of performance index determination by the stochastic method, the charge level of the battery Using the optimization technique to determine the performance index using the optimization technique to determine the fuel economy performance index of hybrid electric vehicles, which makes it possible to maintain the charging level while driving alone and to minimize the actual fuel consumption of the entire vehicle. The purpose is to provide a method.

1 is a view showing for explaining the fuel consumption of a typical internal combustion engine vehicle.

2 is a view showing for explaining the fuel consumption of a typical hybrid electric vehicle.

3 is a schematic flowchart sequentially showing a method for determining a fuel economy performance index of a hybrid electric vehicle according to the present invention.

4A and 4B are graphs showing changes in E-BSFC values for battery SOC changes during charging and discharging.

5A and 5B are graphs showing the distribution of E-BSFC values during charging and discharging.

Figure 6 is a graph showing the fuel efficiency performance analysis results of a vehicle to which the prior art is applied.

Figure 7 is a graph showing the fuel efficiency analysis results of the vehicle to which the present invention is applied.

In order to achieve the above object, there is provided a method for determining a fuel economy performance index of a hybrid electric vehicle according to the present invention, including: (a) setting an SOC lower limit standard (con_lo_soc) and an SOC upper limit standard (con_hi_soc) of a hybrid electric vehicle battery; (b) A coefficient (a_charge, b_charge / a_discharge, b_discharge) determined by a minimum value (best E-BSFC) and a maximum value (worst E-BSFC) for the brake fuel consumption rate of the hybrid electric vehicle engine according to charging or discharging is calculated. Setting; (c) setting a slope according to a predefined control algorithm; (d) determining whether the electric system of the hybrid electric vehicle has been charged; (e) When the condition in step (d) is satisfied, the charging function equation of the brake fuel consumption rate of the hybrid electric vehicle engine for SOC is obtained by the following equation (1).

[Equation 1]

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a schematic flowchart sequentially showing a method for determining a fuel efficiency performance index of a hybrid electric vehicle according to the present invention.

Here, description of the fuel economy performance index determination method of the general hybrid electric vehicle will be omitted, and only the features of the present invention will be described.

Referring to the drawings, the method for determining the fuel economy performance index of the hybrid electric vehicle according to the present invention, first, according to the characteristics or characteristics of the hybrid electric vehicle battery SOC (State Of Charge) lower limit (con_lo_soc) and SOC upper limit criteria (con_hi_soc) is set. (Step 110) In particular, as described below, when the battery use area is determined in consideration of battery life and capacity, con_lo_soc and con_hi_soc values are designated by this. Generally, SOC is set to 0. When fully discharged or fully charged to 1, the battery system may be physically damaged, so the manufacturer of the battery system recommends that it be limited to a certain level. That is, if the battery usage area is limited to SOC 0.4 to 0.7, the above con_lo_soc is 0.4 and con_hi_soc is 0.7. In designing the battery controller, the battery use area may be limited to a smaller area in consideration of battery efficiency. For example, since the battery efficiency is high, the minimum value (best E-BSFC) and the maximum for the brake specific fuel consumption (hereinafter referred to as BSFC) of the hybrid electric vehicle engine according to charging or discharging. A coefficient (a_charge, b_charge / a_discharge, b_discharge) determined by the value (worst E-BSFC) is set. (Step 120) The BSFC will be described in detail, and this BSFC is a value for defining engine efficiency. In other words, it is a coefficient indicating how much fuel is consumed to generate unit power. The smaller this value is, the more efficient the engine is. The engine has different BSFC values depending on the operating conditions, for example, engine speed and engine torque, and the BFC concept of internal combustion engine cars used exclusively for the engine with equivalent Brake Specific Fuel Consumption (E-BSFC). As a concept for applying to a hybrid electric vehicle using a motor at the same time as shown in Equation 1 to be described later. In addition, the concept of E-BSFC takes into account both electric energy and fuel during charging / discharging of a hybrid electric vehicle, which will be described in detail below. First, unlike BSFC, E-BSFC has an equivalent concept of electric energy and fuel. Therefore, it is calculated differently during charging and discharging. Therefore, two values, E-BSFCcharge and E-BSFCdischarge, are required, and since E-BSFC is a concept of estimating the equivalent amount of fuel converted into electrical energy, the value varies depending on how high is the possibility of charging or discharging at present. It uses the state of charge (SOC) of the battery as an indicator for evaluating the possibility of charging or discharging. Conceptually, this is the same as Equation 3, which will be described later. Then, a slope is set according to a predefined control algorithm (step 130).

In addition, it is determined whether the electric system of the hybrid electric vehicle needs to be charged (step 140). Here, whether the electric system is charged or not is determined according to a control signal from a hybrid control unit (HCU).

When the condition at step 140 is satisfied, the charge function equation of the brake fuel consumption rate of the hybrid electric vehicle engine for the SOC is obtained by the following equation (step 150).

[Equation 1]

In Equation 1, E-BSFC_charge (SOC) is the equivalent BSFC of the motor predicted based on the current battery (SOC) at the time of charging, and con_lo_soc is the lower limit of the battery charge level determined according to the battery system specification. .

On the other hand, if the condition in step 140 is not satisfied, the discharge function equation of the brake fuel consumption rate of the hybrid electric vehicle engine for the SOC is obtained as shown in Equation 2 below (step 170).

In Equation 2, E-BSFC_discharge (SOC) is the equivalent BSFC of the motor predicted based on the current battery (SOC) at the time of discharge, and con_lo_soc is the lower limit value of the battery charge level determined according to the battery system specification. In particular, on_lo_soc described above in Equations 1 and 2 is a lower limit of the battery charge level determined according to the battery system specification.

And the coefficient of brake fuel consumption rate of the engine is made as shown in Equation 3 below.

[Equation 3] E-BSFC = f (SOC, con_lo_soc, con_hi_soc, Best E-BSFC, worst E-BSFC) The above Equation 3 is described in more detail, that is, the current battery charge level (SOC) and battery And lower and upper battery allowable charge levels (con_lo_soc, con_hi_soc), the best value of E-BSFC, and the best value of E-BSFC (worst E-BSFC), which are variables determined by the battery controller designer. This means that the E-BSFC is not determined by one value, but by a number of values depending on the operating area of the engine and motor, of which the value is calculated by the controller. Is determined according to the SOC of the vehicle battery, and the best E-BSFC means the best value (minimum value) of the calculated E-BSFC values, and the worst E-BSFC is the most among the calculated E-BSFC values. Bad value (maximum value) means minimum / maximum value (best / worst E-BSFC) The efficiency characteristics of the engine / motor used in the vehicle are determined as described above and below. Further, steps 150 and 170 are performed, and the brake fuel consumption rate of the engine for the charge and discharge is printed, respectively. (Step 160)

As described above, the method for determining the fuel economy performance index of the hybrid electric vehicle according to the present invention is the performance by the conventional probabilistic method in determining the performance index of the hybrid vehicle defined by the equivalent fuel economy concept (NREL method) described above. Instead of making exponential determinations, we use an optimization technique to determine the figure of merit by using the battery charge level as a factor in determining the figure of merit.

Thus, it is possible to maintain the charging level while driving and to minimize the fuel consumption of the entire vehicle with the driving algorithm alone.

As described above, in the energy flow in the hybrid vehicle of FIG. 2, the direction of the arrow means the flow of power, and the discharge state because the energy flows toward the transmission in the electric motor. In contrast, when charging, the direction of the arrow points toward the motor. In this case, the engine fuel consumption FC_e is defined as in Equation 4 below.

[Equation 4]

FC_e = BSFC (We, Te) X Pe

Where We is the engine operating speed, Te is the engine output torque, and Pe is the engine output horsepower.

The equivalent fuel consumption FC_m in the electric motor is defined as in Equation 5 below.

[Equation 5]

FC_m = E-BSFC (Wm, Tm) X Pm

In addition, the fuel consumption (FC) of the entire vehicle is defined as shown in Equation 6 below.

[Equation 6]

FC = FC_e + FC_m

Meanwhile, in Equation 5, E-BSFC is a coefficient for converting electric energy into equivalent fuel consumption in a hybrid vehicle, and is determined as Equations 7 and 8 below according to the vehicle system during discharging and charging.

[Equation 7]

E-BSFC_discharge = 1 / EF_md_p X 1 / EF_bd_p X 1 / EF_mc_l X 1 / EF_bc_l X BSFC_l

[Equation 8]

E-BSFC_charge = EF_mc_p X EF_bc_p X EF_md_l X EF_bd_l X BSFC_l

Here, E-BSFC_charge is E-BSFC in the charged state,

E-BSFC_discharge is E-BSFC in discharge state,

EF_md_p is the motor discharge efficiency at the time of calculation,

EF_mc_p is the motor charging efficiency at the time of calculation,

EF_md_l is the motor discharge efficiency at the later discharge time,

EF_mc_p is the motor charging efficiency at a later charging time,

EF_bd_p is the battery discharge efficiency at the time of calculation,

EF_bc_p is the battery charging efficiency at the time of calculation,

EF_bd_l is the battery discharge efficiency at the later discharge time,

EF_bc_p is the battery charging efficiency at a later charging time.

Since the BSFC values of the motor, the battery efficiency, and the engine are determined by the operating conditions of the power source, Equations 7 and 8 described above can be summarized as a function of Equation 9 below.

[Equation 9]

E-BSFC = f (Te, We, Tm, Wm)

In other words, the E-BSFC is a value determined by the operating point of the power source at the time of the present calculation and the subsequent charging or discharging.

Here, the values at the time of calculation may be obtained by the operating conditions of the engine or the motor, but the values at the later charging and discharging time cannot be determined at the present time, so to estimate the E-BSFC coefficient at the present operating conditions. There is a need for a separate estimation algorithm.

Therefore, in the present invention, as shown in FIG. 3, a control for estimating the E-BSFC coefficient is configured based on the battery charge level.

First, the discharge time will be described.

If the current battery charge level is high, there is a high possibility of recovering the electric energy consumed at the present time in a place where charging efficiency is high. That is, setting the E-BSFC value low increases the use of electrical energy and induces the engine to operate at high efficiency points.

On the other hand, if the current battery charge level is low, the electrical energy consumed at this time should be recovered soon, so it is more likely to recover at a later low charging efficiency. In other words, high E-BSFC values reduce electrical energy usage and induce the electrical system to operate at high efficiency.

The charging time is as follows.

If the current battery charge level is low, charging is induced by setting a high E-BSFC value. On the other hand, if the current battery charge level is high, the charge amount is reduced by measuring the E-BSFC value low.

Here, the electric power of the motor at the time of discharge is positive and the electric power of the motor at the time of charging is calculated as negative. Poetry is reversed.

As described above, the E-BSFC coefficient is expressed as in Equation 3 above.

That is, later operating conditions Te, We, Tm, and Wm are determined by SOC, con_lo_soc, con_hi_soc, best E-BSFC, and wort E-BSFCs, which are the current state of charge of the battery and the battery usage limit coefficient.

And define E-BSFC function for SOC as follows.

The E-BSFC function for the SOC must be defined to implement the above definition. However, such a function can not be universally determined in the form of a function that guarantees optimum fuel efficiency unless a specific driving pattern is specified.

That is, a function form optimized for one driving pattern may show poor results for another driving pattern. Therefore, the form of the function is defined as the most general form of function while satisfying the above definition.

Particularly, in the present invention, the Log-Sigmode function is used. The characteristics of the Log-Sigmode function allow the engine to operate in an area with good engine efficiency until the SOC decreases below a certain level, and when the SOC falls below a certain level. As the E-BSFC coefficient is adjusted rapidly for charging, the result is better than that of the general linear function.

Therefore, the E-BSFC function for SOC is defined as equation (1) and (2). In Equations 1 and 2, the coefficients of a_charge, b_charge, a_discharge, b_discharge, etc. are determined by the best E-BSFC and worst E-BSFC values. A process of obtaining the values of a, discharge, and b_discharge will be described in detail as follows. As described above, Equation 1 causes the E-BSFC_charge to have the worst E-BSFC_charge value when the SOC becomes the con_lo_soc value. Also, when SOC becomes con_hi_soc value, E-BSFC_charge has the best E-BSFC_charge value. From the above, a_charge and b_charge can be determined, and Equation 2 allows the E-BSFC_discharge to have the worst E-BSFC_discharge value when the SOC becomes the con_lo_soc value. Also, when the SOC becomes the con_hi_soc value, the E-BSFC_discharge has the best E-BSFC_discharge value. In this case, a_discharge and b_discharge may be determined. Referring to the graphs of FIGS. 4A and 4B, the SOC is output from a battery management system (BMS). The method of obtaining the slope coefficient is described in detail as follows. Hybrid electric vehicles have a large operating condition depending on the combination of the engine / motor and its driving mode, and are also affected by fuel efficiency. Therefore, a coefficient that can adjust / tune the performance according to the engine / motor combination and its driving mode is required. In the present invention, a slope coefficient is introduced. The PI_charge and PI_discharge coefficients representing the performance of the hybrid vehicle are finally included in the slope ( Only the slope coefficient remains undetermined, which is a tuning parameter determined through optimization in test / simulation on the driving mode, which is the target of optimizing the performance of the hybrid vehicle, i.e., slope through repeated tests or simulations. The PI_charge and PI_discharge coefficients are determined as the final group by determining the optimal value.) At this time, the optimization technique used as a means of determining the slope coefficient can apply an optimization technique already known, such as DOE and SQP. .

In addition, the determination of the best E-BSFC and the worst E-BSFC in Equations 1 and 2 is carried out as follows.

The best E-BSFC and the worst E-BSFC are obtained by calculating the coefficients of all possible E-BSFCs in the operating area of power sources such as engines and motors, and then taking the minimum and maximum values among the values within the distribution of 95% by probability distribution.

5A and 5B show graphs showing the distribution of E-BSFC values.

Determining con_lo_soc and con_hi_soc determines the battery usage area in consideration of battery life and capacity, thereby assigning con_lo_soc and con_hi_soc values. This value is determined by the specifications of the battery and the battery controller (SPEC). [0029] Meanwhile, 6 is a graph showing fuel efficiency analysis simulation results in a vehicle employing a conventional technology, and FIG. 7 is compared with FIG. As a result, it shows a graph showing the fuel efficiency performance analysis results of the vehicle to which the performance index determination method of the present invention is applied.

As shown, a vehicle to which the prior art is applied does not maintain the battery charge level well while driving.

In contrast, the vehicle using the performance index of the present invention maintains the level of charge while driving within a certain range. In addition, since the coefficient of the E-BSFC is determined to improve the fuel economy of the engine even during discharge, it can be seen that the fuel economy of the vehicle is also improved.

As described above, the method for determining the fuel economy performance index of the hybrid electric vehicle according to the present invention has an effect of easily charging the battery while driving the hybrid vehicle and improving fuel economy of the vehicle.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent embodiments are possible. Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

Claims (3)

(a) setting an SOC lower limit criterion (con_lo_soc) and an SOC upper limit criterion (con_hi_soc) of the hybrid electric vehicle battery; (b) A coefficient (a_charge, b_charge / a_discharge, b_discharge) determined by a minimum value (best E-BSFC) and a maximum value (worst E-BSFC) for the brake fuel consumption rate of the hybrid electric vehicle engine according to charging or discharging is calculated. Setting; (c) setting a slope according to a predefined control algorithm; (d) determining whether the electric system of the hybrid electric vehicle has been charged; (e) When the condition in step (d) is satisfied, the fuel economy performance index of the hybrid electric vehicle is characterized by obtaining the charging function equation of the brake fuel consumption rate of the hybrid electric vehicle engine for the SOC by Equation 1 below. How to decide. [Equation 1] In Equation 1, the E-BSFC_charge (SOC), the equivalent BSFC of the motor predicted based on the current battery (SOC) at the time of charging, And con_lo_soc is the lower limit of the battery charge level determined by the battery system specification. The method of claim 1, If the condition in step (d) is not satisfied, the fuel economy performance index determination method of the hybrid electric vehicle, characterized in that to obtain the discharge function equation of the brake fuel consumption rate of the hybrid electric vehicle engine for SOC as . [Equation 2] In Equation 2, the E-BSFC_discharge (SOC) is the equivalent BSFC of the motor predicted based on the current battery (SOC) at the time of discharge, And con_lo_soc is the lower limit of the battery charge level determined by the battery system specification. The method of claim 1, The coefficient of brake fuel consumption rate of the engine is a fuel economy performance index determination method of the hybrid electric vehicle, characterized in that made as shown in Equation 3. [Equation 3] E-BSFC = f (SOC, con_lo_soc, con_hi_soc, best E-BSFC, worst E-BSFC)