WO2010082112A1

WO2010082112A1 - Electric power generation control apparatus

Info

Publication number: WO2010082112A1
Application number: PCT/IB2010/000044
Authority: WO
Inventors: Kayuma Takahashi; Yoichiro Nakahara; Ryo Mochizuki
Original assignee: Nissan Motor Co., Ltd
Priority date: 2009-01-14
Filing date: 2010-01-12
Publication date: 2010-07-22
Also published as: JP2010166663A; JP5277976B2

Abstract

An electricity generation control apparatus is provided with an electric generator (2), a battery (5), a battery condition detecting device (7) and an electric generator output voltage control device (7). The electric generator (2) is configured to generate electricity by being driven by an internal combustion engine (1). The battery (5) stores electricity generated by the electric generator (2). The battery condition detecting device (7) detects a battery condition of the battery (5). The electric generator output voltage control device (7) controls an output voltage of the electric generator (2) to a target output voltage in accordance with an allowable deceleration rate and a battery condition detected by the battery condition detecting device (7) during vehicle deceleration with the electric generator (2) is being driven.

Description

ELECTRIC POWER GENERATION CONTROL APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2009- 005620, filed on January 14, 2009. The entire disclosure of Japanese Patent Application No. 2009-005620 is hereby incorporated herein by reference.

BACKGROUND Field of the Invention

[0002] The present invention generally relates to an electricity generation control apparatus for a vehicle. More specifically, the present invention relates to an electricity generation control apparatus that controls an output voltage of an electric generator during vehicle deceleration. Backgroundinformation

[0003] Vehicles have various electrical components that run on electricity. Accordingly, various electricity generation control apparatus have been proposed for vehicles. For example, Japanese Laid-Open Patent Publication No. 2003-214248 and Japanese Laid-Open Patent Publication No. 2004-120877 both discloses an electricity generation control apparatus that operates a generator to charge a battery. The electricity generation control apparatus disclosed in Japanese Laid-Open Patent Publication No. 2003-214248 charges the battery during a fuel cut operation. The electricity generation control apparatus disclosed in Japanese Laid-Open Patent Publication No. 2004-120877 controls the output voltage of an electric generator based on an allowable deceleration rate.

SUMMARY

[0004] It has been discovered that with the electricity generation control apparatus presented in Japanese Laid-Open Patent Publication No. 2003-214248, there are times when an electric power generating torque of the electric generator becomes too large during deceleration of the vehicle and the deceleration rate increases, thereby degrading the drivability of the vehicle.

[0005] In view of this problem of the drivability degradation problem mentioned above, one object of the present invention is to curb an occurrence of such a drivability degradation during deceleration. [0006] According to one aspect, an electricity generation control apparatus is provided with an electric generator, a battery, a battery condition detecting device and an electric generator output voltage control device. The electric generator is configured to generate electricity by being driven by an internal combustion engine. The battery stores electricity generated by the electric generator. The battery condition detecting device detects a battery condition of the battery. The electric generator output voltage control device controls an output voltage of the electric generator to a target output voltage in accordance with an allowable deceleration rate and a battery condition detected by the battery condition detecting device during vehicle deceleration with the electric generator is being driven.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Referring now to the attached drawings which form a part of this original disclosure:

[0008] Figure 1 is a schematic system diagram showing an electricity generation control apparatus for a vehicle;

[0009] Figure 2 is a flowchart explaining an electricity generation control; [0010] Figure 3 shows plots of a battery charging current versus a battery fluid temperature for different alternator output voltages;

[0011] Figure 4 is a plot illustrating how a battery charging current differs depending on whether or not a concentration polarization exists;

[0012] Figure 5 illustrates a method of calculating a target alternator output current; [0013] Figure 6 is a time chart explaining the operations the electricity generation control; and

[0014] Figure 7 is a time chart explaining a problem of a conventional electricity generation control.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS [0015] Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. [0016] Referring initially to Figure 1, an electricity generation control apparatus for a vehicle is schematically illustrated in accordance with one embodiment. The vehicle electricity generation control apparatus mainly includes an internal combustion engine 1 , an alternator 2 constituting an electric generator, a voltage regulator 3, an electrical load 4, a battery 5, a current sensor 6 and a controller 7. With the illustrated electricity generation control apparatus, an occurrence of a situation in which an electric generator output current exceeding an allowable value is supplied to the battery 5 can be avoided by controlling the output voltage of the electric generator (alternator 2) in accordance with a battery condition. As a result, the vehicle can be prevented from decelerating at a rate exceeding an allowable deceleration rate and the drivability of the vehicle can be improved from the perspective of a driver.

[0017] The engine 1 generates power for driving the vehicle and various auxiliary machines of the vehicle. The alternator 2 is driven by the engine 1 and serves to generate electricity. The voltage regulator 3 is built into the alternator 2 and serves to control a generated output voltage of the alternator 2 to a prescribed target output voltage. The voltage regulator 3 acts to increase a field current and raise the output voltage of the alternator 2 when the output voltage is lower than the target output voltage. The voltage regulator 3 acts to decrease the field current and lower the output voltage of the alternator 2 when the output voltage is higher than the target output voltage.

[0018J The electrical load 4 is an electrical component installed in the vehicle, such as a headlight or a blower fan of an air conditioning system. The electrical load 4 consumes electric power generated by the alternator 2 and, if necessary, electric power stored in the battery 5. The electric power consumption of the electrical load 4 is calculated by the controller 7 based on an on-off signal of the electrical component.

[0019] The battery 5 serves both to store electricity and to supply the stored electricity to the electrical load 4 as necessary. A positive terminal of the battery 5 is connected to the alternator 2 and the electrical load 4 and a negative terminal of the battery 5 is connected to ground. The current sensor 6 is connected to the negative terminal of the battery 5 and serves to detect a charging current supplied to the battery 5 from the alternator 2 and a discharge current supplied from the battery 5 to the electrical load 4. [0020] The controller 7 comprises a microcomputer equipped with a central processing unit (CPU), a read only member (ROM), a random access memory (RAM), and an input/output interface (I/O interface). The controller 7 receives a signal from the current sensor 6 and signals from various other sensors serving to detect operating conditions of the engine 1.

[0021] When a fuel supply to the engine 1 is cut during deceleration of the vehicle, the engine 1 is rotated by rotation transmitted from the wheels of the vehicle. During deceleration of the vehicle, the controller 7 sets the target output voltage of the alternator 2 to a maximum output voltage (14.5 volts) of the alternator 2 and emphasizes charging the battery 5. As a result, an amount by which the engine load increases due to driving the alternator 2 is suppressed and the fuel efficiency of the engine 1 is improved. [0022] However, the size of a rotary torque (hereinafter called "electric power generating torque") inputted to the alternator 2 in order to generate electricity depends on the amount of electric power generated. A peak value of the electric power generating torque occurs immediately after the alternator 2 starts generating electricity, and the larger the peak value is, i.e., the larger the amount of electric power generated is, the greater the degree to which the engine rotational speed will decline. Consequently, when a demand for a large amount of electric power occurs while the vehicle is decelerating, the deceleration rate increases and the drivability is degraded, causing a driver and/or a passenger to experience a feeling that there is something odd about the vehicle. [0023] Figure 7 is a time chart explaining the problem of an increased deceleration rate occurring when a conventional electricity generation control is used. As shown in Figure 7, at a time tl 1, the vehicle starts decelerating and the target output voltage of the alternator 2 is set to a maximum output voltage (14.5 V). Immediately afterward, the electric power generating torque goes to a peak value and the deceleration rate exceeds an allowable deceleration rate. As a result, a driver or passenger experiences a feeling that something is odd about the vehicle.

[0024] Meanwhile, an electricity generation control according to this embodiment serves to curb the occurrence of such a degradation of drivability and improve the fuel efficiency of the vehicle. [0025] Figure 2 is a flowchart explaining an electricity generation control according to this embodiment. The controller 7 executes this routine once per prescribed control cycle

(e.g., 10 ms) while the engine 1 is running.

[0026] In step Sl, the controller 7 determines if the engine 1 is being operated in a fuel cut state. Fuel cut refers to the situation in which the injection of fuel to the cylinders is stopped. The fuel cut is executed when, for example, the vehicle speed is above a prescribed speed or the vehicle is decelerated from the engine rotational speed due to engine braking. If a fuel cut is being executed, the controller 7 proceeds to step S2.

Meanwhile, if a fuel cut is not being executed, the controller 7 ends the control routine for the current cycle.

[0027] In step S2, the controller 7 calculates an allowable deceleration rate based on a vehicle speed. The allowable deceleration rate is calculated to be larger when the vehicle speed is higher.

[0028] In step S3, the controller 7 calculates an allowable output current of the alternator 2 (hereinafter called "alternator allowable output current") for each output voltage based on the allowable deceleration rate.

[0029] In step S4, the controller 7 calculates a portion of the alternator allowable output current that will flow to the battery (hereinafter called "allowable battery charging current") for each output voltage. More specifically, the allowable battery charging current is calculated by subtracting a vehicle consumption current, i.e., the current being consumed by the electrical load, from the alternator allowable output current.

[0030] In step S5, the controller 7 detects the battery conditions of the battery 5. The battery conditions are detected because a battery charging current, described later, changes depending on the battery conditions. The detected battery conditions include a battery state of charge (SOC), a battery temperature, and a determination as to whether or not a concentration polarization of an electrolyte fluid exists in the battery 7.

[0031] In step S6, the controller 7 calculates a maximum output current that will be supplied to the battery 5 (hereinafter called "battery charging current") for each output voltage of the alternator 2 in accordance with a battery condition. Since the maximum output current of the alternator 2 is determined based on the output voltage, the controller 7 calculates the battery charging current by subtracting an amount of electric current currently being consumed by the vehicle from the maximum output current corresponding to each output voltage. The battery charging current increases as the state of charge decreases and as the battery fluid temperature increases. Also, the battery charging current is larger when a concentration polarization does not exist.

[0032] In step S7, the controller 7 calculates a target output voltage of the alternator 2 based on the allowable battery charging current and the battery charging current. The method of calculating is explained in more detail later with reference to Figure 5. [0033] In step S8, the controller 7 controls the output voltage of the alternator 2 to the target output voltage using a feedback control scheme.

[0034] Figure 3 shows plots of battery charging current versus battery fluid temperature for different alternator output voltages. As shown in Figure 3, the higher the battery fluid temperature is, the larger the battery charging current becomes. [0035] Figure 4 is a plot illustrating how a battery charging current differs depending on whether or not a concentration polarization exists, hi Figure 4, the solid-line curve indicates the battery charging current and the broken-line curve indicates the alternator output voltage. As shown in Figure 4, the battery charging current is higher at a time t21 when there is no concentration polarization than at a time t22 when charging stops or a later time t23 when charging starts and a concentration polarization still remains. [0036] Figure 5 illustrates a method of calculating a target alternator output current. In Figure 5, the broken-line curves indicates battery charging current values calculated for each alternator output voltage (first relationship) and the solid-line curve indicates allowable battery charging current values calculated for each alternator output voltage (second relationship). The battery charging current is plotted for a case in which the battery fluid temperature is 0°C and for a case in which the battery fluid temperature is 25°C. Ln both cases, it is assumed that the state of charge is at a prescribed level and a concentration polarization does not exist. As can be seen by arrow A in Figure 5, the battery charging current increases as the battery fluid temperature increases. [0037] A method of calculating the target output voltage when the battery fluid temperature is 0°C, i.e., when the allowable battery charging current is larger than the battery charging current across the entire range of output voltages, will now be explained. [0038] When the battery fluid temperature is 0°C, the battery charging current will be smaller than the allowable battery charging current even if the target output voltage of the alternator 2 is set to the maximum voltage (14.5 V). Consequently, a current exceeding the allowable battery charging current will not flow to the battery 5 and the deceleration rate will not exceed the allowable deceleration rate. Therefore, the controller 7 sets the target output voltage of the alternator 2 to the maximum voltage. [0039] Next, a method of calculating the target output voltage when the battery fluid temperature is 25°C, i.e., when there is a region in which the allowable battery charging current is smaller than the battery charging current, will be explained. In such a case, the target output voltage is set to a value corresponding to an intersection point between the allowable battery charging current and the battery charging current. This method sets the target output voltage to the largest possible value at which the battery 5 can be charged without the deceleration rate exceeding the allowable deceleration rate. As can be seen by arrow B in Figure 5, the target output voltage decreases as the battery fluid temperature increases if the allowable battery charging current is smaller than the battery charging current. In other words, the higher the temperature of the electrolyte fluid of the battery 5 is, the smaller the value to which the target output voltage is set. When the alternator allowable output current is smaller than the battery charging current across the entire range of output voltages, the target output voltage of the alternator 2 is set to a minimum voltage (12 V).

[0040] Figure 6 is a flowchart explaining the operations of an electricity generation control according to this embodiment. Step numbers are provided to clarify the correspondence between the flowchart and the explanation.

[0041] At a time tl, the vehicle starts decelerating and a fuel cut is executed (graph (A) of Figure 6 - step Sl with the result of step Sl being Yes). The controller 7 calculates an allowable deceleration rate based on the vehicle speed (graph (D) of Figure 6 - step S2) and calculates allowable battery charging currents for each output voltage based on the allowable deceleration rate (steps S3 and S4). The controller 7 then calculates battery charging currents for each output voltage based on a battery condition (steps S5 and S6). [0042] Based on the calculated allowable battery charging current and the calculated battery charging current, the controller 7 calculates a target output voltage (graph (B) of Figure 6 - step S7) and executes a feedback control to control the alternator output voltage to the target output voltage (graph (B) of Figure 6 (B) - step S8). More specifically, the controller 7 sets the target output voltage to such a value that the battery charging current will be smaller than the allowable battery charging current and executes feedback control such that the output voltage will equal the target output voltage. As a result, since a current exceeding the allowable battery charging current is prevented from being supplied to the battery 5, the vehicle can be prevented from decelerating at a rate exceeding the allowable deceleration rate and the drivability of the vehicle can be improved from the perspective of a driver.

[0043] When conditions are such that there is a region in which the battery charging current is larger than the allowable battery charging current, the target output voltage is set to a value corresponding to an intersection point between the allowable battery charging current and the battery charging current. In this way, the battery 5 can be charged to the greatest extent possible while ensuring the drivability of the vehicle. As a result, the frequency at which the battery 5 is charged can be reduced and the fuel efficiency can be improved when the engine is running normally without executing a fuel cut. [0044] Although this embodiment explains how the target output voltage is set when the battery fluid temperature changes, the target output voltage can be set in a similar fashion in response to changes in the state of charge or a change in the existence or absence of a concentration polarization of the electrolyte fluid of the battery, hi other words, when there is an intersection point between the allowable battery charging current and the battery charging current, the target output voltage is set to decrease as the battery state of charge decreases. Meanwhile, the target output voltage is set to a smaller value when a concentration polarization does not exist than when a concentration polarization of the electrolyte fluid of the battery exists. In other words, battery charging current is larger when a concentration polarization does not exist. If the graph of Figure 5 were plotting concentration polarization instead of battery fluid temperature, the 25°C line would most closely represent a situation in which no concentration polarization exists and the 0⁰C line would most closely represent a situation which concentration polarization exists. Thus, as seen by arrow A in Figure 5 for the case plotting existence or absence of a concentration polarization, the battery charging current is larger when a concentration polarization does not exist. Also as seen by arrow B in Figure 5 for the case plotting existence or absence of a concentration polarization, the target output voltage is set to a smaller value when a concentration polarization does not exist than when a concentration polarization of the electrolyte fluid of the battery exists if the allowable battery charging current is smaller than the battery charging current.

[0045] In the embodiment, the allowable battery charging current is calculated versus the output voltage based on the allowable deceleration rate and the battery charging current is calculated versus the output voltage based a battery condition. A target output voltage is then set to such a value that the battery charging current will be smaller than the allowable battery charging current and a feedback control is executed such that the output voltage will equal the target output voltage. As a result, since a current exceeding the allowable battery charging current is prevented from being supplied to the battery 5, the vehicletcan be prevented from decelerating at a rate exceeding the allowable deceleration rate and the drivability of the vehicle can be improved from the perspective of a driver. [0046] When conditions are such that there is a region in which the battery charging current is larger than the allowable battery charging current, the target output voltage is set to a value corresponding to an intersection point between the allowable battery charging current and the battery charging current. In this way, the battery 5 can be charged to the greatest extent possible without exceeding the allowable deceleration rate. As a result, the frequency at which the battery 5 is charged can be reduced and the fuel efficiency can be improved when the engine is running normally without executing a fuel cut. Thus, both drivability and fuel efficiency can be improved simultaneously. By taking battery conditions into account, the battery charging current can be calculated more accurately. [0047] While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, although in the embodiment a state of the battery is determined based on the battery state of charge, the battery fluid temperature, and the existence/absence of a concentration polarization, it is also acceptable to use only one of these three conditions. Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An electric power generation control apparatus comprising: an electric generator configured to generate electricity by being driven by an internal combustion engine; a battery that stores electricity generated by the electric generator; a battery condition detecting device that detects a battery condition of the battery; and an electric generator output voltage control device that controls an output voltage of the electric generator to a target output voltage in accordance with an allowable deceleration rate and a battery condition detected by the battery condition detecting device during vehicle deceleration with the electric generator is being driven.

2. The electric power generation control apparatus as recited in claim 1, wherein the battery condition detecting device detects as the battery condition at least one of a state of charge of the battery, a temperature of an electrolyte fluid of the battery, and an existence/absence of a concentration polarization of an electrolyte fluid of the battery.

3. The electric power generation control apparatus as recited in claim 1, further comprising: a vehicle speed sensor that detects a speed of the vehicle, with the electric generator output voltage control device determining the allowable deceleration rate based on a vehicle speed detected by the vehicle speed sensor.

4. The electric power generation control apparatus as recited in claim 1, wherein the electric generator output voltage control device determines a first relationship of a battery charging current supplied to the battery versus the output voltage of the electric generator based the battery condition that was detected, and determines a second relationship of the battery charging current supplied to the battery versus the output voltage of the electric generator based on the allowable deceleration rate, and then the electric generator output voltage control device determines the target output voltage of the electric generator based on the first relationship and the second relationship.

5. The electric power generation control apparatus as recited in claim 4, wherein the electric generator output voltage control device further sets the target output voltage to a highest output voltage value at which the battery charging current obtained with the first relationship does not exceed the battery charging current obtained with the second relationship.

6. The electric power generation control apparatus as recited in claim 4, wherein the electric generator output voltage control device further sets a maximum output voltage value of the electric generator as the target output voltage when the battery charging current obtained with the first relationship based on the maximum output voltage value does not exceed the battery charging current obtained with the second relationship based on the maximum output voltage, and further sets a voltage value corresponding to an intersection point which corresponds to where the first relationship and the second relationship intersect when the intersection point exists.

7. The electric power generation control apparatus as recited in claim 1 , wherein the battery condition detecting device detects a state of charge of the battery as the battery condition; and the electric generator output voltage control device controls the output voltage of the electric generator to a smaller value as the state of charge of the battery becomes smaller.

8. The electric power generation control apparatus as recited in claim 1, wherein the battery condition detecting device detects a temperature of an electrolyte fluid of the battery as the battery condition; and the electric generator output voltage control device controls the output voltage of the electric generator to a smaller value as the temperature of the electrolyte fluid of the battery becomes higher.

9. The electric power generation control apparatus as recited in claim 1, wherein the battery condition detecting device detects a concentration polarization of an electrolyte fluid as the battery condition; and the electric generator output voltage control device controls the output voltage of the electric generator to a smaller value when a concentration polarization of an electrolyte fluid of the battery does not exist than when a concentration polarization of an electrolyte fluid of the battery exists.

10. An electric power generation control apparatus comprising: means for generating electricity by being driven by an internal combustion engine; means for storing electricity generated by the means of generating electricity; means for detecting a battery condition of a battery; and an electric generator output voltage control device that controls an output voltage of the electric generator to a target output voltage in accordance with an allowable deceleration rate and the battery condition detected by the battery condition detecting device during vehicle deceleration with the electric generator is being driven.

11. An electric power generation control method comprising: driving an electric generator with an internal combustion engine; storing electricity generated by the electric generator in a battery; detecting a battery condition of the battery; and controlling an output voltage of the electric generator to a target output in accordance with an allowable deceleration rate and the battery condition that was detected during vehicle deceleration with electricity generated by the electric generator being stored in the battery.