JP5648581B2 - Electric cart equipped with lithium ion battery and charging method of lithium ion battery for electric cart - Google Patents

Description

  The present invention relates to an electric cart equipped with a lithium ion battery and a method for charging a lithium ion battery.

  Lithium-ion batteries are characterized by their small size, light weight, high capacity, and high output. By using them as power sources for electric carts such as golf carts, they can be reduced in weight compared to lead-acid batteries, etc. It becomes possible. Therefore, recently, it has been installed in many electric carts.

  Since the electric cart is equipped with an electric motor, it is possible to perform regenerative braking using the regenerative current generated by the electric motor functioning as a generator when braking or downhill. At the same time, it is possible to charge the lithium ion battery with a regenerative current. However, charging (overcharging) the lithium ion battery beyond the upper limit charging voltage not only causes rapid deterioration of the battery but also causes heat generation and ignition. Therefore, when charging a lithium ion battery, it is necessary to protect the battery by charging it so as not to overcharge.

  Therefore, for example, in Japanese Patent Application Laid-Open No. 2006-115571 (Patent Document 1), the first charge amount is set to be lower than the upper limit charge voltage, and the second and subsequent lithium ions are determined based on the measurement result of the battery voltage during travel. A technology for preventing charging beyond the upper charging limit voltage by determining the charging voltage of the battery is disclosed.

JP 2006-115571 A

  However, in order to employ the technique disclosed in Japanese Patent Application Laid-Open No. 2006-115571 (Patent Document 1), it is necessary to keep the charge amount of the lithium ion battery low, and the characteristics of the lithium ion battery cannot be fully utilized. That is, it is necessary to keep the state of charge (hereinafter referred to as SOC) low when the rated capacity of the lithium ion battery is 100% and complete discharge is defined as 0%. Therefore, the lithium ion battery itself is used with a low SOC despite having a high capacity characteristic, and the travel distance per charge is smaller than the theoretical travel distance when the battery is charged to 100% SOC and traveled. There was a problem of shortening. Even if the charging voltage is set to a low value, the amount of regenerative current generated may change due to changes in conditions such as the driving method, and the charging upper limit voltage may be exceeded.

  An object of the present invention is to provide an electric cart capable of braking an electric cart by making maximum use of a regenerative brake by a regenerative current, and at the same time, safely charging a lithium ion battery, and a method of charging a lithium ion battery for an electric cart. Is to provide.

  Another object of the present invention is to provide an electric cart and a method for charging a lithium ion battery for an electric cart that extend the travelable distance by taking advantage of the characteristics of a lithium ion battery having a large capacity.

  An electric cart of the present invention includes a lithium ion battery in which a plurality of cells are connected, a cell voltage detection unit that individually detects a voltage between terminals of the cells of the lithium ion battery, an electric motor that uses the lithium ion battery as a power source, and An accelerator that outputs a drive signal for driving the electric motor, a motor control unit that supplies the motor current to the electric motor with the drive signal as an input, and flows the regenerative current to the lithium-ion battery during regeneration of the electric motor, and a brake command The braking control unit that uses both the braking mechanical brake device that is in the operating state and the regenerative braking that is obtained by controlling the regenerative current and the mechanical brake that generates the braking command and sets the braking mechanical braking device in the operating state. The motor control unit supplies the regenerative current to the lithium ion when no drive signal is output from the accelerator. And it is configured to flow to down the battery. When the braking control unit detects that the voltage between the terminals of the lithium ion battery cell charged by the regenerative current has risen to a threshold voltage lower than the charging upper limit voltage, it reduces the regenerative current and weakens the regenerative brake. A brake command is output and the mechanical brake is used together. By comprising in this way, it can brake only by regenerative braking and can charge a lithium ion battery until the voltage between the terminals of the cell of a lithium ion battery reaches a threshold voltage. And when the voltage between the terminals of the cells of the lithium ion battery exceeds the threshold voltage, by weakening the regenerative brake and using the mechanical brake together, charging the lithium ion battery while protecting it from overcharging, and It becomes possible to brake the electric cart.

  The method of reducing the regenerative current by the braking control unit is arbitrary as long as the lithium ion battery can be suppressed or prevented from being overcharged early. For example, the regenerative current may be controlled so as to reduce the regenerative current to 1/2 when detecting that the voltage between the terminals of the cell has increased to the threshold voltage. Further, the regenerative current may be decreased step by step, and in that case, it is preferable to increase the brake command in proportion to the rate of decreasing the regenerative current. By reducing the regenerative current and increasing the brake command in this way, it is possible to prevent sudden switching of the brake and to prevent the rider's ride comfort during braking from being impaired.

  In most cases, the lithium ion battery can be protected from overcharge by detecting that the voltage between the terminals of the cell has increased to the threshold voltage and reducing the regenerative current. However, if the charging by the regenerative current is continued, the voltage between terminals of one cell may reach the charging upper limit voltage. Therefore, when the braking control unit detects that the lithium ion battery cell is charged to the upper limit voltage by the regenerative current, the control is performed so that the regenerative current becomes 0, and the braking is performed only by the mechanical brake. You may make it perform. By controlling in this way, it is possible to reliably prevent each cell of the lithium ion battery from being charged exceeding the charging upper limit voltage.

  The electric cart of the present invention may include a charger for charging the mounted lithium ion battery with an external power source. What is necessary is just to make the charging voltage by a charger not exceed a charging upper limit voltage. More preferably, the charger includes a charging voltage setting unit that sets a charging voltage, the charging voltage setting unit sets the charging voltage to a first charging voltage lower than the threshold voltage, and the lithium ion battery is supplied from an external power source. May be charged. If the charging voltage is set in this way, it is possible to perform control using both charging and braking by preferentially using the regenerative brake from the time when charging by the external power supply is completed.

  However, if the first charging voltage set at the beginning is too high when the car is actually driven by charging with the first charging voltage, the use ratio of the mechanical brake increases and the regenerative brake cannot be used much. An improper state may occur. Further, if the first charging voltage set at the beginning is too low, the SOC may be too low and the travelable distance may be shortened. Therefore, if the charging voltage (first charging voltage) by the external power source is changed based on the data at the time of traveling, the lithium ion battery can be charged with a charging voltage suitable for performing braking mainly on the regenerative brake. . For example, when the electric cart of the present invention is a golf cart, in many cases, the traveling course is common and the generation tendency of the regenerative current is often the same. If the charging voltage (first charging voltage) is changed, the lithium ion battery can be charged with an appropriate charging voltage. Therefore, the electric cart is provided with a voltage storage unit that stores the voltage between the terminals of the lithium ion battery cells when the electric cart is running, and between the terminals of the lithium ion battery cells when the electric cart is stored stored in the voltage storage unit. When the peak voltage of the voltage is lower than the charging upper limit voltage, it is conceivable to change the setting of the charging voltage to a second charging voltage that is lower than the charging upper limit voltage and higher than the first charging voltage. When the peak voltage of the voltage between the terminals of the lithium-ion battery cell during traveling is lower than the charging upper limit voltage, it is less likely to be charged beyond the charging upper limit voltage due to the regenerative current, and therefore, is higher than the first charging voltage. Even if charging is performed at a high second charging voltage, the possibility of exceeding the charging upper limit voltage is low. Therefore, by increasing the charging voltage within an allowable range, it can be expected to increase the charge amount of the lithium ion battery and extend the travelable distance.

  Furthermore, a time storage unit for storing the traveling time of the electric cart and the operating time of the mechanical brake is provided, and when the operating time of the mechanical brake with respect to the traveling time of the electric cart exceeds a predetermined ratio, the charging voltage is It is conceivable to change the setting to a third charging voltage lower than the charging voltage of 1. If the operating time of the mechanical brake with respect to the running time of the electric cart exceeds a predetermined ratio, it means that charging by the regenerative current is not sufficiently performed, and much of the regenerated energy is lost. Yes. Therefore, by changing the setting of the charging voltage to the third charging voltage lower than the first charging voltage, the ratio of the mechanical brake is lowered, the ratio of the regenerative brake is increased, and the lithium ion battery is efficiently generated by the regenerative current. Can be charged.

  It should be noted that the operation time of the mechanical brake can be more appropriately determined by weighting according to the value of the regenerative current when the mechanical brake is operated. That is, for example, when the maximum regenerative current is 100 [A], the regenerative current is controlled to 50 [A] when the voltage between the terminals of the lithium ion battery cell rises to the threshold voltage, and the regenerative current is increased to the charging upper limit voltage. If the regenerative current when the mechanical brake is activated is 0 [A], the machine brake operating time is 1 time, and if it is 50 [A], the machine If it is set to 0.5 times the operation time of the brake, the determination can be made more appropriately.

1 is a block diagram of an embodiment in which the present invention is applied to a golf cart. It is a flowchart of control at the time of braking with the golf cart of this Embodiment. It is the figure which showed an example of the waveform of the voltage between terminals of one cell of a lithium ion battery at the time of performing braking control along the flowchart of FIG. 2, and charging / discharging electric current. It is a flowchart which shows the process of determining the charging voltage at the time of charging a lithium ion battery with an external power supply.

  Hereinafter, with reference to the drawings, an embodiment when the present invention is applied to a golf cart as an example of an electric cart will be described. FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a flowchart of control when braking is performed by the golf cart of the embodiment of the present invention, and FIG. 3 is a flowchart of FIG. It is the figure which showed an example of the waveform of the voltage between terminals of one cell of a lithium ion battery at the time of braking control according to a figure, and the charge / discharge current, and FIG. 4 charges a lithium ion battery with an external power supply It is a flowchart which shows the process of determining the charging voltage at the time.

<Configuration of golf cart>
As shown in FIG. 1, the golf cart (electric cart) 1 of the present embodiment mainly includes a lithium ion battery 3 to which a plurality of cells are connected, a control unit 5, an electric motor 7, and a drive signal. Is composed of an accelerator pedal 9 that is an accelerator that outputs a brake and a mechanical brake device 11 for braking. The lithium ion battery 3 is provided with a cell voltage detection unit 4 that individually detects voltages between terminals of a plurality of cells. In FIG. 1, a part of the detection line of the cell voltage detector 4 is shown in a simplified manner. Further, in FIG. 1, only one input / output unit is shown as a representative of the input / output unit of the control unit 5 for simplification of illustration even when there are a plurality of input / output units. The calculation unit of the cell voltage detection unit 4 that individually detects the voltage between terminals of a plurality of cells is realized by a microcomputer 17 in the control unit 5. The plurality of cell voltages detected by the cell voltage detection unit 4 are input to the cell voltage input unit 51 of the control unit 5. Further, a relay 15 constituting a switching circuit is disposed between one end of the lithium ion battery 3 and the charging terminal portion 52 and the charging / discharging terminal portion 53 of the control unit 5. Further, a current detector 13 for detecting a discharge current is disposed between the other end of the lithium ion battery 3 and the input terminal portion 54 of the control unit 5. A pair of output units of the current detector 13 are connected to a current input unit 55 of the control unit 5.

  The control unit 5 includes a microcomputer 17, and the microcomputer 17 functions as a calculation unit of the motor control unit 19 and the braking control unit 21. The motor control unit 19 in the control unit 5 includes a drive circuit that drives and controls the electric motor 7, and a power line of the electric motor 7 is connected to the drive circuit. This drive circuit has an inverter function for converting the DC voltage of the lithium ion battery 3 into an AC voltage, and a converter function for converting the regenerative current generated by the motor into DC. The braking control unit 21 in the control unit 5 controls the combined use of the braking mechanical brake device 11 (mechanical brake) and the regenerative brake. A speed command from the accelerator pedal 9 and vehicle speed data from the vehicle speed sensor 23 are input to the motor control unit 19 and the braking control unit 21.

  In the present embodiment, a charger 25 for charging the lithium ion battery 3 with an external power source is provided. The charger 25 converts an AC voltage from a commercial power source (external power source) 27 into a DC voltage, and adjusts the voltage to a DC voltage necessary for charging the lithium ion battery 3. The output of the charger 25 is output from the charging terminal unit 52 via the control unit 5. When the relay 15 switches the connection from the charge / discharge terminal portion 53 to the charge terminal portion 52 in accordance with a switching command from the operation panel 29 described later, the lithium ion battery 3 is charged. The relay 15 can be switched by operating the operation panel 29. By switching the contact to the A side (charging terminal portion 52 side), the lithium ion battery 3 and the charger 25 are connected, and charging using the commercial power source 27 is performed. By switching the contact of the relay 15 to the B side (charge / discharge terminal portion 53 side), the lithium ion battery 3 and the electric motor 7 are connected via the motor control unit 19 in the control unit 5.

  When the golf cart 1 travels, current flows in both directions between the lithium ion battery 3 and the electric motor 7 via the motor control unit 19 of the control unit 5. Therefore, in the following description, electric power is supplied from the lithium ion battery 3. The current flowing through the motor 7 is a discharge current, and the current flowing from the electric motor 7 to the lithium ion battery 3 is a charging current.

  Furthermore, in the present embodiment, a storage unit 31 is provided, and information for setting a charging voltage when charging the lithium ion battery 3 by the commercial power supply 27 is stored in the storage unit 31. Details will be described later.

  Note that FIG. 1 is a block diagram for explaining the operation of each component, and therefore, a tire for traveling, a steering wheel, a seat on which an occupant is seated and the like are not shown.

<Measurement of charge / discharge current and battery voltage of lithium ion battery>
The current value at the time of charging / discharging of the lithium ion battery 3 is converted into a voltage value by the current detection unit 13 and input to the control unit 5. On the other hand, the voltage between the terminals of the plurality of cells of the lithium ion battery is input to the control unit 5 as it is. These voltage values are converted into digital signals through an A / D converter (not shown) built in the control unit 5 and then input to the microcomputer 17 for use in arithmetic processing.

<Golf cart running and braking>
When the driver depresses the accelerator pedal 9, a speed command is input to the motor control unit 19. The motor control unit 19 performs an inverter operation according to the speed command and outputs a drive current to the electric motor 7. When the accelerator pedal 9 is released, the speed command becomes zero, and the motor control unit 19 performs a converter operation for regenerating the regenerative current regenerated from the electric motor 7 to the lithium ion battery 3. When a direct current is supplied from the lithium ion battery 3 to the electric motor 7 and the electric motor 7 rotates, the driving force is transmitted to the running tire via a clutch and an axle (not shown), and the golf cart 1 starts running.

  The acceleration of the golf cart 1 is executed by converting a speed command output according to the amount by which the driver has depressed the accelerator pedal 9 into a torque command and a current command in the motor control unit 19 of the control unit 5. For deceleration, the speed command becomes zero when the accelerator pedal 9 is released, or the speed of the golf cart 1 detected by the vehicle speed sensor 23 exceeds the speed limit during travel (for example, 20 [km / h]). In this case, the drive circuit in the motor control unit 19 is in a state of performing a converter operation, a regenerative brake mainly generated by regenerating a regenerative current regenerated from the electric motor 7 to the lithium ion battery 3 side, It is implemented in combination with a mechanical brake that operates according to a command. When it is desired to decelerate more than the braking that is automatically performed by the braking control unit 21, the driver can decelerate by forcibly operating the braking mechanical brake device 11 by depressing a brake pedal (not shown). The braking control unit 21 applies mechanical braking according to the amount of depression of the brake pedal.

  When the golf cart 1 travels on a flat road or an uphill slope of a golf course, a discharge current flows from the lithium ion battery 3 to the electric motor 7. When the lithium ion battery 3 is discharged, the voltage of the lithium ion battery decreases. The motor control unit 19 regenerates the regenerative current generated by the electric motor to the lithium ion battery 3 side even when the electric motor is decelerated.

  When the golf cart 1 travels on the down slope of the golf course, the accelerator pedal 9 is released, or when the speed of the golf cart 1 detected by the vehicle speed sensor 23 exceeds the speed limit during traveling, the braking control unit 21 performs braking using both regenerative braking and mechanical braking. At this time, the kinetic energy at the time of braking of the golf cart 1 is transmitted from the tire to the electric motor 7 through the axle, converted into electric energy by the power generation function of the electric motor 7, and returned to the lithium ion battery 3, so-called regeneration. Charging is performed. Such a braking system is called regenerative braking. Since the lithium ion battery 3 is charged by regenerative charging, the voltage of the lithium ion battery 3 rises.

<Operation pattern of golf cart>
A general golf cart operation pattern is as follows.

(1) Charge state: The golf cart 1 is charged in the golf cart garage. In the present embodiment, charging is performed up to a value V ₁ [V] (first charging voltage) that is equal to or lower than the charging upper limit voltage V _f [V]. For example, charging is performed until V ₁ = 4.13 [V / cell] with respect to the charging upper limit voltage V _f = 4.2 [V / cell].

(2) Stop state: When the charging voltage of the charger is reached, charging is terminated. Thereafter, the golf cart 1 is stopped until the start of traveling.

(3) Traveling state: A state in which the driver gets on and travels on the golf course. Depending on the golf course, there are (i) flat roads, (ii) uphill slopes, and (iii) downhill slopes in the course.

(4) Stop state: When the travel of the golf course is completed, the golf cart 1 stops at the golf cart garage.

  The golf cart 1 is operated in an operation pattern in which the states (1) to (4) are one cycle.

  Hereinafter, the braking control in the traveling state (3) and the charging control in the charging state (1) will be described in particular.

<Brake control>
The braking control of the golf cart 1 in the present embodiment will be described with reference to FIG. In the present embodiment, the speed limit is set so as to be switched depending on whether or not the accelerator pedal 9 of the golf cart 1 is released (step ST1). When the speed command becomes 0 by releasing the accelerator pedal 9, the speed limit is set to 0 [km / h] so that the golf cart 1 stops (step ST2), and the accelerator pedal 9 is depressed. The speed limit during travel is set to 20 [km / h] (step ST3). When the accelerator pedal 9 is released, the speed command is naturally 0 [km / h], and the regenerative state is continued until the golf cart 1 stops. When the accelerator pedal 9 is being operated and the speed of the golf cart 1 exceeds the speed limit, it is typically a case where the golf cart 1 is going down a slope. Therefore, at this time, the regenerative state occurs even while the golf cart is running. Therefore, in any case, if the actual speed exceeds the speed limit (0 [km / h] or 20 [km / h]) (step ST4), the voltage of each cell of the lithium ion battery 3 is set. Measurement is performed (step ST5), and the voltage of the cell showing the maximum voltage is set as the maximum cell voltage V _b [V] (step ST6), and the threshold voltage V _ref [V] (in this embodiment, V _ref = 4.15 [ V]) and comparison (step ST7). When the maximum cell voltage V _b [V] does not reach the threshold voltage V _ref [V], the electric motor 7 is controlled to be equal to or less than the maximum current of the electric motor 7 (for example, 100 [A]), Braking is performed only with regenerative braking without applying mechanical braking (step ST8). When the maximum cell voltage V _b [V] exceeds the threshold voltage V _ref [V], the regenerative current is reduced to prevent the lithium ion battery from being overcharged. In the present embodiment, the maximum cell voltage V _b [V] is compared with the charging upper limit voltage V _f [V] (step ST9), and if the charging upper limit voltage V _f [V] is not reached, the regenerative current is 50 [A] The converter function of the motor control unit 19 controls the regeneration of the regenerative current so as to be as follows. However, since the regenerative brake is weakened by reducing the regenerative current, the mechanical brake is also operated to balance the braking (step ST10). When the maximum cell voltage V _b [V] is equal to or higher than the charging upper limit voltage V _f [V], the converter function of the motor control unit 19 stops the conversion operation so that the regenerative current is not regenerated to the lithium ion battery 3 side. As a result, braking is performed only with the mechanical brake (step ST11). When braking is performed using the mechanical brake (step ST10 and step ST11), it is monitored whether the golf cart 1 is below the speed limit (step ST12). Is increased (step ST13). Thereafter, steps ST1 to ST14 are repeated until the golf cart 1 stops (step ST14). In the present embodiment, steps ST1 to ST14 are repeated at intervals of 5 [ms]. When the stop of the golf cart 1 is detected in step ST14, the operation ends. In a state where the accelerator pedal 9 is not released, the golf cart 1 is not stopped in step ST14. Therefore, unless the accelerator pedal 9 is released, the process always returns to step ST1.

The reason why the maximum cell voltage V _b [V] is compared rather than the voltage of the entire lithium ion battery is that the characteristics of the cells constituting the lithium ion battery usually vary. . If the charging upper limit voltage is reached even in one cell, the characteristics of the lithium ion battery 3 will be affected. Therefore, it is desirable to control the voltage based on the cell that reaches the charging upper limit voltage earliest. The cell voltage V _b [V] is a comparison target.

FIG. 3 is an example of a case where braking control is performed along the flowchart of FIG. The solid line (a) is the maximum cell voltage V _b [V], and the solid line (b) is the charge / discharge current of the lithium ion battery 3. In FIG. 3, the charge current is positive and the discharge current is negative. It is drawn.

In the example of FIG. 3, the accelerator pedal 9 is depressed after starting to descend the down slope at time t ₀ . Until the time t ₁ , the lithium ion battery is discharged, and the cell voltage drops from the _first charging voltage V ₁ [V]. In this example, since the maximum cell voltage V _b [V] is lower than the threshold voltage V _ref [V] at time t ₁ , braking is performed only with regenerative braking without using mechanical braking. (Step ST8). Thereafter, the charging by the regenerative current is made at time t _2, since the maximum cell voltage V _b [V] has reached the threshold voltage V _ref [V], reduces the regenerative current, braking line in combination of the mechanical brake (Step ST10). Since the regenerative current has decreased, the slope indicating the increase in the maximum cell voltage V _b [V] has decreased. Furthermore, after that, at time t ₃ , the maximum cell voltage V _b [V] has reached the charging upper limit voltage V _f [V], so that the regenerative current is set to 0 [A] and braking is performed only with the mechanical brake. (Step ST11). Since the regenerative current is 0 [A], charging is not performed and the maximum cell voltage V _b [V] does not increase.

As described above, in the golf cart 1 to which the present invention is applied, the voltage of the lithium ion battery is measured and compared with the threshold voltage V _ref [V] and the charging upper limit voltage V _f [V]. By performing braking control using both, the lithium ion battery can be charged while being protected from overcharging, and the golf cart can be braked.

<Determination of charging voltage>
In the present embodiment, the charging voltage is the first charging voltage (V ₁ = 4.13 [V / cell]). However, it may be desirable to charge with a more appropriate charging voltage depending on the degree of undulation and length of the traveling course. In particular, in the case of golf carts, in many cases, the traveling course is common, and the generation tendency of the regenerative current is often common, and if the charging voltage by the external power source is changed based on the data at the previous driving The lithium ion battery can be charged with a more appropriate charging voltage. Therefore, in the present embodiment, the voltage storage unit 33 that stores the voltage between the terminals of the lithium ion battery 3 when the golf cart 1 travels, and the travel time of the golf cart 1 and the operation time of the mechanical brake are stored. A storage unit 31 including a time storage unit 35 is provided, and the control unit 5 sets the charging voltage of the charger 25 before starting charging with the commercial power supply 27 based on the stored information.

FIG. 4 is a flowchart showing a process until the charging voltage is set. First, as a premise, the golf cart 1 is charged up to the first charging voltage (V ₁ = 4.13 [V / cell]) in accordance with the above <Golf cart operation pattern>, and runs on the course of the golf course. ).

When the commercial power supply 27 and the power supply port of the golf cart 1 are connected by a power supply cable and an instruction to start charging is input from the operation panel 29, the control unit 5 reads from the voltage storage unit 33 the maximum cell voltage V _b [ The peak voltage V _p [V] of V] is read (step ST21). Then, the peak voltage V _p [V] is compared with the charge upper limit voltage V _f [V] (step ST22). When the peak voltage V _p [V] is less than the charge upper limit voltage V _f [V], The charging voltage is changed to a _second charging voltage V ₂ [V] that is lower than the charging upper limit voltage and higher than the first charging voltage (step ST23). For example, 4.15 [V] obtained by adding 0.02 [V] to 4.13 [V] is set as the second charging voltage. This is because it can be determined that even if charging is performed at a voltage higher than the first charging voltage, the charging upper limit voltage is not exceeded. The setting change of the charging voltage is performed using the charging voltage setting unit 26 of the charger 25. When the peak voltage V _p [V] exceeds the charge upper limit voltage V _f [V], the operation time T _m [s] of the mechanical brake during traveling is further calculated (step ST24). The operation time may be simply accumulated, but in this embodiment, the regenerative current is 0 [A], 50 [A], and 100 [A] in the case of the mechanical brake operation time. Weighting. That is,
T _m = (mechanical brake operation time when regenerative current is 0 [A] x 1.0) + (mechanical brake operation time when regenerative current is 50 [A] x 0.5)
(Note that when the regenerative current is 100 [A], it is not counted because the mechanical brake is not operating.) When the operation time T _m [s] obtained in this way exceeds a predetermined ratio with respect to the travel time T [s] of the golf cart 1 (step ST25), it is lower than the first charging voltage. The setting is changed to the third charging voltage V ₃ [V] (step ST26). For example, 4.11 [V] obtained by subtracting 0.02 [V] from 4.13 [V] is set as the third charging voltage. Since the rate at which the mechanical brake is operating is increasing, the rate at which braking is performed with the regenerative brake can be increased by doing so. When the operation time T _m [s] does not exceed a predetermined ratio with respect to the travel time T [s] of the golf cart 1, it is assumed that the first charging voltage V ₁ [V] is an appropriate value. Then, charging is performed again using the first charging voltage V ₁ [V]. Needless to say, the determination of the charging voltage may be performed each time the battery is charged, or may be executed only when desired.

  Note that the set value, threshold value, and the like of the regenerative current are shown as examples, and may be changed as appropriate according to the embodiment.

  According to the present invention, the electric cart can be braked using the regenerative brake by the regenerative current to the maximum, and at the same time, the lithium ion battery can be safely charged. In addition, the ratio of the regenerative brake can be increased with an electric cart that uses both the regenerative brake and the mechanical brake. Therefore, in the electric cart using a lithium ion battery as a power source, the characteristics of the lithium ion battery can be fully utilized.

DESCRIPTION OF SYMBOLS 1 Golf cart 3 Lithium ion battery 5 Control part 7 Electric motor 9 Accelerator pedal 11 Braking mechanical brake device 13 Current detector 15 Relay 17 Microcomputer 19 Motor control part 21 Braking control part 23 Vehicle speed sensor 25 Charger 27 Commercial power supply 29 Operation Panel 31 Storage unit 33 Voltage storage unit 35 Time storage unit

Claims (10)

A lithium ion battery in which a plurality of cells are connected;
A cell voltage detection unit for individually detecting a voltage between terminals of the cell of the lithium ion battery;
An electric motor powered by the lithium ion battery;
An accelerator that outputs a drive signal for driving the electric motor;
A motor controller for supplying a motor current to the electric motor as an input of the drive signal and flowing the regenerative current to the lithium ion battery during regeneration of the electric motor;
A braking mechanical brake device that is activated based on a brake command;
A braking control unit that uses both a regenerative brake obtained by controlling the regenerative current and a mechanical brake generated by generating the brake command and setting the mechanical brake device for braking to an operating state;
The motor control unit is an electric cart configured to flow the regenerative current to the lithium ion battery when the drive signal is not output from the accelerator,
When the braking control unit detects that the inter-terminal voltage of the cell of the lithium ion battery charged by the regenerative current has risen to a threshold voltage lower than a charging upper limit voltage, the braking control unit decreases the regenerative current to reduce the regenerative current. While weakening the brake and outputting the brake command together with the mechanical brake ,
The electric cart further includes a charger for charging the lithium ion battery with an external power source, and a voltage storage unit for storing a voltage between terminals of the cells of the lithium ion battery when the electric cart is running. And
The charger includes a charging voltage setting unit that sets a charging voltage, the charging voltage is set to a first charging voltage lower than the threshold voltage, and the electric motor stored in the voltage storage unit When the peak voltage of the voltage between the terminals of the lithium ion battery when the cart is running is lower than the charging upper limit voltage, the charging voltage is lower than the charging upper limit voltage, and the first An electric cart characterized in that the setting is changed to a second charging voltage higher than the charging voltage .   The brake control unit, when detecting that the voltage between the terminals of the cell has increased to the threshold voltage, controls the regenerative current so as to reduce the regenerative current to ½. The electric cart as described in.   2. The brake control unit according to claim 1, wherein when the braking control unit detects that the lithium ion battery is charged to the threshold voltage, the brake control unit increases the brake command in proportion to a rate of decreasing the regenerative current. Electric cart.   When the braking control unit detects that the cell of the lithium ion battery is charged to the charging upper limit voltage by the regenerative current, the braking control unit performs control so that the regenerative current becomes 0, and the braking is performed only by the mechanical brake. The electric cart according to any one of claims 1 to 3, wherein control is performed so as to perform. The electric cart further includes a time storage unit that stores a travel time of the electric cart and an operation time of the mechanical brake,
The charger changes the charging voltage to a third charging voltage lower than the first charging voltage when the operating time of the mechanical brake with respect to the traveling time of the electric cart exceeds a predetermined ratio. The electric cart according to claim 1 . The electric cart according to claim 5 , wherein the operation time of the mechanical brake is weighted according to a value of a regenerative current when the mechanical brake is operated. A method of charging a lithium ion battery mounted on the electric cart according to claim 1 by an external power source ,
A charging method for a lithium ion battery for an electric cart, wherein the charging voltage is set to a first charging voltage lower than the threshold voltage, and the lithium ion battery is charged. When the peak voltage of the voltage between the terminals of the lithium ion battery stored in the voltage storage unit is lower than the charging upper limit voltage, the charging voltage is set lower than the charging upper limit voltage. 8. The method of charging a lithium ion battery for an electric cart according to claim 7 , wherein the setting is changed to a second charging voltage higher than the first charging voltage, and the lithium ion battery is charged. . The electric cart is further provided with a time storage unit for storing the traveling time of the electric cart and the operation time of the mechanical brake,
When the operation time of the mechanical brake with respect to the travel time of the electric cart exceeds a predetermined ratio, the charging voltage is changed to a third charging voltage lower than the first charging voltage, and the lithium ion The method of charging a lithium ion battery for an electric cart according to claim 7 , wherein the battery is charged. The method for charging a lithium ion battery for an electric cart according to claim 9 , wherein the operation time of the mechanical brake is weighted according to a value of a regenerative current when the mechanical brake is operated.

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