Electrically-driven work vehicle

Abstract

To provide an electrically-driven work vehicle capable of further reducing fuel consumption when the capacity of a secondary battery is comparatively small.SOLUTION: An electrically-driven work vehicle includes: a main generator and an auxiliary generator driven by an engine; an electric motor for traveling driven by electric power supplied from the main generator; an auxiliary machine device driven by electric power supplied from the auxiliary generator; a regenerative device for supplying regenerative electric power generated at the time of vehicle braking of the electric motor for traveling, to the auxiliary machine device; and a battery capable of storing electric power to be supplied from the regenerative device and the auxiliary generator to the auxiliary machine device. The regenerative device determines a first electric discharge interval for discharging the battery according to a fuel consumption rate of the engine, and a second electric discharge interval for discharging the battery according to a magnitude of energy consumption of the vehicle, on the basis of a travel pattern of the electrically-driven work vehicle and the fuel consumption rate of the engine, and supplies electric power from the battery to the auxiliary machine device or the electric motor for traveling, on the basis of the first and second electric discharge intervals.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an electrically powered work vehicle. [Background technology]

[0002] At work sites such as mines, many large dump trucks are in operation to transport ore and stripped soil from the loading area to the dump area. At work sites, the route from the loading area to the dump area is fixed, and if multiple dump trucks of the same size run along one route, they operate 24 hours a day if necessary, repeatedly making round trips to improve transportation efficiency.

[0003] Thus, when operating multiple large dump trucks for long periods of time, importance is placed on transport efficiency, which is indicated by the amount of work (amount of energy) per unit cost (initial cost + running cost). In order to improve transport efficiency, various measures are taken to suppress initial costs and reduce running costs for dump trucks. Of these, reducing running costs can be achieved by reducing the engine's fuel consumption rate [g / kWh] using an electric drive system, a type of drive system that is efficient and has relatively low maintenance costs.

[0004] In the mechanical drive system of a dump truck, engine power is transmitted to the tires using a torque converter and a transmission, whereas in the electric drive system, the engine drives a generator, and the generated power is used to drive an electric motor for traveling connected to the tire axle. In the electric drive system, a highly efficient electric motor is used and the engine can be driven at an operating point with high combustion efficiency, so that an improvement in fuel consumption rate [g / kWh] (so-called fuel efficiency) can be expected. In addition, in the electric drive system, regenerative power can be obtained by generating electrical braking force with the electric motor for traveling on slopes (downhill slopes) that are numerous in work sites such as mines, and further improvement in fuel efficiency can be expected by using this regenerative power. Specifically, the regenerative power generated during braking can be used to drive auxiliary devices, or it can be temporarily charged into a secondary battery and used to drive the vehicle and auxiliary devices during normal driving.

[0005] As such, a technique related to an electric drive system utilizing a secondary battery is known, for example, as described in Patent Document 1. Patent Document 1 discloses a hybrid dump truck for mining having an engine, a generator driven by the engine, a motor that drives wheels using electric power, an electric storage device configured to be able to charge electric power generated by the motor and supply the charged electric power to the motor, and a control device that controls charging to the electric storage device and discharging from the electric storage device, the hybrid dump truck for mining having a load sensor, and the control device having a signal switch that selects a first discharge gain K1 when the load is greater than a threshold value and selects a second discharge gain K2 when the load is less than the threshold value. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2018-103984 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned conventional technology, a relatively large capacity secondary battery is installed, electricity from a generator driven by the engine is stored in the secondary battery, and when a large amount of engine power is required, such as when the vehicle is traveling uphill, electricity is supplied from the secondary battery, thereby reducing fuel consumption.

[0008] On the other hand, in cases where the capacity of the secondary battery to be installed is limited, such as in a system intended to drive auxiliary devices using regenerative power generated by a driving electric motor, the cost required to secure the capacity of the secondary battery can be reduced, but it is thought that the effect of improving engine fuel efficiency will be limited even if the above-mentioned conventional technology is applied.

[0009] The present invention has been made in consideration of the above, and aims to provide an electrically powered work vehicle that can further improve the engine's fuel consumption rate [g / kWh] even when the capacity of the secondary battery is relatively small. [Means for solving the problem]

[0010] The present application includes multiple means for solving the above-mentioned problems, and one example is an electrically driven work vehicle equipped with an engine, a main generator and an auxiliary generator driven by the engine, a traction electric motor driven by power supplied from the main generator, an auxiliary device driven by power supplied from the auxiliary generator, a regenerative device that supplies regenerative power generated when the traction electric motor brakes the vehicle to the auxiliary device, and a battery capable of storing power supplied from the regenerative device and the auxiliary generator to the auxiliary device, the regenerative device determines a first discharge section defined by the driving section or time of the electrically driven vehicle as a section in which the battery is discharged in accordance with the fuel consumption rate of the engine based on the driving pattern of the electrically driven work vehicle and the fuel consumption rate of the engine, and a second discharge section defined by the driving section or time of the electrically driven vehicle as a section in which the battery is discharged in accordance with the magnitude of energy consumed by the vehicle, and supplies power from the battery to the auxiliary device or the traction electric motor based on the first and second discharge sections. Effect of the Invention

[0011] According to the present invention, the fuel consumption rate of the engine can be further improved when the capacity of the secondary battery is relatively small. [Brief description of the drawings]

[0012] [Figure 1] 1 is a side view showing a schematic external appearance of a dump truck, which is an example of an electrically driven work vehicle. [Diagram 2] FIG. 2 is a schematic diagram illustrating a portion of the electric drive system together with the peripheral configuration. [Diagram 3] FIG. 2 is a diagram showing an example of fuel efficiency characteristics of a diesel engine. [Figure 4] FIG. 2 is a diagram showing a driving pattern of a dump truck in a mine, which is an example of a work site, as a change in vehicle speed. [Diagram 5] FIG. 5 is a diagram showing an example of a change in the charge amount (charge and discharge characteristics) in the driving pattern shown in FIG. [Figure 6]FIG. 5 is a diagram showing an example of a change in the fuel consumption rate of the engine in the driving pattern shown in FIG. [Figure 7] 4 is a functional block diagram showing the processing contents of a functional unit related to a discharge section determination process for determining a discharge section, among the processing functions of the regenerative control device; FIG. [Figure 8] 5 is a flowchart showing the process of determining a discharge section in the regenerative control device. [Figure 9] 5 is a diagram showing an example of a case where a fuel efficiency threshold is set for the transition of the engine fuel consumption rate in the driving pattern shown in FIG. 4, and a first and a second discharge interval are set. FIG. [Figure 10] FIG. 10 is a diagram showing an example of the transition of the charge amount (charge and discharge characteristics) when the engine fuel efficiency threshold is set as shown in FIG. 9 in the driving pattern shown in FIG. 4 and the first and second discharge intervals are set. [Figure 11] 1 is a diagram for explaining an improvement in fuel consumption rate according to the present embodiment compared to the conventional technology; [Figure 12] FIG. 2 is a schematic diagram illustrating a portion of an electric drive system according to a comparative example together with its peripheral configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a dump truck having a bed for loading objects will be described as an example of an electrically powered work vehicle, but the present invention can also be applied to other electrically powered work vehicles having wheels, such as a wheel loader.

[0014] FIG. 1 is a side view that shows a schematic appearance of a dump truck that is an example of an electrically powered work vehicle according to this embodiment.

[0015] In Fig. 1, the dump truck 100 is generally composed of a body frame 18 that extends in the front-rear direction to form a support structure, a loading platform (vessel) 7 that is arranged on the upper part of the body frame 18 so as to be calculated in the front-rear direction and whose rear end lower part is tiltably attached to the body frame 18 via a pin connection part 7a, a pair of driven wheels 4L (4R) provided on the left and right of the lower front side of the body frame 18, a pair of drive wheels 5L (5R) provided on the left and right of the lower rear side of the body, a driver's seat 6 provided on the upper front side of the body frame 18, an engine 1 (e.g., a diesel engine) arranged on the body frame 18, and an electric drive system having electric motors 3L, 3R for driving wheels (drive wheels 5L, 5R) using electric power output from a main generator 2 (see Fig. 2 below) driven by the engine 1. In Fig. 1, only one of the pair of driven wheels and drive wheels is shown and marked with a reference symbol, and the other is not shown, with only the reference symbol indicated in parentheses in the drawing.

[0016] FIG. 2 is a schematic diagram illustrating a portion of the electric drive system together with the peripheral configuration.

[0017] In FIG. 2 , the electric drive system includes a main generator 2 and an auxiliary generator 14 driven by an engine 1, a rectifier 8 that rectifies the current (AC power) output from the main generator 2, an inverter 9 that converts the current (DC power) rectified by the rectifier 8 into an AC power drive signal and supplies it to the traveling electric motors 3L, 3R, the traveling electric motors 3L, 3R that drive the drive wheels 5L, 5R (wheels) using power supplied from the main generator 2 via the rectifier 8 and the inverter 9, an auxiliary rectifier 11 that rectifies the current (AC power) output from the auxiliary generator 14, an auxiliary motor 13 which is an auxiliary device such as a cooling blower, and an inverter 9 that converts the current (DC current) rectified by the auxiliary rectifier 11 into an AC power drive signal. The electric drive system is generally provided with an auxiliary inverter 12 that converts the electric power into the auxiliary motor 13 (auxiliary device) and supplies it to the auxiliary motor 13 (auxiliary device), a DC-DC converter 10 (hereinafter also referred to as a regenerative device) that converts and transmits electric power between a circuit downstream of the rectifier 8 on the main generator 2 side (hereinafter referred to as a main circuit) and a circuit downstream of the auxiliary rectifier 11 on the auxiliary generator 14 side (hereinafter referred to as an auxiliary circuit), a secondary battery 17 that stores electric power of the auxiliary circuit, a bidirectional converter 16 that converts electric power between the auxiliary circuit and the secondary battery 17 to control the storage (charging) and discharging of the secondary battery 17, an external resistor 15 that consumes surplus electric power on the main circuit side as necessary, and a regenerative control device 20 that controls the overall operation including the regenerative operation of the electric drive system. Note that the dump truck 100 is equipped with a plurality of sets of cooling blowers (auxiliary inverter 12 and auxiliary motor 13) as auxiliary devices, but in FIG. 2, only one set of auxiliary devices is illustrated for simplicity of illustration.

[0018] The DC-DC converter 10 converts (steps down) power on the main circuit side, such as regenerative power generated by the traveling electric motors 3L, 3R when braking the dump truck 100, and supplies it to the auxiliary circuit side, and uses it to drive the auxiliary motor 13 via the auxiliary inverter 12. This makes it possible to use the regenerative power generated when braking the dump truck 100 to drive the auxiliary devices, thereby reducing fuel consumption accordingly.

[0019] Further, the DC-DC converter 10 converts (steps down) the power on the main circuit side, such as regenerative power generated by the traveling electric motors 3L, 3R when braking the dump truck 100, supplies it to the auxiliary circuit side, and causes it to be stored in the secondary battery 17 via the bidirectional converter 16. The power stored in the secondary battery 17 is then supplied to the auxiliary device during operation other than regeneration of the traveling electric motors 3L, 3R (for example, power running operation of the dump truck 100). That is, in this embodiment, a part of the surplus power that is generated by the traveling electric motors 3L, 3R and is not used to drive the auxiliary device is recovered without being consumed by the external resistor 15, stored in the secondary battery 17, and supplied to the auxiliary device during operation other than regeneration of the traveling electric motors 3L, 3R. This makes it possible to further improve the overall energy efficiency and reduce fuel consumption.

[0020] Here, the basic principles of setting the power capacity of the secondary battery and the timing of power assist in this embodiment will be described.

[0021] First, the setting of the power capacity of the secondary battery 17 to which this embodiment is applied will be described.

[0022] Known hybrid systems that can be installed in electrically powered work vehicles such as dump trucks include systems that are equipped with a relatively large capacity electricity storage device and can run on the electrical system alone (so-called strong hybrid type), and systems that use regenerative energy mainly as the energy source for the electrical system and whose main operation is to assist the engine and drive the auxiliary systems, i.e., systems that are not designed to run the vehicle solely on power supply from the electricity storage device (so-called mild hybrid type).

[0023] Generally, the regenerative power of the electric motor for driving in a large dump truck operating in a mine or the like is roughly several thousand kW, while the power required by the auxiliary equipment is approximately 100 kW, which is an order of magnitude difference. Therefore, the regenerative power of the dump truck is greater than the power required by the auxiliary equipment, and in many cases cannot be absorbed by the power supply to the auxiliary equipment via the regenerative device alone when the vehicle is braking. Therefore, by consuming a part of the regenerative power through an external resistor, the regenerative power that is surplus to the power supply to the auxiliary equipment is dealt with.

[0024] Here, in a large dump truck, it is conceivable that a secondary battery is mounted on the output section of the regenerative device, so that a part of the power consumed by the external resistor is charged to the secondary battery, and the power is utilized during powering of the vehicle. However, since the amount of cargo transported is the most important basic performance index for the dump truck 100 targeted in this embodiment, mounting more batteries, which are heavy objects, not only leads to an increase in costs, but also impairs the amount of cargo transported, which is a basic performance.

[0025] Therefore, in this embodiment, a relatively small secondary battery that is considered to provide the best cost performance when applied to a dump truck, that is, a secondary battery with a relatively small battery capacity, is mounted.

[0026] Next, the setting of the timing of the electric power assist will be described.

[0027] In this embodiment, the travel pattern of the dump truck 100 at the work site is defined on a time axis, and a power assist is performed to supply power from the secondary battery 17 to the auxiliary device (auxiliary inverter 12 and auxiliary motor 13) according to the fuel efficiency of the engine 1, i.e., a timing (first discharge section) for discharging the secondary battery 17, and a timing (second discharge section) for discharging the secondary battery 17 for performing the power assist according to the magnitude of the energy consumed by the dump truck 100 are set. Here, the first and second discharge sections are sections (i.e., periods) defined based on the elapsed time from a predetermined timing (for example, the start of travel in a cycle of transportation work), and the start and end of the first and second discharge sections are defined based on the elapsed time. In the following description, a case will be described in which the first and second discharge sections for performing the power assist are defined by time as described above, but a configuration may be used in which a section between specific positions in a travel section is set as the discharge section based on the position of the dump truck 100.

[0028] First, a case will be described in which the timing for performing electric power assist (first discharge interval) is set according to the fuel consumption rate [g / kWh] (hereinafter, also referred to as fuel efficiency) of the engine 1.

[0029] Fig. 3 shows an example of the fuel economy characteristics of a diesel engine, and shows the fuel economy characteristics as an equal fuel economy map with the diesel engine torque [N m] on the vertical axis and the diesel engine speed [rpm] on the horizontal axis.

[0030] As shown in Figure 3, the fuel efficiency characteristics of diesel engines show a tendency that the fuel efficiency improves as the output (torque x rotation speed) increases and deteriorates as the output decreases. In order to improve the fuel efficiency of diesel engines, it is effective to drive the auxiliary devices by supplying electricity from a secondary battery (hereinafter referred to as power assist) in the range where the fuel efficiency is worse (the range where the output is smaller).

[0031] Therefore, in this embodiment, a first discharge section in which discharge (power assist) from the secondary battery 17 is performed is set in consideration of the timing when the engine 1 (diesel engine) is operating in a region with a smaller output.

[0032] Next, a case where the timing (first discharge section) for performing power assist is set in accordance with the energy consumption of the dump truck 100 will be described.

[0033] FIG. 4 is a diagram showing the driving pattern of a dump truck in a mine, which is an example of a work site, as a change in vehicle speed, with the vertical axis representing vehicle speed [km / h] and the horizontal axis representing time [h].

[0034] As shown in Fig. 4, the change in vehicle speed of the dump truck 100 in a mine repeats approximately the same traveling pattern. For example, the dump truck 100 in a mine repeatedly moves to a loading site to load materials, and moves to an unloading site to unload materials. During this time, the dump truck 100 repeatedly goes up and down the slopes of the mine and accelerates and decelerates, so that the traveling electric motors 3L, 3R repeatedly perform power running and regenerative operations. The regenerative power used for power assist is obtained by the regenerative operation.

[0035] FIG. 5 is a diagram showing an example of the change in charge amount (charge / discharge characteristics) in the driving pattern shown in FIG. 4, with the vertical axis representing the charge amount [kWh] of the secondary battery and the horizontal axis representing time [h].

[0036] Fig. 5 shows the transition of the charge amount (charge / discharge characteristics) of the secondary battery when the dump truck runs in the driving pattern shown in Fig. 4 and the regenerative power obtained by braking the vehicle is immediately discharged the next time the vehicle is powered. In this case, charging and discharging are almost completed in the early section of the driving pattern, and considering the overall energy balance, there is a possibility of further improvement.

[0037] FIG. 6 is a diagram showing an example of the transition of the engine fuel consumption rate in the driving pattern shown in FIG. 4, with the vertical axis representing the fuel consumption rate [g / kwh] and the horizontal axis representing time [h].

[0038] The dump truck driving pattern shown in Figure 4 shows a characteristic having two types of sections: a section where the vehicle speed is high and the output is considered to be relatively high, and a section where the vehicle speed is low and the output is considered to be relatively low. Correspondingly, Figure 6 also shows a characteristic having a section where the fuel consumption rate is good and a section where the fuel consumption rate is poor.

[0039] Here, if discharging of the secondary battery is performed so that charging and discharging is almost completed in the early period of the driving pattern as shown in Figure 5, power assist from the secondary battery will be performed even in the section where the engine has good fuel efficiency as shown in Figure 6, and it is considered that the contribution of the power assist to improving fuel efficiency will not be large. In other words, further reductions in fuel consumption can be expected by suppressing the implementation of power assist (discharging) in the section where the engine has good fuel efficiency as shown in the first half of the driving pattern in Figure 6, while implementing power assist (discharging) in the section where the engine has poor fuel efficiency as shown in the second half of the driving pattern.

[0040] In this embodiment, the first and second discharge sections are set based on the above findings, thereby reducing fuel consumption. That is, when only the fuel efficiency of the engine is considered, it is desirable to perform the power assist in a section where the engine's fuel efficiency is as poor as possible when the regenerative power obtained by the electric braking of the traveling electric motor is charged to the secondary battery and this power is utilized for the power assist of the electric drive unit. However, since diesel engines generally have a characteristic that the fuel efficiency is poor in a region where the output is small, if the power assist section is set in consideration of only the engine's fuel efficiency, it is not possible to use up all of the regenerative power collected in the secondary battery, and there is room for further reduction in fuel consumption. Therefore, in a dump truck traveling pattern having two types of sections, a section where the engine's fuel efficiency is relatively good and a section where the fuel efficiency is relatively poor, as shown in FIG. 6, a section where the secondary battery is discharged (power assist) regardless of the fuel efficiency and where the balance of charging and discharging in the traveling cycle of the dump truck is adjusted to match (hereinafter, also referred to as "other discharge section") is set as the second discharge section.

[0041] In this manner, in the present embodiment, the first discharge interval is set in accordance with the fuel efficiency of the engine 1, and the second discharge interval in which discharging is performed regardless of the fuel efficiency is set, thereby making it possible to further reduce fuel consumption.

[0042] FIG. 7 is a functional block diagram showing the processing contents of a functional unit related to a discharge section determination process for determining a discharge section, among the processing functions of the regenerative control device.

[0043] In Figure 7, the regenerative control device 20 has an engine fuel efficiency point threshold adjustment unit 21, a driving pattern generation unit 22, a secondary battery charge / discharge balance information calculation unit 23, and a battery discharge section judgment unit 24 as functional units related to the discharge section determination process that determines the discharge section.

[0044] The engine fuel efficiency point threshold adjustment unit 21 sets a fuel efficiency threshold to be used for determining the first discharge interval based on engine fuel efficiency information obtained from the ECU 1a that controls the operation of the engine 1, and outputs the fuel efficiency threshold to the battery discharge interval determination unit 24.

[0045] The driving pattern generation unit 22 generates the latest driving pattern at the work site of the dump truck 100 based on position information (information about the driving point) of the dump truck 100 obtained from a GNSS (Global Navigation Satellite System) (not shown) installed on the dump truck 100, gradient information of the dump truck 100 obtained from the GNSS or an inclination sensor (not shown), vehicle speed information of the dump truck 100 obtained via CAN communication, etc., and driving torque information calculated based on information from the ECU 1a, etc., and outputs this as a driving pattern signal to the battery discharge zone judgment unit 24, thereby updating the driving pattern used for processing in the battery discharge zone judgment unit 24.

[0046] The secondary battery charge / discharge balance information calculation unit 23 generates information (secondary battery charge / discharge balance information) indicating the balance of power charged and discharged by the secondary battery 17 during a predetermined period (for example, one cycle of the driving pattern of the dump truck 100) based on information (current / voltage information) related to the current and voltage acquired from the secondary battery 17, and outputs the information to the battery discharge section determination unit 24. Note that one cycle of the driving pattern of the dump truck 100 at a work site such as a mine is, for example, a series of driving operations from a reference point on the road of the dump truck 100 to a loading position where soil or the like is loaded and a soil discharge position where the soil is discharged, and then back to the reference point. However, the reference point may be set at the loading position or the soil discharge position, and one cycle may be a driving operation that passes through the loading position and the soil discharge position multiple times.

[0047] The battery discharge section determination unit 24 determines two types of discharge sections, a first and a second discharge section, based on the engine fuel efficiency information acquired from the ECU 1a, the fuel efficiency threshold from the engine fuel efficiency point threshold adjustment unit 21, the driving pattern acquired as a driving pattern signal from the driving pattern generation unit 22, and the secondary battery charge / discharge balance information acquired from the secondary battery charge / discharge balance information calculation unit 23, and outputs a signal permitting discharge of the secondary battery 17 (discharge permission signal) to the bidirectional converter 16 only in the first and second discharge sections. The bidirectional converter 16 discharges the secondary battery 17 only while the discharge permission signal is output from the battery discharge section determination unit 24 in the first and second discharge sections, and charges the secondary battery 17 in other cases.

[0048] In reality, the driving pattern at a work site such as a mine where the dump truck 100 operates can be roughly predicted in advance before the dump truck 100 is introduced, so the initial value of the fuel efficiency threshold set by the engine fuel efficiency point threshold adjustment unit 21 and the initial value of the driving pattern generated by the driving pattern generation unit 22 can be set in advance based on the predicted driving pattern, and the initial values ​​of the two types of discharge sections, the first and second discharge sections, determined by the battery discharge section determination unit 24 can also be provisionally set when the dump truck 100 is initially introduced to the site.

[0049] FIG. 8 is a flowchart showing the process of determining the discharge section in the regenerative control device.

[0050] 8, the regenerative control device 20 first acquires information used by the engine fuel efficiency point threshold adjustment unit 21 and the battery discharge section determination unit 24 (engine fuel efficiency, fuel consumption [l / h]), information used by the driving pattern generation unit 22 (driving point information, gradient information, vehicle speed information, driving torque information), and information used by the secondary battery charge / discharge balance information calculation unit 23 (current / voltage information) (step S100). Note that the various pieces of information acquired in step S100 are updated sequentially, for example, at the minimum processing cycle of the calculation device constituting the regenerative control device 20, regardless of the cycle of the discharge section determination process.

[0051] After various pieces of information are acquired in step S100, it is then determined whether the engine fuel consumption [l / h] has improved from the previous cycle (step S110).

[0052] If the determination result in step S110 is YES, that is, if it is determined that the engine fuel consumption has improved compared to the previous cycle, it is determined that there is room for further improvement (improvement margin), and the engine fuel efficiency threshold is lowered by a predetermined value to adjust the first discharge interval (step S111), and then the second discharge interval is adjusted (adjusted to match the charge / discharge balance of the secondary battery 17) in accordance with the adjustment of the engine fuel efficiency threshold in step S111 (step S120), and the process ends. By such processing in step S111, the electric power energy discharged from the secondary battery 17 in the first discharge interval increases, and as a result, the fuel reduction effect can be increased.

[0053] Also, if the determination result in step S110 is NO, that is, if it is determined that the engine fuel consumption has not improved (i.e., has worsened) compared to the previous cycle, it is determined that there is a section with poor fuel consumption in the latter half of the driving pattern and that it is necessary to limit the discharge from the secondary battery 17 in the first discharge section, and the engine fuel consumption threshold is raised by a predetermined value to adjust the first discharge section (step S112), and then the second discharge section is adjusted (adjusted to match the charge and discharge balance of the secondary battery 17) in accordance with the adjustment of the engine fuel consumption threshold in step S112 (step S120), and the process ends. By such processing in step S112, the electric power energy discharged from the secondary battery 17 in the first discharge section is reduced, and as a result, the fuel consumption reduction effect can be increased.

[0054] The adjustment range of the engine fuel efficiency threshold in steps S111 and S112 can be set appropriately taking into account the amount of change in the fuel consumption rate of the dump truck 100. For example, the fuel consumption rate [g / kwh] equivalent to 0.1 [L] in fuel volume is set as the change value for the fuel efficiency threshold for each cycle.

[0055] The regenerative control device 20 repeats the process of steps S100 to S120 as the discharge interval determination process for each cycle, thereby setting a combination of the first and second discharge intervals that minimizes (optimizes) the amount of fuel consumed by the engine.

[0056] FIG. 9 is a diagram showing an example in which a fuel efficiency threshold is set for the transition of the engine fuel consumption rate in the driving pattern shown in FIG. 4, and first and second discharge sections are set, with the vertical axis showing fuel consumption rate [g / kwh] and the horizontal axis showing time [h].

[0057] As shown in FIG. 9, when the engine fuel efficiency threshold value of this embodiment is set and the first and second discharge intervals are set, the secondary battery is discharged (power assist) accordingly for the auxiliary device.

[0058] FIG. 10 is a diagram showing an example of the change in the charge amount (charge and discharge characteristics) when the engine fuel efficiency threshold is set as shown in FIG. 9 in the driving pattern shown in FIG. 4 and the first and second discharge sections are set, with the vertical axis showing the charge amount [kWh] of the secondary battery and the horizontal axis showing time [h].

[0059] As shown in FIG. 10, the charge and discharge characteristics of the secondary battery 17 in this embodiment are compared with the charge and discharge characteristics (see FIG. 5) in the case where the control according to this embodiment is not applied and the regenerative power obtained by braking the vehicle is immediately discharged during the next vehicle powering. It can be confirmed that the charge amount of the secondary battery 17 remains until the latter half of the driving pattern, and discharging (power assist) is performed in the section with poor engine fuel efficiency in the latter half of the driving pattern. In addition, since the charge and discharge balance per cycle is adjusted to match, the fuel consumption can be reduced by efficiently using the electric energy. In this way, in this embodiment, it is possible to realize a reduction in the fuel consumption of the engine by utilizing the regenerative power by repeatedly calculating the driving pattern of the dump truck 100 according to the situation of the work site and setting the engine fuel efficiency threshold (first discharge section) and the second discharge section accordingly.

[0060] In FIG. 10, the charge / discharge characteristics (charge / discharge balance) per cycle of the driving pattern are illustrated based on a state in which the charge amount is 0 (zero). However, in practice, taking into account the effects of deterioration during charging and discharging of the secondary battery 17, it is desirable to operate the battery with a reference point of about 50% of the full charge amount or an average value over one cycle of about 50%.

[0061] The effects of the present embodiment configured as above will be described using a comparative example.

[0062] FIG. 12 is a schematic diagram illustrating a portion of an electric drive system shown as a comparative example together with the peripheral configuration.

[0063] In FIG. 12, the electric drive system of the comparative example mainly includes a main generator 2 and an auxiliary generator 14 driven by an engine 1, a rectifier 8 that rectifies the current (AC power) output from the main generator 2, an inverter 9 that converts the current (DC power) rectified by the rectifier 8 into an AC power drive signal and supplies it to the traveling electric motors 3L, 3R, the traveling electric motors 3L, 3R that drive the drive wheels 5L, 5R (wheels) using power supplied from the main generator 2 via the rectifier 8 and the inverter 9, an auxiliary rectifier 11 that rectifies the current (AC power) output from the auxiliary generator 14, an auxiliary motor 13 which is an auxiliary device such as a cooling blower, and an auxiliary inverter 12 that converts the current (DC current) rectified by the auxiliary rectifier 11 into an AC power drive signal and supplies it to the auxiliary motor 13 (auxiliary device).

[0064] 12 to a dump truck operating at a work site such as a mine, a highly efficient electric motor is used and the engine can be driven at an operating point with high combustion efficiency, so a reduction in fuel consumption can be expected. However, with this electric drive system, on slopes (downhill slopes) that are numerous at work sites such as mines, the regenerative power generated by the traveling electric motor can only be consumed by external resistor 15, and further improvement was an issue to be addressed.

[0065] Another conventional technique for addressing this issue is to install a relatively large capacity secondary battery, store electricity from a generator driven by the engine in the secondary battery, and supply electricity from the secondary battery when a large engine power is required, such as when the vehicle is traveling uphill, thereby reducing fuel consumption. On the other hand, when the capacity of the secondary battery is limited, such as in a system intended to drive auxiliary devices using regenerative power generated by a traveling electric motor, the cost required to secure the capacity of the secondary battery is suppressed, but the effect of reducing fuel consumption is considered to be limited even if the above conventional technique is applied.

[0066] In contrast to this, in the present embodiment, there is an engine 1, a main generator 2 and an auxiliary generator 14 driven by the engine, traction electric motors 3L, 3R driven by power supplied from the main generator, auxiliary devices (e.g., an auxiliary inverter 12 and an auxiliary motor 13 constituting a cooling blower) driven by power supplied from the auxiliary generator, a regeneration device (e.g., a DC-DC converter 10) that supplies regenerative power generated when the traction electric motor brakes the vehicle to the auxiliary devices, and a battery that can store the power supplied from the regeneration device and the auxiliary generator to the auxiliary devices. In an electrically powered work vehicle (e.g., a dump truck 100) equipped with a secondary battery 17, the regenerative device determines a first discharge section in which the battery is discharged in accordance with the engine's fuel efficiency and a second discharge section in which the battery is discharged in accordance with the amount of energy consumed by the vehicle based on the driving pattern of the electrically powered work vehicle and the engine's fuel consumption rate, and is configured to supply power from the battery to an auxiliary device or a traveling electric motor based on the first and second discharge sections, thereby making it possible to further reduce fuel consumption when the capacity of the secondary battery is relatively small.

[0067] FIG. 11 is a diagram for explaining the improvement in fuel consumption rate and fuel consumption amount of this embodiment compared to the conventional technology, with the left vertical axis showing fuel consumption rate [g / kwh], the right vertical axis showing fuel consumption amount [l] (accumulated amount), and the horizontal axis showing time [h].

[0068] As shown in FIG. 11, in this embodiment, in sections a and c (sections with high (poor) fuel consumption rate), power assist from the secondary battery 17 to the auxiliary device is performed, so that fuel consumption can be reduced more than with the conventional technology. On the other hand, in this embodiment, in section b (section with low fuel consumption rate), power assist from the secondary battery 17 to the auxiliary device is not performed, so that fuel consumption per unit time increases slightly more than with the conventional technology. However, since section b is a section with low (good) fuel consumption rate, the increase in fuel consumption per unit time is small. And, the total fuel consumption in sections a, b, and c can be reduced more than with the conventional technology.

[0069] <Additional Notes> The present invention is not limited to the above-described embodiments, and includes various modifications and combinations within the scope of the gist of the present invention. The present invention is not limited to those having all the configurations described in the above-described embodiments, and includes those in which some of the configurations are deleted. The above-described configurations, functions, etc. may be realized by designing some or all of them as an integrated circuit, for example. The above-described configurations, functions, etc. may be realized by software, in which a processor interprets and executes a program that realizes each function.

[0070] For example, in this embodiment, an auxiliary device such as a cooling blower has been given as an example of the destination of power supply during discharge (power assist) of the secondary battery, but this is not limited to this. For example, by making the regeneration device (DC-DC converter 10) a bidirectional DC-DC converter, it is also possible to have the power supply during discharge (power assist) of the secondary battery be the driving electric motors 3L, 3R. In such a case, the fuel efficiency improvement effect can be further enhanced by increasing the capacity of the secondary battery. [Explanation of symbols]

[0071] 1...engine, 2...main generator, 3L, 3R...electric motor for driving, 4L, 4R...driven wheels, 5L, 5R...driving wheels, 6...driver's seat, 7...cargo bed (vessel), 7a...pin coupling, 8...rectifier, 9...inverter, 10...DC-DC converter, 11...auxiliary rectifier, 12...auxiliary inverter, 13...auxiliary motor, 14...auxiliary generator, 15...external resistor, 16...bidirectional converter, 17...secondary battery, 18...vehicle frame, 20...regenerative control device, 21...engine fuel consumption point threshold adjustment unit, 22...driving pattern generation unit, 23...secondary battery charge / discharge balance information calculation unit, 24...battery discharge section determination unit, 100...dump truck

Claims

1. The engine, a main generator and an auxiliary generator driven by the engine; a traveling electric motor driven by electric power supplied from the main generator; an auxiliary device driven by power supplied from the auxiliary generator; a regenerative device that supplies regenerative electric power generated when the electric motor for running the vehicle is braked to the auxiliary device; a battery capable of storing electric power supplied from the regenerative device and the auxiliary generator to the auxiliary device, The regenerative device includes: Based on the driving pattern of the electrically driven work vehicle and the fuel consumption rate of the engine, a first discharge section in which the battery is discharged according to a fuel consumption rate of the engine, the first discharge section being defined by a travel section or time of the electrically driven work vehicle; determining a section in which the battery is discharged according to the magnitude of the energy consumption of the vehicle as a travel section of the electrically-driven work vehicle or a second discharge section defined by time; 2. An electrically driven work vehicle, comprising: a battery that supplies electric power to the auxiliary device or the electric motor for traveling based on the first and second discharge sections.

2. 2. The electrically driven work vehicle according to claim 1, The regenerative device includes: repeatedly calculating the driving pattern and the fuel consumption of the engine; determining a discharge timing of the battery so as to minimize fuel consumption of the engine in the driving pattern; an electrically powered work vehicle, wherein power is supplied from the battery to the auxiliary device based on the discharge timing.

3. 2. The electrically driven work vehicle according to claim 1, The regenerative device includes: determining a section in which a fuel consumption rate of the engine is greater than a predetermined fuel efficiency threshold as the first discharge section; 2. An electrically powered work vehicle, comprising: a first discharge section for discharging said electric power from said first discharge section to said second discharge section;

4. 4. The electrically driven work vehicle according to claim 3, The regenerative device includes: After determining the first discharge section by adjusting the fuel efficiency threshold value so that the fuel consumption amount of the engine in the driving pattern is reduced, 2. An electrically powered work vehicle, comprising: a first discharge section for discharging said electric power from said first discharge section to said second discharge section;

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