Electrically powered 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 driven 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 loading areas to dump sites. At work sites, the route from the loading area to the dump site is fixed, and if multiple dump trucks of the same size travel along a single route, they operate 24 hours a day, repeatedly making round trips, thereby improving 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). To improve transport efficiency, dump trucks employ various measures to reduce initial costs and running costs. Reducing running costs can be achieved by using an electric drive system, a type of drive system that is efficient and has relatively low maintenance costs, to reduce the engine's fuel consumption rate [g / kWh].

[0004] In dump trucks, mechanical drive systems transmit engine power to the tires using a torque converter and a transmission. In contrast, electric drive systems use the engine to drive a generator, which then uses the generated electricity to drive an electric motor connected to the tire axle. Electric drive systems use a highly efficient electric motor and can drive the engine at an operating point with high combustion efficiency, which can improve fuel consumption [g / kWh] (i.e., fuel economy). Furthermore, electric drive systems can generate regenerative power by using the electric motor to generate electrical braking force on slopes (downhill slopes), which are common in mines and other work sites. By utilizing this regenerative power, further improvements in fuel economy can be expected. Specifically, the regenerative power generated during braking can be used to drive auxiliary equipment, or it can be temporarily used to charge a secondary battery and be used to drive the vehicle and auxiliary equipment during normal driving.

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

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-103984 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned conventional technology, a secondary battery with a relatively large capacity is installed, and electricity from a generator driven by an engine is stored in the secondary battery. When large 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 equipment using regenerative power generated by a driving electric motor, the cost required to secure the capacity of the secondary battery can be reduced, but even if the above-mentioned conventional technology is applied, the effect of improving the fuel efficiency of the engine is likely to be limited.

[0009] The present invention has been made in consideration of the above, and aims to provide an electrically driven 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 a plurality of means for solving the above-mentioned problems, and an example thereof is a vehicle comprising an engine, a main generator and an auxiliary generator driven by the engine, a traction electric motor driven by electric power supplied from the main generator, an auxiliary device driven by electric power supplied from the auxiliary generator, a regenerative device that supplies regenerative electric power generated by the traction electric motor when braking the vehicle to the auxiliary device, and a storage battery that can store electric power supplied from the regenerative device and the auxiliary generator to the auxiliary device. and capable of discharging the stored power and supplying it to the auxiliary device. With a battery, a regeneration control device that controls the operation of the entire electric drive system; In an electrically driven work vehicle equipped with control the device defines a first discharge section, which is a section in which the battery is discharged according to the engine's fuel consumption rate, based on the driving pattern of the electrically driven work vehicle and the engine's fuel consumption rate, and which is defined by the driving section or time of the electrically driven work vehicle; Electric drive operationThe section in which the battery is discharged is determined to be a travel section of the electrically driven work vehicle or a second discharge section defined by time according to the amount of energy consumed by the vehicle, and power is supplied from the battery to the auxiliary equipment or the electric motor for travel based on the first and second discharge sections. The second discharge section is a section in which the battery is discharged regardless of the fuel consumption rate of the engine, and is a section that is adjusted to balance the charge and discharge in the driving cycle of the electrically driven work vehicle, and the first discharge section and the second discharge section are set during the driving cycle. This shall be done. [Effects 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 explanation of the drawings]

[0012] [Figure 1] 1 is a side view schematically showing the appearance of a dump truck, which is an example of an electrically driven work vehicle. [Figure 2] FIG. 1 is a diagram illustrating a schematic view of a portion of an electric drive system together with its peripheral configuration. [Figure 3] FIG. 2 is a diagram showing an example of fuel efficiency characteristics of a diesel engine. [Figure 4] FIG. 1 is a diagram showing a travel pattern of a dump truck in a mine, which is an example of a work site, as a change in vehicle speed. [Figure 5] 5 is a diagram showing an example of the transition of the charge amount (charge and discharge characteristics) in the driving pattern shown in FIG. 4. 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. 4. [Figure 7] 3 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 regeneration control device; FIG. [Figure 8] 10 is a flowchart showing the processing contents of a discharge interval determination process in the regeneration control device. [Figure 9] 5 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 intervals 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 sections are set. [Figure 11] 10A and 10B are diagrams illustrating an improvement in fuel consumption rate in the present embodiment compared to the prior art. [Figure 12] FIG. 1 is a diagram schematically illustrating a portion of an electric drive system according to a comparative example, together with the peripheral configuration. DETAILED DESCRIPTION OF THE INVENTION

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

[0014] FIG. 1 is a side view that schematically shows the appearance of a dump truck, which is an example of an electrically driven work vehicle according to this embodiment.

[0015] 1, the dump truck 100 is generally composed of a body frame 18 that extends in the fore-and-aft direction and forms a support structure, a loading platform (vessel) 7 that is arranged on top of the body frame 18 so as to be spaced apart in the fore-and-aft direction and whose lower rear end is tiltably attached to the body frame 18 via a pin connection 7a, a pair of driven wheels 4L (4R) provided on the left and right sides of the lower front of the body frame 18, a pair of drive wheels 5L (5R) provided on the left and right sides of the lower rear of the body, a driver's seat 6 provided on the upper front of the body frame 18, an engine 1 (e.g., a diesel engine) arranged on the body frame 18, and an electric drive system including 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. Note that in FIG. 1, only one of the pair of driven wheels and drive wheels is shown and reference numerals are used, while the other is not shown, with only the reference numeral in parentheses in the drawing.

[0016] FIG. 2 is a schematic diagram illustrating a portion of the electric drive system together with its 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 traction electric motors 3L, 3R, the traction 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 that 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 dump truck 100 generally includes an auxiliary inverter 12 that converts power from the auxiliary inverter 12 and supplies it to an auxiliary motor 13 (auxiliary equipment), a DC-DC converter 10 (hereinafter also referred to as a regenerative device) that converts and exchanges power between a circuit downstream of a rectifier 8 on the main generator 2 side (hereinafter referred to as a main circuit) and a circuit downstream of an auxiliary rectifier 11 on the auxiliary generator 14 side (hereinafter referred to as an auxiliary circuit), a secondary battery 17 that stores power from the auxiliary circuit, a bidirectional converter 16 that converts power between the auxiliary circuit and the secondary battery 17 and controls the storage (charging) and discharging of the secondary battery 17, an external resistor 15 that consumes surplus power on the main circuit side as needed, and a regenerative control device 20 that controls the overall operation of the electric drive system, including the regenerative operation. The dump truck 100 is equipped with multiple sets of cooling blowers (auxiliary inverters 12 and auxiliary motors 13) as auxiliary equipment, but for simplicity of illustration, only one set of auxiliary equipment is shown in FIG. 2.

[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, where it is used 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 auxiliary devices, thereby reducing fuel consumption accordingly.

[0019] Furthermore, 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, supplies the power to the auxiliary circuit side, and stores the power in the secondary battery 17 via the bidirectional converter 16. The power stored in the secondary battery 17 is then supplied to the auxiliary equipment during operations other than regeneration of the traveling electric motors 3L, 3R (for example, power running of the dump truck 100). That is, in this embodiment, a portion of the surplus regenerative power generated by the traveling electric motors 3L, 3R that is not used to drive the auxiliary equipment is recovered without being consumed by the external resistor 15, stored in the secondary battery 17, and supplied to the auxiliary equipment during operations other than regeneration of the traveling electric motors 3L, 3R. This makes it possible to further improve 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 fairly large capacity storage device and can run on the electrical system alone (so-called strong hybrid types), and systems that use regenerative energy primarily as an energy source for the electrical system and whose main operation is to assist the engine and drive auxiliary systems, i.e., systems that are not intended to run the vehicle solely on power supplied from the storage device (so-called mild hybrid types).

[0023] Typically, the regenerative power of the electric motor for driving a large dump truck operating in mines and other locations is roughly several thousand kW, while the power required by the auxiliary equipment is approximately 100 kW—a vast difference in magnitude. Therefore, the regenerative power of a dump truck is greater than the power required by the auxiliary equipment, and in many cases cannot be absorbed by the power supplied to the auxiliary equipment via the regenerative device alone during vehicle braking. Therefore, by consuming a portion of the regenerative power using an external resistor, the excess regenerative power relative to the power supplied to the auxiliary equipment can be accommodated.

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

[0025] Therefore, in this embodiment, a relatively small secondary battery, which is considered to have 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 by supplying power from the secondary battery 17 to the auxiliary equipment (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 power assist according to the amount of 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 (e.g., the start of travel in a transport work cycle), and the start and end of the first and second discharge sections are each defined based on the elapsed time. Note that the following description will exemplify a case in which the first and second discharge sections for power assist are each defined by time as described above, but a configuration in which a section between specific positions within a travel section is set based on the position of the dump truck 100 may also be used.

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

[0029] Fig. 3 shows an example of the fuel economy characteristics of a diesel engine, showing 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 economy characteristics of a diesel engine tend to improve as the output (torque x rotation speed) increases and worsen as the output decreases. To improve the fuel economy of a diesel engine, it is effective to drive the auxiliary equipment with power supplied from a secondary battery (hereinafter referred to as power assist) in the range where fuel economy is worse (range where output is lower).

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

[0032] Next, a case where the timing (first discharge interval) for performing power assistance 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 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 location to load materials, and moves to an unloading location to unload materials. During this time, the dump truck 100 repeatedly ascends and descends the slopes of the mine and accelerates and decelerates, so the traveling electric motors 3L, 3R alternate between power running and regenerative operation. The regenerative power used for power assist is obtained through 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 travel 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 is almost completed in the early section of the travel 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 are 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 sections where the engine has good fuel efficiency as shown in Figure 6, and it is thought that the contribution of power assist to improving fuel efficiency will not be significant. In other words, further reductions in fuel consumption can be expected by limiting the implementation of power assist (discharging) in sections 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 sections where the engine has poorer fuel efficiency as shown in the second half of the driving pattern.

[0040] This embodiment aims to reduce fuel consumption by setting first and second discharge sections based on the above findings. That is, when focusing only on the fuel efficiency of the engine, if the regenerative power obtained by the electric braking of the traveling electric motor is charged to a secondary battery and this power is used to power assist the electric drive unit, it is desirable to perform the power assist in sections where the engine's fuel efficiency is as poor as possible. However, since diesel engines generally have characteristics such that fuel efficiency is poor in low-output ranges, if the power assist section is set based only on the engine's fuel efficiency, it is not possible to use up all of the regenerative power recovered in the secondary battery, leaving room for further fuel consumption reduction. Therefore, in a dump truck driving pattern having two types of sections, one where the engine's fuel efficiency is relatively good and the other where the fuel efficiency is relatively poor, as shown in FIG. 6 , a section (hereinafter also referred to as "other discharge section") in which the secondary battery is discharged (power assist) regardless of the fuel efficiency to balance the charge and discharge in the dump truck's driving cycle is set as the second discharge section.

[0041] In this way, in this embodiment, the first discharge interval is set according to the fuel efficiency of the engine 1, and the second discharge interval in which discharge 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 regeneration control device.

[0043] In Figure 7, the regeneration control device 20 has, as functional units related to the discharge section determination process that determines the discharge section, 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 determination unit 24.

[0044] The engine fuel efficiency point threshold adjustment unit 21 sets a fuel efficiency threshold to be used in 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 it to the battery discharge interval determination unit 24.

[0045] The driving pattern generation unit 22 generates the latest driving pattern of the dump truck 100 at the work site based on position information (driving point information) 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 section judgment unit 24, thereby updating the driving pattern used for processing in the battery discharge section 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 driving path of the dump truck 100 to a loading position where earth and sand are loaded and an earth-discharging position where the earth and sand are discharged, and then back to the reference point. However, the reference point may be set at the loading position or the earth-discharging position, or one cycle may be a driving operation that passes through the loading position and the earth-discharging 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 (discharge permission signal) permitting discharge of the secondary battery 17 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 being 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 processing contents of the discharge interval determination processing in the regeneration control device.

[0050] 8, the regeneration 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 (information on engine fuel efficiency and fuel consumption [l / h]), information used by the driving pattern generation unit 22 (information on driving points, gradient information, vehicle speed information, and 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 regeneration 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 compared to 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 first discharge interval is adjusted by lowering the engine fuel efficiency threshold by a predetermined value (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 performing 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] Furthermore, 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 economy in the latter half of the driving pattern and that it is necessary to limit discharge from the secondary battery 17 in the first discharge section, and the engine fuel economy threshold is increased 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 / discharge balance of the secondary battery 17) in accordance with the adjustment of the engine fuel economy threshold in step S112 (step S120), and the process ends. By performing 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 conversion 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 determining the 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 consumption 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 to the auxiliary device.

[0058] FIG. 10 is a diagram showing an example of the change in charge amount (charge / discharge characteristics) when the engine fuel consumption 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 / discharge characteristics of the secondary battery 17 in this embodiment are compared with the charge / 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 seen that the charge amount of the secondary battery 17 remains until the latter half of the driving pattern, and discharging (power assist) occurs in the section of the latter half of the driving pattern where the engine fuel efficiency is poor. Furthermore, since the charge / discharge balance per cycle is adjusted to match, fuel consumption can be reduced by efficiently using electric energy. In this way, in this embodiment, the driving pattern of the dump truck 100 according to the conditions of the work site is repeatedly calculated, and the engine fuel efficiency threshold (first discharge section) and the second discharge section are set accordingly, thereby making it possible to reduce engine fuel consumption by utilizing regenerative power.

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

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

[0062] FIG. 12 is a diagram schematically 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 traction electric motors 3L, 3R, the traction 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 can be used and the engine can be driven at an operating point with high combustion efficiency, which is expected to reduce fuel consumption. However, with this electric drive system, when an electric braking force is generated by the traveling electric motor on slopes (downhill slopes), which are common at work sites such as mines, the regenerative power can only be consumed by external resistor 15, and further improvement was required.

[0065] Another conventional technique for addressing this issue involves installing a relatively large-capacity secondary battery, storing power from a generator driven by the engine in the secondary battery, and supplying power from the secondary battery when a large amount of engine power is required, such as when the vehicle is traveling uphill, thereby reducing fuel consumption. On the other hand, in systems where the capacity of the installed secondary battery is limited, such as in systems that aim to drive auxiliary devices using regenerative power generated by a traction electric motor, although the cost required to secure the capacity of the secondary battery is reduced, the effect of reducing fuel consumption is thought to be limited even if the above conventional technique is applied.

[0066] In contrast to this, in this embodiment, the system includes 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 (for example, an auxiliary inverter 12 and an auxiliary motor 13 constituting a cooling blower) driven by power supplied from the auxiliary generator, a regeneration device (for example, 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 power supplied from the regeneration device and the auxiliary generator to the auxiliary devices. In an electrically driven 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 driven 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 illustrating the improvement in fuel consumption rate and fuel consumption amount of this embodiment compared to the conventional technology, with the left vertical axis representing fuel consumption rate [g / kwh], the right vertical axis representing fuel consumption amount [l] (cumulative amount), and the horizontal axis representing 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 fuel consumption can be reduced more than with 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 fuel consumption per unit time increases slightly more than with conventional technology. However, because section b is a section with low (good) fuel consumption rate, the increase in fuel consumption per unit time is small. Therefore, the total fuel consumption in sections a, b, and c can be reduced more than with 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 thereof. Furthermore, the present invention is not limited to those including all of the configurations described in the above-described embodiments, and includes those in which some of the configurations are omitted. Furthermore, the above-described configurations, functions, etc. may be realized in part or in whole by designing them as, for example, integrated circuits. Furthermore, the above-described configurations, functions, etc. may be realized in software by a processor interpreting and executing a program that realizes each function.

[0070] For example, in the present embodiment, an auxiliary device such as a cooling blower is given as an example of the destination of power supply during discharge (power assist) of the secondary battery, but this is not limited thereto. For example, by making the regeneration device (DC-DC converter 10) a bidirectional DC-DC converter, it is also possible to supply power during discharge (power assist) of the secondary battery to the traction electric motors 3L, 3R, and 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...travel electric motor, 4L, 4R...driven wheels, 5L, 5R...driving wheels, 6...driver's seat, 7...loading platform (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...body frame, 20...regeneration 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 and a main generator and an auxiliary generator driven by the engine; an electric motor for driving the vehicle, the electric motor being driven by the electric power supplied from the main generator; an auxiliary device driven by the power supplied from the auxiliary generator; a regenerative device that supplies regenerative electric power generated by the electric motor for traveling when braking the vehicle to the auxiliary device; a battery capable of storing electric power supplied from the regenerative device and the auxiliary generator to the auxiliary device, and capable of discharging the stored electric power to supply the electric power to the auxiliary device; a regenerative control device that controls the operation of the entire electric drive system, The regenerative control 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 in accordance with the 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 based on the amount of energy consumed by the electrically driven work vehicle as a travel section of the electrically driven work vehicle or a second discharge section defined by time; supplying electric power from the battery to the auxiliary device or the electric motor for traveling based on the first and second discharging sections; the second discharge section is a section in which the battery is discharged regardless of the fuel consumption rate of the engine, and is a section that is adjusted to balance the charge and discharge in the driving cycle of the electrically driven work vehicle, and the first discharge section and the second discharge section are set during the driving cycle.

2. 2. The electrically driven work vehicle according to claim 1, The regenerative control 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 driven 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 control device includes: determining a section in which a fuel consumption rate of the engine is greater than a predetermined fuel consumption threshold as the first discharge section; An electrically driven work vehicle, wherein the second discharge section is determined so that the balance of energy consumption in a driving cycle of the electrically driven work vehicle is balanced.

4. 4. The electrically driven work vehicle according to claim 3, The regenerative control device includes: After determining the first discharge section by adjusting the fuel efficiency threshold so that the fuel consumption amount of the engine in the driving pattern is reduced, An electrically driven work vehicle, wherein the second discharge section is determined so that the balance of energy consumption in a driving cycle of the electrically driven work vehicle is balanced.

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