JP2016142118A - Work vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a work vehicle for actualizing a good brake feeling by reducing loss due to a mechanical brake during the great deceleration of the vehicle without impairing braking performance.SOLUTION: The work vehicle includes a travel part having a plurality of wheels 61 to be driven by a travel motor 9, a regenerative braking device 20 mechanically connected to a propeller shaft 8b as a driving shaft for the travel part for performing regenerative braking operation only out of power-driving operation and the regenerative braking operation, a power storage device 11 to be charged with regenerative electric power generated by the regenerative braking device, and a control device 200 for computing braking power to require the travel part to be output during the braking operation of the work vehicle, and for, when the braking power exceeds braking power to be output by the travel motor 9, giving an instruction to the regenerative braking device 20 to generate the deficient braking power.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a work vehicle including a traveling unit driven by an electric motor.

  JP, 2012-175893, A (patent documents 1) is a background art about a regenerative braking device which transmits torque generated at the time of regeneration of a rotary electric machine to a wheel as regenerative braking power.

  This document describes “regenerative braking control for controlling each of a first regenerative braking means capable of transmitting a regenerative braking force to a front wheel of a vehicle and a second regenerative braking means capable of transmitting a regenerative braking force to a rear wheel of the vehicle. A required regenerative braking force calculating means for calculating a required regenerative braking force which is a total value of regenerative braking forces required for each of the first regenerative braking means and the second regenerative braking means; A distribution ratio calculating means for calculating a distribution ratio that minimizes an energy loss when the braking force is distributed and realized by the first regenerative braking means and the second regenerative braking means; and the calculated distribution ratio. There is described a regenerative braking control device including control means for controlling the first regenerative braking means and the second regenerative braking means so as to realize the required regenerative braking force.

JP 2012-175893 A

  In the above document, the first regenerative braking means includes a first electric motor and a regenerative circuit for driving the left and right front wheels of the vehicle, and the second regenerative braking means includes a second electric motor for driving the left and right rear wheels of the vehicle and a regenerative circuit. A vehicle including a circuit, that is, a vehicle including a first motor that drives a set of front wheels and a second motor that drives a set of rear wheels is disclosed.

  Unlike general vehicles that are primarily intended for “running”, a wheel loader that is primarily intended for “work” has a set of rapid acceleration and rapid deceleration just after that in order to maximize the amount of work per hour. The short time operation described above may be repeated. In executing the sudden deceleration, a braking force exceeding the maximum driving force required by the wheel loader is often required. In that case, the wheel loader has a maximum braking force exceeding the maximum driving force at each rotation speed. Required. On the other hand, generally, the driving force and braking force that can be output by the electric motor are substantially equal. Therefore, when only two electric motors (the first electric motor and the second electric motor) are used as the driving source of the traveling unit in the wheel loader as described in the above document, priority is given to satisfying the maximum driving force required by the wheel loader. Thus, when the performance of the two motors is determined, the total braking force required for sudden deceleration cannot be obtained only by the two motors, resulting in insufficient braking force, resulting in the required braking performance. There is no possibility.

  As a measure for avoiding such a situation, a mechanical braking device (mechanical brake) such as a hydraulic brake is provided, and the mechanical braking force compensates for an insufficient electrical braking force by the electric motor. . However, with this measure, the amount of friction using the mechanical brake becomes a friction loss. Furthermore, since electric brakes and mechanical brakes having different characteristics are used in combination, it becomes difficult to optimally control the braking characteristics of the vehicle, and the necessary braking performance of the entire vehicle may not be obtained. .

  The above problem is not limited to the illustrated wheel loader, and rapid acceleration and rapid deceleration are repeatedly performed in a short time. When executing the rapid deceleration, a braking force exceeding the maximum driving force required during operation is required. This also applies to other work vehicles that can be obtained.

  The present invention has been made in view of the above circumstances, and its purpose is to reduce the loss caused by the mechanical brake even when the vehicle is largely decelerated and to realize a good brake feeling without impairing the braking performance. The object is to provide a working vehicle.

  In order to achieve the above object, the present invention provides a regenerative unit that is mechanically connected to a traveling unit driven by an electric motor and a drive shaft of the traveling unit, and performs only a regenerative braking operation among a power running drive operation and a regenerative braking operation. A braking device, a power storage device that charges the regenerative power generated by the regenerative braking device, and a braking power that requires output from the traveling unit during a braking operation of the work vehicle can be calculated, and the braking power can be output by the electric motor. And a control device that instructs the regenerative braking device to generate a shortage of braking power when the braking power exceeds a certain level.

  According to the present invention, when the work vehicle is greatly decelerated, it is possible to reduce the loss due to the brake and realize a good brake feeling without impairing the braking performance.

The side view of the hybrid type wheel loader which concerns on embodiment of this invention. The figure which shows the system configuration | structure of the wheel loader 100 shown in FIG. The figure which shows schematic structure of a field winding type generator. The figure which shows the drive system structure of the wheel loader using a torque converter. The figure which shows V-shaped excavation operation | movement which is an example of the work pattern of a wheel loader. Functional block diagram showing functions of the control device 200 for performing power control related to the regenerative braking device 20 Output characteristics when the operating range of the regenerative braking device 20 is set to a predetermined vehicle speed range. The figure which shows the temporal relationship of the vehicle speed and the field current of the regenerative braking device 20. The figure which shows the structural example which mounts the regenerative braking device 20 via the transmission 30 in the hybrid type wheel loader. The figure which shows the operation | movement area | region of the regenerative braking device 20 mounted via the transmission 30. FIG. The figure which shows the other example of arrangement | positioning of the regenerative braking device 20. FIG. The figure which shows the operation area | region of the regenerative braking device 20 at the time of continuous descent.

  Hereinafter, an embodiment in which the present invention is applied to a hybrid wheel loader will be described. A hybrid wheel loader generally uses the output of an engine and the power of a power storage device (secondary battery or capacitor) as a main power source, and the main drive target part is a traveling part (wheel part) and a hydraulic working part (front). The hydraulic actuator of the hydraulic working unit is operated by a hydraulic pump driven by an engine or electric motor while driving by driving four wheels of the traveling unit by an electric motor. This is a work vehicle that excavates and transports earth and sand.

  FIG. 1 is a side view of a hybrid wheel loader according to an embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same part in each figure, The description of the said same part may be abbreviate | omitted.

  The wheel loader 100 in FIG. 1 includes a vehicle body 110 and a hydraulic working device 50 attached to the front of the vehicle body 110. The vehicle body 110 employs an articulated steering system (a vehicle body refraction system), and a front vehicle body (front frame) 111 and a rear vehicle body (rear frame) with wheels 61 (front wheels 61a and rear wheels 61b) mounted on the left and right, respectively. 112 are connected by a center joint 64. Although not shown in FIG. 1, steering cylinders 53 (see FIG. 2) are arranged on the left and right sides of the center joint 64 so as to connect the front vehicle body 111 and the rear vehicle body 112. When a steering wheel (not shown) installed in the cab 116 is operated, the rear vehicle body 112 and the front vehicle body 111 are refracted (turned) around the center joint 64 as the steering cylinder 53 extends and contracts. )

  On the rear vehicle body 112, a driver's cab 116 is mounted in the front and an engine chamber 117 is mounted in the rear. The engine room 117 houses the diesel engine 1, the hydraulic pump 4, the control valve 55, the motor generator 6, the power storage device 11, the traveling motor (traveling motor) 9, and the like shown in FIG.

  The hydraulic working device 50 includes a lift arm 121 and a bucket 122, and a lift cylinder 52 and a bucket cylinder 51 that are extended and contracted to drive the lift arm 121 and the bucket 122. One lift arm 121 and one lift cylinder 52 are provided on each of the left and right sides of the front vehicle body 111, but the right lift arm 121 and the lift cylinder 52 hidden in FIG.

  The lift arm 121 rotates in the up and down direction (ie, up and down) as the lift cylinder 52 extends and contracts. The bucket 122 rotates in the vertical direction (dump operation or cloud operation) as the bucket cylinder 51 extends and contracts. The illustrated wheel loader 100 employs a Z link type (bell crank type) as a link mechanism for operating the bucket 122. The link mechanism includes a bucket cylinder 51.

  FIG. 2 is a system configuration diagram of the wheel loader 100 shown in FIG. The wheel loader shown in this figure includes a diesel engine 1, a motor generator (motor / generator (M / G)) 6 mechanically connected to the output shaft of the engine 1 and driven by the engine 1, and a motor generator 6. Is supplied from the hydraulic pump 4 through a control valve 55 and a hydraulic pump 4 that is mechanically connected to the motor generator 6 and driven by at least one of the motor generator 6 and the engine 1. Four wheels via hydraulic actuators (bucket cylinder 51, lift cylinder 52 and steering cylinder 53) driven by pressure oil and propeller shafts (drive shafts) 8a, 8b mechanically connected to both ends of the output shaft The traveling motor 9 that drives 61, the inverter device 10 that controls the traveling motor 9, and the DCDC converter 12 Power storage device 11 that is electrically connected to inverters 7 and 10 (motor generator 6 and traveling motor 9) and transfers DC power between inverters 7 and 10, and hydraulic actuators 51, 52, and 53. An operation device (operation lever 56 and a steering wheel (not shown)) that outputs an operation signal according to the operation amount, and a hybrid by executing various control processes for exhibiting the performance required for the wheel loader 100 And a control device 200 that comprehensively controls the system.

  Furthermore, the wheel loader 100 includes a rotary encoder 62 that detects the rotation amount, rotation angle, and rotation position of each wheel 61 that is used to calculate the speed (vehicle speed) of the wheel loader 100.

  One end of the output shaft of the traveling motor 9 (the output shaft on the front side of the vehicle) is mechanically connected to a propeller shaft 8a that transmits driving force to a set of front wheels 61a. The other end of the output shaft is 1 It is mechanically connected to a propeller shaft 8b that transmits driving force to the rear wheels 61b of the set.

  The driving force input to the propeller shaft 8a is transmitted to the pair of front wheels 61a via the differential gear (Dif), the drive shaft and the gear (G). Similarly, the driving force input to the propeller shaft 8b is It is transmitted to a set of rear wheels 61b via a differential gear (Dif), a drive shaft and a gear (G).

  A regenerative braking device 20 is mechanically connected to the propeller shaft 8b. The regenerative braking device 20 is a device that generates an electrical braking force by input of rotational power from the propeller shaft 8b, that is, a generator, and performs only the regenerative braking operation among the power running drive operation and the regenerative braking operation. The output shaft of the regenerative braking device 20 can be regarded as constituting a part of the propeller shaft 8b that connects the differential on the vehicle rear side and the traveling motor 9. Regenerative electric power generated when the regenerative braking device 20 generates an electric braking force (that is, when a regenerative braking operation is performed) is collected (charged) by the power storage device 11.

  As the regenerative braking device 20, it is preferable to use the field winding generator shown in FIG. A field winding generator generates power using a magnetic field generated by a field current. Since the converter in the field winding generator is a diode rectifier 71 as shown in the figure, it is cheaper than a generator equipped with an inverter. Moreover, the presence or absence and magnitude | size of generation | occurrence | production of the braking force by a field winding type generator (regenerative braking device 20) can be controlled by the field current input into a field winding type generator. For example, when the regenerative braking device 20 is operated under a certain condition, the field current may be controlled to flow while the condition is satisfied, and a magnetic field is generated by the field current. Braking force and regenerative power can be obtained.

  In the above description, the case where one traveling motor 9 drives the four wheels 61a, 61a, 61b, 61b has been described. However, the propeller shafts 8a, 8b are separated and independent, and different motors are connected to the propeller shafts 8a, 8b. A configuration (that is, a total of two traveling motors) may be employed.

  The power storage device 11 preferably has a relatively large electric capacity. For example, a secondary battery such as a lithium battery or an electric double layer capacitor corresponds to this. The DC-DC converter 12 performs voltage step-up / step-down control of the voltage of the power storage device 11, whereby DC power is transferred between the inverters 7, 10 and the power storage device 11.

  The hybrid wheel loader shown in FIGS. 1 and 2 supplies the hydraulic pressure to the hydraulic working device 50 by the hydraulic pump 4 at the front portion, and performs work according to the purpose based on the hydraulic pressure. Regarding this point, excavating and transporting sand and sand with the bucket of the hydraulic working device in the front part while traveling by transmitting the engine power to the wheels via the torque converter (torque converter), transmission (TM) and propeller shaft This is the same as a conventional wheel loader (hereinafter sometimes referred to as a “torque machine”, the schematic configuration of which is shown in FIG. 4). However, unlike the torque converter, the traveling unit is mainly performed by driving the traveling motor 9 using the power generated by the motor generator 6 by the power of the engine 1. At this time, the power storage device 11 absorbs regenerative power during vehicle braking and assists the output of the engine 1, thereby contributing to reduction of vehicle energy consumption.

  The wheel loader to which the present invention is applied has several characteristic operation patterns. Among these, the most typical work form is a V-shaped excavation work as shown in FIG. In this operation, the wheel loader first moves forward with respect to the object to be excavated such as a gravel mountain, and loads a transported object such as gravel into the bucket 122 so as to thrust into the object to be excavated (first advance operation 31). . Thereafter, the vehicle moves backward and returns to the original position (first backward movement 32), and moves forward toward a transport vehicle such as a dump truck while operating the steering wheel and raising the bucket 122 (second forward movement 33). Then, after the bucket 122 is dumped and the transported material is loaded on the transport vehicle (discharged from the bucket 122), the vehicle travels backward again and returns to the original position (second retracting operation 34). As described above, the vehicle moves forward and backward to draw a V-shaped trajectory and repeats excavation work.

  In the V-shaped excavation work, the operation pattern composed of the series of operations 31, 32, 33, and 34 is basically the same, but the time required for this operation pattern (sometimes referred to as cycle time) is the situation at the time. There are longer and shorter. If the moving distance during the V-shaped excavation work is constant, when the cycle time is short, the acceleration / deceleration of the vehicle in each operation 31, 32, 33, 34 increases accordingly. In this case, the acceleration and deceleration of the vehicle are not the same but have different characteristics.

  In the V-shaped excavation work with a particularly short (fast) cycle time, the behavior of the vehicle in the backward movements 32 and 34 that move backward and return to the original position becomes particularly fast (in addition, the forward movements 33 and 34 that follow the backward movements 32 and 34). In anticipation of 31, since the operator often puts the forward / reverse lever “forward” before the reverse is completely completed, a very large deceleration occurs. For example, in the above-described V-shaped excavation work, the deceleration when performing deceleration in the speed range from the maximum speed during the work (for example, about 10 km / h) to about several km / h becomes a particularly large value. The magnitude of the speed is about twice the magnitude of the acceleration during driving. In the above-described torque converter, the torque converter itself can produce a very large braking force by the rotational force applied from the wheels. Therefore, even in the above case (reverse operation 32, 34), the braking force is particularly effective. It is possible to operate without causing a shortage.

  In the hybrid type wheel loader including the present embodiment, when deceleration is necessary, first, braking power is generated by the traveling motor, and the power is applied in a direction to stop the vehicle. However, as described above, when the cycle time is short and particularly large braking power is required for deceleration after acceleration, the braking power (required braking power value) required at that time can be generated by the traveling motor 9. May exceed braking power.

  In this case, a hydraulic brake (mechanical brake) that brakes by bringing the brake pad into contact with the disk rotating with the wheel 61 using hydraulic pressure and converting the kinetic energy of the wheel 61 into thermal energy is used as the traveling motor. If used together with 9, the deficient braking power can be supplemented. However, in this method, kinetic energy is converted into heat energy, which is lost, and the brake pads are also worn. Furthermore, due to the difference in the characteristics of the electrical braking power of the traveling motor 9 and the mechanical braking power of the hydraulic brake, when these two brakes are used together, a smooth braking operation cannot be performed. In some cases, this may lead to a decrease in workability.

  Therefore, in the wheel loader 100 according to the present embodiment configured as described above, the regenerative braking device 20 is installed on the axis of the propeller shaft 8b. If the regenerative braking device 20 is provided in this manner, even if the braking power (required braking power value) required during the braking operation of the wheel loader 100 exceeds the braking power that can be generated by the traveling motor 9, the excess braking is performed. By generating and supplementing the power with the regenerative braking device 20, it is possible to generate the braking power as required by the braking power request value. When braking power is generated by the regenerative braking device 20, the kinetic energy of the wheels 61 is converted into electric energy (regenerative power), and the regenerative power is stored in the power storage device 11. That is, the energy loss accompanying braking can be reduced as compared with the mechanical brake. Further, since the braking power by the regenerative braking device 20 is the same electrical braking power as that of the traveling motor 9, optimum control of the braking characteristics of the vehicle is easy even when used together with the braking by the traveling motor 9, and the mechanical brake The brake performance is not impaired as in the case of using together, and a good brake feeling can be realized.

  The regenerative braking device 20 is controlled by the control device 200 in the same manner as other electric devices mounted on the wheel loader 100. Here, an example of power control performed by the control device 200 in relation to the control of the regenerative braking device 20 will be described. The driving power (driving power) has a sign that is positive when the wheel loader 100 is driven, and the braking power (braking power) is a sign that has a negative sign that is output during the braking operation.

  FIG. 6 is a functional block diagram showing functions provided in the control device 200 for performing power control related to the regenerative braking device 20. As shown in this figure, the control device 200 functions as a required travel power calculation unit 25, a command travel power calculation unit 26, and a travel motor power calculation unit 27. First, the required travel power calculation unit 25 is a power (required travel power) requested by an operator of the wheel loader 100 for a travel unit (all electric actuators necessary for travel of the wheel loader 100 including the travel motor 9 and the regenerative braking device 20). ). The requested travel power is input with a signal indicating the depression amount of the accelerator pedal and the brake pedal, a signal indicating the lever position of the forward / reverse lever for selecting forward or reverse, and vehicle speed data acquired from the output of the rotary encoder 62 Is calculated as When the sign of the required traveling power is positive, it indicates that driving of the wheel 61 is required, and when it is negative, it indicates that braking of the wheel 61 is required.

  In the processing by the requested traveling power calculation unit 25, the forward / reverse lever signal determines, for example, whether or not the direction indicated by the lever position (“forward” and “reverse”) matches the actual vehicle traveling direction. Used for. This is because even when other signals are the same, the required travel power value required differs depending on whether or not the direction indicated by the lever position matches the actual vehicle traveling direction. In addition, by detecting the inconsistency between the two directions and the accelerator signal, it is possible to predict that the operator will demand sudden acceleration or deceleration in the near future. For example, various controls can be started and prepared in anticipation of this. .

  The command travel power calculation unit 26 is a part that calculates power (command travel power) that actually requests an output from the travel unit as a command from the control device 200. The command travel power calculation unit 26 includes the required travel power calculated by the calculation unit 25, the state of the engine 1 (for example, the rotation speed and torque illustrated), the state of the power storage device 11 (for example, the illustrated voltage), and the operator hydraulically The power required for the working unit (all hydraulic actuators mounted on the wheel loader 100 including the bucket cylinder 51, the lift cylinder 52, the steering cylinder 53, etc.) (that is, the power required by the operator for the hydraulic pump 4). On the basis of the demand hydraulic power), a process for limiting the required travel power and / or the required hydraulic power is performed as necessary, and is calculated as a command travel power value.

  The power that can be output from the engine 1 can be calculated from the state of the engine 1, and the power that can be output from the power of the power storage device 11 can be calculated from the state of the power storage device 11. It is possible to calculate the total value of power that can be assigned to the power (total power that can be output). On the other hand, from the required travel power value and the required hydraulic power value, the total value of power required by the travel unit and the hydraulic unit (required power total value) can be calculated. When the total required power exceeds the total power that can be output, it is necessary to perform a process that limits the total required power (output limiting process). As a result, the power that actually instructs the traveling unit to output (command The travel power value may be lower than the required travel power value. In this way, the command travel power calculation unit 26 calculates the command travel power so that the required power total value falls below the total power that can be output.

  The travel motor output calculation unit 27 performs a process of determining the power of the travel motor 9 (“travel motor power” in the figure, which is actually the power output from the travel motor 9). Since the maximum value of the travel motor power depends on the performance of the travel motor 9 and the power of the power storage device 11, the command travel power exceeds the travel motor power, and the travel motor 9 alone cannot output the command travel power. Therefore, the control device 200 performs a calculation for subtracting the travel motor power from the command travel power in parallel with the travel motor power calculation, and sets the calculated value as the insufficient power.

  In the present embodiment, when insufficient power is generated during the braking operation, the regenerative braking device 20 is instructed to generate the insufficient braking power. As a result, the insufficient braking power is output by the regenerative braking device 20, so that the braking performance according to the command traveling power can be ensured. Since the regenerative braking device 20 can control electric output, it can be controlled with the same feeling as the traveling motor 9. Further, when the mechanical brake is used together, the power lost as frictional heat can be collected as regenerative power in the power storage device 11 and reused for driving the electric actuators (the motor generator 6 and the traveling motor 9). This can ultimately lead to a reduction in fuel consumption.

  By the way, the scene where the operation of the regenerative braking device 20 is necessary (that is, when the command traveling power exceeds the traveling motor power) has a close relationship with the vehicle speed as described above, and is within a preset vehicle speed range. It is preferable to instruct the regenerative braking device 20 from the control device 200 to operate. Regarding the determination of the lower limit value of the speed range, when it is assumed that a braking operation is performed at a certain vehicle speed, the braking force that can be output by the traveling motor 9 and the braking force that can be output by the regenerative braking device 20 are substantially the same. It is preferable to set the vehicle speed as the lower limit value of the speed range. And about the upper limit of the said speed range, it is preferable to set the maximum speed during work of a work vehicle to an upper limit. For example, the speed range of the wheel loader is a range from about 10 km / h to about several km / h, which is the maximum speed during V-shaped excavation work.

  If the speed range in which the regenerative braking device 20 operates in this way is set in advance, the specifications and performance of the regenerative braking device 20 can be optimized for use with a wheel loader. For example, the regenerative braking device 20 can be downsized. Can do.

  The output characteristic when the operating range of the regenerative braking device 20 is set to the aforementioned vehicle speed range is shown in the NT diagram of FIG. In this figure, the horizontal axis (N) indicates the rotational speeds of the traveling motor 9 and the regenerative braking device 20, and the vertical axis (T) indicates the torque (braking force) of the traveling motor 9 and the regenerative braking device 20. On the horizontal axis of FIG. 7, for the sake of convenience, the rotational speed is converted into the vehicle speed, and the upper limit value is Bkm / h (10 km / h in the above speed range (lower limit value is Akm / h (corresponding to several km / h)). Equivalent)) is shown on the horizontal axis. The maximum value of the braking force that can be output by the traveling motor 9 at each rotational speed is indicated by a broken line in the figure. The maximum value of the total braking force that can be output by the traveling motor 9 and the regenerative braking device 20 at each rotational speed is This is indicated by the solid line in the figure. As a result, a value obtained by subtracting the point on the broken line from the point on the solid line at a certain rotational speed becomes the maximum value of the braking force that can be output by the regenerative braking device 20 at the rotational speed. The hatching in the figure indicates the range of braking force that can be output by the regenerative braking device 20 in the range of A to B km / h where the regenerative braking device 20 outputs the braking force. As shown in this figure, in the predetermined speed range (A to Bkm / h), even if the braking force of the traveling motor 9 is insufficient, the insufficient amount can be supplemented by the braking force of the regenerative braking device 20.

  When the regenerative braking device 20 is the field winding generator shown in FIG. 3, the braking force of the regenerative braking device 20 can be controlled by the field current, but the current value of the field current is changed to the target value. There is a time delay between the time when the instruction is given (instruction timing) and the time when the field current actually reaches the target value (arrival timing). Therefore, when the regenerative braking device 20 is operated in the preset speed range as described above, the current value of the field current reaches the target value when the vehicle speed enters the speed range. It is preferable to determine the instruction timing of the field current control in consideration of the time constant of the field current, the vehicle speed, and the acceleration at that time. A control example (waveform) of the field current in this case is shown in FIG.

  As shown in FIG. 8, control is performed so that the field current of the regenerative braking device 20 (field winding generator) rises within a preset speed range (A to Bkm / h). Normally, the time constant of the field current of the field winding generator is about several tens of milliseconds to several seconds, the vehicle speed and acceleration at that time are calculated, and the time required to operate the vehicle is calculated. The field current control is started at a vehicle speed having a required time similar to the time constant of the magnetic current. In the example of FIG. 8, since the vehicle speed enters the speed range from a state where the vehicle speed exceeds the upper limit value (Bkm / h) of the speed range, the current value of the field current is the speed B at the timing when the vehicle speed reaches the speed B. The instruction timing is determined so as to reach the target value at.

  As described above, in the present embodiment, the field current of the regenerative braking device 20 (field winding generator) is controlled only in accordance with the vehicle speed at that time, and within a preset speed range. The braking force control can be performed.

  In the example of FIG. 8, the current value of the field current is constant (target value at the speed B) in the speed range of A to Bkm / h, but this is only an example, and the current value is matched to the vehicle speed. Needless to say, it may be changed. In contrast to the example of FIG. 8, when the vehicle speed enters the speed range from a state below the lower limit value (Bkm / h) of the speed range, the field current is The instruction timing may be determined so that the current value reaches the target value at the speed A. That is, the timing at which the field current reaches the target value of the field current at the speed when entering the speed range (the upper limit value or the lower limit value of the speed range) matches the timing at which the vehicle speed enters the speed range. The instruction timing may be determined (or as close as possible), and the field current may be controlled based on the instruction timing.

  Next, an embodiment in which the regenerative braking device 20 is connected to the propeller shaft 8b via a transmission will be described. FIG. 9 shows a configuration diagram of the wheel loader in this case. As shown in FIG. 9, the regenerative braking device 20 is connected to the propeller shaft 8 b via a transmission (TM) 30. The transmission 30 appropriately changes the rotational speed of the power input from the propeller shaft 8b in accordance with the vehicle speed and transmits it to the regenerative braking device 20.

  With this configuration, the speed range in which the regenerative braking device 20 can be used can be expanded according to the gear ratio of the transmission 30. For example, the operating range of the regenerative braking device 20 when the transmission 30 is set to the second speed is shown by hatching in FIG. In this case, the operation range of the regenerative braking device 20 when the transmission 30 is at the first speed is the range indicated by hatching in FIG.

  As in the present embodiment, the operating range of the regenerative braking device 20 can be expanded by shifting the transmission 30 according to the vehicle speed. As a result, the regenerative braking device 20 can be operated in a higher rotation range, and the regenerative braking device 20 can be further downsized.

  In the above embodiment, the operation range of the regenerative braking device 20 has been described as a speed range in which a large braking force is required mainly during braking in excavation work. This is because, in excavation work in a short cycle time, the vehicle itself requires a larger braking force than the braking force output by the traveling motor 9.

  However, the use range of the regenerative braking device 20 is not limited to the time of the excavation work. In other words, in a traveling state that requires a relatively large braking force, the regenerative braking device 20 can recover good braking characteristics and regenerative energy even in other speed ranges. One of the driving conditions is continuous downhill. In this case, although depending on the slope of the slope, a relatively large braking force is required to prevent the vehicle descending speed from increasing. Furthermore, when the downhill traveling time becomes longer, the heat generated by the traveling motor 9 or the mechanical brake may increase. At this time, when the regenerative braking device 20 is used in combination, a large braking force can be obtained as a whole vehicle, and the heat generated by the traveling motor 9 or the mechanical brake can be reduced. The operation range of the regenerative braking device 20 at this time is shown in FIG. As shown in FIG. 12, in this embodiment, the braking force is generated from the maximum speed of the vehicle. Moreover, what is necessary is just to let the minimum operation speed of the regenerative braking device 20 be the minimum operation speed in the excavation operation shown in the previous embodiment, for example. (For example, the speed Akm / h shown in FIG. 7). At this time, the operating range is expanded to the high speed side, but the power of the regenerative braking device 20 is the same as that during excavation. For this reason, the structure of the regenerative braking device 20 does not change greatly, and the heat capacity that increases with the continuous use time of the regenerative braking device 20 is increased to increase the heat capacity by increasing the size of the regenerative braking device 20. This will be possible. As described above, the operation range of the regenerative braking device 20 is not limited to the speed, but can be used as needed in a scene where a large braking force is required.

  As described above, in each embodiment, since the generator 20 performs braking that has been conventionally performed by a mechanical brake such as a hydraulic brake, the amount of recovered regenerative power can be increased and the fuel consumption can be reduced. . Furthermore, since the generator 20 can be electrically braked similarly to the traveling motor 9, the feeling at the time of braking is improved as compared with the case where a mechanical brake is used together. Furthermore, since the frequency of use of mechanical brakes is reduced, the life of consumables such as brake pads can be extended.

  The regenerative braking device 20 is not limited to the position shown in FIG. 2 as long as the regenerative braking device 20 is driven by the rotational power from the propeller shafts 8a and 8b of the traveling unit. For example, as shown in FIG. 11, the regenerative braking device 20 may be disposed at a position ahead of the vehicle from the center joint 64 existing on the drive shaft 8a.

  By the way, although each said embodiment demonstrated the case where the shortage in which command driving power exceeded driving motor power was output with the regenerative braking device 20, the braking power which the said shortage can generate | occur | produce with the regenerative braking device 20 was demonstrated. In the case of exceeding, the excess braking power may be generated by the hydraulic brake, and the command traveling power may be output by using the traveling motor 9, the regenerative braking device 20 and the hydraulic brake in combination. A plurality of regenerative braking devices 20 may be mounted.

  In the above description, the regenerative braking device 20 is controlled based on the vehicle speed calculated based on the output of the rotary encoder 62. However, any sensor capable of detecting the wheel speed can be substituted for the rotary encoder 62. Further, instead of the vehicle speed, the regenerative braking device 20 may be controlled based on the rotational speed of the propeller shafts 8a and 8b, the rotational speed of the traveling motor 9, or the current value to the traveling motor 9.

  In addition, the hybrid system described above has a configuration generally referred to as a series type. However, the present invention is not limited to the configuration of FIG. 2 and can be applied if the system includes at least the series type configuration. is there.

  In addition, the hybrid wheel loader using the engine 1 and the power storage device 11 as output sources has been described as an example. However, the present invention can also be applied to an electric wheel loader that does not include an engine. Furthermore, the present invention is not limited to the wheel loader exemplified above, but can be applied to any vehicle (for example, forklift) in which rapid deceleration after acceleration is frequently seen in the usage mode.

  The present invention is not limited to the above-described embodiments, and includes various modifications within the scope not departing from the gist thereof. For example, the present invention is not limited to the one having all the configurations described in the above embodiments, and includes a configuration in which a part of the configuration is deleted. In addition, part of the configuration according to one embodiment can be added to or replaced with the configuration according to another embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Torque converter, 3 ... Transmission (TM), 4 ... Hydraulic pump, 50 ... Front hydraulic working device, 6 ... Motor generator (MG), 7 ... Inverter, 8a, 8b ... Propeller shaft, 9 ... Running Electric motor, 10 ... inverter, 11 ... power storage device, 12 ... DCDC converter, 200 ... control device, 20 ... regenerative braking device, 25 ... required travel power calculation unit, 26 ... command travel power calculation unit, 27 ... travel motor power calculation unit , 30 ... Transmission (TM), 64 ... Center joint

Claims (4)

A traveling unit driven by an electric motor;
A regenerative braking device that is mechanically coupled to the drive shaft of the traveling unit and performs only a regenerative braking operation among a power running drive operation and a regenerative braking operation;
A power storage device for charging the regenerative power generated by the regenerative braking device;
When the braking power of the work vehicle is calculated, a braking power that requests output from the traveling unit is calculated, and when the braking power exceeds the braking power that can be output by the electric motor, the regeneration power is generated so that the insufficient braking power is generated. A work vehicle comprising: a control device that instructs a braking device. The work vehicle according to claim 1,
The work vehicle, wherein the control device instructs the regenerative braking device to operate within a preset vehicle speed range. The work vehicle according to claim 2,
The regenerative braking device is a field winding generator that generates power using a magnetic field generated by a field current,
The control device, based on the timing at which the vehicle speed enters the vehicle speed range and the timing at which the field current reaches the target value of the field current at the speed at which the vehicle speed enters the vehicle speed, A work vehicle that controls field current. The work vehicle according to claim 1,
The work vehicle, wherein the regenerative braking device is mechanically connected to the drive shaft via a transmission.

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