Travel controller for work vehicle

A vehicle 1 used for work at elevated locations comprises a travel body 10, whose front wheels 11a, 11b are drive wheels, a steering cylinder 17, two travel motors 12, a battery B, an inverter IV, a travel operation lever 41, and a steering dial 42. In the vehicle, the steering cylinder 17 drives a steering mechanism 13, which directs the drive wheels 11a, 11b, to change the steering angle of the drive wheels 11a, 11b, and the travel motors 12a, 12b, which receive electric power from the battery B, respectively, drive the drive wheels 11a, 11b. The inverter IV converts DC power from the battery B to AC power, which is supply to the travel motors 12a, 12b to drive the rotation of both the drive motors. The travel operation lever 41 is operated for travel control while the steering dial 42 is operated to steer the travel body 10. The vehicle further comprises a steering control unit 53 and an inverter control unit 51. The steering control unit 53 controls the operation of the steering cylinder 17, so that the steering angle of the drive wheels corresponds to the operation of the steering dial 42, and the inverter control unit 51 controls the operation of the inverter IV to rotate the travel motors 12a, 12b at a speed that corresponds to the operation of the travel operation lever 41.

TECHNICAL FIELD

The present invention relates to a work vehicle comprising a travel controller, the right and left wheels of which vehicle are driven by battery-powered induction motors, and particularly to a work vehicle whose induction motors are controlled through an inverter.

TECHNICAL BACKGROUND

There are various forms of automotive work vehicles that are used for transportation work in factories or for interior work in buildings. However, there is known a work vehicle that comprises a relatively small travel body with front and rear and right and left wheels, an elevating device (for example, a scissors-linkage or a telescopic motion column) provided on the travel body, and an aerial platform mounted on the elevating device, which is actuated to extend and contract itself in the up and down direction for lifting and lowering the aerial platform. In such a work vehicle, the operator who is onboard on the aerial platform can operate the movement of the travel body and the up and down of the aerial platform (refer, for example, to patent reference 1).Patent reference 1: Japanese Laid-Open Patent Publication No. 2007-99439

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Exhaust gas and noise should be avoided especially indoors, so an indoor-type work vehicle of the above mentioned construction is preferably designed with induction motors (travel motors), which are provided at the right and left drive wheels, respectively, with a battery built in the travel body as electrical power source. However, the capacity of the battery has a limit, and the recharging of the battery requires a certain facility and a time. As a result, it is not convenient for the work vehicle that the battery should come into need of being recharged, once the vehicle has started traveling or the day's work. To effectively reduce the consumption of electrical energy in a battery-powered work vehicle, each induction motor is provided with an inverter, so that the operation of each of the induction motors is independently controlled through the respective inverter to achieve its optimal rotational speed, in response to the changing travel condition of the work vehicle. However, there are problems that this control is much complicated because an inverter is provided for each induction motor and that this complication leads to a high manufacturing cost.

The present invention aims at solving these problems, and it is the objective of the invention to provide a work vehicle whose wheels are driven by induction motors powered by a battery and controlled through an inverter by a simplified control, and thereby achieving a low manufacturing cost, and yet, efficient use of electrical power from the battery.

Means to Solve the Problems

To solve the above mentioned problems, a work vehicle according to the present invention (for example, an aerial platform vehicle1, which is used for work at elevated locations, described in the preferred embodiment section) comprises wheels on its front and rear, and right and left sides, a steering actuator (for example, a steering cylinder17described in the preferred embodiment), two induction motors (for example, travel motors12a,12bdescribed in the preferred embodiment), a battery for providing electric power to the two induction motors, an inverter, travel-operating means (for example, a travel operation lever41described in the preferred embodiment), steering-operating means (for example, a steering dial42described in the preferred embodiment), steering-controlling means, and inverter-controlling means. In the vehicle, the steering actuator drives a link mechanism that directs a pair of right and left drive wheels and thereby changes steering angles at the drive wheels, and the two induction motors independently drive the pair of right and left drive wheels, respectively. The inverter converts DC power from the battery to AC power, and supplies the AC power to the two induction motors for driving both the induction motors to rotate. The travel-operating means is operated for travel control of a travel body, i.e., the body of the vehicle, and the steering-operating means is operated to set a turning direction for the travel body. The steering-controlling means controls the operation of the steering actuator such that the steering angle of the drive wheels correspond to the operation of the steering-operating means, and the inverter-controlling means controls the operation of the inverter to rotate the induction motors at a speed that corresponds to the operation of the travel-operating means.

In a work vehicle in this configuration, one inverter integrally controls the operation of the two induction motors for driving the wheels. Thus, this design achieves simplification and cost-efficiency for control system. Furthermore, the two induction motors are operated, through the inverter, at optimal rotational speed that corresponds to the operation of the operating means. As a result, this design also achieves efficient use of electricity and extends the period of use of the aerial platform vehicle available on a single charge.

It is preferable that a work vehicle in the above configuration comprise steering-angle-detecting means, which detects steering angles at the drive wheels. In this case, if a steering is detected by the steering-angle-detecting means (for example, if the steering angle at the drive wheels becomes equal to or larger than a predetermined angle), then the inverter-controlling means controls the operation of the induction motors through the inverter such that the motors acquire a characteristic that their torque output changes more gradually than otherwise over a corresponding rotational speed change.

In this case, it is preferable that the inverter-controlling means control the operation of the induction motors through the inverter such that the motors acquire a characteristic that their torque output changes more gradually over a corresponding rotational speed change as the difference in rotational speed between the inner and outer wheels of the drive wheels becomes larger, which difference corresponds to the steering angle at the drive wheels detected by the steering-angle-detecting means.

It is more preferable that the vehicle further comprise temperature-detecting means, which is attached to these two induction motors and which detects the temperature of the windings of the induction motors. In this case, the inverter-controlling means controls the operation of the induction motors through the inverter such that the induction motors acquire a characteristic that their torque output changes more gradually over a corresponding rotational speed change as the temperature of the windings of the motors detected by the temperature-detecting means becomes lower.

By controlling the operation of the induction motors through the inverter such that the motors acquire a characteristic that their torque output changes more gradually for a corresponding rotational speed change during a steering (so-called re-boost control), the difference in torque that results from the difference in rotational speed between the inner and outer wheels during the steering is minimized for smooth turning, which leads to good drivability. This results in efficient use of electricity, which extends the period of use of the aerial platform vehicle available on a single charge. In addition, during the steering, the torque output of the induction motors is reduced by the re-boost control. However, the speed of the vehicle falls from that in straight travel because travel resistance remains unchanged. This is preferable on the point of safety.

It is preferable that the above described work vehicle further comprise tilt-angle-detecting means, which detects the tilt angle of the travel body, and motor-temperature-detecting means, which detects the temperature of the windings of the induction motors. In this case, while the tilt angle detected by the tilt-angle-detecting means is equal to or larger than a predetermined angle, if the temperature of the windings of the induction motors detected by the motor-temperature-detecting means is higher than a predetermined upper limit for allowable temperature, then the inverter-controlling means restricts the rotation of the induction motors, whose operation is otherwise controlled in correspondence to the operation of the travel-operating means.

In this case, although the travel-operating means outputs a travel command value in correspondence to its operation, while the tilt angle detected by the tilt-angle-detecting means is equal to or larger than a predetermined angle, if the temperature of the windings of the induction motors detected by the motor-temperature-detecting means is higher than a predetermined upper limit for allowable temperature, then the inverter-controlling means restricts the frequency of the alternating current that is set based on the travel command value, in correspondence to the detected temperature of the windings of the induction motors, and sets this restricted frequency as a command frequency.

While the tilt angle of the travel body is equal to or higher than a predetermined angle, if the temperature of the windings of the induction motors becomes higher than a predetermined upper limit for allowable temperature, then the frequency that is set based on the travel command value is restricted in correspondence to the temperature of the windings of the induction motors, and this restricted frequency is set as the command frequency. This is a so-called cutback function, and it prevents malfunction of the induction motors and also prevents the travel body from deviating while the vehicle is traveling over a sloped ground. This is an improvement in work safety.

It is preferable that the above described work vehicle further comprise an elevating device, which is provided on the travel body and is extended upward or contracted downward for realizing ascending and descending motions, and retraction-detecting means, which detects whether the elevating device is retracted on the travel body or not. In this case, while the tilt angle detected by the tilt-angle-detecting means is equal to or larger than a predetermined angle, and while the retraction of the elevating device is detected by the retraction-detecting means, if the temperature of the windings of the induction motors detected by the motor-temperature-detecting means is higher than a predetermined upper limit for allowable temperature, then the inverter-controlling means restricts the frequency of the alternating current that is set based on the travel command value, in correspondence to the detected temperature of the windings of the induction motors, and sets this restricted frequency as the command frequency. This arrangement adds a condition that the elevating device is retracted on the travel body, to the cutback function, which works in correspondence to the temperature of the windings of the induction motors while the vehicle is traveling over a sloped ground. Therefore, safety in carrying out work is improved.

It is more preferable that the above work vehicle comprise motor-current-detecting means, which detects electrical currents through the induction motors. In this case, while the tilt angle detected by the tilt-angle-detecting means is equal to or larger than a predetermined angle, if the electrical current values of the induction motors detected by the motor-current-detecting means are lower than the lower limit for allowable electrical current value, which limit is predetermined in correspondence to the tilt angle, then the inverter-controlling means stops the operation of the inverter. This is a work-safety measure to stop the operation of the induction motors for preventing the vehicle from deviating over a sloped ground, which deviation may occur if the induction motors experience a deficiency in torque-generating electrical current under the cutback function.

It is even more preferable that the above work vehicle further comprise an elevating device, which is provided on the travel body and is extended upward or contracted downward for realizing ascending and descending motions, and retraction-detecting means, which detects whether the elevating device is retracted on the travel body or not. In this case, while the tilt angle detected by the tilt-angle-detecting means is equal to or larger than a predetermined angle, and while the retraction of the elevating device is detected by the retraction-detecting means, if the electrical current value of the induction motors detected by the motor-current-detecting means is lower than the lower limit for allowable electrical current value, which limit is predetermined in correspondence to the tilt angle, then the inverter-controlling means stops the operation of the inverter. This arrangement sets a condition that the elevating device should be retracted on the travel body before the operation of the inverter is stopped when the electrical current value of the induction motors becomes lower than the lower limit for allowable current value while the vehicle is traveling over a sloped ground. This is a further work-safety improvement.

Additionally, it is preferable that the work vehicle comprise braking means, which restrains at least one of the front or rear pair of right and left wheels from rotating when the inverter-controlling means stops the operation of the inverter. This arrangement is a further work-safety improvement, which prevents the vehicle from rolling back by activating the braking means (so-called negative brake) and thereby stopping the rotation of the wheels when the operation of the inverter is stopped, i.e., the operation of the induction motors is stopped because the electrical current value of the motors has become lower than the lower limit while the vehicle is traveling over a sloped ground.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of the invention is described with reference to these drawings. An aerial platform vehicle1according to the present invention is a so-called vertically ascending and descending vehicle used for work at elevated locations and comprises, as shown inFIG. 1, a travel body10capable of traveling on four tire wheels11, which are provided on the front and rear and right and left sides, a scissors-linkage20provided on the upper part of the travel body10, and an aerial platform30supported by the scissors-linkage20for a worker to ride.

A pair of left and right front wheels11a,11bof the tire wheels11(hereinafter, the left front wheel is referred to with alphanumeric11a, and the right front wheel with11b) are the wheels that are used for driving and steering the vehicle. For driving the front pair of left and right wheels11a,11bindependently from each other, two travel motors (induction motors)12a,12b(hereinafter, the left travel motor is referred to with alphanumeric12a, and the right travel motor with12b; refer toFIG. 2) are correspondingly built in the travel body10. While the front pair of left and right wheels11a,11bare driven each by the respective travel motors12a,12b, these wheels11a,11bare turned to steer the vehicle to a desirable direction (refer toFIG. 3). The travel motors12a,12bare provided integrally with so-called negative brakes14, each of which stops the rotation of and locks the rotational axis of the corresponding motor. The rear pair of left and right wheels11c,11d(hereinafter, the left rear wheel is referred to with alphanumeric11c, and the right rear wheel with11d) are non-driven wheels and are mounted, respectively, on a shaft19(refer toFIG. 3) that protrudes on the right and left sides of the travel body10.

In this embodiment, the travel motors12a,12bhave a characteristic that a relatively small torque difference results from the difference in rotational speed between the inner wheel and the outer wheel during the steering of the vehicle and that energy in the battery B is used efficiently with relatively small starting torque in lower frequency band (at the time of no load) as indicated by a circle inFIG. 8.

The scissors-linkage20comprises a plurality of link members20a, every two members of which are connected centrally with pivots20bin an “X” figure. These link members are provided in plurality upwardly on the right and left sides of the travel body10. The lower end of a respective link member20apositioned above and the upper end of a respective link member20apositioned below are connected with each other by a pivot20cwhile the link members20apositioned on the right side and those positioned on the left side are connected with each other by link rods20d, which extend horizontally in the right and left direction with respect to the travel body10. Furthermore, in the scissors-linkage20, the lower ends of the link members20apositioned lowest on the front side of the travel body10are connected pivotally to the upper part of the travel body10while those of the link members20apositioned lowest on the rear side are provided with rollers20e, which roll along the rails (not shown) provided on the upper part of the travel body10. Moreover, in the scissors-linkage20, the upper ends of the link members20apositioned highest on the front side of the travel body10are connected pivotally to the lower part of the aerial platform30while those of the link members20apositioned highest on the rear side are provided with rollers20f, which roll along the rails (not shown) provided on the lower part of the aerial platform30. The scissors-linkage20, which is constructed as described above, is extended and contracted by an ascent and descent cylinder21, which is provided between the mechanism20and the travel body10, for moving the aerial platform30upward and downward.

The aerial platform30is provided with a balustrade31for protection of the worker aboard from falling and with a control box40, which is attached to the balustrade. The control box40includes a travel operation lever41for switching the state of the travel body10between start and stop, and forward and backward, a steering dial42for steering the travel body10(i.e., for directing the front wheels11a,11b) while the vehicle is traveling, and an ascent and descent operation lever43for lifting and lowering the aerial platform30(refer toFIG. 2). As a result, the worker who is on the aerial platform30can operate the travel operation lever41, steering dial42and ascent and descent operation lever43to control the traveling of the travel body10and the ascent and descent of the aerial platform30for the purpose of reaching a desirable location and position.

The steering dial42is connected through a steering device to the left and right front wheels11a,11bto steer the vehicle (refer toFIG. 3). The steering device comprises a steering mechanism13, which is linked to the front wheels11a,11b, a steering cylinder (hydraulic cylinder)17, which drives the steering mechanism13to change the steering angles γL, γRof the front wheels11a,11b, (refer toFIG. 4, which describes the deflection-angles of the front wheels11a,11bwith respect to the center line of the travel body10in the front and rear direction), steering angle detectors61(for example, potentiometers), which are attached to the pair of left and right front wheels11a,11b, respectively, for finding the steering angles at the front wheels11a,11b, the above mentioned steering dial42for setting a target steering angle for the front wheels11a,11b, and a controller50, which controls the operation of the steering cylinder17in correspondence to the turning of the steering dial42.

As shown inFIG. 3, the steering mechanism13comprises a pair of knuckle arms14, which, respectively, support the front wheels11a,11bpivotally around king pin shafts15, and a tie rod16, which connects the pair of knuckle arms14with joint pins P1. The steering angle detectors61are attached on the knuckle arms14, respectively, for finding the steering angles at the left and right front wheels11a,11b, respectively, from the turning angles of the knuckle arms14around the king pin shafts15. One end of the steering cylinder17is connected to the left knuckle arm14of the steering mechanism13with a joint pin P2while the other end is connected to a cylinder connection point (not shown) of the travel body10with a joint pin P3.

With this configuration, in the steering device, the steering cylinder17is extended or contracted to swing the left front wheel11aaround the king pin shaft15and, simultaneously in the same direction, the right front wheel11b, which is linked through the tie rod16, thereby changing the steering angles at the front wheels (steering wheels)11a,11b. In other words, the steering cylinder17is extended to turn the left and right front wheels11a,11brightward, and it is contracted to turn them leftward.

It is so designed that the pair of left and right front wheels11a,11bcreate a difference between their angles with respect to the travel body10when they are turned in the steering of the travel body10by the steering mechanism13(specifically, the angle of the wheel that happens to be positioned inward in the turning always becomes larger than that of the wheel positioned outward at a constant rate). Now, refer toFIG. 4for the following explanation. When the steering cylinder17is not extended with zero extension (Δ=0), the steering angles γL, γRat the left and right front wheels11a,11bare both zero (γL=0, γR=0) (refer toFIG. 4A).

Here, the sign of the steering angles at the front wheels11a,11bis so defined that when the wheels are directed rightward, the values of their angles are positive, and when the wheels are directed leftward, the values are negative. When the extension Δ is a positive value (Δ>0), the steering angles γL, γRat the left and right front wheels11a,11bbecome also positive (γL>0, γR>0) (refer toFIG. 4B). In this shown state, because of the above mentioned characteristic of the steering mechanism13, the relation between the steering angle γLat the left front wheel11aand the steering angle γRat the right front wheel11bis described as |γL|<|γR|. Likewise, when the extension Δ is a negative value (Δ<0), the steering angles γL, γRat the front wheels11a,11bbecome also negative (γL<0, γR<0) (refer toFIG. 4C. In this state, because of the characteristic of the steering mechanism13, the relation between the steering angle γLat the left front wheel11aand the steering angle γRat the right front wheel11bis described as |γL|>|γR|.

The center of the circle drawn by the turning of the aerial platform vehicle1always coincides approximately on the axis of the rear wheels11c,11d, and this center point moves from infinity to the rear wheels as the degree of the steering angle increases (zero steering angle=straight progression) (refer toFIG. 6A). In the present invention, the vehicle is so designed that when the maximum steering angle is applied in the rightward turning, the non-drive wheel on the right side (right rear wheel)11dbecomes the center for the turning circle (refer toFIG. 6B), and that if the turning is leftward at the maximum angle, then the non-drive wheel on the left side (left rear wheel)11cbecomes the center for the turning circle (refer toFIG. 6C).

Now, referring toFIG. 2, the travel control of the aerial platform vehicle1, which has the above described configuration, is explained in relation to the operations of the levers and the dial provided on the control box40.FIG. 2shows transmission paths for signals and motions concerning the driving and steering of the travel body10and the lifting and lowering of the aerial platform30.

The travel operation lever41, which is provided on the control box40of the aerial platform30, takes its neutral position (upright position shown inFIG. 5) when it is not operated. From the neutral position as reference, the travel operation lever41is tilted forward or backward, and if the worker operating the lever releases it from his hand, it automatically returns from the tilted position to the neutral position by the force of a built-in spring. The operational state (the direction and degree of the tilting with respect to the non-operational state as neutral position) of the travel operation lever41is detected by a move and stop operation detector41a, which comprises, for example, a potentiometer, provided in the control box40. The information of the operational state of the travel operation lever41detected by the move and stop operation detector41ais input to the inverter control unit51of the controller50(provided in the aerial platform30or in the travel body10).

The tilting forward of the travel operation lever41from the neutral position corresponds to a command that makes the travel body10move forward. The larger the tilting angle of the operation lever, the larger value is set for the travel speed forward by the inverter control unit51of the controller50. On the other hand, the tilting backward of the travel operation lever41from the neutral position corresponds to a command that makes the travel body10move backward. The larger the tilting angle of the operation lever, the larger value is set for the travel speed backward by the inverter control unit51of the controller50. In this embodiment, in either case where the travel operation lever41is tiled forward or backward (i.e., the lever is operated either for forward drive or for rearward drive), the speed of the vehicle is varied continuously without any step by the inverter control unit51. In other words, the travel body10travels smoothly with its speed being continuously varied either in forward drive or in rearward drive. In addition, the returning of the travel operation lever41to the neutral position corresponds to a command that stop the travel body10.

The steering dial42takes its neutral position (the position where mark M1provided on the steering dial42meets mark M2provided on the control box40as shown inFIG. 5) when it is not operated. From the neutral position, the steering dial is turned rightward (clockwise) or leftward (counterclockwise), and if the worker operating the dial releases it, it automatically returns to the neutral position by the force of a built-in spring. The operational state of the steering dial42(the direction and degree of the turning operation from the neutral position as reference) is detected by a steering operation detector42a, which comprises, for example, a potentiometer, provided in the control box40. The operational information of the steering dial42detected by the steering operation detector42ais input to the steering control unit53of the controller50.

The clockwise turning of the steering dial42corresponds to a command that directs the front wheels11a,11brightward. The larger the degree of the rightward turning of the dial from its neutral position, the larger value is set for the rightward target steering angle by the steering control unit53of the controller50. On the other hand, the counterclockwise turning of the steering dial42corresponds to a command that directs the front wheels11a,11bleftward. The larger the degree of the leftward turning of the dial from its neutral position, the larger value is set for the leftward target steering angle by the steering control unit53of the controller50. In addition, the returning of the steering dial42to its neutral position corresponds to a command that makes the steering angles at the front wheels11a,11bto zero (refer toFIG. 4A, where γL=γR=0).

The ascent and descent operation lever43takes its neutral position (upright position as shown inFIG. 5) when it is not operated. From the neutral position as reference, the ascent and descent operation lever43is tilted forward or backward, and if the worker operating the lever releases it, the lever automatically returns to the neutral position by the force of a built-in spring. The operational state of the ascent and descent operation lever43(the direction and degree of the tilting of the lever with respect to the neutral position) is detected by an ascent and descent operation detector43a, which comprises a potentiometer, provided in the control box40. The information of the operational state of the ascent and descent operation lever43detected by the ascent and descent operation detector43ais input to the ascent and descent control unit52of the controller50.

The tilting forward of the ascent and descent operation lever43from its neutral position corresponds to a command that lowers the aerial platform30. The larger the degree of the tilting, the larger value is set for the target lowering speed by the ascent and descent control unit52of the controller50. On the other hand, the tilting backward of the ascent and descent operation lever43from its neutral position corresponds to a command that lifts the aerial platform30. The larger the degree of the tilting, the larger value is set for the target lifting speed by the ascent and descent control unit52of the controller50. Furthermore, the returning of the ascent and descent operation lever43to the neutral position corresponds to a command that stops the movement of the aerial platform30.

The travel body10houses two travel motors (induction motors)12a,12b, a battery B, and an inverter IV. The travel motors are for driving a pair of left and right drive wheels11a,11b, with each motor independently driving a respective drive wheel. For powering the motors, the inverter IV converts the DC power being supplied from the battery B to AC power, which is then supplied to the travel motors12a,12b(refer toFIG. 2). The inverter control unit51of the controller50controls the operation of the inverter IV such that the travel motors12a,12brotate together at the rotational speed and in the direction that corresponds to the operational state of the travel operation lever41. As a result, the worker on the aerial platform30can control the start and stop, the travel directions (forward or rearward) and the traveling speed of the travel body10by operating the travel operation lever41.

The travel body10also houses a hydraulic pump P, which is driven by an electric motor M as drive source (refer toFIG. 2). Part of the pressured oil discharged from the hydraulic pump P is supplied through a steering control valve71to the above mentioned steering cylinder17(refer toFIG. 4), and the steering control unit53of the controller50drives electromagnetically the spool (not shown) of the steering control valve71to the position and in the direction that corresponds to the operational state of the steering dial42. As a result, the worker on the aerial platform30can control the extension and contraction of the steering cylinder17by operating the steering dial42, and thereby, can control the direction of the front wheels11a,11bthat steer the travel body10.

Other part of the pressured oil discharged from the hydraulic pump P is supplied through an ascent and descent control valve72to the above mentioned ascent and descent cylinder21, and the controller50drives electromagnetically the spool (not shown) of the ascent and descent control valve72to the position and in the direction that corresponds to the operational state of the ascent and descent operation lever43. As a result, the worker on the aerial platform30can control the extension and contraction of the ascent and descent cylinder21by operating the ascent and descent operation lever43, and thereby, can control the lifting and lowering of the aerial platform30.

The travel body10is provided with a steering angle detector61, a tilt angle detector62, a battery voltage detector63, a motor temperature detector64and a motor current detector65. The steering angle detector61detects the steering angles at the pair of left and right front wheels11a,11bas the rotational angles around the king pin shafts15of the front wheels11a,11b, and the tilt angle detector62detects the tilt angle of the travel body10. The battery voltage detector63detects the voltage of the battery B; the motor temperature detector64detects the temperatures of the windings of the travel motors12a,12b; and the motor current detector65detects electrical currents through the travel motors12a,12b. In addition, the scissors-linkage20is provided with an ascent and descent speed detector66and a retraction detector67. The ascent and descent speed detector66detects the ascending and descending speed of the aerial platform30from the operational speed of the ascent and descent cylinder21, and the retraction detector67detects if the scissors-linkage20is retracted on the travel body10. All the information detected by these detectors61-67is input to the controller50.

The controller50comprises the inverter control unit51, the steering control unit53and the ascent and descent control unit52.

The inverter control unit51controls the operation of the inverter IV so that the two travel motors12a,12brotate together at the rotational speed (i.e., velocity) that corresponds to the operational state of the travel operation lever41(i.e., the direction and degree of the tilt from the neutral position), which is detected by the move and stop operation detector41a. In addition, if it is determined that a steering operation is being carried out, from the information detected by the steering angle detector61(for example, if the steering angles of the drive wheels11a,11bhave become equal to or larger than a predetermined angle), then the inverter control unit51executes power control (so-called re-boost control) of the travel motors12a,12bthrough the inverter IV, so that these motors acquire a gradually changing output torque characteristic in correspondence to their rotational speed.

More specifically, the inverter control unit51performs power control (re-boost control) of the travel motors12a,12bthrough the inverter IV in correspondence to the steering angles of the drive wheels11a,11bdetected by the steering angle detector62, and the inverter control unit51makes the torque output of the travel motors12a,12bover their corresponding range of rotational speed, more gradually changing as the rotational difference becomes larger between the inwardly and outwardly positioned drive wheels11a,11b(i.e., the torque curve is more flattened from A to B as shown inFIG. 7).

Now, the re-boost control mentioned above is explained in reference toFIG. 7. When the re-boost control is executed during the steering, in other words, when the slope of the torque curve is made more gradual as indicated by “A→B” inFIG. 7, the torque output of the inner wheel and that of the outer wheel are reduced, respectively, TA→TBand tA→tBwhile the rotational speeds of the inner and outer wheels remains at NAand nA, respectively. As a result, the difference in torque between the inner wheel and the outer wheel has become smaller (Δ(TA−tA)>Δ(TB−tB)). This condition improves drive efficiency. However, because the resistance to the travel motion does not change, the speed of the vehicle falls, with the rotational speeds of the inner and outer wheels, respectively, falling as indicated in the figure, NA→NBand nA→nB. Then, since the power of the travel motors12a,12bis constant, the torque outputs of the inner and outer wheels increase as TB→TCand tB→tC, and along with the torque increase, the speed of the vehicle start to increase up to a point where there is a balance between the torque outputs TC, tCof the inner and outer wheels and the travel resistance. By the way, in the present invention, the difference in rotational speed between the inner and outer wheels of the drive wheels11a,11bbecomes largest when the steering angle reaches 45 degrees, and at this angle, the re-boost control, which controls the travel motors12a,12bthrough the inverter IV, is executed such that the curve depicting the output torque characteristic of the travel motors12a,12bover a range of rotational speed is made most gradual. As described above, the aerial platform vehicle1according to the present invention can perform a smooth turning, though its travel speed decreases from that in linear travel, because the difference in torque between the inner and outer wheels is made smaller during the steering. In addition, as the drive efficiency improves, the vehicle can be driven in an energy-saving manner, contributing to a reduction in power consumption from the battery. The curved lines shown in the graph inFIG. 7exaggerate real changes that take place, to depict what has been described above.

Furthermore, the inverter control unit51is provided, in advance, with four inverter control patterns A-D, which are described inFIG. 9, and the inverter control unit selects and executes one of the control patterns in correspondence to the tilt angle of the travel body10and the retraction state of the scissors-linkage20.

Pattern A is for a condition where the tilt angle of the travel body10detected by the tilt angle detector62is smaller than a predetermined angle, and the retracted state of the scissors-linkage20is detected by the retraction detector67. In this control pattern, the inverter control unit51sets, as command frequency, the frequency that has been increased from zero as initial value in correspondence to the increased travel command value.

Pattern B is for a condition where the tilt angle of the travel body10detected by the tilt angle detector62is equal to or larger than the predetermined angle, and the retracted state of the scissors-linkage20is detected by the retraction detector67. In this pattern, the inverter control unit51sets, as command frequency, the frequency that has been increased in correspondence to the increased travel command value, from the minimum frequency that generates a torque necessary for preventing the travel body10from deviating, as initial value, which torque is predetermined in correspondence to the tilt angle of the travel body10.

Moreover, in control patterns A and B, the inverter control unit51sets the command frequency such that this frequency does not exceed the maximum frequency that generates the torque necessary for preventing the travel body10from deviating, which torque is predetermined in correspondence to the tilt angle of the travel body10, regardless of the operational state of the travel operation lever41.

Pattern C is for a condition where the tilt angle of the travel body10detected by the tilt angle detector62is smaller than the predetermined angle, and the retracted state of the scissors-linkage20is not detected by the retraction detector67. In this pattern, the inverter control unit51sets, as command frequency, the frequency that has been increased from zero as initial value in correspondence to the increased travel command value. However, if the command frequency happens to exceed a predetermined frequency, then the command frequency is set not to exceed the predetermined frequency, regardless of the operational state of the travel operation lever41.

Pattern D is for a condition where the tilt angle of the travel body10detected by the tilt angle detector62is equal to or larger than the predetermined angle, and the retracted state of the scissors-linkage20is not detected by the retraction detector67. In this control pattern, the inverter control unit51restricts the operation of the inverter IV.

In addition to these control patterns, the inverter control unit51has a so-called cutback function. While the vehicle is traveling over a sloped ground, if the voltage of the battery B becomes lower than a predetermined value or higher than a predetermined value, or if the temperature of the windings of the travel motors12a,12bbecomes higher than a predetermined value, then the inverter control unit51restricts the frequency set on the basis of the travel command value, by a cutback rate that is based on these detected values, and the inverter control unit sets this restricted frequency as command frequency, thereby maintaining the torque outputs of the motors and preventing the vehicle from deviating.

More specifically, if the tilt angle of the travel body10detected by the tilt angle detector62is equal to or larger than a predetermined angle, and if the retracted state of the scissors-linkage20is detected by the retraction detector67, and if the voltage of the battery B detected by the battery voltage detector63is out of an allowable range of voltage value, then the inverter control unit51restricts the frequency that is set on the basis of the travel command value, in correspondence to the detected voltage value of the battery B, and the inverter control unit sets this restricted frequency as command frequency.

For example, the allowable voltage values are set as equal to or higher than 20 volts and lower than 30 volts. If the voltage of the battery is within the allowable range, then, as shown inFIG. 10, the cutback rate is set at 0% (in this case, the frequency set on the basis of the travel command value is set as command frequency). If the voltage is out of the allowable range, and the detected value is higher than 0 but lower than 18 volts or is equal to or higher than 35 volts, then the cutback rate is set to 100%. If the voltage is out of the allowable range, and the detected value is in the range equal to or higher than 18 volts but lower than 20 volts, then the cutback rate is set to decrease from 100% as initial value, as the detected value increases, and if the detected value is in the range equal to or higher than 30 volts but lower than 35 volts, then the cutback rate is set to increase from 0% as initial value, as the detected value increases. The inverter control unit51restricts the frequency set on the basis of the travel command value, in correspondence to the cutback rate determined in the above described ways, and sets this restricted frequency as command frequency.

In addition, if the tilt angle of the travel body10detected by the tilt angle detector62is equal to or larger than a predetermined angle, and if the retracted state of the scissors-linkage20is detected by the retraction detector67, and if the temperature of the windings of the travel motors12a,12bdetected by the motor temperature detector64is higher than a predetermined allowable limit, then the inverter control unit51restricts the frequency set on the basis of the travel command value, in correspondence to the detected temperature of the windings of the travel motors12a,12b, and the inverter control unit sets this restricted frequency as command frequency.

For example, the allowable temperature range is set as 0 degree to 120 degrees C. If the temperature of the windings is within the allowable range, then, as shown inFIG. 11, the cutback rate is set at 0% (in this case, the frequency set on the basis of the travel command value is set as command frequency). If the temperature is out of the allowable range, and the temperature of the windings is equal to or higher than 120 degrees but lower than 150 degrees C., then the cutback rate is set to a value that is proportional to the difference of the detected temperature from the upper limit of the allowable temperature (=120 degrees C.), with the value of 100% at 150 degrees C. and above. The inverter control unit51restricts the frequency set on the basis of the travel command value, in correspondence to the cutback rate determined in the above described ways, and sets this restricted frequency as command frequency.

After the above described cutback function has become effective, if the travel body10experiences a shortage of torque output, then the vehicle might recede over a sloped ground. To prevent such an accident, if the tilt angle of the travel body10detected by the tilt angle detector62is equal to or larger than a predetermined angle, and if the retracted state of the scissors-linkage20is detected by the retraction detector67, and if the electrical current value of the travel motors12a,12bdetected by the motor current detector65is smaller than a predetermined allowable limit, then the inverter control unit51stops the operation of the inverter IV. When the travel motors12a,12bstop operating, the negative brakes14, which are attached to these motors12a,12b, are activated.

Now, the relation between the degree of the tilting (i.e., the is operational degree) of the travel operation lever41and the command frequency output by the inverter control unit51is described in reference toFIG. 12. The travel operation lever41is tilted from its upright neutral position, through an insensitive area, which is indicated by a shaded section inFIG. 12A, to operational degree x, then to operational degree y and up to operational degree z. In the graph shown inFIG. 12B, solid line represents the command frequency that is set with the travel operation lever41in a condition where the tilt angle of the travel body10detected by the tilt angle detector62is equal to or larger than a predetermined angle, and the retracted state of the scissors-linkage20is detected by the retraction detector67(i.e., the vehicle is traveling over a sloped ground). As a contrast, the graph inFIG. 12Balso includes an alternate long and short dash line that represents the command frequency that is set with the travel operation lever41in a condition where the tilt angle of the travel body10detected by the tilt angle detector62is smaller than the predetermined angle, and the retracted state of the scissors-linkage20is detected by the retraction detector67(i.e., the vehicle is traveling over a flat ground).

As shown inFIGS. 12A and 12B, while the vehicle is traveling over a sloped ground, if the travel operation lever41is tilted, through the insensitive area to operational degree x, then the command frequency is set at the minimum frequency Hmin that generates the torque necessary for preventing the travel body10from deviating, which torque is predetermined in correspondence to the tilt angle of the travel body10. If the travel operation lever41is tilted further, then with the minimum frequency Hmin as initial value, the command frequency is set to the frequency that has been increased in correspondence to the increased travel command value, i.e., the increased degree of the tilting operation. When the tilting of the travel operation lever41reaches operational degree y, the command frequency to be set becomes the maximum frequency Hmax that generates the torque necessary for preventing the travel body10from deviating, which torque is predetermined in correspondence to the tilt angle of the travel body10. After this point, even if the travel operation lever41is further tilted from operational degree y to operational degree z, the command frequency is set and maintained at the maximum Hmax, never to exceed it, for maintaining the torque output of the travel motors12a,12bto prevent the vehicle from deviating over a sloped ground.

The relation between the tilting of the travel operation lever41and the command frequency output by the inverter control unit51is not limited by what is described above. For example, after the initial value is set, the command frequency may be set in proportion to the operational degree of the travel operation lever41as represented by dotted line (B) in the graph ofFIG. 12B. With this arrangement, the aerial platform vehicle1can run smoothly.

The steering control unit53receives the information of the operational state (the direction and degree of the turning from the neutral position) of the steering dial42, which information is detected by the steering operation detector42a. Based on the information, the steering control unit53sets a target steering angle for one of the front wheels whose side corresponds to the detected operational state of the steering dial42, and controls the steering control valve71and thereby the extension of the steering cylinder17in accordance with the characteristic of the steering mechanism13, so that the steering angle detected by the steering angle detector61provided at the front wheel on the turning side comes to the target steering angle.

Furthermore, the steering control unit53controls the operation of the steering cylinder17in consideration of the characteristic of the steering mechanism13. Specifically, when the steering dial42is operated for the travel body10to take a right turn, the steering control unit directs the pair of left and right drive wheels11a,11bsuch that the left and right drive wheels, respectively, take circular paths, the centers of whose circles are located at the right side non-drive wheel (right rear wheel)11d(refer toFIG. 6B). On the other hand, when the steering dial42is operated for the travel body10to take a left turn, the steering control unit directs the pair of left and right drive wheels11a,11bsuch that the left and right drive wheels, respectively, take circular paths, the centers of whose circles are located at the left side non-drive wheel (left rear wheel)11c(refer toFIG. 6C).

The ascent and descent control unit52receives the information of the operational state (the direction and degree of the tilting from the neutral position) of the ascent and descent operation lever43, which information is detected by the ascent and descent operation detector43a. Based on the information, the ascent and descent control unit52sets a target ascending or descending speed for the aerial platform30in correspondence to the detected operational state of the ascent and descent operation lever43, and shifts the spool of the ascent and descent control valve72and thereby controls the operational speed of the ascent and descent cylinder21, so that the ascending or descending speed of the aerial platform30detected by the ascent and descent speed detector66comes to the target ascending or descending speed.

Now, the explanation proceeds to how the aerial platform vehicle1, which is equipped with the above described controller, is used for work at elevated locations. At first, a worker boards the aerial platform30while the scissors-linkage20is retracted on the travel body10. Then, he operates the travel operation lever41and the steering dial42on the control box40, which operation directs and drives the left and right steering drive wheels11a,11b, so that the aerial platform vehicle1is moved to a site where work is to be performed.

During the travel, while the tilt angle of the travel body10is smaller than a predetermined angle (i.e., the vehicle is traveling over a flat ground), the inverter control unit51selects and executes control pattern A (refer toFIG. 9). In this control pattern, the command frequency increases in correspondence to the increased degree of the tilting of the travel operation lever41(refer toFIG. 12B), which results in the corresponding increase in the vehicle speed.

During the travel, if the tilt angle of the travel body10becomes larger than the predetermined angle (i.e., the vehicle is traveling over a sloped ground), then the inverter control unit51selects and executes control pattern B (refer toFIG. 9). In this control pattern, the command frequency is set to the frequency that has been increased in correspondence to the increased travel command value, from the minimum frequency that generates a torque necessary for preventing the travel body10from deviating, as initial value, which torque is predetermined in correspondence to the tilt angle of the travel body10(refer toFIG. 12B). As a result, the travel body10never skids over the sloped ground even if the travel operation lever41is at its neutral position. Also, the vehicle speed can be increased (up to a predetermined upper limit) in correspondence to the increased degree of the tilting of the travel operation lever41.

However, while the vehicle is traveling over a sloped ground, if the voltage of the battery B becomes lower or higher than a predetermined value, or if the temperature of the windings of the travel motor12a,12bbecomes higher than a predetermined value, then the inverter control unit51initiates the above mentioned cutback function, in which the power to the travel motors12a,12bis restricted on the basis of the cutback rate that is predetermined in correspondence to the voltage value of the battery B or to the temperature value of the windings of the travel motors12a,12b, which values are subject to the cutback function.

Under the influence of the cutback function, if the electrical current value of the travel motors12a,12bbecomes smaller than the lower limit of the allowable range that is predetermined in correspondence to the tilt angle of the vehicle, i.e., if it is not possible to keep a torque necessary for preventing the travel body10from deviating, which torque is predetermined in correspondence to the tilt angle of the travel body, then the inverter control unit51stops the operation of the inverter IV and thereby cuts power off to the travel motors12a,12b. In this instance, the negative brakes14, which have been disengaged up to this point, are activated to stop the rotation of and lock the rotational shafts of the travel motors12a,12b. In this way, the aerial platform vehicle1according to the present embodiment is prevented from deviating over any sloped ground.

After the vehicle has reached the work site, the worker operates the ascent and descent operation lever43on the control box40to extend the ascent and descent cylinder21and thereby extend the scissors-linkage20, so that the aerial platform30is brought to a desired elevation. If it is necessary to move the aerial platform vehicle1during the work, then the worker operates the travel operation lever41and the steering dial42, which operation directs and drives the left and right steering drive wheels11a,11b, so that the vehicle is moved to a desired position.

In this instance, if the tilt angle of the travel body10is smaller than a predetermined angle (i.e., the vehicle is traveling over a flat ground), the inverter control unit51selects and executes control pattern C (refer toFIG. 9). In this control pattern, the command frequency is increased in correspondence to the increased degree of the tilting of the travel operation lever41, which results in the corresponding increase in the vehicle speed. However, this is a travel over a flat ground without retraction of the scissors-linkage20, so the speed of the vehicle needs to be relatively low for safety. Therefore, the upper limit of the command frequency is set lower, regardless of the operational degree of the operation lever41.

Furthermore, if the scissors-linkage20is not retracted, then the vehicle is restrained from making a high speed travel or a travel over a sloped ground, to ensure safety for work at elevated positions. As a result, the vehicle is allowed to travel only at a low speed over a flat ground. Therefore, the torques to be generated by the travel motors12a,12bare relatively small, and the excitation currents provided to the motors are reduced accordingly in this embodiment. As a result, the consumption of electricity is cut down, avoiding inefficient use of the battery B and thereby extending the life of the battery B.

If the tilt angle of the travel body10becomes equal to or larger than a predetermined angle (i.e., the vehicle is traveling over a sloped ground), in other words, the vehicle is traveling over a sloped ground without retraction of the scissors-linkage20, then the inverter control unit51selects and executes control pattern D (refer toFIG. 9). In this control pattern, the operation of the inverter IV is restrained not to allow movement of the travel body10for safety.

After the work is finished, the worker operates the ascent and descent operation lever43to retract the scissors-linkage20by contracting the ascent and descent cylinder21, and thereby lowering the aerial platform30on the travel body10. He or she, then, operates the travel operation lever41and the steering dial42, making the inverter control unit51select and execute control pattern A or B to drive the left and right drive wheels11a,11b, so that the aerial platform vehicle1is taken to a garage.

In the above described embodiment, while the travel operation lever41is being operated, one inverter powers the two induction motors at an optimal rotational speed in correspondence to the operational degree of the travel operation lever41. As a result, the aerial platform vehicle1according to the present invention, even though its system for controlling the motors is simple, avoids wasteful power consumption and extends the period of use of the aerial platform vehicle available on a single charge.

In addition, in this embodiment, while the steering dial42is being operated, the inverter control unit51controls the driving of the travel motors12a,12bthrough the inverter IV such that the output torque characteristic demonstrates a more gradual change with respect to the change in the rotational speed of the travel motors12a,12b. In this way, a reduction is made in the difference in torque between the inner and outer wheels, which difference arises from the difference in rotational speed during the vehicle's turning, resulting in a more energy-efficient travel of the vehicle. According to this design, while the steering dial42is being operated, the speed of the vehicle is reduced from that in linear travel as mentioned above. This is preferable for the sake of safety. However, in this instance, the aerial platform vehicle1can be accelerated by further tilting the travel operation lever41for compensating the speed reduction that occurs during the steering.

In the above described embodiment, the travel operation lever41(travel-operating means), which is used for controlling the forward or rearward driving of the travel body10, and the steering dial42(steering-operating means), which is used for controlling the turning direction of the travel body10, are provided separately. However, this embodiment is not limited to this. For example, only one tilting lever may be provided to be moved from its neutral position into forward, rearward, rightward and leftward directions, and into slanted or middle directions therebetween, for controlling the forward, rearward and turning movements in correspondence to the degree and direction of the tilting of the lever.

The present invention has been explained with respect to a preferred embodiment. However, the scope of the present invention is not limited by the above described embodiment. The embodiment can be modified or improved appropriately within the scope of the invention and without deviating from the essence of the invention.

For example, the travel motors (induction motors)12a,12bused in the above embodiment can have a property that the output torque increases as the temperature of the windings becomes lower (refer toFIG. 13), and temperature-detecting means may be provided and attached to the two travel motors (induction motors)12a,12b. In this case, the lower the temperature of the windings of the travel motors12a,12bdetected by the temperature-detecting means, the inverter control unit51can control the operation of the travel motors12a,12bthrough the inverter IV to achieve a more gradually changing output torque characteristic for the range in rotational speed of the travel motors. The addition of this arrangement can compensate the output torque characteristic for the rise that could have otherwise occurred because of a fall in the temperature of the windings of the travel motors12a,12b(as shown inFIG. 7, where the torque curve is shifted lower from TLto A). As a result, the operation of the travel motors12a,12bis controlled more accurately through the inverter IV during the steering, and the aerial platform vehicle1according to the present invention achieves an efficient drivability especially for the steering, contributing to energy saving for the battery B. By the way, in stead of the temperature of the windings of the motors12a,12b, ambient temperature may be applied in the same way.