EP3868700B1

EP3868700B1 - Travel control device for vehicle with an aerial work platform

Info

Publication number: EP3868700B1
Application number: EP21156932.2A
Authority: EP
Inventors: Mitsuru Sato; Takuya Aoki; Kou YAEGASHI
Original assignee: Aichi Corp
Current assignee: Aichi Corp
Priority date: 2020-02-18
Filing date: 2021-02-12
Publication date: 2023-07-12
Anticipated expiration: 2041-02-12
Also published as: JP7453015B2; EP3868700A1; JP2021130523A

Description

Technical field

The present invention relates to a vehicle with an aerial work platform and a travel control device for said vehicle configured such that a traveling operation can be performed from a work platform provided at a tip end of a boom according to the preamble of claim 1.

Technical background

A known exemplary vehicle with an aerial work platform includes a self-propelled vehicle with an aerial work platform that comprises a traveling body having wheels and capable of traveling, a revolving superstructure provided on the traveling body in a horizontally rotatable manner, a boom provided on the revolving superstructure in a vertically swingable and axially extendable manner, and a work platform supported at a tip end of the boom in a horizontally swingable manner. The above-mentioned vehicle with the aerial work platform comprises an operation device in the work platform and is configured such that the operation device is manipulated to allow a horizontal rotation of the revolving superstructure, a vertical swing or other actuations of the boom, and a pivotal actuation (horizontal swing) of the work platform as well as allow the traveling body to travel, as described in, for instance, Japanese Laid-Open Patent Publication No. 2001-180899(A ). The operation device includes a traveling lever that is tiltably operable in a back-and-forth direction from a neutral state with its upwardly extending and a steering lever tiltably operable in a right-and-left direction and is configured to move a vehicle body forward or backward in response to the tilting operation performed on the traveling lever while controlling a travel speed thereof and displace a steering angle of the wheels in response to the tilting operation performed on the steering lever.
The vehicle with an aerial work platform and a travel control device for said vehicle according to the preamble of claim 1 is known from the International patent application WO 2018/162882 . Herein a base unit for a lifting vehicle is disclosed with an embodiment (figure 1) including an extendable boom carrying on its tip end a cage for a human operator. In the cage a control console is mounted that can be operated by the human operator. The extendable boom is mounted on base unit including a wheel holding chassis, which wheels may be steerable by a steering mechanism. The rising structure of the extendable boom may be folded onto the wheel basis.
In a self-propelled vehicle with an aerial work platform as described in Japanese Laid-Open Patent Publication No. 2001-180899(A ), a travel speed of a vehicle body is limited to be a travel speed (allowable travel speed) or less at which safe turning travel is achieved, depending on a steering angle of a steering wheel. In general, however, in such self-propelled vehicle with the aerial work platform, the steering angle is always displaced at a constant speed irrespective of the travel speed, which causes that when, for example, a traveling body travels at a relatively high-speed, course change actuation of the traveling body sensitively responds to a steering operation of an operator, resulting in that the operations corresponding to travel of the traveling body may not be facilitated. Moreover, there arises a problem that a rapid movement of a work platform supported at a tip end of a boom deteriorates ride comfort of the operator boarding on the work platform.

Problem to be solved with the invention

The present invention has been made in view of the aforementioned problem, and an aim thereof is to provide a vehicle with an aerial work platform and a travel control device for said vehicle according to the preamble of claim 1 with an improved operability of the traveling body.

Means to solve the problems

To solve the above problem, the present invention provides a vehicle with an aerial work platform and a travel control device for said vehicle according to claim 1. The steering operation device that is provided in the work platform and operated by the operator boarding on the work platform is for example, a steering lever 72 in the embodiment, the steering actuator that causes the steering wheel to perform steering actuation is for example, a steering cylinder 66 in the embodiment, the steering actuator controller that controls actuation of the steering actuator in response to operation of the steering operation device is for example, a steering-angle control unit 52 in the embodiment, and the travel control device that is configured to comprise a speed index-value detector that detects a speed index value indicative of a travel speed of the traveling body is for example, a steering-angle control unit 52 in the embodiment.
In the vehicle with an aerial work platform and a travel control device for said vehicle with the above configuration, the steering actuator controller is preferably configured to correct the actuation speed of the steering actuator responsive to the operation of the steering operation device so that it decreases as the speed index value detected by the speed index-value detector increases.
In the vehicle with an aerial work platform and a travel control device for said vehicle with the above configuration, it is preferable that the steering actuator controller is configured not to correct the actuation speed of the steering actuator responsive to the operation of the steering operation device when the speed index value detected by the speed index-value detector is less than a predetermined value.
The vehicle with an aerial work platform and a travel control device for said vehicle with the above configuration preferably further comprises a traveling operation device that is provided in the work platform and operated by the operator boarding on the work platform (for example, a traveling operation lever 71 in the embodiment), a travel speed controller that controls the travel speed of the traveling body in response to operation of the traveling operation device (for example, a controller 50 in the embodiment), and the speed index-value detector configured to detect the speed index value based on the operation of the traveling operation device.

Advantageous effects of the invention

With the vehicle with an aerial work platform and a travel control device for said vehicle according to the present invention, the steering actuator controller controls the steering actuator that causes the steering wheels of the traveling body to perform the steering actuation depending on the speed index value indicative of the travel speed of the traveling body detected by the speed index-value detector in addition to in response to the operation of the steering operation device. This allows the actuation speed of the steering actuator based on the travel speed of the traveling body to be controlled and accordingly prevents the course change actuation of the traveling body at such as a higher speed from sensitively responding to the steering operation of the operator, which resulting in enhancing the operability of the traveling body.
In the vehicle with an aerial work platform and a travel control device for said vehicle with the above configuration, the steering actuator controller is configured not to correct the actuation speed of the steering actuator responsive to the operation of the steering operation device when the speed index value detected by the speed index-value detector is less than a predetermined value. Since the course change actuation of the traveling body may not sensitively respond while the traveling body travels at low speed, steering control is performed in a conventionally known manner.
Further in addition, the vehicle with an aerial work platform and a travel control device for said vehicle with the above configuration may be configured to comprise the traveling operation device that is provided in the work platform and operated by the operator boarding on the work platform, the travel speed controller that controls the travel speed of the traveling body in response to the operation of the traveling operation device, and the speed index-value detector that detects the speed index value based on an operation of the traveling operation device. When so configured, it eliminates the need for allocation of additional instruments for measuring a travel speed of the traveling body and therefore a manufacturing cost and an increase in the number of steps of the manufacturing process can be reduced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only.

Brief description of the drawings

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention.

FIG. 1 is a side view and a plan view of a self-propelled vehicle with an aerial work platform according to the present invention by way of example of a vehicle with an aerial work platform;
FIG. 2 is a block diagram illustrating a configuration associated with actuation control for the vehicle with the aerial work platform;
FIG. 3 is a hydraulic circuit diagram illustrating a part of a configuration associated with steering control for the vehicle with the aerial work platform; and
FIG. 4 is a graph showing correlation between an operation amount of a traveling operation lever of the vehicle with the aerial work platform and a flow rate of hydraulic oil for displacement of a steering angle.

Description of the embodiments

The embodiment according to the present invention will be described below with reference to the accompanying drawings. By way of example of a vehicle with an aerial work platform according to the present invention, FIG. 1 illustrates a self-propelled vehicle with an aerial work platform 1. The vehicle with the aerial work platform 1 comprises a traveling body 10 configured to be capable of traveling, a horizontally rotatable revolving superstructure 20 provided on the traveling body 10, a vertically swingable boom 30 provided on the revolving superstructure 20, and a work platform 40 provided at a tip end of the boom 30.
The traveling body 10 comprises a pair of right and left steering wheels 12 (left steering wheel 12L and right steering wheel 12R) and a pair of right and left driving wheels 13 (left driving wheel 13L and right driving wheel 13R), which are each rotatably mounted to a traveling body frame 11. As illustrated in FIG. 1(a), a movement of the traveling body 10 to the left in the figure corresponds to a forward movement and a movement thereof to the right in the figure corresponds to a backward movement. The steering actuation (displacement of steering angle) of the left steering wheel 12L and right steering wheel 12R is configured to be performed with a steering device 60. The steering device 60 comprises a steering bracket 61 which is pivotably coupled to the traveling body frame 11 with a king pin 62 and rotatably supports the corresponding steering wheel 12 and a knuckle arm 63 for transmitting a force for rotating the steering bracket 61 around the king pin 62 (further the force for steering actuation of the steering wheel 12).
The steering bracket 61, the king pin 62, and the knuckle arm 63 are provided in correspondence to the respective left steering wheel 12L and right steering wheel 12R. The steering bracket 61, king pin 62, and knuckle arm 63 for the left steering wheel 12L are denoted by prefixing the letter "left" to each name and by each reference numeral followed by the letter "L". The steering bracket 61, king pin 62, and knuckle arm 63 for the right steering wheel 12R are denoted by prefixing the letter "right" to each name and by each reference numeral followed by the letter "R". FIG. 1(b) illustrates a state in which a left knuckle arm 63L is hidden by a steering cylinder 66 and a steering arm 67, which will be described later.
The left knuckle arm 63L and a right knuckle arm 63R are coupled to each other with a tie rod 64. More specifically, a first end of the tie rod 64 is pivotably fixed to the left knuckle arm 63L with a left connecting pin 65L, and a second end of the tie rod 64 is pivotably fixed to the right knuckle arm 63R with a right connecting pin 65R. The right and left knuckle arms are coupled to each other with the tie rod 64 whereby the respective steering brackets synchronously rotate (therefore a steering angle of steering wheel 12 is responsively displaced), as described above.
In addition, a left steering bracket 61L comprises the steering arm 67 for coupling to the steering cylinder 66 serving as a drive source for displacement of the steering angles of the right and left steering wheels 12. The steering cylinder 66 and the steering arm 67 are coupled through a cylinder connecting pin 68 to each other. This consequently allows the left steering bracket 61L to rotate around a left king pin 62L in response to extension and contraction of a rod of the steering cylinder 66. The movement of the left steering bracket 61L is transmitted to the right knuckle arm 63R through the tie rod 64 so that a right steering bracket 61R rotates around a right king pin 62R in conjunction with the movement of the left steering bracket 61L. In the steering device 60 illustrated in FIG. 1(b), as a cylinder rod of the steering cylinder 66 extends from a neutral position, the steering angle of steering wheel 12 is displaced to the left from a center line (alternate long and short dash line in FIG. 1(b)), as viewing in a direction of the revolving superstructure 20 from the work platform 40, and moreover, with a forward movement in this state, it follows that an advancing direction of the traveling body 10 turns to the right. Alternatively, as the cylinder rod of the steering cylinder 66 contracts from the neutral position, the steering angle of steering wheel 12 is displaced to the right from the center line, as viewing in the direction of the revolving superstructure 20 from the work platform 40, and moreover, with a forward movement in this state, it follows that the advancing direction of the traveling body 10 turns to the left.
A pivot mechanism 15 is provided in an upper central portion of the traveling body frame 11 and configured to rotate the revolving superstructure 20 in a direction denoted by an arrow A in FIG. 1(b). The pivot mechanism 15 comprises an outer ring fixed to the traveling body frame 11, an inner ring that is engaged with the outer ring and fixed to the revolving superstructure 20, and a rotary center joint (not illustrated) for supplying hydraulic oil to various actuators (which will be described later) provided in the revolving superstructure 20. The boom 30 is provided on an upper portion of the revolving superstructure 20 and configured to move rotationally (vertically swingable) in a direction denoted by an arrow B in FIG. 1(a) around a pivot pin 34. The boom 30 comprises a base boom 31 pivotably coupled to the revolving superstructure 20, an intermediate boom 32 assembled into the base boom 31 in telescopic form, and a top boom 33, which are configured to be axially extendable. A vertical post 37 is provided at a tip end of the top boom 33 so as to be vertically swingable through a pivot pin 33a.
The work platform 40 is provided on an upper portion of the vertical post 37 so as to move pivotally (horizontally swingable) around a pivot pin 37a in a direction denoted by an arrow C in FIG. 1(b). The work platform 40 comprises a substantially rectangular-shaped work floor 41 on which an operator M can board and a handrail 42 erected around the work floor 41. The work platform 40 includes an operation device 70 for performing controls such as travel control of the traveling body 10 and actuation control of the boom 30.
Next, with reference to FIG. 2, a control device will be described that performs, based on an operation of the operation device 70, the travel control of the traveling body 10 and the actuation control of the revolving superstructure 20, the boom 30, and work platform 40. The control device controls various actuators that actuate the traveling body 10, the revolving superstructure 20, the boom 30, and work platform 40. The control device comprises the operation device 70 provided in the work platform 40 described above, a hydraulic unit 80 that supplies hydraulic oil as a drive source for the various actuators to the various actuators described above, a controller 50 that is provided in the revolving superstructure 20 and controls the hydraulic oil supplied from the hydraulic unit 80 to the various actuators in response to operations performed on various operation levers provided in the operation device 70.
The actuators installed in the vehicle with the aerial work platform 1 include an actuator for driving and traveling for which the traveling body 10 is driven to travel, and an upper drive actuator for activating movements of the revolving superstructure 20, the boom 30, and the work platform 40. The actuator for driving and traveling according to the embodiment comprises a travel actuator that moves the traveling body 10 forward or backward in a predetermined speed range, a steering actuator that causes the steering wheel 12 to perform steering actuation, and a braking actuator that brakes the traveling body 10 during traveling. FIG. 2 illustrates a traveling motor 16 corresponding to the travel actuator, the steering cylinder 66 corresponding to the steering actuator, and a brake cylinder 18 corresponding to the braking actuator. The upper drive actuator comprises a rotating motor 26, a boom vertical swing cylinder 35, a boom axial extension cylinder 36, and a swing motor 46.
The traveling motor 16 transmits rotation of a motor shaft driven with oil pressure of the supplied hydraulic oil to the driving wheel 13 (refer to FIG. 1) to rotate the motor shaft normally or reversely thereby rotating the driving wheel 13 normally or reversely so as to move the traveling body 10 (refer to FIG. 1) forward or backward. In addition, the traveling motor 16 controls a rotation speed of the motor shaft to change a travel speed of the traveling body 10. The brake cylinder 18 functions as a negative brake that, when the hydraulic oil is not being supplied, brakes and locks the rotation of the motor shaft of the traveling motor 16 by force of a built-in spring to brake a rotation of the driving wheel 13. The steering cylinder 66, which adopts a single rod cylinder having two ports, includes the cylinder rod that has a tip end coupled to the steering arm 67 (refer to FIG. 1(b)) and extends and contracts to cause the steering wheel 12 to perform the steering actuation.
The rotating motor 26, which is provided in the revolving superstructure 20, transmits the rotation of the motor shaft thereof to the inner ring engaged with the outer ring fixed to the traveling body frame 11 to rotate the rotating motor 26 normally or reversely so as to rotate the revolving superstructure 20 in a clockwise or counterclockwise direction (refer to the arrow A in FIG. 1(b)) relative to the traveling body 10. The boom vertical swing cylinder 35, which is mounted on the revolving superstructure 20 and the boom 30, extends and contracts the cylinder rod to vertically swing the boom 30 in the direction denoted by the arrow B in FIG. 1(a) around the pivot pin 34. The boom axial extension cylinder 36, which is provided within the boom 30, extends and contracts the cylinder rod to extend and contract the intermediate boom 32 and the top boom 33 assembled into the base boom 31 in telescopic form.
The swing motor 46, which is provided in the work platform 40, allows the work platform 40 to be pivotally actuated (horizontal swing actuation) in a direction denoted by the arrow C in FIG. 1(b) relative to the vertical post 37 through the use of the rotation of the motor shaft driven with the oil pressure of the supplied hydraulic oil. Further, an upper leveling cylinder (not illustrated) is mounted on the tip end of the top boom 33 and the vertical post 37. A closed circuit is formed, with a hydraulic hose, between the upper leveling cylinder and a lower leveling cylinder (not illustrated) mounted on the base boom 31 and the revolving superstructure 20. Accordingly, axially extendable actuation of the upper leveling cylinder in response to axially extendable actuation of the lower leveling cylinder swings the vertical post 37 vertically relative to the top boom 33 to keep a floor surface of the work platform 40 in a horizontal state at all times irrespective of a vertical swing angle of the boom 30.
The hydraulic unit 80, which supplies the hydraulic oil as a drive source for actuation of the various actuators described above, comprises an engine E provided in the revolving superstructure 20, a hydraulic pump P driven with the engine E, a hydraulic oil tank T, and a control valve unit 85 that controls a supply direction and supply amount of the hydraulic oil supplied from the hydraulic pump P to each hydraulic actuator. The control valve unit 85 comprises a plurality of control valves provided in correspondence to each hydraulic actuator. These control valves include a travel control valve V1 for drive control of the traveling motor 16, a brake control valve V2 that controls the brake cylinder 18, a steering-direction switching valve V3 and a steering-angular-velocity control valve V4 that control the steering cylinder 66, a rotation control valve V5, a vertical swing control valve V6, an extension control valve V7, and a swing control valve V8.
The operation device 70 included in the control device illustrated in FIG. 2 comprises: a traveling operation lever 71 that is operated to, with respect to the traveling body 10, mainly, start and stop, move forward and backward, and switch a travel speed; a steering lever 72 that is operated to perform steered manipulation of the traveling body 10 (steering operation of the steering wheel 12); a rotation operation lever 73 that is operated to perform a rotation operation of the revolving superstructure 20; a boom operation lever 74 that is operated tod perform vertical swing and extension and contraction operations of the boom 30; and a horizontal swing operation lever 75 that is operated to perform a horizontal swing operation (rotation operation) of the work platform 40. Each of the respective operation levers is located in a neutral position in which the lever is oriented vertically in a non-operating state and configured to tiltably operable in a direction determined upon operating each operation lever with this neutral position as a reference. Also, the controller 50 controls each control valve in the control valve unit 85 in response to a tilting operation performed on each operation lever described above.
A description will now be given of the control of each control valve in response to the tilting operation performed on each operation lever. First, the traveling operation lever 71 is tiltably operable in a back-and-forth direction based on the neutral position. When the traveling operation lever 71 is operated to tilt forward, the controller 50 controls a supply direction and flow rate of the hydraulic oil supplied to the traveling motor 16 with the travel control valve V1 so that the traveling body 10 moves forward at a speed corresponding to the tilt angle of the lever. On the other hand, when the traveling operation lever 71 is operated to tilt backward, it controls the travel control valve V1 so that the supply direction of the hydraulic oil supplied to the traveling motor 16 is a direction opposite to that when the traveling operation lever 71 is tilted forward and controls the flow rate of the hydraulic oil with the travel control valve V1 so that the traveling body 10 moves backward at a speed corresponding to the tilt angle of the lever.
Upon the traveling operation lever 71 being operated to tilt to any of the forward and backward directions from a neutral state, the controller 50 also controls the brake control valve V2 into an open state to supply the hydraulic oil to the brake cylinder 18. As a result, a brake lock state in the motor shaft of the traveling motor 16 is released to cause the motor shaft to be rotatable. Contrastingly, when the traveling operation lever 71 is in the neutral position or when it returns to the neutral position from a state where it is operated to tilt, the controller 50 controls the brake control valve V2 into a closed state to suspend the supply of hydraulic oil to the brake cylinder 18. This causes the motor shaft of the traveling motor 16 to be in the brake lock state to brake the rotation of the driving wheel 13.
The steering lever 72 is tiltably operable in a right-and-left direction based on the neutral position. The controller 50 displaces the steering angle of the steering wheel 12 so that when the traveling body 10 moves forward with the steering lever 72 being operated to tilt to the left, it turns to the left and when the traveling body 10 moves forward with the steering lever 72 being operated to tilt to the right, it turns to the right. The steering angular actuation of the steering wheel 12 is performed by control of the steering-direction switching valve V3 and the steering-angular-velocity control valve V4 with the steering-angle control unit 52 in the controller 50. The contents in which the steering-direction switching valve V3 and the steering-angular-velocity control valve V4 are controlled with the steering-angle control unit 52, will be discussed in more detailed below.
The rotation operation lever 73 is configured to be tiltably operable in a right-and-left direction based on the neutral position. The controller 50 controls a spool movement direction and valve opening degree of the rotation control valve V5 to drive the rotating motor 26 so that when the operation lever is operated to tilt to the right, the revolving superstructure 20 rotates in a clockwise direction as viewed in FIG. 1(b) and when the lever is operated to tilt to the left, the revolving superstructure 20 rotates in a counterclockwise direction as viewed in FIG. 1(b).
The boom operation lever 74 is configured to be tiltably operable in back-and-forth and right-and-left directions based on the neutral position. When the boom operation lever 74 is operated to tilt in the back-and-forth direction, the controller 50 switches a spool movement direction of the vertical swing control valve V6 depending on a tilt direction of the operation lever and controls a valve opening degree to a predetermined value to drive the boom vertical swing cylinder 35 so as to vertically swing the boom 30.
Contrastingly, when the boom operation lever 74 is operated to tilt in the right-and-left direction, the controller 50 switches a spool movement direction of the extension control valve V7 depending on a tilt direction of the operation lever and controls a valve opening degree to a predetermined value to drive the boom axial extension cylinder 36 so as to axially extend the boom 30. The horizontal swing operation lever 75 is configured to be tiltably operable in a right-and-left direction based on the neutral position. When the operation lever is operated to tilt to the right, the controller 50 controls a spool movement direction and valve opening degree of the swing control valve V8 until the work platform 40 is oriented in the counterclockwise in a direction denoted by the arrow C in FIG. 1(b) and at an angle corresponding to the tilt angle of the operation lever. Alternatively, when the horizontal swing operation lever 75 is operated to tilt to the left, the controller 50 controls the spool movement direction and valve opening degree of the swing control valve V8 until the work platform 40 is oriented in the clockwise in a direction denoted by the arrow C in FIG. 1(b) and at an angle corresponding to the tilt angle of the operation lever.
The contents in which the steering-direction switching valve V3 and the steering-angular-velocity control valve V4 are controlled with the steering-angle control unit 52, will be discussed with reference to FIGS. 3 and 4 in more detailed below. With reference to FIG. 3, a hydraulic circuit where it is associated with actuation control of the steering cylinder 66, will be described. In FIG. 3, the steering-direction switching valve V3, which is a 4-port 3-position directional control valve, is to be in an all-ports-open state at a spool position (hereinafter, referred to as "normal position") in a state in which the steering-direction switching valve V3 is not subjected to any control. In that case, the cylinder rod of the steering cylinder 66 is positioned at a position where the steering angle of the steering wheel 12 is held in a straight-ahead direction (hereinafter, also referred to as " straight travel position"). A holding valve (not illustrated) is provided in each of two hydraulic paths that couple the steering cylinder 66 and the steering-direction switching valve V3. The cylinder rod of the steering cylinder 66 is configured to hold the position at the time even when the steering-direction switching valve V3 enters the all-ports-open state (or equivalently, keep the steering angle of the steering wheel 12 as it is).
In this state, when, for example, the steering lever 72 is operated to tilt to the right, the steering-angle control unit 52 excites a solenoid on the left side in the figure to move a spool from the normal position to the right and switches to a position where a port P (supply port of hydraulic oil) and a port A communicate with each other and a port B and a port T (port for hydraulic oil to return to the hydraulic oil tank T) communicate with each other. This allows that the hydraulic oil supplied to the port P is discharged from the port A and is moved to a direction in which the cylinder rod of the steering cylinder 66 extends. When the steering lever 72 is operated to tilt to the right, the steering-angle control unit 52 contrastingly excites a solenoid on the right side in the figure to move a spool from the normal position to the left direction and switches to a position where the port P and the port B communicate with each other and the port A and the port T communicate with each other. Accordingly, the hydraulic oil supplied to the port P is discharged from the port B and is moved to a direction in which the cylinder rod of the steering cylinder 66 contracts.
The direction steering-angular-velocity control valve V4 comprises a 2-port 2-position proportional valve V4a and a 4-port 2-position pilot switching valve V4b. In a normal position of a spool in the proportional valve V4a, a portion between the supply port of the hydraulic oil and an output port is closed. Upon the steering lever 72 being operated to tilt to any of the right and left directions, the steering-angle control unit 52 moves the spool to the right in the figure and controls a valve opening degree depending on the tilt angle of the traveling operation lever 71 to control a flow rate of the hydraulic oil passing through the proportional valve V4a.
In the normal position of the spool in the pilot switching valve V4b, a first supply port P1 coupled to an output port of the proportional valve V4a and the port A communicate with each other, and a portion between a second supply port P2 to which the hydraulic oil is supplied from the hydraulic pump P and the port B is closed. When the spool of the proportional valve V4a is in the normal position, pilot pressure of the hydraulic oil which is branched from a path of the hydraulic oil supplied from the hydraulic pump P to the second supply port P2, allows the spool to move to the left in the figure so that the portion between the first supply port P1 and the port A is closed and the second supply port P2 and the port B communicate with each other.
Contrastingly, when the spool of the proportional valve V4a moves from the normal position to the right in the figure so that the hydraulic oil is discharged from the output port of the proportional valve V4a, pilot pressure of the hydraulic oil which is branched from a path between the output port of the proportional valve V4a and the first supply port P1 of the pilot switching valve V4b, allows the spool of the pilot switching valve V4b to move to the right in the figure. Accordingly, the first supply port P1 and the port A communicate with each other and the portion between the second supply port P2 and the port B is closed.
In the pilot switching valve V4b, when the portion between the first supply port P1 and the port A is closed and the second supply port P2 and the port B communicate with each other, the hydraulic oil supplied from the hydraulic pump P is discharged to a path for actuation of other actuators (rotating motor 26, boom vertical swing cylinder 35, boom axial extension cylinder 36, and swing motor 46). In addition, a 2-port 2-position unloader valve Vu is arranged between a hydraulic path discharged from the port B of the pilot switching valve V4b and a recirculation path to the hydraulic oil tank T.
When a spool of the unloader valve Vu is in the normal position, a supply port and an output port are in communication with each other and the hydraulic oil discharged from the port B of the pilot switching valve V4b returns to the hydraulic oil tank T. When any of the rotation operation lever 73, the boom operation lever 74, and the horizontal swing operation lever 75 is operated to tilt, the steering-angle control unit 52 allows the spool of the pilot switching valve V4b to move to the left in the figure and prevents the hydraulic oil from passing from the first supply port P1 to the port A while it allows the hydraulic oil from passing from the second supply port P2 to the port B.
With the hydraulic circuit illustrated in FIG. 3, while the steering lever 72 is in the neutral position, when the proportional valve V4a falls into an uncontrollable state with remaining open due to some cause (such as contamination with foreign substances), a spool of the steering-direction switching valve V3 is in the normal position (all-ports-open state) whereby the hydraulic oil supplied from the steering-angular-velocity control valve V4 directly returns to the hydraulic oil tank T. Accordingly, no fluctuation in the cylinder rod of the steering cylinder 66 under these circumstances prevents displacement of the steering angle of the steering wheel 12 irrespective of the steering lever 72 not being operated.
While the steering lever 72 is in the neutral position, when the spool of the steering-direction switching valve V3 falls into an uncontrollable state with remaining in any of right and left positions (or equivalently, in such condition that the hydraulic oil can be supplied to the steering cylinder 66) due to some cause, the spool of the proportional valve V4a is in the normal position so that: the portion between the supply port and the output port of the proportional valve V4a is closed; the pilot pressure of the hydraulic oil supplied from the hydraulic pump P allows the spool of the pilot switching valve V4b to move from the normal position to the left as viewed in FIG. 3 whereby the portion between the first supply port P1 and the port A is closed; and the hydraulic oil supplied from the hydraulic pump P to the second supply port P2 returns directly from the port B to the hydraulic oil tank T.
Therefore, even in the case where while the steering lever 72 is in the neutral position, when the proportional valve V4a of the steering-direction switching valve V3 or the steering-angular-velocity control valve V4 falls into an uncontrollable state with remaining open due to some cause, the steering angle of the steering wheel 12 is not displaced unless directed by an operator.
The contents in which the proportional valve V4a of the steering-angular-velocity control valve V4 is controlled with the steering-angle control unit 52 when the steering lever 72 is operated to tilt, will be discussed in more detailed below. The steering-angle control unit 52, upon the steering lever 72 being operated to tilt from the neutral position to the right or to the left, regulates an opening degree of the proportional valve V4a depending on a travel speed of the traveling body 10 (or, more properly, an index value (speed index value) indicative of a travel speed of the traveling body 10) to control a flow rate of the hydraulic oil supplied to the steering-direction switching valve V3. Examples of the speed index value of the traveling body 10 may include a speed index value in which speed information output from the provided instrument for measuring the travel speed of the traveling body 10 is employed therefor. According to the embodiment, a tilt angle of the traveling operation lever 71 is used as a speed index value of the traveling body 10.
With reference to graphs illustrated in FIG. 4, the contents in which the proportional valve V4a is controlled depending on a tilt angle of the traveling operation lever 71, will be discussed in more detailed below. In the graphs shown in FIG. 4, a horizontal axis represents an opening degree (operation amount) of the traveling operation lever 71 and a vertical axis represents a flow rate of the hydraulic oil supplied to the steering-direction switching valve V3 (liters per minute (L/min)). FIG. 4(a) shows a flow rate of the hydraulic oil through the proportional valve V4a with respect to an opening degree of the traveling operation lever 71 with a travel mode being set to a low-speed mode or a middle-speed mode. FIG. 4(b) shows a flow rate of the hydraulic oil through the proportional valve V4a with respect to an opening degree of the traveling operation lever 71 with the travel mode being set to a high-speed mode.
In the embodiment, three travel modes of the low-speed mode, the middle-speed mode, and the high-speed mode are included and the maximum travel speed of the traveling body 10 is limited to a speed corresponding to each travel mode. According to the embodiment, the low-speed mode, the middle-speed mode, and the high-speed mode are set to be 1.2 km/h, 3.0 km/h, and 7.2 km/h, respectively. With such specification, the travel speed of the traveling body 10 is controlled to be the maximum travel speed corresponding to the predetermined travel mode when the travel speed of the traveling body 10 become increasingly higher depending on the opening degree of the traveling operation lever 71 and the opening degree reaches 100(%). The travel modes can be changed over with a travel mode selection switch (not illustrated) provided in the operation device 70.
As shown in FIG. 4(a), when a travel mode is set to the low-speed mode or the middle-speed mode, the steering-angle control unit 52 controls the proportional valve V4a to ensure a controlled flow rate with respect to the steering-direction switching valve V3 remained constant irrespective of the opening degree of the traveling operation lever 71. Provided that the controlled flow rate is controlled to be 17.6 (L/min) with the steering lever 72 being operated to tilt to the right and controlled to be 12.6 (L/min) with the steering lever 72 being operated to tilt to the left. Such specifications are made, on occasion where the single rod cylinder is adopted as the steering cylinder 66, to ensure consistency of displacement velocities of the steering angles between displacement to the right and displacement to the left with respect to the steering angle of the steering wheel 12.
More specifically, due to a structure of the single rod cylinder, the volume of hydraulic oil required to move the cylinder rod by the same distance differs depending on both cases of extending and contracting it from the neutral position. More hydraulic oil is required to extend the cylinder rod than to contract it, in particular. In the embodiment, upon the steering lever 72 being operated to tilt to the right, the steering cylinder 66 extends whereby the steering angle of the steering wheel 12 is displaced to the left with respect to a forward movement direction (refer to FIG. 1(a)) so that it follows that the traveling body 10 turns to the right while moving forward. Contrastingly, upon the steering lever 72 being operated to tilt to the left, the steering cylinder 66 contracts whereby the steering angle of the steering wheel 12 is displaced to the right with respect to the forward movement direction so that it follows that the traveling body 10 turns to the left while moving forward. Accordingly, the hydraulic oil is supplied to the steering-direction switching valve V3 (further steering cylinder 66) at a faster flow rate when the steering lever 72 is operated to tilt to the right than that of being operated to tilt to the left so that the displacement velocities in the right and left directions of the steering angle of the steering wheel 12 can coincide with each other. Therefore, the time difference in the time till each steering angle reaches a predetermined angle due to the presence of the differences in the steering direction can be eliminated, which enhancing the operability of the traveling body 10.
Alternatively, when the travel mode is set to the high-speed mode, the steering-angle control unit 52 changes the flow rate of the hydraulic oil supplied to the steering-direction switching valve V3 depending on the opening degree of the traveling operation lever 71. More specifically, when the opening degree of the traveling operation lever 71 ranges from 0% to 20%, the opening degree of the proportional valve V4a is controlled so that the controlled flow rate is the same as that in the low-speed mode and the middle-speed mode, as shown in the graph of FIG. 4(b). This means that the controlled flow rate is set to be 17.6 (L/min) with the steering lever 72 being operated to tilt to the right and set to be 12.6 (L/min) with the steering lever 72 being operated to tilt to the left.
When the opening degree of the traveling operation lever 71 ranges from 20% to 80%, the opening degree of the proportional valve V4a is corrected so that the controlled flow rate gradually decreases depending on such opening degree. More specifically, the opening degree of the proportional valve V4a is control so as to obtain the controlled flow rate shown in the graph of FIG. 4(b) depending on the opening degree of the traveling operation lever 71, within the range so that the controlled flow rate is set to be from 17.6 to 11.2 (L/min) with the steering lever 72 being operated to tilt to the right and set to be from 12.6 to 6.2 (L/min) with the steering lever 72 being operated to tilt to the left.
Further, when the opening degree of the traveling operation lever 71 ranges from 80% to 100%, the opening degree of the proportional valve V4a is controlled to ensure the controlled flow rate remained constant at 11.2 (L/min) with the steering lever 72 being operated to tilt to the right and to ensure the controlled flow rate remained constant at 6.2 (L/min) with the steering lever 72 being operated to tilt to the left.
As described above, the steering-angle control unit 52 corrects, when the high-speed mode is selected, so that an actuation speed of the steering wheel 12 decreases as the travel speed of the traveling body 10 increases. This prevents course change actuation of the traveling body 10 from sensitively responding to an operation of the steering lever 72, enhancing the operability of the traveling body 10. The actuation speed of the steering wheel 12, however, is not corrected in the same manner as above based on the fact that, when the opening degree of the traveling operation lever 71 ranges from 0% to 20%, the traveling body 10 travels at low speed and the course change actuation of the traveling body may not sensitively respond.
It will be appreciated that the present invention will not be limited to the embodiments described above, but various modifications are possible without departing from the technical scope of the present invention, which is defined by the appended claims. According to the embodiment, examples of a driving and traveling actuator for travel control of the traveling body 10 include the actuators which adopt oil pressure as drive source, such as the traveling motor 16, the steering cylinder 66, and the brake cylinder 18, and however, are not limited to the above but may include various actuators such as an electric motor and an internal combustion engine. While the steering operation is performed with the steering lever 72 in the embodiment, steering operation performed with a steering dial may be applicable. In addition, while a vehicle with an aerial work platform which comprises a telescopic boom that is vertically swingable, axially extendable, and rotatable, has been exemplified and described in the above embodiment, a vehicle with an aerial work platform comprising such as an articulating boom may be applicable.

Claims

A vehicle (1) with an aerial work platform (40) and a travel control device (50) for said vehicle (1), comprising:
- a traveling body (10) having a steering wheel (12, 12L, 12R) and capable of traveling;

- a revolving superstructure (20) provided on the traveling body (10) in a rotatable manner;

- a boom (30; 31, 32, 33) provided on the revolving superstructure (20) in a vertically swingable manner;

- a work platform (40) provided at a tip end of the boom (30; 31, 32, 33) and configured to allow an operator (M) to board thereon; and

- a steering operation device (72) provided in the work platform (40) and configured to be operated by the operator (M) in the work platform (40);
characterized in that the vehicle also comprises:
a steering actuator (66) configured to cause the steering wheel (12, 12L, 12R) to perform steering actuation; and a steering actuator controller (52) configured to:
- control actuation of the steering actuator (66) in response to operation of the steering operation device (72), and

correct an actuation speed of the steering actuator (66) responsive to the operation of the steering operation device (72) depending on the speed index value detected by the speed index-value detector to control the actuation of the steering actuator (66) so as to achieve the corrected actuation speed,

the travel control device (50) comprises a speed index-value detector configured to detect a speed index value indicative of a travel speed of the traveling body (10), and

the steering actuator controller (52) is configured to control the actuation of the steering actuator (66) in response to the operation of the steering operation device (72) and depending on the speed index value detected by the speed index-value detector.
The vehicle (1) with an aerial work platform (40) and a travel control device (50) for said vehicle (1) according to claim 1, characterized in that the steering actuator controller (52) is configured to correct the actuation speed of the steering actuator (66) responsive to the operation of the steering operation device (72) so that the actuation speed decreases as the speed index value detected by the speed index-value detector increases.
The vehicle (1) with an aerial work platform (40) and a travel control device (50) for said vehicle (1) according to claim 2, characterized in that the steering actuator controller (52) is configured not to correct the actuation speed of the steering actuator (66) responsive to the operation of the steering operation device (72) when the speed index value detected by the speed index-value detector is less than a predetermined value.
The vehicle (1) with an aerial work platform (40) and a travel control device (50) for said vehicle (1) according to any of claims 1 to 3, characterized in that it comprises
a traveling operation device provided in the work platform (40) and configured to be operated by the operator (M) in the work platform (40) and a travel speed controller configured to control the travel speed of the traveling body (10) in response to the operation of the traveling operation device, and

the speed index-value detector is configured to detect the speed index value based on the operation of the traveling operation device.