COMBINED MOTOR GRADER STEERING AND CONTROL SYSTEM

[0001] This application claims the benefit of commonly-owned US Provisional Patent Application No. 61/066,544 filed February 21, 2008.

Field of Invention

[0002] The invention relates generally to the field of construction vehicles and in particular, a combined steering and control system for such a vehicle.

Background of Invention

[0003] A construction vehicle, such as a motor grader, a snow plow, or a loader, is generally employed for carrying out work functions in addition to basic transportation. Such a construction vehicle has at least one, sometimes more, work tool, such as a blade or a plow for performing a desired work function. A relatively large number of hydraulic actuators are often utilized to move and position a work tool relative to the frame of the vehicle in order to perform a work function. These hydraulic actuators are controlled by an operator located in a cab of a construction vehicle. As is often the case, work functions of a work tool are generally carried out while the construction vehicle is moving. Steering therefore is often required at the same time the vehicle is performing a work function.

[0004] Construction vehicles are relatively complicated and require considerable operator skill to control to fully utilize the capabilities of the machine. For example, traditionally, various functions of a motor grader are controlled by manual shift levers which are associated with hydraulic control valves for adjusting hydraulic components. There may be manual shift levers for lifting up a side or both sides of a blade, sliding a blade laterally right or left, tilting a blade, switching a blade into or out of floating mode, among others. Detailed descriptions of these functions and some other functions of a motor grader may be found in, for example, United States Patent No. 6,523,617, issued February 25, 2003, the contents of which are incorporated herein by reference in their entirety.

[0005] These control levers are typically mounted for movement in fore and aft direction of a motor grader. An operator located in a cab of such a motor grader operates these levers to

control the operation of the work tool. Because of the number of levers required and the complexity of the controls, operating these control levers may require significant amount of training. There has also been concern with respect to operator fatigue.

[0006] More recently, it has been proposed to use joystick type controllers for controlling various functions of a motor grader. These attempts generally displace the existing mechanical linkage controls with some form of multi-functional control, either through joysticks, and/or, electrical switches. Joystick type controllers combine several control functions into one control device. Unfortunately, controllers of this type also can be quite complicated and may require considerable level of skill to operate. [0007] There also have been proposals to extend use of joystick type of controllers to steering. However, steering motion required by such a steering device tends to be non- intuitive. Additionally, a typical joystick steering application requires an operator to keep a hand on that joystick control at all times. This can cause considerable fatigue, as during a full work shift, there may be little chance for an operator to rest those muscles, or to reposition his hand for muscle relief. Additionally, some extra efforts may be required to operate both a steering joystick and a control joystick at the same time.

[0008] The foregoing creates challenges and constraints for providing a steering and control system for a construction vehicle. It is an object of the present invention to mitigate or obviate at least one of the above mentioned disadvantages.

Summary of Invention

[0009] The present invention is directed to a combined steering and control system for a construction vehicle, such as a motor grader. A broad aspect of the present invention involves a steering device having a plurality of control switches arranged thereon or adjacent thereto. A steering controller provides a steering scale ratio between the steering device and the dirigible wheels of the vehicle, allowing a reduced range of movement of the steering device whilst maintaining full steering movement of the wheels. In this way, an operator may operate the steering device whilst maintaining continued operation of the adjacent control switches.

[0010] In one embodiment, the present invention provides a combined steering and control system for a motor grader. A plurality of control switches are arranged on a steering device.

The control switches communicate with work tool actuators, which control and move the work tool as directed. An operator manipulates control switches to direct the motion and position of a work tool. The steering device has a neutral position. As the steering device is displaced from its neutral position, a steering input signal is generated to indicate a steering wheel angle. A steering controller generates a steering control signal responsive to road speed, to cause steerable road wheels to turn at a requested road wheel angle. The steering device has a limited range of rotation to permit operator to maintain continued access to all control switches within the full range of rotation of the steering device. The ratio of requested road wheel angle to steering wheel angle defines a steering scale ratio. Preferably, the steering scale ratio is not a constant. Varying the steering scale ratio with road speed and road wheel angle permits effective steering control and full required turn of road wheels even though the steering device has a limited range of rotation.

[0011] In one aspect of the invention, there is provided a combined steering and control system of a construction vehicle. The construction vehicle is carried by road wheels, at least one of the road wheels being steerable. The construction vehicle has at least one work tool that is movable relative to the construction vehicle, motion and positioning of the work tool being controlled by work tool actuators. The system includes a steering device that has an elongated hand grip region, an upper face and a lower face, a plurality of control switches positioned adjacent the hand grip region and moving conjointly with the steering device when the steering device is being displaced from its neutral position, a speed sensor for measuring road speed of the vehicle, a road wheel sensor for detecting road wheel angle of the at least one steerable road wheel, and a steering controller communicating with the steering device, the speed sensor and the road wheel sensor. Each of the plurality of control switches is actuatable to generate a control signal for controlling operation of at least one of the work tool actuators. The steering controller generates a steering control signal responsive to a steering input signal corresponding to a steering wheel angle, the steering control signal causing the at least one steerable road wheel to be turned to a requested turned angle. The steering control signal is generated according to a function describing a ratio of the requested angle to the steering wheel angle, which preferably varies with at least one of the road speed and the road wheel angle.

[0012] As one feature of this aspect of the invention, the steering scale ratio, i.e., the ratio of the requested angle to the steering wheel angle, increases with the road wheel angle. As another feature, the steering scale ratio decreases with the road speed. As yet another feature, the steering device is rotatably mounted to the construction vehicle and rotation of the steering device produces the steering input signal.

[0013] In another aspect of the invention, there is provided a combined steering and control system of a construction vehicle. The construction vehicle is carried by road wheels, at least one of said road wheels being steerable by a hydraulic cylinder controlled by a hydraulic valve. The construction vehicle has at least a work tool, which is movable relative to the construction vehicle. Motion and positioning of the work tool is controlled by work tool actuators. The combined steering and control system includes a steering device, displacement of the steering device from a neutral position generating a steering input signal to indicate a steering wheel angle, a plurality of control switches disposed adjacent or on the steering device, a road wheel angle sensor for detecting road wheel angle of the at least one steerable road wheel, and a steering controller in communication with the steering device, the road wheel angle sensor and the hydraulic valve. The steering device having an elongated hand grip region, the plurality of control switches being preferably positioned adjacent the hand grip region and moving conjointly with the steering device when the steering device is being displaced from the neutral position. Each of the plurality of control switches is actuatable to generate a control signal for controlling operation of at least one of the work tool actuators. The steering controller generates a steering control signal responsive to the steering input signal, which actuates the hydraulic valve to control the hydraulic cylinder to steer the at least one steerable road wheel to a requested turned angle. A ratio of the requested turned angle to the steering wheel angle defines a steering scale ratio. The steering controller generates the steering control signal according to a function describing the steering scale ratio.

[0014] In one feature of this aspect of the invention, the steering controller further comprises a steering angle module and a ground speed module, the steering angle module being in communication with the steering device to receive the steering input signal and the ground speed module being in communication with a speed measurement device to receive a signal representing road speed of the vehicle. The steering angle module and the ground speed

module scale the steering input signal according to the steering scale ratio to obtain a value of the requested turned angle.

[0015] In another feature of this aspect of the invention, the steering controller is configured to modify the steering control signal for dead-band compensation prior to applying the steering control signal to the hydraulic valve.

[0016] In yet another feature of this aspect of the invention, the steering controller further comprises an enable switch, the enable switch disconnecting the steering controller from the hydraulic valve upon detection of a pre-selected trigger condition.

[0017] In yet another feature of this aspect of the invention, the system further includes an on/off valve, the on/off valve being controllable by the steering controller to interrupt fluid communication between the hydraulic valve and the hydraulic cylinder upon detection of a preselected trigger condition.

[0018] In other aspects the invention provides various combinations and subsets of the aspects described above.

Brief Description of Drawings

[0019] For the purposes of description, but not of limitation, the foregoing and other aspects of the invention are explained in greater detail with reference to the accompanying drawings, in which:

[0020] Figure 1 is a schematic diagram showing a combined steering and control system implemented in an exemplary configuration;

[0021] Figures 2 A through 2C illustrate in schematic diagrams an exemplary implementation of the steering control portion of the system shown in Figure 1;

[0022] Figure 3A is a front view of a steering device according to an embodiment of the present invention for using in the system shown in Figure 1; [0023] Figure 3B is a back view of the steering device of Figure 3 A; [0024] Figure 4A is a side view of the steering device of Figure 3 A; [0025] Figure 4B is a perspective view of the steering device of Figure 3 A;

[0026] Figure 5 is a front view of another example of a steering device for use in the system shown in Figure 1;

[0027] Figure 6A is a front perspective view of yet another example of a steering device for use in the system shown in Figure 1; [0028] Figure 6B is a rear view of the steering device of Figure 6 A; and

[0029] Figure 7 shows a series of exemplary steering scale ratio curves to illustrate variation of steering scale ratios with road speed and road wheel angle.

Detailed Description of Embodiments

[0030] The description which follows and the embodiments described therein are provided by way of illustration of an example, or examples, of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation, and not limitation, of those principles and of the invention. In the description which follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals.

[0031] The present invention relates to a combined steering and control system for a construction vehicle, such as a motor grader. A broad aspect of the present invention involves a steering device having a plurality of control switches arranged thereon or adjacent thereto. A steering controller provides a steering scale ratio, allowing an operator to operate the steering device while maintaining continued access to and operation of the adjacent control switches within the full range of rotation of the steering device.

[0032] Figure 1 shows schematically a combined steering and control system according to an embodiment of the present invention. The system is generally indicated with reference numeral 100. The system 100 has a steering device 110 for generating a steering input signal according to its displacement α from its neutral position A, a road wheel angle sensor 120 for detecting a road wheel angle β turned from a neutral position B of road wheel or road wheels, a vehicle ECM (electronic control module) 130, which is coupled to a speed sensor (not shown) for measuring road speed v of the construction vehicle, and a steering controller such as an

SCU 140 (steering control unit) to cause steerable road wheel 150 or wheels to turn to a requested angle φ from the neutral position B.

[0033] When road wheels are all in their respective neutral position, the construction vehicle moves essentially along a straight line. The construction vehicle turns, or moves along a curve, when at least one road wheel is displaced from its neutral position at an angle, or road wheel angle. SCU 140 communicates with the steering device 110, the road wheel angle sensor 120, and vehicle ECM 130, for example, through direct electrical connection or data communication. When there is a steering input signal generated by the steering device, e.g. when the steering device is turned, the SCU generates a steering control signal, responsive to steering input signal α, and preferably also to at least one of road wheel angle β and road speed v of the construction vehicle. The steering control signal requests steerable road wheels 150 to be turned at a requested angle φ. Steerable road wheels (typically front road wheels of a motor grader) are road wheels that can be actively turned thereby directing traveling directions of the construction vehicle. As will be described in detail later, suitable hydraulic road wheel actuators or mechanical or electro-mechanical means may be used to turn or position steerable road wheels. In response to the steering control signal, steerable road wheels are turned until the requested road wheel angle φ is reached.

[0034] In general, a steering input signal corresponds to a steering wheel angle α, an angle at which a steering wheel is turned from its neutral position A. This is typically the case when a traditional steering wheel is used and a steering input signal is generated by rotation of the steering wheel about its rotation axis. A linear steering sensor (not shown), for example, may be mounted adjacent the steering wheel or column for detecting the rotation and generating the steering input signal that varies linearly with the steering wheel angle. However, a steering input signal may also be mapped to a notional steering wheel angle from magnitude of the steering input signal, even when such a steering input signal is generated not from rotation but from other types of displacement of the steering device 110 from its neutral position A, such as movement along a predetermined track or displacement of a joystick from its central position. In general, the steering wheel angle α does not equal the requested road wheel angle. They are related by a steering scale ratio. A ratio of requested road wheel angle φ to steering wheel angle α forms the steering scale ratio. Preferably, steering scale ratio is not a constant; instead,

it varies with a number of input parameters, such as road speed v and road wheel angle β. For example, as will be described further, steering scale ratio may generally increase as road wheel angle increases and decrease as the vehicle's road speed increases. Nevertheless, the steering scale ratio may also remain constant with respect to one or more of the input parameters, or all of them.

[0035] In addition to providing an input device for an operator to generate a steering input signal, steering device 110 also has a plurality of control switches 160 positioned thereon (or adjacent thereto) so that an operator may easily access the control switches 160 to manipulate motion and positioning of a work tool of the construction vehicle while steering the construction vehicle. Control signals generated by control switches 160 are communicated to their respective work tool actuators 170, preferably via a work tool controller (not shown). An operator manipulates control switches 160 to generate control commands, in the form of control signals, to actuate the respective work tool actuators 170, thereby controlling the motion and positioning of the work tool. [0036] Figure 2A illustrates in greater detail one arrangement of internal components of the SCU 140. Also shown in Figure 2A are hydraulic and mechanical components interfacing with or controlled by the SCU to illustrate its operation. The SCU 140 includes a steering angle module 142 and a ground speed module 144. The steering angle module is coupled to a hub control unit (HCU) 112, which is coupled to a steering angle sensor and passes the steering wheel angle α to the steering angle module. The HCU 112 generates a resistance force to counter the displacement of the steering device, to simulate the expected experience provided by a steering wheel mechanically linked to steerable road wheels. The vehicle ECM 130 is coupled to a ground speed sensor or some other suitable measurement unit. The connection between the vehicle ECM 130 and speed sensor or speed measurement unit may be a direct electrical connection or through control area network (CAN) protocol, a specialized data communication protocol. The vehicle ECM 130 passes a signal representing ground speed to the ground speed module 144.

[0037] The steering angle module 142 first determines a desired road wheel angle from the steering wheel angle, scaled with the steering scale ratio. The ground speed module 144 is interfaced with the vehicle ECM 130, which provides a signal representing vehicle ground

speed v. The ground speed module 144 takes into account the vehicle ground speed to further scale the desired road wheel angle determined by the steering angle module 142, to obtain the value of the desired road wheel angle φ. Current road wheel angle β is measured with a road wheel angle sensor 120, such as kingpin angle sensor 122, or any other suitable means as will be described later. A signal corresponding to the difference between φ and β is generated and transmitted to a closed-loop control unit 146. The closed-loop control unit 146 generates a road wheel steering control signal corresponding to the difference, which is passed to a hydraulic control and actuation subsystem to turn road wheels, until the difference is reduced to zero, i.e., until the road wheels are turned to the desired road wheel angle. [0038] Controlled turning of road wheels may be carried out hydraulically or mechanically, or through a combination of both. The hydraulic and mechanical arrangement shown in Figure 2A provides one such example, though it will be understood that this is not the only way of achieving controlled turning of road wheels. According to the arrangement shown in Figure 2A, a proportional valve 124, such as a solenoid operated spool valve, is directed by the steering control signal and regulates fluid flow into or out of hydraulic cylinders 126 for positioning cylinder pistons. An Ackerman mechanism 128 is linked to the cylinder pistons and driven by the hydraulic cylinders 126 to position the left and right road wheels at desired angles. Although other mechanical linkages may be used between the hydraulic cylinders and the road wheels, an Ackerman mechanism is preferred as it allows the left and right road wheels to trace out circles of different radii when the vehicle moves along a curve.

[0039] As is known to those skilled in the art, when a control signal is first applied to control valves or when direction of a control signal is first reversed, control valves, hydraulic cylinders, road wheels, or some or all of them, may experience a delay following the application or reverse of direction of control signal. The zone of control signal in which this happens is often referred to as dead-band zone of the control signal. To compensate for dead- band, one may calibrate the control signal taking into account response in the expected dead- band zone and increase the control signal correspondingly, so that the actual response of the road wheels to control signals may approach the theoretical behavior. Preferably, the SCU 140 includes a dead-band compensation unit 148 to modify the steering control signal to

compensate for dead-band, before the steering control signal is applied to the proportional valve 124.

[0040] An enable switch 152 is placed at the interface between SCU 140 and the hydraulic components. The enable switch 152 is turned off to prevent the steering control signal from being passed to the hydraulic components, upon detection of certain pre-selected trigger conditions. One of such pre-selected trigger conditions may be a mismatch between steering wheel angle and expected road wheel angle, which may result from the steering device being left in a position not matched with the position of the road wheels while the construction vehicle is not energized. During start-up, this mismatch may cause unintended and erratic movement of road wheels. To prevent any such unforeseen steering motion, the enable switch 152 would sever the communication between the SCU and hydraulic proportional valve, upon detection of such a mismatch. A supervisory enable logic unit 154 is provided for controlling on and off of the enable switch 152 upon detection of such a mismatch, or other conditions preselected for triggering the enable switch. Some other such pre-selected trigger conditions may include the detection of a road wheel angle sensor failure, a steering wheel angle sensor failure, or other similar failures in the steering system, to name a few examples. When the trigger condition ceases to exist, for example, when the steering device is returned to its expected displacement range corresponding to the road wheel angle, the supervisory enable logic unit 154 closes the enable switch 152, allowing the resumed control of road wheels by the steering device.

[0041] Figure 2B is another block diagram illustrating the steering control portion of the system 100, with additional hydraulic and mechanical components also shown to illustrate their interaction and connection with the steering control portion of the system. Conveniently, SCU 140 is not directly connected to HCU 112 or vehicle ECM 130. Instead, a CAN bus 114 is provided. SCU 140, HCU 112, and vehicle ECM 130 are all connected to CAN bus 114, thereby allowing data communication between and among these units. A road wheel angle sensor 120, such as a kingpin angle sensor 122, is disposed adjacent one of the kingpins 132 to sense the road wheel angle. Sensor signal is communicated to SCU 140 electrically, through a direct electric connection as indicated by the dashed lines or may be transmitted to SCU through CAN bus 114, among other suitable connection arrangements. As noted earlier, in

addition to using a kingpin angle sensor 122 to detect road wheel angle, road wheel angle may be detected using any other suitable means. For example, one may take advantage of mechanical and/or hydraulic linkage between hydraulic cylinder 126 and the road wheels to detect/determine road wheel angle by detecting piston position of hydraulic cylinders. A cylinder position sensor 134 may be used to detect road wheel angle. It will be apparent to one skilled in the art that detecting road wheel angle is not limited to these two examples provided herein and other suitable means may be employed.

[0042] Figure 2C illustrates in a block diagram another implementation of the steering control portion of the control system 100. As in Figure 2B, electric connections and data communications are indicated with dashed or dotted lines and hydraulic communications are indicated with solid lines. This implementation differs from that shown in Figures 1 and Figures 2A and 2B in that redundancy is built into the system, though it will be appreciated that redundancy is not necessary for the operation of the control system 100, and that the implementation illustrated in Figure 2C is but an example of providing redundancy. As illustrated in Figure 2C, in addition to primary components, which include a primary SCU 140, a primary proportional valve 124, and a primary hydraulic power unit 156, there are also provided on standby secondary components, which include a secondary SCU 140', a secondary proportional valve 122', and a secondary hydraulic power unit 156'. During normal operation, the secondary components are on standby, not activated. When a failure is detected in the primary control portion, e.g., in any one of the primary components or the communication among and between any of the primary components, the secondary components are activated to provide the required steering function, thus mitigating any possible adverse consequences caused by the failure in any of the primary components. The activation of the secondary components may be controlled by a separate central processor (not shown) or may be built into the secondary SCU 140'.

[0043] Further, in addition to an enable switch 152, a hydraulic ON/OFF valve 158 may be disposed between the proportional valve 124 and the hydraulic cylinder 126. The hydraulic ON/OFF valve 158 is controlled by the SCU 140, to cut off further hydraulic fluid communication, i.e., hydraulic fluid flow, between the proportional valve and the hydraulic cylinder 126, upon detection of any pre-selected trigger conditions. Similar to the enable

switch 152, the hydraulic ON/OFF valve 158 allows the system to quickly disable the proportional valves upon detection of a pre-selected trigger condition. Similarly, a secondary hydraulic ON/OFF valve 158' can be disposed between the secondary proportional valve 122' and the secondary hydraulic cylinder 126, to provide the desired redundancy. [0044] Similar redundancy may also be provided in road wheel angle sensors, for example, by placing a road wheel angle sensor adjacent each of the right and left kingpins, or using the cylinder position sensor 134 as a secondary road wheel angle sensor. Similarly, a steering device may have multiple steering wheel sensors 116 to provide the desirable redundancy. Although three steering wheel angle sensors 116, 116', 116" are shown in Figure 2C, it is understood that two may be sufficient, or more could be desirable.

[0045] Reference is now made to Figures 3A and 3B. A fan-shaped steering yoke 200, as an exemplary steering device 110, is illustrated. The fan-shaped steering yoke 200 has two elongated hand grip regions 202 disposed at the right and left sides of the steering yoke. These hand grip regions 202 are suitably sized so that an operator can comfortably grip the hand grip regions to operate the fan-shaped steering yoke 200. These hand grip regions may be straight, or may have a gentle curve, or take the form of an arc. When an operator grips the hand grip region in a normal operation state, one end of a hand grip region is closer to the operator's thumb and is indicated as thumb end 204. The fan-shaped steering yoke 200 has an upper face 206, directed toward the operator and a lower face 208, directed away from the operator, when the steering device is in its installed position. The upper face and switch arrangement may be better seen in Figure 3A while the lower face is better seen in Figure 3B.

[0046] The fan-shaped steering yoke 200 is configured for rotationally mounting to the vehicle. Figure 4A shows the fan-shaped steering yoke 200 mounted to a rotation shaft 210. The steering yoke has a neutral position A. At its neutral position A, the steering yoke causes all road wheels to be at their respective neutral position. An angular displacement from the steering yoke's neutral position A defines a steering wheel angle α. At its neutral position A, α = 0. A sensor 116 (not shown in Figure 4A; but see Figure 2C) may be deployed adjacent the steering yoke or the rotation shaft 210 to detect the steering wheel angle α. When the yoke is turned, a signal from the sensor 116, namely a steering input signal, is generated and communicated to the SCU 140. Of course, although Figure 4A shows a wheel-like steering

device mounted on a rotation shaft is, it is understood that any moveable steering device may be developed, using its displacement from a neutral position to indicate a desirable steering wheel angle, whether such displacement is a linear, curvilinear or angular displacement, or any combination thereof. [0047] A number of control switches, such as thumb wheels, push buttons, paddle switches, two-way buttons, are arranged on or adjacent steering device 110. Conveniently, they are positioned on the steering device 110 so that as the steering device 110 is being turned about its rotation axis, these control switches move conjointly with the steering device and therefore allow an operator to maintain contact with and operation of these control switches without having to move his hands away from the hand grip regions. Figures 3 A and 3B illustrate an arrangement of control switches on the fan-shaped steering yoke 200.

[0048] Conveniently, control switches can be arranged near a thumb area 212, namely in a region adjacent the thumb end 204 or on upper face 206 extending from the thumb end 204. For example, a push button 214, a two-way button 216 and a first thumb wheel 218 may be arranged in the thumb area 212. Where two hand grip regions are provided, two sets of push buttons, two-way buttons and thumb wheels may be provided. In one arrangement, adjacent a hand grip region 202, there is disposed a paddle switch 220. hi addition to these control switches placed on upper face 206 and at locations adjacent hand grip regions, additional control switches may be placed in an index finger area 222, namely, in a region on the lower face 208 extending from the thumb end 204, where an operator can easily access these additional control switches using an index finger. For example, two additional thumb wheels 224 may be disposed in the index finger area 222. Conveniently, these additional thumb wheels 224 are oriented as horizontal thumb wheels, i.e., rotating the thumb wheels, i.e., moving edges of these additional thumb wheels in a direction generally transverse to an elongated hand grip region generates a control signal.

[0049] As will be appreciated, a work tool of a construction vehicle may require continued control. For example, an operator may need to adjust continuously blade tilt while steering the vehicle. These continuous control functions may be conveniently provided by proportional switches. As is known, thumbwheels, paddle switches and two-way buttons are types of proportional switches, which produce electric signals in proportion to amount of displacement

from a neutral point or duration of continued activation. A slider switch is another example of a proportional switch. A thumb wheel may be biased toward its neutral position. Conveniently, the first thumb wheel 218 is oriented as a vertical thumb wheel, i.e., it generates a control signal when it is rotated such that its edge moves in a direction generally along the length of a hand grip region. Maintaining the thumb wheel at a displaced position produces an electrical signal proportional to the displacement. Similarly, a two-way button generates a control signal when it is displaced in any one of two distinct directions, such as an X-direction and a Y- direction, generally transverse to the X-direction. The travel of the two-way button in either X- direction or Y-direction from its neutral position provides a control signal, proportional to the travel. The travel may be either positive or negative. Two-way button 216 may be oriented such that it is activated, i.e., generates an X-travel control signal, when it is pushed left or right, i.e., laterally in a direction generally transverse to the elongated hand grip region 202, and generates a Y-travel control signal when it is pushed up or down, i.e., generally along the elongated hand grip region 202. Placing these control switches adjacent the thumb end 204 allows an operator to maintain continued access, therefore continued manipulation of the control switches, whilst also maintaining continued steering control.

[0050] The following table provides an example of one possible configuration of these control switches, i.e., assignment of control functions to these control switches:

[0051] It will be appreciated that control switches 160 do not have to be positioned on a steering device 110. It is sufficient that the control switches 160 are placed adjacent hand grip regions so that these switches can be easily accessed. For example, some or all of these control switches may be mounted on a movable support that moves conjointly with the steering device.

These control switches, carried by the movable support, then will move with the steering device when the steering device is being displaced, e.g., rotated about its rotation axis. Fixedly mounted control switches, on the other hand, may put a too restrictive limitation on acceptable maximum range of displacement of the steering device, though may still be acceptable for certain applications of the present invention, where the physical configuration of the operator's cab permits or demands such placement.

[0052] Figure 5 illustrates a steering wheel 500, another example of a steering device 110. This example illustrates an alternative configuration of control switches and geometry of steering device. Steering wheel 500 has a general shape of a conventional steering wheel, with the addition of two control panel areas 502 placed on steering wheel ring 504 and a central panel region 506, joined to the steering wheel ring 504 at support regions 508. Each of the arcs 510 of the steering wheel ring 504 between a control panel area 502 and a support region 508 forms a hand grip region. Several control switches 160 are disposed in each of the control panel areas 502. Additional control switches 160, such as "up" and "down" buttons 512, may be disposed in the central panel region 506. In addition, display control 514 can be disposed in the central panel region 506. Display control 514 includes a control keypad or other control buttons to specify and customize how information relating to status of work tool(s) and the construction vehicle is displayed in a display panel (not shown).

[0053] Figures 6A and 6B illustrate in front perspective view and rear view, respectively, another steering yoke 600, yet another example of a steering device 110. Steering yoke 600 has a central hole 602 for mounting to a steering shaft 210 (not shown in Figures 6A, 6B). The steering yoke has two elongated hand grip regions, namely a left arm 604 and a right arm 606 joined at bottom by a lower connection portion, forming a general open profile. Control switches are arranged adjacent terminal ends of the left and right arms. According to one arrangement of control switches, a left two-way button 216 and a left thumb wheel 218 are disposed in a region on the upper surface of the left thumb end 608, a corresponding right two- way button 216 and a right thumb wheel 218 arranged on the upper surface of the right thumb end 610. On the lower surface and at locations adjacent hand grip regions, namely left thumb end 608 and right thumb end 610, two additional left thumb wheels 218 and two left push buttons 214 are arranged in a region on the lower face extending from the left thumb end 608.

Additional corresponding right thumb wheels 218 and push buttons 214 are arranged on the lower surface extending from the right thumb end 610 of the right arm 606. Conveniently, these additional thumb wheels arranged on the lower surface are horizontal thumb wheels and the thumb wheels arranged on the upper surface are vertical thumb wheels, for easy control. Assignments of control functions to these control switches may be similarly configured as that for the yoke 200 shown in Figures 3A and 3B.

[0054] Steering device 110 is only allowed a limited displacement range. This allows an operator to steer a construction vehicle using the steering device and manipulate various control switches placed on or adjacent the steering device at the same time within the full range of the steering device's displacement. In general, the range of angular displacement should not be too large. For example, allowing maximum rotation angle to exceed 180° in one direction from neutral may cause considerable operation difficulty because an operator's hands may be forced into uncomfortable positions at or near maximum rotation angles. On the other hand, if the maximum rotation angle is too small (e.g., less than 20°), a small turn of a steering device 110 may necessitate a significant change in road wheel angle. It is found that a maximum rotation angle of 50° from neutral in both left and right directions generally produces satisfactory results, though a variation of ±10°, i.e., a maximum rotation angle in the range of from 40° to 60° may still provide acceptable results. Preferably, maximum rotation angle should be no more than 90°, to minimize operation difficulty.

[0055] Steering device 110, used in combination with other components of the system 100, allows effective steering control even though range of rotation (or displacement) of steering device is limited. To accomplish this, SCU 140 generates a steering scale ratio according to a function or profile that depends on a number of input parameters. Generally, at relatively higher road speeds (for example, at 50 km/hour), it is rarely necessary to turn road wheel angles at large road wheel angles (such as more than 45°) and it also can be unsafe to do so. Large turning of steerable road wheels is often required (and possible) only at small (for example, 10 km/hour) or near zero road speed. Accordingly, the function or profile is preferably selected so that a variable steering scale ratio decreases as the vehicle's road speed increases. The steering scale ratios are smaller at larger vehicle road speeds.

[0056] In addition, at any given speed, it is generally desirable that response of steerable road wheel to displacement of steering device varies with road wheel angle, i.e., steering scale ratio varies with road wheel angle. More specifically, it is desirable to select a steering scale ratio that increases with road wheel angle. At small road wheel angles (e.g., when a steerable road wheel is turned no more than 2° or 3° from its neutral position), a small steering scale ratio is selected, hi other words, a given change in steering wheel angle produces a corresponding change in road wheel angle that is only a small fraction (e.g., less than 10%) thereof. This allows accurate steering of road wheels when the vehicle is generally moving along a straight line. This also allows orienting road wheels to their respective neutral position more easily. At large road wheel angles, a large steering scale ratio is selected, i.e., a given change in steering wheel angle may cause a steerable road wheel to displace the same amount or more. This allows fast turning of steerable road wheels when steering wheel is near or approaching its maximum rotation angle, thus achieving the designed maximum road wheel angle even though a steering wheel may have only a limited range of rotation. Nevertheless, while a variable steering scale ratio may be generally desirable, there may be situations where a constant steering scale ratio is more appropriate.

[0057] Figure 7 illustrates an exemplary profile selected for steering scale ratios according to one design. A series of steering scale ratio curves, each for a constant speed v, are shown in Figure 7. These curves illustrate the variation of steering scale ratio with road speed v and road wheel angle β. The top curve 710 of the series represents a steering scale ratio curve at road speed v = 0. The bottom curve 720 of the series represents a steering scale ratio curve at "roading" speed, or normal speed (for example, 50 km/hour) of a construction vehicle traveling on highways from one work site to another. Intermediate curves 730 between the top curve 710 and the bottom curve 720 represent steering scale ratio curves at intermediate speeds between 0 and the roading speed. Displacement of steering scale ratio curves represents decrease of steering scale ratios at a given angle as road speed increases.

[0058] Each curve represents variation of response of steerable road wheels to rotation or displacement of steering device at a given speed. These curves all show increase as steering wheel angle, i.e., road wheel angle increases. Although not necessary, these curves are not linear. Slopes of these steering ratio curves all increase at large steering wheel angles, thus

providing an even faster turning of steerable road wheels at larger steering wheel angles compared to that possible with linearly increasing steering scale ratios. Of course, the steering scale ratio may be selected so that the ratio does not vary with road wheel angle (or steering wheel angle), in which case the series of scale ratio curves becomes a series of straight lines (a special type of "curve"), the slope of each straight line being determined by road speed. It is also contemplated that the steering scale ratio does not vary with road speed or any other parameters, and is thus a pre-selected constant.

[0059] Various embodiments of the invention have now been described in detail. Those skilled in the art will appreciate that numerous modifications, adaptations and variations may be made to the embodiments without departing from the scope of the invention. Since changes in and or additions to the above-described best mode may be made without departing from the nature, spirit or scope of the invention, the invention is not to be limited to those details but only by the appended claims.