Work vehicles, such as a motor grader, can be used in construction and maintenance for creating a flat surface at various angles, slopes, and elevations. When paving a road for instance, a motor grader can be used to prepare a base foundation to create a wide flat surface for to support a layer of asphalt. A motor grader can include two or more axles, with an engine and cab disposed above the axles at the rear end of the vehicle and another axle disposed at the front end of the vehicle. A blade, also called a moldboard, is attached to the vehicle between the front axle and rear axle.
Motor graders include a drawbar assembly attached near the nose of the grader which is pulled by the grader as it moves forward. The drawbar assembly rotatably supports a circle drive member at a free end of the drawbar assembly and the circle drive member supports a work implement such as the blade, also known as a mold board. The angle of the work implement beneath the drawbar assembly can be adjusted by the rotation of the circle drive member relative to the drawbar assembly.
In addition, to the blade being rotated about a rotational fixed axis, the blade is also adjustable to a selected angle with respect to the circle drive member. This angle is known as blade slope. The elevation of the blade is also adjustable.
To properly grade a surface, the motor grader includes a plurality of sensors which measure the orientation of the vehicle with respect to gravity and the location of the blade with respect to the vehicle. A rotation sensor located at the circle drive member provides a rotational angle of the blade with respect to a longitudinal axis defined by a length of the vehicle. A blade slope sensor provides a slope angle of the blade with respect to a lateral axis which is generally aligned with a vehicle lateral axis, such as defined by the vehicle axles. A mainfall sensor provides an angle of travel of the vehicle with respect to gravity.
Machine control systems, which include 2 dimensional (2D) and 3 dimensional (3D) machine control systems, are located at the surface being graded to provide grade information to the motor grader. A vehicle grade control system receives signals from the machine control system to enable the motor grader to grade the surface. The motor grader includes a grade control system operatively coupled to each of the sensors, so that the surface being graded can be graded to the desired slope, angle, and elevation. The desired grade of the surface is planned ahead of or during a grading operation.
Machine control systems can provide slope, angle, and elevation signals to the vehicle grade control system to enable the motor grader or an operator to adjust the slope, angle, and elevation of the blade. The vehicle grade control system can be configured to automatically control the slope, angle, and elevation of the blade to grade the surface based on desired slopes, angles, and elevations as is known by those skilled in the art. In these automatic systems, adjustments to the position of the blade with respect to the vehicle are made constantly to the blade in order to achieve the slope, angle and/or elevation targets. Many vehicle grade control systems offer an included or optional display that indicates to the operator how well the vehicle grade control system is keeping up to the target slope, angle, and/or elevation. These displays are called “light bars” in the trade. The operator uses the feedback from the light bars to adjust vehicle speed if desired. The operator, however, may not be sufficiently skilled, for instance due to lack of experience, in making adjustments to vehicle speed. Errors in grading the surface to the desired grade can result.
Therefore, a need exists for a controlling the vehicle speed based on the desired surface grade.