Hydrostatic Road Machine Start Control to Prevent Hill Rollback
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Solution Overview
Problem
Existing road machines with hydrostatic transmission systems face challenges in preventing backward rolling during hill starts due to the lack of precise control over the timing of brake release and hydraulic pump discharge quantity increase.
Innovation Solution
A road machine with a travel switch, hydrostatic transmission, pump regulator, and controller that increases the discharge quantity of the hydraulic pump and adjusts the pump command current to predetermined values to ensure forward motion without backward rolling, by synchronizing the brake release with the increase in hydraulic pump discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the discharge quantity of the hydraulic pump is increased to prevent backward rolling, then the forward rotation torque is improved, but the machine may experience sudden movement or instability
Solution Approach 1:
The controller increases the pump command current to a predetermined value before the travel switch is turned ON, so that the discharge quantity of the hydraulic pump is increased in advance. This preliminary action ensures that sufficient forward rotation torque is available when movement begins, preventing backward rolling while maintaining stability through controlled gradual increase rather than sudden full power application.
Solution Approach 2:
The system dynamically adjusts the pump command current based on the state of the travel switch. The controller increases the current to a predetermined value when the switch is OFF, and when the switch is turned ON, it controls the gradual increase of discharge quantity. This dynamic adjustment optimizes the balance between generating sufficient torque and maintaining stable, controlled movement.
2Power
If the pump command current is increased to maximum value immediately, then the forward rotation torque is maximized, but the machine may move too suddenly causing instability
Solution Approach 1:
The controller increases the pump command current to a predetermined value (but not maximum) before the travel switch is turned ON. This preliminary action prepares the hydraulic system with sufficient power while avoiding immediate maximum power application that would cause sudden movement. The gradual increase approach ensures smooth starting operation.
Solution Approach 2:
The system changes the pump command current parameter from a maximum value approach to a predetermined value approach. By controlling the current to a specific predetermined value rather than maximum, and then gradually increasing discharge quantity when the travel switch is activated, the system achieves both sufficient power and smooth, controlled operation.
3Reliability
If the discharge quantity control is delayed until the travel switch is turned ON, then the control system is simpler, but backward rolling cannot be prevented at hill starts
Solution Approach 1:
The controller increases the pump command current to a predetermined value in advance, before the travel switch is turned ON. This preliminary action ensures that the hydraulic pump is already prepared with the necessary discharge quantity to generate sufficient torque when movement begins, reliably preventing backward rolling on hills. The control logic remains relatively simple by using a single predetermined value threshold.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively prevents backward rolling during hill starts by ensuring a forward rotation torque exceeds the reverse rotation torque, allowing smooth and reliable movement of the road machine up hills without damaging brakes or degrading the work surface.
Implementation Method 1
a hydrostatic transmission including a traveling hydraulic pump and a traveling hydraulic motor
Implementation Method 2
the controller is configured to increase the current value of the pump command current to a predetermined value smaller than a maximum current value in response to the travel switch being turned ON
Data Source
AI summary
A road machine includes a travel switch to cause the road machine to start traveling, a hydrostatic transmission including a traveling hydraulic pump and a traveling hydraulic motor, a pump regulator to control the discharge quantity of the traveling hydraulic pump; and a controller to control the pump regulator using a pump command current. The pump regulator increases the discharge quantity of the traveling hydraulic pump as the pump command current increases, and the controller increases the pump command current to a predetermined value smaller than a maximum current value in response to the travel switch being turned ON. Alternatively, the pump regulator increases the discharge quantity of the traveling hydraulic pump as the pump command current decreases, and the controller decreases the pump command current to a predetermined value greater than a minimum current value in response to the travel switch being turned ON.