Hydraulic Pump Control Device for Excavator Engine Startability
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Solution Overview
Problem
Construction machines equipped with negative control type hydraulic pumps face challenges in maintaining engine startability, especially in high-altitude or low-temperature environments where the viscosity of hydraulic fluid increases, leading to higher starting torque and reduced engine startability due to the swash plate's maximum capacity inclination angle.
Innovation Solution
A hydraulic pump control device that includes an accumulator and solenoid valve to compensate for negative signal pressure by supplying signal pressure from the accumulator to the regulator, maintaining the swash plate's inclination angle at minimum capacity during engine startup, thereby improving startability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the swash plate is positioned at maximum capacity inclination angle, then the hydraulic pump can provide high flow rate and starting torque, but the engine startability is reduced in high-altitude or low-temperature environments due to increased hydraulic fluid viscosity
Solution Approach 1:
The control device performs preliminary action by detecting engine startup conditions (via start signal or low rotational speed detection) and proactively adjusting the swash plate inclination angle to minimum capacity before the engine actually starts. This preliminary adjustment ensures that when the engine starts, the hydraulic pump is not imposing excessive resistance torque, thereby improving startability in cold or high-altitude environments while still maintaining the ability to provide high starting torque when needed.
2Reliability
If the swash plate inclination angle is reduced to minimum capacity during engine startup, then engine startability is improved, but the hydraulic pump discharge flow rate is reduced
Solution Approach 1:
The control device implements dynamic adjustment of the swash plate inclination angle based on real-time operating conditions. During engine startup, the angle is dynamically reduced to minimum capacity to improve startability. Once the engine reaches a predetermined rotational speed or the start signal is cleared, the angle is dynamically increased to provide the required discharge flow rate. This dynamic control resolves the contradiction by adapting the pump capacity to the actual operational phase.
Solution Approach 2:
The control device changes the physical parameter of swash plate inclination angle based on detected operating conditions. By transitioning the angle parameter between minimum and maximum capacity positions according to engine startup status, the system optimizes both startability and hydraulic output performance without permanent compromise.
3Device complexity
If the negative control system uses only negative signal pressure from the orifice, then the control structure is simple, but the swash plate cannot be maintained at minimum capacity when negative signal pressure is insufficient during engine startup
Solution Approach 1:
The control device merges two pressure signal sources: the traditional negative signal pressure from the orifice and a new reference pressure signal from a reference orifice. These two pressure sources are combined in a pressure balancing mechanism to jointly control the swash plate position. This merging provides sufficient control pressure during engine startup when single-source negative pressure is insufficient, while maintaining relatively simple control structure through the use of additional orifice and pressure balancing components.
Solution Approach 2:
The control device introduces a reference orifice as an intermediary element that generates a stable reference pressure signal. This intermediary pressure source mediates the control of swash plate position during critical startup conditions, ensuring reliable minimum capacity positioning even when the primary negative signal pressure from the main orifice is insufficient due to low flow conditions.
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
The solution ensures improved engine startability by maintaining the swash plate's inclination angle at minimum capacity, even with low negative signal pressure, facilitating rapid engine revving and operator convenience in challenging environments.
Implementation Method 1
an accumulator (16) storing a signal pressure of pump control
Implementation Method 2
an orifice (4) installed on a downstream side of the bypass path (3) to generate negative signal pressure
Implementation Method 3
a solenoid valve (17) supplying or intercepting signal pressure from the accumulator (16) when the solenoid valve (17) is shifted in accordance with applying of a solenoid control signal
Data Source
AI summary
A negative control type hydraulic pump control device mounted on a construction machine such as an excavator is provided. The hydraulic pump control device includes an accumulator storing a control signal pressure, a solenoid valve supplying any one of the signal pressure from the accumulator and a negative signal pressure to the regulator when a solenoid valve is shifted in accordance with applying of the control signal, and an operation lever locking unit turning ON/OFF the control signal applied to the solenoid valve in accordance with a driver's operation, wherein an inclination angle of a swash plate of a hydraulic pump is maintained with a minimum capacity by compensating for the negative signal pressure caused by hydraulic fluid supplied from the accumulator through shifting of the solenoid valve when an engine starts.