Hydraulic Pump Torque Control for Hybrid Construction Machinery
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Solution Overview
Problem
Hybrid construction machines face inefficiencies in fuel consumption and engine performance due to insufficient motor generator assist during low-load operations, leading to potential engine stall and increased emissions, while downsizing the motor generator to reduce size and power consumption is hindered by the need for higher torque assist.
Innovation Solution
A control device for hybrid construction machines that includes actual rotation speed detection, target rotation speed setup, load detection, assist output computation, and pump displacement adjustment to reduce absorption torque upper limits when rotation speed deviation exceeds a certain threshold, thereby minimizing transient assist output and preventing engine stall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the motor generator is downsized to reduce electric power consumption and size, then the fuel efficiency and compactness are improved, but the torque assist capability is insufficient leading to engine stall
Solution Approach 1:
The patent applies dynamics by making the pump absorption torque upper limit changeable based on operating conditions. The control device dynamically adjusts the absorption torque upper limit according to the difference between actual and target rotation speeds, allowing the system to adapt to varying load conditions without requiring a large motor generator. This dynamic adjustment enables a compact motor generator to provide sufficient torque assist when needed while maintaining fuel efficiency during normal operation.
Solution Approach 2:
The patent changes the parameter of absorption torque upper limit based on rotation speed deviation. When the difference between actual and target rotation speeds exceeds a threshold, the absorption torque upper limit is reduced. This parameter change allows the system to prevent engine stall by controlling pump torque during transient conditions, enabling the use of a smaller motor generator with lower electric power consumption.
2Productivity
If the absorption torque upper limit is increased to improve response to operator input, then the productivity is improved, but the engine rotation speed drops causing lug-down and increased fuel consumption
Solution Approach 1:
The patent implements feedback control by continuously monitoring the difference between actual and target rotation speeds. When this difference exceeds a predetermined value, the control device reduces the absorption torque upper limit to prevent excessive engine load and fuel consumption. This feedback mechanism ensures that the system responds appropriately to operating conditions, maintaining productivity while preventing energy loss through lug-down events.
Solution Approach 2:
The patent makes the absorption torque upper limit dynamic rather than fixed. By adjusting the absorption torque upper limit based on real-time rotation speed conditions, the system optimizes the balance between productivity and fuel efficiency. The dynamic adjustment allows high torque absorption when the engine can handle the load, and reduces torque absorption when rotation speed deviation indicates potential lug-down, thereby reducing fuel consumption.
3Reliability
If the motor generator provides high transient assist output to prevent engine stall, then the reliability is improved, but the electric power consumption increases and the motor generator size must be increased
Solution Approach 1:
The patent changes the absorption torque upper limit parameter based on rotation speed deviation to prevent engine stall without requiring high transient assist output from the motor generator. By reducing the absorption torque upper limit when the difference between actual and target rotation speeds exceeds a threshold, the system prevents situations that would require large motor generator intervention, thereby reducing electric power consumption and allowing for a compact motor generator design.
Solution Approach 2:
The patent takes preliminary action by controlling the pump absorption torque before engine stall occurs. By monitoring rotation speed deviation and preemptively reducing the absorption torque upper limit when necessary, the system prevents engine stall conditions from developing, eliminating the need for high transient assist output from the motor generator and reducing overall electric power consumption.
Data Source
AI summary
Target rotation speed setup section for setting a target engine rotation speed; load detection for detecting a hydraulic pump load; an assist output computation section for calculating an assist output to be generated by a motor generator in accordance with a rotation speed deviation ΔN, which is the difference between an actual and target rotation speed, or in accordance with the hydraulic pump load; an absorption torque upper limit computation section for calculating an absorption torque upper limit value of the hydraulic pump; and an operation signal generation section for generating the operation signal to be output to a pump displacement adjustment device. When the rotation speed deviation ΔN is equal to or more than a setting NC determined in accordance with the assist output value, the absorption torque upper limit computation section reduces the absorption torque upper limit value of the hydraulic pump from the calculated value.