Hybrid Vehicle Line Pressure Control During Pump Transition
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Solution Overview
Problem
In hybrid vehicles, the transition of hydraulic pressure sources from an electrically driven oil pump to a mechanical oil pump leads to excessive line pressure, reducing fuel economy and causing judder due to interference with clutch pressure feedback control during slip control.
Innovation Solution
A line pressure control apparatus and method that adjusts the line pressure command to reduce the indicated pressure to a required level when transitioning from the electrically driven oil pump to the mechanical oil pump, ensuring compatibility with fuel economy improvements and judder prevention by using a mechanical oil pump and an electrically driven oil pump in parallel, with a line pressure controller managing the hydraulic pressure sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the line pressure command is held at a high value during the transition from electrically driven oil pump to mechanical oil pump, then the hydraulic pressure response characteristic is secured, but the actual line pressure becomes excessively high which reduces fuel economy performance
Solution Approach 1:
The patent applies dynamics by making the line pressure command dynamically adjustable based on the operating region. The controller switches between different pressure command strategies: in the first region (electrically driven pump only), a high initial pressure command is used to ensure response characteristics; in the second region (transition period with both pumps), the pressure command is reduced to avoid excessive pressure and improve fuel economy; in the third region (mechanical pump only), normal pressure control is restored. This dynamic adjustment resolves the contradiction between maintaining response characteristics and improving fuel economy.
Solution Approach 2:
The patent changes the parameter of line pressure command value based on the operating region. By detecting which region the system is in (first region with electrically driven pump, second region during transition, or third region with mechanical pump), the controller adjusts the pressure command parameter accordingly. This parameter change allows the system to optimize between response characteristics and fuel economy at different stages of the transition process.
2Use of energy by moving object
If the line pressure command is reduced to the necessary pressure during the transition region to improve fuel economy, then fuel economy performance is improved, but the reduction of line pressure command and feedback control of clutch pressure interfere with each other causing variation of actual clutch pressure and judder
Solution Approach 1:
The patent applies preliminary action by detecting the operating region in advance and preemptively adjusting the line pressure command before the actual pressure transition occurs. When the controller detects entry into the second region (transition period), it proactively reduces the pressure command to prevent excessive pressure buildup, thereby improving fuel economy before the problem arises. This preliminary adjustment prevents the need for aggressive pressure reduction that would cause interference with feedback control.
Solution Approach 2:
The patent uses the region detection mechanism as an intermediary to mediate between the conflicting requirements of fuel economy and clutch pressure stability. By introducing the region detection as an intermediate control layer, the system can make smooth, gradual pressure adjustments during the transition rather than abrupt changes. This intermediary control prevents direct interference between pressure reduction and feedback control, eliminating judder while still achieving fuel economy improvements.
3Loss of energy
If the electrically operated motor performs constant torque control, then the motor operates efficiently, but the revolution speed is not raised even when hydraulic pressure needs to increase, preventing sufficient discharge pressure
Solution Approach 1:
The patent applies dynamics by switching the motor control strategy based on the operating region. In the first region where only the electrically driven pump operates, the motor performs constant torque control to maintain efficiency. However, when transitioning to the second region where the mechanical pump joins operation, the system naturally allows the motor speed to increase as the mechanical pump provides additional discharge pressure capability. This dynamic control strategy resolves the contradiction by matching motor control mode to the actual hydraulic system configuration.
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 achieves improved fuel economy and prevents judder by optimizing line pressure control, ensuring the hydraulic pressure sources are managed effectively during transitions, thereby enhancing the performance of hybrid vehicles.
Implementation Method 1
a mechanical oil pump and an electrically driven oil pump which are respectively, parallelized to each other on a hydraulic pressure circuit
Data Source
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AI summary
In line pressure control apparatus and method for a vehicle, a line pressure controller outputs a line pressure command to reduce an indicated pressure toward a required indicated pressure by which a required pressure can be secured and which is lower than an initial stage indicated pressure from the initial stage indicated pressure preset to be higher than the required pressure, while a state of each of an electrically driven oil pump (sub=O/P) and a mechanical oil pump (M-O/P) enters a first region (a) and outputs the line pressure command to hold the indicated pressure at a time point at which the first region is ended, while the state enters a second region (b), when a hydraulic pressure source is transitioned from the electrically driven oil pump to the mechanical oil pump.