Hybrid Clutch Hydraulic Control for Low-Battery Engine Start

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Solution Overview

Problem

Hybrid vehicles face issues with engine startability deterioration and clutch controllability due to torque differences between the engine and motor, especially when the battery is low, leading to potential engine stalling and clutch engagement failures.

Innovation Solution

A method of controlling a hybrid vehicle using a friction engagement element operated by hydraulic pressure from a mechanical oil pump, where the engine is started by a starter, and the clutch is engaged after motor activation, with initial hydraulic pressure control from an electric oil pump followed by a mechanical pump to ensure timely and precise engagement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the engine is started by the starter and the clutch is engaged immediately, then the engine power can be transmitted to the wheels, but the engine startability deteriorates due to torque difference between engine and motor

Engineering Contradiction:

Improveengine startabilityVSAvoidengine operation stability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The motor is activated in advance before clutch engagement to rotate the motor shaft and build kinetic energy. This preliminary action ensures that when the clutch engages, the motor can immediately absorb engine torque without causing engine stall, thus improving engine startability while maintaining operation stability

Inventive Principle:

Principle #10Preliminary action

2Speed

If the motor is activated before clutch engagement, then the engine startability improves, but the battery power consumption increases

Engineering Contradiction:

Improveengine startabilityVSAvoidbattery power consumption

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

Instead of fully activating the motor before clutch engagement, the invention applies partial action by only rotating the motor shaft to a sufficient speed without generating full motor torque. This reduces battery power consumption while still achieving the goal of improving engine startability through the flywheel effect

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If the mechanical oil pump is used to supply hydraulic pressure to the clutch, then the clutch controllability improves, but the clutch engagement timing is delayed because the motor must be activated first

Engineering Contradiction:

Improveclutch controllabilityVSAvoidclutch engagement timing

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The mechanical oil pump is activated in advance along with the motor, preparing the hydraulic pressure system before clutch engagement is needed. This preliminary action ensures that hydraulic pressure is ready when the clutch needs to engage, maintaining clutch controllability while minimizing engagement timing delay

Inventive Principle:

Principle #10Preliminary action

4Loss of energy

If the hybrid vehicle operates in EV traveling mode during startup, then fuel efficiency improves, but the engine cannot be started when battery power is low

Engineering Contradiction:

Improvefuel efficiencyVSAvoidengine startability

Core Design Contradiction:

Loss of energyVSEase of operation

Solution Approach 1:

When EV traveling mode is determined to be unavailable due to low battery power, the system preliminarily activates the motor and mechanical oil pump before engine start attempt. This preparation ensures that the motor can immediately absorb engine torque during startup and the clutch can be properly engaged, enabling engine startability even when battery power is low

Inventive Principle:

Principle #10Preliminary action

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

This approach enhances engine startability and clutch controllability by promptly engaging the clutch, reduces power consumption, and ensures reliable operation even with low battery conditions, while minimizing engine startability deterioration.

Implementation Method 1

a mechanical oil pump which is driven by the motor and supplies oil to the friction engagement element

Methodology Applied

Scientific EffectHydraulic pressure: Hydraulic Press

Implementation Method 2

a clutch (friction engagement element) provided between the engine and the motor so as to be connectable and disconnectable

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS12415501B2Method of controlling hybrid vehicle and control system

Publication Date: 2025.09.16 MAZDA MOTOR CORP

AI summary

A method of controlling a hybrid vehicle including an engine, a motor, a starter, a friction engagement element provided between the engine and the motor, and a mechanical oil pump which is driven by the motor and supplies oil to the friction engagement element, is provided. When the friction engagement element is in a disengaged state, a first traveling mode using the motor is performed. When it is in an engaged state, a second traveling mode at least using the engine is performed. The method includes, when the first traveling mode is unperformable, starting the engine by the starter to perform the second traveling mode, activating the motor and performing a hydraulic pressure control for shifting the friction engagement element from the disengaged to engaged state after starting the engine. The hydraulic pressure control uses at least the hydraulic pressure from the mechanical oil pump driven by activating the motor.