Single-Cylinder Engine Start via Motor-Assisted Compression
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Solution Overview
Problem
Existing straddled vehicle engines face challenges in shortening the time period from engine start instruction to engine start completion due to the limitations of the compression release mechanism, which reduces torque and prolongs the engine start time, especially in single-cylinder engines.
Innovation Solution
The implementation of a permanent magnet type motor connected to the crankshaft, which applies a force to the piston during the compression stroke to assist combustion, thereby reducing the need for the compression release mechanism and increasing the rotation speed of the crankshaft, ensuring a faster engine start by maintaining higher combustion forces and reducing the operation of the compression release mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the compression release mechanism is used to reduce load torque during compression stroke, then the engine can start more easily, but the torque applied to the crankshaft decreases and the engine start time is prolonged
Solution Approach 1:
The system performs preliminary action by operating the compression release mechanism in advance during the first compression stroke to reduce the compression load. This preliminary reduction of compression resistance enables the crankshaft to achieve sufficient rotation speed before combustion occurs, thereby shortening the overall engine start time while maintaining ease of starting.
Solution Approach 2:
The permanent magnet motor continues to apply torque to the crankshaft continuously from the start phase through the initial combustion cycles. This continuous torque application ensures that the crankshaft maintains adequate rotation speed without interruption, preventing the need for repeated compression release operations and reducing the total engine start time.
2Speed
If the permanent magnet motor applies force to the piston during compression stroke, then the crankshaft rotation speed increases, but the motor size increases
Solution Approach 1:
The permanent magnet motor applies torque partially - specifically during the compression stroke and initial combustion cycles - rather than continuously at full capacity. By providing just enough torque to maintain crankshaft rotation speed above the compression release activation threshold, the motor can be downsized while still achieving the speed enhancement needed to reduce engine start time.
Solution Approach 2:
The system changes the operating parameters by controlling the motor torque output dynamically based on crankshaft position and rotation speed. The motor operates at variable torque levels rather than constant high torque, allowing for a smaller motor design that still achieves the necessary crankshaft speed increase during the critical start phase.
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 configuration significantly shortens the time required for engine start completion by maintaining higher rotation speeds and reducing the reliance on the compression release mechanism, thereby improving the early-start ability of single-cylinder engines while allowing for a downsized motor design.
Implementation Method 1
a permanent magnet type motor 20, the rotor 30 of which is connected to the crankshaft 15
Implementation Method 2
the compression release mechanism D opens the exhaust valve 18 in a compression stroke
Implementation Method 3
the piston 13 is moved to and fro by combustion of the mixed gas
Data Source
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AI summary
[PROBLEM] To provide a straddled vehicle that is able to shorten a time period until completion of engine start after an engine start instruction. [SOLUTION] An engine unit includes a single-cylinder engine, a compression release mechanism, a drive wheel, a permanent magnet type motor, a battery, an inverter including a plurality of switching parts, and a control device. The control device controls the switching parts in such a manner that, upon reception of a start instruction for starting the single-cylinder engine, the permanent magnet type motor moves a piston so as to operate the compression release mechanism in a compression stroke of a first combustion cycle, and then the permanent magnet type motor applies a force to the piston via a crankshaft such that the rotation speed of the crankshaft in a second combustion cycle exceeds the pressure-reduction upper limit speed for the compression release mechanism, so that the piston is moved without operating the compression release mechanism in a compression stroke of the second combustion cycle, thus assisting compression of the mixed gas.