Engine Unit Crankshaft Restart via Brushless Motor
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Solution Overview
Problem
Existing engine starters require a large starter motor to generate high output torque, leading to poor mountability on vehicles and prolonged restart times after a combustion stop instruction is received.
Innovation Solution
A four-stroke engine unit with a three-phase brushless motor, an inverter, and a control device that drives the crankshaft in forward rotation from a stopped position to the compression stroke, allowing for reduced output torque requirements and faster restarts by leveraging inertial force and torque pulsation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large starter motor is used to generate high output torque for overcoming the high-load region, then the engine can start reliably, but the motor size increases leading to poor mountability
Solution Approach 1:
The control device performs preliminary action by controlling the starter motor to rotate the crankshaft in advance until the piston reaches a predetermined position (compression stroke or expansion stroke) before actual engine start. This preliminary rotation stores inertial force that will be used to overcome the high-load region, allowing a smaller motor to achieve reliable starting
Solution Approach 2:
The invention changes the operating parameters of the starter motor by controlling it to operate in two distinct phases: first phase rotates the crankshaft to a predetermined position with controlled speed, second phase utilizes the stored inertial force to overcome the high-load region. This parameter change allows the motor to deliver high torque only when needed rather than continuously
2Speed
If the crankshaft is driven in reverse rotation to the expansion stroke, then the forward rotation can cover the entire low-load region increasing rotation speed, but the restart time after combustion stop is prolonged
Solution Approach 1:
Instead of the conventional reverse rotation to expansion stroke, this invention inverts the approach by controlling the crankshaft to rotate forward to the compression stroke. This inversion allows the crankshaft to be positioned optimally for rapid restart while minimizing the rotation distance required after combustion stop, thereby reducing restart time
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 enables improved mountability and reduced restart times by using a three-phase brushless motor with controlled voltage and torque management, allowing the engine to start efficiently with lower output torque and smaller motor size.
Implementation Method 1
a three-phase brushless motor that starts the four-stroke engine body by driving the crankshaft in forward rotation
Implementation Method 2
an inverter including a plurality of switching parts by which a voltage applied from the battery to the three-phase brushless motor is controlled
Implementation Method 3
both a high inertial force generated by such a high rotation speed and an output torque of the starter motor can be used to overcome the high-load region
Data Source
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AI summary
The present invention provides, for example, an engine unit that has a high-load region and a low-load region and that can achieve mountability to vehicle and shortening of the length of time required for restarting after a combustion stop instruction. The engine unit includes a four-stroke engine body, a three-phase brushless motor, an inverter, and a control device. After a combustion operation of the four-stroke engine body and forward rotation of a crankshaft are stopped, the control device controls a voltage applied from a battery to the three-phase brushless motor by controlling a plurality of switching parts of the inverter under a state where a start instruction is not received while the combustion operation of the four-stroke engine body and the forward rotation of the crankshaft are stopped, to drive the crankshaft in forward rotation from a stopped position to a compression stroke included in four strokes. Upon receiving the start instruction, the control device drives the crankshaft in forward rotation from a position where the crankshaft is located at a time point when the start instruction is received.