Hybrid Vehicle Engine Speed Control via Main-Side Ratio
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Solution Overview
Problem
In hybrid vehicles with a specific hardware configuration, the allowable maximum rotational speed of the engine is often set too low, leading to excessive limitation of engine speed and deterioration in drivability, especially when the front and rear wheels are less likely to slip due to idling.
Innovation Solution
A hybrid vehicle system that includes an engine, a first motor, a differential unit, a second motor, and a driving force split device, with a controller that adjusts the allowable maximum rotational speed based on the main-side ratio and other conditions to balance part protection and drivability, allowing higher speeds when the main-side ratio is lower and restricting speeds when it is higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the allowable maximum rotational speed of the engine is always set to a relatively low value regardless of the main-side ratio, then parts are protected from high-speed damage, but the rotational speed of the engine is excessively limited when the front and rear wheels are less likely to slip due to idling, causing deterioration in drivability
Solution Approach 1:
The patent applies dynamics by making the allowable maximum rotational speed variable rather than fixed. The controller dynamically adjusts the allowable maximum rotational speed based on the main-side ratio, which changes according to driving conditions. When the main-side ratio is high (front wheels more likely to slip), the allowable maximum rotational speed is set lower for protection. When the main-side ratio is low (front and rear wheels less likely to slip), the allowable maximum rotational speed is set higher for better drivability. This dynamic adjustment resolves the contradiction between part protection and drivability.
2Ease of operation
If the allowable maximum rotational speed of the engine is set high to improve drivability, then the engine can rotate faster when needed, but parts may be damaged due to excessive rotational speed
Solution Approach 1:
The patent applies parameter changes by modifying the allowable maximum rotational speed parameter based on the main-side ratio condition. Instead of using a single fixed value, the system changes this critical parameter according to the distribution of driving force between front and rear wheels. The controller calculates the main-side ratio and adjusts the allowable maximum rotational speed accordingly, ensuring parts are protected when the ratio is high while allowing higher speeds when the ratio is low, thus resolving the contradiction between drivability and part protection.
Data Source
AI summary
In a hybrid vehicle including an engine, a first motor, a differential unit, a second motor, a driving force split device, and a controller, the controller is configured to control the engine, the first motor, and the second motor such that the hybrid vehicle travels with the engine rotating within a range of an allowable maximum rotational speed for control or less. In this case, the controller is configured to set the allowable maximum rotational speed such that the allowable maximum rotational speed is higher when a main-side ratio is lower than when the main-side ratio is higher. The main-side ratio is a ratio of a driving force that is transmitted to main drive wheels to the total driving force that is transmitted from a drive shaft to the main drive wheels and sub drive wheels via the driving force split device.