Systems and methods for controlling engine speed in a hybrid vehicle

Abstract

Methods and systems are provided for controlling an engine speed in a hybrid vehicle system during steady-state conditions and in response to transient acceleration and / or deceleration requests. In one example, an engine speed is controlled to an optimal engine speed for fuel economy during steady-state conditions, and in response to an acceleration or deceleration request, a target engine speed is obtained from a rate-limited optimal engine speed to vehicle speed ratio, and the engine is controlled to the target engine speed provided the target speed is below a threshold difference from optimal engine speed. In this way, the vehicle system may simulate a fixed ratio transmission during accelerations and decelerations, while maintaining optimal engine speed for fuel economy at steady state.

Description

technical field [0001] The present description generally relates to methods and systems for controlling hybrid vehicle engine speed to simulate a fixed ratio transmission during transient operating conditions while controlling engine speed to an optimum engine speed for fuel economy during steady state conditions. Background technique [0002] Hybrid electric vehicle (HEV) powertrain systems such as split-split hybrids and series hybrids allow engine speed to be selected independently of vehicle speed and modified at a rate independent of vehicle acceleration. Optionally, vehicles equipped with manual or automatic step ratio transmissions operate at engine speeds at fixed ratios to vehicle speed. More specifically, engine speed and the rate of change of engine speed are related to vehicle speed and its acceleration or deceleration, except during transitions from one of the available gear ratios to another. [0003] The ability to decouple engine speed from vehicle speed pro...

AI Technical Summary

Problems solved by technology

[0004] However, in some examples, the ability to vary engine speed independently of vehicle speed can result in unintuitive engine speed behavior for vehicle operators accustomed to vehicle powertrains, such as with step ratio transmissions

In one approach, given the independent nature of engine speed, the ratio of engine speed to vehicle speed can be limited to a fixed set of gear ratios, however this comes at the expense of improved fuel economy

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