CVT Engine Compression Braking via Power-Based Speed Profiles
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Solution Overview
Problem
Existing methods for engine compression braking in vehicles with continuously variable transmissions (CVTs) often fail to deliver the demanded power during deceleration due to reliance on vehicle speed and brake pedal position, leading to inadequate deceleration and increased noise and vibration (NVH), especially when battery charge limits are low.
Innovation Solution
A method that adjusts engine speed in a CVT based on power-based target engine speed profiles, which vary with driver-demanded deceleration power and battery charge power limit, allowing for shifting between engine speed-to-vehicle speed profiles to ensure adequate deceleration power delivery while reducing NVH.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If engine speed is adjusted according to fixed engine speed-to-vehicle speed profiles based on vehicle speed and brake pedal position, then NVH is reduced, but the demanded deceleration power is not delivered
Solution Approach 1:
The patent transitions from static fixed engine speed-to-vehicle speed profiles to dynamic power-based target engine speed profiles. The controller continuously adjusts the target engine speed based on real-time wheel power demand and battery charge power limit, allowing the system to adapt to changing operating conditions and deliver the required deceleration power while managing NVH.
Solution Approach 2:
The patent changes the control parameter from vehicle speed and brake pedal position to wheel power demand and battery charge power limit. This parameter change enables the system to directly control engine speed based on the actual power requirements for deceleration, ensuring that the demanded deceleration power is delivered while accounting for battery charge limitations.
2Power
If regenerative braking is used to meet negative torque demand, then battery charge limit is exceeded, but deceleration performance is insufficient
Solution Approach 1:
The patent implements feedback control by continuously monitoring the battery charge power limit and adjusting the compression braking power request accordingly. The controller uses the battery charge power limit as a feedback signal to determine the appropriate engine speed target, ensuring that regenerative braking operates within battery acceptance capabilities while maintaining required deceleration performance.
Solution Approach 2:
The patent segments the braking system into two independent but coordinated components: regenerative braking and compression braking. The controller divides the total negative torque demand between these two systems based on battery charge power limit, allowing each system to operate within its optimal range and capabilities.
3Power
If compression braking power request is increased to meet driver demanded deceleration, then deceleration performance improves, but NVH increases
Solution Approach 1:
The patent uses dynamic power-based target engine speed profiles to continuously adjust engine speed during compression braking events. This dynamic adjustment allows the system to optimize the balance between deceleration power delivery and NVH reduction by adapting engine speed to real-time power demands rather than following fixed profiles.
Solution Approach 2:
The patent changes engine speed control parameters based on wheel power demand and battery charge power limit, enabling precise control of compression braking intensity. This parameter adjustment allows the system to deliver required deceleration power while minimizing NVH by avoiding excessive engine speeds.
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 ensures the vehicle decelerates at the demanded rate under all operating conditions, including when the accelerator pedal is depressed, by continuously adjusting engine speed according to the power-based target engine speed, thereby reducing NVH and improving deceleration performance.
Implementation Method 1
the CVT may take the form of a planetary gear set and a generator. Torque of the generator may be adjusted so that engine speed may be controlled independent of wheel speed
Implementation Method 2
at least a portion of the vehicle's kinetic energy may be transferred through the planetary gear set and to the engine via adjusting a torque of the generator
Implementation Method 3
Engine compression braking may be used to produce negative wheel torque in order to meet a negative driver demand
Data Source
AI summary
Methods and systems are provided for operating a continuously variable transmission (CVT) of a driveline of a vehicle during a request for engine compression braking. In one example, a method may include, responsive to an engine compression braking request, operating a CVT via a controller to adjust engine speed according to an engine speed-to-vehicle speed profile selected based on a power-based target engine speed for the engine compression braking request. The power-based target engine speed may vary continuously with driver demanded power and a battery charge power limit of the vehicle.