Clutch Torque Estimation Using Kalman Filter State Observer
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Solution Overview
Problem
In hybrid vehicles, starting the internal combustion engine from electric driving mode requires precise knowledge of the torque transmitted by the separating clutch to avoid torque fluctuations at the drive wheels, which is challenging due to unknown parameters like clutch wear and viscosity, leading to suboptimal starting processes and increased costs from separate starter systems.
Innovation Solution
A method using a state estimator, such as a Kalman filter, to determine the actual torque transmitted by the clutch by distinguishing between theoretically transmittable torque and interfering torque, with a state space model of the drive train, allowing for precise torque control and compensation of combustion engine drag torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate starter system is used to start the internal combustion engine, then the starting process is reliable and the electric machine is not influenced by the starter, but the vehicle requires additional installation space, additional costs, and extensive expansion of the on-board electrical system
Solution Approach 1:
The patent merges the starting function with the existing electric machine and separating clutch system. The electric machine, already present for hybrid operation, is used to start the internal combustion engine by transmitting torque through the separating clutch, eliminating the need for a separate starter system and its associated components
Solution Approach 2:
The electric machine serves multiple functions: it acts as a motor during electric driving mode and as a starter during engine starting mode. The separating clutch also serves dual purposes - connecting/disconnecting the engine from the transmission during hybrid operation and transmitting starting torque during engine start-up
2Device complexity
If the internal combustion engine is started via the electric machine of the hybrid drive by closing the separating clutch, then the separate starter system and its additional costs are eliminated, but precise knowledge of the torque transmitted by the separating clutch is required to avoid torque fluctuations at the drive wheels
Solution Approach 1:
The patent replaces direct mechanical torque measurement (which would require complex sensors and measurement systems) with a mathematical model-based calculation approach. The clutch torque is determined through a state space model that processes readily available signals from the clutch control device, observer, and state estimator, substituting mechanical measurement with computational analysis
Solution Approach 2:
The patent introduces a state estimator and observer as intermediary components that process control signals and system states to derive the clutch torque. These intermediaries translate easily measurable quantities (control pressure, rotational speeds) into the difficult-to-measure clutch torque through mathematical relationships
3Ease of manufacture
If the torque transmitted by the clutch is determined using known parameters (hydraulic control pressure, clutch temperature), then the determination process is simple, but only a relatively rough estimate of the torque can be obtained due to unknown parameters like clutch wear and viscosity
Solution Approach 1:
The patent implements a feedback mechanism where the state estimator continuously monitors the actual system behavior (rotational speeds, torques) and compares it with the model-based predictions. The estimation is adjusted based on this feedback, allowing the system to account for unknown parameters like clutch wear and viscosity without requiring direct measurement of these parameters
Solution Approach 2:
The patent transforms the torque determination from a static calculation based on fixed parameters to a dynamic estimation process. The state space model and observer adapt to changing conditions (clutch wear, temperature, viscosity) by continuously updating the torque estimate based on current system state and historical data
Data Source
Figure 1
AI summary
A method for the approximate determination of the torque which is actually transmitted by a clutch of a drive train of a vehicle, having the following steps: - setting of a closed state of the clutch and transmission of a torque via the drive train, - provision of a state-space model which depicts the drive train, in particular a Kalman filter, determination of a torque which can be transmitted theoretically or is transmitted by the clutch in the closed state, - approximate determination of the torque which is actually transmitted by the clutch by adding of the torque which can be transmitted theoretically or is transmitted and an arithmetically determined interference torque, wherein the interference torque is determined on the basis of the state-space model and actual torques which are transmitted by actual rotational speeds of individual drive-train components and/or by individual drive-train components.