Brake Hydraulic Pressure Control for Hill Start Assist
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Solution Overview
Problem
The existing brake hydraulic pressure control systems for vehicles face challenges in maintaining a stable brake hydraulic pressure when the electric motor continues to rotate due to inertial force after current cessation, potentially leading to pressure drops below the reference brake pressure during hill start assist control.
Innovation Solution
A brake hydraulic pressure control system that includes an electric motor-driven piston, an operation amount detecting unit, and an offset pressure setting unit to adjust the holding control start reference pressure and fluid pressure based on the rotational speed of the electric motor, ensuring the brake hydraulic pressure remains above the reference brake pressure by setting a higher holding control start reference pressure and adding an offset pressure as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the electric motor rotates to greatly reduce the brake hydraulic pressure to the reference brake pressure, then the brake hydraulic pressure control can be achieved, but the electric motor continues to rotate due to inertial force causing the brake hydraulic pressure to drop below the reference brake pressure
Solution Approach 1:
The control unit predicts the rotational speed of the electric motor based on the current rotational speed and a predetermined acceleration, and determines the holding control start reference pressure in advance before the motor completes its rotation. This preliminary action allows the system to prepare the appropriate pressure threshold before the motor's inertial rotation causes pressure drop, thereby preventing the brake hydraulic pressure from falling below the reference brake pressure.
Solution Approach 2:
The control unit continuously monitors the operational state of the electric motor and adjusts the holding control start reference pressure dynamically based on the predicted rotational speed. This feedback mechanism ensures that the control system responds to changing motor conditions and maintains brake hydraulic pressure within the required range, preventing both excessive pressure and dangerous pressure drops.
2Reliability
If the holding control start reference pressure is set higher than the reference brake pressure to prevent pressure drop, then the brake hydraulic pressure stability is improved, but the system complexity increases due to dynamic pressure adjustment
Solution Approach 1:
The control unit automatically determines the holding control start reference pressure based on the predicted rotational speed of the electric motor without requiring external intervention or complex manual adjustments. The system uses its own operational data (motor rotational speed and acceleration) to self-adjust the pressure threshold, simplifying the overall control architecture while maintaining high reliability.
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
Effectively prevents brake hydraulic pressure from dropping below the reference brake pressure during hill start assist, ensuring the vehicle remains stationary by dynamically adjusting the fluid pressure in response to the electric motor's rotational speed, thereby maintaining control and preventing overshooting.
Implementation Method 1
a wheel cylinder for braking wheels by a brake hydraulic pressure corresponding to a displacement amount of the forward and backward operation of the piston
Implementation Method 2
as the electric motor rotates by inertial force even if current flowing in the electric motor is stopped
Data Source
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AI summary
Brake hydraulic pressure is appropriately prevented from becoming lower than a reference brake pressure for holding control. When a physical amount correlating with the rotational speed of an electric motor has become higher than or equal to a predetermined value, an HSA start reference pressure setting unit sets an HSA start reference pressure (B) to a value higher than a reference brake pressure (E), and if the HSA start reference pressure (B) at a time (t3) when a driver required fluid pressure (C) has become lower than the HSA start reference pressure (B) is higher than the reference brake pressure (E), an HSA required fluid pressure setting unit sets an HSA required fluid pressure at a time when the driver required fluid pressure (C) has become lower than the HSA start reference pressure (B) to a value higher than the reference brake pressure.