Regenerative Braking Torque Transition via Pump Speed Control
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Solution Overview
Problem
Traditional regenerative braking systems in vehicles face challenges in reducing generator braking torque to zero efficiently, leading to high pump efficiency requirements and noise/vibration issues during brake pressure buildup, which affects the transition from regenerative to hydraulic braking modes.
Innovation Solution
A method that uses a control unit to manage brake fluid delivery at low rates, optimizing pump speed and generator braking torque to build up brake pressure smoothly, reducing noise and vibration, and allowing for a longer regenerative braking phase with high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the generator braking torque is reduced to zero before the vehicle comes to a standstill, then the generator is protected from damage, but the braking effect of the generator is lost and brake pressure must be built up using the pump
Solution Approach 1:
The system performs preliminary action by building up brake pressure in the brake circuit before the generator braking torque is completely reduced to zero. This ensures that when the generator is deactivated for protection, the hydraulic braking system is already pressurized and ready to maintain braking effect, avoiding a sudden loss of braking force.
Solution Approach 2:
The system ensures continuity of useful action by overlapping the generator braking phase with the brake pressure buildup phase. The generator continues to provide braking torque while the pump simultaneously builds up hydraulic pressure, ensuring uninterrupted braking effect throughout the transition.
2Loss of time
If the pump operates at high rotational speed to build up brake pressure quickly, then the brake pressure buildup time is reduced, but noise and vibration increase significantly
Solution Approach 1:
The system applies dynamics by continuously adapting the pump rotational speed to the current brake pressure level and vehicle deceleration requirements. The pump speed is dynamically adjusted rather than operating at a fixed high speed, allowing optimal balance between pressure buildup rate and noise/vibration levels at each moment of the braking process.
Solution Approach 2:
The system changes parameters by varying the pump rotational speed as a variable parameter rather than keeping it constant. The pump speed is modified according to the current operating conditions, including the current brake pressure, vehicle velocity, and required deceleration, achieving efficient pressure buildup while limiting noise and vibration.
3Manufacturing precision
If the brake fluid volume transferred at the start of brake pressure buildup is increased to overcome dead volume and system elasticity, then the actual brake pressure is achieved faster, but the pump must operate at comparatively high efficiency
Solution Approach 1:
The system performs preliminary action by using the generator braking torque to initiate the braking effect while the pump begins transferring brake fluid. This preliminary phase allows the system to start overcoming dead volume and elasticity effects without requiring the pump to immediately deliver high pressure, reducing initial energy consumption.
Solution Approach 2:
The generator braking torque acts as an intermediary during the transition phase. It provides temporary braking support while the hydraulic system is being pressurized, allowing the pump to operate at lower efficiency levels during the initial phase of brake fluid transfer without compromising overall braking performance.
4Loss of energy
If the regenerative braking phase is extended to improve energy recovery, then the hydraulic brake pressure must be maintained without pump operation, but this requires precise coordination between generator torque reduction and pressure buildup
Solution Approach 1:
The system applies feedback by continuously monitoring the brake pressure level, generator braking torque, and vehicle deceleration. This feedback information is used to dynamically adjust the pump rotational speed and generator torque reduction rate, ensuring precise coordination during the extended regenerative braking phase and enabling accurate control without excessive complexity.
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 enables a quiet and efficient brake pressure buildup, maintaining setpoint braking torque while reducing generator braking torque, allowing for a seamless transition between regenerative and hydraulic braking modes with improved dynamics and reduced energy consumption.
Implementation Method 1
a generator is activated between times t0' and t1' in such a way that a generator braking torque M_gen (in Nm) not equal to zero (which may correspond to brake actuation distance s) is exerted on at least one wheel of the vehicle
Implementation Method 2
an (almost) linearly increasing setpoint brake pressure/target pressure p_setpoint (in bar) (starting from an initial brake pressure p0) should be built up in at least one brake circuit and/or at least one wheel brake cylinder of the braking system between times t1' and t2'
Data Source
AI summary
A method/controller for operating a vehicle regenerative braking system by operating in a first braking mode, in which a generator braking torque of a generator is not zero and is equal to a first regenerative portion predefined for the first mode, and controlling the system out of the first mode into a second braking mode having a second regenerative portion, which is smaller than the first portion, so that brake fluid is pumped out of a storage volume of the system into at least one wheel brake cylinder and/or at least one brake circuit of the system via at least one brake fluid delivery mechanism; by activating the delivery mechanism via a setpoint delivery output variable, which is established/predefined for a setpoint brake pressure having a setpoint pressure rise which increases over time, so that an actual brake pressure having an actual pressure rise increase over time is built up.