EPAS Rack Assembly for Solid Axle Steering
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Solution Overview
Problem
Hydraulically-operated recirculating ball nut gear systems in solid axle front suspensions are heavy, costly, and provide limited performance features, while imposing significant compliance burdens on the steering system.
Innovation Solution
Implementing an Electric Power Assisted Steering (EPAS) system that includes an idler arm, an EPAS rack assembly with an input shaft, a rack, an electric motor, and an output link, which reduces weight, cost, and compliance burdens by providing powered assistance and additional performance features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydraulically-operated recirculating ball nut gear system is used in solid axle front suspension, then the system provides durable steering operation, but the system becomes heavy and costly
Solution Approach 1:
The patent replaces the hydraulically-operated mechanical steering system with an electrically-operated rack and pinion system. The electric motor provides power assistance through direct mechanical coupling to the pinion gear, eliminating the need for hydraulic pumps, reservoirs, and complex fluid distribution systems. This substitution of hydraulic mechanics with electric-mechanical actuation reduces overall system weight while maintaining steering durability through controlled electric motor operation.
Solution Approach 2:
The patent extracts and removes the hydraulic components (pump, reservoir, fluid lines) from the steering system, retaining only the essential mechanical elements (rack, pinion, electric motor). By taking out the heavy hydraulic subsystem and replacing it with a compact electric motor, the system achieves weight reduction while preserving the core steering function and durability requirements.
2Adaptability or versatility
If a hydraulically-operated recirculating ball nut gear system is used in solid axle front suspension, then the system provides steering function, but the system becomes costly with limited performance features
Solution Approach 1:
The electric motor in the rack and pinion system serves multiple functions: it provides power assistance during steering maneuvers, enables precise steering angle control, and can be integrated with vehicle stability control systems. This multi-functionality is achieved through the programmable nature of electric motors, which can adapt their torque and speed characteristics based on driving conditions, thereby providing enhanced performance features at lower cost compared to specialized hydraulic components.
Solution Approach 2:
The patent utilizes the ability to change electrical parameters (voltage, current, pulse width modulation duty cycle) to the electric motor to achieve variable steering assistance levels. This parameter control allows the system to adapt performance characteristics dynamically, providing enhanced versatility in handling different driving scenarios while using a single, cost-effective electric motor platform rather than multiple fixed-function hydraulic components.
3Ease of operation
If a hydraulically-operated recirculating ball nut gear system is used in solid axle front suspension, then the system provides steering operation, but significant compliance burdens are imposed on the steering system
Solution Approach 1:
The patent replaces the compliance-prone hydraulic system with a rigidly-coupled electric motor to pinion gear mechanism. The direct drive connection eliminates hydraulic fluid compliance, line expansion, and pressure fluctuation issues. The electric motor's rotational inertia and controlled torque delivery provide inherent mechanical stability, reducing unwanted compliance effects while simplifying the overall system architecture.
Solution Approach 2:
Instead of using a passive hydraulic system that relies on fluid pressure to transmit steering forces, the patent inverts the approach by using an active electric motor that directly generates and controls steering torque. This inversion from passive hydraulic pressure transmission to active electric torque generation eliminates the compliance issues inherent in fluid-based systems while reducing mechanical 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
The EPAS system is lighter and less costly than traditional systems, offering a broader range of performance features and reduced steering system compliance, enhancing vehicle durability and efficiency.
Implementation Method 1
the electric motor is to provide powered assistance to movement of the rack
Data Source
AI summary
Electric power assisted steering (EPAS) systems for solid axle front suspension vehicles are described. An example EPAS system includes an idler arm having a first end and a second end. The first end of the idler arm is coupled to a frame of the vehicle. The example EPAS system further includes an EPAS rack assembly having an input shaft, a rack, an electric motor, and an output link. The rack is coupled to the input shaft and is movable in response to movement of the input shaft. The electric motor is coupled to the rack. The electric motor provides powered assistance to movement of the rack. The output link has a first end and a second end. The first end of the output link is coupled to the rack. The second end of the output link is coupled to the second end of the idler arm.