Electric Power Steering Rack Support Reduces Kickback
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Solution Overview
Problem
Existing electric power steering systems face challenges in reducing kickback and vibration transmission to the steering wheel, particularly in vehicles with high weight, leading to discomfort and increased wear due to direct rigidity-based support structures and gear backlash.
Innovation Solution
An electric power steering apparatus with a sub-frame attached to the vehicle body without elastic members, a gearbox supported by a rolling type rack supporting device with a rolling element, and a torque sensor to control assistive steering force against counter torque from the wheels, enhancing transmission efficiency and abrasion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rigid support structure is used to support the gear box with high rigidity, then steering performance and response are improved, but kickback and vibration are directly transmitted to the steering wheel
Solution Approach 1:
The patent introduces a rack supporting device with rolling elements as an intermediary component between the rack shaft and gear box. This mediator supports the rack shaft while absorbing vibrations and reducing kickback transmission to the steering wheel, thus resolving the contradiction between maintaining steering performance and reducing harmful vibrations.
Solution Approach 2:
The patent changes the support parameters of the rack shaft by introducing rolling elements that provide both rigid support for steering response and vibration absorption capabilities. This parameter change allows the system to maintain high steering performance while reducing kickback and vibration transmission.
2Ease of operation
If backlash in the gear part is increased, then ease of operation is improved, but hammering sound and vibration are increased
Solution Approach 1:
The rack supporting device with rolling elements acts as a mediator that fills and stabilizes the backlash space in the gear engagement. This intermediary component maintains the necessary clearance for smooth steering operation while preventing excessive gear tooth separation that causes hammering sounds.
Solution Approach 2:
The rolling elements in the rack supporting device provide beforehand cushioning by pre-positioning support points that absorb impact forces before they can cause hammering sounds during gear engagement, while still allowing sufficient backlash for smooth operation.
3Object-affected harmful factors
If elastic members are used to support the gear box, then vibration absorption is improved, but steering response delay occurs
Solution Approach 1:
The rack supporting device serves as an intermediary vibration absorption mechanism that is localized to the rack shaft support points rather than using elastic members for the entire gear box mounting. This intermediary approach provides vibration absorption at critical points without introducing overall system compliance that would cause steering response delay.
Solution Approach 2:
The patent changes the vibration absorption parameter from using elastic mounting members for the gear box to using rolling elements for rack shaft support. This parameter change maintains rigid gear box mounting for fast steering response while providing localized vibration absorption where needed.
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 solution effectively suppresses kickback and vibration transmission, maintains high steering performance, and reduces wear, providing a comfortable and durable steering experience even under heavy loads.
Implementation Method 1
a rack supporting device which supports the rack shaft, comprising a rolling element which rolls on a surface of the rack shaft
Data Source
AI summary
Since a rigid supporting structure for a gear box GB and a rolling type rack supporting device RSD are employed, an electric power steering apparatus having no response delay and having a high transmission efficiency can be realized. Further, a high steering performance required for a long period and a steering assist force that is increasing recently can be efficiently transmitted to wheels. Further, when the wheels collide with a shoulder of a road to receive a counter input, a torque sensor TS detects a torque and an assist steering force against the counter input is outputted to an output shaft OS. Consequently, the torque of the counter input is restrained from being transmitted to a steering shaft SS side. Thus, a kick back and a vibration are advantageously hardly transmitted to a steering wheel SW from the wheels.