Development of a steering-system model considering viscous friction and its verification

Shin

2020

Applied Sciences

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When a vehicle goes on the straight road with a bank angle, a steering pull makes the driver exert a constant steering torque to the steering wheel, which causes an annoying steering feel to the driver. This paper proposes a steering pull model and sensitivity analysis on the steering pull. In order to develop the steering pull model, pulling forces on the tires, such as plysteer and conicity forces, lateral force due to slip angle, lifting forces due to cast and kingpin, and camber force are modeled. A steering system is also modeled because the generated pulling forces are attenuated as it is transmitted through the steering system. Each component of the steering system, such as lower body linkages, rack and pinion gear, universal joint, and steering column with electric power steering (EPS) system is modeled, and then they are integrated into a complete steering system. Finally, the steering pull model is developed by integrating the pulling force model with the steering system model. For verification, the steering pull of a vehicle is estimated based on the model, and the results are compared with the experimental results. For the verification experiments, a steering pull measurement system using a global positioning system (GPS) and its accessories are used. The result comparison showed that the developed steering pull model provides very accurate estimation results. Based on the steering pull model, the sensitivity of steering pull factors, such as caster angle, kingpin angle, camber angle, rack friction force, and anti-rattle spring (ARS) stiffness is analyzed.

Section: Friction Model In Steering Systemmentioning

confidence: 99%

Steering Pull Model and Its Sensitivity Analysis

Shin

2020

Applied Sciences

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“…When a vehicle goes on a bumpy road, vibration and impact occur and are delivered to the steering system. In order to avoid tooth failure caused by these vibration and impact, the worm gear in the steering system needs flexibility and clearance in terms of design and assembly (Shin et al, 2014;Baxter and Dyer, 1988). In C-EPS systems, a worm wheel is located in the steering column and rotated by it.…”

Section: Misalignmentmentioning

confidence: 99%

“…EPS systems have a lot of advantages over other power steering systems such as better energy efficiency and space usage due to its compactness and modulization (Zanten, 2000). However, one issue that keeps being raised so far by many automotive engineers and magazines is steering feel (Zaremba et al, 1998;Shin et al, 2014;Dong et al, 2010). Especially for C-EPS systems, for example, when a driver turns the steering wheel and needs 10 Nm for steering assist, an electric motor gives 10 Nm to the driver through a worm gear.…”

Section: Introductionmentioning

confidence: 99%

Worm gear efficiency model considering misalignment in electric power steering systems

2018

Mech. Sci.

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Abstract. This study proposes a worm gear efficiency model considering misalignment in electric power steering systems. A worm gear is used in Column type Electric Power Steering (C-EPS) systems and an Anti-Rattle Spring (ARS) is employed in C-EPS systems in order to prevent rattling when the vehicle goes on a bumpy road. This ARS plays a role of preventing rattling by applying preload to one end of the worm shaft but it also generates undesirable friction by causing misalignment of the worm shaft. In order to propose the worm gear efficiency model considering misalignment, geometrical and tribological analyses were performed in this study. For geometrical analysis, normal load on gear teeth was calculated using output torque, pitch diameter of worm wheel, lead angle and normal pressure angle and this normal load was converted to normal pressure at the contact point. Contact points between the tooth flanks of the worm and worm wheel were obtained by mathematically analyzing the geometry, and Hertz's theory was employed in order to calculate contact area at the contact point. Finally, misalignment by an ARS was also considered into the geometry. Friction coefficients between the tooth flanks were also researched in this study. A pin-on-disk type tribometer was set up to measure friction coefficients and friction coefficients at all conditions were measured by the tribometer. In order to validate the worm gear efficiency model, a worm gear was prepared and the efficiency of the worm gear was predicted by the model. As the final procedure of the study, a worm gear efficiency measurement system was set and the efficiency of the worm gear was measured and the results were compared with the predicted results. The efficiency considering misalignment gives more accurate results than the efficiency without misalignment.

“…Modern power steering systems can be classified into three systems: hydraulic power steering (HPS), electrohydraulic power steering (EHPS), and electric power steering (EPS). 2…”

Section: Introductionmentioning

confidence: 99%

Hardware-in-the-loop simulations of an electrohydraulic power steering system for developing the motor speed map of heavy commercial vehicles

Proceedings of the Institution of Mechanical Engineers, Part D:

Chu

2015

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This study proposes hardware-in-the-loop simulations to develop the motor speed map of electrohydraulic power steering systems for heavy commercial vehicles. The current method that relies on the test driver’s hands and feet to obtain electrohydraulic power steering motor speed maps causes a number of problems, such as inaccurate steering rates and vehicle speeds and the risk of rollover during tests. In order to overcome these weaknesses, this study employs a hardware-in-the-loop simulation system, a vehicle model, and an experimental development method. A hardware-in-the-loop simulation system was set up to simulate a steering system on the road. The system includes a system drive, data acquisition, system controller sets, and an electrohydraulic power steering system. This hardware-in-the-loop simulation system is controlled in real time because the amount of the torque from the resistant torque motor, which applies the self-aligning moments generated between the ground and the tires to the steering system, is affected by the steering angle of the steering-wheel motor. For calculation of the resistant torque with respect to various driving conditions, a vehicle model was employed in this study. It includes calculation of the self-aligning moments with the tire property data, the moments due to the kingpin inclination, the vehicle dynamics, and the steering-system modeling. The resultant values were input into the resistant torque motor. In addition to the hardware-in-the-loop simulation system and the vehicle model, the concept of a desirable steering torque which parameterizes the steering feel was introduced in this study. Using the desirable steering torque, the steering feel could be quantified, and desirable steering feels were established. In this study, in order to validate the hardware-in-the-loop simulations, a heavy commercial vehicle was designated as the target vehicle. The target vehicle’s tire and specifications such as the dimensions, the weight, the steering system, and the mechanical links were adopted, and a desirable steering-torque map was established by a professional test driver. The development results were presented.