**1. Introduction**

The driver-operated steering system is the basic equipment of the modern car and will remain so for a long time, despite the introduction of autonomous vehicle technology. According to the SAE classification (level of steering automation [1]), from L1 to L3 or even partially L4, the steering system will remain an element used by drivers. Persons with reduced mobility require a special adjustment of this system to the individual characteristics of their disability. This adjustment often requires additional, very expensive mechanical systems, thus cannot be considered for mass production. In addition, adjusting the parameters of the steering system to the individual characteristics of a fully able-bodied driver in modern cars is very limited and comes down to the tilt of the steering wheel or, by adjusting the seat, to changing the driver's distance from the steering wheel. The approach presented by the authors is based on universal design but complemented with additional individual adjustment of the steering system to specific users. The definition of "universal design" is included in the Convention on the Rights of Persons with Disabilities [2]: "Universal design" means the design of products, environments, programs, and services to be usable by all people, to the greatest extent possible, without the need for adaptation or specialized design. "Universal design" shall not exclude assistive devices for particular groups of persons with disabilities where this is needed. This additional help is implemented using the "custom design" methodology. If something is custom designed, it is made according to someone's special requirements. This approach also applies to people with special needs who, depending on their limitations, have individual needs, the fulfilment of which ensures their greater independence and the ability to function in society.

A detailed analysis of the division into a group of able-bodied and disabled people does not give a clear answer as to the border between these groups. This border is blurred.

**Citation:** Choroma ´nski, W.; Grabarek, I.; Kozłowski, M. Integrated Design of a Custom Steering System in Cars and Verification of Its Correct Functioning. *Energies* **2021**, *14*, 6740. https:// doi.org/10.3390/en14206740

Academic Editors: Wojciech Wach, Guzek Marek and Rafał Jurecki

Received: 29 August 2021 Accepted: 8 October 2021 Published: 16 October 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Do we, for example, include the elderly with a number of age-related ailments in the group of disabled or nondisabled people? Failure to answer this question requires a special approach to the design of control devices used in vehicles. Speaking about universal design of the steering system, the authors require one basic condition to be met at the beginning, namely equipping the vehicle with a "steer by wire" system, i.e., the one that does not have a mechanical position between the steering wheel and the steering system [3]. The "steer by wire" technology was initially introduced in aviation (in particular when piloting large passenger jets), due to the high physical effort required from pilots using classic solutions of control devices. In the automotive industry, according to the authors, it is an indispensable solution in the universal design methodology. The elements of the steering system that should be subject to universal design and elements that should be additionally adapted to the individual characteristics of the driver with the use of "custom design" are defined below. They are divided into parametric and structural factors. In addition to classic adjustments (e.g., tilting the steering wheel, adjusting the driver's position in relation to the steering system by changing the position of the seat), the following can be mentioned:

	- Gear ratio of the steering system:

$$d = \frac{\text{\textdegree angle of the starting wheel}}{\text{\textdegree triangle angle of the car wheels}} \tag{1}$$

	- Constructional solution for the steering system (steering wheel, multifunction steering wheel, joystick, sensor) for cooperation with bionic systems (e.g., bionic prosthesis after limb amputation).

The abovementioned systems must be consistent in the IT sense, e.g., integrated in the CAN bus. The steering system control calculations in the "steer by wire" technology should be performed by the host computer. The cost of adjusting the parametric and structural factors is relatively low. The question arises of how to verify the correct functioning of individual factors, and how to take into account the preferences of drivers. Correctness is understood as safety and comfort (as defined by drivers) in performing individual maneuvers. In the article, the authors do not analyze the problem of the reliability of operation of individual systems. It is a separate problem playing an important role in the "steer by wire" solutions, in particular in the automotive industry [5]. A separate problem, discussed in the article, is the training of drivers and verification of their skills. The article proposes a methodology for evaluating the functionality of new solutions consisting, inter alia, in:


The implementation of automated driving as well as of new interface solutions requires adequate training and, before that, an appropriate choice adequate to the driver's needs. A consequence of the changes in interface design will be the need for a selection and certification procedure for new equipment. The increasing level of automation in transport also foresees additional training for drivers to verify their, sometimes completely new, skills necessary when using nonstandard solutions. The authors propose their vision of

a procedure for implementing new steering system designs, which defines the necessary conditions that must be met before a given solution is implemented in individual vehicles.

#### **2. Materials and Methods**

The main aim of the experiment was an attempt to introduce correctness measures for maneuvers performed with the use of a multifunction steering wheel and to propose an evaluation of the biomechanical factors of the driver through the use of the electromyography (EMG) [6] measurement. The tests were carried out in a dynamic physical simulator by Aerospace Industries (Figure 1). Partial results of these studies have been published in previous papers [7–9].

**Figure 1.** Car driving simulator of ETC PZL Aerospace Industries. Source: ETC PZL [10].

The description of the experiment conducted by the authors includes:


#### *2.1. Research Sample*

At this stage of the research, the group of participants in the experiment was limited to able-bodied drivers. The participation of disabled drivers required the adaptation of the dynamic simulator to enable the driver's cabin on a wheelchair to enter and exit the simulator. The study of this group of people is planned in the next stage. The research group consisted of 30 men aged 20–23. All drivers had a driving license. The second important limitation was the assumed number of test runs. Each driver performed two road tests, driving the vehicle using three steering wheels consecutively. In each test, the driver made three runs: with the classic steering system, and the ECO steering wheel with two gear ratios. In order to simplify the descriptions, in the tests in question, the following symbols were introduced: NOR (max rotation ±720◦) standard steering wheel, ECO 180 steering wheel, for which the max rotation was ± 180◦, and ECO 120, for which the max rotation was ±120◦. The maximum turn of each steering wheel corresponded to a steering angle of the front wheels of ±35◦. The participants of the experiment did not constitute a representative sample for adult Polish citizens. It was a rather simple sample. With such a small sample, striving for a high "representativeness" of the sample would be even a methodological error. The dispersion of the results would probably render the obtained results worthless (they would be characterized by a very large dispersion).

#### *2.2. Research Object*

The tests were carried out in a simulator but were related to a specific vehicle solution. The mentioned solution is an "eco-car" developed under the [11] project (this car is shown

in Figure 2a). The design of the vehicle was based on the principles of universal design, i.e., it was assumed that it will be an electric vehicle intended for rental by drivers of various abilities, including drivers using active (hand-powered) wheelchairs. The implementation of the universal design postulated required the design of a number of solutions ensuring the required functionality of the eco-car, such as:


**Figure 2.** (**a**) Eco-car created within the [11] project, (**b**) multifunctional steering wheel the car is equipped with, (**c**) tested steering wheel installed in the simulator.

The car tested in the simulator was equipped with a designed multifunction steering wheel (see Figure 2b) to test its functionality. The versatility of the multifunctional steering wheel consists of the fact that, although it is aimed to be used by people with limited or complete lack of lower mobility, it does not exclude the possibility of steering the vehicle by able-bodied people. The tested eco-steering prototype is characterized by the fact that the main steering activities are performed only through the upper limbs, which is possible thanks to the steer-by-wire system of the designed eco-car. Two additional rings (hereinafter the "O-rings") that the steering wheel is equipped with are used for braking (smaller ring) and acceleration/maintaining a constant speed (larger ring). The orange color of both O-rings allows for their faster identification during use. In the case of this solution, the angle of rotation of the steering wheel was limited. People with paresis of the lower limbs often also have manual limitations of the upper limbs, in particular the

hands, so in their case, limiting the range of steering wheel rotation may facilitate steering. Taking this into account, the steering gear ratio has been programmatically limited to a rotation angle of 180 or 120 degrees per full turn of the car's front wheels. In addition to O-rings, the steering wheel is equipped with function buttons located on its rim, which are operated without taking hands off the steering wheel. The vehicle with the said steering wheel was recreated in a dynamic simulator of motor vehicles.
