Comparison of Footrest Vibrations in the Case of an ICE-Based and Battery-Based Two-Wheeler ^†

Abstract

The current work investigates the comfort of two-wheeler riders and compares the footrest vibration between an internal combustion-engine-based and electric two-wheeler. The Retrofit Hero Honda CD-100 two-wheeler is considered for the study and is further converted into the electric mode in the laboratory. Electric two-wheelers, even though they have fewer moving parts than internal combustion engine-based two-wheelers, encounter vibrations that emerge from road excitations. Cracks, potholes, and irregular humps on the road are the major influencers of these vibrations. These vibrations, when they transfer to the human body, have been reported to cause major injuries to the human body in the long run. By performing several trials on actual road conditions, with both the rider as well as pillion, the vibration dose value is calculated at the footrest. Different scenarios, such as a random speed test, a 20 kmph speed test and a 30 kmph speed test, are conducted on the two-wheeler. The vibration dose value (VDV) method is used to analyze the rider’s comfort. A comparison is made between the internal combustion engine-based and electric-based two-wheeler to determine its comfort level at the footrest. It is found that the VDV as well as the RMS acceleration decreased considerably in the case of the electric two-wheeler when compared to the internal combustion engine-based vehicle. However, it is found that as the speed is increased, the vibrations increased as well. Hence, further scope is found for the improvement and inculcation of vibration damping at the locations where the vibrations are pronounced in order to improve the overall riding experience of a two-wheeler rider.

1. Introduction

One of the common problems found in two-wheelers is footrest vibration, which causes the rider discomfort. Two-wheelers are popular due to their ease of transportation, fuel efficiency and convenience [1]. However, the design of the mechanical components in these vehicles contributes to vibrations, especially at the footrest area [2,3].

Supports in two-wheelers are an essential component, providing stability and support for the rider’s feet during maneuver. They are attached to the chassis of the vehicle and are prone to vibration during travel. These vibrations are prone to causing injuries to the rider [4]. Engine imbalance is one of the major reasons for footrest vibrations in internal combustion engine (ICE)-based vehicles. In many vehicles, the engine is positioned near the footrest area, and any imbalance in the engine can lead to the propagation of vibrations to the footrest. Engine imbalances occur due to manufacturing defects, wear and tear, uneven power delivery and the resultant vibrations of reciprocating parts [5,6].

Road conditions are additional significant factors affecting the rider’s comfort [7]. Cracks, potholes, uneven road bumps and poorly maintained roads lead to jolts and vibrations, causing the rider discomfort [8,9]. These vibrations directly transfer to the human body through the footrest, and the continuous exposure to these leads to chronic injuries being caused to the rider [10,11]. Lower back pain, musculoskeletal disorders and many chronic injuries have been reported by researchers with regard to two-wheeler riders [12,13]. Furthermore, the design quality of the footrest can contribute to these issues. The transmission of vibrations to the feet of the rider essentially decreases the riding performance [14,15].

Research that aims to reduce footrest vibrations is crucial to ensure the rider’s safety and overall riding experience [16]. Manufacturers continuously strive to develop better and more comfortable designs to eradicate these issues, especially in off-road conditions. Electric vehicles today face issues regarding vibrations in different parts [17,18]. This is due to the absence of an engine in battery-powered vehicles. However, poorly maintained roads affect the rider’s comfort even in battery-powered vehicles [19]. Overall, the conversion to an electric powertrain can lead to a significant reduction in the mechanical and combustion-related vibrations typically associated with ICE vehicles. However, it is essential to note that the road conditions, vehicle speed, acoustic changes and rider’s riding style are all influential parameters and affect the vibrations in the E2W.

The ISO 2631 standard [20] provides guidance on the measurement of vibrations, the mounting position, as well as the safe limits of vibration. Due to the sensitivity of the human body to these vibrations, particularly in the case of women, ISO 2631 offers a safety limit criteria, as indicated in

Table 1. ISO 2631 comfort level criteria.

Acceleration (m/s2).	Category
Less than 0.315	Not uncomfortable
0.315–0.63	A little uncomfortable
0.5–1	Fairly uncomfortable
0.8–1.6	Uncomfortable
1.25–2.5	Very uncomfortable
Greater than 2.5	Extremely uncomfortable

.

In conclusion, footrest vibrations and their mitigation are of prime importance in two-wheelers, and determine the overall riding experience. This paper provides a comparison of the footrest vibrations in an ICE-based and electric two-wheeler. Addressing these issues will enhance the ride quality, reduce discomfort, and improve the overall riding experience.

2. Methodology

This experimental study shows a comparison of footrest vibrations in the case of an ICE-based vehicle and an electric two-wheeler (E2W). The initial study involves experimentation using the ICE vehicle, which is later converted to an electric vehicle to further study the vibration characteristics.

The transformation of the ICE-based two-wheeler into an electric two-wheeler took place within a controlled laboratory environment. The process involved the removal of original components like the engine, exhaust systems, and fuel tank. Subsequently, a high-efficiency 2000 W hub motor with strong regenerative capabilities was installed on the rear wheel. This motor features a drum brake mechanism. The power for the electric vehicle is provided by a 72 V, 40 AH Li-ion battery pack, which is supported by a 10 A charger for recharging. The vehicle’s integral setup also encompasses a motor controller, Battery Management System (BMS), and a throttle assembly. To ensure its proper illumination and functionality, a DC-to-DC converter is utilized. This converter efficiently transforms the battery’s high 72 V voltage into the required 12 V for the various lighting systems integrated into the vehicle. This facilitates the proper operation of all lighting functions.

The measurement of the acceleration was carried out by mounting the accelerometer on the footrest of the two-wheeler. The two-wheeler was tested under an actual driving scenario considering both the rider and pillion with a payload of 160 kgf. The road considered was a normal asphalt road with potholes and humps. The footrest of the vehicle, as shown in Figure 1, was the strategic location considered for the study. A PCB Piezotronics accelerometer with a sensitivity of 103.6 mV/g mounted on the footrest, as shown in Figure 1, acquired the acceleration signals that were required to measure the rider’s comfort. The software used was the National Instrument’s LabVIEW software (LabVIEW 2019).

The two-wheeler chosen for the study was the conventional ICE-powered Hero Honda, CD 100 SS, which was later converted into an electric two-wheeler for the study. At 20 kmph, 30 kmph, and a random speed, the vehicle was examined for vibration characteristics. For the tests conducted at 20 kmph and 30 kmph, the distance travelled was around 300 m. Several gear combinations were tested at a random 1 km distance to determine the random speed and vibrational characteristics. The software’s acceleration values were then utilized to determine the VDV. To determine the level of comfort, the VDV was finally compared to the ISO 2631 standard.

While travelling on the road, the vehicle experiences vibrations through various strategic locations of its body. These vibrations transfer to the human body and cause the rider discomfort. The mounting of accelerometers and the acquisition of the frequency responses are required for the measurement of these vibrations [12]. The acceleration is expressed as “g” values in the accelerometer’s output; g is equal to 9.81 m/s². The vibration dose value (VDV) method was used to calculate the vibration, which was then compared to the ISO 2631 standard to obtain the rider’s comfort. The calculation is as shown in Equation (1) [13].

Experimental Challenges

The present research focuses on assessing the random vibrations induced by varying road conditions, making it challenging to accurately predict the exact magnitude of vibration at any given moment. Within this study, measurements were carried out to assess vertical vibrations since they exert the most significant impact on the human body. It is important to acknowledge that the consistency of road uniformity, as well as the presence of cracks and potholes, may vary due to differing environmental conditions and the passage of time. As the experiments were carried out on different days and under varying climates, adhering to the exact same route for each trial during testing was difficult, and minor deviations in the vehicle’s path were inevitable.

3. Results and Discussion

The plots in this section clearly indicate the decrement in the vibrations after the conversion of the vehicle from an ICE-based to electric two-wheeler. Further, the VDV result shown in

Table 2. VDV Comparison.

Accelerometer Mounting Position	VDV @ Random Speed Test	VDV @ 20 kmph Speed Test	VDV @ 30 kmph Speed Test
ICE footrest	13.68 ms−1.75	14.66 ms−1.75	15.02 ms−1.75
E2W footrest	12.55 ms−1.75	14.45 ms−1.75	13.88 ms−1.75

also indicates the decrease in the vibration exposure in the electric two-wheeler when compared to the ICE-based vehicle.

3.1. Random Speed Test

The comparison of the vibrations in the footrest of the ICE-based and E2W vehicles is shown in Figure 2. This test was conducted by riding the vehicle for 1 km and randomly shifting the gears as well as braking, recreating the actual driving scenario of a typical Indian road. It can be observed that the RMS acceleration after the vehicle was converted to an E2W decreased when compared to the ICE-based two-wheeler. This is due to the absence of reciprocating parts in the electric two-wheeler. There was an approximately 85% decrease in the peak amplitude in the case of the E2W when compared to the ICE-based vehicle.

3.2. The 20 kmph Speed Test

Figure 3 shows the comparison of the footrest vibration before and after the conversion of the two-wheeler from an ICE-based vehicle to an E2W. This test was conducted by running the vehicle for a stretch of approximately 300 m at a speed of 20 kmph. The RMS value of the footrest decreased in the case of the E2W when compared to the ICE based-vehicle. However, the requirement for a suitable damping treatment was always appreciable.

3.3. The 30 kmph Speed Test

Figure 4 shows the comparison of the footrest vibration in the case of the ICE-based and electric two-wheeler. This test was conducted by running the vehicle for approximately 300 m at a speed of 30 kmph. The RMS value of acceleration decreased in the case of the E2W when compared to the ICE-based vehicle, as shown in the figure. However, the vibrations resulting from the E2W further require damping treatment in order to improve the rider’s comfort. Further, the calculation of the VDV as per Equation (1) gives scope to predict the rider’s comfort as per the ISO 2631 standard.

From Table 2, the VDV results for the test conducted at a random speed for a 1 km distance in the case of the ICE-based two-wheeler are higher than those for the E2W. This is because of the presence of a greater number of moving parts in the ICE two-wheeler and fewer moving parts in the E2W. As the engine is placed very close to the rider’s foot, the vibration is pronounced at that region. These vibrations are prone to causing the rider discomfort.

Observing the results from the 20 kmph speed test, the vibration is slightly decreased in the case of the E2W in comparison to the ICE-based two-wheeler. A dangerous VDV of 15.02 m/s^1.75 is observed at higher speeds in the 30 kmph test. This is because the VDV increases with the increase in the speed of the vehicle.

The overall results indicate that, even though the VDV is decreases in the case of the E2W when compared to the ICE-based two-wheeler, an efficient method of vibration dampening is very much essential for achieving good rider comfort in comparison to the ISO 2631 standard. As the current study compares the vibration at the footrest of vehicles, it indicates that a suitable damper design could effectively increase the rider’s comfort.

4. Conclusions

Vehicles, particularly two-wheelers, frequently experience whole-body vibration. The conditions of the road, the travelling speed, the vibration transferred to the human body, and the vibration absorbers in the vehicle play an important role in providing a safe and comfortable ride. Vehicles powered by IC engines are prone to causing considerable vibrations due to the presence of reciprocating parts. However, the comfort of electric vehicles mainly depends on the condition of the road. E2Ws, when travelling over potholes, cracks and humps in the road, encounter jolts and vibrations that can severely affect the rider’s comfort in the long run. Several locations on the two-wheeler, such as the footrest, can transfer these vibrations to the human body, causing discomfort. The current study on the footrest compares the vibrations and rider’s comfort in the case of an ICE-based and electric two-wheeler, and the following conclusions are drawn:

• The RMS acceleration values decrease in the E2W when compared to the ICE-based two-wheeler. This is due to there being fewer moving parts in the E2W when compared to the ICE two-wheeler.
• Even though the VDV decreases in the case of the E2W when compared to the ICE-based two-wheeler, the values increase with an increase in the speed. This is due to an increase in the vibration amplitude, resulting from the road and riding speed. Hence, a slow speed is always advisable for two-wheeler riders.
• Finding the strategic locations of vibration and a suitable damping treatment is essential in order to reduce these vibrations in two-wheelers; this is also the scope of future a study.