Experiment Design

𝐑𝟏(𝑖) = 𝑟1 ( 3.41 )

3.4 Driving Experiments and Data Analysis

The longitudinal control driver model was validated in the CUED driving simulator using both the drive-cycle following and car following scenarios.

3.4.1 Experiment Design

The CUED driving simulator has been used for a variety of experiments since its conception in 2003. At the start of this project, its software and hardware were upgraded by the author of this thesis to reflect improvements in technology.

The simulator has a fixed base and three 4K 65 inch screens providing the driver with a 120° field of view. The seat is positioned so that the vertical distance between base of the seat and the pad of the pedal is the same as that measured in a Volvo truck cab. The horizontal distance between the seat and the pedal is also set to match the Volvo cab, taking into account that both the Volvo seat, and simulator seat are adjustable in the longitudinal direction of the vehicle. No other controls are available to the driver. Figure 3-18 illustrates the layout of the driving simulator.

96 Driver Model

Figure 3-18 – Driving simulator plan view

The simulator operates using Simulink Real-Time over three computers – the Host PC, Target PC, and Audio PC. The Target PC operates the vehicle model in real time and interfaces with the analogue sensors; the Host PC produces the graphical interface of the simulator and the Audio PC produces an engine sounds audio track to provide extra speed feedback to the driver.

In the Drive-Cycle following task, only the centre screen is used. The driver is presented with a graph previewing the next four seconds of speed demand and illustrating the past four seconds of speed demand and achieved speed.

In the car-following scenario (Figure 3-19), all three screens are used. A virtual driving environment was created using Simulink 3D Animation. The virtual road consists of a straight road with houses lining either side. The wide field of view assists with the driver’s perception of speed.

Adjustable Seat Accelerator

Pedal Three 65 inch screens

forming 120° driver field of view

3.4 Driving Experiments and Data Analysis 97

Figure 3-19 – Driving simulator set up for a car following scenario

The Target PC records the three pedal signals, pedal position, pedal force, and feedback force, at 50Hz. The simulated vehicle speed and displacement are also recorded at 50Hz. These signals are fed to the Host PC for storage.

The noise synthesizer’s purpose is to produce an additional feedback loop to the driver, incorporating engine and vehicle information through the frequency spectrum and amplitude of engine and vehicle sounds. Specifically, engine noise and tyre noise and recreated, with the aim of improving the driver’s perception of speed. The Host PC sends on the simulated vehicle speed and recorded pedal positon via Ethernet connection to the Audio PC.

At 0.02s intervals, the Audio PC assesses the speed and pedal position from the Host PC. In order to represent the engine and tyre noise of the vehicle, two key frequencies, the engine noise centre frequency and tyre noise centre frequency, are then calculated using equations ( 3.42 ) and ( 3.43 ) below:

𝑓𝑒𝑛𝑔 =

𝑣𝐺𝐺𝑒𝑎𝑟𝐺𝐹𝐷

𝑟𝑊ℎ𝑒𝑒𝑙

98 Driver Model 𝑓𝑡𝑦𝑟𝑒 =

𝑣 𝑙𝑡𝑟𝑒𝑎𝑑

( 3.43 ) where 𝑙𝑡𝑟𝑒𝑎𝑑 is a characteristic length of the tyre tread. For the trucks modelled here, the tyre tread

length is set to 5cm.

Two tenth order band pass Butterworth filters are defined to produce engine and tyre noise. The centre frequencies from ( 3.42 ) and ( 3.43 ) are used and each filter has -3dB cut-off frequencies at 90% and 110% of the centre frequency. Each filter is then applied to a 0.2s clip of white noise, before the two clips are summed in the time domain.

A gain is applied to define the amplitude of the new signal as

𝐴𝑛𝑜𝑖𝑠𝑒 = 1 2( 𝜙𝑝𝑒𝑑𝑎𝑙𝑣 𝜙𝑚𝑎𝑥𝑣𝑚𝑎𝑥 + 1) ( 3.44 )

Figure 3-20 illustrates the complete sound process in block diagram form. The noise signal is output to a set of headphones to provide the driver with audio feedback.

Figure 3-20 – Audio generation in the driving simulator. Equation numbers are included for the centre frequencies of the noise filters, and of the amplitude function

3.4.2 Participants

Nine human drivers were selected to participate in the validation of the driver model. The drivers were between 23 and 55 years old and all held driving licences. One out of the nine drivers were

Tyre Noise Filter ( 3.43 ) Engine Noise Filter ( 3.42 ) White noise 𝑣

+

+

𝜙

3.4 Driving Experiments and Data Analysis 99 female. Drivers 1 to 7 were non-HGV drivers, and drivers 8 and 9 were professional, and experienced, HGV drivers.

3.4.3 Procedure

The experiment was divided into two halves – the drive cycle scenario and the car-following scenario.

In the first scenario, drive cycle following, the Modified Millbrook Suburban Drive Cycle for HGVs was set as the target speed. The driver was given a practice run through to familiarise themselves with the behaviour of the vehicle and the dynamics of the pedal. Drivers were asked to follow the target speed. The test was then completed three times, to improve the reliability of the results.

In the second scenario, car following, the speed of the target vehicle was set as the Modified Millbrook Suburban Drive Cycle for HGVs. Again, the driver was allowed a familiarisation run to get used to the virtual world. Drivers were asked to follow the vehicle in front at a safe distance, as they normally would on the road. Again, once the familiarisation run was completed, the test was repeated three times, resulting in four runs in total.

When all drivers had completed the experiment, the data was analysed and driver behaviours compared.