Testing a Heavy Duty Class 8 Truck

Testing a Heavy Duty Class 8 Truck

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Description: Electrified accessories, Hardware-in-the-loop Testing of a Heavy Duty Class 8 Truck,HARDWARE-IN-THE-LOOP (HIL) TEST STAND, DESCRIPTION, FUNCTIONALITY, Hardware and Software Boundaries for the HIL Test Stand, Electric Engine Fan, Marine Tactical Vehicle Replacement.

Author: Ashok Nedungadi and John Bishop (Fellow) | Visits: 1630 | Page Views: 2232
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Les Rencontres Scientifiques d'IFP Energies nouvelles - Int. Scient. Conf. on hybrid and electric vehicles � RHEVE 2011 6-7 December 2011 � Proceedings � Copyright � 2011, IFPEN

Hardware-in-the-loop Testing of a Heavy Duty Class 8 Truck
Ashok Nedungadi, John Bishop
Southwest Research Institute, San Antonio, TX 78228, USA, anedungadi@swri.org Southwest Research Institute, San Antonio, TX 78228, USA, john.bishop@swri.org

Abstract -- Hardware-in-the-loop Testing of a Heavy Duty Class 8 Truck -- This paper describes an engine-in-the-loop test facility to quantify the fuel economy benefits of electrified accessories. Engine emissions were not included in this study. The vehicle modeling and simulation software that is at the core of this component-in-the-loop test is mentioned. The two main mechanical accessories of the heavy duty Class 8 truck, the engine fan and water pump, were electrified. The reasoning for this is also presented in this paper. The configuration of the electric fan and water pump are described in more detail. Two different on-road driving cycles are compared in terms of fuel consumption of the engine with mechanical and electrical accessories. Discussions include advantages and disadvantages of electrified accessories, and which drive cycles appear to favor accessory electrification.

Electrified accessories continue to be a major focus for engine OEMs to gain additional fuel economy. In the past, the heavy truck accessories that have been targeted include (ordered in terms of impact on fuel economy): engine cooling fan, air-conditioning compressor, brake system air compressor, engine water pump and power steering pump. The motivation for targeting vehicle accessory systems are: (a) the mechanical accessory systems are generally designed to meet a low engine speed requirement; (b) their design generally results in the accessories being oversized during higher engine speed operation; (c) some accessory systems have a constant power draw even when not in use [Ref 1, 2]. Figure 1 shows examples of accessory systems that have excessive capacity at higher engine speeds [Ref 3].
35 30 25 20 15 10 5 0 0 1 2 3 4 5 ROTATION SPEED (X 1000 rpm)

In addition to improved fuel economy, the literature has reported several advantages for accessory electrification, namely: improved vehicle performance, accessory performance, and engine cooling and improved emissions due to more effective thermal management with better engine cooling/heating distribution [Ref 4, 5]. The downside of electrified accessories is the potential need for a 42 V electrical bus that is not standard on current truck chassis. The truck industry has ample examples that quantify the fuel economy benefits of electrified accessories over transient and highway driving cycles. It should be noted that the examples and the fuel savings discussed within this paper are application and duty cycle dependent. A 1.2% improvement in fuel economy was reported for a Volvo tractor with a Cummins N14-480 Hp (343 kW) engine over the EPA FTP drive cycle [Ref 6]. The repeatability between individual tests was not available in the cited reference. A Peterbilt tractor/trailer with a Cummins ISL 246kW engine reported energy consumption of an electrical pump to be from 6% to 19% less than that of the mechanical pump [Ref 7]. Faster warm-up in an automotive diesel engine reduced emissions and a Toyota Prius demonstrated improved fuel economy of 1% to 4% [Ref 8, 9]. To further demonstrate this, a study was conducted of a heavy tractor truck with a 246 kW engine that was driven across the U.S; the results are summarized in Table 1 [Ref 10]. The study was performed during the summer months and utilized the air conditioner during most of the trip. The vehicle used 836.6 Liters of diesel fuel during the 3952 km trip. It was estimated that the electric cooling fans saved 349.7 liters of diesel fuel during this trip [Ref 10]. Much of the fuel savings is due to a more efficient and smaller air-conditioning compressor and

Figure 1: Accessory Systems with Excessive Capacity

FLO W RATE (L/m in)

Les Rencontres Scientifiques d'IFP Energies nouvelles - RHEVE 2011

electric engine cooling fans that replaced the high power mechanically driven engine fan.

Table 1 � Energy Savings Summary for a Heavy Tractor Study Subsystem Mech. Elec. Energy Energy Energy (diesel L) Savings (diesel L) (diesel L) Water Pump Cooling Fans A/C Comp. Air Comp. Total 10.8 351.3 47.1 13.9 422.7 1.1 1.7 3.6 0.9 7.0 9.7 349.7 43.5 13.0 415.7


Figure 2 shows a conceptual illustration of the HIL test stand at Southwest Research Institute (SwRI).

The automotive literature has reported several applicable concepts for replacing today's engine driven accessories, namely variable speed belt drives, two speed belt drives, electric cooling fan and variable cooling fan drive. Although, all the aforementioned concepts reduce power requirements on the vehicle, there are some obvious disadvantages, such as complexity of the variable belt drive, overheating of the variable fan connection, and the shift shock for the two speed belt drive systems [Ref 11, 12, 13, 14]. The literature has similar data on reduced energy of electric steering pumps [Ref 12], brake system air compressors [Ref 10]. A host of competitive accessory systems have been proposed and studied in the literature, namely continuously belt drive systems, twospeed belt drive system, viscous fan clutch, magnetorheological couplings, variable air conditioning compressors, and variable displacement pumps [Ref 12]. Finally, it has been reported that HC and CO emissions can be reduced by 17% with a 10% increase in NOx emissions as a result of better engine cooling that results in faster warm-up and improved thermal control of the cylinder head and block [Ref 13, 14]. The main conclusions that can be drawn from the above literature survey on electrified accessories are that the fuel economy benefits are dependent upon vehicle type, drive cycle and the type of accessory drive used. With the multitude of competitive accessory systems currently available in the market, the cost for testing each vehicle/accessory drive combination on a chassis dynamometer is cost and time prohibitive. The concept of hardware-in-the-loop testing has been proposed as an alternative to quantify the performance of a hardware component in a fictitious vehicle executing a drive cycle.

Figure 2: Conceptual Illustration of the SwRI HIL Test Stand

The main components of the HIL test stand, illustrated in Figure 2 are: � A Cummins ISL-425 Hp (317 kW)/1695 Nm (Model year 2008) � This is the main test component in the HIL setup (engine-in-the-loop) � A GE absorbing/motoring 600/550 Hp (447/410 kW) @ 1640/3000 RPM � Torque transducer coupled to the engine (HBM T10FS, 10 kN-m � This is used to measure engine torque in steady state and transient conditions. � High velocity fan � Triangle Engineering VAB48/15 Hp (11 kW) with a variable frequency motor drive � The output flow from this fan can be varied to simulate air flow into the engine radiator of a vehicle moving at various speeds. � A Micro Autobox from dSPACE for data acquisition and control purposes. � VPSET (Vehicle Powertrain Systems Evaluation Toolkit) � This is the vehicle modeling and simulation software that complements the HIL test stand with software modules of the fictitious vehicle powertrain and drive cycles [Ref 15]. Figure 3 shows the actual engine-in-the-loop test stand

Les Rencontres Scientifiques d'IFP Energies nouvelles - RHEVE 2011

Figure 3: The engine-in-the-loop test stand

Figure 4: Hardware and Software Boundaries for the HIL Test Stand



The vehicle being tested in the HIL test stand is first modeled using the VPSET vehicle modeling and simulation software tool. VPSET is a general purpose software tool that is based on the Matlab/Simulink computing environment. In the case of the engine-inthe-loop test, the engine model is omitted in the vehicle model. In place of the engine model, the real engine is coupled to the vehicle model via the torque and speed sensor. The vehicle model receives analog torque and speed signals that are then converted into model variables that drive the vehicle powertrain in the simulation model. It is this combination of hardware and simulation software that makes up the HIL test stand. The torque produced by the hardware engine in the test stand is fed into the dynamic vehicle model in simulation, which results in a vehicle speed. This vehicle speed is used to calculate a new engine speed, which becomes the dynamometer speed setpoint for the engine in the HIL test cell. The driver module in the simulation model generates an engine torque command based on desired and actual vehicle speed. This engine torque command serves as the throttle command for the engine in the HIL test cell. This control loop is maintained at 100 Hz. Since the dynamometer is in speed mode, it can emulate transmission shifting adequately. In this HIL test stand, the engine behaves as if it were in the actual vehicle executing the driving profile. A Micro Motion fuel rate sensor, along with a day tank and heat exchanger to maintain fuel temperature, measures the instantaneous fuel rate of the engine in the HIL test stand. Figure 4 shows the boundaries of the hardware and software for the HIL test stand.

Table 1 summarizes the validation of the HIL test stand. Actual vehicle test data was compared with HIL predicted fuel economy. These comparisons of the HIL test results with actual vehicle test data for a drive cycle with city and highway driving cycles.
TABLE 1: Comparison of HIL with Actual Vehicle Test Data

Drive Cycle

Test Data (mpg)

HIL Average/Standard Deviation (mpg) 4.68/0.028 4.485/0.012

Percent Difference (%) 0.4 0.9

Urban driving UrbanHighway Combined

4.698 4.443

To further validate the engine fan on-off logic, the temperature at which the engine fan turned on (engine coolant outlet temperature = 950 C) and that at which the engine fan turned off (engine coolant outlet temperature = 900 C) was compared to a similar vehicle that was tested on a chassis dynamometer over the same drive cycle. The aforementioned temperatures were determined so that the engine on the HIL test stand had similar on-off periods as the engine on the chassis dynamometer.



The engine fan and water pump were the only two accessories that were selected for electrification. The main reason for this was that the engine fan and water pump were the mechanical accessories with the highest mechanical power drain on the engine. The AC compressor was not used in the HIL test. Figure 5 shows the electrified engine fan assembly with a series of 8 fans arranged on a structure that has the same "foot-print" as the existing current cooling fan of the Cummins ISL engine. Each electric fan is an EMP FiL11 24 Volt fan with the ability for independent speed control and can consume a maximum of 480 W at maximum cooling potential. The 8 electric fans shown in

Les Rencontres Scientifiques d'IFP Energies nouvelles - RHEVE 2011

Figure 5 can be speed controlled to optimize engine cooling.

Figure 6: Trapezoidal Driving Profile

Figure 5: The Electric Engine Fan

The electric water pump is an EMP WP29 that operates on a 24 Volt bus and consumes a maximum of 480 Watts at full power for maximum cooling. A total of two electric water pumps in a parallel configuration were found to be necessary to provide adequate cooling of the engine block. The stock alternator of the Cummins ISL engine was replaced with a 28V/200 Amp Leece-Neville Model A0014964PA high capacity alternator.

Table 2 summarizes the fuel economy for the HIL tests using the trapezoidal driving profile in Figure 6. The average percent error between desired and actual distance travelled, for the tests summarized in Table 2, is 2.5%. The engine fan was ON for 68% of the drive cycle duration. In a parallel test, the effect of the engine fan alone on fuel economy was analyzed by turning off the engine fan and providing engine cooling with the external fan of the HIL test stand. The temperature that the external fan was turned on to maximum speed to 0 cool the engine was set at 95 C. When the engine coolant outlet temperature reached 900C, the external fan speed was set to be proportional to vehicle speed. This test provides an upper estimate of potential fuel economy savings as a result of an electric engine fan. Therefore, for the tests presented in this paper, the electrical energy that would be consumed by the electric fans was not accounted for. The electrical energy to run the fans will be accounted for in future tests. Table 2 shows an average of 1.9 % fuel economy improvement when the engine fan is turned off. Figures 7 and 8 show the engine speed and torque operating points and histogram, respectively, while the vehicle is executing the trapezoidal driving profile. The vertical axis of Figure 8 is seconds totalized at each operating condition. These figures will be important for future optimization of the electrical accessory control.



The vehicle model that was simulated in the HIL test stand is a MTVR (Marine Tactical Vehicle Replacement) MK-23 with a gross weight of 12,610 kg. The selected driving cycle was a trapezoidal driving cycle (see Figure 6) since it has an acceleration, steady state cruise and deceleration region. These regions were used to study the behavior of the engine in the HIL test stand during a typical acceleration, cruise and deceleration.

Les Rencontres Scientifiques d'IFP Energies nouvelles - RHEVE 2011

Table 2: HIL Test Results of the Baseline MTVR over a 50 mph (80 kph) Trapezoidal Driving Cycle

Trapezoidal 50 mph (80 kph) Driving Cycle Test # Fuel Economy (mpg) Engine Fan ON 6.16 6.22 6.16 6.15 6.15 6.165 0.026 Fuel Economy (mpg) � Engine Fan OFF (Simulated Electric Fan) 6.28 6.22 6.28 6.30 6.35 6.285 0.044
Figure 8: Histogram of engine speed and torque for the Trapezoidal profile

1 2 3 4 5 Average Standard Deviation Error Band of average at 95 % confidence level


0.054 Table 3 summarizes the HIL tests over the heavy heavyduty diesel truck transient cycle (HHDDT). This drive cycle is shown in Figure 9.

Figure 7: Engine speed and torque Operating Points for the Trapezoidal Profile Figure 9: The Heavy Heavy-duty Transient drive cycle

Les Rencontres Scientifiques d'IFP Energies nouvelles - RHEVE 2011

Table 3: HIL Test Results of the Baseline MTVR over the HHDDT Cycle

HHDDT Driving Cycle Test # Fuel Economy (mpg) Engine Fan ON Fuel Economy (mpg) � Engine Fan OFF (Simulated Electric Fan) 6.37 6.33 6.37 6.38 6.32 6.354 0.026 0.032

1 2 3 4 5 Average Standard Deviation Error Band (%)

6.38 6.32 6.29 6.42 6.28 6.338 0.057 0.071

3. "Development of the Variable Displacement Vane Pump for the Automotive Power Steering System", SAE Paper 930261, T. Mochizuki 4. "Development and Verification of a Heavy Duty 42/14 V Electric Powertrain Cooling System", SAE Paper 2003-01-3416, R. Chalgren and L. Barron 5. "Advanced Engine Cooling Thermal Management System on a Dual Voltage 42V-14V Minivan', SAE Paper 2001-01-1742, M. Chanfreau, et al. 6. "Front End Auxiliary Drive (FEAD) Configurations Focussing on CO2 Benefits", SAE Paper 2004-010596, S. Akehurst et al. 7. "Electrification and Integration of Accessories on a Class 8 Tractor", SAE Paper 2005-01-0016, B, Surampudi et al. 8. "Effect of New Cooling System in a Diesel Engine on Engine Performance and Emissions Characteristics", SAE Paper 2009-01-0177 9. "Development of a New 1.8-Liter Engine for Hybrid Vehicles", SAE Paper 2009-01-1061, N. Kawamoto et al. 10. "Accessory Electrification in Class 8 Tractors", SAE Paper 2006-01-0215, J.Redfield et al..

Table 3 shows an average of 0.25% fuel economy improvement when the engine fan is turned off. The average percent error between desired and actual distance travelled, for the tests summarized in Table 3, is 0.1%. The engine fan was ON for 13.5% of the drive cycle duration.



This paper discusses the advantages of electrifying engine accessories on a heavy duty truck. The presented HIL concept can be expanded to any powertrain component to understand how it performs in a virtual vehicle, while experiencing the same operating demands as if it were in a real vehicle. The fuel economy savings from electrification of the engine accessories are drive cycle dependent and can range from less than 1% to 2% in fuel savings, depending on engine fan cycle frequency and duration. Drive cycles with longer durations of highway speeds (higher engine fan ON time) appear to favor drive cycles with highwayurban speeds in terms of fuel savings. Currently, the team is working on advanced engine fan and water pump controls to maximize fuel savings for heavy truck applications.

11. "Continuously Variable Accessory Drive System", SAE Paper 970007, S. Yasuhara et al. 12. "E3 System � A two Speed Accessory Belt Drive for Reduced Fuel Consumption", SAE Paper 2008-011521, I. Ali et al 13. "Adaptive Control of an Externally Controlled Engine Cooling Fan-Drive", SAE Paper 2006-01-1036, N.Bhat et al. 14. "Fuel Cell APU for Silent Watch and Mild Electrification of a Medium Truck", SAE Paper 200401-1477, Z. Filipi, et al. 15. A. Nedungadi, M. Pozolo, M. Mimnagh, "A general purpose vehicle powertrain modeling and simulation software � VPSET", World Automation conference 2008, Big Island, Hawaii

1. "The System Performance Benefits of Lubrication Flow Control", SAE Paper 2004-01-2687, P.G. Evans and K. Johanson 2. "Magneto-Rheological Coupling Based Hydraulic Power Steering: Low Cost Solution for Fuel Economy Improvement", SAE Paper 2009-01-0046, B. Murty et al.