Hybrid Car Proposal

Jeremy Rutman - Last update 9.2005

Introduction

We would like to take an existing car body and convert it to an electric/gas hybrid. The purpose is to

a) demonstrate increased efficiencies due to hybrid drive

b) provide a platform for demonstrating/testing various alternative energy systems, including polymer fuel cells (Tel Aviv University), solid oxide fuel cells (Technion), and composite flywheels (Technion)

c) demonstrate use of alternative fuels - boron hydride cells (Medicel), and biodiesel.

Background

A hybrid vehicle combines two or more power sources to combine the environmental benefits of electric drive (low emissions) with the range and power of an ICE (Internal Combustion Engine). There are several varieties of hybrid, the main ones being series and parallel.

Series Hybrid

The series system uses an ICE to run a generator that charges the batteries. These batteries power the electric motor that applies torque to the wheels.

Parallel Hybrid

The parallel system uses both ICE and electric motor to apply torque to the wheels.

Split Parallel Hybrid

A variant of the parallel, this system uses an extra set of drive wheels to separate the electric and ICE drives.

“Combined Series-Parallel” (Toyota Prius)

The combined series-parallel as in the Prius uses a power-splitter to vary the fraction of total ICE torque sent to the generator.

A brief comparison is shown below [[1]]

Comparison of series to parallel hybrid

After considering the various possibilities we chose a series hybrid since it is mechanically simple and is compatible with future improvements (fuel cell or flywheel power sources). The split-parallel is a possibility using a Subaru 'tender'; this would allow us to avoid the double conversion of mechanical energy -> generator ->electrical energy-> electric motor (mechanical energy). One of the requirements we have arrived at is use of diesel; this allows use of 'biodiesel' [[2]], a non-polluting green alternative to regular diesel. The series hybrid is easy to do with diesel, just using a diesel generator. The split parallel is also doable with a diesel engine, but requires finding a 4wd diesel vehicle; the Subaru tender is not diesel.

MOTOR,CONTROLLER, GEAR, DIFFERENTIAL

We estimate the power required for reasonable operation of a 1000kg auto to be about 15kW continuous, 30kW maximum. As shown below, this allows one to climb a continuous ~17% grade at 30km/hr, or to travel at 100km/hr on level ground (assuming 2m² frontal area and wind resistance coefficient c_p=0.37)

Total power at 30km/hr for various grades

Total power to overcome wind resistance as function of speed

For all alternatives the motor/controller chosen are Solectria due to their high efficiency and foolproof operation. The combination of AC24 motor, DMOC445 controller, and AT1200PP provides 40kW max (17kW continuous) power to the wheels, and includes everything needed for the conversion including inverter, gearbox, differential, parking pawl, and user interface (connections to brake lights, speedometer, gas and brake pedals, etc.)

From the Solectria pdf’s : “The Solectria DS 5-90P Drive System features an AT1200PP Gearbox with internal differential and parking pawl. This drive system is designed with front wheel compact sedans in mind. Vehicle conversions are made fast and easy, because this single piece unit will easily replace the engine and transmission of many compact production front wheel drive vehicles.”

Batteries

For all systems we will need batteries in addition to the motor/controller and gearbox. The batteries we have priced so far include lead acid and NiMH. Lead acid are cheaper and more available while NiMH have ~ 2x energy density. Mercury cadmium batteries are environmentally unfriendly and slowly dropping out of the race. Lithium apparently have too low power densities to be useful here (e.g. Tadiran).

The Solectria controller runs from a battery voltage between 120VDC and 336VDC.

The peak power of the AC24 motor is unpublished, but its predecessor has a published peak of 40kW. From the graph above of the peak power for the DMOC445 controller it appears that ~170VDC is enough to provide this power. To facilitate charging from 220VAC systems a battery voltage of ~200-220VDC seems reasonable.

Assuming a battery voltage of 36V and impedance of 0.03Ω, then 6 batteries in series will run at 36V*6=216V with an impedance of 0.18Ω; charging this with a rectified 220VAC(rms) source will give a current of 22A, a reasonable current for a power of 5kW. To load down the generator more we can use another set of 6 batteries in parallel with the first set, halving the impedance and doubling the current (and power).

The total battery capacity (Watt-Hours) for the parallel hybrid system needs to be large enough to start the vehicle from rest and run it at low speeds, while the total capacity for series is determined by the generator power and desired driving time.

We took a somewhat arbitrary figure of 30 minutes total electric power at 10kW average, for a total battery capacity of 5kWH . Looking at lead acid and NiMH batteries we find that NiMH motorcycle batteries or Optima lead acid are good picks.

Various batteries found so far (considering lead-acid and NiMH) for 5kWH capacity

Generator

For the series system we will need a gas-driven source of electric power. In principle the possible sources include the fuel cell, gas turbine+generator, and ICE+generator. Removing the ‘exotic’ elements of fuel cell and gas turbine leaves the ICE+generator, which can be found on the market for reasonable cost.

*company*	*Part*	*engine*	*kW max*	*kW cont*	Kg	*g/kWh*	*fuel*	$	dimensions
Baldor	PC90VE		9kW	8kW	98.0			~2000
Baldor	PCM60RE		6kW				gas LP NG	1950
Baldor	DG6E	Hatz1B40	6kW	5.5kW	111.8		diesel	3242
Lombardini	6LD435			6kW	85.0		diesel	2443
Lombardini	12LD435			13kW			diesel	5231
Yanmar	YDG6000			6kW	134.0		diesel	3500
Yanmar	L100AE			6kW			diesel	3100
Yanmar	4W315			5kW	115.9		diesel	3500	82cmX64cmX55cm
Yanmar	DX4500	L70		3.6kW	32.7		diesel	1485
Yanmar	DX6500EC	L100		4.95kW	47.7			2645
norpro	5PD	lombardini 15LD400	5kW	4.5kW	51.8			2431	63cmX55cmX48cm
Honda	3W737			5kW	80.5		gas	1700	83cmX55cmX51cm
Honda	GX340			6kW			gas	1760
Honda	GX610-QDW		13.4kW		42.0	313	gas
Honda	GX620-QDW		14.9kW	10kW	42.0	313	gas	2723
Honda	HPP6-B		6.6kW	5.5kW	138.0		gas, LP, NG	2633	77cmX56cmX56cm
Coleman	PM0558023	GenTek OHV	9.6kW	8kW	110.5		gas	1600
baldor	pcm60re	robin subaru EN24	6kW	6kW	90.9		gas/LP/NG	2190	69cmX46cmX51cm

Prices for some small gensets

We see in the table above that diesels are more expensive than gas. The noise generated in either case is on the order of 76-80dB(A) at 7 meters. Conceivably the noise can be attenuated by the enclosure and system used for air cooling of the generator.

Energy efficiency of generator:

Looking at the Honda GX620-QDW we find a fuel consumption of 313g fuel (benzene) per kWh. At 10kW power(~90km/hr on level road) this corresponds to 10*313g/90km=3.4l/100km or 28km/l=67mpg.

Consumption info for the diesel Lombardini 6LD435 is not available; with our 'diesel' requirement this is one of the good candidates (cheaper and lighter than others).

Budget

Summing the prices and weights we come to the following table:

Weight and cost budget for series hybrid

Integration

We have made .dxf models of all the relevant parts (existing car frame, motor, generator, batteries) and have integrated all parts into the frame as shown below. The main point is to make sure a small car has enough space to fit everything. The generator comes with vibration isolation. The motor is mounted to thick aluminum strips bolted to the floor of the front engine compartment, to provide sufficient 'contra' against the torque of the motor.

Status

We currently have the facilities (professional garage and tools), personnel (team of technion students, retired mechanics, and some interested people), and authorization (from Ministry of Transportation) to carry out the project. The bottom line is that we are stuck due to lack of funds.