Gas Electric SUV

GEV1

Plug-in Hybrid

 

 

This document describes the design of a Gas Electric SUV based on a 4 Cylinder Manual transmission FWD 2001 Ford Escape.  I hesitate to call it a PHEV (Plug in Hybrid Electric Vehicle) because it is very different than most typical Plug-n Hybrid Vehicles.

 

This design includes two fairly independent drive trains.  It retains all of the pre-conversion, ICE Front Wheel Drive components.  To this is added, an independent battery electric rear wheel drive system.  The rear differential from a 4WD Escape will be installed and driven by an 11 inch Netgain TransWarp motor.

 

Most Hybrids have a highly interactive computer controlled small battery electric drive system that is turned on and off to optimize gas mileage.  These systems are very efficient.  But, they often operate without one piece of important information.  This is the intention of the driver.  In systems with an EV Mode switch, the driver has some control.  The driver knows, for instance, if the planned round trip is within the range of the battery and can be made without gas.

 

This design uses the EV mode switch and no computer.  If your planned round trip is within the range of the battery, you use EV Mode.  When you plan to drive beyond the range of the battery, use gas on the outbound trip and switch to electric on the way home when within the range of your destination in battery mode.

 

The EV mode switch is actually a fuel pump and ignition, kill switch.  If you start in EV mode, the fuel pump will not come on.  Just turn the key on without the extra click to start.  Put the transmission in neutral and drive away.

 

In electric mode there is no Air Conditioning and no Power steering.  A check valve is added to the power steering system between the high-pressure line and the low-pressure line to eliminate the resistance of the pump when the ICE is off.

 

The Accelerator peal linkage will operate both the engine and the motor.  For this reason only one mode can be used at a time. 

 

If a 2008 or later is used it has electric Power steering.  If a 2001 – 2007 is used electric power steering may be added at some point.  A 2001 4-cylinder FFWD Manual transmission has been purchased for this project.

 

 

A 3.0 V6 is not good choice because of weight problems. Automatic transmission presents problems in EV mode.  It is expected to have too much drag in EV mode.  It might work if placed in neutral, but is probably not good for the transmission for anything more than short distances.  It also presents a weight problem. The V6, Automatic is 550 pounds heavier than 4 cyl, 5-speed manual. 

 

There are further reasons to use the FWD 4 Cylinder with the 5 speed Manual Transmission.  There is more room for additional components.  There is no Transfer Case, crossover pipe, resonator and front drive shaft half.  The simplified exhaust system and drive train make motor placement and connection to the imported rear end less complex.  Tis is not to say simple or, perhaps, even possible.

 

There is no shifting and reverse in Electric mode is done with a switch and a reverse contactor.

 

An electric vacuum pump will provide vacuum boost in both electric and gas mode.

 

An 11 inch Netgain series wound electric motor will be mounted between the transfer case and the differential by shortening the drive shaft.

A Kelly 650 Amp controller with regenerative braking will be used.  Initially an on/off brake switch will operate it.  At some point brake pedal position may be used to provide variable regen. There will be a switch on the dash so it can be disabled during gas mode.  If enabled during gas mode the traction battery can be charged at the cost of reduced gas mileage.

 

 

An Iota DC to DC converter will be used to keep the accessory battery charged during EV Mode.

 

The all-electric range Objective is 8 – 16 miles.  The plan is to use 12 - 50 AH, Group 22, 12V, Gel Batteries.  These batteries weigh 40 pounds each for a pack weight of 480 pounds and a pack voltage of 144 volts.  The range is based on keeping the pack above 50% SOC.  Thr payload will be 367 pounds.

 

At some later point the Battery Pack may be upgraded to LiFePO4 batteries.  This will consist of 48 – 100 AH, 3V elements weighing 7.75 pounds each for a total pack weight of 372 pounds and a payload of  475 pounds increasing the range to over 30 miles.  In this pack more of the capacity can be safely used.

 

Bleow are some of the alternatives considered.

 

The most critical part of this design is the rear wheel drive train.  A FWD candidate vehicle was chosen because it has no transfer case and no computer knowledge or control of the rear axle.

 

The rear axle from a 4WD Escape will be installed.  This axle will be driven with the 11” Netgain motor through a shortened rear section of stock drive shaft.

 

Installation of the rear axle should not be a problem, because this vehicle comes in both FWD and 4WD or AWD models. The rear end of the FWD model accommodates both the differential and the drive shaft.  The rear springs from an Escape with the towing package will replace the current spring at the same time.

 

The axle ratio of the new rear end is important.  The lower the ratio the better.  A ratio between, 4:1 to 6:1, would be desirable.  Published rear axle ratios for this vehicle are confusing and unclear.  Published FWD final drive ratios vary by year.  Rear axle ratios seem to be consistently 2.93:1.

 

Final Drive Axle Ratio (:1) 4.588

 

First Gear Ratio (:1) 3.666

Second Gear Ratio (:1) 2.058

Third Gear Ratio (:1) 1.310

Fourth Gear Ratio (:1) 1.030

Fifth Gear Ratio (:1) 0.837

Reverse Ratio (:1) 3.454

 

By driving the car and observing speed and RPM, the front wheel final drive ratio has been calculated to be 4.9:1

 

Fourth Gear   speed      RPM

30        1800

40        2400

50        3000

60                3600

 

Calculated Axle Ratio   4.9:1

 

More work needs to be done to assure efficient battery usage and acceptable vehicle performance.  Without a favorable rear axle ratio, the project cannot be completed successfully.

You can see in the photo below the hole at the center of the rear end where the differential will bolt in.

 

 

In this photo you can see the differential with the half axles hanging from straps. To the left is the Rotary Blade Coupling (RBC).  To the right is the two-piece drive shaft.  Unfortunately neither half has a universal at both ends.  The front half shaft has a universal at the rear to connect to the center bearing support.  The rear half shaft also has a universal at the rear to connect to the RBC on the front of the differential..  The half that attaches to the differential will be customized, with a universal at both ends, and cut to the require length so that it fits between the motor and the differential.

 

Above is the FWD rear end and below is the 4WD rear end.

 

 

The motor will be mounted forward of the fuel tank.  The fuel tank is shaped to accommodate the RBC and the drive shaft.  On the stock 4WD vehicle there is a universal joint is at the center of the drive shaft.  The intention is to connect the universal on the front end of the modified rear half of the drive shaft, to the universal joint on the rear end of the motor.  Hopefully the rear end of the rear half of the drive shaft will fit with the differential as in the stock setup.  The problem lies in the fact that the universal on the 11-inch motor may be lower than the center support bearing for the original two piece drive shaft. 

 

 

Rotary Blade Coupling (RBC)

 

High revolutions of the drive shaft causes turbulence in the RBC increasing pressure closing the clutch in the RBC and engaging the rear axles.  Is it possible that high revolutions of the rear wheels will not cause turbulence in the fluid and not engage the clutch in the RBC?

 


An inside look at Ford’s rotary blade coupling shows all key parts, including an electromagnetic lockup clutch, which actually is held by a ball in a ramp to eliminate the need for continuous current flow to the clutch to maintain lockup.

In the above drawing, on the left of the RBC is the Differential and on the right is the drive shaft. The Blue Magnetic lock up is on the left.  The clutch blades are in the center and the output shaft is on the right.   It is my guess, and I wish I knew for sure, that the drive shaft turns the input shaft to the RBC and the clutch blades through a permanent hard connection.  The RBC output shaft cannot turn the clutch blades until the clutch is engaged.  At that point it is merely turning with the blades.  The torque is provided by the drive shaft.  When torque from the drive shaft stops, the clutch looses momentum and pressure drops and the clutch disengages.

This device balances torque between the front and rear wheels in a 4WD Escape.  This is a FWD vehicle has no transfer case and will have only the rear end from a 4WD.  I will connect the 11 inch motor to the RBC using a shortened modified drive shaft.

 

It is my understanding that the 2001 to 2004 have the same RBC. It is also my understanding that during this period the RBC has both a 3 disc silicone filled hydraulic clutch and a magnetic lockup.  I am concerned about the hydraulic mode, magnetic lock up off.

 

In the RBC, when the input shaft spins at rpm higher than the output shaft the RBC clutch engages.

 

On the other hand if the output shaft is spinning and the input shaft is not, will the RBC clutch engage?

 

All documentation focuses on difference in RPM between the input and output RBC shafts.

 

Does it really mean that the only difference that matters, is when the input shaft rpm is significantly higher than the output rpm in the RBC, or will an output RPM higher than the input also engage the RBC clutch?

 

This can't happen on a stock 4WD Escape unless towed front wheels up, but it is my conclusion that - the idle (motor off) input shaft will not lock and turn when the output shaft is turning as a result of rear wheel rotation.

 


Another view of the rotary blade pump shows the blade, with its cutout sections and rectangular protrusions. This coupling is installed just forward of the rear axle housing.

 

RBC Descriptioin:

http://www.romaine.name/escape//how_4x4_works.htm

Transfer Case Description:

http://www.vibratesoftware.com/html_help/html/Diagnosis/Transfer_Case_Gear_Ratios_Main.htm#Ford

 

 

A 2002 manual transmission 4WD Ford Escape can be safely flat towed at speeds up to 55 MPH for unlimited distances.

http://www.motorhomemagazine.com/output.cfm?ID=201529

 

On a 4x4 vehicle, it is recommended that the vehicle

be towed with a wheel lift and dolly or flatbed equipment with

all the wheels off the ground.

 

http://www.motorcraftservice.com/vdirs/quickref/RTS%202002%20Towing%20Manual.pdf

Measurements

 

There are two body rails that run down the center of the car.  The outside dimension is 14 inches.

At the midpoint in the length of these rails is a bridge between the two designed to support the center drive shaft bearing.  Two bolts, on 7 inch centers, hang from the bridge

 

 

Bottom of Differential frame to ground               9”

From Bottom of Rail to Ground                                    13’

Floor to Ground                                                           16”

Out side Center Rails                                                    14”

From Center bearing to front end of Rail                       26”

 

Bearing Bolt centers                                                      7”

Rail ends to bearing bolts passenger side                       17”

Bearing bolt to rear rail end driver side              18”

Rail length Driver side (longer rail)                                 36”

 

If the 9 inch motor can be located close to the floor between thee body  rails, that leaves 7 inches of ground clearance between the bottom of the motor and the ground.

 

This car would work fine with a 9 inch motor through a transmission in second gear.  My truck is an example of this.  It weighs 4500 pounds and runs fine in second gear at 144 volts with a Curtis 500 amp controller.

 

The Escape will weigh less than 4000 pounds and has a 2.93 rear axle ratio and the Rotary Blade Coupling.  The more I understand the RBC, the more it sounds like an asset.  The silicone fluid coupling actually reduces stress on the differential from torque of the electric motor.  While at the same time offering the magnetic lock up for the option of applying full torque.

 

Some time ago, Lowell Simmons described to me a dual chain direct drive system he has used successfully.  If I had a 3:1 link between the motor and the drive shaft, I would be approximating the 8.39 ratio I have in second gear in my truck.  The 9 inch motor is a better fits than the 11 inch.  The center of motor shaft is lower than the rear end shaft input.  A gear reduction between the motor and the drive shaft offsets the motor output.  Whether a chain drive or a gear box using 30 teeth on the motor shaft and ten teeth on the drive shaft and leaving the rear half shaft on its center bearing at the center of the car, we may have better alignment.  This results in an 8.79 ratio, slightly lower than my truck in second.

 

How does EPT2 run in 5th gear (2.95:1) with a 9 inch Netgain?

 

As an experiment, I have driven my pickup truck with the 9 inch motor and the 500 amp Curtis controller in 5th gear.  In 5th gear the truck has a final drive ration of 2.95:1 almost identical to the Escape rear axle ratio of 2.93:1.   I did not expect this to work if at all.  I also expected very high current draw compared to normal driving in 1st and 2nd gears.

 

It actually was able to get moving slowly, and once over 15 mph was more responsive all with current draw of no more than twice normal for short periods of time.  This all very subjective and would not be acceptable performance in any car.  But it gives me hope that with a larger motor and/or a higher capacity controller with different programming, there may be hope for direct drive with a 2.93:1 axle ratio.

 

Will the Motor fit under the car?

 

I have purchased two 12" cake pans and some sheet metal.  I plan to make a model of the 11 inch motor and mount it under  the car.  The motor is actually 111.45 inches in diameter, so this will be close to actual size.  Netgains mockup costs over $300.

 

I am interested in advice from anyone who has done either chain or gear reduction successfully.

 

 

 

The Questions

 

Is an 11 inch Netgain TransWarp motor large enough for direct drive in this 3800 pound car with a 2.93 ratio differential?

 

 

How will it be suspended?

 

Is the rear half of the drive shaft suitable for use between the motor and the differential?

 

Does it have a universal joint on both ends?

 

Can the RBC tolerate running in gas mode with the input shaft idle and the rear wheels turning?

 

Can the RBC run void or partially void of silicone fluid?

 

Can Locking Hubs be used to eliminate RBC rotation in the rear?

 

Can Locking Hubs be used to eliminate drive train drag in the front?

 

What are the consequences of driving in gas mode with the electric motor, locked to the rear wheels and, spinning?