# Automotive Coupling electric motor to gas engine in series

1. Oct 19, 2016

### Roberto palacio

Would it be possible to couple and electric motor to gas engine in series so both would increase the overall power.I currently building a twin engine car with two gas engines coupled together crank to crank like the old school twin dragsters.I would like to connect a large D.C. Motor in front of the gas engine,with a clutch in between which would release after a preset rpm so not do drag the gas engine down.With the current gas engines I have them timed 45 degrees apart and and have no synchronization problems.How would the electric motor act??I would also get a hybrid feature for cruising around,just turn off the rear motor let the big D.C. Motor take over.THere is a
Lot of space for the big d.c motor once I remove the first engine.

2. Oct 19, 2016

### Staff: Mentor

Parallel hybrids - which most hybrids are - get power from the electric and gas motors simultaneously.

But on the same shaft? I'd be worried about compatibility of the systems. I, do the have similar rpm ranges and do you still have a gearbox after them?

3. Oct 19, 2016

### Roberto palacio

As for the current gas engines the engines are bolted together with no gearbox in between the engines are GM ls v8s max rpm 6500.A big DC brushed motors I seen have a same max rpm of 4000 rpm.

4. Oct 19, 2016

### RonL

A main point to remember/learn is that an electric motor will only draw energy from it's source, equal to it's load. How you share their abilities will be critical.

ps. I should have said difficult

Last edited: Oct 19, 2016
5. Oct 19, 2016

### phyzguy

This site has a nice animation of how the Toyota Prius couples the gas engine to the electric motor using a planetary transmission. With the very different RPM/torque characteristics of the gas engine and the electric motor, I don't think you want to just bolt the shafts together.

6. Oct 19, 2016

### JBA

It also depends on what point of power/torque delivery you want to provide the electric motor boost; because electric motors deliver their maximum torque at their lowest rpm (locked rotor position) this is why in the high performance electric vs. ICE vehicle challenges the single gear electrics always win at launch but fade at the top end. (which is also a result of their battery's maximum wattage delivery capability).
If you want the boost at launch then directly connecting to engine shaft but you may want to do so with a one way clutch so that you can simply cut electric supply to the electric motor, and let it coast down, while the engine delivers the power for the remainder of the run.
Alternatively, although not the general philosophy and not really the best way of applying these types of combinations, if you want the boost at higher vehicle speeds then you will want the electric motor to be turning at it lowest possible speed at the power up point; but, using an electric motor in this manner this really is not the best approach because of the torque vs speed characteristic of electric motors.

7. Oct 19, 2016

### Roberto palacio

That's how I was looking at it launch off idle with both motors running somewhere in the 2-3k rpm range the electric motor would cut out and decouple from the engine.If the batteries were charged I could possibly drive around on the electric motor only just letting the gas engine windmill along for the ride obviously it wont running just rotating.

8. Oct 19, 2016

### Tom.G

Then you would have the electric motor driving an air compressor whose output is blocked (the gas engine) while also trying to drive the vehicle. Not a very efficient use of battery power.

9. Oct 20, 2016

### JBA

Wit regard to your planned linking and launching with the electric motor running at a 2-3K rpm, this will give you a boost but not really take advantage of the maximum launch torque available at lower rpm's. I would suggest that you consider a combination of the planetary gear suggested above with the one way clutch as a way to get more benefit from the engine plus electric motor combination.

10. Oct 20, 2016

### jack action

Why wouldn't you couple the motors with a 1.625:1 ratio (= 6500 / 4000) and used the electric motor as a booster? That is the principle behind the BAS Hybrid. The most difficult problem is to synch the «accelerators» of both motors.

11. Oct 21, 2016

### JBA

What is your primary application goal for selecting an engine/motor hybrid system between drag strip and street performance. The BAS system is targeted at a general efficiency role but will not provide the type of launch punch you will want for drag competition. At the same time, unless you have already added supercharging; then, from a performance vs weight and cost standpoint supercharging is a better first step because it will provide both a launch boost and a sustained power boost throughout the run.
Don't misunderstand, I am a tremendous fan and promoter of electric vehicles both transitional hybrid and full electric; but to provide the best performance they have to be formulated in the correct manner and applied as appropriate for the service.

12. Oct 22, 2016

### NTL2009

What are you using for batteries?

As others have said, a motor provides low end torque. But if you are already spinning the tires at the start, this extra torque cannot be utilized.

You need to take an overall system view.

13. Dec 7, 2016

### marcusl

Twin-engine dragsters date from a time when the horsepower available from a single engine was limited. Today it is no problem to build a single engine that can produce as much power as can be harnessed by the tires. Don't understand why you need to do two anymore.

14. Dec 11, 2016

Every watched the Lucas Oil Pro Pulling competitions? Most of those rigs have up to four engines, and some of them have two or three gas turbine engines. Not sure how the transmissions work, but multi-engine vehicles are definitely still around.

15. Dec 11, 2016

### marcusl

Hah, I didn't think about truck pulls. The added weight of multiple engines is probably as important as the extra power.

16. Feb 7, 2017

### RogueOne

It is cheaper to use two engines than it is to build an engine that is twice as powerful. I can get a pair of used Chevy 5.3L LS V8s for about $1400. That's about 700 horsepower for$1400. The overall system durability increases due to the division of labor between the two engines and the fact that you don't need to increase the internal stresses of either engine in order to get sufficient power. You also have the advantage of having a backup engine to help finish the race (salvage as many points as possible) or just get your boat back to shore. Boat racing, pulling trucks, pulling tractors, airplanes, trains, etc etc. The only guys who aren't going to dual engines are in applications where weight and packaging requirements are not able to be met with twin engines.