[unclehan]

I realize the motor (MG2) on the Prius is 67 HP and the gas engine is 76 HP.

Why not use a motor with more HP and an engine with smaller HP?

The way I see it, normal crusing, even at highway speed takes so little HP, maybe 20 or 30 HP?

The main reason they need the power is for acceleration. So why not get a big 100 HP motor that'll be perfect for the short temporary acceleration, and a weaker engine, something like 30 HP, to drammatically cut down on the engine size (which improves economy)?

Because when you have the engine that's even more powerful than the motor, then I don't see the point of using the motor to accelerate. You can just use the engine to accelerate the car with a gearbox, like the Honda Insight.

 

[KTPhil]

I'm sure the Toyota systems engineers considered the balance of power between the two under all driving conditions, and found this combination the best overall. They don't call it "synergy" drive for no reason-- it's the combination that was optimized, not one aspect of performance.

That said, I expect in a few years when many cars are hybrids, there will be a choice among various models that include various combinations of power, economy, and emissions.

 

[hyperion]

Also by using Toyotas system of power transfer the transmission and the ability of "shifting gears" was eliminated for somthing better. It is a compromise but well tested and successful. I'm sure Toyotas engineers tried every combination before selecting the present result.

 

[KTPhil]

In fact, I believe this car was designed first in software, then in hardware. It is common in HW/SW projects to begin with a simulation, then introduce hardware in the loop in stages until you have the complete system. It is in this initial simulation that I expect they traded off various powerplants, gearing, batteries, MPG, power, emissions. "Driving" in the simulator would let them optimize the driver's experience. I think this is where being first put them way ahead in making a practical, almost transparent hybrid system.

 

[KMO]

Where's the power for this big motor going to come from? The whole electrical system would have to be greatly beefed up to drive it. At present the motor is 50kW, but the maximum output from the battery is only 25kW. The motor can only operate at its peak when it's also drawing 25kW from the engine, via the generator.

If you had a 100hp motor and a 30hp engine, you'd be drawing a peak whopping 70hp from the battery, and the engine would struggle to top it up again. The whole thing wouldn't be very efficient, and it would probably be significantly more expensive - the smaller engine wouldn't be much cheaper, but the heftier electric bits would add quite a bit of cost.

And remember, ALL power in the Prius ultimately comes from the engine. The aim is to run the engine as efficiently as possible. Having a massive motor won't improve things. It's not an electric car, alas.

A bigger motor might make sense in a future plug-in hybrid with larger battery capacity, where a bigger motor would be needed to make longer electric-only journeys a practical proposition.

 

[mrv]

specs for the 2006 Highlander Hybrid:
http://www.toyota.com/vehicles/minisite ... HIHY06.pdf

gasoline engine:
3.3-liter double overhead cam (DOHC)
24-valve VVT-i V6
208 hp (155 kw) @ 5,600 rpm
212 lb-ft @ 4,400 rpm

Electric Motor
Function Drive front wheels, regeneration during braking
Motor Type Permanent magnet motor
Power Output 167 hp (123 kw) @ 4,500 rpm
Maximum Torque 247 lb.-ft. @ 0.1,500 rpm
Maximum Voltage AC 650V

Rear Electric Motor (4WD-i models)
Function Drive rear wheels, regeneration during braking
Motor Type Permanent magnet motor
Power Output 68 hp (50 kw) @ 4,610.5,120 rpm
Maximum Torque 96 lb.-ft. @ 0.610 rpm
Maximum Voltage AC 650V

Traction Battery
Type Sealed Nickel Metal Hydride (Ni-MH)
Maximum Power Output 45 kw
Voltage 288V

Hybrid System Net Power 268 hp (200 kw)


(looks to me that the same 2004+ battery is being stepped up to 650V, as opposed to the 500V on the Prius...)

 

[unclehan]

Where's the power for this big motor going to come from? The whole electrical system would have to be greatly beefed up to drive it. At present the motor is 50kW, but the maximum output from the battery is only 25kW. The motor can only operate at its peak when it's also drawing 25kW from the engine, via the generator.

If you had a 100hp motor and a 30hp engine, you'd be drawing a peak whopping 70hp from the battery, and the engine would struggle to top it up again. The whole thing wouldn't be very efficient, and it would probably be significantly more expensive - the smaller engine wouldn't be much cheaper, but the heftier electric bits would add quite a bit of cost.

And remember, ALL power in the Prius ultimately comes from the engine. The aim is to run the engine as efficiently as possible. Having a massive motor won't improve things. It's not an electric car, alas.

A bigger motor might make sense in a future plug-in hybrid with larger battery capacity, where a bigger motor would be needed to make longer electric-only journeys a practical proposition.

I think since we are talking about acceleration, it directly has to do with weight.

Maybe a motor that is twice more powerful will also be twice as heavy. Maybe a battery that has a higher output power will also be more heavy. Are power and weight pretty correlated when it comes to electric components?

Does anyone know how much the battery and motor weight on the current Prius?

So therefore maybe having a more powerful motor will add the weight so much it'll cancel out the benefit. Not to mention a lot more expensive.

What about capacitors? can those be used to supply a powerful surge for a very short time? like in acceleration. Or are those bulky and expensive too?

 

[efusco]

Bing, Bing, Bing....Michelle's the winner!!

The HiHy and 400h are, quietly tho' it may be shown, the next generation of HSD.

A modest increase in battery capacity with a significant step up in inverter function allowing for a more powerful motor(s).

Next generation Prius could, in good likelyhood, achieve just what you mention...I doubt the ICE would be smaller, but likely the battery capacity (Li+ gel?) will be greater...though lighter, and the Inverter will be markedly beefed up to allow greater function of a larger MG which can deliver more torque, more HP, and regenerate more power to boot.

That'd be my guess, anyway, looking at what's been done with the HiHy, and 400h.

 

[priusenvy]

The main reason they need the power is for acceleration. So why not get a big 100 HP motor that'll be perfect for the short temporary acceleration, and a weaker engine, something like 30 HP, to drammatically cut down on the engine size (which improves economy)?

Acceleration might be the most frequent reason to require maximum power, but isn't the only important reason. Think about extended uphill climbs of several miles, long enough to drain the battery. As it is, the current Prius had adequate power with the ICE for mountain driving. If it had significantly less power, to the point where I could only drive 55mph on I-80 going up to Lake Tahoe, I wouldn't have considered buying one.

Maybe someday when the power density in affordable battery technology is much higher, a smaller ICE could be considered.

 

[C.Rickey Hirose]

The main reason they need the power is for acceleration. So why not get a big 100 HP motor that'll be perfect for the short temporary acceleration, and a weaker engine, something like 30 HP, to drammatically cut down on the engine size (which improves economy)?

Acceleration might be the most frequent reason to require maximum power, but isn't the only important reason. Think about extended uphill climbs of several miles, long enough to drain the battery. As it is, the current Prius had adequate power with the ICE for mountain driving. If it had significantly less power, to the point where I could only drive 55mph on I-80 going up to Lake Tahoe, I wouldn't have considered buying one.

Maybe someday when the power density in affordable battery technology is much higher, a smaller ICE could be considered.

Actually, had a customer once told me that he took the Classic Prius then
with only 33kw electric motor and 273 volts battery pack going up Colorado's peak over 13.000 ft
elevation all going up. No power loss but the ICE engine was probably revving 4 to 4500 RPM just to make enough juice for the task of constant
battery energy depleation.

Bigger motors _Electrics_ will be on the Mid-Size soon to show up HH or
the Highlander hybrids. Toyota told us that to tell the customers 3 seconds
less than the ICE V6 version from 0 to 60 mph ! It is all about getting accelertation get up and go... more powerfull-feeling...

 

[Paul]

Think about extended uphill climbs of several miles, long enough to drain the battery. ...
Maybe someday when the power density in affordable battery technology is much higher, a smaller ICE could be considered.

I don't think the battery does or ever will provide more than a few minutes total of transient power on hills. It doesn't need to do more to provide the benefits of a hybrid. It's not an electric car.

The ICE in the NA Prius is clearly sized to drive continously up the steepest anticipated hills in NA, fully loaded and at a speed "acceptable" to the customer.

Future options might be varaible compression ratio, cylinder deactivation, or dividing the ICE into two smaller engines.

 

[DaveinOlyWA]

i dont see that the ICE is too big at all.

without the ICE, how fast can you go? 40?

so with a 20 hp ICE, what would acceleration from 40 to 60 mph be?

2 days? 3 days? i feel that performance would be unacceptable with a smaller ICE without doubling the output of the electric motor. i just cant see anyone questioning something like this when it seems that so many other top level engineers cant duplicate or match it.

bigger sure, in fact its already here. smaller?? well not unless you want something like a go cart