It's a Question of Total HP?

Austingreen, good thought. I don't have enough info for 2010 Prius but this is for the Iconic Prius (04-09).

MG2 power peaks at 20-26 MPH but the total HSD power peaks at 53 MPH.

At 53 MPH, ICE output should be at peak power (76hp @ 5,000 RPM) and MG1 at near peak (9,800) RPM and MG2 at 3,150 RPM. That means MG2 is contributing just 34 hp to total 110hp.

MG2 at 3,150 RPM should be able to generate more power than 34 hp (see graph below). This indicates the bottleneck is the HV battery power. Therefore, a more powerful battery should boost the peak total power.



It may be the same case with 2010 Prius but we won't know for sure until we have the power curve for the new high speed MG2.

 

I didn't realize the battery/hybrid system was rated at 27kW (36hp). The Electric motor is RATED at 80hp but only outputs the maximum throughput of the battery/hybrid system. So that answers the OP's question on why the Prius is not rated at an overall 178hp.

op2:

 

A more powerful battery pack would run afoul the patents on large NiMh batteries, plus increase the price of the vehicle.

Tom

 

Frist let me say, I am convinced that gas power(98hp) + battery power (36hp) gives us peak hp in the prius. My mind was wandering to the next question, can we simply increase battery power and get more hp out of the prius, and if so how much with the current hsd?

Thanks, the graph and power figures help with my understanding. If the 2010 mg2 has a similar power curve to the wheels, there could be more in the upper range of speeds but this would be a slight degradation from peak.

My understanding of the hsd is only partial, and not intuitive. The rpm speed that the engine turns makes my head hurt, so I've turned up the stereo so that it does not bother me. Let me put down my understanding so you can correct any misconceptions. The ecu selects rpm range of the ice based on its needed power. When the ice is providing driving power the sun gear hooked to mg1 spins at a rate to set the eCvt to the ratio. Given the gear ratios of the psd, 72% of the ice power is sent to the ring gear attached to mg2 and 28% is used to generate electricity at mg1. The ecu can take this power and apply it plus battery power to mg2. The battery can provide up to 27kw or be charged up to ??? kw(I don't know this number).

If this scenario is true than the highest hp available given unlimited battery power is 0.72*98 + 80 or about 150hp. This will drop depending on horsepower provided by mg2 at its rpm. I am guessing this peak would be significantly reduce fuel economy.

The other scenario is given a larger battery pack mg1 could be controlled to provide power instead of generating it. I'm not sure the hardware is in the system to do this. Let's say it could be set to be energy neutral then we get 98+80 or about 178hp at the peak.

This may be the reason we don't have it in our gen IIIs, but they did increase power from 25kw to 27kw. Soon toyota will be forced by competition to use Lithium chemistries and that patent will just be a bad memory.

My bigger question is why in the phv-prius which has Li batteries the hp did not go up. This would not be restricted by any Nimh patents. If we can really get 178 hp I am very interested in buying or building an aftermarket kit. Software would be the gating item here. If the peak hp is really only 10% more with a bigger battery or ultra cap then that kit is much less valuable to me.

 

Not quite. I believe it is 72% of ICE torque, not power, sent towards MG2. The actual power split between MG1 and MG2 paths also depends on their respective RPMs, which vary with other conditions.

 

This is the torque ratio. The torque ratio is fixed because of the fixed gearing. Power, on the other hand, is work per unit time, which means the power ratio varies depending on the relative speeds of the parts.

The NiMh battery patent is due to run out soon. I think it only has a few more years.

Tom

 

You can calculate the power rating of MG1. Since we know 28% of ICE torque (105 x 0.28 = 29.4 lbs-ft) goes to MG1 and it has 10,000 RPM max. This works out to 56 hp and if we take 95% efficiency of the generator, we are left with 53 hp.

We know MG2 is capable of only 80 hp at peak RPM and if we use 95% efficiency, it need to consume 84 hp. MG1 can feed 53 hp leaving the HV battery only 31 hp to feed. HV battery is rated for 36 hp but there may be more losses due to the inverter.

As far as this exercise goes, Toyota sized the HV battery precisely at what MG2 can handle. Increasing the battery size will not increase the peak power of HSD. To increase the system peak power, PSD will need to split more torque to the wheels and less to MG1.

This also reveals that majority of the power is going through the generator, making Prius more series hybrid than parallel (56hp Series vs 42hp Parallel) at this instant in time. On the other hand, if you are cruising on the highway with low MG1 RPM, majority of the power will go through the Parallel route.

The balancing act of parallel and series ratio is really eCVT in action. Series is utilized for acceleration with more thrust (torque) from electric motor (MG2). Parallel is utilized for efficiency whenever low torque (up to 72% of ICE torque) is needed.

It is beautifully and elegant setup to get the best of both Series and Parallel worlds and a proper name was given (Hybrid Synergy Drive).

 

I believe the patent for "large format" is 8Ah at the cell level. Adding more cell to the pack would make it more powerful but it will increase the price.

 

We will see battery overheat to increase the battery power because of its internal resistance.
Please remember Toyota uses identical battery modules among Gen2 and Gen3, but Gen3 battery pack has better cooling capability, then we see more power on the Gen3 than Gen2.

Gen2 Plug-in prototype has two battery packs, then the system power becomes 56kW(ICE) + 2 X 22kW(battery) = 100kW.

Ken@Japan

 

Doh,

Yes splitting the torque makes the numbers make more sense, and conservation of power makes the movements of mg1 make more sense at least to me.

If I have this right as long as mg1 is within its limits it can be ignored for maximum horsepower of the system with a larger power battery, and the horse power would be given by 72% of ice torque plus the torque given by 60 watts at the rpm multiplied by the rpm and hp constant.

I couldn't find the ratio between the ring gear rpm and mph for gen III. I assume it changed with the changes in mg2.

Thanks for helping me understand the hsd.

 

Can MG1 rev to 10,000 rpm under acceleration as well as braking and if so, can it always do so?

 

The torque split ratio is always 72% vs 27%.
However, power split ratio is dynamically changed, ie; 100% of engine power goes to ring gear when MG1 rpm=0.
Therefore, the simple sum of power sources shows the system power, ICE power + battery power.

Gen2:final gear ratio=4.113:185/65R15 tire diameter=621mm
-> Gen2 = 17.7 mph @ 1000 ring gear rpm
Gen3:final gear ratio=3.267:195/65R15 tire diameter=634mm
-> Gen3 = 22.7 mph @ 1000 ring gear rpm

Ken@Japan

 

MG2 is used for regen braking. MG1's primary role is generator. It can act as a motor in some cases. I am not sure if MG1 can reach 10,000 rpm as a motor.

 

Right, as long as MG1 can supply maximum power, more powerful battery won't help because MG2 can't consume any extra electricity.

You have the idea right. Since the RPM of the ICE and MG2 are different, it should look something like this.

(0.72 x ICE Torque x ICE RPM) + (MG2 Torque x MG2 RPM) / 5252

 

Because of the gearing, there is a fixed relationship between the motor generator speed, ice speed, and the speed of the ring attached through gearing to MG2 and other gearing to the wheels. The coefficients are rounded

MG1rpm = 3.6xICErpm - 2.6xRINGrpm

With the ice providing power to MG1, MG1rpm will be positive and will act as a generator. The maximum ICErpm is 5200, so RINGrpm must be at most (3.6*5200-10,000)/2.6 or 3350 rpm.

If you brake at these speeds the car will remove power from the ice, and MG1 will quickly slow down.

MG1 will go in the other direction in the ICE off condition, but software rotates the engine at about 46 mph. If the engine only revs at 1000rpm this will keep MG1 bellow 10000 rpm until the ring gear is spinning at 5230 rpm which is 118 mph. It is likely the software will spin the engine faster to keep MG1 at a slower speed.

MG1 can also rotate backward if is drawing power from MG2, but the ice speed will keep this number low.

 

Please note the EV max speed on both Toyota's plug-in Gen2 and Gen3 prototypes are 100km/h(62.15mph).
TOYOTA: News Releases
TOYOTA: News Releases > TMC Introduces 'Prius Plug-in Hybrid' into Key Markets
Toyota does not change the rear ratios between PHEV and HV Prius.

Gen2 PHEV ring gear = 3514 rpm @ 100km -> MG1 = -9136 rpm
Gen3 PHEV ring gear = 2734 rpm @ 100km -> MG1 = -7108 rpm

We see the max EV speed on the HV Prius are...
Gen2 42mph -> MG1 = -6174 rpm
Gen3 46mph -> MG1 = -5261 rpm

Why does Prius need a few thousands rpm allowance?
My guess is Prius needs the MG1 rpm number as low as possible to start the ICE @ 1000 rpm.

Gen2 MG1 = -6174 rpm (ICE=0rpm) -> -2574 rpm (ICE=1000rpm)
Gen3 MG1 = -5261 rpm (ICE=0rpm) -> -1661 rpm (ICE=1000rpm)

It will be hard to change the MG1 rpm numbers (3600rpm) within a second or two when starting the ICE at high speed.
I think the max EV speed on the HV Prius is reasonable for the smooth ICE starting at such high speed.

Ken@Japan

 

Gen3 is really set up to be PHV friendly by keeping the MG1 spinning as low as possible in EV mode.

 

Governing equations (neglecting the MG2 stepdown gears):

Torque Balance:
Drive_T = 72/28 MG1_T + MG2_T

Gearing Relationships:
Drive_RPM = 1.3844 ICE_RPM - 0.3849 MG1_RPM
MG2_RPM = Drive_RPM

Power Balance:
Drive_T * Drive_RPM = ICE_T * ICE_RPM + MG1_T * MG1_RPM + MG2_T * MG2_RPM

Relationship governing drive power from pedal position:
Drive_T * Drive_RPM = f(pedal position, other things)

Relationship governing battery power management:
ICE_T * ICE_RPM = f(Drive_T * Drive_RPM, battery state)

Relationships governing best engine efficiency (operating line):
ICE_T = f(ICE_RPM)

So we have 7 equations and 8 unknowns. The last degree of freedom is eliminated because Drive_RPM is fixed by the vehicle speed.

So for any vehicle speed, pedal position, battery state, etc., we can solve for everything else.

 

Thanks, that means the number I had wrong was MG1's rpm when the ICE turns on. I hope you don't mind me correcting my previous post with this information.

That makes sense. Now if only we had a button to tell the prius we aren't planning to start the engine on this glide.

Thank you so much for the information.

 

Hi Ken,

It seems that the direction of MG1 is not right.

Since MG1=3.6*ICE-2.6*MG2, MG1 should be -ve when ICE=0 and MG2 is +ve for forward moving direction.

MG1 just change speed not direction.

Gen2 MG1 = -6174 rpm (ICE=0rpm) -> -2574 rpm (ICE=1000rpm) -> 3600 rpm change
Gen3 MG1 = -5261 rpm (ICE=0rpm) -> -1661 rpm (ICE=1000rpm)-> 3600 rpm change