How has Hybrid Synergy Drive changed since gen 1?

I'm sure others will respond. The aerodynamics has improved with a fall in the Coefficient of Drag (Cd), weight loss and low rolling resistance tyres. Not sure about the relative contributions of each though.

 

The electric motor is actually SMALLER.

This is what TOYOTA said - Toyota Unveils Advanced Technologies in All-New Prius | Toyota USA Newsroom

 

Well, it wasn't always called HSD. Early on the name was THS(Toyota hybrid system).

The PSD itself hasn't changed much. There might be more or less teeth on the gears that shifts the ratios and percent of the ICE torque going to M/G1 a little.
The gen1 Prius refresh and export model switched from off the shelf cylinderical battery cells to the square prizmatic ones that are better at shedding heat.
The gen2 had larger motors. At least in North America, it had the thermos to save coolant heat for the next start up.
Gen3 introduced a reduction gear between M/G2 and the drivetrain this allowed the motor to be come smaller.
The gen4 further refined the system in the gen3 for cost and efficiency.

Without a plug, hybrids are still gasoline only cars, and much of the Prius' efficiency improvements are due to changes to the ICE. I already mentioned the thermos, but there is the exhaust heat recovery system and cooled EGR on the gen3 and up. The gen3 also got an ICE with a better efficiency sweet spot that improved efficiency at higher speeds. there are improvements to valve timing. These ICE improvements don't require a hybrid system to help with efficiency.

 

Here is a link to info about the next gen Camry HSD to be introduced at the Detroit Auto Show next month. The improvements are similar to those in the Gen 4 Prius:

Advancement of Toyota Hybrid System II (THS-II) | TOYOTA Global Newsroom

 

Gen 1 and 2 used a chain to transfer energy from M/G2 to the differential, with Gen 3 this was gears, and Gen 4 moved M/G2 closer to the 'rear end'.

Gen1 HV battery was prone to corrosion that Gen 2 solved.

I think Gen 1 had to run the engine above 39 MPH, Gen 2 43 MPH. Gen3 (in large part because of the extra Planetary gear Trollbait mentioned) could go 62 MPH in electric and Gen 4 84 MPH. A wide range of choices when to use the engine gives the computers chances to optimize fuel economy.

in Gen 1, many accessories (like A/C) were belt driven and used power even when not needed. (worse they made the engine start if needed) By Gen 2only accessories the engine needs (water pump) were belted. By Gen 3 no engine driven belts at all. The computers control when the car needs that energy expended.

 

For the internal layout of the transaxles, there's three basic designs, of which WeberAuto has done overview videos.

P110 (Gen 0), P111 (Gen 1), P112 (Gen 2):

P310 family (all current hybrid generations of Lexus RX 400h/450h/Highlander, Estima, Camry, Lexus ES 300h/Avalon, Alphard/Vellfire, Sai/Lexus HS 250h, RAV4/NX 300h, and the first generation Nissan Altima Hybrid), P410 (Gen 3 including PiP and Prius v/a/+, Auris/Corolla Hybrid, Lexus CT 200h, Noah/Voxy/Esquire Hybrid, Mazda Axela Hybrid), and P510 (Prius c, Yaris Hybrid, Sienta Hybrid):

P610 (Gen 4 including Prime):

Note that the video I linked for the P610 is describing the Aisin HD-10, HD-20, and Ford HF-35 gearboxes, and not the actual P610. However, there's only a slight difference in layout internally, with the removal of one gear - MG2 and the PSD's ring gear are geared to the same gear, rather than two separate gears on the same shaft.

Also, the next-generation Camry Hybrid will use a gearbox of very similar design to the P610, just enlarged appropriately. I'm guessing it'll be called the P710, Toyota is not inventive with their model numbers here.

All known Toyota-designed power split device-based transmissions (including the L110/L110F (two-speed reduction gearing for MG2, rear-wheel/all-wheel drive), L210 (single-speed reduction gearing for MG2, rear-wheel drive - I think it's basically the P310 adapted for RWD), and as far as I know the L310 (4-speed reduction gearing for both MG2 and the power split device, rear-wheel drive)) use the same gearing in the power split device itself - 78 teeth for the PSD ring gear, 30 teeth for the PSD sun gear, and 23 teeth for the PSD planets. Note that the Ford-designed gearboxes (Aisin HD-10, HD-20, Ford HF-35) do use different gearing than that.

 

Hey where did you find this information? I'd like to find out such details for the 2018 HyCam if that is possible.

 

I can only say, I am really good at Trivial Pursuit. I absorb odd facts and remember them. Sadly, that does not include people's names.

The Prius gets the cutting edge and the techies here obsess over each detail. (including me) Then the technology goes into normal cars and normal drivers just don't care.

 

I don't think it is really possible to figure this out experimentally. The EV button has an artificial limit of 25 MPH for EV mode.

The car will generally keep the ICE off if you can keep the torque meter below a spot just above the word ECO. The car will get up to about 40-45 MPH under electric power using this technique.

Neither of these figures represent the maximum theoretical EV speed.

The fastest my Camry has gone under EV power on a relatively flat road is around 70 MPH. This happened after a long downhill overcharged the battery and the car wanted to bleed off some charge. Under normal conditions there is no way to make this happen.

I expect that the maximum EV speed for the Camry is similar to the gen 4 figure of 84 MPH but I'd really like to know. I don't drive fast enough to test this out on the road...

 

If you decelerate, (say from 85 MPH) at some point the engine will stop; that is the the theoretical max EV MPH. It is only spinning the engine because it has to.

 

I think it's a lot of incremental changes everywhere.

Aerodynamic improvements maybe yielded 1 mpg

Engine efficiency improvements over the generations probably yielded 5 mpg (lower friction piston sleeves, lighter oil, slight improvements elsewhere)

I'm with you on the Gen 4 vs. Gen 4 Eco. I bet the car comes with lower rolling resistance tires than standard, a hamstrung Normal mode, no rear wiper (better aerodynamics).... just every little thing optimized for efficiency. For what it's worth, I think it was a smart move, too. Those going for top economy will not complain as much about it being gutless , if they bought the Eco model. Those who want an efficient car, but also want it to move faster will avoid the Eco model.

They just REALLY understand continuous improvement. bigger diameter tires also leads to lower rolling resistance. (they were pretty dinky on Gen 1...)

Not sure about the HSD changes. Seems like the kind of thing that someone might analyze on YouTube, have you looked there?

 

^ Just read that araticle. Yep, it's a lot of incremental improvements all over the car, down to the most minute detail.