According to EPA we have Gen 1 - 41 mpg Gen 2 - 46 mpg Gen 3 - 50 mpg Gen 4 - 52 mpg Gen 4 Eco - 56 mpg The Camry hybrid has an even more notable jump from 33 mpg in 07-11 to 40 mpg in 2012 and up models. Toyota claims that the extra mpg of Eco version above the regular Gen 4 is due to lighter lithium batteries and not carrying a spare tire, but I don't know that I fully believe that given it's a 65 lb difference. I know that in recent years, all cars have gotten a lot of various changes aimed at raising EPA numbers but that don't necessarily correlate to real-world efficiency improvements. For example, nearly every newer model has had changes made to the pedal response curve. This is why even crapboxes like the Ford Focus have a "Sport Mode" button, since EPA tests based on standard settings when you turn on the car. They use software to cripple the engine so it gets high numbers on the test, but in order for the car to merge safely on the highway you have to hit the Sport button and/or floor the pedal. The engines are plenty capable, but with the pedal 50% depressed they are not running anywhere near 50% of RPM range. My question is how much and in what ways has Hybrid Synergy Drive itself changed? Have gear ratios changed, electrical motors gotten bigger, inverters/batteries/other electronics optimized? Or is it mostly software tricks and tweaks and dangerously low rolling resistance tires that has eked out this extra performance? I am not trying to point a finger at Toyota, far from it. I want to learn about the real engineering such as engine optimization, aerodynamics, etc. which I think is getting lost in the woodwork in the numbers-gaming.
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.
Gen 1.5 (which is what we got in North America) Raised engine rpm limit to increase hp (4,000rpm to 4,500rpm) Increased power of electric motor Changed battery from D-Cells to NiMH Lightweight 14" alloy wheels Gen 2 2nd gen Toyota Hybrid System (THS-II) aka HSD Raised engine rpm limit again to 5,000rpm. Hp +6 EV motor power increases. hp: +23, tq: + 36 System capable of accepting up to 500V. (Using the inverter) Battery is smaller Rubber bladder inside the fuel tank gives AT-PZEV rating by eliminating evaporative emissions (emissions are 30% lower than the Gen 1.5) 3 litre thermos to keep hot coolant warm for up to 3 days. This will be circulated the next time the car is started to heat up the engine faster Cd = 0.26 LED brakelights to reduce power consumption Lightweight 15" alloys with aerodynamic plastic wheel rings Switched to electric A/C compressor Electric motor power steering assist Gen 3 Larger 1.8 litre motor for increased torque (and a bit of hp too). Increased torque means the engine can run at a lower rpm for the same output Thermal efficiency rises to 38.5% - world's best Electric water pump (fully beltless engine) Smaller, lighter (33%) and slightly more powerful (+10kW) MG2. However, torque number is down (although I doubt 295 lb-ft of torque was ever put through in a Gen 2 Prius lol) MG2's lower torque is offset by the introduction of a reduction gear in the Power Split Device More compact MG1 Power Split Device is lighter and reduces torque losses by as much as 20% Inverter can up the system voltage to 650V Smaller IGBT transistors in the inverter Inverter has a new direct cooling system to reduce size and weight Taken together, the inverter, motor and PSD are smaller and 20% lighter Exhaust Gas Recirculation System Exhaust Heat Recovery System (replaces the coolant thermos). Heats up coolant using exhaust heat Carbon capture canister replaces the rubber bladder for evaporative emissions control (actually introduced in the 2007 Camry Hybrid. Toyota also tinkered with a pressurized tank with the 2005 HiHy/RXh) Increased regen capability (less electrical energy loss so more goes into the battery) Electric current consumption is reduced by 18%-29% Weight of braking system reduced by 18% Increased battery output (slightly) More compact battery Aluminium hood, rear hatch, front suspension axle, brake calipers and brake cylinder Super High Tensile Steel in rocker panels, centre pillar, roof reinforcements Cd = 0.25 (underfloor panels, aero corners for front/rear bumpers, 2 rear underbody stabilising fins to straighten airflow before exiting at the rear) LED taillights/brakelights (90% power reduction) Optional LED low beams (20%-30% power reduction) Ejector cycle system for A/C compression Uses energy that is normally lost Reduces compressor workload Compressor energy consumption reduced by 10.5% (while cooling performance improves by 7%) A/C compressor speed is continuously variable Lightweight 15" alloys with aerodynamic plastic full wheel covers Gen 4 Same 1.8 litre but max torque is tuned at a low 3,600rpm 40% thermal efficiency - world's best (again) Redesigned intake port geometry to increase tumble ratio for better combustion efficiency Large-volume cooled EGR and redesigned EGR passage to better distribute EGR gas to each cylinder Resin cylinder heat cover aids in weight and size reduction Power Split Device Smaller (47mm narrower) with a new parallel reduction gear format 20% lower loss than the Gen 3's PSD Motor Rolling-coil structure is smaller with a higher power density 20% reduction in parasitic loss Inverter Smaller in volume (12.6L down to 8.2L) Double-sized layered cooling structure Intelligent power module board size reduced by 31% More efficient power devices (e.g. semiconductors) help contribute to a reduction of loss by ~20% Batteries NiMH battery reduced in size (13.7%) and lighter (by 1kg) once again (now fits under the rear seat) Charging performance for the NiMH is improved by 28% Newly developed Li-Ion battery (~15-20% lighter and 15% smaller than the NiMH) Smaller, lighter and quieter electric water pump Air filter for the battery cooling system to reduce dust build-up Active Grille Shutter for faster warm up and less drag Improved Exhaust Heat Exchanger for the Exhaust Heat Recovery System Improved ejector cycle system A/C evaporator LED low & high beams LED licence plate lights LED parking lights Flat front pillars with airflow correcting garnishes (doubles as a rain gutter for the windshield) Vortex generators near the mirrors (although it's more for stability than aerodynamics) Cd = 0.24 Aluminium rear door frames Peak of roof moved forward again (like the Gen 2) to reduce drag Height of the car is lowered by 0.78" Redesigned door handles to remove the gap and improve aerodynamics Lightweight 15" alloys with full plastic wheel covers 17" alloys also undergo lightweight treatment and utilise plastic inserts for aerodynamics and reduced weight Prius Prime/PHV One-way clutch to enable MG1 to assist with forward motive force World's first gas-injected heat pump Carbon-fibre rear hatch (-8lbs over aluminium hatch) And this is just the improvements to fuel economy and emissions. There are also improvements to ride comfort, NVH, ecology and so forth for Gen 3 and Gen 4. Edtit: Added Prime features
Hey where did you find this information? I'd like to find out such details for the 2018 HyCam if that is possible.
I think our best chance might be just driving with the radio off to see, lol. Found this for the Prius, I've looked and looked but never found anything comparable for HyCam John's Stuff - Toyota Prius and more
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.
