Hybrid Synergy Drive

The HSD also combines an electric drive and a planetary gearset which performs similarly to a continuously variable transmission.

In a conventional automobile the geared transmission delivers different discrete engine speed-torque power requirements to the wheels.

Geared transmissions may be manual, with a clutch, or automatic, with a torque converter, but both allow the engine and the wheels to rotate at different speeds.

This limited gear-ratio set forces the engine crankshaft to rotate at speeds where the ICE is less efficient, i.e., where a liter of fuel produces fewer joules.

This is why the engine for an engine-generator is often much smaller, more efficient, more reliable, and longer life than one designed for an automobile or other variable speed application.

However, a continuously variable transmission allows the driver (or the automobile computer) to effectively select the optimal gear ratio required for any desired speed or power.

A computer running appropriate programs controls the systems and directs the power flow from the different engine + motor sources.

This power split achieves the benefits of a continuously variable transmission (CVT), except that the torque/speed conversion uses an electric motor rather than a direct mechanical gear train connection.

(See: Plug-in hybrid) In practice, HSD equipped cars can be driven a mile or two without gasoline, as an emergency measure to reach a gas station.

An HSD transaxle contains a planetary gear set that adjusts and blends the amount of torque from the engine and motor(s) as it's needed by the front wheels.

The differential is an epicyclic gear set (also called a "power split device"); that and the two motor-generators are all contained in a single transaxle housing that is bolted to the engine.

The battery pack of the first generation Toyota Prius consisted of 228 cells packaged in 38 modules, while the second generation Prius consisted of 28 Panasonic prismatic nickel metal hydride modules, each containing six 1.2 volt cells, connected in series to produce a nominal voltage of 201.6 volts.

The discharge power capability of the second gen Prius pack is about 20 kW at 50% state of charge (SoC).

[13] A button labelled "EV" maintains electric vehicle mode after being powered on and under most low-load conditions at less than 25 mph (40 km/h) if the traction battery has enough charge.

[14][15] Only the Toyota Prius Plug-in Hybrid has a longer driving all-electric range in blended operation electric-gasoline of 11 mi (18 km) (EPA rating) until the battery is depleted.

The larger battery pack enables all-electric operation at higher speeds and longer distances than the conventional Prius hybrid.

[19] The HSD drive works by shunting electrical power between the two motor generators, running off the battery pack, to even out the load on the internal combustion engine.

Here are a few of them: The Toyota Prius has modest acceleration but has extremely high efficiency for a midsized four-door sedan: usually significantly better than 40 mpg (US) (5.9 L/100 km) is typical of brief city jaunts; 55 mpg (4.3 L/100 km) is not uncommon, especially for extended drives at modest speeds (a longer drive allows the engine to warm up fully).

The Highlander Hybrid (also sold as the Kluger in some countries) offers better acceleration performance compared to its non-hybrid version.

The original Prius used shrink-wrapped 1.2 volt D cells, and all subsequent THS/HSD vehicles have used custom 7.2 V battery modules mounted in a carrier.

[33] Although not part of the THS/HSD as such, starting with the 2004 Prius, all THS/HSD vehicles have been fitted with an electric air-conditioning compressor, instead of the conventional engine-driven type.

[34] The updated version of HSD first delivered in the model year 2006 RX 400h is similar to THS/THS-II, with the addition of a second planetary gearset, which Toyota calls the Motor Speed Reduction Device (MSRD); it is compounded with the first planetary gearset (PSD) by coupling the two ring gears (R1 and R2) together.

On October 13, 2015, Toyota announced details of the Fourth Generation Hybrid Synergy Drive which was introduced for the 2016 model year.

With the Fourth Generation HSD, Toyota is also offering a four-wheel drive option, dubbed "E-Four", similar to the 2005 RX400h and Highlander Hybrid, in which an electric traction motor is added to the rear, but is not mechanically coupled to the internal combustion engine or front inverter.

Antonov eventually took legal recourse in the German court system, where decisions are usually made relatively swiftly.

The patent holder seeks to impose a levy on each vehicle sold, which could make the hybrid SUV less competitive.

In 2009, the Presidential Task Force on the Auto Industry said that "GM is at least one generation behind Toyota on advanced, 'green' powertrain development".

Some early non-production plug-in hybrid electric vehicle conversions have been based on the version of HSD found in the 2004 and 2005 model year Prius.

A company planning to offer conversions to consumers named EDrive systems will be using Valence Li-ion batteries and have 35 miles (56 km) of electric range.

Both of these systems leave the existing HSD system mostly unchanged and could be similarly applied to other hybrid powertrain flavors by simply replacing the stock NiMH batteries with a higher capacity battery pack and a charger to refill them for about $0.03 per mile from standard household outlets.