Cadillac adding new top-end high-tech model to line-up; production in 4Q 2015
Kia Optima T-Hybrid mild diesel hybrid concept for Paris features 48V system, lead-carbon battery

Volvo Buses officially launches the all-new plug-in Electric Hybrid bus

Volvo 7900 Electric Hybrid with overhead conductive charging station and pantograph extended. Click to enlarge.

As previously announced (earlier post), Volvo Buses will officially launch the new plug-in 7900 Electric Hybrid bus at the International IAA Commercial Vehicles show in September. The plug-in hybrid drive reduces diesel fuel consumption and carbon dioxide emissions by up to 75%, compared to a conventional diesel bus. Total energy consumption is reduced by 60%.

The Volvo Electric Hybrid Driveline is an extension of the well-proven driveline used in the Volvo 7900 Hybrid. The difference lies in a more powerful electric motor, increased energy storage and equipment for overhead conductive opportunity charging. The bus is equipped with a 150 kW electric motor that delivers maximum torque of 1200 N·m (85 lb-ft) and is powered by a 19 kWh Li-ion battery pack as well as a 240 hp/918 N·m Volvo D5K 240, 4-cylinder, in-line Euro 6 diesel engine with common rail injection.

The battery pack uses a heater/cooler system which operates both at the ramp and when driving. The bus is rapid-charged at select bus stops via a pantograph. Recharging takes approximately 6 minutes at end stations. The bus, which can operate about 70% of the time on electricity, has an electric range of about 7 kilometers (4.3 miles).

Volvo Electric Hybrid drive system
  1. Diesel engine
  2. Electric motor/generator (I-SAM)
  3. Gearbox
  4. ESS (Electrical Storage System)
  5. Power electronics
  1. Charging interface onboard
  2. Charging interface off-board
  3. Power charger
  4. Grid
  5. Electrified auxiliaries

The bus runs primarily in electric mode. To enable full electric drive, the bus is equipped with electric power steering; an electrical air compressor ; and a DC/DC unit that converts 600 V power to 24 V power. The DC/DC unit replaces the conventional alternator. The vehicle switches between hybrid drive and full electric drive depending on the current conditions.

When additional power is required or when battery capacity reaches a pre-determined level, the bus goes into hybrid drive. The diesel engine and electric motor then propel the vehicle together. Torque is distributed between the two units depending on the ESS charge status, speed and other conditions.

During braking or retardation, kinetic energy is generated and used to charge the ESS. This regenerated energy is later used for propulsion or for auxiliary consumers such as the air compressor, DC/DC unit or air conditioning system.

Volvo has already signed contracts with several European cities for the first deliveries. Hamburg, Luxembourg and Stockholm will implement the new bus system in 2014 and 2015. Series production is scheduled to start in early 2016.

I am very proud to launch this ground-breaking bus system. Electric-hybrid buses and full-electric buses are tomorrow’s solution for urban public transport. They will allow us to reduce energy consumption, air pollution, climate impact and noise, which are some of the biggest challenges facing large cities worldwide.

—Håkan Agnevall, President Volvo Bus Corporation

Noise is a growing problem in many cities. The noise level beside an Electric Hybrid is 65 decibels, that is to say normal conversation level. The Volvo 7900 Electric Hybrid runs in electric mode on average 70% of the route, silent and emission-free.

Three Volvo Electric Hybrids have run in a field test in Gothenburg over the past year, a test that has verified the reduction in energy consumption and emissions. (Earlier post.)

As of this autumn and for two years ahead, eight Volvo Electric Hybrids will be put into regular operation in central Stockholm. This is part of ZeEUS, an EU project being conducted in six European countries.


Roger Pham

That is true. The rear wheels can brake, but they cannot lockup or the car will spin out of control. Anti-wheel-lock monitor will reduce the regenerative braking on the rear wheels if wheel locking up is detected, while the front friction brakes will have to do the rest of the braking that the rear wheels can't handle. On model with 160 kW of e-motor power, perhaps 80 kW of motor can go on the front axle in order to do faster regen braking. Model with only 80 kW of e-motor power cannot generate much braking force at 40-60 mph anyway so will be OK to locate them just on the rear axle.

3-speed transmission: With the load-leveling capability of the e-motor, there will be fewer gear ratio needed to operate the engine at optimal point, especially with the presence of the turbocharger. For example, instead of shifting gear, the e-motor will fill in when extra torque is needed and will absorb extra torque and recharge the battery when one slacks off on the gas pedal. This will avoid wear and tear on the transmission gear shift mechanism and will make PHEV's more reliable and lower maintenance requirement.

The car can run on the third gear most of the time without requiring gear shift, except when the "Power" mode is selected, then the gear shift will be done to boost acceleration, or when the gas pedal is floored, for "war-emergency power."

The advantage of the turbocharger is that it gives the engine much higher torque at higher rpm's, hence steeper power increase with engine rpm in order to match the steep increase in power demand of the car at higher speeds, thereby allowing the car to remain in third gear all the way to top speed of 120 mph on engine power. So, engine will be in third gear all the wayfrom 20 mph to topspeed at 120 mph, and does not require gear shifting for most of the time. A big turbocharger is desirable for this reason for gobs of power at high speeds, without requiring a waste gate, due to the availability of electric boost, no need for early spool up of the turbocharger, though a VGT is still desirable as an option, for the "Fast and Furious" street light drag racers!


I doubt if we will see too many 8-passenger, 5000+ lbs steel monsters manufactured in 2025 or so.

Families are getting smaller and the new generations are not so inclined to impress their neighbors as their ancestors were.

Better designed, under 2000 lbs units, with enough enterior room for 4 to 6 (normal size) people will become common place by 2020 or soon thereafter.

Oversized people may have to buy large pick-ups or large VUS? However, fewer oversized customers may exist.

Roger Pham

The Tesla Model S is made out of aluminum mostly. That's why a hypothetical PHEV version with 10 kWh battery pack and a minimum engine size of 1 liter with minimum transmission of 3-speed can weigh around 3,000 lbs.

FYI, the Tesla Model S BEV with 85-kWh pack weighs in at 4,600 lbs, close to the 5,000-lb steel monster that you're alluding to, and can sit 7-8 people, and people are waiting to buy it! nearly $100,000 USD. Just imagine if this same-size car of the same maker, with similar performance specs and load capacity, will list for $40,000, with 360-mile range per fillup, and 40-60-mi electric range!
Would you buy this PHEV for this much with 360-mi range and 3-minute fillup? Or rather pay double for the BEV version with 265-mi range and 1/2-hr fast charge?



I must admit that Extended range BEVs, with current rather primitive Heavy inefficient batteries, are not the best economic solutions. They would make more sense when batteries reach 600+ Wh/Kg. Something around 1000 full cycles @ 500 Km each would be more than enough. That will probably not happen before 2020+.

Meanwhile, there are many excellent affordable HEVs around. Many will soon give 50+ mpg. A few may reach 60 mpg.

OTOH, higher priced PHEVs can do better. Many can do close to 100 mpg. A few may soon reach 125+ mpg.

Also, many lighter improved ICEVs will soon reach 50 mpg and will force HEV manufacturers to do better and they will.

Lower priced, higher efficiency batteries and lighter bodies will benefit all four technologies by 2020 or so.


Despite burning close to half a gallon of fuel yesterday, my PHEV's lifetime average fuel economy is 126.3 MPG.

The near future brings better, cheaper batteries and more charging opportunities.  It will be easier and easier to hit 125 MPG.


Incidentally, my average fuel economy on this tank is over 1500 MPG, and will still be over 300 MPG when I hit the end of the tank a couple of weeks from now.

Roger Pham

Considering that a typical Ford Fusion gets about 26 mpg, your saved 80% of potential fuel that would have been used. This is very good for a PHEV-20.
If each city would mandate charging spots similar to handicap parking slots, then more people will be motivated to buy PHEV-20, which is more economical than PHEV-40 or PHEV-60 and allows batteries to be spread out to more vehicles.


I'd bet that even topping off the batteries of conventional hybrids (Prius, Camry, etc.) whenever they stop for more than a few minutes would yield substantial benefits.

The comments to this entry are closed.