Among the bus branch, the hybrid drive of the Solaris Urbino 18 is rated the absolute innovative drive. When searching for the optimum solution, we resorted to the experience gathered by the Allison Transmission Co. (a branch of the global player General Motors), whose hybrid drive has convincingly proved successful in hundreds of American buses.

The most simple way to describe the hybrid drive is: Emplyemnt of electric motors in order to support the Diesel drive, which, accordingly, operates at maximum fuel efficiency at all times. Unused energy under operation is being stored in special batteries, which are also being charged while braking. The energy stored this way is being re-used to accelerate the vehicle.

The Diesel engines Cummins ISLe4 with a power output of 340 hp and a capacity of 8.9 liters, and the ISBe4 engine with an power output of 250 hp and a capacity of 6.7 liters have been adapted for use with the hybrid drive. The second drive element, and its main component, is the EP DRIVE system of the Allison company.

The hybrid drive has found ist place in the anterior of the vehicle, behind the wheel arch, allowing for a total of 53 + 1 seats. All in all, the Solaris Urbino 18 Hybrid Drive can transport up to 161 passengers. This figure may vary optionally, according to the client‘s individual demands. The hybrid drive works on the second (center) axle. It is accompanied by the roof-mounted batteries and an inverter, allowing for an optimal dispersion of acle loads.

The EP drive system is the central element of the hybrid drive, where the blending of the two engine torques takes place. It consists of two electric motors, two syncronous clutches and three planetary transmissions. Optically, it resembles the traditional gear box.

The BATTERIES - The energy derived from braking is being stored in a special battery mounted oin the roof of the bus. Thus, the batteries employed in the hybrid drive are being charged every time the bus brakes and are completely independent of any outside source od energy. The lifetime expectancy of the nickel-metal-hydride batteries (NiMH), weighing in on 410 kilograms totals about 6 years, depending on bus operation.

The INVERTER, a so-called Dual Power Inverter Module (DPIM) is an improtant electrical componant of the Allison system. It consists of two inverter modules AC/DC - DC/AC, weighing a total of 75 kilograms. The module temperature is helt at a constant level by an oil radiator.

The CONTROL UNIT - the system is completed by two circuit board mounted control units of the Allison 1000 / 2000 type. The first unit‘s task is controlling the hybrid drive, while the second unit coordinates coopeartion with the other drive modules.