A Solaris hybrid bus Following the world-wide trend of searching for alternative sources of energy, we have added a new vehicle to our product range: the hybrid-drive Solaris Urbino. This innovative drive solution helps to
significantly reduce fuel consumption and exhaust emissions.
The premiere of our hybrid bus is scheduled for September of this year at the Hanover IAA. The presentation of this prototype tops the months-long effort of our engineering bureau. It goes without saying that working out a new product in such a short time would not have been possible without the support of our experienced partners, the Allison and Cummins companies.
The prototype of the hybrid drive Urbino 18 is based on the classic skeleton construction made of stain-resistant steel, as used for the whole range of Urbino low floor city buses.
The Cummins ISLe4 Diesel engine with 340 hp has a capacity of 8.9 liters and a maximum torque of 1,500 Nm at 1,200 rpm.
The second drive element, and its main component, is the EP DRIVE system by Allison. 
The Cummins engine and the Allison system together form the hybrid drive, distinguishing itself by properties of the parallel and series connection alike.
The hybrid drive has been placed at the front part of the bus, immediately behind the fender shield. Thus, it was possible to obtain 50 + 1 seats, 14 of which are accessible directly from the low floor section. The hybrid drive Solaris Urbino 18 prototype can carry a total of 131 passengers. This figure can be optionally altered to meet the requirements of the customer.
The drive system has been placed in the front part of the bus, behind the first left-hand fender shield. The drive train is diverted to the second (center) axle.
The hybrid drive is completed with roof-mounted batteries and an inverter. The following chart gives a schematic illustration of the hybrid drive in the Solaris Urbino 18 prototype.
Schematic illustration of the hybrid drive in the Solaris Urbino 18: 
THE EV DRIVE
Is the central element of the hybrid drive, in which the combination of the torques of both engines takes place (blending). It consists of two electric engines, two synchronous couplings, and three planetary transmissions. Optically, the EV module resembles a traditional gear box, and weighs 464 kilograms.
Description of the illustrations. 
THE BATTERY
The energy reconditioned during the slowing-down process, converted accordingly, is generated in special roof-mounted batteries. Thus, the batteries utilized by the hybrid drive don‘t need to be recharged through outside sources of energy.
The lifetime expectancy of the nickel-hydride batteries (NiMH), weighing 410 kilograms, amount to about 6 years, depending on the kind of use of the bus.
THE DUAL MODULE (DPIM)
The DPIM (dual power inverter module) is an important electric component of the Allison system. The DPIM consists of two converter modules AC/DC - DC/AC, with a total weight of 91 kilograms. The temperature of the module is kept constant by an oil radiator.
The shortest possible description of the dual mode drive is: use of the electric engines in order to assist the standard Diesel drive, at its optimum load. By a separate control unit, which coordinates the activity of the two drive systems, they are ideally synchronized.
THE DIESEL ENGINE
The Cummins ISLe4 engine, with a capacity of 8.9 liters and a maximum torque of 1,500 Nm at 1,200 rpm, has been adapted for use in hybrid drive systems and complies with the Euro 4 standard. This unit is economical with regards to fuel consumption. Its main distinctions from the standard version are, among others, its electronic programming, elimination of the starter engine, and an adapter kit.
THE CONTROL UNIT
The system is completed by two control units, mounted onto printed circuit boards. The 1,000/2,000-type units made by Allison weigh only 2.3 kilograms. Among the tasks of the first unit are checking and controlling the hybrid drive, while the second unit coordinates the cooperation with the other vehicle modules.
The hybrid bus doesn‘t force any radical changes upon the driver concerning technical aspects and vehicle control. The control switches on the instrument panel
The hybrid bus doesn‘t force any radical changes upon the driver concerning technical aspects and vehicle control. The control switches on the instrument panel are analog to the traditional bus versions. A so-called DNR control unit (drive, neutral, reverse) has been introduced to operate the hybrid drive. The traditional brake is used only rarely in the hybrid vehicle, as releasing the accelerator is sufficient to slow down the bus. The brake intensity is adjusted by the DNR control unit, which also allows basic diagnostics of the drive system.
EXPERIENCE IN USE
Allison has performed a series of tests in Seattle, Washington (USA) in March of this year, during which the parameters of conventional drive buses were compared to those of analog hybrid drive buses. The results clearly speak in favor of the hybrid drive.
The test results proved as follows:
- lower fuel consumption (by 20 to 43 percent)
- reduction of pollutant emissions (by 10 to 39 percent concerning nitric oxides)
- reduction of solid particles in the exhaust fumes by 51 to 97 percent.
The majority of bus operators will get convinced by the first argument, the reduction in fuel consumption in hybrid buses.
Solaris Bus & Coach is planning its own studies of hybrid buses in comparison to traditionally powered vehicles, analog to the tests conducted in the United States. These will be the first comparative tests of their kind in Europe.
Further parameters of the hybrid drive Solaris Urbino 18:
1. Front suspension / steering ZF RL 75 EC
2. drive axle AV 132 80/5
3. rear axle AVN 132
4. central lubrication system KFBS1 with auto diagnosis
5. articulation joint Hemscheidt, puller-type
Press releases
Information Solaris
Solaris Bus & Coach sp. z o.o. is a leading producer of city and intercity buses in Europe. It focuses on the development of low-emission and zero-emission vehicles, i. e. electric and hydrogen buses as well as trolleybuses. Over 25,000 Solaris vehicles have been delivered so far and they ply the streets in 850 towns and cities across 33 countries located throughout Europe as well as beyond it. Solaris is part of the Spanish CAF Group (Construcciones y Auxiliar de Ferrocarriles) S.A. From conception, to the design and manufacturing phases, all Solaris buses are produced in Poland. All activities undertaken by the company are in line with its mission, which is reflected in the brand’s promise: to change the image of public transport. Solaris also actively partners with public transport operators and provides them with comprehensive support in their transition to zero-emission mobility. Solaris products have been repeatedly awarded for quality and innovation. The Urbino 18 hydrogen bus has won the prestigious 'Bus of the Year 2025' title.
Additional information
Mateusz Figaszewski
Institutional Partnerships and External Relations Director
mateusz.figaszewski@solarisbus.com
