On August 20, when the journalist of Commercial Vehicle News arrived in Chongqing, the sauna day has just passed, but the high temperature of 37 degrees still set off a heat wave. The scorching weather not only disturbed peoples nerve, but also tested the just-run gas-electric hybrid buses.

Overcome high temperature for smooth drive in Chongqing

On July 30, the highest temperature of downtown Chongqing soared to 40.1 degrees, registering a record same-period high since the introduction of meteorological records in 1951, and lasted until the ensuing week. During this period, the nerve of Liu Weixing, deputy general manager of Chongqing Public Traffic Bus Co., Ltd. (Chongqing Bus), was tense, because Chongqing Bus had just put into operation 30 hybrid buses on June 11. High temperature is a special test for the technical conditions of Chongqings buses, whether traditional models or hybrid models, if they overcome the high temperature, they will run smoothly. In general, engines and tires will be hot at high temperature and braking and air-conditioning performance will also be affected. Given that, Chongqing Bus chose June as the time to input vehicles to directly confront the hybrid system with most severe high-temperature test in July and August.

In hybrid bus operation, Chongqing Bus made no exception. Liu revealed, Based on the characteristics and technical requirements of hybrid vehicles, we chose Road 818 with moderate ramps and poor road conditions, which is an intermediate one among Chongqings bus lines.

According to the source, the line has a full length of 34 kilometers stretching from Chongqing Railway Station to Jiugongmiao. Now, almost all the vehicles running on Road 818 are hybrid ones, which drive every day without special treatment like traditional buses. Five round trips a day total more than 300 kilometers at most and average about 260. Both the railway station and Jiugongmiao have a large passenger flow, and the passenger capacity of a vehicle can top 100 in morning and evening peak hours. Liu said.

To ensure that hybrid buses passed the severe test, Liu conducted frequent line supervision. In the just-completed sum-up meeting, Liu announced encouraging news: the results of the continuous test of 30 12-meter hybrid buses show that the vehicles have run in good conditions at the high temperature lasting more than a week, with a gas saving ratio of more than 25%, ranking top in the country compared with the performance of the similar hybrid buses in other cities.

Lius remarks reassured Yuchais technical and service staff, because these 30 hybrid buses are equipped with the hybrid system independently developed by Yuchai. In fact, high temperature tests not only overall performance of the vehicles but also the performance of the hybrid system.

To give service support to the hybrid system, Wang Dongdong, engineer of the Engineering Department of Yuchai New Energy Power, came to Chongqing this April. From hybrid system installation to trial operation, to bulk input afterwards, he conducted full-course follow-up and periodically acquired data to analyze the operations of the hybrid system. Besides, Yuchai staffed two special hybrid system technicians for him.

Operation flexibility avoids traffic congestion

Over the more than three months since being put into operation, the 30 hybrid buses running on Road 818 have been praised by citizens and drivers.

"In vehicle operation, hybrid buses broke the restriction of traditional buses starting up by turning on ignition switches. Vehicles become automatically electrically-driven after start-up and shift to engine drive when the speed reaches 15km/h; the hybrid system has also enhanced engines power performance so that you do not have to step hard on the gas uphill, just a gentle step, the electric motor will boost the engine. The steeper a ramp, the more powerful the system. Liu was satisfied with the change in hybrid system operations.

This is because that the automatic clutch mechanism of Yuchai hybrid system is between the engine and electric motor, can accomplish a flexible switch between electric drive, engine drive and hybrid drive through program control. Besides, Yuchai hybrid system adopts Yuchais patented mode of automatic control acting on the clutch master cylinder, which can accomplish automatic clutch control while retaining the traditional clutch mechanism. Once the electric control system fails, the driver can still drive conventionally. It has increased vehicle reliability.

This has solved a big trouble for public transport companies. If the engine fails, the electric drive system can operate independently to take the vehicle to a section with a light traffic; if the electric drive system fails, engine drive may be used directly. This is a great advantage for buses and is of great value to solving urban traffic congestions.

Energy conservation, environmental protection to enhance city image

In enhancing the city image and building an environmental city, hybrid buses are also in good shape. On July 21, the Rally on Building National Environmental Protection Model Cities took place in Chongqing, kicking off the efforts to build national environmental protection model cities.

According to the test results, the noise of hybrid buses is less than 75 decibels, far lower than the prescribed noise limitation for buses. However, the most prominent characteristic of hybrid systems is energy conservation and emission reduction. Actual operations show that a 12-meter hybrid bus consumes 43 cubic meters of gas per 100 kilometers with the air-conditioner on and only 36 with the air-conditioner off, while a traditional bus consumes roughly 47 cubic meters with the air-conditioner off. The gas saving ratio of a hybrid bus is more than 25%.

Of the cities where hybrid buses run, Chongqing Buss gas saving ratio of more than 25% is marveling. To this, Liu said, Chongqings hilly road conditions are suitable to hybrid bus operations; vehicles use electricity uphill and charge downhill. In normal work conditions, a bus on Road 818 can be fully charged downhill from Eling to Shangqingsi. This is a three-kilometer long ramp, which is a normal road condition in Chongqing.

According to Wang Dongdong, the high gas saving ratio is partially due to the special road condition, but the fuel saving ratio of Yuchais hybrid systems can also top 20% in other cities. Once, a bus plant chose Yuchai engines for hybrid system matching, but failed to control fuel consumption however hard they tried, and finally turned to Yuchai. As an engine manufacturer, Yuchai enjoys an exceptional advantage in work condition calibration and fuel consumption control of engines. Wang said.

According to the source, now, Chongqings natural gas price has surged to RMB 4.6/m3. If vehicles are more gas-conserving, it means lower operating cost for Chongqing Bus Group which assumes sole responsibility for profits and losses. Liu said in view of the outstanding performance of Yuchai hybrid system and the further improvement in product performance, the company will keep to Yuchais hybrid system. The follow-up 20 buses with Yuchai hybrid system will be in place before the end of this year.

(Source: Li Ling, Commercial Vehicle News)