In clear steps from hydraulic to electric

The development of electric drives for mobile equipment is now happening with great pace. ELSTO Drives & Controls, an important player on the mechanical drives market, with plenty of practical electrification expertise, acts on a regular basis as sparring partner for VDL Translift. This Dronten based company produces a number of different body systems for waste collection vehicles. The Translift produced systems are installed increasingly on electric truck chassisTogether with ELSTO the VDL engineers develop innovative and sturdy solutions.

VDL Translift produces body systems in a number of variants for waste collection and waste transport vehicles. The company produces side loaders with an FS system (fixed body), side loaders with an IES swap body system (quick change body), but also systems that are loaded with a crane, to empty underground  and street level containers. In addition to this VDL builds waste collection systems on fully electric trich chassis.

In the past the body systems were primarily hydraulically driven. E.g. driving the compactor screws, powering container lift systems, and lifting and emptying wheelie bins. Over the last few years the electrification of these systems was studied. Bas Suidgeest, Project engineer at VDL Translift, explains what has been achieved so far in this field. “For compacting and compressing the waste in the collection vehicle, two screws are used that press the waste to the rear. This is a rotary movement that is now driven electrically” In the past we used hydraulic motors that drove the screws via planetary gearboxes. Both the motors and the gearboxes are heavily loaded in waste collection applications. The load largely depends on the type of waste handled by the screws.  “The load and wear pattern differ per fraction that is being picked up by the waste collection vehicle “explains Suidgeest. “Is it paper, residual waste, plastics or biodegradable waste?  With plastics the wear and tear is much less, while for instance cardboard is very hard. In the past we had problems with the planetary gearboxes every now and then. Then ELSTO appeared on the scene. They could supply the gearboxes that were strong enough to cope with every day waste collection duties.

Transmission specialist ELSTO Drives & Controls has been a VDL Translift supply partner for many years now, supplying Bonfilioli planetary gearboxes. Later the supply of ELSTO electric motors, frequency inverters and control cabinets were added. Gerben Worst Senior Account Manager at ELSTO explains the construction. “The compression screw is driven by the output shaft of the gearbox. On the input shaft the hydraulic motor used to be fitted. To enable the use of electric motors an extra reduction stage was added, to compensate for the higher motor speed. ELSTO supplies the gearbox with an electric or hydraulic motor. For the electric version we developed a dedicated control cabinet that we assemble in our workshop”.

Two years ago VDL Translift built the first prototype where the compactor screws were driven electrically. Soon after the first two customer vehicles followed. “It started with electrifying the chassis,” explains Suidgeest. About three years ago we built four prototype vehicles that could be driven electrically. In the waste collection sector this is an important advantage, while these vehicles are often operated in inner cities and do not clock up many miles. After that we made plans to electrify the body structure of these vehicles. A logical next step was the electrification of the compactor screws, in particular while this concerns a simple rotary movement.”

During the electrification of the screws much time was spent on studying the power consumption of the electric drives. It took quite some time and effort to optimize this. The VDL and ELSTO engineers closely cooperated on this subject. It also proved difficult to estimate the electric motor power. Suidgeest “We used the hydraulic version as a starting point. Electric motors can provide well above their nominal power until their thermal limit is reached. A waste collection vehicle empties containers, then compresses the waste, drives away and stops again. Sometimes 10 metres, sometimes 500. After each cycle the electric motor can cool down before it can start afresh again. We put a lot of research into determining the optimum nominal power. We did not want to install a motor that was too big, too heavy and too expensive.” In the end we chose an air-cooled servomotor. “It is more economical and requires less maintenance.”

The electric motors and the motor cabling are IP65 rated in view of the operating environment. The frequency inverters and other electronic components are mounted inside a control box and are protected from the elements. Both the electric motor and the gearbox are calculated to achieve a certain lifetime. The previous generation gearboxes had a shorter lifetime due to contamination and moisture. For that reason we approached ELSTO. Suidgeest: “ The lifetime depends largely on the manner the equipment is used. Is the waste collection vehicle used in a 1 shift working day, or is it used in 3 shifts in a 24 hour period? On the motor side the load is quite low. On the other hand the gears directly connected to the screws must  transfer the full force. We see some wear, but this minimal.”

“There are more hydraulic drives on the VDL vehicles bodies that have a good electrification potential. At the moment we are looking into which movements we can also electrify,” explains VDL  Translift managing director Mathijs van der Mast. “Technical students are currently working on the subject, first describing the movement and analysing the forces involved in the movement. Based on feasibility, potential energy savings and reduction of complexity we will decide what to do. What first, and what makes sense? Point on the horizon is a completely fossil free vehicle. So no fuel, but also no hydraulic fluids. Leaks are always possible, and sometimes it goes wrong when an hydraulic hose breaks. Also connecting up an electric drive is much simpler compared to an hydraulic system.” But van der Mast knows too you cannot electrify literally anything. “At the moment we cannot do without hydraulics for some type of drives. It has a number of strong points. It is compact and powerful. We do see that suppliers of hydraulics add more and more electrical drives to their portfolios. Things are definitely starting to shift.

The VDL engineers use the ELSTO Drives & Controls engineers on a regular basis as a sparring partner. Sharing knowledge is an important part of this. “Our engineering team consist  of a mix of automotive- and mechanical engineers complete with the associated software knowledge,” according to Suidgeest. “At the moment we gather a lot of knowledge regarding electrification. This is also done during sparring sessions with suppliers as ELSTO. It is all part of the transition to electric.

Van der Mast is very happy with the cooperation. “In the past another VDL company also used planetary gearboxes. My colleague there was always very positive about ELSTO. The fact they are independent was a definite plus for us. Some companies are only pushing their own solution or their own brand while you at that moment are not yet ready to make a choice for a given solution.

According to Worst this is caused by the ELSTO background: “We have long been a supplier of products for the machine building industry. For quite some time we see a shift there towards system integration. We keep an open mind for new applications and together with the customer we see what the right solution is”.