The Poclain hydrostatic transmission for an affordable 4x4 solution

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1 The Poclain hydrostatic transmission for an affordable 4x4 solution Poclain Powertrain s technical proposal is a surprise in the automobile industry: a hydrostatic transmission in order to enjoy four driving wheels at an affordable cost. The Poclain group generally delivers this type of product on construction equipment and some heavy trucks. The Addidrive system thus allows a transmission to be installed on the rear axle of an automobile or a light-duty commercial vehicle without having the longitudinal shaft hole constraints and for an additional weight of less than a conventional 4x4 transmission. This solution has already appealed to a leading manufacturer who should market it from 2018.

2 CONVENTIONAL 4X4 (KERAX, MIDLUM type) HYDROSTATIC 4X4 (LANDER OPTITRACK type) Front axle Front transmission Transfer box (TB) Rear transmission Rear axle Hydraulic motors Hydraulic power unit Rear transmission Rear axle Addidrive Assist system on the front axle of a Renault Trucks Premium Lander OptiTrack heavy truck The Poclain group is a specialist in power hydrostatic transmissions on heavy vehicles for agriculture, construction or handling. This company founded in 1926 produced its first hydraulic motor in 1958 and its first large shovel equipped with a four-wheel hydrostatic system in Poclain Hydraulics separated from the Poclain group 30 years ago and became an independent company. In 2012, the Poclain Véhicules division was created to develop the group on new markets, in particular the on-road market. Heavy truck makers such as MAN, Renault Trucks, Mercedes-Benz or Volvo Trucks have already adopted a hydrostatic transmission with a similar principle on the front axles (see our file, Hydrostatic front traction, off-road automated gearbox and consumption management at Renault Trucks). In 2013, the Poclain group decided to open up to the automobile market and created a dedicated subsidiary: Poclain Powertrain. This structure has the mission of placing a version of the Addidrive hydraulic integral transmission intended for private automobiles and light-duty commercial vehicles on the market. This choice is the result of a market study on 4x4 offerings. Eric Vives, director of Poclain Powertrain: The integral transmission means safety and mobility. However, it is expensive and therefore reserved to an elite of experts or premium category vehicles. Our proposal aims at a final customer surcharge of only 1,000, i.e. half the cost of current solutions. He adds: There is a real market. For example, the price of a 4x4 in Brazil is more than 20,000 whereas there is a largely untapped market between 10,000 and 15,000 euros. Poclain Powertrain proposes adding a transmission for the rear axle on vehicles with no provision for this option, specifically on front-traction vehicles in the first market segments or on light-duty commercial vehicles. Presentation of the transmission The Addidrive transmission consists of a pump that recovers part of the power from the internal combustion engine, pipes and a hydraulic motor driving the rear wheels.

3 The pump s input shaft is attached to the differential housing and the front right wheel shaft passes coaxially inside. The only major modifications on the power train besides this housing are the pump attachment (that can if needed include a wheel shaft bearing) and the length of the right wheel shaft. Two two-way oil pipes connect the pump to the rear axle s hydraulic motor which drives the wheels via a differential and two conventional shafts. Hydraulic pump The pump s flow depends on the automobile s speed. The pump and the motor have the same displacement. The pump and the motor are equipped with a multi-disk clutch in order to limit mechanical drag. An electric charge pump incorporated into the hydraulic motor and connected to the two actuators via a third pipe performs two functions: boosting (leak compensation and retention of a minimum pressure in the circuits) and clutch operation below 10 bars. The oil filter is part of this pump s circuit. Disconnection is also required beyond 40 to 50 km/h depending on the wheel diameter, in order to protect the motor from over-revving, i.e. an estimated max. speed of 400 RPM.

4 Central hydraulic motor The hydrostatic transmission is engaged by the driver by actuating a button and its activation time is less than 0.5 s. No electronic control is required in this case. Serge Nicoloff, Poclain Powertrain s marketing specialist: If requested by the manufacturer, engagement can be automated by detecting front wheel skidding or predicting ESP program skidding. This small program could be incorporated into the engine control unit. There is no blocking of the differentials but they may possibly be limited-slip on each axle even though the spirit of the project is to remain at an affordable cost. The power is limited to 30 KW and the pressure to 450 bars. Wheel motor transmission In some cases, control arms, springs or shock absorbers could impede the passage of the wheel drive shafts. To deal with this, Poclain Powertrain has developed an alternative product: hydraulic motors in the hubs instead of the rear motor. Sized so as not to increase the track, these motors have a displacement twice as small as that of the motor and the unsprung excess mass is 5 kg. Each of the two power pipes then passes via a coupling that distributes the oil to each

5 motor, with free movement between the two motors acting as a differential. It is no longer possible to install a limited-slip axle and there is no provision for a flow equalizer that would provide a similar result. The charge pump supporting the filter is independent in this case. On the exhibited demonstrator (Peugeot 208), it has been housed in the space for the spare tire. Pump technology Poclain-specific pump and motor technology has been used: whereas its rivals' hydrostatic transmissions use axial pistons, Poclain has developed a concept of radial pistons and external cam rings. Serge Nicoloff: On construction equipment, the pumps and motors are disconnected by sending a pressure onto the opposite side of the pistons to move them away from the cam rings. The springs ensuring piston contact with the cam rings are then compressed. For this project, this solution is too noisy and we have had to add clutches onto the input shafts. Pumps and motors of this size obviously did not exist in the Poclain range; they have been specially developed for this project. A plant in India will be built solely for producing them. One of Poclain s industrial challenges will be to produce high volumes at a small price whereas their various markets were aimed at niches with significantly more expensive products. The plant will be sized to produce around a hundred thousand units of each component per year.

6 Commercialization The weight of all the components is 40 kg but the total, including the various supports and protections, reaches 60 kg, i.e. an average of 15 kg less than a mechanical transmission. The pump and central motor dimensions should not pose an installation problem as their diameter does not exceed 13 cm. Fuel consumption and CO2 emissions due to this assembly are also limited. Serge Nicoloff: Our calculations show that the drag should generate 2 to 3 g of CO2 per km and the excess weight of 1 to 1.5 g/km over a NEDC cycle. Maintenance would be limited to replacing the filter every 4 years. The demonstrator is equipped with a rear trailing arm axle that is not the best architecture for a drive axle but the torque to be passed remains low (30 KW at 400 RPM, i.e. 716 Nm whereas the max. torque on the front axle in first gear varies from 2,000 to 4,000 Nm depending on the powertrain. An agreement has already been signed with a manufacturer for the supply of an Addidrive central motor transmission from The Poclain group was awarded the Trophée d Or at Equip Auto s Grands Prix Internationaux de l Innovation in the original equipment category for this solution. Author: Yvonnick Gazeau Source: Poclain Powertrain All written information present on this site remains the sole property of auto-innovations.com. Any publication, copying, distribution or retransmission of this information is strictly prohibited without the written agreement of auto-innovations.com.