22 October, 2019

Tailor-made cooling for mobile machines

10 June, 2016

Modern cooling systems are now reaching the limit of what is physically possible in terms of their capacity. Therefore it is important to work with a system partner with experience when developing new designs, writes Simon Withington, product specialist coolers, Hydac Technology Ltd.

Today the design, configuration and integration of the cooling package within the overall system are fundamental in the optimisation of cooling performance. Cooling systems for mobile machines must be continually adapted to fulfil legislation requirements in order to comply with the current emissions directive 97/68/EC and the resulting increased requirements for cooling, combined with noise reduction (EC2000/14/EC).

Anyone who has looked under the bonnet of a modern mobile machine will wonder where any additional space is supposed to come from. The following example illustrates the development process of a new concept, from enquiry to final series production, taking into account the available space and compliance with the exhaust emissions level Tier IV.

Self-propelled field sprayer

The project in which Hydac acted as development partner involved a new cooling system for a self-propelled field sprayer. The machine was to be given a completely new design. The main requirement was to substantially improve visibility for the driver and in addition, reduce the noise level. The demand for greater driver visibility resulted in a reduction of the cooling pack installation space. Once the bonnet had been redesigned, a specification drawing for the cooler was made, based on remaining installation space.

The dimensions were projected linearly at the concept stage to meet the increased load from the engine. Hydac created a model using their cooler calculation software on the basis of the specification drawing. Taking into account the technical specifications of the engine manufacturer and the information provided in respect of the hydraulic and gear oil circuit, an initial calculation run was started.

Specialists are required

Given the specified ambient temperature of 49degC, and the fact that the cooling air heats up intensely from one cooling circuit to the other, the specified capacity could not be achieved in the water cooler section based on the existing stacked cooling system.

Hydac prepared a basic calculation for this. The calculation was based purely on physics principles and had nothing to do with the size and final configuration of the cooling system. Hydac initial calculations showed that the water cooler would have a temperature difference in the coolant of approx. 20degC, at maximum dissipation. The specification of the engine manufacturer was:

• Maximum permitted coolant temperature: 107degC.

• Thermostat opens at: 88degC.

• Thermostat opens completely at: 94degC.

The outlet temperature of the coolant was therefore lower than the opening temperature of the engine thermostat, either preventing it from opening or causing it to hunt (opening and closing in quick succession). In order to achieve smooth engine operation, the manufacturer recommended a Delta T in the coolant circuit of approximately 5degC to a maximum of 10degC.

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