Test rig puts the brakes on automotive motors

ZF's range of contact-free hysteresis brakes has provided the high-speed capability and torque levels required for use on a series of motor test rigs at IMRA Europe.

ZF's range of contact-free hysteresis brakes has provided the high-speed capability and torque levels required for use on a series of motor test rigs at IMRA Europe.

Designed to test prototype actuators for the Aisin Seiki Group, the IMRA rigs met load and breaking demands more consistently thanks to the use of ZF Tiratron hysteresis units over alternative braking methods.

Added benefits of the ZF system included data feedback processing via ZF's intelligent ERM control system used in conjunction with simple encoders and a custom shaft assembly.

IMRA Europe SA forms one of five R and D companies within the Aisin Seiki Group, one of the largest Japanese OEM automotive component manufacturers.

IMRA Europe's HQ is in Sophia Antipolis, near Nice, with research centres based in Kassel, Germany, and at the University of Sussex campus near Brighton.

IMRA's UK centre at Falmer, near Brighton has been commissioned to research and develop high performance motor actuators for the next generation of cars in which many functions that are currently either mechanically or hydraulically driven, eg steering, oil, water pumps and air-conditioning, will soon be powered by the high performance actuators being tested at the UK site.

One of the most important performance criteria on which the motors were tested was the amount of torque ripple they produced.

These variations in torque can cause negative effects on noise and the 'feel' of the car so it was essential that the design of the rig did not create any additional ripple effects, therefore skewing the results of the tests.

However, IMRA found that there are in fact very few methods of applying load that do not cause such effects, with the only practical options being powder, eddy-current and of course, hysteresis brakes.

After receiving the first batch of motors, Adam Pride, principle engineer at IMRA, saw a 9Nm EBU1000/10 hysteresis brake from the ZF Tiratron range as the favourable choice.

Reasons for the selection included operational benefits over powder brakes in terms of lower levels of parasitic torque and higher speed capability.

Advantages over eddy-current brakes included more precise low speed control and the ability of the EBU unit to provide full torque at zero rpm, an especially important factor in the testing procedure, as many actuators are required to start against full load.

A hysteresis brake has additional advantages over other forms of torque control systems, which include open-loop control using a simple DC power supply and, in the case of the IMRA application, closed-loop controlled by a ZF ERM unit.

The ERM control module has the capability to perform calculations and provide feedback from simple sensing encoders attached to the EBU input/output shafts.

In order to gain the most precise results possible, double-ended shafts were custom made for the application and supplied ready-fitted by ZF's specialist distributor for southern England, Surrey based Clark Electric Clutch.

Graham Butler, Managing Director of Clark Electric Clutch, explained that 'flexibility and cost were also major factors in the recommendation of ZF's hysteresis brakes for the application'.

Following the successful operation of the initial rig, delivery of a second series of motors with different capacities led to the construction of a new test system, which was specified with a 2.5Nm EBU 500/3 unit and utilised the previous ERM control panel.

Pride comments that 'using the ZF clutch system allowed us to tailor our test rigs with the minimum of investment in terms of capital cost and design time.

In fact, the EBU range covers just about all the motors used in medium size automotive actuator applications'.

The hysteresis range of brakes and clutches transmit torque via a magnetic flux, avoiding wear and the creation of dust particulates.

This makes them ideal for use in test rigs and production environments where levels of air-born contamination have to be minimised.

They are especially useful for winding-on applications in cable manufacturing or food packaging industries.

Four different versions are available to cover most requirements with torque capacities ranging from 0.4 to 38Nm and offer levels of up to 760Nm when used in conjunction with a gearbox or input.

When used as a brake, units can provide (continuous) slip powers from 250 to 2000W and peak capabilities of twice these figures.

The range is backed up by one of the most respected manufacturers of driveline technology in the world with production centres, partners and representatives on every continent.

In the industrial sector, ZF is at the forefront of developments, from individual units to complete systems solutions for all types of machinery and production units, including those used in robotic systems and the fast growing factory automation sector.

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