Latest Test Bench Technology at GKN
- NOVOTEST Test Engineering

Low CO2 Emission due to Cutting-edge Test Bench Technology

Every year, millions of cars are produced worldwide. And there is always the same challenge for every vehicle in every country of the earth: The power of the motor is to be transmitted to the wheels with as little loss and fuel consumption and yet as reliably as possible. GKN Driveline has tackled this challenge.

When it comes to test benches, Blum-Novotest GmbH is the partner of GKN Driveline. To date, the company has already supplied more than 20 systems ranging from NVH and quasi-static ones through to 4-square test rigs. Thus, GKN Driveline relies on the entire range of drive shaft test rigs of Blum-Novotest. We spoke to Michael Hagen, responsible for test rigs in the research and development centre at GKN Driveline in Lohmar.

Mr Hagen, your cooperation with Blum-Novotest has apparently been working for quite some time now. How did it actually come about?

The test rig industry is rather small, and people know one another. In our case, it has been already since 1992. In recent years this cooperation was intensified because we had to part with one of our long-standing partners. Apart from Blum-Novotest, 20 other companies were considered as possible successors theoretically able to build test rigs for GKN Driveline. After thorough investigation, we decided in favour of Blum-Novotest and another manufacturer. 

Why did you decide to go for Blum-Novotest GmbH?

When selecting a partner for the production of test rigs, there are essentially only three criteria for GKN Driveline: Function, reliable delivery and price. We were looking for a partner with whom we could jointly develop test rigs and adapt them to the needs of our end customers. Moreover, it was important for the prospective company to have some after sales experience, i.e. in the field of repair, maintenance and calibration of facilities. Building a test rig is not a serial project, but something individual. It takes time to reach an understanding since the wording of the requirements specifications can be interpreted in different ways. It became apparent quickly that the chemistry is right between Blum-Novotest and us, and that we speak the same language. In addition, the company has many highly competent associates who are real experts in their respective fields. Thus they are able to meet GKN Driveline´s criteria with flying colours. Blum-Novotest’s decades of experience quickly pay off, because, due to their profound experience, they do not make any mistakes in the first place.

You mentioned decades of experience and good chemistry. Where else is Blum-Novotest a step ahead according to your opinion?

Their experience is reflected in the quality of their test rigs, of course, as illustrated by the following example: Wherever vibration analyses and vibration measurements are conducted, a test rig might develop its own natural vibration. The objective is to prevent this vibration from generating, since they would appear in the measuring results and it is very difficult or even impossible to filter out this vibration at the end. Blum-Novotest does outstanding design work and perfectly masters this problem.

You have just commissioned an NVH test rig of Blum-Novotest. What does NVH stand for and how is the thest bench used?

NVH stands for Noise, Vibration and Harshness, and the measurement thereof. NVH test rigs are used in drive shaft development and production. During tests, they measure the forces generated or transmitted by the drive shaft. An NVH test rig also simulates the load ratios in a car.

Bernd Donners, Test Rig Planning Electrics, Stefan Reuters, Test Rig Plannig Mechanics
and Thomas Pannhausen, Sales Manager NOVOTEST Test Engineering
Long been working very well together: GKN Driveline & Blum-Novotest

What is the typical process of a drive shaft test on an NVH test rig and how long does it take? 

This depends on the type of test and can take anywhere from ten minutes up to four hours. We usually run combined tests that take three to four hours. Under rotation, torque is built up, a steering angle is generated or a spring travel simulation is performed. No noise is measured on principle, but rather the frequencies generated by the transmitted vibrations are recorded. We measure plunging forces or the forces generated in the joint. These forces are ultimately responsible for noises being generated and transmitted. There is a basic test during which the excitation and the vibration of the motor is simulated: Using a hydraulic cylinder, a slight oscillating is caused at the drive shaft. Since the measurement is performed under torque, the drive shaft is under very high stress. In the load cells on the other side, the spectrum caused by the drive shaft is recorded via frequency analysis. In another test variant, the transmission side stands still and the drive shaft is turned under load and is angled, which generates forces in the joint. These forces, in turn, generate noise depending on the rotation speed. In this process, it has to be determined which noises are generated by the motor and which by the shaft itself. This is done by means of force measurement, since the frequencies generated there are the same ones that also excite the car body.

So using the test rigs, the drive shafts are optimised in such a way that vibration and the resulting noise generation are reduced to a minimum. Apart from these, are there any other advantages? 

Yes, there are definitely some. When testing a drive shaft, you can also determine and optimise its efficiency. Such optimisation lets you save up to two grams of CO2. Especially with respect to the CO2 limits specified by the federal government, carmakers immediately prick their ears up when they hear they might be able to save two grams of CO2 per kilometre with a drive shaft.

You mentioned carmakers. Which ones do you count among your customers?

GKN Driveline has a market share of 43 % in the area of drive shafts and I would not know which of the renowned automotive manufacturers is not supplied by us. However, our customers may be divided into two groups: the manufacturers who purchase all their drive shafts from us and the others who have their own in-house manufacturing and only purchase certain parts.

Do you use any other Blum-Novotest test rigs apart from those for drive shafts?

Apart from drive shafts, GKN also produces other driveline products such as differentials, power trains and eDrive transmissions. There are not any standard test rigs for these products yet. We are trying to change this in cooperation with Blum-Novotest. The hydraulic test rig we are currently developing jointly is one example. 

What are your expectations and wishes for the future cooperation with Blum-Novotest? 

Since I am in charge of technology, the technical improvement of test rigs is primarily important to me. Of course, the price always matters since we continue to expect good quality at fair prices also in future. However, the main thing we wish for is a reliable, long and successful partnership.