The MTS Vehicle Dynamics Simulator consists of seven hydraulic actuators, one “road” actuator under each wheel, and three “downforce” actuators that connect directly to the chassis. The combination of all seven hydraulics makes it possible to replicate the suspension movements seen by the car at the track. The road actuators are used to simulate the track surface, such as the roughness, bumps, and curbs. Whereas the downforce actuators are used to simulate loads from aerodynamics, banking and load transfer due to cornering, braking or accelerating.
To replicate the track on the simulator, the engineers at Öhlins can use either data acquired at the track by the customer or they can generate a file using information from the team about the vehicle and the track. With the data measured from simulation, the engineers can accurately verify and optimize performance parameters such as tire load variation, a measurement of mechanical grip, for various chassis and suspension settings.
The Öhlins 7-post rig can test vehicles of all sizes ranging from Formula SAE or quarter midgets on up. The track width and wheelbase dimensional limitations are
min. 25 in. (63.5 cm)
max. 142 in. (360.5) cm
min. 42 in. (106.5 cm)
max. 83 in. (210.5 cm)
road actuators = 6000 lbs (28kN)
downforce actuators = 3000 lbs (14kN)
The stroke of the downforce and road actuators are 12 in. and 10 in., respectively. The testing process can be performed by two methods, track replication or generic input. The track replication method will help tune your suspension for a specific track or segment of a track while generic input will help improve the car in general . In order to replicate a track that you would like to test, you will need to supply us with some car information and track data, please refer to the Pre and Post-information section. The system can record other various sensors that your car is equipped with during the test, such as load cells, potentiometers, accelerometers, etc.
Before you arrive, the 4 position controlled actuators are moved to the proper track and wheelbase, but to attach the down-force actuators to your vehicle, some brackets will have to first be mounted to your chassis in three places, also before you arrive. The most common layout is 2 in front and 1 in the rear. The specific bracket locations will depend on the design of your chassis , the dimensional limitations of the rig and the forces that needs to be applied. The team must contact Öhlins prior to making these attachments to verify that the locations that have been selected are suitable for the type of testing to be performed. Keep in mind that the farther apart the front 2 brackets are the more torque can be applied to induce roll, however, the smaller the allowable angular displacement. The same situation applies to the distance between the front and rear brackets to induce pitch. Below is a drawing of an example bracket (see figures 1 & 2) and the specific bracket locations of a few common chassis. Our shake rig is quite adaptable, so there are other locations and/or brackets that your team can use, but please contact us first to see if they are acceptable. The engineers at Öhlins can assist with selecting the most suitable locations for your vehicle and testing needs.
The bracket should fit the ¾ inch rod end on the downforce post see figure 3 for an example. The brackets will allow more misalignment with the added inserts, shown in figure 4.
Figure 1 Figure 2
Figure 3 Figure 4
3/4" Rod End Example Insert
Based on a 105” – 112” wheelbase, the two front brackets are generally welded to the chassis’s frame rails just in front of the anti-roll bar and the rear bracket is mounted in the center of the chassis’s rear cross member just behind the fuel tank. It is not necessary for the brackets to be welded but if they are not, keep in mind that they must withstand 3000 lbs of force, in either direction.
Öhlins has brackets to fit most open wheel cars both front and rear but some of them require that the wings be removed. In this case, the teams can compensate for the difference in weight by using ballast. If your chassis is new to us we will need to have a discussion about how to attach the downforce actuators. Below is an example of how a Champ Car is fitted to the shake rig:
The information needed to get the rig ready for testing your vehicle is the front and rear track width, wheelbase, distance to downforce brackets, and unsprung weights. If you would like us to prepare a specific track file for you then we will need either the damper displacements and/or damper load cell data traces (logged at 200 Hz or more, preferably 500Hz) as well as the corresponding motion ratios, spring rates, and center of gravity location. Then, we will need to test the car with the exact same set up as when the data was collected so that we can compare the track and rig data to ensure proper suspension loads and travels. This is done in the beginning of the first test day. Once we have finished generating the drive file to match the track, you are free to make any changes that you want to test. We allow the teams to drop off their truck and/or trailer the day before and for an extra fee we can connect the car to the rig that night to reduce down time on the first day of testing. After your testing is complete you will be given both the raw data and the data in a format we believe is most useful when tuning your suspension, called the RunLog. If you have any questions regarding the results or would like help interpreting them we do offer analysis guidance and/or trackside support. Öhlins can also help with statistical analysis to quantify which parameters are affecting the on track performance the most.
Additional customer sensors such as damper potentiometers can be recorded with our system. To do this the team has to provide cables with male(female at rig) 9 pin D-sub connectors at least 5 feet long with the pin out listed in the table below. Please let us know which sensors you will want to use before the test so we can prepare these channels. Also, you will need to give us the calibrations for the sensors or inform us that you want to calibrate the sensors before we start testing. This calibration process adds about half an hour to the preparation time for four dampers potentiometers.