BRNGT4

Does anyone have a definitive answer as to what the level sensors do. The GT4 has four of them and i highly doubt that they are just there for the headlights. I ask this because i have the extended monoballs on the rear and installing those causes the bracket for the sensor to move as well. I have my doubts that the reason my car has been acting funny is because of the movement in the sensor. So if anyone knows for sure what exactly the level sensors are for please educate us.

orthojoe

Are you using the RSS XL monoballs? We discovered the issue during the install on my car and RSS made brackets to account for the issue.

What issues are you having with the car?

okie981

When I made this post:
https://rennlist.com/forums/gt4/9735...l#post13928959

I didn't realize the GT4 had 4 of these sensors, never really noticed it when I looked under my own car. I thought the car only had 2, 1 front and 1 rear. That's why I thought they were only for headlights. When I saw your recent posts on other threads I went searching my 981 Boxster S Service Information document and found in the section on PASM that the 4 sensors, one on each corner of the car, are used by PASM for pitch and roll inputs.

From the 981 Boxster SIT document:

"4.5 Porsche Active Suspension Management (PASM)
PASM is a shock absorber system for active and continuous damper control at the front and rear axle and is optional on the Boxster models. PASM has been revised and enhanced to optimize the control and the resulting improvement of the driving comfort and driving dynamics. In contrast to the previous models, there are four additional angle sensors on the front and rear axle and another front left body acceleration sensor for even more precise control. The damping force for each wheel is individually regulated, depending on driving style and driving conditions. The result is significantly enhanced comfort in both programs.
Angle sensors
The four angle sensors at the front and rear axle are used in addition to the body acceleration sensors for detecting and evaluating rolling and pitching movements. The road conditions are also determined according to the angular velocity and transmitted to the control unit."

One can assume PASM on the GT4 is similar to the Boxster version. I'm editing my older post in the other thread to make a cross-post to this post.

If you have disabled PASM and are using another suspension computer like DSC, I guess it depends on if DSC takes inputs from the 4 angle sensors whether or not you need to leave the sensors intact.

jmartpr

From the looks of the way the sensor is actuated is kind of a lever mechanism. Could it be that moving the position changes the movement ratio and thus different readings? On the DSC I can't confirm it uses them but chances are very high as DSC uses every input available to make the suspension fully active with a wider range of adjustment.

Tom@TPC Racing

Yes, DSC does use data from the factory ride height sensors. In the DSC tuning software, Velocity table(as in suspension travel velocity, not vehicle velocity). See screenshot below from DSC tuning software.




DSC uses the ride height sensor data to determine whether each corner is on compression or rebound, and the rate of travel defined as Low-speed, Med-speed, and Hi-speed.
Low-speed is <3.0 inches per second of travel
Med-speed is 3.1 to 6.0 inches per second of travel
Hi-speed is >6.1 inches per second of travel

With Low, Med, and Hi-speed adjustment on compression and rebound, just the DSC Velocity table alone makes the shocks 6-way adjustable. DSC is an extremely powerful tool.

FYI, any DSC user who has changed their ride height should Zero the ride height sensors to new ride height so that the system doesn't think the suspension is compression or rebound when the vehicle is standing still! Same goes for PASM, PSM, ABS, and headlamp leveling in order for these systems to function properly! For the factory systems is more so for the PSM and ABS, the PASM does very limited things(if any) to velocity, the changes are mostly to lateral G.

The old days are gone when people can change ride heights without zero'ing the electronic systems on thesse newer car. Factory systems needs PIWIS to zero. DSC needs free DSC tuning software, a PC, and mini-usb cable. Here's a youtube video on zero'ing ride height sensor for DSC (we call it "Zero Travel" procedure)-

Mech33

Tom, what is the latency from when the shock compression speed changes, to when DSC receives an accurate measurement of the new speed, to when dampening coefficients are physically changed in the shock based on DSC commands (total loop)?

And based on that latency, how much travel occurs in the shock at the high compression speeds before DSC can actually start influencing the travel?

Tom@TPC Racing

By your questions, sounds like you are a system design engineer by profession, so to answer your questions to the level that you expect, I have the following answers from our system design engineers. Just to clarify, I am not a design engineer by profession although I do design some mechanical parts that go on race cars. My primary role is product and setup support for end users. Anyway, below are the answers for your questions right from our design engineers-

The velocity loop involves many conditions from the other sensors on CAN along with the ride height sensors. For the most part it reads the ride height at a rate of 10kHz then looks for a ride height change of at least .032"(0.821mm). The .032" movement then is filtered using the DSP micro to determine if a consistent velocity as compared to the last .032"/1ms(millisecond) earlier was greater or less to determine the velocity direction then the difference determines the rate. This is a very simplistic answer to what is really going on as it uses the other CAN data as well, 10kHz sample rate filtered to a 0.032"/1ms window to update the next change.

The limitation here isn't in the electronics, it is in the shocks. The OE(Bilstein) shocks which can only change the internal valve position in a non-pressure condition so unless the shock is in a vibration that unloads the valve it’s movement is somewhat delayed mechanically. The Tractive shocks respond in 3-6ms and impervious to pressure so they will take full advantage of the velocity unlike the OE that respond in >20ms unloaded. Example is in 6 inches at 125 mph the DSC can re-valve all shocks using Tractive.

The response time of the OE(Bilstein) shocks is predicated on the hydraulic load and ranges 20-100ms. The velocity function is highly effective in adjusting the rebound to improve grip and comfort. During braking the front compression is adjusted the raising brake line pressure from CAN data before the compression(front dive) even occurs. This characteristic is reported by many DSC users which improves vehicle stability during braking. Despite of the OE shock's limitation the level of performance that can be had from OE shocks with DSC is very good as optimizing the OE shocks is what DSC does.

However to get the full benefits of the velocity tuning Tractive shocks operate in the 6-10ms range. Velocity tuning is very accurate in the 2-10 in/sec area .

Velocity is only 1 out of 7 tuning tables in the DSC software. Velocity function is not applicable on 987/997 cars since these earlier cars aren't factory equipped with ride height sensor at all four corners.

MarcD147

thanks Tom for the level of detail in your answer !!

Mech33

Thanks Tom for the transparency; interesting discussion and response (for me at least). It sounds like the physical response of the OEM GT3/GT4 shocks are the limiting factor on the control loop speed, especially because other inputs are used to determine what's going on.

That makes a lot of sense to use data like brake pressure (and probably change in steering wheel angle vs. vehicle speed) as faster inputs into the model of the vehicle dynamics rather than simply waiting for the resulting compression of the suspension itself (and picking that up via the level sensors). Simply using the level sensors and differentiating / filtering doesn't feel ideal, but they can be used to update / correct the vehicle model in real time of course.

Cool product idea, and it sounds like folks like it.

Any thoughts on why Porsche doesn't control the shocks in this type of way from the factory? Seems like low hanging fruit since it's firmware / software updates on top of the existing hardware platform.

Tom@TPC Racing

Thanks! We have no idea why but we are happy that they aren't. The idea for DSC started when Mike Levitas bought a 997.1 Carrera S back in 2005. This was the first Porsche production car with PASM. Being a pro race car driver and race engineer he was fascinated by the OEM literature on PASM and excited to drive the car. But when he got the car the suspension fell short of his expectation which left a void in him to design a better system. 12 years later, here we are.

acalayag

Thank God I found this post. Been struggling with my GT4’s suspension fault errors for a year on T6 at Laguna Seca when the suspension fully compresses. All this after I installed the RSS XL front mono ball ends and CS camber plates. I also installed the special sensor brackets for the RSS XL. However, the sensors have never been reset/recalibrated to zero. The dealer due to seeing the aftermarket mono ball ends didn’t want to diagnose or even tell me all it needs is a recalibration. And I was ridiculously told the solution won’t fall under warranty since the problem only happens in track conditions

Tom, I’ve been wanting a DSC but held back until my suspension fault issue is fixed. Ironically, it looks like the DSC install process would actually fix the issue. Can you confirm the DSC zero’ing does the same thing as PIWIS to zero out the sensors for the stock PASM controller?

Tom@TPC Racing

Hello. DSC V3 has Travel Sensor Functions that not only zero's the sensors it can also monitor and data log the sensors' activity. Once the sensors are zero'ed to car's ride height the other systems on the car will recognize the setting as zero. DSC users can see how far off the actual values are before zero'ing.
Below are images of a Travel Sensor(aka Ride Height Sensor). There's one sensor per corner on 991/981 cars.
When the car's ride height is lowered or when LCA(Lower Control Am) shims are added to the "inside" for the bracket or when longer inner portion LCA is installed this sensor's resting position will change. This change can affect some of the electronic systems on the car; from head lamp leveling, to FAL, to other driving performance functions.




Disclaimer: If the suspension is setup in such as way that the sensor itself is mechanically out of range(sensor's travel range bottomed out) then this in itself will causes an error message. This is completely unrelated to DSC and can only be fixed by mechanical labor.

acalayag

Thanks Tom, When I took it to the dealer, they said it's the right rear sensor that's triggering the fault. I finally have the TPC offset toe link installed correctly and will call you to order the DSC.

Tom@TPC Racing

You're welcome. It is plausible for one sensor to trigger a fault if shims were added on one corner which changed the resting position of the sensor enough. Corner balancing changes the resting position as well but usually that's only a small change not enough to trigger fault.

Tom@TPC Racing

For those interested, here's a video on how to zero the ride height level sensors using DSC -