Germany 2012 Free Practice 3

Time of Session:

ToS (h:m:s)**

00:36:53          Grosjean reporting issues with gear shifting, asks, “are you sure everything is really right with the gearbox? Downshift don’t seems good.” Engineer confirms they can see the issue occurring over telemetry data, asked to then box and select neutral gear to coast down pit lane into the box. Grosjean responds, “but I can’t pull downshift.” Then the engineer asks him to “try not to shift” gears, but continues to ask him to shift into neutral to coast in the box when he comes in. Finally, the team confirms to Grosjean the issue is “we lost clutch LVDT”, so the team is working on a solution to be able to “keep running.”

** Time of session is the session time at which the message was heard on the television broadcast, as radio communications are delayed from when they actually occur.

What happened? The clutch slave cylinder is instrumented with a displacement sensor that is vital to all clutch operation and that is what failed for Grosjean. There are displacement sensors on the steering wheel clutch paddles as well. The outputs of both sensors are input factors into a multi-dimensional map with clutch slave hydraulic pressure as the dependent function. In a basic sense, the displacement of paddles and slave cylinder are mapped together to control how much the slave is displaced to release the clutch diaphragm. The clutch map is constantly tuned for driver preferences and clutch parameters. Bite point find procedures are fundamental to this tuning, but we’ll discuss those at another time.

What is an LVDT? The acronym stands for “Linear Variable Differential Transformer.” In our basic discussion here, we don’t need to go into how the sensor actual works. Just remember that it outputs physical linear displacement as a voltage to the data system, which is then calibrated to a parameter within the software. For a bit more information on LVDT sensors used in clutch slave instrumentation, please visit Active Sensors site here: http://www.activesensors.com/motorsport-position-sensors/clutch-position-sensors

Active Sensors is one of a few popular suppliers of LVDT sensors for motorsport use and most importantly, will work closely with teams to develop bespoke sensors for specific packaging requirements.

How did they fix the issue for Grosjean to continue? There are many redundant systems and protocols designed into a Formula 1 car to be able to compensate for failures. It would be reasonable to believe that maybe the clutch slave actuation was mapped only to hydraulic pressure, thus eliminating the failed LVDT from closed-loop control.

Germany 2012 Free Practice 2

Time of Session:

ToS (h:m:s)**

01:11:50          Glock sitting in the garage debriefing with his engineer, reports “for some reason” the quick-shift adjustment lever for brake balance is stuck “very hard” with him needing to “really hammer on it” to be able to move it. Engineer responds, “So, presuming you can’t do it with your left hand anymore, huh?” Glock replies can indeed move it, but only after pushing it “hard”

** Time of session is the session time at which the message was heard on the television broadcast, as radio communications are delayed from when they actually occur.

We often hear about drivers adjusting brake balance to compensate for rotor temperatures, KERS dynamics, or corner entry issues, but what really is it and how do they adjust it?

There are two separate master cylinders on two separate hydraulic circuits that actuate the brake calipers, with one master for the front calipers and another master for the rear calipers. Both cylinders are actuated together by the one single brake pedal. Any 4-wheeled car obviously requires more braking energy across the front axle to manage inertia of the mass of the vehicle, but how is more energy achieved at the front when there is only one single brake pedal?

The two separate master cylinder pistons are connected to the chassis from the brake pedal via a “balance bar” or also known as a “bias bar.” The balance bar mechanically dictates the ratio of piston displacement between the front and rear cylinder as the pedal is pressed. Basically, for any given distance the pedal is displaced, the front cylinder will be displaced more than the rear cylinder. With more piston displacement in the front cylinder, the front hydraulic circuit will experience a higher pressure than the rear which has less piston displacement. There are other means of fine tuning hydraulic pressure through piston and cylinder diameters, but we don’t need to discuss that for this basic explanation.

The balance bar is adjustable to mechanically alter the ratio of piston displacement. Mechanical adjustment is available to the driver in the cockpit as a “quick-shift” lever for large macro adjustments or a knob for finer adjustments. Levers can be set to make adjustments as large as 1.5% in one fast movement. The direction of lever actuation is usually intuitive for the driver to be able to use it without thinking too much about it or looking down at it. For example, moving the brake balance rearwards involves pulling the lever back, with pushing it forward to move balance towards the front. On in-car camera feeds, Schumacher is often seen actuating the quick shift lever multiple times during a lap from corner to corner.

What is the brake balance number we often hear about over the radio? Often when engineers request a driver to change brake balance, they not only ask for the percent of change, but also discuss the final total percentage. Formula 1 cars usually operate with a brake balance of approximately 56-60%. That percentage number is the ratio of total hydraulic pressure in both circuits, relative to the front axle. Basically, just keep in mind that it essentially means, 56-60% of the total braking force is being applied to the front brakes.

How is brake balance calculated? A hydraulic pressure transducer sensor is located at each master cylinder. Each sensor will thus have its own calibrated parameter in the data system. With the logged brake pressure data from each separate hydraulic circuit, we can then calculate brake balance with the follow basic equation:

First, let’s set up our 2 variables:

Fpress = Front Brake Hydraulic Circuit Pressure                                                        Rpress = Rear Brake Hydraulic Circuit Pressure

Brake Balance =

[(Fpress) / (Fpress + Rpress)] * 100%

As you can see, all the equation did was to determine the ratio of front force to the total force and multiply that number by 100 to present it as a percentage. On some in-car photos and videos, you can see the brake balance percentage designated on the steering wheel dash as “BBal.” Now you know how the data system and engineers measured and calculated that number we hear so often.

Germany 2012 Free Practice 1

Germany 2012 Hockenheim Track Map

Germany 2012 Hockenheim Track Map

POST SESSION COMMENTARY

Time of Session:

ToS (h:m:s)**

–:–:–   Ricciardo will do 2 timed laps with “constant passes” of constant speed aero testing on the straight after T6 and T11, in 4th gear, maintaining a speed of 200kph. After the first outing, he will box for a front wing flap adjustment before going back out again to do two more constant speed “passes” on his second timed lap.

–:–:–   Heikki reminded to maintain “cruise control” mode engagement as long as possible on braking into T6 because they are performing their constant speed aero test on the straight before the hairpin.

–:–:–   Kimi, running Lotus’ new double-DRS, is also reminded of his constant speed aero test parameters, with no DRS activation on his first timed lap, “aero cruise” steering wheel switch position “2”, in 6th gear, starting from the exit of T6.

–:–:–   While on track for his install lap, Schumacher is reminded to activate “cruise mode 2, if possible”

–:–:–   For Clos’ first timed outing, he is reminded of “what is important” is to “check the aero balance on the car”

–:–:–   Grosjean asks to box for changes, with his engineer acknowledging the request and asking for a constant speed aero test with “aero” steering wheel setting position “2”, in 6th gear, on the straight after T6 on his inlap.

–:–:–   As Clos sits in the garage before another outing, his engineer recounts the changes they just made to the car, including reducing front ride height for “correcting aero balance” and “tire pressure adjustments” to help with issues of mid-speed and high-speed understeer.

–:–:–   Massa told to pass through pit lane to perform a practice launch start at the end of pit lane to go back out to run only one lap around with “a constant speed again on the inlap” for “aero mapping”

00:38:21          Heikki will make an outing on medium primes. The front wing flap angle has been adjusted with a “reasonable step to see if it improves the balance”

00:31:56          Alonso complains of lap traffic holding him up and requests to box. Engineer denies his request and asks for one more lap to do a “constant speed” before boxing

00:23:48          Massa asked to perform “constant speeds again” before boxing as the rain returns and increases.

** Time of session is the session time at which the message was heard on the television broadcast, as radio communications are delayed from when they actually occur. The messages without time of session notation is due to an FOM change in the Pit Lane Channel broadcasting lacking a ‘time remaining’ display during the entire session.

We already spoke a bit about what constant speed aero tests are for and what is aero balance for the Valencia Free Practice 1 post here: http://f1pitradio.com/2012/06/23/valencia-2012-free-practice-1/ , but let’s look at it in a bit more detail in seeing a bit of what makes it tangible and quantifiable to engineers and data.

Before we begin, let’s remember that aerodynamic downforce is the force acting upon tire contact patch from aero influences reacting to the geometric shapes of the car. Those aero influences are obviously due to the bodywork, such as wings and the floor attached to the sprung mass of the car, while the tire contact patches are essentially connected to the unsprung mass of the upright corner assembles. The primary connection between the sprung and unsprung mass is the push/pullrods. Aerodynamically induced force acting upon the bodywork is thus transferred to the contact patches via the push/pullrods. As the prime load paths of force between the chassis and tires, the rods are instrumented with axial load cell strain gauge sensors, with one sensor per rod.  In the data system, each sensor will have its own calibrated parameter indicating the force applied to it at any given point on the track, able to be logged at a maximum of 400 kilosamples per second.

So, let’s say we’re analyzing a section of data from a constant speed aero test. In theory, let’s pretend the car drove perfectly straight, had no bumps in the road, and the platform of the car was perfectly managed by the cruise mode engine map, fixed drive gear, and constant vehicle velocity. With our hypothetically stable car, we will see our 4 load cells maintain stable values of force acting upon them from two things: The weight of the sprung chassis mass, and the aerodynamically induced downforce. With those 4 values, we can now calculate the aero balance of whatever setup we had on our car at the time. A basic calculation is as follows:

First, let’s set up names for all of our variables:

RodFL = Force measured at the Front Left rod                                                            RodFR = Force measured at the Front Right rod                                                         RodRL = Force measured at the Rear Left rod                                                           RodRR = Force measured at the Rear Right rod                                                      SprungF = Weight of the sprung mass forward of the center of gravity                    SprungR = Weight of the sprung mass rearward of the center of gravity

Aero Balance  =

[((RodFL+RodFR) – (SprungF)) / ((RodFL+RodFR+RodRL+RodRR) – (SprungF + SprungR))] * 100%

As you can see, all the equation did was subtract out the weight of the sprung chassis to isolate what the aero forces have induced, and then found the ratio of the total aero force relative to the front of the car. F1 cars typically operate with a 38-40% aero balance, being 38-40% of the total induced aero dynamic downforce is acting on the front tires. If you don’t care about the math, just remember as you’re listening to radio messages what that number means when you hear them mention it.

What are some of the things teams can do with the final number of calculated aero balance? As Rob Smedley informed Massa of what parameters he needed to set for constant speed aero testing, he mentioned its importance for “aero mapping.”

What is an aero map? An aero map is simply a multidimensional plot with an aerodynamic factor as a dependent function, exactly similar an engine map. Many different input variables may be ride height, wing angles, or changes in the numerous bodywork parts afforded to an F1 car. Aerodynamic functions may include factors such as aero balance, total downforce, drag, lift vs drag efficiency, etc. Below is an example of a map of aero balance as a function of front and rear ride height. The bands of color in the z-axis represent ranges of aero balance in units of percentage and the front and rear ride heights are on the x and y axis in units of millimeters.  Teams obviously possess maps generated from software simulation and wind tunnel testing, but this is their chance to validate those maps against real-world track conditions.

Aero Balance Map

Aero Balance map as a function of front & rear ride height