Front hub instrumentation
Within the tight confines of a Formula One car, the need to record thousands of channels of data from hundreds of sensors means packaging instrumentation needs careful forethought. A case in point would be the need to place sensors around the wheel hubs, as various aspects of wheel, brake and suspension data need to be recorded. This area inside the wheel is only reached through slim wishbones, and with the limited volume available inside the 13 in wheels, space for packaging is at a premium.
Instrumentation around the hub is typically to record wheel speed, brake temperature, brake wear and pushrod load. This is repeated for each of the car’s hubs, the sensors and interface units being common to all four corners.
A differential Hall effect non-contact sensor is used to detect wheel speed. Pointed at a ferrous feature on the brake disc bell, such as the disc mounting bolts, as each bolt passes no more than 1.5 mm over the sensor, the sensor output changes in order to calculate wheel speed. Due to the importance of this data, teams will run two wheel speed sensors to safeguard against one failing.
A vital factor in surviving a race is the management of brake temperatures. High brake temperatures leads to oxidisation of the carbon brake disc surface, which in turn leads to excessive wear. Monitoring brake temperature is achieved with an infrared temperature sensor, which is typically mounted on the carbon fibre brake ducts around the upright, with a clear line of sight at the brake disc’s surface. The sensor picks up the thermal radiation produced by the glowing brake disc and outputs this as an analogue voltage.
It’s also critical with Formula One’s carbon-carbon brakes that disc/pad wear is not excessive. Thinning brake discs will run hotter, which will in turn accelerate wear, leading eventually to catastrophic failure of the brake disc. Brake wear is monitored by measuring the displacement of the pads in the caliper via a small LVDT mounted between the caliper body and the pad. This has to be a specifically developed LVDT, due to the high temperatures found in such close proximity to the brake discs – even the back of the pad can reach temperatures of 400 C.
Connecting to the back of the upright, the instrumentation for the front suspension pushrod (or pullrod) is also passed through into the wheel. Pushrod loads are recorded for tracking suspension movement, and peak loads are also measured to ensure the safety of the composite suspension elements. An overload could lead to the carbon fibre suspension failing, so a load sensor is built in line with the pushrod, the cabling for which runs down inside the pushrod into hub area, rather than externally into the chassis where the pushrod meets the rocker.
Cables for these sensors need to be fed back into the car’s CANbus. With four cables, each with three to five wires of 22-24SWG, the cable bundle would be significant, and to pass this much though the wishbones – which already carry wheel retaining tethers and brake lines – is impractical. So the sensors are all connected to a Hub Interface Unit, which acts as a ‘satellite’ to the car’s main network and allows connectivity to the ECU via a single cable passing through the wishbone. Measuring just 55 x 39 mm and weighing 55 g, it takes up minimal space inside the wheel. This means the loom can pass back into the chassis loom via a simple two-wire link.
Fig. 1 - Red Bull’s front hub showing the cabling for the brake wear and temperature sensors (Photo: Craig Scarborough)
Written by Craig Scarborough