Application · Powertrain
Measuring torque on a truck solid axle, with strain gages inside the axle shaft
In brief
Torque on a truck solid axle is measured by deep-bore gaging. The axle housing leaves no room for a slip ring or a telemetry transmitter around the shaft, so the gages go inside it. A hole is drilled through the center of the production axle shaft, past the hub bearings, and strain gages are applied to its wall. The wires come out through the center of the hub to a slip ring or a telemetry package bolted to the standard wheel.
- Up to 36
- circuits on the Wheel Instrumentation System
- 1 024 ppr
- optional encoder for wheel speed, up to
- 9 V
- standard batteries of the Telemetry Wheel Package
Why a solid axle cannot be instrumented from the outside
On a half-shaft, a tubular slip ring or a telemetry transmitter is mounted around the shaft. On trucks and other vehicles with solid axles, this is not possible. The axle housing restricts the space around the drive axle.
The torque is still measured on the production part, from inside the axle shaft.
Strain gages on the wall of a bore
Michigan Scientific instruments the inside of the axle. A hole is drilled through the center of the shaft and extends past the hub bearings. Strain gages are applied to the walls of the hole.
The torque between the differential and the hub is then measured directly, without any interaction with bearings or seals. The bore has a minimal effect on the torsional stiffness of the axle.
From the bore to the recorder
The signal wires are routed out through the center of the hub. From there, a slip ring or a telemetry package on the wheel carries the signal to the data acquisition system.
- 01
Gage the production axle shaft
The production axle is drilled through the shaft and strain gages are applied within the bore.
Custom strain gage transducers - 02
Seal the wires at the hub with a connector
The wires come out through the center of the hub and end in a sealed connector, to which the slip ring or the telemetry package is plugged.
- 03
Mount a slip ring or a telemetry package on the wheel
Both are mounted directly to the standard wheel, with the wheel mounting hardware. The Wheel Instrumentation System mounts through a plate and collet lug nuts machined for the vehicle, and fits heavy trucks.
Wheel Instrumentation System - 04
Record torque with wheel speed
An optional encoder on the slip ring gives wheel speed, so torque and speed are recorded together.
Slip ring or telemetry at the wheel
The signal can be routed through either a slip ring or a wireless telemetry system. Both sit outboard of the vehicle wheel.
- Slip ring: optional encoder for wheel speed. It can be mounted to a Wheel Instrumentation Package that contains strain gage and thermocouple amplifiers.
- Telemetry Wheel Package: weatherproof, powered with standard 9 V batteries, and low profile to limit the extension past the vehicle body.
- Wheel Instrumentation System: 4 to 36 circuits, up to 2 000 rpm, waterproof for on-road and off-road driving.
The same gaged axle on a dynamometer
Deep-bore gaged axle shafts are also used in the lab, on a dynamometer that measures the torque and the speed of the axle. Wireless telemetry is used there: its digital link has no contact, so nothing wears during long dynamometer runs.
The method is used on Class 8 electric trucks, where efficiency decides the range on one charge. On the road, the efficiency of the axle is found by comparing the torque into the axle with the torque measured at the wheel by a wheel torque transducer.
What you get
The torque between the differential and the hub of a truck solid axle, measured on the production shaft with no effect from bearings or seals. The signal is taken at the wheel, by a slip ring or by telemetry, on the road or on a dynamometer.
Frequent questions
What is deep-bore gaging?
Deep-bore gaging is a method of applying strain gages inside a deep bore in a component. On a solid axle, a hole is drilled through the center of the shaft, past the hub bearings, and the gages are applied to its wall.
Does drilling the axle shaft change its stiffness?
The bore has a minimal effect on the torsional stiffness of the axle.
Why not use a tubular slip ring or clamp-on telemetry on a truck axle?
There is no room. On a solid axle, the axle housing restricts the space around the drive axle, so a tubular slip ring or a telemetry transmitter cannot be mounted around the shaft.
Can a deep-bore gaged axle be used on a dynamometer?
Yes. Deep-bore gaged axle shafts are used in lab testing, with a wireless telemetry system. Its non-contacting digital link does not wear out during prolonged dynamometer runs.
Similar applications
All applications-
Powertrain Axle and half-shaft torque Drive torque measured on the production shaft, with a slip ring or telemetry to bring the signal out. -
Electric EV powertrain torque Torque at each stage of the electric drivetrain, from gearbox shafts to the wheel, to see where power is lost. -
Powertrain Drive shaft measurements Torque, strain and temperature from a drive shaft with no free end, through a slip ring that slides over the shaft.