Chassis Dynamometer

Overview

A chassis dynamometer, commonly referred to as a rolling road or roller test bench, is specialised indoor test bench equipment designed to simulate real-world on-road driving conditions to evaluate key vehicle performance metrics such as power delivery, fuel economy, and tailpipe emissions. Its core principle involves using rollers to replicate the road surface, a loading device to simulate driving resistance, and flywheel sets or electronic control systems to mimic vehicle inertia, effectively reproducing diverse on-road driving conditions within a controlled indoor environment.

Chassis dynamometers are widely utilised across automotive R&D, production quality control, workshop fault diagnosis, and official type-approval certification. In periodic vehicle roadworthiness inspections, they serve as the central equipment for executing short-cycle loaded emission tests and selected power performance evaluations. With the automotive industry advancing towards electrification and intelligent mobility, chassis dynamometers continue to evolve to accommodate new energy vehicle (NEV) testing and the functional validation of intelligent connected vehicles (ICVs).

Operating Principle and Core Structure

The operating principle of a chassis dynamometer involves positioning the vehicle's driven wheels on a set of rollers, where the rotation of the rollers equates to a moving road surface. During testing, the vehicle drives the rollers, while the internal loading unit—known as the Power Absorption Unit (PAU)—simulates aerodynamic drag, rolling resistance, and gradient resistance experienced during real-world driving. Concurrently, an inertia simulation system (either a mechanical flywheel assembly or a modern electric inertia system) replicates the vehicle's inertial mass during acceleration and coastdown.

Its core structure primarily comprises:

• Roller assembly: Supports the driven wheels and replicates the road surface. These are mainly categorised into single-roller setups (large diameter, high precision, tailored for R&D) and twin-roller setups (smaller diameter, cost-effective, suited for inspection centres and repair workshops).

• Loading unit: Also termed the Power Absorption Unit (PAU), this is the actuator that simulates driving resistance. Mainstream variants include eddy-current dynamometers and electric dynamometers (DC/AC), with AC electric dynamometers capable of regenerative energy recovery and electrical inertia simulation.

• Inertia simulation unit: Used to replicate the vehicle’s mass inertia. While conventional setups relied on mechanical flywheel combinations, cutting-edge systems utilise electrical inertia simulation via control algorithms for stepless adjustment, substantially simplifying the mechanical architecture.

• Instrumentation and control system: Comprising computers, sensors, and dedicated control software, this system manages real-time data acquisition for torque and wheel speed, computes parameters such as power output, and executes closed-loop control based on road load simulation equations.

Classifications and Key Technologies

Main Classifications:

Key Technical Metrics and Industry Trends:

• Electrical inertia simulation: Replaces mechanical flywheels with advanced control algorithms to achieve stepless inertia regulation, significantly enhancing simulation precision and equipment versatility.

• High-precision control: Delivers load response times of under 0.2 seconds and load cell accuracy of up to ±0.1% FS, ensuring faithful replication of road load resistance.

• Electrification and intelligent connectivity adaptation: Capable of simulating performance across varying battery States of Charge (SOC) and integrating into EMC anechoic chambers with turntable systems to simulate steering inputs for ADAS functional validation.

Regulatory and Calibration Standards

As critical equipment in vehicle emission inspection, chassis dynamometers are governed by strict regulatory frameworks and metrological calibration standards.

• Core calibration specification: JJF 1221-2025 "Calibration Specification for Chassis Dynamometers for Vehicle Exhaust Pollutant Testing" officially came into effect on 8 March 2026. This updated standard introduces major technical changes across its scope of application, metrological parameters, and calibration methods—such as tightening the maximum permissible error for main roller linear speed from ±0.5 km/h to ±0.2 km/h, reducing the allowable error for constant-load coastdown time from ±3.0% to ±2.0%, and mandating that parasitic power loss must not exceed 2.5 kW.

• General verification regulation: JJG 653-2003 "Verification Regulation for Dynamometers" governs the initial verification, subsequent verification, and in-service testing of various dynamometers, including automotive chassis dynamometers.

• Operational standard: Association standard T/SZJL 10-2024 "Technical Specification for Operation and Maintenance of Motor Vehicle Pollutant Emission Inspection Equipment" sets out clear operational and maintenance requirements for chassis dynamometers.

In daily vehicle inspection operations, routine self-checks of the chassis dynamometer (such as coastdown and parasitic loss checks) are essential to safeguard testing data integrity. Any failure during self-checks requires an immediate operational halt for maintenance; continuing operation risks invalidating vehicle emissions test results and may incur regulatory penalties.