Capabilities: The machine is capable of "surge torque" of 50 N-m (440 inch-pounds) at any speed to 1800 degrees per second, reducing to a continuous 25 N·m (220 inch-pounds) after 2 seconds. The maximum torque utilized is controlled through the servo amplifier by the individual program. Maximum "no-load" speed is 2600 degrees per second. Frequency response depends on the inertia of the vehicle steering system, which is dominated by the steering wheel inertia. In testing of a simulated airbag-equipped full-size car (inertia 62 gram-meters2 (0.55 lb-in-sec2), the -3 db frequency response bandwidth was measured as 6 Hz at ±30 degrees and 4.2 Hz at ±60 degrees; and ramp speed in a 180 degree, 0.1 second trapezoidal command was measured as 1800 degrees/second. Holding torque gradient is essentially infinite, due to a fast integrator in the forward servo loop. Steady state torque measurement is linear to 1.0 percent (0.5 N-m max deviation from a least-squares straight line over ±50 N-m). Accuracy of moving torque is 0.3 N-m over ±10 N-m (±2.6 inch-pounds over 88.5 inch-pounds); and ±0.2 N-m over ±5 N-m.
Operation: The steering wheel is fitted with four switches and two direction indicator lights. ON/OFF and DRIVER/GROUND paddle switches enable or disable the entire system and the grounding solenoid relay. Two thumb-operated switches are provided. The ENERGIZE switch controlled by the right-hand thumb energizes the system by switching the battery to series connection and (after the servo amplifier self-checks for faults) releases the fail-safe brake; and the PROGRAM switch controlled by the left-hand thumb controls the program sequence. Unless the ENERGIZE switch is depressed, the motor shaft is locked by the failsafe brake, and the servo amplifier output stage is unpowered. The PROGRAM switch is used to enable the program sequence counter when depressed and hold it in reset when released. The PROGRAM switch also engages the system grounding brakes, unless that function is prevented by the DRIVER/GROUND switch. The direction indicator "klutzlights", provided for drivers with short memories, indicate the direction of the selected initial turn. They are turned ON by the ENERGIZE switch, and OFF by the PROGRAM switch.
In operation, the driver selects the steering program, the steer amplitude, and the direction of the initial turn using the hand-held command module. The ENERGIZE switch is depressed, to power the system. The failsafe brake is released, but since in the absence of a program there is a zero angle command, normal driving is possible. If the grounding switch is set to GROUND, depressing the PROGRAM switch will ground the input wheel and initiate the steer program. After this, releasing the ENERGIZE switch will unground the input wheel and lock the input and output together with whatever angular relationship exists at the time; while releasing the PROGRAM switch will center the second steering wheel with respect to the first with the driver supplying the necessary grounding torque.
If the grounding switch is set to OFF when the PROGRAM switch is depressed, the input wheel is ungrounded, and the driver can steer to control the general path of the vehicle by manually adding to or subtracting from the motor-actuated steering wheel rotation.
The steering machine is described in greater detail in SAE Paper 971057, which was presented at the February 1997 SAE Congress.
The report ”A Programmable Steering Machine for Vehicle Handling Tests” describes the steering machine's design and operation, its measured capabilities, and some of the SAE, ISO, and rollover test protocols for which it is designed. This report is available here, in Adobe Acrobat PDF format.
This page last modified 10/23/00