Page 24 - PEN eBook March 2023

MOTOR CONTROL Motor Control

haptic feedback from the tires, especially when a vehicle is large, such as a truck. Other constraints
are determined by safety regulations, particularly for automatic guided vehicles. These constraints
require adopting an efficient, accurate and redundant system. Gallium nitride technology helps the

designers in all these areas.

DIFFERENT TYPES OF EPS

EPS reduces energy consumption because it assists only when the driver actuates the steering
wheel. A downside to EPS is the challenge to mimic the tactile feel of “traditional” hydraulic power
steering. The working principle of EPS is simple: There are sensors at the steering column to detect
the steering angle and torque, an electronic
control unit (ECU) that analyzes the signals
and determines the amount of assistance

needed and an electric motor mounted at
the steering column or rack that actuates the
assistance force according to the instruction
from the ECU. Depending on the actuating
mechanism, several types of EPS are widely
used in production cars. In this article, we
will take a look at some of them.

Column-type EPS (Figure 1) is widely used
in small economical vehicles. In column
Power Steering with EPS, the motor is mounted at the steering

column and drives the steering shaft directly.
GaN ePower ICs Figure 1: Column-type EPS. The assistance motor is inside the Its advantage is simple construction and low

red box.

By Marco Palma, director of motor drive systems and applications at Efficient
Power Conversion (EPC) cost. Because the motor is located inside the

dashboard, it is not subjected to water and
In modern cars, the increased weight and the wider front tires make unassisted steering impractical extreme temperatures; thus, the production
because of increased resistance to the operator; thus, several years ago, power steering was cost could be lowered further. The motor is
adopted. In the beginning, the assistance to the driver was accomplished with hydraulic systems, mounted at the top of the steering shaft,
and always-operating pumps were used to provide the necessary pressure to the liquid used in the increasing inertia and friction, but eliminates
circuit. However, the governments’ call to reduce emissions required car manufacturers to shift to the haptic feedback for the driver.

electric power steering (EPS).
Parallel-axis EPS (Figure 2) has the motor
With EPS, the hydraulic system is replaced with an electric motor that aids the driver only when mounted in the rack between the tires.
needed. Its digital assistance control can be modified online to adapt to driving conditions. There The construction method determines the
are, however, several design constraints to consider. One is that the driver does not want to lack the cost and the driver’s “feeling” while driving. Figure 2: Parallel-axis EPS. The motor shaft is parallel to the
rack inside the red box.

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