Page 38 - Understanding Automotive Electronics

2735 | CH 1 Page 25 Tuesday, March 10, 1998 10:52 AM

AUTOMOTIVE FUNDAMENTALS 1

When steering the car, the driver must provide sufficient torque to
overcome the restoring torque. Because the restoring torque is proportional to
the vehicle weight for any given steering angle, considerable driver effort is
required for large cars, particularly at low speeds and when parking.
In order to overcome this effort in relatively large cars, a power steering
system is added. This system consists of an engine-driven hydraulic pump, a
hydraulic actuator, and control valve.Whenever the steering wheel is turned, a
proportioning valve opens, allowing hydraulic pressure to activate the
actuator. The high-pressure hydraulic fluid pushes on one side of the piston.
The piston, in turn, is connected to the steering linkage and provides
mechanical torque to assist the driver in turning. This hydraulic force is often
called steering boost. The desired boost varies with vehicle speed, as depicted
in Figure 1.18.
This graph shows that the available boost from the pump increases with
engine speed (or vehicle speed), whereas the desired boost decreases with
increasing speed. In Chapter 8, we discuss an electronic control system that can
adjust the available boost as a function of speed to desirable levels.
In addition to the automotive systems described above, electronics is
involved in the implementation of cruise control systems, heating and air
conditioning systems, as well as entertainment and some safety systems.
Moreover, electronics is responsible for introducing new systems that could, in
fact, not exist without electronics, such as navigation systems, communication
systems, and electronic diagnostic systems.

Figure 1.18
Desired Boost Versus
Speed

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 25