Our bus is equipped with a Howard Steering system. I have no idea how to work it. There is a knob that adjusts the air pressure as well as a trim button.
What is the proper air pressure and what does the trim button do?
Many thanks.
AJ
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Our bus is equipped with a Howard Steering system. I have no idea how to work it. There is a knob that adjusts the air pressure as well as a trim button.
What is the proper air pressure and what does the trim button do?
Many thanks.
AJ
Hello AJ,
I have had two Monaco products in the past with Howard Power steering systems. Here is a short summary.
1. It is an hydraulic assist.
2. The pressure setting controls the amount of resistance to motion that the unit provides. The higher the number the more resistance.
3. The trim button is used in higher winds to allow the bus to track against a force (wind or road crowning)
4. Unit does help in front blow-outs (have experience)
The way I used the system was turned it on after driving out of park or home. Set pressure somewhere around 110. The left it alone. If going down the road felt like I was fighting crown or wind I would hold the steering where in position that would correct situation and push the trim button for a short while. That would change the neutral point of the wheel to the "corrected" position.
On the Prevost (except for the front blow-out situation) I do not feel the need of the unit.
Let me know if you need an other advice.
Have fun
Hi AJ,
I had the same on the Liberty and it's how Kim described it. I rarely used it except in a strong crosswind when it came it very handy.
Mike
A.J.,
here is an article about that system.
Steering Geometry A number of factors contribute to the tendency of a heavy vehicle to wander while in motion. Steering geometry is one. "It is mistakenly believed that slanting the kingpin (referred to as caster angle) is the best method for dealing with heavy vehicle directional stability problems," Howard says. "However, this is not the way it works out. As road conditions change, castering the steered wheels creates an opposite effect."
One of the main benefits of caster angle is to help steered wheels return to center after turning a corner. As the steered wheels reach the on-center position, the centering force reverses from right-to-left and left-to-right, resulting in weak and indecisive steered wheel centering.
Where positive directional control is needed most-in the straight-ahead position-it is the least effective and contributes very little to directional stability, Howard says. Additionally, with each degree of positive caster angle, there is an increase in caster offset that has a destabilizing effect on heavy vehicle steering as road conditions change.
Caster offset is the distance from a line drawn through the kingpin (pivot point) and the center of where the tire contacts the road. Because the contact point of the tire trails the pivot line of the castered wheels, side forces such as crosswinds and the gravitational pull on a slanted road cause the steered wheels to turn in the direction that force is being applied.
For this same reason, caster offset allows a vehicle to freely turn to the low side on a slanted or crowned highway, creating "steering wheel pull" that requires counteractive driver steering input to keep the vehicle from leaving the road. One only has to consider the many millions of miles driven on crowned and slanted highways each year to appreciate the amount of driving fatigue that is directly caused by caster offset, Howard says.
However, the most fatiguing aspect of driving a heavy truck is controlling the crosswind steering input. The amount of adverse steering input caused by crosswinds is directly related to the amount of caster offset.
"It's a classic example of trading good for bad," Howard says. "The small amount of stability gained from castering the steering wheels on a nonwindy day is paid for many times over when driving in a crosswind."
Power steering helps optimize driver controllability. However, it is not the design function of power steering to make heavy vehicles directionally stable, according to Howard. Power steering plays only a secondary role in heavy vehicle directional stability.
The power assist function of the steering gear becomes active when steering input reaches a predetermined level. When driver steering input is released, the power assist is no longer active and allows free return to the direction determined by the castering effect of the steered wheels.
Steering Improvements The Howard Power Center Steering System solves the castering problems and much more, according to Howard. The system stabilizes the steered wheels and prevents road wander, slanted-road steering wheel pull, steering over-control, crosswind steering effect, and steering-induced dynamic sway. Coastal Transport drivers also report improvements in steering on rutted roads.
The system is designed to work with the truck's power steering and will shut down automatically if the power steering fails. A control panel on the truck dash makes it easy for drivers to change settings to adjust for varying road conditions.
System components include a zero-backlash hydraulic centering cylinder that is attached to either the steering gear Pitman arm or the steering tie rod. The cylinder has two pistons working toward a center stop that holds the piston rod captive in the on-center position.
As the steered wheels are turned away from center, one of the pistons is displaced. When the driver releases the steering wheel, the piston returns the piston rod to the on-center position. The pressure on both sides of the captured piston rod keeps the steered wheels on-center, tracking with accuracy that cannot be achieved with the steering geometry and mechanical components that make up a current heavy truck steering system, according to Howard.
The hydraulic power source is an air-over-hydraulic reservoir accumulator. Air pressure is regulated by the controls on the truck dash. The accumulator has a neoprene diaphragm that keeps air from coming in contact with the hydraulic fluid.
Pneumatic Valves Dual fail-safe electric pneumatic valves-one on the top and one on the bottom of the accumulator-dump the air pressure when the system is turned off. The pressure is recharged each time the system is activated.
The hydraulic centering cylinder incorporates a separate trim cylinder that can be driver-adjusted for different driving conditions, including crosswinds. When trimming the system, the driver steers straight.
The tolerance for backlash in the trim cylinder is held to less than one-thousandth of an inch. This is achieved with check valves that allow only bubble-free hydraulic fluid to enter the cylinder. During operation, fluid exiting the cylinder flows to the pressure accumulator through a different return line.