Hydraulic Power Steering has improved quite a bit since a man named Fitts installed a system into an antique car back in 1876!
The small amount of strength required to turn a steering wheel and make a modern vehicle turn with the assistance of a high-power device is a significant departure from the original. Some of us remember when cars did not have power steering, even as late as the 1970’s! Imagine operating a piece of heavy construction equipment eight hours per day and fighting a behemoth of a steering wheel with every turn. Hydraulic Power Steering is the ergonomic aid which keeps a vehicle running not only straight but allows for ease of control and safe maneuverability.
With Hydraulic Power Steering, you can use a small steering wheel to turn a vehicle the size of a house with very little force.
How Hydraulic Power Steering Works
The easy turn of a steering wheel powers a CharLynn steering device, manufactured by Eaton Corporation. As you turn the wheel, a hydraulic flow path is opened which sends fluid to power a pair of hydraulic cylinders or another actuator which will cause the wheels to change direction. Depending on the direction of the turn, clockwise or counterclockwise, fluid is directed to opposing actuators, right and left. The positive flow would be going to the cap or blind side of the left cylinder – causing it to extend – and rod side of the right cylinder – causing it to retract. Return flow from both cylinders would take the opposite path.
We have suppliers for each component of the system, the steering wheel with and without a horn, steering column with or without tilt, and the steering control. Column lengths are all custom and tilts are available in a variety of tilt points. The column connects the steering wheel to the steering control.
Hydraulic Power Steering Design Considerations
Sizing the device correctly is what determines how many rotations of the steering wheel are needed to achieve the turn required. These devices are available from compact to high flow sizes to handle large vehicle steering applications. There are also two-speed steering controls. The operator can flip a switch and change between road steering and field steering, allowing for much finer steering adjustments as you work in tight quarters.
Eaton offers several special circuits to customize your application:
- Versa Steer: Similar to 2 speed. The operator can switch to Versa Steer and go full left to full right in less than 1 turn of the wheel.
- Cylinder Damping: Can help smooth the steering on larger vehicles.
- Wide Angle Steering: Designed for vehicles with articulated steering systems.
- Q-Amp Load Sensing: Allows for smooth controls at higher speeds while traveling on the road.
What do you want to happen when you let go of the steering wheel? Do you want the vehicle to react like a car, where the vehicle tries to get back to tracking straight? In Eaton terminology, this is referred to as a load reaction. Do you want the wheel to stay in the current position? In Eaton terminology, this is referred to as a non-load reaction. In non-load reaction, when you release the steering wheel, the vehicle will keep the current path.
To choose the correct steering unit, you not only need to know the flow rate and pressure required, you will also need to specify the type of pump you are using:
- Fixed displacement pump.
- Variable displacement pump.
You can also specify relief valves built into the steering controls to make sure you don’t over pressurize your steering cylinders.
It is also important when sizing the steering flow that you need to be able to reliably control the vehicle’s steering when you are running at idle speed. You are not always at full RPM when you need to turn the vehicle, if you undersize the steering flow, you may have very sluggish steering when you operate at a low engine RPM.
When it is time to develop a new steering package, Cross Company has an experienced team which can help you decide which unit will provide the best response in your application.
