New approach to steering off-road vehicles

Dr. Neil Canter, Contributing Editor | TLT Tech Beat January 2014

A more efficient steering system has been developed that improves productivity and reduces fuel consumption.

KEY CONCEPTS
• Off-highway machines using standard hydraulic steering technology are inefficient because 25 to 30 percent of the hydraulic power is lost as heat.
• Pump-controlled steering has been developed and involves the use of a variable displacement pump dedicated for each steering actuator.
• Compared to standard hydraulic steering, pump-controlled steering in a front loader achieved a fuel savings of nearly 15 percent and a productivity improvement of nearly 23 percent.

THE MOVEMENT TO IMPROVE THE EFFICIENCY OF MOBILE VEHICLES also includes off-road equipment. Hydraulic fluids, which have been treated just as commodity lubricants, are taking on more importance in helping to increase the efficiency of off-road equipment.

In a previous TLT article, viscosity index (VI) improvers were identified as helping to improve the performance of off-road equipment by enabling end-users to find the right viscosity window, which maximizes fuel economy and productivity while minimizing emissions (1). The idea is to have a hydraulic fluid operate in an optimum viscosity range to minimize excessive leakage that can occur at too low a viscosity and also minimize pump starvation that can occur if the viscosity is too high.

Research is continuing to determine how to improve the hydraulic systems used in off-road equipment. The development of displacement-controlled actuators is described in a previous TLT article (2). Use of displacement-controlled actuators led to an energy savings of 39 percent in a commercially available excavator that had been using load-sensing hydraulic systems.

Another system where improved efficiency is needed is steering. Monika Ivantysynova, Maha Fluid Power Systems Professor in the department of mechanical engineering at Purdue University in West, Lafayette, Ind., says, “Currently, steering of off-highway machines is done using standard hydraulic steering technology which involves the use of a central displacement pump that delivers hydraulic fluid through a series of valves to different actuators.”

Ivantysynova explains that the off highway equipment operator initiates steering through mechanical input by turning a wheel. This step is amplified by the standard hydraulic steering system.

The problem with standard hydraulic steering is the multiple valves set up between the displacement pump and the steering actuator. These valves control fluid power, not just for steering but for other working hydraulic functions. Upstream of the steering valve is a priority-steering valve that ensures fluid is available for steering and may restrict fluid flow for other functions.

Ivantysynova says, “The multiple restrictions from these valves limits fluid flow by throttling and hinders the power available to the off-highway equipment. The result is that much of the power is converted to heat, which is lost to the environment.”

Ivantysynova estimates that as much as 25 to 30 percent of the hydraulic power is lost as heat. A need exists for a more efficient steering system that will improve productivity and reduce fuel consumption. Such a system has now been developed.

PUMP-CONTROLLED STEERING
Ivantysynova, in collaboration with her co-researcher, Naseem Daher, has developed a new approach known as pumpcontrolled steering that relies on a variable displacement pump dedicated for the steering actuator. She says, “In multi-actuator machines, the new pump-controlled actuation technology requires each actuator to have its own pump, thus eliminating the need for valves. This enables the pressure flow from the pump to be optimized for each actuator.”

For off-highway equipment, the question may be asked about whether there is sufficient room for multiple pumps and whether the weight of the vehicle may actually rise, which would lead to lower fuel economy. Ivantysynova answers, “This is not the case with pump-controlled steering. As an example, if a 200-kilowatt pump used in a specific application is replaced with four pumps that each generate 50 kilowatts, less space is required for the multiple pumps and the equipment containing the multiple pumps weighs less.”

The result of pump-controlled steering is a significant increase in productivity combined with a significant reduction in the amount of energy lost as heat. Ivantysynova says, “In our approach, energy is not wasted as heat but, rather, used to provide much better control over each actuator.”

The researchers installed the pump-controlled steering system in a front loader shown in Figure 1. A servo- pump and a torque feedback device were installed into the front loader, which control articulation velocity and steering wheel torque, respectively. Under identical operating conditions to what was done with the standard hydraulic steering system, a fuel savings of nearly 15 percent and an improvement in productivity of nearly 23 percent were achieved. This leads to a total fuel efficiency increase of nearly 43 percent for the front loader.


Figure 1. Testing in the front loader shown indicates that a new technology known as pump-controlled steering exhibits superior fuel savings and productivity compared to standard hydraulic steering. (Courtesy of Purdue University)

Ivantysynova says, “We believe that fuel savings of at least 20 percent can be found with the pump-controlled steering system. Another benefit is that using the system leads to less operator fatigue because there is less difficulty in turning the wheel. Safety is also enhanced with our new steering system via active safety functions.”

The operator does not face the same amount of torque when turning the steering wheel with the new system. Though this may lead to a problem because of the lack of tactile feedback, safeguards have been put in place to regulate torque feedback.

Retrofitting off-highway equipment to the pump steering system is not difficult, according to Ivantysynova. The same hydraulic fluid used in the current steering system can be used in the new system.

The researchers are in the process of looking for partners to run additional testing on off-highway equipment to validate pump-controlled steering. Additional information can be found in a presentation given at a recent conference (3) or by contacting Ivantysynova at mivantys@purdue.edu.

REFERENCES
1. Canter, N. (2011), “Viscosity Index Improvers,” TLT, 67 (9), pp. 10-22.
2. Canter, N. (2008), “Improving Efficiency of Mobile Hydraulic Systems,” TLT, 64 (10), pp. 14-15.
3. Ivantysynova, M. and Daher, N. (2013), “Pump Controlled Steer-by-wire System,” Presented at the SAE 2013 Commercial Vehicle Engineering Congress, Oct. 1-3, Rosemont, Ill.

Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat items can be sent to him at neilcanter@comcast.net.