A Brief Analysis of the Slipping Phenomenon of Single Steel Wheel Vibratory Rollers in Deserts

With the in-depth development of the western region and the increase in national investment in highway construction in the west, the demand for desert-adaptive rollers is increasing day by day. Due to the low moisture content of sand and soil, the internal friction force is small, and the density of the pile gap is small, resulting in low adhesion. As a result, the rubber wheels of ordinary single-drum vibratory rollers often slip. There are many factors contributing to this phenomenon, and it is rather difficult to establish a mathematical model. This article only analyzes this phenomenon from the following five aspects based on the current understanding.

The influence of one tire:

Desert slippage is often manifested as the rear rubber wheels slipping when retreating. When moving forward, as the rear rubber wheels advance on the road surface passed by the front steel wheels, the density of the road surface is high, thus the adhesion is high, the road surface has strong passing capacity, and it is relatively less likely to skid. When retreating, the rear rubber wheel moves forward on soft dry sand. At this time, the rubber wheel sinks more, the passage resistance doubles, and the adhesion decreases several times, making it difficult to retreat.

The influence of weight distribution between the front and rear vehicles:

Based on past experience, when designing the weight distribution of the front and rear wheels of a fully hydraulic single steel wheel, to enhance the compaction effect, the weight distribution of the front steel wheel is approximately twice that of the rear rubber wheel. When driving in the desert, if the load distribution on the rear rubber wheels is too light, it is easy to cause insufficient adhesion of the rubber wheels, resulting in slippage. To enhance the adhesion of the rear rubber wheels, the distributed load on the rear wheels can be appropriately increased, thereby reducing the slippage of the rear wheels.

The influence of three rolling radii:

From a design perspective, the formula for calculating rotational speed or displacement should be = (1)

= × (2

In the formula, V represents the displacement of the pump

r - The rolling radius of the front wheels

V - Displacement of the motor

r - The rolling radius of the rear wheels

n1 - The rotational speed of the front wheel motor

i - The wheel edge reduction ratio of the front wheels

n2 - The rotational speed of the rear wheel motor

i - The reduction ratio of the rear wheels

n - The rotational speed of the pump

In the actual design process, if r is used instead of r (Note: r, r respectively represent the natural state radii of the front wheel and the rear wheel), for the front steel wheel, it is acceptable to regard it as fully rigid. As for the rear rubber wheel, there is a significant elastic deformation, so r is less than r. This will inevitably lead to an increase in the actual n2 and a decrease in n1. Once n1 decreases, its linear velocity will correspondingly decrease, and the phenomenon of soil accumulation will occur. Once n2 increases, it will cause its actual rolling linear velocity V to be greater than or equal to V (pure rolling linear velocity), resulting in the sliding of the rear rubber wheel and subsequent slippage. When the rear wheel slips, the rotational speed of the front wheel n1 drops to 0, while that of the rear wheel n2 increases. Equation (2) tends to infinity on the right side, causing r on the left side to tend to 0. Then the slip rate δ of the rubber wheel is 1- (3). It is easy to see that when r approaches 0, δ→ 100%, and it is completely slipping.

The influence of torque distribution between the front and rear wheels:

If the torque provided by the hydraulic circuit to the rear rubber wheel is too large, compared with the front steel wheel, the rear rubber wheel will exceed the torque by too much, thus it is prone to slipping first. Once the rear rubber wheel slips, the flow from the front steel wheel will flow to the rear rubber wheel, and the corresponding decrease in the front steel wheel will prevent it from slipping. We believe that the front and rear flow rates should be controlled independently to reduce the driving torque of the rear wheels, thereby decreasing their driving force and lowering the shear stress on the soil layer of the rear wheels, which can suppress the sliding of the rubber wheels.

The influence of adhesion coefficient and resistance coefficient:

In the conventional design, the adhesion coefficient and resistance coefficient of the rubber wheels we select are 0.65 and 0.15 respectively. It is feasible to design a roller for construction on ordinary roads in this way and has also been recognized by practice. However, when driving in the desert, due to its particularity, such values tend to undercalculate the actual resistance and overcalculate the theoretical adhesion force, thereby affecting the calculation of the entire machine system and climbing ability. Based on the analysis of the thickness of the desert bedding and the experience from desert tests, it is more in line with reality to take the adhesion coefficient value a little lower and the resistance coefficient value a little higher.

Conclusion

Improving the adhesion of off-road mobile vehicles is an eternal pursuit of construction machinery designers. Due to a layer of elastic sand blocking the contact between the tire and the hard road surface, the adhesion of the tire decreases, resulting in skidding. We can improve the passing capacity of road rollers in deserts from the following aspects:

In terms of adhesion and resistance adjustment:

◆ Adopt large-diameter, wide-base low-pressure smooth tires or sand-tolerant tires specially designed for deserts.

Reduce the weight distribution gap between the front and rear wheels and design balanced weights at the front and rear.

When designing the entire machine, it is recommended to take the adhesion coefficient and resistance coefficient of the rubber wheel as 0.32 and 0.23 respectively.

Increase the diameter of the front steel wheel within the allowable range, and thin inserts can be added to the outer ring of the steel wheel. In terms of torque adjustment:

Reduce the driving torque of the rear rubber wheel appropriately and increase the driving torque of the front steel wheel.

Increasing the reduction ratio of the wheel-side reducer will help to enhance the driving torque of the steel wheel.

From the perspective of reducing linear velocity:

When designing, carefully calculate the rolling radius and use it in the corresponding formula for calculation.