Development of Anti-cavitation Vane for Travel Motor of 7-ton Hydraulic Excavator

ProductIntroduction

Development of Anti-cavitation Vane for Travel Motor of7-ton Hydraulic Excavator
SUZUKI Jun1

Introduction

The existing hydraulic travel motor for 7-ton hydraulicexcavators is equipped with an add-on shockless relief
valve as standard. The shockless relief valve (hereinafterthe "relief valve") has the same structure as that of thehydraulic travel motor for mid-size excavators. Thismeans that the relief valve consists of many parts and isexpensive.
Then, we have developed another valve for 7-ton hydraulic excavators that can replace the existing relief
valve. This paper introduces this new, simple anti-cavitation valve (hereinafter the "anti-cavitation valve").

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cles. It has thus been difficult to use the anti-cavitation
valve in this motor. Still, in response to the recent market
demand for cost reduction, we have developed a simple
anti-cavitation valve for the travel motor for 7-ton hydraulic excavators that can replace the relief valve. Fig. 1
shows the appearance of the product.

Overview of the Product2. 1 Background
MAG Series hydraulic travel motors are available in a
product lineup of 11 models for 1-ton to 35-ton hydraulicexcavators (Table 1). While motors for mini excavatorsof 6-ton or smaller are equipped with an anti-cavitation
valve as standard, those for 7-ton or larger excavators areequipped with a relief valve as standard. We tried tomount the anti-cavitation valve that is used in the smallerclass motors on the hydraulic travel motor MAG-50VP1100F for 7-ton class excavators but it could not preventthe occurrence of cavitation because a large inertia force
is applied to the motor during the braking of large vehi-Table 1MAG Series product lineup

Fig. 1 Appearance of the product(MAG-50VP-1100F with anti-cavitation valve)

2. 2 Functions and Features of Relief Valve
The existing relief valve plays the role of relieving thepressure surge during the vehicle's braking, suppressing
the cavitation, and adjusting the braking feeling. Whenthe brake is applied, the counterbalance valve mounted
on the travel motor closes its opening on the outlet sideearlier. The relief valve is then operated to generate abraking torque and absorb the inertia force during braking. It also adjusts the shockless operation pressure andtime to obtain the desirable pressure rise characteristics
during braking, achieving the braking feeling demanded
by customers.
[During traveling]
Fig. 2 shows the hydraulic circuit diagram of the relief
valve during traveling. When the pressure oil flows into
the Pin port, the counterbalance valve is in the travel position. The oil is guided into the hydraulic circuit, starting
the motor.

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Fig. 4

Fig. 2

Hydraulic circuit diagram of relief valve(during traveling)[During braking]Fig. 3 shows the hydraulic circuit diagram of the reliefvalve during braking. While the supply of the oil to thePin port is interrupted, the motor is kept running due tothe inertia force of the vehicle. This raises the braking
pressure to generate a braking torque, absorbing the inertia force. When the braking pressure is equal to or higher
than the relief valve settings, the pressure escapes to theother side as indicated by the arrow (green), suppressing
cavitation. The shockless relief valve shows a two-stepincrease in braking pressure as shown in Fig. 4. The pressure waveform shown in Fig. 4 represents measurements
obtained with a flywheel testing machine.

Fig. 3

Braking pressure characteristics of motor with reliefvalve

2. 3 F unctions and Features of Anti-cavitation
Valve
Unlike the relief valve, the anti-cavitation valve does
not have a surge relief function supposed to work during
braking. That is why it is necessary to tune the openingcharacteristics of the counterbalance valve to generate abraking torque, absorb the inertia force during braking,and keep the braking pressure within the allowable limits. Cavitation is suppressed by bypassing the high-pressure fluid to the low-pressure side using the anti-cavitation and counterbalance valves.
Figs. 5 and 6 show the hydraulic circuit diagram of theanti-cavitation valve during traveling and braking respectively. Adjusting the opening characteristics of the counterbalance valve enables various pressure rise characteristics to be obtained during braking, achieving thebraking feeling demanded by customers. Table 2 shows acomparison in functions between the relief and anti-cavitation valves.

Hydraulic circuit diagram of relief valve(during braking)Fig. 5 H ydraulic circuit diagram of anti-cavitation
valve (during travelling)― 29 ―

Development of Anti-cavitation Vane for Travel Motor of 7-ton Hydraulic Excavator

Fig. 83Fig. 6

Hydraulic circuit diagram of anti-cavitation valve(during braking)Table 2Comparison of functions between relief andanti-cavitation valvesFig. 7Section view of relief valve

Technical Challenges in Introducing Anti-cavitation Valves

The challenges in introducing the anti-cavitation valve
to the motor for 7-ton excavators are to ensure that thevalve can keep the braking pressure from rising up to theupper limit, absorb the inertia force, and attain the braking feeling demanded by customers by tuning the opening characteristics of the counterbalance valve as well as
by suppressing cavitation during braking of the 7-ton vehicle.

42. 4 Comparison of Valve Structure
Figs. 7 and 8 show the structure of the relief and anticavitation valves respectively. While the relief valve consists of 33 parts and is expensive, the anti-cavitationvalve is simple and consists of only 10 parts.

Section view of anti-cavitation valveF eatures of Anti-cavitation Valve for
7-ton Hydraulic Excavators

As mentioned above, unlike the relief valve, the anticavitation valve can adjust its opening characteristics andclosing time to achieve various pressure rise characteristics during braking. With the anti-cavitation valve, it ispossible to achieve a moderate increase in braking pressure as shown in Fig. 9, thereby enabling the vehicle's
driver to feel good braking and keeping the pressure
surge within the allowable limits. Besides this, it has
been confirmed that other pressure rise characteristics asshown in Figs. 10 and 11 can be obtained. Note that this
newly developed valve offers motor performance and durability that are equivalent to those of the existing relief
valve since this new product is an alternative to the existing counterpart.

Fig. 9― 30 ―

Braking pressure characteristics of motor with
anti-cavitation valve [1]KAYABA TECHNICAL REVIEW No. 66 APR. 2023

5To introduce the anti-cavitation valve to the travel motor, it is necessary to match the motor with the vehicle byadjusting the opening characteristics of the counterbalance valve. In reality, drivers may encounter various
types of excavator crawler (steel, rubber) and various
types of road surface (sheet steel, soil, concrete) depending on the vehicle class and model, so it is diﬃcult to exactly estimate the braking feeling only through verification with flywheel testing.
The test data obtained in this development project will
be applied to analysis modeling, reducing the time needed to match motors with vehicles. This will certainly improve the estimation technique. In the future, we would
like to determine, through simulation, the motor behavior
in operation modes that are difficult to reproduce in abench test, contributing to the clarification of failure phenomena occurring in commercially available excavators.

Fig. 10 B raking pressure characteristics of motor with
anti-cavitation valve [2]Fig. 11In ClosingBraking pressure characteristics of motor withanti-cavitation valve [3]Author

SUZUKI JunJoined the company in 2007. Pump
and Motor Design Sect., Sagami Hydraulic Engineering Dept., Engineering Headquarters, HC Operations
Engaged in design and developmentof hydraulic motor products.

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