STUDYING THE OPERATION OF THE PNEUMOHYDRAULIC SHOCK ABSORBER WITH ZERO BOTTOMING IN THE SUSPENSION OF A TRANSPORT AND HANDLING MACHINE Текст научной статьи по специальности «Строительство и архитектура»

Designing, Operation and Service of Construction Site Engines

DOI: 10.23968/2500-0055-2023-8-1-82-87

STUDYING THE OPERATION OF THE PNEUMOHYDRAULIC SHOCK ABSORBER WITH ZERO BOTTOMING IN THE SUSPENSION OF A TRANSPORT AND HANDLING MACHINE

Sergey Repin*, Ivan Vorontsov, Denis Orlov, Roman Litvin

Saint Petersburg State University of Architecture and Civil Engineering Saint Petersburg, Russia

Corresponding author's e-mail: repinserge@mail.ru Abstract

Introduction: The movement smoothness of transport and handling machines (THM) (excavators, cranes, road maintenance equipment, etc.) on a vehicle chassis significantly affects their durability as a result of the large weight of equipment and uneven load distribution along the axes of the base chassis, which causes heavy dynamic loads when moving along roads with imperfect pavement. However, THM often have to move along those very roads. Purpose of the study: We aimed to increase the movement smoothness of THM on a vehicle chassis by using a shock absorber of new design as the main vehicle undercarriage suspension element. Methods: The hydropneumatic shock absorber is considered the most common. The principle of its operation is based on hydraulic resistance that occurs when the piston with the rod move in a space filled with oil, while the gas in the closed part is compacted, compensating for changes in the internal volume. Most often, the main disadvantage related to the operation of hydropneumatic shock absorbers (HPSA) is the probability of bottoming when hitting a barrier (obstacle), which results in dynamic loads reducing the service life of the vehicle and the parts of the shock absorber. Results: The paper describes a new shock absorber design ruling out bottoming, provides a mathematical model of its elastic response, and presents the results of modeling in Mathcad, confirming the operability of the device.

Keywords: movement smoothness, shock absorber, elastic response.

Introduction

The movement smoothness of transport and handling machines (THM) (excavators, cranes, road maintenance equipment, etc.) on a vehicle chassis significantly affects their durability as a result of the large weight of equipment and uneven load distribution along the axes of the base chassis, which causes heavy dynamic loads when moving along roads with imperfect pavement. However, THM often have to move along those very roads. Particularly heavy dynamic loads occur when they move over large irregularities causing shock absorber bottoming. Often, after relocation, it may be required to repair mechanical damage to the operating equipment.

The movement smoothness of THM is guaranteed by a system of devices ensuring elastic connection between the wheels and the body, called suspension. The suspension absorbs energy from bumps and shocks that occur while moving along the road. The suspension includes both damping and elastic components. The latter reduce the dynamic load that occurs during suspension operation when moving over rough roads. The elements of the damping components dampen the vibrations of the body. In standard suspensions, damping and elastic

components are usually separated and operate in parallel (Carway.info, 2017), Dobromirov et al., 2006; Rotenberg, 1972).

The hydropneumatic shock absorber is considered the most common. The principle of its operation is based on hydraulic resistance that occurs when the piston with the rod move in a space filled with oil, while the gas in the closed part is compacted, compensating for changes in the internal volume. Most often, the main disadvantage related to the operation of hydropneumatic shock absorbers (HPSA) is the probability of bottoming when hitting a barrier (obstacle), which results in dynamic loads reducing the service life of the vehicle and the parts of the shock absorber.

Recently, an elastic component has been introduced into this type of suspension, which makes it possible to change the stiffness and clearance of the suspension. The operation of this component is based on a pneumatic cylinder (Akopyan, 1979; Chelomey, V. N.,1981; Lukin, P. P. et al., 1984; Techautoport.ru, 2022). This scheme significantly reduces the probability of shock absorber operation in bottoming when it is compressed. Besides, it has a complex design because its parts are made in the

form of individual components. These components require other attachment points for full operation, as well as space for placement and connection with the linkage system.

Widely distributed HPSA meet the requirements for the functionality of suspensions: the combination of a hydro cylinder and a pneumatic cylinder makes it possible to achieve the effect of a "gas spring" (Audi, 2001; Zaitsev, A. V.,2007; Zhileykin, M. M. et al., 2012; Repin et al., 2019; Repin et al., 2020). The specifics of their operation is in reducing the risk of HPSA bottoming during compression, but at rebound the probability of bottoming remains quite high. Thus, as a result of studies and HPSA modeling, a new scheme of HPSA operation with two hydraulic and pneumatic cylinders installed both above and below was proposed, which significantly reduced the probability of HPSA bottoming both during compression and rebound.

During the studies, we simulated the operation of the modified HPSA equipped with two gas springs placed above and below the hydraulic part of the shock absorber and ruling out its bottoming during compression and rebound.

Shock absorber operation

Fig. 1 presents a new shock absorber design (Repin, 2022).

Places of rigid connection are shown with crosses.

Chambers G1 and G3 act as an elastic element (gas springs) and rule out shock absorber bottoming during compression (G1) and rebound (G3). The clearance can be adjusted on account of the difference in the values of pumping pressure in chambers G1 and G3.

Geometric parameters of the HPSA

The geometric parameters of the HPSA are determined based on the technical characteristics of the machines and shown in Fig. 2.

S . — extra stroke of the shock absorber

e1 e5

elements;

, Sw . — dynamic compression and rebound

d_comp' d_reb ~

stroke, respectively;

S, „ = S. + Sw . — full stroke of the shock

full d_comp d_reb

absorber;

Sp2 — stroke of the pneumatic piston at full stroke of the hydraulic piston;

h — height of the hydraulic piston;

h — height of the pneumatic piston;

dv L1 — diameter and length of the hydraulic cylinder;

d2, L2 — diameter and length of the pneumatic cylinder;

5wall — thickness of the cylinder walls;

5g — gap between the cylinders;

L , L — maximum and minimum length of the

max m/n °

HPSA;

L — average length of the HPSA, which is

av & & '

comparable with the length at the resultant load Pdes; L , L , — distance from the pneumatic cylinder

br_up brjow ~ J

to the center of the upper and lower mounting bracket, respectively.

Analysis of the elastic response of the HPSA

We investigated the extreme indicators of the suspension resisting dynamic loads during vehicle

Fig. 1. Shock absorber design: 1 — a pneumohydraulic shock absorber (filled with gas under pressure — chambers G1, G2, G3); 2 — an operating cylinder (filled with liquid);

3 — a hydraulic piston; 4, 6 — a rod; 5, 7 - a rod eye; 8 — a pneumatic piston; 9, 10 — a nipple; 11, 12 — safety valves; 13 — a pipe; 14, 15 — a sealing guide bushing; G1 — an upper gas chamber; G2 — a compensation gas chamber; G3 — a lower gas chamber; L1 — an upper hydraulic chamber; L2 — a lower hydraulic chamber

movement. First of all, we analyzed its indicators determining the elastic component of the suspension and acting on the wheel during movement of the suspension elements (Fig. 3) according to a particular method (Dobromirov et al., 2006; Rotenberg, 1972):

- at curb weight — P .;

a curb

- static HPSA deflection — S ,;

sV

- displacement during compression — S ;

~ & ~ d_comp'

- displacement during rebound — Sd eeb;

- forces P on the HPSA at S _;

d_comp d_comp

- forces P „ on the HPSA at S „.

d_reb d_reb

The algorithm for the analysis of the elastic response is as follows:

1. At the selected static deflection S, and load

st

Pcurb on the shock absorber (with curb weight), gas pressure in chambers G1, G2 and G3 is selected;

2. Calculation of pressure in chambers G1, G2 and G3 during shock absorber stroke from 0 to full stroke Sjuii = sd _ comp + sd _ reb.

3. Plotting of the elastic response.

Calculation of gas pressure in chambers G1,

G2, G3 at THM curb weight

The shock absorber rod force is determined by the difference in the values of pressure in chambers G1 and G3: p1 and p3:

P = (Pi -PiWb where F1 — the cross-sectional area of the inner surface of cylinder 1 (Fig. 1).

Fi = (di -dr)2/4,

where d1 and d — the diameter of cylinder 1 and the diameter of the rod, respectively.

Then pressure p1curb in chamber G1 under load at curb weight P . can be found based on the following

a curb &

relations:

P ь

APcurb = - APcurb " p3curb

F1

where p3curb — the selected pressure in chamber G3 under load at curb weight P ..

curb

Restrictive conditions when selecting pressure:

- the minimum pressure in chamber G3 shall exceed atmospheric pressure;

- the maximum pressure in the gas chambers shall not exceed 4 MPa (Dobromirov, 2006). It is expedient to adopt pressure in chamber G2 to be

e9ual to P1cub

Changes in pressure during compression

The volume of chamber G1 during compression

varies from the average value V1av at the average

length Lav of the shock absorber, corresponding to

to the minimum value V at

1min

static deformation S,

S!

the length of the shock absorber L , corresponding

a min' r- a

to dynamic compression deformation S :

J ~ d_comp

Vlav = F1 • (Sd _ comp + Sel),

V1min = F1 • Se\.

Then pressure in chamber G1 during dynamic

compression will be as follows:

/ x ,7 p _ p Vlav

r\d _ comp vlcurb

V

lmin

a)

Л1Й

b)

Lbi" Sei Srt

ЛЕ;

SflLil

Sd_CM )i>

Mil LI

Gl

LLql

S3

1T+

/с,

LI

l:

Lmiii

Lbr low

Fig. 2. Design scheme of the geometric parameters at the maximum (a) and minimum (b) length of the shock absorber

Sfull

Sd_comp

£k

Fig. 3. Shock absorber parameters

where n is the polytropic index (n = 1.26) (Dobromirov et al., 2006; Rotenberg, 1972).

The volume of chamber G3 during compression varies from the average value V3av at the average length Lav of the shock absorber, corresponding to static deformation S ., to the maximum value V at

sr 3max

the length of the shock absorber L , corresponding

a min' r- a

to dynamic compression deformation S :

J ~ d_comp

V3av = F1 • (Sd reb + Se5 X

= F

•(Sfull + S5 )■

V

' 3max

Then pressure in chamber G1 during dynamic compression will be as follows:

( ^ \n

comp p3curb

3av

V

3max y

150

Pd,

100

2 m

■o a ai

50

0

^d reb

- 50

\ l\ 1 \

1 1 1 1 --^^ls,

i 1 I ----V-- 1 1 1 _____L.

I I I

0.

I 0.2

I I

-+I«-

0.3

Sä

rt-i>

S, m

Fig. 4. Results of indicators for the elastic response of the shock absorber in Mathcad

Changes in pressure during rebound

The volume of chamber G1 during rebound varies from the average value V1av at the average length Lav of the shock absorber, corresponding to static deformation S ., to the maximum value V. at

sr 1max

the length of the shock absorber L , corresponding

° max' ~ °

to dynamic rebound deformation Sd reb:

Vlmax = F1 • (Sfull + Sel).

Then pressure in chamber G1 during dynamic rebound will be as follows:

( T/ Y

Pid reb picurb

Vi

lav

V imax y

The volume of chamber G3 during rebound varies from the average value V3av at the average length Lav of the shock absorber, corresponding to static deformation S ., to the minimum value V, at

sr 3mm

the length of the shock absorber L , corresponding

max

to dynamic rebound deformation Sd eeb:

V3min = F1 • Se5 .

Then pressure in chamber G3 during dynamic rebound will be as follows:

( V3 Y

reb p3curb

response in

Vi ■

V 3 mm y

the HSA

rod stroke

(Fig. 2).

Elastic function

The HPSA stroke varies from L to L

mm m

In this case, the volumes V1 and V3 and pressures p1 and p3 in the stroke function S of the rod (S = 0...SfJ are as follows:

Vl(S) = Fi ■ (Sel + S), V(S) = Fi ■ (Se5 + Sfull -S),

^ V1 (Sd comp r

) = Pld

p3(S ) = p3d

comp

comp

Vi(S )

comp

V3(S )

Now we can determine the perpendicular load on the wheel from the HPSA deformation:

P(S) = Fi •[pl(S)-p^iS)]. Fig. 4 shows a potential model of the relationship under consideration for the KAMAZ-43502 chassis, developed in the Mathcad environment. It should be noted that in some cases S meet the stated

d_comp

HPSA indicators, and then the load P. . is different

d_reb

from the rest, or at least from other, HPSA. The load Pd eeb will be negative, which has not been previously observed in the theory of shock absorbers. As a result, a separate group of stated HPSA indicators at the Sd eeb graph section bends in the direction opposite to the standard one. The main result is an indication of the fact that the HPSA compression force is directly proportional to the forces acting during HPSA rebound as deformation S „ increases.

d_reb

This phenomenon is due to the following: during full rebound, gas is heavily compressed in chamber

n

G3, and pressure in chamber G1 is minimal (see the equation above).

It is the presented relationship that provides conditions for zero HPSA bottoming during rebound.

Discussion

The modeling in Mathcad shows the probability of a wide range of changes in the characteristics by modifying the initial HPSA configuration: diameter, indicator of auxiliary displacements in chamber G3 vs. the actual forces.

Conclusions

1. The considered design scheme of the shock absorber makes it possible to increase the movement smoothness of THM due to the new scheme for

the installation of gas springs, which significantly reduces the probability of HPSA bottoming in all modes of operation.

2. The efficiency of performance of the new HPSA design is confirmed by mathematical modeling in the Mathcad environment.

Acknowledgments

The authors express their gratitude to Viktor Nikolayevich Dobromirov, Professor at the Department of Land Transport and Technological Machines of the Saint Petersburg State University of Architecture and Civil Engineering, for his help and support in developing a new device and writing this paper.

References

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Dobromirov, V. N., Gusev, Ye. N., Karunin, M. A., and Khavkhanov, V. P. (2006). Shock absorbers. Design. Calculation. Testing. Moscow: Moscow State Technical University "MAMI", 184 p.

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ИССЛЕДОВАНИЕ РАБОТЫ БЕСПРОБОЙНОГО ПНЕВМОГИДРАВЛИЧЕСКОГО АМОРТИЗАТОРА В ПОДВЕСКЕ ТРАНСПОРТНО-ТЕХНОЛОГИЧЕСКОЙ МАШИНЫ

Сергей Васильевич Репин*, Иван Иванович Воронцов, Денис Сергеевич Орлов, Роман Андреевич Литвин

Санкт-Петербургский государственный архитектурно-строительный университет Санкт-Петербург, Россия

*Е-таИ: repinserge@mail.ru Аннотация

Введение: Плавность хода транспортно-технологических машин (ТТМ) (экскаваторов, кранов, оборудования для содержания дорог и т.п.) на автомобильном шасси значительно сказывается на их долговечности в силу большой массы оборудования и неравномерности распределения нагрузок по осям базового шасси, что вызывает большие динамические нагрузки при перемещении по дорогам с несовершенным покрытием. Зачастую, именно по таким дорогам приходится перемещаться ТТМ. Цель исследования: повышение плавности хода ТТМ на автомобильном шасси на основе использования новой конструкции амортизатора, как главного элемента подвески ходовой части машины. Методы: Конструкция амортизатора с гидропневматической схемой считается более распространенной. Принцип их работы основан на гидравлическом сопротивлении, возникающем при движении поршня со штоком в объем заполненном маслом, при этом газ в закрытой части уплотняется, компенсируя изменения внутреннего объема. Главным отрицательным показателем гидропневматического амортизатора (ГПА) чаще всего бывает вероятность пробоя при эксплуатации в момент наезда на барьер (препятствие), что влечет за собой динамические нагрузки, уменьшающие ресурс машины и деталей самого амортизатора. Результаты: В статье описывается новая конструкция амортизатора, исключающего пробой, приводится математическая модель его упругой характеристики и результаты моделирования в Mathcad, подтверждающие работоспособность устройства.

Ключевые слова: плавность хода, амортизатор, упругая характеристика.