Reasonable matching between the hottest hydraulic

2022-07-31
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Reasonable matching of hydraulic torque converter and diesel engine and its influencing factors Abstract: the characteristics and reasonable matching of hydraulic torque converter and diesel engine in construction machinery are analyzed, and the factors affecting their common working points are discussed

key words: construction machinery; Hydraulic torque converter; Diesel engine

introduction

construction machinery usually uses diesel engine as the power source. Because the torque adaptation coefficient of diesel engine is small, it is difficult to adapt to the requirements of frequent changes in external loads of construction machinery; Or working under the condition of insufficient load for a long time, which reduces the power utilization of the engine. When the hydraulic torque converter is used to form the hydraulic mechanical transmission, the construction machinery can obtain better traction characteristics, have automatic adaptability to the fluctuation of load, reduce vibration and impact, avoid engine flameout, realize stepless speed change, reduce shift times, and make full use of engine power. However, whether the matching of hydraulic torque converter and diesel engine is reasonable or not has an important impact on their respective performance and the overall performance of construction machinery. Therefore, this paper will analyze the working characteristics, reasonable matching relationship between hydraulic torque converter and diesel engine in construction machinery, as well as various factors affecting their common working points

1 engine characteristics after several cycles of test

1.1 speed characteristics of diesel engine

speed characteristics refer to the changing relationship between the speed NF of diesel engine and its output torque MF, power NF and specific fuel consumption GF. In order to improve the over speed and idle speed instability of diesel engine, the diesel engine with full program governor is usually used in construction machinery. Its speed characteristics are shown in Figure 1

Figure 1 speed characteristic of diesel engine

at maximum fuel supply, the obtained speed characteristic is called the external characteristic of the engine, such as the ABC section of the curve; The speed characteristic when the governor works is called speed regulation characteristic, such as the CD section of the curve

1.2 typical working conditions and evaluation parameters

(1) maximum power working conditions of engine: ne - rated (calibrated) power, NE - rated speed, me - rated torque

(2) maximum torque working condition of engine: mm - maximum torque, NM - speed under maximum torque working condition

(3) maximum idling speed condition: generally nmax = (1..2) ne, and the corresponding M and N are close to 0

(4) no load minimum speed condition (idle condition): at this time, the engine output power and torque are close to zero

(5) engine adaptability coefficient: KF =mm/me generally KF ≤ 1.4 The engine is unstable in AB section, but stable in BC and CD sections

2 characteristics of hydraulic torque converter

2.1 original (type) characteristics

original characteristics refer to the impeller torque coefficient λ b. Torque ratio K, efficiency η And the speed ratio I. λ b=f(i)、K=g(i)、 η= H (I) respectively represents the load characteristics, torque converter characteristics and economic characteristics of the torque converter. For a series of torque converters with similar geometry but different dimensions, their original characteristic curves are the same. As shown in Figure 2

Fig. 2 original characteristic curve of torque converter Fig. 3 load characteristic of torque converter

2.2 input (load) characteristic

input characteristic refers to the relationship between pump wheel torque MB and speed Nb, which is determined by torque equation MB= γλ Bd5nb2 decision. When working oil( γ) When the torque converter (D5) is determined, under a certain I working condition, the change of MB with Nb is a quadratic parabola passing through the origin. When the working conditions change, λ B also changes, and a cluster of parabolas can be obtained, as shown in Figure 3

2.3 typical working conditions and evaluation parameters

(1) efficiency characteristics: use η= G3 (I) indicates. Maximum efficiency condition: i* η*、λ b*、K*.

(2) starting (maximum torque coefficient) working condition: I0 = 0 η 0=0、 λ b 0、K0。 K0 ≥ 3

(3) efficient working range: use η When it is ≥ 75%, j = i2/i1 should be larger

(4) stepless torque converter: k = G2 (I). The torque converter coefficient changes with different working conditions I

(5) automatic adaptability: MT =g4 (NT), when the load decreases, the speed automatically increases; Otherwise, the speed decreases

(6) energy capacity characteristics: use λ B = G1 (I) indicates the torque absorbed by the torque converter from the engine and its change

(7) permeability and permeability coefficient: in energy capacity characteristic curve λ B = on G1 (I), when D λ Negative permeability (centrifugal turbine) when b/di> 0; When D λ B/di < 0 has positive penetrability (centripetal turbine); When D λ It has impermeability when b/di = 0 (axial flow turbine). Penetration coefficient: Π=λ b 0/ λ b*。

3 matching of engine and hydraulic torque converter

3.1 reasonable matching

(1) give full play to the power of diesel engine: use the highest efficiency i* working condition of torque converter to transfer the rated power ne of engine, as shown in curve ① in Figure 4. Enable the vehicle to achieve maximum average speed or maximum operating productivity

Figure 4 ideal matching of engine and hydraulic torque converter Figure 5 Effect of diesel engine throttle on common working range

(2) stable engine operation and low fuel consumption: the highest efficiency i* working condition of torque converter is used to transmit the power and torque when the engine has the lowest fuel consumption, as shown in curve ② in Figure 4. Make the vehicle have good economy

The hardness test of stainless steel should consider its mechanical properties

(3) meet the requirements of the equipment manufacturing industry chain for vehicle operation and speed: use the maximum torque coefficient K (or low speed ratio) of the torque converter to transfer the maximum torque mm of the engine, as shown in curve ③ in Figure 4. Make the vehicle have good acceleration performance and starting performance, and obtain the maximum traction, shovel and digging force

3.2 factors affecting common working point

3.2.1 when the engine model is selected

(1) the engine throttle changes. As shown in Figure 5, ABCC 'refers to the matching with the torque converter when the throttle is fully open. Matching points 1 and B' refer to the matching with the torque converter when the throttle is turned off. Matching points 3 and 'refer to the matching with the torque converter when the throttle is reduced again. Matching points 5, 6 and 7 All matching points are located in the curve polygon efabcc '

(2) the engine drives other working devices at the same time to change the power. As shown in Figure 6, curve AB is the total output torque of the diesel engine, curve CD is the effective torque output by the diesel engine to the torque converter after deducting the torque consumed by the torque converter oil pump and oil pipe hydraulic resistance, and curve EF is the torque input to the torque converter after deducting the torque consumed by the working oil pump. At this time, the diesel engine also drives other working mechanisms

(3) adjust the intermediate transmission ratio. As shown in Figure 7: an intermediate drive is installed between the engine and the hydraulic torque converter, and the engine output torque and speed change, i.e. M '= MEIM η m,n'=ne/im. When Im> 1, the torque curve moves to the upper left, the load parabola moves to the lower right, and the common working range moves to the right accordingly; When Im <1, the reverse is true. The intermediate transmission ratio IM can be selected to make the matching meet the expected requirements

Fig. 6 matching of engine output torque and hydraulic torque converter Fig. 7 change of common working range under different intermediate transmission ratios

3.2.2 change of common working range under different effective diameters of hydraulic torque converter

d > D ′ (1) pump wheel torque coefficient λ b: Change λ B match points can be changed. For example, measures such as design blade shape, rotatable pump impeller blades, rotatable guide impeller blades, dual guide rollers, dual turbines, etc. will not only change λ b. Other performance parameters such as K0, J η Etc. λ B. when it increases, the common working range moves to the low speed zone

(2) penetration coefficient Π: The penetrability shall be small within the range of low and medium speed ratio, generally Π ≤1. 3. When the running resistance increased and the vehicle speed decreased, the engine speed did not decrease much in the 1930s to ensure the oil pump power and operation speed. In the high speed ratio region, the ability of the pump impeller to absorb power decreases sharply with the turbine speed approaching the pump impeller speed, so the engine power can be used reasonably. It is better to have a certain negative permeability in the low speed ratio region, so as to reduce the absorbed power of the torque converter and improve the power utilization of the engine

figure 8

(3) effective diameter of torque converter: as shown in Figure 8. When D increases, the common operating range moves to the low speed region

(4) torque converter working condition I: when I changes, the matching working point also changes. As shown in Figure 8

4 conclusion

(1) when the engine is directly connected to the hydraulic torque converter and the torque converter type is selected, the λ B can be determined by the original characteristics. At this time, the matching is to correctly select the diameter D of the torque converter

(2) if torque converter type λ B and diameter D are selected. At this time, a speed increase or reduction device can be installed between the engine and the torque converter, that is, the matching can be changed by the change of IM. A controllable stepless transmission can also be installed to make the im realize stepless change according to the matching requirements

(3) when the diameter D and speed NB have been determined, the required energy capacity can be obtained by designing the structure or size of the torque converter and its blades λ B to change the matching, or the controllable stepless variable energy capacity torque converter can be used

(4) the hydraulic torque converter for construction machinery is generally a centripetal turbine because of its large capacity and high efficiency. K0 ≥ 3, J ≥ 2.4, Π ≤1. 3. K should be large and j should be wide to make full use of engine power and improve traction and speed

(5) during one operation cycle of construction machinery, engine power shall be distributed according to working conditions. If the loader is shoveling in, all the effective power shall be input to the torque converter; When turning the bucket and transporting materials, the power can be distributed to the torque converter and the working oil pump

References:

[1] zhujingchang Design and calculation of hydraulic torque converter [ m ]. Beijing: National Defense Industry Press, 1991

[2] Wei Chenguan Controllable variable energy capacity double pump impeller hydraulic torque converter [ J ]. Engineering machinery, 1979 (9):

[3] yuyongmian, et al Parameter selection of single-stage centripetal turbine hydraulic torque converter series [ J ]. Construction machinery, 1981 (1):

[ 4 ] Qi Renxian. Hydraulic transmission and hydraulic transmission [ m ]. Beijing: Metallurgical Industry Press.1981. (end)

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