原文：
很多工程机械的工况要求其工作马达在下面两种状态下交替工作：一种是要求马达输出大转矩，保持低转速；另一种是要求马达输出小转矩，保持高转速。而此时由于液压油的压力和流量不易改变，满足不了工况要求。为了达到设计目的，我们只能采用以下两种办法：一种是选用变量马达，另一种办法是采用两个定量马达并联和串联切换的方法。下面介绍一种能实现马达串并联切换，从而实现高低速的液控换向阀。 该液控双速阀结构紧凑、操作方便，能极大地简化油路连接，即使在液压油流量和液压一定时，也能可靠方便的实现马达的高低速切换。 该阀地结构原理和工作过程见图1。该液控双速阀地阀体6为不规则的长方体，中部有一空腔，阀体6上开有6个油口与空腔相通，两个星形密封圈18分别安装在阀体6空腔中的两个沟槽中，实现阀体6与阀芯8的密封，防止液压油泄漏。阀体6的两端分别装有上端盖13和下端盖1，每个短盖分别用4个螺钉11及弹簧垫圈10固定在阀体6上，端盖为举行壳体，上端盖上的油口Ⅲ(12)为控制油口。O形圈9放置于上端盖13的沟槽中。滑动阀芯8装于配于阀体6的空腔中，阀芯8为圆柱形，上面开有3个油道和一个挡圈安装沟槽，分别有一个挡圈19、垫圈4和弹簧3依次穿在阀芯上的挡圈沟槽一端，弹簧的一端压着垫圈4，另一端将压盖2压紧在下端盖1的内壁上。如上端盖13的空腔内无液压油时，弹簧3则将挡圈19压紧于阀体6上，此时，阀体6上的6个油口经阀芯上的3个油道行程3组通口，第1组为油口Ⅵ(16)、油口Ⅵ(17)，第二组为油口Ⅰ(5)、油口Ⅳ(14)，第3组为油口Ⅱ(7)、油口Ⅴ(15)，实现马达Ⅰ(20)和马达Ⅱ(21)的串联;当压力油从油口Ⅲ(12)进入上端盖13的空腔时,阀芯8在压力为2×106~3×106Pa的液压油的作用下向弹簧3一侧滑动，直到阀芯8的另一端面顶在压盖2上，阀芯8才停止移动，此时，阀体6上的6个油口经阀芯上的3个油道形成两组通口，一组为油口Ⅰ(15)、油口Ⅵ(16)、油口Ⅶ(17)，另异族为油口Ⅱ(7)、油口Ⅳ(14)、油口Ⅴ(15)，实现马达Ⅰ(20)和马达Ⅱ(21)的并联。 该阀已在徐工研究院开发的水平定向钻机上取得成功应用，同时也为其它液压系列解决此类工况提供了新的途径，具有很好的应用前景。 　

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A lot of construction machinery, expects its work under the motor turn in the following two tasks: one requiring a large torque of the motor output, maintaining low speed; The other is a small torque motor output, maintain a high speed. But this time as the hydraulic oil pressure and flow is not easy to change, can not satisfy the conditions required. In order to achieve the design objective, we can only use the following two ways: one is selected motor variables, another approach is to use two motors in parallel, and tandem switching quantitative methods. Here are a kind of series and parallel to achieve the motor switch to high speed of the liquid control valve. The two-speed hydraulic control valve, compact structure, easy operation, can greatly simplify the oil line connections, even in the hydraulic oil flow and hydraulic pressure is constant, can also facilitate the realization of reliable high-speed motor switch. The valve to the structure and working principle of the process shown in Figure 1. The two-speed hydraulic control valve to valve 6 for the irregular rectangular, with a central cavity, the valve 6 to open a six oil port connected with the cavity, the two star-shaped ring 18 is installed in the valve body 6 empty cavity in the two grooves to achieve the spool valve body 6 and 8 of the seal to prevent leakage of hydraulic oil. Valve 6 on the cover with both ends of cover 13 and 1, respectively, each with four short cap screws 11 and spring washer 10 fixed to the body 6, the end caps to hold the shell, the top cover of the oil I Ⅲ (12) for the control port. 9 O-ring placed in a trench on the cover 13. Slide valve 8 installed in the cavity with the valve 6, the spool 8 for the cylindrical, open top with three oil channels and installation of a ring groove, respectively, a ring 19, spring washers 4 and 3 turn to wear the ring groove on the spool end, pressing one end of the spring washer 4, the other side of the gland cover 1 2 compress the inner walls of the next. As the cavity of cover 13 without hydraulic oil, the spring 3 will ring 19 compress the body 6, on this point, valve 6, the six oil and export oil valve on the Road trip 3 Group 3 openings, group 1 for the oil port Ⅵ (16), the oil port Ⅵ (17), the second group the oil port Ⅰ (5), the oil port Ⅳ (14), group 3 oil port Ⅱ (7 ), the oil port Ⅴ (15), achieved motor Ⅰ (20) and motor Ⅱ (21) in the series; when the pressure oil from an oil port Ⅲ (12) into the cavity on the end cap 13, the spool 8 in pressure of 2 × 106 ~ 3 × 106Pa of hydraulic oil under the action of the spring 3 to the side of the slide, the other end until the spool 8, the top 2 in the gland, the spool 8, stopped moving, this time, the body 6 of 6 a valve on the oil and export oil tract in two groups of three openings, a group for the oil port Ⅰ (15), the oil port Ⅵ (16), the oil port Ⅶ (17), another mixed as oil export Ⅱ (7 ), oil export Ⅳ (14), the oil port Ⅴ (15), achieved motor Ⅰ (20) and motor Ⅱ (21) in parallel. The valve has been developed by the Institute of Xugong horizontal directional drilling applications to succeed, but also for other conditions such hydraulic series solution provides new ways, with good prospects.