University of Natural Sciences, according to the power flow design closed 2K-H gear mechanism Wang Qiongying (School of Mechanical Engineering, Xiangtan University, Xiangtan, 411105) gear combination mechanism.
Key words: differential ratio; closed chain; power flow parallel single-free charge kinematic chain on any two components of the two-degree-of-freedom 2K-H differential gear train, can form a closed gear combination mechanism. The kinematic chain for parallel connection is called a closed chain, which utilizes a constraint introduced by one of the low sub-two high sub-members, so that the entire mechanism has a degree of freedom of 1 and the transmission ratio between the closed ends of the differential gear train (for example, iab) ) is equal to the external closed chain transmission ratio (ab). Obviously, the closed chain provides an external transmission channel for the differential gear train, and the branching of the transmission line, power flow direction and distribution are urgently needed to be clarified. The differential ratio triangular structure diagram can be used to conveniently and accurately determine the power flow direction and the distribution ratio, and then the closed gear mechanism for different purposes can be correctly designed according to the power flow direction.
1 The ratio of the differential ratio sign and the power property acting on the three basic components of the differential gear train maintains a determined proportional relationship. The ratio of its power is related to the size of the absolute gear ratio. Among them, the ratio of the relative gear ratio (such as iHb) to its absolute gear ratio (ab) is called the differential ratio Hb, and its magnitude represents the inverse ratio of the transmitted power between the two basic components; and the symbols indicate the similarities and differences of their power properties.
If the differential ratio is positive, for example, Hb=:Hb/iab>0, then Nb/Na<0. from equation (2) indicates that the power properties of the wheels a and b are different, one is the input power and the other is the output. Power, power will flow from the active component to the driven component.
If the differential ratio is negative, for example, Hb<0, then Nb/N>0, indicating that the power properties of the two wheels are the same, or the same as the input power, or the same output power, no power will flow between the two wheels.
From the differential ratio triangle structure diagram, the relationship between the number and the shape of the differential ratio can be visually seen. In the figure, the arrow on the same side: the opposite two differential ratios of 1999 are reciprocal to each other, and the product is equal to 1 or 1, that is, only one of the three differential ratios with the same order is negative, and the other two are positive. Values, their product is equal to one, that is, in the differential gear train, there is a similar relationship between the relative gear ratios, such as 4 = 1 = "etc. There is a relationship between the two absolute gear ratios: when the closed chain gear ratio /bH(=/bH) or /ab(= /ab) is known, and the difference is poor. The structural parameter of the differential ratio dihedral structure and the functional structure diagram of the moving wheel system = (1) Zb/Za, and the iaH is obtained from the equation (7), and the iab or ibH can be obtained by the equation (6). Thus, all relatives The symbol and the ratio of the gear ratio and the differential ratio can be determined.
2 power splitting and closed power flow If the closed chain closes the differential ratio negative side (a), inside the differential gear train, there is no power flowing between the two components, and the external power is only connected to the external closed chain Flows to another component to form a power split. Its characteristic is that it is first divided into two channels at the input end and flowed to the output end for synthesis and then output.
If the closed chain closes the differential ratio positive edge (b), then the two form a closed loop, and the power flow flowing through the positive edge will flow back through the closed chain, causing part of the power flow to circulate continuously during the process, called blocking Power flow. It will add power and reduce efficiency, so this situation should not be used in this motion system.
It is a closed planetary gear train and is a negative mechanism (Y = one zb / za < 0). If the motion is input by the wheel a, output from the tie rod H, the closed chain formed by the fixed axle train a'-g'b' closes the negative side of the output end, and its closed chain transmission ratio iHb = 0. Since iHb= The differential ratio of the closed edge is = iH) / iHb < 0, so the other two differential ratios are positive (a) is the motion decomposition, which can achieve power shunt, so each part size can be smaller. In ibH0, and the shirt >0; and iaH>0, then iab=iaHH/0, then b=iHb/iab<0, the closed chain closes the differential ratio positive edge (see b) to indicate that the components a, b are both For the initiative. At the output end H, part of the output motion is fed back to the wheel b via the closed chain and then combined with the motion sent from the input end in the differential gear train. At the same time as the motion feedback, a closed power flow will occur.
If there are two center wheels a and b, then lba=lba=nb/na, if the output motion closes the center wheel b and the tie rod H, then lbn=nb/nn, the output motion 3 control principle and design basis (9) It can be seen that (10), the output motion nn is a function of the closed chain transmission ratio lbn (or lba), and the magnitude and direction of the output motion can be controlled by changing the size and sign of the closed chain transmission ratio.
Machinery should be designed to work in this area.
The gear ratio of the star train is at least greater than the planetary gear train of the same parameters. When zone B, power flows back and moves in the opposite direction. Requires closed chain transmission ratio iH
The 0 of the A zone, which closes the input end and is the negative side of the differential ratio (ifb/iab<0), has a power split and is a forward motion. When iba continuously passes from small to large / =1, the combined motion of the output member H can achieve a continuous change from deceleration to speed, expanding the shift range.
The belt-type continuously variable transmission shown can be used as a closed chain as long as it is continuously changed. Change the transmission ratio to 4-2U1 near 1/ifb on the iacadca PuDnsimgLousenghtsreserve.]; 7A value, do not need to change its symbol (ie, do not change the number of external engagement) the transmission can work across the B, C two areas, so that the tie rod Obtaining forward, pause and reverse movements to achieve "zero-crossing speed regulation. However, because the differential of the input end is closed compared to the positive side, in the closed chain, the closed closed power flow is exactly opposite to the part of the input power flow. Offset, power consumption is extremely high, efficiency is extremely low, and strong vibration and noise occur. Especially in the C zone that can be reversed, the power flow is reversed from the follower b to the active part H, which causes its zero point. "Floating", the reason for the unstable work, thus limiting the practical application of the belt-type continuously variable transmission, the design should avoid working in these two areas.
5 Conclusion The core problem of designing a closed 2K-H gear mechanism is to determine the symbol and size of the closed chain gear ratio according to the power flow direction, as well as the structural parameters, so that the output motion meets the required working range. Therefore, the use and guidance of the design is the most simple and accurate. The power flow direction can be conveniently determined by using the triangular structure diagram, and the power distribution of each branch is calculated according to the magnitude of the differential ratio of each side.
It must be pointed out that the input and output components of the same mechanism are interchanged, and the composition and motion characteristics of the mechanism will also change.
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