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In various vehicle power transmission systems, in general, mechanical transmission has the advantages of high transmission efficiency and large power capacity, but it is difficult to obtain perfect transmission characteristics of a continuously variable transmission (CVT). Although there are some types of mechanical continuously variable transmissions, since they are actually based on friction transmission, the efficiency, power capacity and available speed ratio range are both low. At present, the most typical split-type transmission model based on the two-degree-of-freedom planetary manifold is shown in the figure. In the figure, the triangle C represents one or a group of confluence planetary rows and its input/output triads, and *E is the power source (engine ). Although it can improve the power capacity and efficiency, its speed ratio has become narrower. If no improvement measures are taken, it will affect the performance of the vehicle. Therefore, it is only suitable for light-duty vehicles with small workload and changes. The scope is greatly limited.
Aiming at the inevitable inherent contradiction of the existing split-type transmission models based on the two-degree-of-freedom planetary manifold mechanism, we explored and proposed a new type of compound stepless automatic transmission system with power split and two-way convergence. 78/ (hereinafter referred to as CCVT, whose model is shown) is intended to enable simultaneous improvement in transmission efficiency, expansion of power capacity and speed ratio variation.
1 The working principle of the new composite continuously variable transmission is as follows / the typical typical solution ", the speed n* set in it, and the variable speed nb input from the b-axis of the CVT output on the other input element, then A variable output speed nc, nc and nb will be generated linearly on the output element. Here, the CVT can be any of various conventional mechanical, electrical, hydraulic or hydraulic drives.
The confluence planetary row (group) in the system has a positive convergence characteristic, which is a positive confluence. If n/ decreases with nb (ncw-nb), the planetary row (group) is said to have a reverse The convergence feature is reversed.
In fact, the converging planetary rows (groups) of the various/existing typical solutions as shown are, and can only be, unidirectionally converged, ie either forward or reverse. It is the main cause of the inherent contradiction between transmission efficiency and shift range.
See, the basic idea of ​​the new CCVT system is to construct a two-way confluence planetary row assembly C0 consisting of at least one forward and one reverse confluence planetary row to replace the one-way sink of the existing solution. Flowing the planetary row C, and downstream of the output shafts c and d of the positive and negative confluence planetary row groups, a step-by-step automatic change section (block) mechanism C! is added. The mechanism is designed to follow the CVT output speed nb at When the reciprocating change to the upper and lower limits within a given speed ratio range, the output shafts c and d of the assembly C0 are alternately turned on in a confluent manner of 'forward, reverse, forward, reverse, reverse...' without impact. First, the working section (block) of Q is replaced at the same time, and the power is output downstream to the different fixed speed ratios designed according to certain criteria, and the speed and torque of the continuously changing segment are smoothed at the end of each segment. Connected to form a large stepless speed range 3,47. The following two types of CCVT are machine-combined (CVT for belt or chain mechanical continuously variable transmission), machine-electric composite (CVT for speed-regulating motor) The object analyzes the key mechanism of CCVT in a two-way convergence planetary row group Topology. For detailed principles and specific construction of the two types of CCVT systems, please refer to the author's other related papers, which will not be repeated here.
Analysis of 2 double planetary row topology layout schemes Screening an input component on the input flow from the power source engine iE output shaft uaShin2g single planetary row confluence characteristics http:// planetary mechanism by sun gear, ring gear, with Under the planetary carrier group of the planetary gears, only the remaining nine schemes are compared and analyzed in more depth. to make. For a single planetary row mechanism, according to the combination of two inputs and one output, the power transmission scheme has 3! = 6 kinds, the specific structure is as shown in the six possible transmission schemes of the single planetary row mechanism. Analysis of the topology layout of the two pairs of planetary arrays One of the keys to the new CCVT system is to construct a planetary row consisting of forward and reverse planetary rows, which inevitably involves the topology layout of at least two planetary row combinations. Excellent problem. The composite stepless transmission for vehicles generally needs to set 4-5 working segments (speed). In the design, only two combinations of planetary rows can be used to meet the requirements of vehicle driving.
Of course, in the case of more than two planetary rows, the topology with forward and reverse functions can also be constructed according to different combinations, but the basic idea is to establish two forward and reverse flow mechanisms, except for the three planetary rows. Perhaps there is still practical value, the rest of the topology is too complicated, so this paper mainly analyzes the topology layout of the combination of two planetary rows.
The single planetary row has six possible structural forms according to the combination of two inputs and one output. For the dual planetary row combination, the structure is composed of two single planetary rows, which can theoretically be combined into 3!3! = 36 basic connection schemes, ie 36 topological layouts. The dual planetary row mechanism used in CCVT should be screened in these 36 topological layouts. In addition to the principles that must be followed in general planetary gear mechanisms, it is necessary to specifically consider whether the following factors constitute the forward and reverse two-way planetary rows; the load rate on the CVT (defined as the characteristics of the CCVT transmitted by the CVT transmission branch) One is to implement stepless speed regulation of a system that transmits large power through a CVT transmission split with a smaller power capacity.
In the CVT gear ratio range, if the CVT load rate is lower, the system is more efficient, compact and lightweight, and the structural strength is reduced. Generally speaking, in the machine-combined composite mold, the speed ratio of the flexible belt type mechanical CVT can be varied from 0.4 to 1/0.4, and the speed ratio of the motor-electrical composite mode speed-regulating motor can be taken as *=-1~+1 (h) Defined as the ratio of motor to engine speed), in addition, the planetary row parameters must meet the conditions of 4/3 <4. According to the kinematics and dynamics relationship between the components of a single planetary row, according to the specific connection method, the relationship between the rotational speeds of the two planetary rows is established, and the CVT load during the working of the positive and reverse planetary rows can be calculated separately. The calculation formula of the rate Pcvt/P;=fo) or Pcvt/P<;= ki), fc, ki are the parameters of the positive and negative confluence planetary rows, respectively, the ratio of the ring gear to the number of teeth of the sun gear; Pcvt is the CVT The power delivered, Pe is the total power delivered by the CCVT system. Taking the topology scheme 1 listed in Table 1 as an example, ignoring the efficiency and other factors (temporaryly taken as 1) can be deduced to correspond to the forward and reverse planetary row work. For specific topology schemes, both forward and reverse can be obtained separately. The function expressions F(k2) and F(ki) of the maximum load rate are obtained, and then minF(k2) and minF(ki) are obtained; and then minF(k2) and minF(ki) of each scheme are compared, thereby Screen out the CVT load rate is lower and more suitable.
For the topological form of the same planetary row structure, when the machine-machine mode and the machine-electric mode are selected, the load rate on the CVT may be greatly different, which may result in different structural selection, so separate analysis is required.
Table 1, Table 2, and Table 3 list the topology diagrams and input and output forms of nine schemes that satisfy the forward and reverse conditions (the upper half of the planetary row group symmetric topology, and the left planet row definition). For the reverse planetary row 1, the right planetary row is defined as the positive planetary row 2; J, T, and Q represent the planet carrier, the sun gear, and the ring gear of the planetary row, respectively. The left two axes are the input shafts, respectively, and the engine. Connected to the CVT, the two axes on the right are the output shafts). In addition, the expressions of F(iDe, k2) and F(iDe, k,), the calculated machine-machine mode and the machine-electric mode minF(k2) and minF(ki) values ​​are also listed in the table.
3) The achievability and complexity of the structure.
Among the above factors, Article 1 is a prerequisite, and it is the key to the formation of CCVT. Through analysis one by one, it is easy to find that among the 36 possible topological layouts, only 9 kinds of schematic diagrams of the forward and reverse convergence scheme numbers are included at the same time: the remaining 271 can be eliminated first. The ratio of the power transmitted by shing to tW-bookmark2 to the total power transmitted by the CCVT system); the comparison and comparison of the topologies of the table 19 (1) The comparison and comparison of 29 topologies of the electric machine model 2) to remove. It can also be seen from the analysis and comparison in the table that the schemes 1, 5 corresponding to the machine-one mode, the schemes 1, 3, and 5 corresponding to the machine-electric mode have 2500), that is, the load rate of the CVT is low, Therefore, you can consider the choice.
Considering the achievability and complexity of the structure, the structure of the scheme 1 is simple and feasible, and easy to implement. There are two stacking structures on the output end of the scheme 5, which is slightly complicated. The connection between the two planetary rows in the scheme 3 is Structurally it is more difficult to achieve. Therefore, scheme 1 can be selected as the recommended optimal topology scheme, and scheme 5 is used as the suboptimal alternative scheme.
They are all extreme values ​​of the maximum load rate value, and their values ​​are obtained at the boundary value of kKkn. For example, minF(k2) in scheme 1 is obtained at 4 and ki=1.33, respectively. In order to avoid the generality, taking the machine-electric mode as an example, the sub-topology of the load rate F(iDe, k2) and F(iD, ki) of the speed-regulating motor in the scheme 1 with its own speed ratio is divided. Schematic diagram of the engine input motor input machine one machine mode one electric mode can be seen from the table, in some cases there is a CVT load rate greater than 1, mainly due to the existence of more reverse planetary row work in these systems An example of the variation of the load ratio of the speed-regulated motor and its own speed ratio is obtained by analyzing the example. The power transmitted by the CVT shunt of the electric drive accounts for the ratio of the total power transmitted by the system, and the positive and negative confluences are both at 0. 222~ 0.40 change. It can be seen that the electric drive branch with smaller power capacity (about 40% of total power) can implement stepless speed regulation for the system that transmits larger power, or the total power that can be transmitted by the CCVT system can reach at least the electric drive. The road bears 25 times the transmitted power. For the serious cycle power of the system, c should firstly be efficient, compact and lightweight, and reduce the structural strength requirements in the screening scheme. The speed ratio of the variable speed motor in the system is the same as above, ki, 2 Select the more commonly used structural parameters of the planetary row structure, fancy = 2.5, 2 = 3.5., give the variation law of iDe, fc), iDe, kl) under the above parameters.
favorable. If the machine-to-machine mode is analyzed, a similar knot can be obtained. Conclusion From the above-mentioned analytical methodology, the scheme 1 with the optimal topological layout can be selected from many schemes as the recommendation for the composite planetary transmission group of the continuously variable transmission. Basic type, scheme 5 is a sub-optimal alternative. They have the characteristics of small shunt power, compact structure, easy to implement, and are suitable for use in practical applications. The specific topology is selected to optimize the planetary row parameters of CCVT. The establishment of the segment speed ratio and other subsequent optimization design work laid a solid foundation.