Adjustable hydraulic transmission

Hydraulic transmission applications and benefits

Brief description of the constructions of the main links

In Fig. 5, the hydraulic transmission is shown assembled, and in Fig. 6 – in a disassembled state.
The main links of the hydraulic transmission are: drive shaft 1, driven shaft 2, two pistons 3, housing 4, core 5, control lever 6, sleeve 7, two covers 8, two thrust compensators 9. 

Shafts 1, 2 are the same in design, but for a reduction gear, the part of the shaft under the piston, like the driving piston, can be shorter than that of the driven shaft.

This part of the shaft is made in the form of a cylindrical cam with an eccentricity е to the axis of the rest of the shaft. The parameters of the working surfaces of the pistons and the sleeve depend on the value of е . A piston is installed on the cam with the possibility of free rotation.
The pistons-3 are also the same in design but may differ in length as noted above. Rotating, the drive shaft displaces the working fluid through the piston under pressure through the channel in the core into the “driven” cavity. The driven piston under the influence of this pressure rotates the driven shaft. As in the pump, the working surface of the pistons is processed according to a special hypotrochoid, the diameter of the circumscribed circle of which is d₃=12_е.
Case-4 is a device in which the rotation conversion mechanism is located. In the middle part of the body there is a longitudinal window for the output of the sleeve control lever 6. The inner cylindrical surface is a guide for free longitudinal movement of the sleeve. Core-5 divides the inner cavity of the sleeve into two chambers. The central hole of the core is intended for shaft supports, which determine the thickness of the part. The flat ends of the core in contact with the shafts and pistons limit the longitudinal displacement of the part. The outer curly surface of the part is processed with the possibility of sliding the sleeve along it without breaking the tightness. 4 longitudinal channels are made in the sleeve for communication between the “leading” and “slave” chambers of the sleeve. 

The control lever 6 is fixedly connected to the sleeve and serves to move the sleeve longitudinally, thereby proportionally changing the revolutions of the driven shaft.

Sleeve 7 serves to change the ratio of chamber volumes on both sides of the core when adjusting the gear ratio of the shaft rotation speeds. This is achieved by longitudinal displacement of the sleeve. The outer cylindrical surface of the sleeve is processed with the possibility of longitudinal displacement along the inner guide surface of the housing. There may be several longitudinal channels on the outer surface for better communication of the cavities outside the sleeve with each other during movement. The inner surface of the sleeve must be machined on a special figured surface, on which the pistons precisely slide and roll. Mathematical formulas of this surface are calculated and derived.
Covers 8 serve to support the shafts and limit the longitudinal displacement of the pistons and eccentrics with the shafts, which, during the operation of the pump, slide freely with their flat ends along the inner flat end of each cover.
Thrust compensator 9 must be installed at each end of the sleeve. The compensator is an assembly of several ring parts and a set of rollers.

The compensator serves two functions:

-compensation for the displacement of the eccentric of the shaft with the piston on it relative to the axis of the shaft without breaking the tightness;

̶ to perceive the axial force from the internal pressure of the working fluid on the movable end wall and the end part of the sleeve without braking between them.

Note: The illustrations do not show auxiliary parts such as seals, bearings, supports, fasteners, etc.

General description of the functioning of the hydraulic transmission

Based on the device structure described in detail above, the sequence of operation of the hydraulic transmission is analyzed below. The following figures show:
– in Fig.7a ̶ a general view of the transmission in a longitudinal section;

– Fig. 7b is a schematic simplified sketch for understanding the principle of transmission operation;

– in Fig. 8a – a view of the cavity of the drive shaft in a transverse section;

– in Fig. 8b – a view of the cavity of the driven shaft in a transverse section. For the simplest coverage of the principle of hydraulic transmission operation, we will accept the following conventions and initial positions:
– we use shaft 1 as a driver, and 2 as a slave; ̶ the current intermediate position of the pistons and shafts is shown by the main lines, and the initial position is shown by thin lines, in which one of the tops of each piston is on the vertical, but on the driving piston in the upper position (Fig. 9a), and on the driven piston – in the lower position (Fig. 9b). – first, consider the steady state, when the gear ratio u does not change and the position of the control lever 6 corresponds to an equal volume of cavities, i.e. h1 \u003d h2 (Fig. 8), and therefore, the revolutions of the shafts n1 \u003d n2 are also equal. So, the initial position of the RPM is shown by fragment 30 with the top C0 of the driving piston in the highest position (Fig. 9a) and fragment 30 “with the top Co” of the driven piston in the lower position (Fig. 9b). At this and at any other time in the cross section of the device, the profile of the piston has at least 4 points of contact with the sleeve, which divide the space between the piston and the sleeve into parts that are variable in volume. When the shaft 1 with the cam is rotated at the angle &alpha counterclockwise, the piston has taken position 3&alpha, the fluid is forced out of the cavities M, m through the channels ①, ② in the core (Fig. 9a) and enters the cavities M2 and m (Fig. 9b), rotating the shaft 2 with the cam in the opposite direction by the angle &beta . At the same time, the driven piston has taken position 3&beta, the liquid is displaced from the cavities N2, n2 and enters the expandable cavities N, n through the channels ③, ④ (Fig. 9a). Such fluid circulation processes occur constantly, applying pressure sequentially to each section of the piston and thereby rotating the driven shaft continuously. When shaft 1 rotates in the opposite direction – clockwise, all of the above fluid flows change the direction of flow and impact on the pistons, thereby changing the rotation of the driven shaft to the opposite. The speeds of rotation of the shafts are multidirectional, but due to the initial equality of the volumes of liquid around them, the speeds are equal in absolute value. When the position of the control lever 6 is changed so that h1 ≠ h2 (Fig. 8), the volumes of liquid inside the sleeve to the right and left of the core 5 will also be unequal, leading to an inequality of speeds n1 and n2 rotated