Control system for shifting a drive transmission

#This invention relates to multi-speed drive transmissions for vehicles or the like and more particularly to fluid operated control systems for shifting transmissions between drive ratios in response to movement of an operator's shift lever or the like.

#Prior U.S. Pat. No. 3,508,450 discloses a highly advantageous form of transmission in which a shift is effected by disconnecting the internal change speed gears from both the driving engine and the wheel drive line of the vehicle and then temporarily braking the gears to a stationary or near stationary condition so that disengagements and re-engagements are readily accomplished without requiring synchronizers or the like. After re-engagement of the gears to establish a newly selected drive ratio, the brakes are released and input and output clutches re-engage to re-establish drive through the transmission. Another prior U.S. Pat. No. 3,570,636 describes a fluid circuit for automatically cycling the various pneumatic devices in a transmission of this kind to accomplish a selected shift.

#Utilizing the control system of prior U.S. Pat. No. 3,570,636, the operator need only move the shift lever from one position to another to effect a shift. The necessary timed actuations and de-actuations of the several pneumatic devices including input and output clutches are then sequenced automatically by the control system. The structures of the above-identified prior U.S. patents combine the compactness, economy and basic efficiency of so-called standard or manual transmissions with the superior shifting performance and much of the ease of control of so-called automatic transmissions. In addition, the absence of synchronizers enables realization of a large number of drive ratios in a transmission having a small number of change speed gears.

#In the accompanying drawings:

#FIG. 1 is a schematic diagram of a typical transmission to which the invention may be applied and shows a control system of present invention connected therewith,

#FIGS. 2A, 2B and 2C, which may be juxtaposed as illustrated in FIG. 2D, jointly constitute a fluid circuit diagram illustrating a preferred embodiment of the control system of the present invention,

#Referring initially to FIG. 1 of the drawings, there is shown a vehicle transmission 11 of the form to which the control system 12 of the present invention may advantageously be applied. The transmission 11 may be of known form such as is described in prior U.S. Pat. Nos. 3,570,636, and 3,667,309 for example, and therefore will be herein described only briefly to the extent necessary to understand the co-action of the control circuit 12 with the transmission.

#A transmission 11 of this form has three principal sections including an input section 13, an output section 14 and a change speed gear section 16. Input section 13 includes a rotatable input member 15 which may be coupled to a driving engine and a rotatable intermediate shaft 17 which also extends into the change speed gear section 16. An input clutch 18 may be engaged to transmit power from the input member 15 to shaft 17 and is self-controlled for this purpose. In particular, a pressure tending to engage the input clutch 18 is generated by a volume of oil 19 which rotates with the input member 15 and therefore generates a centrifugal force within the oil volume which is proportional to input speed. The centrifugally generated force creates a fluid pressure acting on a movable plate 21 and through engagement springs 22 exerts a pressure tending to engage clutch 18. Disengagement springs 23 act between plate 21 and the input clutch 18 in a direction tending to disengage the clutch. Accordingly, the input clutch 18 undergoes a self-modulated engagement as input speed increases above engine idling speed and the rising centrifugal pressure within oil volume 19 acts to increase the force tending to engage the clutch. Clutch 18 automatically disengages when the input speed drops below a predetermined low value and disengagement springs 23 are able to overcome the forces tending to engage the clutch.

#Input clutch 18 may be forcibly disengaged for the purpose of shifting speed ratios, without regard to the pressure exerted by rotating oil volume 19, by application of pressurized air from control system 12 to a piston 24 through a control conduit 26. Rotation of the intermediate shaft 17 may then be stopped, to facilitate gear shifting by application of pressurized air to an input brake 27 through another control conduit 28.