Continuously variable ratio transmission control system

Claim 2

A continuously variable ratio transmission control system having an inner servo loop for adjusting the transmission speed ratio in accordance with the position of an actuator member (98), and an outer servo loop for adjusting the position of the actuator member in a manner to establish a desired speed ratio in. said transmission, and apparatus for operating the outer servo loop, comprising means (120) for determining the ratio error according to the difference between the actual speed ratio and the desired speed ratio, and means (120, 160) for adjusting the actuator member in a direction to reduce such.ratio error,.characterised in that the response of the inner loop is such that the rate of change of speed ratio with respect to actuator member position is a non-constant function of the actual speed ratio, the rate adjustment means (120, 160) is effective when the ratio error is at or above a predetermined value to regulate the rate of adjustment of the actuator member (98) so that the rate of change of actuator member position with respect to time is a direct function of the ratio error to relatively quickly reduce such error to the predetermined value below which further adjustment would compromise system stability in .view of the non-constant response of the inner servo loop, thereby providing an overall system response with satisfactory shift feel, and the rate adjustment means is further effective when the ratio error is below the predetermined value to regulate the rate of adjustment of the actuator member so that the rate of change of actuator member position with respect to time is a non-constant function of the actual speed ratio and in inverse relationship to the non-constant function of the inner loop to yield a substantially constant rate of change of speed ratio with respect to time for all actual speed ratio values for relatively slowly reducing such error, thereby bringing the actual speed ratio into correspondence with the desired speed ratio in a stable manner.

Claim 3

A continuously variable ratio transmission control system according to claim 1, characterised in that the rate of adjustment of the actuator member (98) is regulated according to a first engageable mode of operation wherein the rate of change of actuator member position with respect to time is a direct function of the ratio error, thereby providing relatively fast overall system response with acceptable shift feel, or a second engageable mode of operation wherein the rate of change of actuator member position with respect to time is a non-constant function of the actual speed ratio, and in inverse relationship to the non-constant response of the inner loop to yield a substantially constant rate of change of speed ratio with respect to time for all actual speed - ratio values, thereby providing stable and consistent overall system response, and either the first or the second mode of operation is engaged so that when the magnitude of the ratio error is at or above a predetermined error value, the first mode of operation is engaged to reduce the ratio error to the predetermined value below which further adjustment would compromise system stability in view of the non-constant response of the inner servo loop, and so that when the ratio error is below the predetermined value, the second mode of operation is engaged to reduce the remaining ratio error in a stable manner, whereby the ratio control system is operated in a manner to provide stable response when the ratio error is relatively small without sacrificing speed of response when the ratio error is relatively large.

Claim 4

A continuously variable ratio transmission control system according to claim 1 or 2, characterised in that the means (120, 160) for adjusting the actuator member (98) is effective when the ratio error exceeds a dead-band ratio error value to adjust the actuator member in a direction to reduce such ratio error, means is effective for establishing a predetermined ratio error value substantially in excess of the dead-band ratio error value, above which the primary control objective is to'achieve speed of response with acceptable shift feel.and below- which the primary control objective is to achieve stable response with minimal overshoot of the actual speed ratio with respect to the desired speed ratio, first means is effective when the ratio error is at or above the predetermined ratio error value for establishing an outer loop response function such that the rate of change of actuator member position with respect to time varies in direct relation to the ratio error to yield an overall response function such that the rate of change of speed ratio with respect to time achieves the primary objective of speed of response with acceptable shift feel and second means is effective when the ratio error is below the predetermined value for establishing an outer loop response function such that the rate of change of actuator position with respect to time varies in relation to the actual speed ratio, such relation being inverse with respect to the response function of the inner loop to thereby yield an overall response function such that the rate of change of speed ratio with respect to time is substantially constant for all actual speed ratio values to achieve the primary objective of stable response with minimal overshoot of the actual speed ratio with respect to the desired speed ratio.

Claim 5

- A continuously variable ratio transmission control system according to claim 1 or 2, for use in a motor vehicle, characterised in that apparatus for controlling the speed ratio between the input and output shafts of the transmission by driving the actual speed ratio towards a desired speed ratio so as to reduce the ratio error therebetween comprises means including an inner servo loop for determining the actual speed ratio in accordance with the position of the actuator member (98) such that the rate of change of speed ratio with respect to actuator member position is related to the speed ratio by a non-constant inner loop gain function, means including an outer servo loop for adjusting the position of the actuator member in accordance with a fast response mode of operation at all times except when the ratio error is sufficiently small for the system to be otherwise in danger of becoming unstable due to the actual speed ratio excessively overshooting the desired speed ratio, during which times the adjustment is made in accordance with a stable mode of operation, means for controlling the rate of change of the position of the actuator member with respect to time in the fast response mode of operation over a first range of rate values, such rate of change being determined in relation to the ratio error and the actual speed ratio by a first outer loop gain function which is effective in conjunction with the first range of rate values to drive the actual speed ratio relatively rapidly towards the desired speed ratio at an overall rate of change in speed ratio with respect to time that provides a desired shift feel, and means for controlling the rate of change of the position of the actuator member with respect to time in the stable response mode of operation over a second range of rate values which is generally lower than the first range of rate values, such rate of change being determined in relation to the speed ratio by a second outer loop gain function which is approximately the inverse of the aforesaid non-constant inner loop gain function and which is effective in conjunction with such non-constant inner loop gain function'to drive the actual speed-ratio relatively slowly towards the desired speed ratio at an overall rate of change of speed ratio with respect to time that is approximately constant over the speed ratio range so as to provide system repeatability and that is sufficiently low to provide system stability by preventing the actual speed ratio from excessively overshooting the desired speed ratio.