System for controlling a continuously variable transmission in response to a sensed wheel deceleration
First Claim
1. A shift control system, comprising:
- continuously variable transmission; and
shift controller which controls a transmission ratio of said continuously variable transmission between a maximum ratio and a minimum ratio when a normal drive range is selected, and which, when an engine brake range is selected, prevents the transmission ratio from decreasing beyond a shift limit of the engine brake range which is greater than said minimum ratio;
wherein said shift control system further comprises a wheel condition sensing means for sensing a revolving condition of a wheel of a vehicle to determine a wheel deceleration, and said shift controller decreases said shift limit of said engine brake range when the wheel deceleration is equal to or greater than a predetermined deceleration value;
wherein said shift controller comprises a limit changing means for normally holding said shift limit of said engine brake range equal to a normal limit ratio and changing said shift limit to a modified limit ratio which is smaller than said normal limit ratio when the wheel deceleration is equal to or greater than the predetermined deceleration value, and said wheel deceleration is a rate of decrease of a drive wheel speed of the vehicle with respect to time; and
wherein said shift controller comprises a limit restoring means for restoring said shift limit of said engine brake range from said modified limit ratio to said normal limit ratio when said engine brake range is not selected.
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Accused Products
Abstract
In order to improve steering performance and braking performance specifically on a low μ road surface during operation of engine braking, there are provided, in a shift control system of a continuously variable transmission, a sensor for determining a wheel deceleration, and a shift controller for changing a shift pattern adequately. When an engine brake range such as a 2 range or an L range is selected, and the wheel deceleration becomes greater than a predetermined deceleration level, the shift controller changes an upshift limit of the engine brake range, to a smaller transmission ratio. By reducing the transmission ratio in this way, the shift control system can reduce an engine braking force applied to the drive wheels and an inertia torque of the transmission against the driving force applied to the drive wheels by the road surface, so that the wheel speed can readily increase to achieve a desirable degree of wheel slip.
49 Citations
20 Claims
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1. A shift control system, comprising:
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continuously variable transmission; and shift controller which controls a transmission ratio of said continuously variable transmission between a maximum ratio and a minimum ratio when a normal drive range is selected, and which, when an engine brake range is selected, prevents the transmission ratio from decreasing beyond a shift limit of the engine brake range which is greater than said minimum ratio; wherein said shift control system further comprises a wheel condition sensing means for sensing a revolving condition of a wheel of a vehicle to determine a wheel deceleration, and said shift controller decreases said shift limit of said engine brake range when the wheel deceleration is equal to or greater than a predetermined deceleration value; wherein said shift controller comprises a limit changing means for normally holding said shift limit of said engine brake range equal to a normal limit ratio and changing said shift limit to a modified limit ratio which is smaller than said normal limit ratio when the wheel deceleration is equal to or greater than the predetermined deceleration value, and said wheel deceleration is a rate of decrease of a drive wheel speed of the vehicle with respect to time; and wherein said shift controller comprises a limit restoring means for restoring said shift limit of said engine brake range from said modified limit ratio to said normal limit ratio when said engine brake range is not selected. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A shift control system, comprising:
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a continuously variable transmission; and a shift controller which controls a transmission ratio of said continuously variable transmission between a maximum ratio and a minimum ratio when a normal drive range is selected, and which, when an engine brake range is selected, prevents the transmission ratio from decreasing beyond a shift limit of the engine brake range which is greater than said minimum ratio; wherein said shift control system further comprises a wheel condition sensing means for sensing a revolving condition of a wheel of a vehicle to determine a wheel deceleration, and said shift controller decreases said shift limit of said engine brake range when the wheel deceleration is equal to or greater than a predetermined deceleration value; wherein said shift controller comprises a limit changing means for normally holding said shift limit of said engine brake range equal to a normal limit ratio and changing said shift limit to a modified limit ratio which is smaller than said normal limit ratio when the wheel deceleration is equal to or greater than the predetermined deceleration value, and said wheel deceleration is a rate of decrease of a drive wheel speed of the vehicle with respect to time; and wherein said transmission has a plurality of shift positions comprising a P position for parking, an R position for reverse, an N position for neutral, a D position for selecting said normal drive range, a second low speed position for selecting a second low speed range in which said transmission ratio is prevented from being decreased beyond a second shift limit to obtain an engine braking effect, and a first low speed position for selecting a first low speed range in which said transmission ratio is prevented from being decreased beyond a first shift limit to obtain the engine braking effect; and
wherein said limit changing means of said shift controller normally holds said first and second shift limits equal to first and second normal limit ratios respectively, and changing said first and second shift limits to first and second modified limit ratios, respectively, when said wheel deceleration is equal to or greater than said predetermined wheel deceleration value, said first normal limit ratio is greater than said second normal limit ratio, said first modified limit ratio is smaller than said first normal limit ratio, and said second modified limit ratio is smaller than said second normal limit ratio. - View Dependent Claims (18)
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19. A shift control system, comprising:
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a transmission system comprising a continuously variable transmission; a sensing means comprising a vehicle condition sensing means for sensing a vehicle operating condition, a wheel condition sensing means for sensing a revolving condition of a wheel of a vehicle to determine a wheel deceleration and a shift position sensing means for sensing a shift position of said transmission by sensing a position of a movable member of said transmission system, and producing a shift position signal representing said shift position of said transmission, said shift position signal being in a first signal state when said movable member is in a position to select a normal drive range and in a second signal state when said movable member is in a position to select an engine brake range; and a shift controller for controlling a transmission ratio of said continuously variable transmission in accordance with said vehicle operating condition between a maximum ratio (Cmax) and a minimum ratio (Cmin) when said shift position signal is in said first signal state indicating said normal drive range, and for controlling the transmission ratio of said continuously variable transmission in accordance with said vehicle operating condition between said maximum ratio (Cmax) and a shift limit which is equal to or smaller than said maximum ratio when said shift position signal is in said second signal state indicating said engine brake range; wherein said shift controller comprises a limit changing means for normally holding said shift limit of said engine brake range equal to a normal limit ratio (CLmin, C2min) and changing said shift limit to a modified limit ratio (C'"'"'Lmin, C'"'"'2min) which is smaller than said normal limit ratio when the wheel deceleration is equal to or greater than the predetermined deceleration value. - View Dependent Claims (20)
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Specification