System for controlling torque transmission in a four wheel drive vehicle

A system for controlling torque transmission between an engine of a four wheel drive vehicle and each of its driven wheel, two of which steer the vehicle and are driven by front drive axle means and two of which are driven by rear drive axle means, said system comprising:

• a center differential having an input shaft operably to said engine and two rotary power output shafts for driving said front and rear drive axle means, said center differential including a gear set arrangement for establishing a drive path from said input shaft to both of said output shafts;
• means for biasing torque between said two power shafts, said biasing means including an electromagnetically actuated clutch assembly having a series of interleaved friction members which are permitted to turn relative to one another when the clutch assembly is less than fully engaged, some of said friction members being arranged to turn with one output shaft and the remainder turning with the other output shaft;
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• an information processing unit having operative means for receiving a plurality of inputs including an input indicative of the rotational speed of said output shafts and an input indicative of present engine operating conditions and an input indicative of the steering angle of the vehicle, and processing unit further including means for processing said inputs to generate a calculated control output which regulate the torque level to be established between said friction members of the clutch assembly in a manner biasing torque between the output shafts in accordance with vehicle operating conditions and operator demand;
• said processing unit including detecting means for determining wheel slip as a function of one of output shaft acceleration rate and the relative turning speeds of said output shaft in conjunction with steering angle, and for generating an output indicative of the wheel slip.

A system for controlling torque transmission between an engine of a four wheel drive vehicle and each of its driven wheels, two of which are driven by front drive axle means and two of which are driven by rear drive axle means, said system comprising:

• a center differential having three shafts interconnected in a driving relationship by a gear set, one of said shafts being operably connected to said engine with the other two shafts being respectively connected to the front and rear drive axle means, said gear set dividing the torque imparted to said center differential through said input shaft to each of said other two shafts in a predetermined manner, means for biasing torque between said other two shafts, said biasing means including an electromagnetically actuated clutch assembly having a series of interleaved friction members which are permitted to turn relative to one another, some of said friction members being arranged to turn with one of said shafts and the remainder turning with the other shaft, the turning rates of said friction members being governed by the torque established therebetween;
• means for monitoring vehicle operation and operator demand on said engine, said monitoring means including means for sensing the rotational speed of each of said other two shafts and developing outputs reflecting the respective shaft speed;
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• control circuitry means connected to said monitoring means, said control circuitry means including first operative means for determining when a slip condition exists between said two other shafts, second operative means arranged in combination with said first operative means for establishing a target clutch torque to be applied between said friction members, and third operative means for energizing said clutch assembly to a level determined by the target clutch torque and as a function of vehicle operating conditions and operator demands in the engine;
• said second operative means including first means for computing total torque delivered to the transfer case and second means for establishing the target clutch torque as a function of total torque delivered to the transfer case.

In combination with a four wheel drive vehicle having front and rear road wheels driven by an engine and a steering mechanism for effecting the steering angle of at least one pair of the front and rear road wheels, a system for continuously distributing driving torque to all four wheels of said vehicle comprising:

• a fluid containing transfer case connected to said engine and having an input shaft connected to front and rear drive axles, said transfer case further including a multimembered gear set for connecting said input shaft with the front and rear drive axles such that torque is normally split between both of said drive axles in a predetermined manner;
• modulatable biasing clutch means operatively connected with said transfer case and including an electromagnetically actuated clutch assembly with friction members, some of which turn with the front drive axle means and others which turn with the rear drive axle means, said clutch assembly being operably effective to bias torque through said gear set as a function of the torque through said gear set as a function of the torque level established between said friction members;
• first operative means for establishing whether acceleration of said front drive axle exceeds a predetermined limit and for generating a wheel slip indication when said predetermined limit is exceeded;
• second operative means for establishing whether acceleration of said rear drive axle exceeds a predetermined limit and for generating a wheel slip indication when said predetermined limit is exceeded;
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• third operative means connected to said electromagnetically actuated clutch and responsive to an indication of wheel slip from either said first or second operative means for regulating the level of torque established between said friction members to correct for wheel slip.

In combination with a four wheel drive vehicle having front and rear pairs of wheels driven by an engine, and a steering mechanism for effecting the steering angle of at least one pair of the front and rear wheels, a system for biasing torque to all four wheels of said vehicle comprising:

• a fluid containing transfer case connected to said engine for operatively transmitting input power and torque to all four wheels of said vehicle, said transfer case including front and rear drive shafts and a gear arrangement defining a first driving connection which interconnects said drive shafts in a manner such that input torque to the transfer case is divided between said shafts in a ratio fixed by the gear arrangement;
• a clutch assembly operatively connected with said transfer case for defining a second driving connected between said drive shafts and arranged such that torque may be shifted between said shafts, said clutch assembly including interleaved friction members some of which turn with the front drive shaft with the remaining members turning with the rear drive shaft and an electromagnetic energizer for modulating the torque level between said friction members as a function of a control command applied to said energizer;
• first operative means for establishing whether acceleration of said front drive shaft exceeds a predetermined limit and for generating a wheel slip indication when said predetermined limit is exceeded;
• second operative means for establishing whether acceleration of said rear drive shaft exceeds a predetermined limit and for generating a wheel slip indication when said predetermined limit is exceeded;
• third operative means for detecting a relative slip condition between said front and rear drive shaft and developing a wheel slip indication when said slip condition exceeds a predetermined limit;
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• control means connected to said electromagnetic energizer and responsive to an indication of wheel slip from either said first, second or third operative means for regulating the level of torque to be established between said friction members to correct for wheel slip.

A method for controlling a steerable four wheel drive vehicle having an operator controlled engine, front and rear drive axles and a transfer case connected to the engine, said transfer case including a planetary gear differential controlled by an electromagnetic clutch for biasing torque between the front and rear drive axles, said method comprising the steps of:

• sensing front and rear drive axle speeds;
• sensing the steering angle of the vehicle;
• detecting a slip condition between front and rear drive axles utilizing the sensed speeds and present steering angle, and developing a first output indicative of a slip condition;
• computing total torque delivered to said transfer case;
• developing a second output in response to an indication of a slip condition and as a function of total torque delivered to said transfer case, said output being indicative of a level of torque required to be developed by said clutch to correct the detected slip condition, and controlling application of the electromagnetic clutch with said output for a predetermined time period and in a manner biasing torque between the front and rear drive axles.

A system for distributing torque to all four drive wheels of a vehicle including front and rear drive axles and an engine, said system comprising:

• a transfer case connected to said engine and including an input shaft connected to said front and rear drive axles, said transfer case further including a differential for interconnecting said input shaft with the front and rear drive axles so as to transmit torque therefrom to both of said front and rear drive axles in a predetermined manner;
• modulatable biasing clutch means operatively connected with the transfer case and including an electromagnetically actuated clutch assembly with an energizeable magnetic coil, said clutch assembly operative to redistribute the input torque to the transfer case in accordance with the energization of the magnetic coil so as to alter the torque split from a nominal value established by the differential to an adjusted value for improving traction and vehicle handling conditions;
• means including sensor means for producing signals indicative of vehicle operating conditions including vehicle speed and front and rear drive shaft speeds;
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• characterized by controller means for receiving and analyzing the vehicle operating conditions for producing a desired slip speed setpoint signal which is a function of the vehicle operating conditions;
• feedback control loop means including means for comparing the actual slip speed relationship between the speed of the front drive shaft and the speed of the rear drive shaft with the desired slip speed setpoint signal to establish a slip speed error signal;
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• switch logic means operative when the slip speed error signal is above a predetermined upper limit to produce a maximum clutch command signal and operative when the slip speed error signal is below a lower limit to produce a zero clutch energization signal.

A system for distributing torque to all four drive wheels of a vehicle including front and rear drive axles and an engine, said system comprising:

• a transfer case connected to said engine and including an input shaft connected to said front and rear drive axles, said transfer case further including a differential for interconnecting said input shaft with the front and rear drive axles so as to transmit torque therefrom to both of said front and rear drive axles in a predetermined manner;
• modulatable biasing clutch means operatively associated with the transfer case and including an electromagnetically actuated clutch assembly with an energizeable magnetic coil, said clutch assembly operative to redistribute the input torque to the transfer case in accordance with the energization of the magnetic coil so as to alter the torque split from a nominal value established by the differential to an adjusted value for improving traction and vehicle handling conditions;
• means including sensor means for producing signals indicative of vehicle operating conditions including vehicle speed and front and rear drive shaft speeds;
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• characterized by controller means for receiving and analyzing the vehicle operating conditions for producing a desired slip speed setpoint signal which is a function of the vehicle operating conditions;
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• feedback control loop means for producing a feedback signal of the actual slip speed relationship between the speed of the front drive shaft and the speed of the rear drive shaft and means for producing control of the energization of the magnetic coil based on said feedback signal.

A system for distributing torque to all four drive wheels of a vehicle powered by an engine, said system comprising:

• a transfer case connected to said engine and having an input shaft connected to front and rear drive axles, said transfer case further including a differential for interconnecting said input shaft with the front and rear drive axles such that torque is transmitted to both of said drive axles in a predetermined manner;
• control system means including sensor means for monitoring drive axle rotational speeds and engine operating conditions, wheel slip detector means for detecting a slip condition between said front and rear drive axles and for generating an output, clutch torque command generator means responsive to the output of said wheel slip detector means for calculating and generating a target torque level output which is computed as a function of total torque delivered to said transfer case and delivered to a clutch actuator means;
• said clutch torque command generator means including means for increasing the torque level to the target torque level over a predetermined time period and then maintaining the torque level generally constant for a second predetermined time period;
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• modulatable biasing clutch means operatively connected with the transfer case and including an electromagnetically actuated clutch assembly with friction members which are operably effective to interconnect two members of said differential, wherein said clutch actuator means regulates the electromagnet clutch assembly in a manner controlling the operable effectiveness of said clutch assembly and thereby controlling torque transmission to the front and rear drive axles as a function of a torque level established between said friction members.