All-wheel drive failsafe action axle torque calculation method

A method of controlling an all-wheel drive system of a vehicle includes supplying torque to front and rear wheels of the vehicle, sensing a failure of the all-wheel drive system, and adjusting a crankshaft torque of an engine of the vehicle so that the front wheel torque remains constant regardless of a failure of the all-wheel drive system.

BACKGROUND

An all-wheel drive system can provide increased traction and stability for the vehicle. However, whenever there is a failure of the all-wheel drive system, the vehicle may revert back to a front-wheel drive system. Thus, the torque supplied to the rear wheels is then redistributed to the front wheels, which can cause an increased amount of torque to be supplied to the front wheels. Therefore it is important to determine how the torque should be limited to provide a smooth operation of the vehicle in the event of a failure of the all-wheel drive system.

SUMMARY

According to one aspect, a method of controlling an all-wheel drive system of a vehicle includes supplying torque to front and rear wheels of the vehicle, sensing a failure of the all-wheel drive system, and adjusting a crankshaft torque of an engine of the vehicle so that the front wheel torque remains constant regardless of a failure of the all-wheel drive system.

According to another aspect, a method of controlling a vehicle with an all-wheel drive system includes sensing a gear position of a transmission of the vehicle, supplying torque of a crankshaft of an engine to front wheels and rear wheels of the vehicle, and sensing a rotational speed of the crankshaft. The method also includes detecting whether there is a failure of the all-wheel drive system, and limiting the supplied torque to the front wheels for a predetermined time period after a failure of the all-wheel drive system is detected. The limited torque supplied to the front wheels is based upon the gear position of the transmission and the rotational speed of the crankshaft.

According to a further aspect, a vehicle includes an all-wheel drive system that includes an engine that outputs crankshaft torque through a crankshaft, a transmission that is coupled to the engine and supplies front wheel torque to front wheels of the vehicle, a propeller shaft rotated by the transmission, and a rear differential unit powered by the propeller shaft and supplies rear wheel torque to rear wheels of the vehicle. The vehicle also includes a controller that controls operation of the all-wheel drive system and is configured to receive signals indicative of a failure of the all-wheel drive system. The controller is configured to adjust the crankshaft torque upon receiving a failure signal so that the front wheel torque remains constant during a predetermined time period in which the failure of the all-wheel drive system occurs.

DETAILED DESCRIPTION

It should, of course, be understood the drawing and description herein are merely illustrative and that various modifications and changes can be made in the structures disclosed without departing from the present disclosure. It will be appreciated that the various identified components of the vehicle disclosed herein are merely terms of art that may vary from one manufacturer to another and should not be deemed to limit the present disclosure.

Referring now toFIG. 1, a vehicle100includes an all-wheel drive system102that is controlled by a controller104to distribute torque from an engine106to both front wheels LF, RF and rear wheels LR, RR coupled to the engine106. The engine torque is initially supplied to a transmission108that provides speed and torque conversions and then transmits the torque to the front wheels LF, RF through front axles112,114. The front axles112,114extend in a lateral direction of the vehicle100. Suspension and brake components, although not illustrated, can be connected to the front axles112,114. Additionally, the transmission108supplies torque to a propeller shaft116. The propeller shaft116powers a rear differential unit118. The rear differential unit118then supplies torque to the rear wheels LR, RR through rear axles122,124.

The vehicle100, as depicted inFIG. 1, could be any number of vehicles. In particular, the vehicle100can be an automobile, a truck, a van, or variants thereof. Further, it will be appreciated that the later described elements and methods could be employed in many other types of vehicles including motorcycles and commercial vehicles without departing from the scope of the disclosure.

The engine106schematically depicted inFIG. 1can be of a single cylinder or multi-cylinder arrangement. Further, the engine106can be powered by any number of fuels including, for example, gasoline, diesel, and natural gas. Further still, the engine106could be powered by a single fuel or by a plurality of fuels. Additionally, the engine106can be of a hybrid-type arrangement. The engine106may operate in ranges from approximately 600 revolutions per minute to over 7,000 revolutions per minute, if fueled by gasoline. Naturally, if the engine106were fueled by diesel, lower operating ranges would be expected. Although the engine106is illustrated as being disposed in a front part of the vehicle100, it is envisioned that the engine106could be located in other parts of the vehicle100without departing from the scope of the disclosure. The engine106is connected to the controller104so that various operating parameters of the engine106may be monitored and controlled by the controller104. The engine106may be oriented in a longitudinal or transverse position in the vehicle100.

The engine106outputs torque through a crankshaft126as is known in the art. A crankshaft sensor128may be disposed near the crankshaft126to measure a rotational speed of the crankshaft126. The crankshaft sensor128may use any number of contact or non-contact type technologies for sensing the rotational speed of the crankshaft126. The crankshaft sensor128can be connected to the controller104for communication therebetween.

The transmission108can include a gear position sensor132which senses a gear position of the transmission108. Naturally, the higher the gear selected for the vehicle100, the faster of a ground speed for the vehicle is possible. The gear position sensor132communicates with the controller104as will be described hereinafter. The gear position sensor132may sense the gear position of the transmission108of the vehicle100by any number of techniques known in the art. The gear position sensor132may be proximal to the transmission108or may be disposed in other locations of the vehicle100.

The transmission108can also include a torque converter134. The torque converter134can be a type of fluid coupling that is used to transfer the torque from the engine106to the front and rear wheels LF, RF, LR, RR, as is known in the art. The torque converter134is configured to multiply torque when there is a substantial difference between input and output rotational speeds of the engine106and the front and rear wheels LF, RF, LR, RR. Therefore, the torque converter134can function as a reduction gear.

Also within the transmission108is a gear train136. The gear train136serves to translate the rotational speed of the crankshaft126into a rotational speed that is acceptable for the front and rear wheels LF, RF, LR, RR. For simplicity, the gear train136is not illustrated in detail. However, it will be appreciated that the gear train136can be comprised of a plurality of gears in a known arrangement.

A connecting shaft138longitudinally extends between the gear train136and the torque converter134for the transmission of torque. Further, a shaft sensor140is disposed so as to sense a rotational speed of the connecting shaft138. Like the crankshaft sensor128, the shaft sensor140may be of a contact or non-contact type. The shaft sensor140is connected to the controller104as will be described later.

Although the transmission108has been described as being an automatic transmission, in view of the torque converter134, it will be appreciated that a manual transmission could be used in place of an automatic transmission without departing from the scope of the disclosure. Further, it is envisioned that the present disclosure could also encompass a vehicle with a semi-automatic transmission in which the driver of the vehicle selects the desired gear, but the clutch is automatically engaged as needed.

As illustrated, the transmission outputs torque to a plurality of sources. Specifically, the transmission108outputs torque to the left front axle112and the right front axle114. The transmission108also transmits torque to the propeller shaft116. The propeller shaft116is illustrated as being located in a laterally central portion of the vehicle100and extends in a longitudinal direction of the vehicle100. The propeller shaft116can be a torque tube with a single universal joint or a Hotchkiss drive with two or more joints. The propeller shaft116serves to transfer rotational energy between the transmission108and the rear differential unit118. A transmission output shaft sensor142can be mounted near the propeller shaft116so as to measure a rotational speed of the propeller shaft116. The transmission output shaft sensor142is connected to the controller104. The transmission output shaft sensor142can also be of a contact or non-contact type, which is known in the art.

With continued attention toFIG. 1, the rear differential unit118receives rotational energy from the propeller shaft116. Additionally, the rear differential unit118outputs torque to the left rear axle122and the right rear axle124to rotate the rear wheels LR, RR, respectively. The rear axles122,124extend in the lateral direction of the vehicle100. As will be appreciated various types of braking and suspension components could be attached to the axles122,124. The rear differential unit118can include a number of gears which are not illustrated. The rear differential unit118can also include a number of clutches. This arrangement allows the left rear wheel LR to spin at a different rotational rate than the right rear wheel RR.

An oil pump motor144can be associated with the rear differential unit118. The oil pump motor144can supply fluid to the rear differential unit118for operational purposes. Further, the oil pump motor144may be connected to the controller104so as to allow data communication therebetween. By connecting the oil pump motor144to the controller104, the controller104can monitor and control the oil pump motor144for optimal operation.

A temperature sensor146can be provided to the rear differential unit118. The temperature sensor146can sense a temperature within the rear differential unit118. The temperature sensor146is connected to the controller104and can provide this temperature data to the controller104. The temperature information can be used by the controller104to determine if the all-wheel drive system102is in a failure mode. The sensor146can be of a contact or non-contact type.

The vehicle100can also include a ground speed sensor148. As illustrated, the ground speed sensor148is a single component that is connected to the controller104. However, it will be appreciated that the ground speed sensor148could alternatively be a number of units that are connected to the controller104. As illustrated, the ground speed sensor148is connected to sense rotational speed of the front and rear wheels LF, RF, LR, RR. However, other techniques are also possible. For example, the ground speed sensor148could utilize various types of non-contact means for determining a speed of the vehicle100, such as, a global positioning system module.

FIG. 1shows the four wheels LF, RF, LR, RR disposed at near corners of the vehicle100. However, the front and rear wheels LF, RF, LR, RR could be located laterally inward/outward and longitudinally inward/outward from the location illustrated without departing from the scope of the disclosure. It would be expected that the front and rear wheels LF, RF, LR, RR could rotate between zero and approximately 1,800 revolutions per minute. While the front wheels LF, RF are illustrated as being a same lateral distance apart as the rear wheels LR, RR, it will be appreciated that a distance between the front wheels LF, RF could be different than a distance between the rear wheels LR, RR, i.e., in a staggered arrangement.

The vehicle100also includes the controller104that among other things controls the all-wheel drive system102. As illustrated, the controller104is located near a rear end of the vehicle100. However, the controller104could be located in any number of places in the vehicle100without departing from the scope of this disclosure. The controller104is connected to the engine106, the crankshaft sensor128, the gear position sensor132, the shaft sensor140, the transmission output shaft sensor142, the oil pump motor144, the temperature sensor146, and the ground speed sensor148so as to allow two way communication between the controller104and the described components. Further, although shown as being connected to the various components with wires, it will be understood that the controller104could be interfaced with the other components through a variety of other connection methods including, for example, wireless communication. The controller104may be any number of central processing units or programmable logic controllers.

With regard to control of the all-wheel drive system102, the controller104is able to adjust the torque from the crankshaft126whenever the controller104determines that at least one component of the all-wheel drive system102has failed so that the front wheel torque, i.e., the torque supplied to the front wheels LF, RF, remains substantially constant. The controller104is able to determine if the all-wheel drive system102is in a failure mode based at least upon the signals received from the engine106, the crankshaft sensor128, the gear position sensor132, the shaft sensor140, the transmission output shaft sensor142, the oil pump motor144, the temperature sensor146, and the ground speed sensor148. It will be appreciated that the controller104could also determine that the all-wheel drive system102is in a failure mode based upon other signals received from different sensors not specifically described herein.

The controller104is configured to adjust the torque output from the crankshaft126of the engine106upon receiving what the controller104determines to be a failure signal so that the torque of the front wheels LF, RF remains approximately constant, by according to one aspect, determining the adjusted crankshaft torque with the following equation: ACT=CFWT/(GR×E)/TCG. The symbol ACT equals the adjusted crankshaft torque, the symbol CFWT equals a calculated front wheel torque, the symbol GR equals a transmission gear ratio, the symbol E equals a transmission efficiency, and the symbol TCG equals a torque converter gain.

The controller104controls the all-wheel drive system102so that a value of the rear wheel torque, i.e., the torque at the rear wheels LR, RR, equals approximately zero subsequent to the controller104determining that the all-wheel drive system102has failed. Thus, the torque supplied to the front wheels LF, RF is greater than the torque supplied to the rear wheels LR, RR. The controller104is configured to adjust the torque from the crankshaft126by adjusting operating parameters of the engine106. For example, to reduce the torque from the crankshaft126, the controller104could reduce the amount of fuel supplied to the engine106or retard the timing of the engine106. By reducing the crankshaft torque, the controller104ensures that the front wheels LF, RF do not receive a dramatic increase in torque when the torque originally destined for the rear wheels LR, RR is redistributed to the front wheels when the all-wheel drive system102fails.

The controller104can include a number of look-up tables. These look-up tables may include the transmission gear ratio, the transmission efficiency, and the torque converter gain. The torque converter gain is based upon a rotational speed of the torque converter134. The rotational speed of the torque converter134can be determined either from actual measurement or by calculation. The controller104is also configured to calculate the front wheel torque based upon the gear position and the crankshaft torque. The gear position is determined based upon a signal received from the gear position sensor132and the crankshaft torque is determined based upon a signal from the crankshaft sensor128.

With reference toFIGS. 2 and 3, a method of controlling a vehicle with an all-wheel drive system and a method of controlling an all-wheel drive system of a vehicle, are shown. While, for purposes of simplicity of explanation, the methods have steps shown and described as executing serially, it is to be understood and appreciated that the present invention is not limited by the illustrated order, as some steps could occur in different orders and/or concurrently with other steps from those shown and described herein.

With reference toFIG. 2, an exemplary method of controlling the vehicle100with the all-wheel drive system102is illustrated. In Step200, a gear position of the transmission108is determined by the controller104receiving a gear position signal from the gear position sensor132. In Step210, torque is supplied to front wheels LF, RF and rear wheels LR, RR in a manner as previously described. In Step220, a rotational speed of the crankshaft126is sensed by the crankshaft sensor128. By sensing the rotational speed of the crankshaft126, the controller104can determine the engine torque. In Step230, detection of whether there is a failure of the all-wheel drive system102occurs by the controller104analyzing the signals received from the engine106, the crankshaft sensor128, the gear position sensor132, the shaft sensor140, the transmission output shaft sensor142, the oil pump motor144, the temperature sensor146, and the ground speed sensor148. In Step240, the supplied torque to the front and rear wheels LF, RF, LR, RR is limited for a predetermined period of time after a failure of the all-wheel drive system102is detected. The torque can be limited by adjusting the rotational speed of the crankshaft126. As will be appreciated, the rotational speed of the crankshaft126is not directly controlled. Rather, the rotational speed of the crankshaft126is indirectly controlled by any number of methods, including for example, by adjusting throttle, by adjusting fuel injection, and/or by adjusting spark timing. Further, the limited torque supplied to the front wheels LF, RF is based upon the gear position of the vehicle100and the torque output from the crankshaft128. The predetermined time period can be anywhere from one to approximately five seconds, with a general duration of about three seconds. This provides a sufficient time for the driver of the vehicle100to adjust to the failure of the all-wheel drive system102. By taking into account the gear position of the transmission108and the amount of torque output by the crankshaft126, the proper amount of torque can be supplied to the front wheels LF, RF, thereby ensuring smooth operation of the vehicle100.

The limited torque supplied to the rear wheels LR, RR during the predetermined period of time is equal to approximately zero. After the predetermined time period, the torque from the crankshaft126is increased at a predetermined rate until it is equal to the crankshaft torque prior to the failure of the all-wheel drive system102. Naturally, this outcome is based upon no other system or diver-input changes. According to one aspect, this predetermined rate is about 1.5 Newton-meters per ten milliseconds. It is noted that the crankshaft torque can be controlled by controlling the rotational speed of the crankshaft126with the controller104, as described hereinbefore.

With reference toFIG. 3, an exemplary method of controlling the all-wheel drive system102with the vehicle100is shown. In Step300, torque is supplied to the front and rear wheels LF, RF, LR, RR of the vehicle100in a manner as previously described. In Step310, a value of the torque that is supplied to the front wheels LF, RF is calculated based upon the signals received by the controller104from the gear position sensor132and the crankshaft sensor128. In Step320, a failure of the all-wheel drive system102is sensed by the controller104analyzing the signals received from the engine106, the crankshaft sensor128, the gear position sensor132, the shaft sensor140, the transmission output shaft sensor142, the oil pump motor144, the temperature sensor146, and the ground speed sensor148. In Step330, the torque supplied by the crankshaft126of the engine106is adjusted so that the front wheel torque remains constant regardless of the failure of the all-wheel drive system102. The crankshaft torque can be adjusting by changing the rotational speed of the crankshaft126. The torque supplied to the front wheels LF, RF subsequent to a failure of the all-wheel drive system102is greater than the torque supplied to the rear wheels LR, RR subsequent to a failure of the all-wheel drive system102. The crankshaft torque may be adjusted so that a value of the torque supplied to the rear wheels LR, RR subsequent to a failure of the all-wheel drive system102is equal to approximately zero. Further, the adjusted crankshaft torque can be determined based upon the calculated front wheel torque. The transmission gear ratio, the transaxle efficiency, and the torque converter gain can be determined from the look-up table. The torque converter gain is based upon a rotational speed of the torque converter134of the vehicle100.