Traction Control for Moving a Vehicle From Deep Snow

1. Field of the Invention

This invention relates to electronic control of the driving wheels of a vehicle having an internal combustion engine.

2. Prior Art

Traction control of various types is known. For example, it is known to reduce the power applied to the driving wheels through various combinations of controlling engine operating parameters such as spark advance, fuel injection and throttle control. Braking may also be used to control driving wheel rotation.

Even though such control of the driving wheels is known, there still is a need to improve the performance of traction control in various operating environments. Conditions such as low speed and deep snow are addressed, in part, by this invention.

In accordance with an embodiment of this invention there is used an available preview of the surface friction conditions from increased slip targets to increase tire tractive forces up to a maximum possible at or near zero vehicle speeds, indicating a stuck vehicle. This invention is advantageous because there are increased chances for moving a vehicle from a snow bank, stuck in snow or similar stuck condition.

FIGS. 1A and 1B are graphic representations of wheel speed and torque during a spin on ice at or near zero vehicle speed indicating a stuck conditions; and

FIGS. 2A and 2B are a logic flow description of a traction control system in accordance with an embodiment of this invention.

When trying to move a vehicle in deep snow the following traction control strategy in accordance with an embodiment of this invention is used.

During the first attempts to remove the vehicle, such as the first couple of tip-ins, identify that the vehicle is stuck by monitoring of non-driven wheels and then start increasing the slip target. The slip target is the amount of wheel slip of the driving wheels allowed before reducing driving power to the driving wheels. This will cause more wheel slip and in some cases this could be beneficial. For example, this may help remove the loose material, such as snow, underneath the tire and bring the tire in contact with firmer, hopefully higher-mu ground layer.

If the above approach does not cause the vehicle to move, then proceed with the approach based on "preview" of underlying surface which was provided by the above approach. Such an action has a potential to increase the tractive force up to 100% as shown in FIGS. 1A and 1B indicating of initial wheel spin and torque on ice.

Referring to FIGS. 2A and 2B, logic flow starts at a block 20 and goes to a decision block 21 wherein it is asked if the vehicle speed is less than or equal to a stuck velocity for at least a predetermined number of seconds or if the stuck flag is on. If the answer is no, the logic flow goes to an exit block 22. If the answer is yes, logic flow goes to a block 23 wherein the vehicle stuck flag is set. Logic flow then goes to a decision block 24 wherein it is asked if wheel spin is greater than or equal to a limiting spin. The limiting spin is used to determine surface friction coefficients which are then stored for future use. The spin needs to be above such limiting value for the surface friction coefficient identification to be valid. If yes, logic flow goes to a block 25 wherein wheels are spinning, which facilitates identification of the road-mu. Logic flow then goes to a node 26 which then goes to a block 27 wherein there is gradually increased the slip target multiplier. If the answer in block 24 is no, logic flow goes to node 26 and block 27. Logic flow then goes to a block 28 in FIG. 2B wherein it is asked if the velocity is less than or equal to the stuck velocity. If the answer is no, the stuck flag is reset at a block 29. If the answer is yes, logic flow goes to a block 30 wherein it is asked if the time is greater than the predetermined time. If no, logic flow goes to an exit block 31. Logic flow from block 29 also goes to exit block 31.

If the answer in block 30 is yes, signifying that sufficient time has been spent in trying to move through an excessive wheel spin, the logic flow goes to a block 32 wherein the maximum engine torque based on estimated mu is clipped. Logic flow then goes to a decision block 33 wherein it is asked if the wheel is still spinning on the next gas pedal tip-in. If the answer is yes, logic flow goes to a block 34 wherein there is a reduced max clip engine torque. Logic flow then goes to a node 35 and then to a decision block 36. If at decision block 33 the answer was no, logic flow goes to a block 37 wherein there is an increased maximum clip engine torque. Logic flow from block 37 goes to node 35 and decision block 36. At decision block 36 it is asked if the vehicle speed is less than or equal to the stuck velocity, i.e. is the vehicle still in a stuck condition. If the answer is yes, logic flow goes to an exit block 37. If the answer is no, logic flow goes to a block 38 wherein there is reset the stuck flag and the target slip indicating that the vehicle is no more in a stuck condition. From block 38 logic flow goes to an exit block 39.

Various modifications and variations will no longer doubt occur to those skilled in the various arts to which this invention pertains. Such variations which basically rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention.