Vehicle recovery system

Abstract

The present invention relates to a vehicle recovery system (1) for a vehicle having at least one driven wheel. The vehicle recovery system (1) is operable to self-recover the vehicle from terrain having a deformable surface affording insufficient traction at the at least one driven wheel to mobilise the vehicle. A recovery controller (2) is provided to maintain at least substantially continuous rotation of said at least one driven wheel at a target recovery speed or within a target recovery speed range to increase the available traction at each driven wheel. The present invention also relates to a vehicle having a vehicle recovery system (1).

Claims

1. A system for a vehicle having at least one driven wheel, the system being operable to recover the vehicle from terrain having a deformable surface affording insufficient traction at said at least one driven wheel to mobilize the vehicle, the system comprising: a controller configured to maintain at least substantially continuous rotation of said at least one driven wheel of the vehicle at a target recovery speed suitable for increasing the available traction at said at least one driven wheel, the target recovery speed being predefined in dependence on a type of terrain from which the vehicle is to be recovered, and the controller being further configured to alter a rate of change of a rotational speed of said at least one driven wheel in proportion to a difference between a measured rotational speed of said at least one driven wheel and the predefined target recovery speed, such that the rate of change of rotational speed of said at least one driven wheel reduces as the measured rotational speed converges with the predefined target recovery speed.

2. A system as claimed in claim 1, wherein the controller is configured to control a vehicle powertrain to control the rotational speed of said at least one driven wheel.

3. A system as claimed in claim 2, wherein the controller is configured to (i) increase an idle speed of the vehicle powertrain to initiate vehicle recovery, (ii) decrease the idle speed of the vehicle powertrain when the vehicle has been recovered, or both.

4. A system as claimed in claim 1, wherein the controller is configured to control the rotational speed of said at least one driven wheel by controlling application of a braking force.

5. A system as claimed in claim 1, wherein the controller is configured to maintain continuous rotation of said at least one driven wheel for a pre-determined period of time.

6. A system as claimed in claim 1, wherein the controller determines when the vehicle has recovered by detecting one or more of the following conditions: (a) a decrease in the rotational speed of said at least one driven wheel; (b) a change in required torque to maintain rotational speed of said at least one driven wheel; (c) motion of the vehicle; (d) an increase in the vehicle speed-over-ground.

7. A system as claimed in claim 1, wherein the controller is configured to reduce the rotational speed of said at least one driven wheel when the vehicle has recovered.

8. A system as claimed in claim 1, wherein, when operating in said recovery mode, the controller is further configured to perform one or more of the following functions: (a) raise a height of a vehicle suspension; (b) alter a steering angle of said at least one driven wheel; (c) alter tire pressure in said at least one driven wheel; (d) disable a hill descent control; and (e) select a pre-configured gear ratio.

9. A system as claimed in claim 1, further comprising means to generate driver notifications during operation of the system to notify the driver of the current operating status or to provide driver instructions as to any appropriate manual intervention.

10. A vehicle comprising a system as claimed in claim 1.

11. A system as claimed in claim 1, wherein the predefined target recovery speed corresponds to a rotational wheel speed equivalent to a vehicle speed of less than or equal to 3.1 m/h (5 km/h).

12. A system as claimed in claim 1, wherein the controller comprises an input for receiving a signal indicative of the terrain type.

13. A system as claimed in claim 12, comprising a selector for generating the signal indicative of the terrain type in response to a driver selection.

14. A system as claimed in claim 1, wherein the predefined target recovery speed is a predefined upper rotational speed threshold or a predefined lower rotational speed threshold of a predefined target recovery speed range, or wherein the predefined target recovery speed lies between a predefined upper rotational speed threshold and a predefined lower rotational speed threshold of a predefined target recovery speed range.

15. A system as claimed in claim 1, wherein the type of terrain from which the vehicle is to be removed comprises at least one of sand or snow.

16. A system as claimed in claim 1, wherein the type of terrain from which the vehicle is to be removed comprises snow.

17. A system as claimed in claim 1, wherein the type of terrain from which the vehicle is at least one of to be removed comprises sand.

18. A system as claimed in claim 1, wherein the type of terrain from which the vehicle is to be removed comprises loose terrain.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

(2) FIG. 1 shows a schematic representation of an off-road recovery system according to an embodiment of the present invention;

(3) FIG. 2 is a first graph showing the individual and average wheel speed during a recovery event performed by the off-road recovery system according to an embodiment of the present invention;

(4) FIG. 3 is a flow chart illustrating the control process a recovery event performed by the off-road recovery system according to an embodiment of the present invention; and

(5) FIG. 4 is a second graph showing the engine idle speed and average wheel speed during the recovery event illustrated in FIG. 3.

DETAILED DESCRIPTION

(6) A vehicle recovery system 1 in accordance with an embodiment of the present invention will now be described with reference to FIGS. 1 to 4. The vehicle recovery system 1 comprises an off-road recovery module (ORR) 2 which provides a driver selectable recovery mode for recovering a motor vehicle (not shown) which is immobilised in a deformable surface, such as deep sand or snow. The vehicle has four wheels all of which are driven by an internal combustion engine via an automatic transmission. The vehicle also has a transfer case for selecting high and low transfer ratios.

(7) As shown in FIG. 1, the ORR 2 forms a part of a powertrain control module (PCM) 3 and communicates with a torque idle speed module 4, an engine idle speed controller module 5, a torque structure module 6, and a torque monitor 7. The torque structure module 6 converts a torque demand into fuel, throttle opening, ignition timing etc., in order to deliver the requested torque via actuation of the combustion engine. The ORR 2 receives operating data from a brake pedal switch 8, an accelerator pedal sensor 9, an instrument pack module (IPC) 11, an anti-lock brake module (ABS) 13, a park brake module (PBM) 15, a transmission control module (TCM) 17, a transfer case control module (TCCM) 19, a chassis control module (CHCM) 21, a body control module (BCM) 23 and optionally a tyre pressure monitoring and inflation system 25.

(8) A menu selection joystick 27 is provided on the IPC 11 to allow a user to select and engage the ORR 2. The ORR 2 and the IPC 11 communicate with each other to enable/disable selection of the ORR 2. A display option for selecting the ORR 2 can, for example, be obscured on the IPC 11 if the required parameters are not satisfied.

(9) The ABS 13 is coupled to four wheel sensors 29 (one for each wheel) for measuring wheel speed (rpm). The ABS 13 outputs vehicle operating data to the ORR 2, including: longitudinal acceleration data; hill descent control status data (i.e. engaged/dis-engaged); measured wheel speed data for each wheel; and vehicle speed data (the average wheel speed). The PBM 15 outputs park brake status data (i.e. engaged/dis-engaged) to the ORR 2. The TCM 17 outputs transmission data, including the engaged gear; the selected gear; and the transmission oil temperature, to the ORR 2. The TCCM 19 outputs transfer case data to indicate whether the high or low transfer ratio is engaged. The BCM 23 notifies the ORR 2 of the vehicle door status to indicate whether the vehicle doors are open or closed.

(10) A drive mode selector 31 is provided on the CHCM 21 to allow a user to select a pre-defined vehicle drive mode, for example to configure the vehicle for driving over a particular type of terrain. The CHCM 21 outputs drive mode data and suspension mode data to the ORR 2. The tyre pressure monitoring and inflation system 25 receives a tyre pressure signal from a tyre pressure monitor 33 and can control a tyre inflation system 35. The PCM 3 outputs ORR status information to the IPC 11, the ABS 13, the CHCM 21 and the tyre pressure monitoring and inflation system 25.

(11) The PCM 3 is configured to control operation of the engine by outputting engine control signals to a fuel injection system 37, a throttle position system 39 and an ignition timing system 41. The idle speed controller module 5 controls an engine idle speed (rpm) E.sub.i by varying the engine control signals. The idle speed controller 5 maintains the engine idle speed E.sub.i above a pre-defined base idle speed and below a pre-defined maximum idle speed, for example 1500 rpm.

(12) As shown in FIG. 2, the ORR 2 is configured to control the rotational speed of the driven wheels of the vehicle to achieve a target recovery wheel speed V.sub.TGT of approximately 3 km/h. The ORR 2 maintains an individual wheel speed V.sub.I and an average driven wheel speed V.sub.AV within a pre-defined target recovery speed range V.sub.R by controlling the engine idle speed E.sub.i. It will be appreciated that during recovery the vehicle remains stationary as the driven wheels rotate. The quoted rotational speed of the driven wheels (the target recovery wheel speed V.sub.TGT, the individual wheel speed V.sub.I and the average driven wheel speed V.sub.AV) correspond to the rotational speed of the wheel(s) if the vehicle was travelling on hard-packed, level ground.

(13) More specifically, the ORR 2 maintains the individual and average wheel speeds V.sub.I, V.sub.AV between an upper wheel speed control threshold V.sub.UP and a lower wheel speed control threshold V.sub.LOW. The wheel speed control thresholds V.sub.UP, V.sub.LOW are pre-defined in the ORR 2 and can be calibrated independently of each other. When engaged, the ORR 2 communicates with the engine idle speed controller module 5 to control the engine idle speed E.sub.I to achieve the target recovery wheel speed V.sub.TGT. The engine idle speed controller module 5 reduces the operating speed of the engine when the individual and average wheel speeds V.sub.I. V.sub.AV rise above the upper wheel speed control threshold V.sub.UP; and increases the operating speed of the engine when the individual and average wheel speeds V.sub.I, V.sub.AV fall below the lower wheel speed control threshold V.sub.LOW. The engine is thereby controlled to provide continuous rotation of the driven wheels within the target recovery speed range V.sub.R. The ORR 2 can automatically apply a braking force to one or more driven wheels to maintain individual wheel speeds V.sub.I below the wheel speed control thresholds V.sub.UP.

(14) The ORR 2 is configured to vary the rate at which the engine idle speed changes as a function of the amount by which the measured wheel speed V.sub.I, V.sub.AV exceeds the upper or lower wheel speed control threshold V.sub.UP, V.sub.LOW. The rate of change is directly proportional to the difference between the measured wheel speed V.sub.I, V.sub.AV and the wheel speed control thresholds V.sub.UP, V.sub.LOW.

(15) The ORR 2 also defines upper and lower hysteresis thresholds H.sub.UP, H.sub.LOW within the respective upper and lower wheel speed control thresholds V.sub.UP, V.sub.LOW. The hysteresis thresholds H.sub.UP, H.sub.LOW are applied when the wheel speed is returning to the target recovery wheel speed V.sub.TGT having exceeded the upper and lower wheel speed control thresholds V.sub.UP, V.sub.LOW. The ORR 2 increases or decreases the engine idle speed E.sub.I until the measured wheel speed is above or below the respective lower and upper hysteresis thresholds H.sub.LOW, H.sub.UP. By implementing hysteresis, the ORR 2 can reduce changes in the engine speed to provide improved wheel speed control.

(16) When any individual wheel speed V.sub.I exceeds the upper wheel speed control threshold V.sub.UP, the ORR 2 reduces the target engine idle speed at a controlled rate (Section B). As outlined above, the rate at which the engine idle speed is reduced is a function of the amount that the individual wheel speed V.sub.I exceeds the upper wheel speed control threshold V.sub.UP. The engine idle speed E.sub.i continues to decrease until the individual wheel speed has fallen below the upper wheel speed control threshold V.sub.UP and the upper hysteresis threshold H.sub.UP. When the average wheel speeds V.sub.AV falls below the lower wheel speed control threshold V.sub.LOW, the ORR 2 increases the target engine idle speed at a calibratable rate (Section D). The rate at which the engine idle speed is increased is a function of the amount that the average driven wheel speed V.sub.AV has fallen below the lower wheel speed control threshold V.sub.LOW. The engine idle speed E.sub.i continues to increase until the average driven wheel speed V.sub.AV exceeds the lower wheel speed control threshold V.sub.LOW and the lower hysteresis threshold H.sub.LOW.

(17) In the present embodiment, the ORR 2 can be engaged only if the following vehicle conditions are satisfied: (a) the vehicle is stationary (or vehicle speeda calibratable threshold); (b) the vehicle doors are closed; (c) a pre-configured gear is selected (1.sup.st gear, 2.sup.nd gear or a reverse gear); (d) the low transfer ratio is selected (where available); (e) the parking brake is released; (f) an automatic vehicle hold (.sub.AVH) is not activated; (g) transmission oil temperature is below a threshold; (h) engine oil temperature is below a threshold; and (i) engine coolant temperature is below a threshold.

(18) If these vehicle conditions are not satisfied, the ORR 2 is disabled and cannot be selected via the IPC 11. If the ORR 2 detects that any of these conditions are no longer satisfied during operation, the ORR 2 dis-engages. It will be appreciated that alternate embodiments of the present invention could omit one or more of these vehicle conditions.

(19) A flow chart 100 showing the process steps for engaging the ORR 2 is shown in FIG. 3 and the procedural events are summarised in TABLE A below.

(20) TABLE-US-00001 TABLE A Tran- ORR Driver sition Event Status Notification T0 Ignition On Inactive No message T5 Driver requests ORR but Inactive 15 Display reason for vehicle settings do not ORR not allowed allow ORR T10 Driver requests ORR and Initialise Configuring Vehicle Enable Conditions are met T15 Vehicle Configuration Initialise Release Brake To complete or timeout Commence T20 Foot brake released Active ORR Active: Press Brake or Accelerator to Cancel T30 Wheel Rotation Detected Active ORR Active: Press Brake or Accelerator to Cancel T40 ORR not successful Active ORR Not Possible (Timeout, no wheel speed delected etc.) T45 ORR successful Active ORR Finishing T47 ORR not able to recover Active le ORR Not Possible vehicle T50 Smooth cancel complete Reset ORR Finishing T55 Vehicle Re-Configuration Inactive No message complete or in progress of being completed T60 ORR Enable conditions not Reset ORR Finishing met OR brake pressed T65 ORR Enable conditions not Reset ORR Finishing met T90 ORR System Fault Inactive ORR Fault T95 Driver requests ORR and Inactive ORR Fault there is an ORR System Fault

(21) Once the vehicle conditions outlined above have been satisfied, the ORR 2 is initialised (Step S0) by pressing the service (foot) brake without the accelerator pedal being pressed. The ORR 2 is then initialised (Transition T10) and the vehicle is configured (Step S1) by performing one or more of the following operations: (a) The ABS 13 raises a target control speed, for example to a value of approximately 10 km/h (based on the expected upper vehicle speed for an engine speed of 1500 rpm, with 2nd gear and low transfer ratio selected), for controlling application of a braking force when the effective wheel speed exceeds the lower target control speed; (b) The CHCM 21 raises the air suspension to Off Road Recovery height after verifying that the lateral acceleration and/or vehicle attitude is within limits; (c) The CHCM 21 sets the drive mode to a pre-defined setting for driving on sand; and (d) The tyre pressure monitoring and inflation system 25 optionally reduces the tyre pressure to increase their contact area.

(22) Once the vehicle has been configured, the ORR 2 is activated by the driver releasing the service (foot) brake (Step S2). The engine idle speed E.sub.i is then increased (Step S3) until the upper wheel speed control threshold V.sub.UP is exceeded for a predetermined period of time by either an individual wheel speed V.sub.I or the average vehicle speed V.sub.AV (Step S5). As described herein, the ORR 2 maintains the engine idle speed between the upper and lower wheel speed control thresholds V.sub.UP, V.sub.LOW for a predetermined period of time.

(23) The ORR 2 can determine whether the vehicle has been successfully recovered using one or more of the following techniques: (a) a speed over ground measurement (for example determined from a satellite navigation system, or a dedicated speed over ground sensor) exceeds a calibrated threshold; (b) a measured change in longitudinal and/or vertical acceleration exceeds a threshold; (c) a rate of decrease in a requested engine torque (including the idle speed control requested torque) exceeds a threshold; and (d) a substantive change in the required torque to maintain rotational speed of the wheels.

(24) In a vehicle having a non-driven wheel(s), the ORR 2 can determine that the vehicle has been successfully recovered by determining when a measured wheel speed of the non-driven wheel exceeds a threshold. A filter can be applied to the measurements to reduce noise and to help avoid false recovery detection.

(25) If the ORR 2 determines that the vehicle has been successfully recovered or that recovery cannot be completed, the engine idle speed is lowered to a base idle speed (Step S6). The vehicle is then re-configured to the state prior to activation of the off-road recovery (Step S7). The ORR 2 is then deactivated (Step S0).

(26) In the event that a fault is detected at any stage, the ORR 2 may be deactivated (Step S8) and the driver optionally informed via a message displayed on the IPC 11. The ORR 2 will also be de-activated (Transition T60) if one or more of the following events occur: (a) the service (foot) brake is pressed, for example beyond a predetermined threshold pedal pressure limit; (b) the transmission is moved out of gear; (c) the measured wheel speed exceeds a cut-off threshold; and (d) the driver cancels using a vehicle interface.

(27) The engine speeds and average wheel speed V.sub.AV during a typical recovery event are shown in FIG. 4. The vehicle is initially immobilised in sand with the engine operating at the base idle speed. For example, the driven wheels can become entrenched as they dig into the upper layer of a loose material, such as sand. However, the wheels are not rotating and the average wheel speed V.sub.AV is zero since resistance to motion is too great (Step S0). The ORR 2 is activated by the driver (Step S1) and the vehicle automatically configures for optimal recovery. When the vehicle is configured, the driver releases the service (foot) brake and the ORR 2 starts to increase the engine idle speed E.sub.I. The wheels do not rotate initially due to operation of the torque converter, but the increase in the engine idle speed E.sub.i overcomes the resistance and the wheels start to rotate (Step S3). As described herein, the ORR 2 maintains the individual and average wheel speeds V.sub.I, V.sub.AV within the upper and lower wheel speed control thresholds V.sub.UP, V.sub.LOW by making small changes to the engine idle speed E.sub.i and the vehicle self recovers (Step S5). The average wheel speed V.sub.AV increases and recovery of the vehicle is detected and the engine speed E.sub.i is reduced (Step S6). The vehicle recovery is then completed or cancelled and the vehicle state reset (Step S0). A message is displayed on the IPC 11 to inform the driver about the status of the ORR 2.

(28) The present embodiment has been described with reference to a vehicle having an automatic transmission. However, the system could be implemented on a manual transmission vehicle, for example by providing driver prompts to engage the appropriate gears.

(29) It will be appreciated that various changes and modifications can be implemented in the embodiment described herein without departing from the present invention. For example, a closed loop wheel speed control system can be implemented to control the rotational wheel speed of each individual driven wheel. The invention has been described with reference to varying the requested engine torque to control the rotational wheel speed. Alternatively, or in addition, a braking force could be applied to control the rotational speed of one or more of said driven wheels. The wheel torque management could be varied by controlling clutch engagement to control the transfer of torque from the powertrain to the driven wheels.

(30) The present invention could also be implemented in a hybrid vehicle or an electric vehicle. The ORR 2 could be adapted to select electric only drive when operating to self-recover the vehicle. An electric drive motor(s) can provide fine control of wheel torque at low rotational speeds. This may provide improved wheel speed control at very low speeds than may be readily achievable using an internal combustion engine in conjunction with a torque converter or a clutch arrangement.

(31) Furthermore, the present invention has been described with reference to a four-wheeled vehicle having four driven wheels. However, the invention can be implemented in a four-wheeled vehicle having only two driven wheels. The present invention can be applied to a range of vehicle transmission types, for example automatic, manual, automated manual, dual clutch, continuously variable transmission (CVT) etc. Furthermore, it is not necessary that the vehicle has a transfer case.

(32) The present application is related to the Applicant's earlier application GB 1205708.9, entitled Vehicle Traction Control filed on 30.sup.th Mar. 2012, the contents of which are incorporated herein in their entirety by reference.

(33) It will be appreciated also that the present invention can be implemented in a vehicle having one or more electric motors for driving one or more wheels. The electric motor(s) can, for example maintain rotation of at least one driven wheel at a target recovery speed or within a target recovery speed range. The vehicle could, for example, be a hybrid vehicle, a hybrid electric vehicle or an electric vehicle (EV).