AN ENGINE BRAKE CONTROL DEVICE

Abstract: An engine brake control device comprising a fuel cutting unit, slippage detecting unit, and a control unit, whereby, when an engine braking operation is underway, the fuel cutting unit stops the supply of fuel to the engine, but if a slippage of the driven wheels of the vehicle is detected by the slippage detecting unit, while the fuel cutting operation is being executed by the fuel supply cutting unit, the control units prohibits the operation of the fuel supply cutting unit, and therefore, when a slippage of the driven wheels is caused by an engine braking operation, fuel is fed into the engine and the slippage of the driven wheel is prevented.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine brake control device by which a loss of traction (hereinafter referred to as slippage) by a driven wheel is prevented during a reduction of a vehicle speed. 2. Description of the Related Art Document DE 31 43 479 A1 discloses a control apparatus for preventing the wheels of a vehicle from slipping. To this end, the rotational speed of the wheels is detected by means of sensors attached to each wheel and the respective electric sensor output signals representing the vehicle speed are supplied to a control means. On the basis of the sensor output signals it is determined by the control means whether a braking force is applied to the wheels of the vehicle. Furthermore, it is determined by means of corresponding sensors whether the wheel brake is activated by the driver. In particular, if a braking force applied to the wheels of the vehicle is provided by the engine which tends to cause a blocking of the wheels, whereas the wheel brakes are not activated at the same time, the control means operates a hydraulic actuator connected to the throttle valve to vary the opening degree of the throttle valve in order to provide an accelerating force of the engine until the tendency of the blocking of the wheels has disappeared. Moreover, U.S. Patent 3,802,528 discloses an arrangement for an automatic torque control, by which the degree of opening of the throttle valve is increased when a slippage occurs. Generally, a fuel supply to the engine is stopped during a reduction of the vehicle speed, i.e., when the engine speed is higher than a predetermined value and the throttle valve is closed, so that a discharge of unburnt components of an exhausted gas is prevented and the fuel consumption is reduced. In an engine provided with this prior art engine brake control device, air is fed into the engine when a slippage of the driven wheel occurs during a reduction of the vehicle speed. Nevertheless, when an excessive engine braking force is produced, for example, due to a rapid shift from a high to a low gear, the engine brake force can not be sufficiently reduced by only feeding air into the engine, and therefore, slippage of the driven wheel may still occur when the above prior art device is used. SUMMARY OF THE INVENTION An object of the present invention is to provide an engine brake control device capable of preventing a slippage of a driven wheel of a vehicle at the first sign of a loss of traction by cancelling the fuel cut operation and supplying fuel to the engine. According to the present invention, this object is accomplished by an engine brake control device for a vehicle having a driven wheel and a non-driven wheel, said device comprising a fuel supply means for supplying fuel to an engine, a first determining means for determining whether or not an engine brake operation is underway, a fuel supply cutting means for stopping a supply of fuel to the engine by said fuel supply means in response to a determination by said first determining means that an engine brake operation is underway, a second determining means for determining whether or not a slippage of the driven wheel of the vehicle has occurred, a control means for prohibiting an operation of the fuel supply cutting means and allowing fuel to be supplied to the engine in response to a determination by said second determining means that a slippage of the driven wheel of the vehicle has occurred, and an engine speed detecting means for detecting an engine speed, said engine brake control means being characterized in that a detecting means for detecting a degree of opening of a throttle valve is provided, and once a slipping of the driven wheel of the vehicle has occurred, the prohibition of the fuel cut operation is maintained until the throttle valve is opened again. The present invention may be more fully understood from the description of a preferred embodiment of the invention set forth below, together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Fig. 1 is a schematic diagram of a vehicle to which the present invention is applied; Fig. 2 is a flow chart of the execution of the process of cutting a supply of fuel to the engine; and Fig. 3 is a flow chart of the execution of the control of the operation of the prohibition flag for prohibiting a cut of the fuel supply to the engine. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 1, reference numeral 1 designates a electronic control unit. The electronic control unit 1 is constructed as a digital computer and comprises a ROM (read only memory) 3, a RAM (random access memory) 4, a CPU (microprocessor, etc.) 5, an input port 6, and an output port 7. The ROM 3, the RAM 4, the CPU 5, the input port 6, and the output port 7 are interconnected via a bidirectional bus 2. A right front (RF) wheel 9 and a left front (LF) wheel 10 of a vehicle are non-driven wheels, and an RF wheel speed sensor 11 for detecting a speed of rotation of the RF wheel 9 and an LF wheel speed sensor 12 for detecting a speed rotation of the LF wheel 10 are mounted at the RF wheel 9 and LF wheel 10, respectively. The signals output by these wheel speed sensors 11 and 12 are input to the input port 6. An output shaft speed sensor 15 is attached to a transmission 13, and is used to detect a speed of rotation of the output shaft 14 which corresponds to the speed of rotation of the driven wheels 20. The signals output by the output shaft speed sensor 15 are also input to the input port 6. Further, an engine speed sensor 17 for detecting an engine speed NE is mounted to the engine, and a degree of opening detecting sensor 18 for detecting a degree of opening of a throttle valve 21 is mounted to the throttle valve 21. The signals output by these sensors 17 and 18 are input to the input port 6. Note, the output port 7 is connected to a fuel injector 19. The operation of this embodiment will be now explained. When an accelerator pedal is released, the throttle valve 21 is closed and a signal is input to the input port 6. At this time, the engine speed N E is detected by a engine speed sensor 17, and a signal is output thereby to the input port 6. In the CPU 5, the engine speed N E is compared with a predetermined fuel cut speed N C stored in the ROM 3. When the throttle value 21 is closed and N E ≧ N C , a signal for stopping a supply of fuel to the engine (hereinafter referred to as a fuel cut) is output from the output port 7 to the fuel injector 19, and the fuel supply to the engine is stopped, i.e., a fuel cut operation is executed. Therefore, a discharge of unburnt components in the exhausted gas is prevented, the fuel consumption is reduced and a strong engine braking effect is produced. When the engine braking operation is carried out, slippage of the driven wheels 20 may occur if the vehicle is running on a low friction surface road, for example, on a road covered with ice and snow. Slippage of the driven wheels 20 is determined by comparing the speed of rotation of the driven wheels 20 with the speed of rotation of the non-driven wheels 9 and 10. Namely, slippage of the driven wheels 20 is determined when the following equation is satisfied: where: N R : a speed of rotation of the output shaft N FR : a speed of rotation of the RF wheel N FL : a speed of rotation of the LF wheel A: a coefficient for conversion of N R to a speed of rotation of a driven wheel B: a coefficient for cancelling an error in measurement and a difference between the speed of rotation of the RF wheel and the speed of rotation of the LF wheel when the vehicle is turning. Slippage of the driven wheels 20 is determined by the CPU 5. Namely, each speed N R , N FR , and N FL is detected by the output shaft speed sensor 15, the RF wheel speed sensor 11, and the LF wheel speed sensor 12, respectively, and the signals output from these sensors 11, 12, and 15 are input to the input port 6. If slippage is determined, a signal prohibiting a fuel cut is output from the output port 7 to the fuel injector 19, and fuel is supplied to the engine, and therefore, the engine braking effect is reduced and a slippage of the driven wheels 20 is avoided. Figure 2 is a flow chart of the execution of the fuel cut process when reducing the vehicle speed. Referring to Fig. 2, in step 50, it is determined whether or not the throttle valve 21 is closed. If the throttle valve 21 is not closed, the routine goes to step 51, and it is determined whether or not the cut flag is set. If the cut flag is not set, the processing cycle is completed, but if the cut flag is set, the routine goes to step 52 and the cut flag is reset. When it is determined in step 50 that the throttle valve 21 is closed, the routine goes to step 53 and it is determined whether or not the cut flag is set. If the cut flag is not set, the routine goes to step 54 and it is determined whether or not the engine speed N E is equal to or larger than the fuel cut speed N C . If N E < N C , the processing cycle is completed. In this case, the signal for stopping the fuel supply is not output, and therefore, the fuel cut operation is not executed, but if N E ≧ N C , the routine goes to step 55 and the cut flag is set. The routine then goes to step 56, where it is determined whether or not the fuel cut prohibition flag (hereinafter referred to as the prohibition flag) is set. If the prohibition flag is not set, the cut flag is maintained in the set state and the routine goes to step 57, where a signal for stopping the fuel supply is output, and therefore, a fuel cut operation is executed. When it is determined in step 56 that the prohibition flag is set, the routine goes to step 58 and the cut flag is reset, and therefore, the signal for stopping the fuel supply is not output. When it is determined in step 53 that the cut flag is set, the routine goes to step 59 and it is determined whether or not the engine speed N E is equal to or smaller than a predetermined fuel feed speed N F stored in the ROM 3. If N E ≦ N F , the routine goes to step 58 and the cut flag is reset, and therefore, the signal for stopping the fuel supply is not output. If N E > N F in step 59, the routine goes to step 56 and it is determined whether or not the prohibition flag is set. If the prohibition flag is not set, the cut flag is maintained in the set state and the routine goes to step 57. In step 57, the signal for stopping the fuel supply is output, and therefore, the fuel cut operation is executed. When it is determined in step 56 that the prohibition flag is set, the routine goes to step 58 and the cut flag is reset, and therefore, the signal for stopping the fuel supply is not output. Figure 3 is a flow chart of the execution of the control of the operation of the prohibition flag. Referring to Fig. 3, in step 60 it is determined whether or not slippage has occurred at the driven wheels 20, by comparing the speed of rotation of the driven wheels 20 with speed of rotation of the non-driven wheels 9 and 10. If i.e., slippage has occurred at the driven wheels 20, the routine goes to step 61 and it is determined whether or not the prohibition flag is set. If the prohibition flag is set, the processing cycle is completed, but if the prohibition flag is not set, the routine goes to step 62 and the prohibition flag is set. Therefore, in the fuel cut routine (Fig. 2), the fuel cut operation is prohibited and fuel is supplied to the engine. When it is determined in step 60 that slippage of the driven wheels 20 has not occurred, the routine goes to step 63 and it is determined whether or not the prohibition flag is set. If the prohibition flag is not set, the processing cycle is completed, and therefore, the fuel cut operation is not prohibited. But, if the prohibition flag is set, the routine goes to step 64, where it is determined whether or not the throttle valve 21 is closed. If the throttle valve 21 is closed, the prohibition flag is maintained in the set state, and therefore, the fuel cut operation is prohibited and fuel is supplied to the engine. When it is determined in step 64 that the throttle valve 21 is not closed, the routine goes to step 65 and the prohibition flag is reset. In step 64, once slippage of the driven wheels 20 is determined, the prohibition flag is maintained in the set stage until the throttle valve 21 is again opened, i.e., until the accelerater pedal is operated, and therefore, a frequent repetition of alternate fuel feed and fuel cut operations is prevented. Although the invention has been described with reference to a specific embodiment chosen for the purpose of illustration, it should be apparent that numerous modifications can be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.

Claims: An engine brake control device for a vehicle having a driven wheel (20) and a non-driven wheel (9, 10), said device comprising: a fuel supply means (19) for supplying fuel to an engine, a first determining means (1, 18) for determining whether or not an engine brake operation is underway, a fuel supply cutting means (1, 19) for stopping a supply of fuel to the engine by said fuel supply means in response to a determination by said first determining means (1, 18) that an engine brake operation is underway, a second determining means (1, 11, 12, 20) for determining whether or not a slippage of the driven wheel (20) of the vehicle has occurred, a control means (1) for prohibiting an operation of the fuel supply cutting means (1, 19) and allowing fuel to be supplied to the engine in response to a determination by said second determining means (1, 11, 12, 20) that a slippage of the driven wheel (20) of the vehicle has occurred, and an engine speed detecting means (14, 15) for detecting an engine speed, said engine brake control means being characterized in that a detecting means (18) for detecting a degree of opening of a throttle valve (21) is provided, and once a slipping of the driven wheel (20) of the vehicle has occurred, the prohibition of the fuel cut operation is maintained until the throttle valve (21) is opened again. An engine brake control device according to claim 1, being characterized in that said fuel supply means (19) comprises a fuel injector. An engine brake control device according to claim 1, being characterized in that said first determining means (1, 8) determines that said engine brake operation of said engine is underway in response to signals output by said engine speed detecting means (14, 15) and said detecting means (18) when an engine speed is higher than a predetermined fuel cut speed and when said throttle valve (21) is closed. An engine brake control device according to claim 3, being characterized in that the fuel supply cutting operation by said fuel supply cutting means (1, 19) is stopped and fuel is supplied to said engine when said engine speed becomes lower than a fuel feeding speed or when said throttle valve (21) is opened. An engine brake control device according to claim 1, being characterized in that said control means (1) continues to prohibit an operation of said fuel supply cutting means (1, 19) while an engine brake operation is underway. An engine brake control device according to claim 1, being characterized in that said second determining means (1, 11, 12, 20) determines that the slippage of said driven wheel (20) has occurred when a speed of rotation of said driven wheel (20) is lower than a speed of rotation of the non-driven wheel (9, 10). An engine brake control device according to claim 6, being characterized in that said second determining means (1, 11, 12, 20) comprises a first detecting device (15) for detecting the speed of rotation of the driven wheel (20), and a second detecting device (11, 12) for detecting the speed of rotation of the non-driven wheel (9, 10). An engine brake control device according to claim 7, being characterized in that said engine is provided with a transmission (13) having an output shaft (14), and said first detecting device (15) detects a speed of rotation of the driven wheel (20) from a speed of rotation of the output shaft (14). An engine brake control device according to claim 7, being characterized in that said vehicle has two non-driven wheels (9, 10) and said second detecting device (11, 12) comprises two speed of rotation sensors (11, 12) for detecting the speed of rotation of the non-driven wheels (9, 10). An engine brake control device according to claim 9, being characterized in that said speed of rotation of the non-driven wheel (9, 10) is determined by the mean value of the speeds of rotation of said two non-driven wheels (9, 10).

Inventors: KOMODA, TAKAO
Applicants: TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1988
Main classification: B60K28
IPC codes: F02D41, B60T8, F02D29