DIFFERENTIAL CONTROL DEVICE

Abstract: A differential control device (10) for controlling the differential of a differential gear (14) having a limited slip differential (12) includes a sensor (16) for detecting drive torque, a controller (18) for receiving the detected torque from the sensor (16) to compare the size of the torque with a predetermined value and an actuator (20). The actuator (20) is controlled by the controller (18) to operate the limited slip differential (12) for limiting the differential when the detected torque exceeds the predetermined value.

Description: BACKGROUND OF THE INVENTION Field of the Invention: This invention relates to a differential control device and, more particularly, to a device which controls the differential of a differential gear provided with a limited slip differential and installed on a vehicle. Description of the Prior Art: A differential gear capable of limiting the differential is provided with a limited slip differential including a plurality of friction disks and a hydraulic device for operating these friction disks or the like, in addition to a usual differential mechanism, in order to limit the differential produced in the differential mechanism by the contact of the friction disks. Thus, when the travelling speed exceeds a predetermined value, the differential is limited to improve travelling stability (for example, Japanese Patent Public Disclosure (KOKAI) 237242/85), or the limitation of the differential is released according to the size of turning angle to achieve both turning performance and travelling performance. SUMMARY OF THE INVENTION Though the tractive forces of tyres need to be sufficiently ensured at the time of starting of a vehicle, acceleration with high speed, travelling on an uphill road and traction etc., any device for limiting the differential when the vehicle speed exceeds a predetermined value cannot obtain the necessary tractive forces. An object of the present invention is to provide a differential control device for controlling a limited slip differential to ensure the tractive forces at the time of starting, acceleration with high speed, travelling on an uphill road and traction and so on. According to the present invention, there is provided a differential control device for controlling differential movement of a differential gear having a limited slip differential, the limited slip differential comprising a plurality of first plates engaging with a wheel axle connected to a side gear and a plurality of second plates engaging with a case connected to a ring gear, wherein a friction force generated between the first and second plates is used for controlling the differential movement between two wheel axles, characterized by a controller for comparing the size of drive torque fixed by a drive condition with a predetermined value, and means for operating said limited slip differential, the means being controlled by said controller to operate said limited slip differential so as to limit the differential movement when the drive torque exceeds the predetermined value. According to the present invention, there is also provided a device for controlling the differential of a differential gear having a limited slip differential, which comprises means for detecting a drive torque condition, a controller for obtaining torque based on a signal from said means and comparing the obtained torque with a predetermined value and means controlled by a signal from said controller to operate said limited slip differential so as to limit the differential when the obtained torque exceeds the predetermined value. The controller compares the torque with a predetermined value and, when the torque exceeds the predetermined value, operates the operating means to limit the differential. Thus, the differential between left and right tires is limited so that large torque may be given to the tires. Further, when attaching much importance to the turning performance, the controller, for example, handles a steering angle in preference to the torque and releases the limitation of the differential when the steering angle exceeds a predetermined value. Since the necessary drive torque is increased at the time of starting, acceleration with high speed, travelling on an uphill road and traction etc. to increase the tractive forces of tires, the travelling of a vehicle is smoothed. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and features of the invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing a differential control device; Fig. 2 is a flow chart showing the control of the differential; Fig. 3 is a sectional view showing a differential gear; Fig. 4 is a flow chart showing another embodiment of control; Figs. 5 and 6 are plan views showing sensors for detecting shift position; and Figs. 7 and 8 are flow charts showing further embodiments of control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figs. 1 and 3, a differential control device 10 limits the differential of a differential gear 14 having a limited slip differential 12 and comprises means 16 for detecting drive torque, a controller 18 and operating means 20. Any differential gear may be used so long as it is provided with the limited slip differential. The differential gear 14 shown in Fig. 3 is constituted from a differential case 22, a plurality of pinions 24 and a pair of side gears 26 (each one of them is shown in the drawing) respectively disposed in the differential case 22 and shafts 28 connected to respective side gears 26. A drive pinion (not shown) meshes with a ring gear 29 to transmit drive force. The limited slip differential 12 limits the differential of the differential gear 14 and is provided with a plurality of first friction disks 30 engaging one side gear 26 and a plurality of second friction disks 32 engaging the differential case 22. A first differential carrier 34 is fixedly disposed to surround and support rotatably the differential case 22. A second differential carrier 36 is fixed to the first differential carrier 34. A cylindrical spacer 38 is mounted unrotatably on the shaft 28 through splines. The first friction disks 30 are supported on the spacer 38 through splines unrotatably but axially movably of the shaft 28. On the other hand, a transmitting member 40 unrotatably connected with the differential case 22 through splines is disposed to surround the shaft 28. The transmitting member 40 is provided with a portion having a diameter which is expanded at a position beyond the first differential carrier 34. The second friction disks 32 are supported on the expanded diameter portion through splines unrotatably but axially movably. The first and second friction disks 30,32 are disposed alternatively. The second differential carrier 36 surrounds the expanded diameter portion of the transmitting member 40. The differential carrier 36 is provided with a piston chamber 42 in which a first piston 44 is disposed slidably but unrotatably. A second piston 46 is disposed spacedly from the first piston 44 and supported on the spacer 38 through splines unrotatably but axially movably. A thrust bearing 48 is disposed between the first and second pistons 44,46. When liquid pressure is introduced from the outside into the piston chamber 42, the first piston 44 is pressed against the second piston 46 through the thrust bearing 48 to produce frictional force in proportion to the press force between the first and second friction disks 30,32. By this frictional force is limited the differential of the differential gear 14. At this time, the reaction generated in the transmitting member 40 is transmitted to a thrust washer 50 disposed between the differential carriers 34,36, a thrust washer 52 disposed on the transmitting member 40 and a thrust bearing 54 disposed between both washers. The differential carrier 34 receives the reaction thus transmitted. The means 16 for detecting torque is a wheel torque meter or other torque detectors to detect the drive torque of a drive shaft or propeller shaft at the neighborhood of a driving wheel. The controller 18 is a CPU or computer for receiving signals from the torque detecting means 16 to judge the size of torque, determine whether or not the differential should be limited or the limitation of the differential is released and then control as will be later described. In an embodiment shown in Figs. 1 and 2, signals from a steering angle sensor 60 and a vehicle speed sensor 62 are sent to the input of the controller 18. The operating means 20 shown in the embodiment is provided with a liquid pump 64, an unloading relief valve 66, an accumulator 68, a current control pressure-reducing valve 70 and a check valve 72. A pipe 74 is connected to the pump 64 and the second differential carrier 36 of the limited slip differential 12 to communicate to the piston chamber 42. The unloading relief valve 66 is incorporated in the pipe 74 and the current control pressure-reducing valve 70 is incorporated in a portion of the pipe leading from the unloading relief valve 66 to the limited slip differential 12. Further, the accumulator 68 is connected between the unloading relief valve 66 and the current control pressure-reducing valve 70. The check valve 72 is incorporated between the unloading relief valve 66 and the accumulator 68. The check valve 72 allows liquid or pressure to be respectively sent or transmitted only from the unloading relief valve 66 to the accumulator 68. When pressurized liquid is supplied from the pump 64, an unloading seat of the unloading relief valve 66 is closed and the check valve 72 is opened. As a result, the pressurized liquid is introduced from the pump 64 through the pipe 74 into the accumulator 68 to increase liquid pressure therein. When the pressure in the accumulator 68 reaches pressure adjusted by the unloading relief valve 66, the unloading relief valve 66 is instantly opened to return pressurized liquid from the pump 64 to a reservoir tank 76 and the check valve 72 is closed. Thus, constant pressure is accumulated in the accumulator 68. The current control pressure-reducing valve 70 has a pilot section provided with a DC solenoid. Output pressure therefrom is controlled continuously and non-steplessly by controlling input current to the solenoid. The controlled pressure in this case is substantially proportional to the input current. Then, proper pressure may be obtained by controlling input current given to the current control pressure-reducing valve 70 by the controller 18. The controller 18 judges as shown in Fig. 2, for example, to control the operating means 20. After initialization (80), a steering angle S is detected (82) by the steering angle sensor 60 and compared (84) with a set value So. When the steering angle is not smaller than the set value, the limitation of the differential of the differential gear 14 is released (86). Namely, any differential will be produced and turning will be done without any trouble. When the steering angle S is smaller than the set value So, a vehicle travels straight or approximately straight forward. Then, vehicle speed U is detected (88) by the speed sensor 62 and compared (90) with the set values U₁,U₂ (U₂ > U₁). When the vehicle speed U is not lower than the set value U₂, the vehicle is travelling with high speed. When the vehicle speed U is not higher than the set value U₁, the vehicle is travelling with low speed such as starting, travelling on an uphill road and traction. When the vehicle speed U is not lower than the set value U₂ or not higher than the set value U₁, the torque T is detected (92) by the torque detecting means 16 and compared (94) with a predetermined value T₀. When the torque T is not smaller than the predetermined value T₀, the differential is limited (96). In this case, the predetermined value T₀ is set to zero or above. In the embodiment, the current control pressure-reducing valve 70 supplies pressure in proportion to current to the limited slip differential 12. Thus, the differential may be limited in proportion to the size of the torque T. The relationship between the torque T and the pressure P to be given to the liquid chamber 42 and the relationship between the pressure P and the current i are stored as respective maps in the controller 18 to limit the differential by utilizing these relationships. The controller 18 obtains (98) the pressure P according to the torque T and the current i according to the pressure P from the maps. The current i is then supplied to the current control pressure-reducing valve 70. Thus, the pressure P is supplied to the limited slip differential 12, so that the first piston 44 presses the second piston 46 with the force in proportion to the pressure. Therefore, the first and second friction disks 30,32 contact each other to generate the frictional force in proportion to the pressure and limit the differential of the differential gear 14. When the vehicle speed U is over the set values U₁ up to U₂, or when the torque T is smaller than the predetermined value T₀ even if the vehicle speed u is not lower than the set value U₂ or not higher than the set value U₁, the limitation of the differential is released (100). While the drive torque is detected directly according to the embodiment noted above, hereinafter will be described another embodiments in which a drive torque condition is detected to obtain torque with the controller 18 on the basis of the detected torque condition. The obtained torque may be compared with a predetermined value for controlling the operating means 20. In the following embodiment, however, since the operating means 20 is provided with the current control pressure-reducing valve 70 which controls the output pressure continuously according to the obtained torque, the operating means 20 is controlled without comparing the obtained torque with the predetermined value. In the embodiment shown in Fig. 4, means 110 for detecting the drive torque condition includes a sensor 112 for detecting a shift position of a transmission and a sensor 114 for detecting an engine speed. The shift position detecting sensor 112 in a manual operation, as shown in Fig. 5, is constituted from a detecting plate 118 having switches 119a,119b ... 119f disposed respectively at the shift positions occupied by a shift lever 116 in the first speed to fifth speed and reverse drive. Each switch may be a limit switch, a proximity switch or other switches. When the shift lever 116 is shifted, the switch in the corresponding shift position is turned on. The shift position sensor 112 in an automatic operation is constituted from solenoid valves and a neutral start switch 120 shown in Fig. 6. That is, a plurality of solenoid valves S₁, S₂, S₃ are used to shift gears of a transmission, and the relationship shown on the following table, for example, is established between their operational conditions and the shift positions of the gears; Solenoid valve S₁ S₂ S₃ Reverse * Neutral * Forward drive First speed * Second speed * * * Third speed * * Over drive * On the other hand, the neutral start switch 120 includes a printed circuit substrate 121a and a change-over lever 121b. According to the position of the change-over lever 121b are detected parking P, reverse R, neutral N, forward drive D and so on. Then, the shift position may be known by the combination of the signals of solenoid valves and neutral start switch 120. The controller 18 is provided with maps 122 each stored the correlation between the engine speed and torque of a propeller shaft (the correlations are shown only in one map for convenience in Fig. 4) in every shift position. When the signal from the shift position sensor 112 is sent to the input of the controller 18, the map corresponding to the shift position is first selected, and thereafter the torque of the propeller shaft is obtained by the signal from the engine speed sensor 114. The operating means 20 operates the limited slip differential 12 by controlling current corresponding to the obtained torque. In the embodiment shown in Fig. 7, means 130 for detecting a drive torque condition includes a vehicle speed sensor 132 and an engine speed sensor 134. On the basis of signals from these sensors, the controller 18 obtains the torque as follows; On respective maps 136 in the controller 18 are previously stored the reduction gear ratios of transmission in the first to fifth speed and reverse drive in correlation with the vehicle speed U and engine speed ω at every gear reduction ratio (the correlations are shown only in one map in Fig. 7 for convenience). On the other hand, the correlation between the engine speed ω and the engine torque T₂ is stored in a map 138. When the vehicle speed U and engine speed ω are sent to the input of the controller 18, the controller 18 obtains the reduction ratio i k corresponding to both signals from the maps 136 and obtains the engine torque T₂ from the map 138 on the basis of the engine speed. Thereafter, the product of reduction ratio i k and engine torque T₂ is calculated (140) to obtain the torque T₃ of the propeller shaft (142). The operating means 20 is operated to give the frictional force corresponding to the torque T₃ to the limited slip differential 12. In the embodiment shown in Fig. 8, the controller 18 calculatively obtains the reduction ratio on the basis of signals of the vehicle speed sensor 132 and engine speed sensor 134. Namely, initialization is carried out (150), the vehicle speed U is read (152) and the engine speed ω is read (154). Assuming (156) k = 1, this value of k is compared (158) with 6. In this case, the comparison of k with 6 is based on the assumption that the transmission has five forward stages and one rearward stage. When the value k is larger than 6, the torque T₃ is set (160) to zero. When the value k is not large than 6, presumed engine speed ω k is obtained (162) from the product of the reduction ratio i k in k-th speed (the reduction ratios from k=1 to k=5 are previously stored in the controller 18), aconstant a determined by the final reduction ratio of the differential gear and the diameter of a tire etc. and the vehicle speed U to compare (164) the detected engine speed ω with the calculated engine speed ω k . When the detected engine speed ω falls within 10% of the presumed engine speed ω k , for example, the reduction ratio I is set (166) to i k . On the other hand, when the detected engine speed ω is outside said range, k is (168) set to (k+1) and k thus set is compared (158) with 6. In the controller 18 is previously stored (170) he correlation between the engine speed ω and the engine torque T₂ to obtain the engine torque T₂ from the detected engine speed ω. The torque T₃ of the propeller shaft which is to be given to the limited slip differential 12 by the operating means 20 is calculated (172) from the reduction ratio I and engine torque T₂ and outputted (174).

Claims: A differential control device (10) for controlling differential movement of a differential gear (14) having a limited slip differential (12), the limited slip differential (12) comprising a plurality of first plates (30) engaging with a wheel axle (28) connected to a side gear (28) and a plurality of second plates (32) engaging with a case (40) connected to a ring gear (29), wherein a friction force generated between the first and second plates (30,32) is used for controlling the differential movement between two wheel axles, characterized by a controller (18) for comparing the size of drive torque fixed by a drive condition with a predetermined value, and means (20) for operating said limited slip differential (12), the means (20) being controlled by said controller (18) to operate said limited slip differential (20) so as to limit the differential movement when the drive torque exceeds the predetermined value. A differential control device (10) as claimed in Claim 1, further comprising detecting means (16), and wherein said drive torque fixed by the drive condition is detected by the detecting means (16) and inputted into said controller (18). A differential control device (10) as claimed in Claim 2, further comprising steering angle detecting means (80), and wherein the controller (18) handles the detected steering angle in preference to the drive torque and releases the limitation of the differential movement when the detected steering angle exceeds a predetermined value. A differential control device (10) as claimed in Claim 2, further comprising a vehicle speed sensor (62), and wherein the controller (18) handles the drive torque when the vehicle speed detected by the sensor (62) is not smaller than a predetermined first value, or not larger than a predetermined second value which is smaller than the first value. A differential control device (10) as claimed in Claim 2, wherein said operating means (20) is capable of supplying pressures in proportion to torques to the limited slip differential (12), and wherein the controller (18) controls said limited slip differential (12) through said operating means (20) to limit the differential movement continuously. A differential control device (10) as claimed in Claim 1, further comprising detecting means (110,130) signals of which are inputted into said controller (18), and wherein said controller (18) obtains said drive torque fixed by the drive condition on the basis of the signals from said detecting means (110,130). A differential control device (10) as claimed in Claim 6, wherein said detecting means (110) includes a sensor (112) for detecting a shift position of a transmission and a sensor (114) for detecting an engine speed. A differential control device (10) as claimed in Claim 7, wherein said sensor (112) is constituted from a detecting plate (118) having switches disposed respectively at the shift positions occupied by a shift lever (118). A differential control device (10) as claimed in Claim 7, wherein said sensor (112) is constituted from solenoid valves and a neutral start switch (120). A differential control device (10) as claimed in Claim 8 or 9, wherein said controller (18) obtains said drive torque as a torque of propeller shaft from the detected engine speed in every shift position of the transmission. A differential control device (10) as claimed in Claim 6, wherein said detecting means (130) includes a vehicle speed sensor (132) and an engine speed sensor (134). A differential control device (10) as claimed in Claim 11, wherein said controller (18) obtains a reduction ratio from the detected vehicle speed and detected engine speed and an engine torque from the detected engine speed, and further obtains the drive torque as a torque of a propeller shaft by the product of the reduction ratio and the engine torque. A differential control device (10) as claimed in Claim 6, wherein said operating means (20) is capable of supplying pressures in proportion to torques to the limited slip differential (12), and wherein said controller (18) controls said limited slip differential (12) through said operating means (20) to limit the differential movement continuously.

Inventors: AONO, KOICHI, OUCHI, MITSUYUKI
Applicants: TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1987
Main classification: B60K23
IPC codes: F16D48, B60K23