REGENERATIVE BRAKING SYSTEM FOR CAR

Abstract: When a hydraulic circuit of a regenerative braking system is not operated, effective maximum displacement controlling current and minimum displacement controlling current for a pump/motor (1) are studied on the basis of a variation of the sensed displacement angle (2) when the maximum permissible current and the minimum operating current previously given to a displacement angle controlling electromagnetic proportional control valve (3) are respectively decreased and increased stepwise, thereby determining the displacement controlling current corresponding to a capacity variation of 1 cc.

Description: Background of the Invention The present invention relates to a regenerative braking system for a car, and particularly to a regenerative braking system for a car wherein the decelerating energy of a car is captured and used for the starting/accelerating energy, and more particular to a regenerative braking system for a car comprising a hydraulic oil circuit formed of a high pressure accumulator, a pump/motor, a circuit shut-off walve, and a low pressure accumulator; means for sensing the displacement angle of said pump/motor; a displacement angle controlling electromagnetic proportional control valve for actually controlling the displacement capacity of said pump/motor. In a PTO (Power-take-off) output unit (system) or a deceleration energy recovery system as conventionally known, a part of kinetic energy dissipated mainly as heat at a brake or engine during the deceleration of a car is captured in the form of hydraulic operating oil and accumulated in an accumulator. And the accumulated energy is utilized for the starting energy and accelerating energy of the car. For example, as the oldest one, in 1976 C. J. Lorence Corporation in England announced the development of such a system using a bus of British Leyland Corporation. Since then, various researches and developments have been made in Europe. Recently, Japanese Patent Application Laid-open Nos. 62-15128, 62-37215, 62-39327 etc. have disclosed a deceleration energy recovery system which is essentially formed of a transmission (hereinafter referred to as T/M), a multi-stage gear-changed PTO unit, a PTO output shaft, a pump/motor, a hydraulic oil circuit, an electromagnetic clutch, an accumulator, and a control unit. The T/M includes a counter shaft driven through an engine clutch, a main shaft connected to a wheel driving line, and a multi-staged gear train mechanism transferring the rotation of the counter shaft to the main shaft through the gears. The multi-stage gear-changed PTO unit includes a counter shaft PTO gear disconnectably coupled to the counter shaft through a counter shaft PTO gear synchronizer, a main shaft PTO gear coupled to the counter shaft PTO gear and disconnectably coupled to the main shaft through a main shaft PTO gear synchronizer, and a PTO output shaft driven through driving gears coupled to the main shaft PTO gear. The pump/motor is coupled to the PTO output shaft, the hydraulic oil circuit consists of a high pressure oil line and a low pressure oil line and serves to connect the accumulator to an oil tank through the pump/motor, and the electromagnetic clutch serves to connect/disconnect the oil circuit to/from the PTO shaft. The control unit controls the electromagnetic clutch and works the pump/motor as either of a pump or motor in response to the running condition of the car. Namely, for working the pump/motor as a pump, the torque of the wheels during the decelerating mode serves to accumulate the operating oil into the accumulator through the PTO unit thereby to capture the kinetic energy, i.e. braking energy mainly lost as heat in the brake or engine, and for working the pump/motor as a motor, the operating oil accumulated in the accumulator serves to generate starting/accelerating torque to drive the wheels through the PTO unit. The control manner of this control unit is as follows: 1 ○ When the car start with the inner pressure of the accumulator being sufficient, the pump/motor is controlled to serve as a variable capacity type motor, the capacity of which is controlled by varing the displacement angle (incline angle) of the swash plate or shaft in response to the accelerator pedal positions. Since the pump/motor is also connected to the electromagnetic clutch, when the electromagnetic clutch is coupled to the PTO unit by the control unit, the pump/motor drives the car based on the hydraulic power accumulated in the oil circuit. In the meantime, when the car speed exceeds a preset value corresponding to the gear position selected by a driver, the engine clutch is coupled to the engine for the engine cruising. At the same time the PTO unit is gear-changed so as to turn off the counter shaft synchronizer which was on and turn on the main shaft synchronizer which was off, and the combined cruising of the pump/motor with the engine is carried out according to the hydraulic power based on the pedal position only if the accelerator pedal is largely operated by the foot. 2 ○ During the braking mode, the electromagnetic clutch is made on, and the displacement angle control signal (pump capacity control signal) according to the brake pedal position is supplied to the pump/motor for the corresponding pumping operation while at the same time the engine is declutched. Thus, the control unit controls the engine clutch to decouple the engine from the driving line of the wheels in order to capture a part of the braking energy which is to be consumed in the engine during the braking mode and to relieve the captured energy during the accelerating mode, while coupling the engine to the driving line in order to use the engine power solely or in combination with the motor during the starting/accelerating mode. In such a prior art, the displacement capacity of the hydraulic operating oil, i.e. the incline angle, of the pump/motor is controlled according to the position of a brake pedal in the braking mode or the position of an accelerator pedal in the accelerating mode. However, since an electromagnetic proportional control valve for the displacement capacity (angle) of the pump/motor has electromagnetic hysteresis and electrical noise margin, if the capacity of the pump/motor is assumed to have 0 ∼ 255cc as shown in Fig.1, the control current for the displacement angle (hereinafter referred to as displacement controlling current) of the pump/motor fails to range from the minimum 0A to the maximum 1A, while ranges from 0.25A to 0.95A. Therefore, even though the displacement controlling current of 0.5A is supplied to the pump/motor, the capacity of the pump/motor actually fails to have 125cc which is 1/2 of the capacity, while has about 85cc, whereby a required capacity fails to exactly correspond to the actual capacity. Furthermore, since such a characteristic as shown in Fig.1 varies due to the electromagnetic hysteresis and electrical noise margin, a required capacity of the pump/motor can not be settled. US-A-4 741 410 discloses a regenerative braking system for cars of the same type as described in the preamble of claim 1 and the first paragraph of description page 1. The known regenerative braking system is primarily adapted for inexpensive retrofitting of existing vehicles such as vans and buses. However, the sensing means of that regenerative braking system does only sense whether or not the displacement angle of the pump/motor is zero or not. Moreover, this prior art regenerative braking system has essentially the same drawbacks as discussed above. Summary of the Invention It is accordingly an object of the present invention to provide a regenerative braking system for a car which can study the displacement capacity (angle) of a pump/motor used in a hydaulic oil circuit regardless of the variation of the characteristic of the pump/motor. The study principle of the present invention will be at first described herebelow. As shown in Fig.1, the displacement capacity of the pump/motor is controlled over the range from 0 to 250cc which correspond to the range of the displacement controlling current of 0.25 ∼0.95A, while the output voltage of a sensor used for sensing the displacement capacity (hereinafter referred to as displacement sensor) ranges from 0.5V∼2.75V corresponding to the capacity of 0∼250cc as shown in Fig. 2. Therefore, the relationship between the displacement controlling current (A) and the output voltage (V) of the displacement sensor is such that the displacement controlling current I MIN (0.25A) for minimizing the capacity of the pump/motor to zero corresponds to the output voltage V MIN (0.5V) of the displacement sensor and that the displacement controlling current I MAX (0.95A) for maximizing the capacity of the pump/motor to 250cc corresponds to the output voltage V MAX (2.75V) of the displacement sensor. If the range of the displacement controlling current from 0.25 to 0.95A is divided by the capacity of 250cc to determine control current corresponding to a unit capacity, the study of the displacement capacity can be excluded. As above described, however, it is possible that the maximum/minimum output voltage of the displacement sensor and therefore the corresponding displacement controlling current vary from the positions shown in Fig.3 due to the electromagnetic hysteresis and the noise margin. Therefore, if the displacement capacity control without considering such a variation is carried out, it will be inaccurate. This is why the study of the displacement capacity is required. According to the present invention, control means provide the maximum permissible current and the minimum operating current for a displacement angle controlling electromagnetic proportional control valve when a hydraulic oil circuit including a pump/motor is not operated, i.e. when the pump/motor is not used. Then, the control means decrease stepwise the maximum permissible current and increase stepwise the minimum operating current. As a result, a variation taking place at the output of the displacement sensor is detected as shown in Fig.3 by points A and B to study each displacement controlling current respectively corresponding to the above noted maximum and minimum capacities of the pump/motor, whereby the displacement controlling current for the pump/motor is determined per a unit capacity from the difference between both values of the current. Hereby, the displacement angle of the pump/motor is precisely made to correspond to the controlling current for the proportional control valve in the energy recovery/regenerative modes. Brief Description of the Drawings The present invention will be more apparent to those skilled in the art, from the following drawings in which: Fig.1 show a graph illustrating the relationship between displacement controlling current and displacement capacity, Fig.2 show a graph illustrating the relationship between the output voltage of a displacement angle sensor and displacement capacity, and Fig.3 show a graph illustrating the relationship between displacement controlling current and the output voltage of the displacement angle sensor. Fig.4 shows a schematic diagram of a regenerative braking system for car with a pump/motor studying its displacement capacity in accordance with the present invention, Fig.5 shows a flow chart for determining a maximum displacement controlling current according to the present invention, Fig.6 shows a flow chart for determining a minimum displacement controlling current according to the present invention, and Figs.7 shows a flow chart for determining displacement angle controlling current per unit capacity of the pump/motor according to the present invention. Throughout the figures, the same reference numerals indicate identical or corresponding portions. Detailed Description of the Preferred Embodiments There will now be described the embodiments of a regenerative braking system for car according to the present invention. Referring now to Fig.4, the arrangement of the regenerative braking system (hereinafter referred to as RBS) includes; a pump/motor 1; a displacement sensor 2 for sensing the displacement angle (incline angle) of the pump/motor 1; a displacement angle controlling proportional electromagnetic valve 3 for controlling the displacement angle of the pump/motor 1; a transmission (hereinafter abbreviated as T/M) 4; a gear position sensor 5 for sensing the gear position of the T/M 4; a PTO unit 6 for taking off the driving force of wheels 7 as hydraulic braking force through an axle 8 or conversely for transferring the hydraulic driving force to the wheels 7 through the axle 8; an electromagnetic clutch 9 for connecting or disconnecting the driving force between the PTO unit 6 and the pump/motor 1; a circuit shut-off valve 10; a high pressure accumulator 11; a low pressure accumulator 12 forming a hydraulic circuit together with the pump/motor 1, the circuit shut-off valve 10,and the high pressure accumulator 11; and a micro-processor 13 (hereinafter abbreviated as MPU) as control means for displacement controlling current corresponding to the capacity of the pump/motor 1 when it finds from the output or states of the gear position sensor 5, the electromagnetic clutch 9, and the circuit shut-off valve 10 that the pump/motor 1 is not being used. The operation of this embodiment shown in Fig.1 will be described with reference to an interrupt routine, shown in Figs.5 to 7 for determining displacement controlling current corresponding to a unit capacity of the pump/motor 1, stored in and executed by the MPU 13 shown in Fig.1. Starting this routine, the MPU 13 checks from the gear position sensor 5 whether or not the gear position is one of neutral (N), reverse (R), and parking (P) (step T1 in Fig.5), checks whether or not the electromagnetic clutch 9 is on (step T2), and checks whether or not the circuit shut-off valve 10 is on (step T3), whereby the MPU 13 checks whether or not the hydraulic circuit including the pump/motor 1 is operated. In those steps, when the gear position is not any one of N, R, P, when the magnetic clutch 9 is on, or when the circuit shut-off valve 10 is on, the MPU 13 finds that the hydraulic circuit is enabled to operate. In this condition, it is meaningless and dangerous to study the displacement angle of the pump/motor 1 in this condition, so that the routine ends. If it is found in any one of steps T1, T2, and T3 that the pump/motor 1 is being used, the MPU 13 gives to the proportional electromagnetic valve 3 the maximum permissible current (1A in Fig.3) which necessarily gives the pump/motor 1 the maximum displacement angle, and stores it (step S1). Then, the output voltage V O of the displacement sensor 2 at the moment is stored in a memory V M (not shown) (step S2). Next, for the safety's sake, that is for the hydraulic circuit not to have the operating state since it takes some time from the time when the proportional valve 3 is given controlling current to the time when the displacement angle of the pump/motor 1 has the value corresponding to the controlling current, whether or not the hydraulic circuit is enabled to operate like in steps T1∼T3 is checked in steps S3 ∼S5. As a result, if it is found that the hydraulic circuit is enabled to operate, the routine ends, while if it is found that the hydraulic circuit is not used, the displacement controlling current I is reduced by 2.5 mA (step S6), and it is checked whether or not the output voltage V O of the displacement sensor 2 at the moment is equal to the voltage stored in the memory V M , i.e. V M =V O (step S7). During the interval of V M =V O , steps S3 ∼S7 are repeated to reduce the displacement controlling current I by 2.5 mA. When it is found that V M ≠ V O (point A in Fig.3), it is assumed in step S8 that the displacement controlling current I at the moment plus 2.5 mA be the actual maximum displacement controlling current I MAX (0.95A in Fig.3), while the voltage stored in the memory V M is set as the maximum output voltage V MAX of the displacement sensor 2 (step S9), and this routine ends. Subsequently, the MPU 13 starts the program shown in Fig.6 for the determination of the minimum displacement controlling current. The MPU checks like the routine in Fig.5 whether or not the hydraulic circuit is operating (steps T11 ∼T13), where if it finds that the pump/motor 1 is not operating in any one of steps T11∼T13, the MPU 13 gives to the proportional electromagnetic valve 3 the minimum operating current (0.2A in Fig.3) which necessarily gives the pump/motor 1 the minimum displacement angle, and stores it (step S11). Then, the output voltage V O of the displacement sensor 2 at the moment is stored in the memory V M (step S12). Next, for the safety's sake, whether or not the hydraulic circuit is enabled to operate like in steps T11 ∼T13 is again checked in steps S13 ∼S15. As a result, if it is found that the hydraulic circuit is enabled to operate, the routine ends, while if it is found that the hydraulic circuit is not used, the displacement controlling current I is increased by 2.5 mA (step S16), and it is checked whether or not the output voltage V O of the displacement sensor 2 at the moment is equal to the voltage stored in the memory V M , i.e. V M =V O (step S17). During the interval of V M =V O , steps S13∼S17 are repeated to increase the displacement controlling current I by 2.5 mA. When it is found that V M ≠V O (point B in Fig.3), it is assumed in step S18 that the displacement controlling current I at the moment minus 2.5 mA be the actual minimum displacement controlling current I MIN (0.25A in Fig.3), while the voltage stored in the memory V M is set as the minimum output voltage V MIN of the displacement sensor 2 (step S19), and this routine ends. Determining the actual maximum/minimum displacement controlling current from the above routines shown in Figs.5 and 6, the MPU 13 executes the program shown in Fig.7. At first, the dynamic range I ST of the displacement controlling current for controlling the unchangeable capacity 0∼250cc of the pump/motor 1 is determined by subtracting the minimum displacement controlling current I MIN from the maximum displacement controlling current I MAX in step S21 in Fig.7. Then, the dynamic range I ST is divided by the maximum capacity 250cc of the pump/motor 1 to determine the displacement controlling current I VN per unit capacity 1cc in this example in step S22, whereby the program ends. Consequently, the displacement controlling current I VN thus determined is used to determine the displacement controlling current, by 0.25A plus I VN × the displacement capacity of the pump/motor 1 as required in the example shown in Fig.1 for controlling the hydraulic circuit in the braking mode or accelerating mode.

Claims: 1. A regenerative braking system for car comprising: a hydraulic oil circuit formed of a high pressure accumulator (11), a pump/motor (1), a circuit shut-off valve (10), and a low pressure accumulator (12); means (2) for sensing the displacement angle of said pump/motor (1); a displacement angle controlling electromagnetic proportional control valve (3) for actually controlling the displacement capacity of said pump/motor (1); characterized by control means (13) for giving to said control valve (3) the maximum permissible current (I MAX ) and the minimum operating current (I MIN ) when said hydraulic circuit is not operated, thereby studying the maximum and minimum displacement controlling current of said pump/motor (1) on the basis of a variation of the sensed displacement angle when the maximum permissible current (I MAX ) and the minimum operating current (I MIN ) are respectively decreased and increased stepwise, thereby determining a displacement controlling current per a unit capacity for said control valve (3). 2. A regenerative braking system for car according to claim 1, further including means (5) for sensing the position of a gear (4) and an electromagnetic clutch (9) for connecting or disconnecting said pump/motor (1) to or from a PTO unit (6), said control means (13) finding that said hydraulic circuit is not operated if the conditions that the sensed gear position is any one of neutral (N), reverse (R) and parking (P), that said electromagnetic clutch (9) is off, and that said circuit shut-off valve (10) is off are fulfilled. 3. A regenerative braking system for car according to claim 2, wherein said control means (13) again check whether or not said hydraulic circuit is not operated after the maximum permissible current (I MAX ) and the minimum operating current (I MIN ) have been given to said control valve (3). 4. A regenerative braking system for car according to claim 1, wherein said control means (13) determine the displacement controlling current per a unit capacity by substracting the minimum displacement controlling current (I MIN ) from the maximum displacement controlling current (I MAX ) and by dividing the difference by the maximum capacity.

Inventors: SHIMA, TAKASHI, TANAKA, KOJI
Applicants: ISUZU MOTORS LIMITED
Application year: 1989
Main classification: B60K6
IPC codes: B60K25, B60T1, B60K6, F16H61