WO1993005567A1

WO1993005567A1 - Computer controlled vehicle drive system

Info

Publication number: WO1993005567A1
Application number: PCT/US1992/001642
Authority: WO
Inventors: Bryan W. Strohm
Original assignee: Strohm Bryan W
Priority date: 1991-08-29
Filing date: 1992-02-28
Publication date: 1993-03-18
Also published as: AU2256392A

Abstract

The invention comprises a vehicle drive system and method for driving a vehicle. The vehicle drive system includes two electric reversible motors (11, 12) that provide inputs (13, 14) to a planetary gear system (17), and one output shaft (18) from the planetary gear system. By rotating the two motors (11, 12) in directions and at rpms according to a predefined curve, any desired output torque and rpm may be achieved. Specifically, optimum torque is achieved by independently varying the rates of acceleration and deceleration of each motor to produce optimum leverage at any desired output rpm.

Description

COMPUTER CONTROLLED VEHICLE DRIVE SYSTEM

Field of the Invention

This invention relates to electrically powered vehicle drive systems which are computer controlled, and, in particular, to vehicle drive systems which yield a predefined torque during acceleration of the vehicle. Background of the Invention

Recently, the prospect of powering commercial automobiles with electric sources has been demonstrated to be feasible by various automobile manufacturers. However, before becoming commercially viable, both the performance and the cost of electrically driven automobiles must be comparable to gas-powered vehicles. Important performance factors include the acceleration rate of the vehicle from a velocity of zero and at various highway speeds, and the length of time the vehicle is able to operate without being refueled or recharged.

A variety of electrically driven systems have been developed over the last several years. Many, such as the inventions disclosed in U.S. patent nos.

3,596,154, 3,646,414, 4,361,788, 4,471,273 and 4,629,947, are dual electric motor drive systems. Each motor in these systems individually drives a single wheel or set of wheels and can be separately controlled. Problems encountered with earlier systems, including the loss of torque by the complimentary motor if the wheel(s) driven by other motor loses its adhesion to the surface on which it drives (U.S. patent nos. 3,596,154, 3,646,414) and overload protection (U.S. patent no. 4,361,788), are resolved with these inventions. However, even though these systems utilize more than one electric motor for the vehicle drive system, the motors do not cooperate by jointly contributing or driving a single wheel or single axle. Such use of motors would be desirable as it could potentially result in the requirement for smaller, less expensive motors.

To utilize an electrically powered vehicle for a wide range of highways speeds, a transmission may be employed and used in a manner similar to the use of a transmission in a gas-powered vehicle. The control device disclosed in U.S. patent no. 4,096,418 works in conjunction with a transmission to assist in obtaining the desired acceleration by addressing the impairment of the buildup characteristic of the motor current. However, it is desirable to develop an electrically powered vehicle which does not require a conventional transmission system which includes a mechanism to adjust the gear ratio to keep manufacturing and maintenance costs at a minimum. Using conventional techniques, elimination of the capability to adjust the gear ratio of the transmission would require prohibitively expensive motors and large power supplies. Therefore, an alternative is needed. It is also desirable to achieve a substantial torque under any circumstances (vehicle speed and engine rpm). This is difficult when conventional transmission systems are employed.

Also of importance is the length of time the vehicle can be operated without being refueled or recharged to allow the consumer to travel long distances and/or to take several short trips before recharging. Systems which can be recharged during the operation of the vehicle are disclosed in U.S. patent nos. 4,363,999 and 4,629,947. The invention disclosed in U.S. patent no. 4,363,999 is a multi-motor propulsion and braking system in which each DC motor is coupled with a single wheel and together are controlled by an electronic circuit. The control circuit varies the amount of energy transferred from the power sources to the motors during acceleration and may control the amount of electrical energy transferred from the motors to the power sources (recharging) during braking of the vehicle. The dual motor electric drive system disclosed in U.S. patent no. 4,629,947 also provides a mechanism for recharging the power source of the vehicle through the provision of an additional energy source such as a motor-generator or a motor- generator together with a flywheel. It is desirable to utilize the energy "lost" to braking the vehicle to recharge the power supply. Objects of the Invention

Accordingly, it is one object of the present invention to provide a computer controlled vehicle drive system that is able to maintain predefined torque over a wide range of rpms without the use of a transmission.

It is another object of the present invention to provide a vehicle drive system which is comprised of reliable components and is inexpensive to manufacture and maintain. It is another object of the present invention to provide an electrical vehicle drive system which is efficient in that it utilizes a mechanism to minimize the system's energy loss by recharging the power source when the vehicle is braking. Brief Description of the Drawings

Fig. 1 shows a block diagram of one embodiment of the vehicle drive system according to the present invention.

Fig. 2 shows a graph of one embodiment of the relationship between the rotational speed and direction of the two motors and the rotational speed and direction of the differential output shaft with respect to time of the present invention in which the motors are defined to alternately accelerate and decelerate to achieve the desired rotational speed, acceleration and torque of the differential output shaft.

Fig. 3 shows a flow chart depicting one embodiment of the general operation of the electric power source according to the present invention.

Fig. 4 shows a graph of one embodiment of the relationship between the rotational speed and direction of the two motor input rpms to the rotational speed of the output shaft rpm. Summary of the Invention The invention comprises a vehicle drive system and method for driving a vehicle. The vehicle drive system includes two electric reversible motors that provide inputs to a planetary gear system, and one output shaft from the planetary gear system. By rotating the two motors in directions and at rpms according to a predefined curve, any desired output torque and rpm may be achieved. Specifically, optimum torque is achieved by independently varying the rates of acceleration and deceleration of each motor to produce optimum leverage at any desired output rpm. Detailed Description

Referring now to Fig. 1, there is shown a block diagram of the vehicle drive system according to the present invention. The vehicle drive system includes first and second reversible electric motors 11, 12, each having output shafts 13, 14, respectively. First and second motor output shafts 13, 14 are connected to first and second input shafts 15, 16, respectively, of planetary gear system 17. Planetary gear system output shaft 18 is connected to load 19 of the vehicle, typically the rear wheels. The vehicle drive system also includes an electrical power source comprising power supply 20, first and second variable speed drives 21, 22, computer 23, and input 24. Power supply 20 comprises a group of rechargeable batteries. Variable speed drives 21 , 22, well known in the art, are connected to first and second motors 11, 12, respectively, and are capable of independently supplying a variable and reversible current to motors 11, 12. Motors 11, 12 each have an integral generator whereby a signal provided to motors 11, 12 to place a load on the motors will invoke the generating capability of the motor. Computer 23 provides a means for defining a predetermined relationship between the rpm and rotational direction of first and second motors 11, 12, and gear system output shaft 18. Input 24 provides a means for designating a desired change in vehicle speed through devices such as an accelerator, brake, and torque adjustment means. The vehicle drive system also includes first and second speed sensors 25, 26, operatively connected to motor output shafts 13, 14, respectively, and provide feedback to computer 23.

The gearing ratios of differential 17 may be selected to average the rotations of motors 11, 12 to result in the desired rpm of gear system output shaft 18. In this manner, motors 11, 12 both contribute to driving load 19 of the vehicle. It will also be appreciated that motors 11, 12 may rotate in opposite directions with respect to each other. It will be further appreciated that planetary gear system 17 may comprise an input sun gear, input planetary gears, and an output ring gear or system 17 may comprise a differential, which is well known in the art.

Fig. 2 shows a graph of one embodiment of the relationship between the rotational speed and direction of motors 11, 12 and the rotational speed and direction of differential output shaft 18 with respect to time. In this embodiment, motors 11, 12 are alternately accelerated and decelerated to achieve the desired rotational speed, acceleration and torque of differential output shaft 18, and, hence, of the vehicle. Specifically, first motor 11, illustrated by first input curve 30, initially is accelerated to a negative rpm from zero (0) rpm and then decelerated to zero (0) and accelerated in the reverse direction to its peak positive rpm. After reaching its peak rpm, first motor 11 continues to decelerate and accelerate alternately according to first input curve 30. Second motor 12, illustrated by second input curve 31, also is alternately accelerated and decelerated, but in the opposite direction of first motor 11. Because differential 17 averages the directions and rpms of both motors 11, 12, differential output shaft 18 will initially rotate in the same direction as second motor 12. The rotational speed of differential output shaft 18 is shown by output curve 32. Differential output shaft 18 according to Fig. 2 is constantly accelerating as the slope of output curve 32 is constant. Referring now to Fig. 4, there is shown a graph of one embodiment of the relationship between the rotational speed and direction of input motors 11, 12 to the rotational speed and direction of output shaft 18. The rpms of motors 11, 12 is shown versus the rpm of output shaft 18 as first and second motor curves 33, 34. Gear ratio curve 35 is the relationship between differential 17 and output shaft 18. It will be appreciated that a relationship exists between the torque of the vehicle drive system and the rates of acceleration and deceleration of motors 11, 12. If the rates of alternating acceleration and deceleration of motors 11, 12 are increased, the slopes of input motor curves 33, 34 increase and the torque of differential output shaft 18 increases. Similarly, if the alternating rates decrease, the torque of differential output shaft 18 decreases. The rates of alternating acceleration and deceleration may be measured in terms of transition points. In Fig. 4, two representative transitions points 36, 37 are denoted. Transition point 36 is one in which second motor, curve 34, has reached its peak rpm and first motor, curve 33, changes from accelerating toward a negative rpm to decelerating toward zero (0) rpm. At transition point 37, first motor, curve 33, has reached its peak rpm and second motor, curve 34, changes from decelerating to accelerating. Thus, the system's torque is controlled by controlling the number of transitions of motors 11 , 12. It will be further appreciated that the vehicle need not be stationary for the application of such a relationship. The same frequency of transitions and torque may be achieved when starting at an output rpm which is different from zero (0). Therefore, a predefined torque may be maintained over a wide range of rpms. Referring now to Fig. 3, there is shown a flow chart of the general operation of the electric power source according to the present invention. At start 100 of the operation, variables, including the identification of motors A and B, are initialized in step 101. The rpms of motors A and B and values from input means 24 are read in step 102. The rpms of both motors A and B are then compared to their peak allowable rpm, P_A and P_B, respectively, in step 103. If either the rpm of motors A or B exceeds or equals its peak allowable rpm, P_A and P_B, the assignment of motors A and B is exchanged in step 104. In step 105, adjustments are made to compensate for motor inefficiencies, external variables, and monitoring systems. For example, if external forces place an additional load on motors 11, 12 such that motors 11, 12 are not rotating as programmed and expected, the actual rpms are compared to the expected rpms in step 105, and, if necessary, additional power may be provided to motors 11, 12. If the vehicle were to hit a patch of ice or any slippery surface in which no load is exerted by the road surface and therefore the rpm of differential output shaft 18 exceeds that which is expected, step 105 would adjust the rpms of motors 11, 12 to result in the correct rpm of differential output shaft 18. Also, individual motors may, due to its own inefficiencies such as those caused by extensive use, not rotate exactly as commanded. Adjustments of this type may also be made in step 105. Following the adjustments of step 105, step 106 compares the rpm of motor A with the load limit of motor A. Herein, load limit refers to the speed below which applying a load to the motor does not effectively brake the motor. If the rpm of motor A exceeds its load limit, either a load is applied to motor A in step 107, otherwise, power is applied to motor A in step 108. For example, if the rpm of motor A exceeds its load limit and it is desired to decelerate motor A according to the defining means of computer 23, then a load is applied to motor A as in step 107. Next, in step 109, the rpm of motor B is compared to load limit of motor B. Similar to the steps 107 or 108 taken for motor A, if the rpm of motor B is outside its load limit, either a load is applied to motor B in step 110, otherwise, power is applied to motor B in step 111. For example, if the rpm of motor B exceeds it load limit and it is desired to decelerate motor B according to the defining means, then a load is applied to motor B as in step 110. The process then continues by returning to step 102 to read new values.

The operation of the vehicle drive system according to the present invention includes the cooperation between the electric power source and means 25, 26 for monitoring the rotational output of first and second motors 11, 12. Referring to Fig. 1 , first and second speed sensors 25, 26 are connected to first and second frequency-to-voltage converters 40, 41 which are in turn connected to first and second rpm monitors 42, 43 within computer 23. The rpms of each motor are then read according to step 102 (Fig. 3).

In addition to the rpms of each motor, operator input 24 from devices such as accelerator, or throttle, 44, brake 45, or torque adjustment means 46 are read in step 102. If input from accelerator 44 indicates that the present output rpms are below desired levels, then computer 23 causes an increase in differential output shaft 18 rpm while brake 45 signals computer 23 to cause a decrease in differential output shaft 18 rpm. When braking, a load will be applied to either or both motors 11, 12 which can contribute to the recharging of power source 20. Optionally, a mechanical brake may also be applied to the vehicle's wheels. Also, input from torque adjustment means 46 may be read in step 102. In this manner, the desired performance of the vehicle drive system can be modified by the operator by providing a value which changes the rates of acceleration of motors 11 and/or 12 to achieve the desired torque.

Microcomputer 23, such as an Apple computer having software written using techniques well known in the art, may be employed to read the input signals and generate the output signals necessary to control the system. Specifically, the software includes equations capable of determining the relationship between the first and second motor 11, 12 speeds and the output speed as shown in Fig. 4. In one embodiment, these relationships may be based on the input from torque control 46. Specifically, if a high torque is desired, then there will be only a small difference between the acceleration rates of the two motors, so the motors will reverse directions more frequently before the maximum output speed is reached. If a low torque is desired, then there will be a greater difference between the acceleration rates of the two motors, and they will not reverse directions as frequently before maximum output speed is reached. Thus, the torque input allows the software to define a predetermined relationship between the rpm and rotation direction of the first and second motors, and the differential output shaft. The computer has as additional inputs for signals from throttle 44 and brake

45. These signals are combined to indicate a desired output rpm 32. The computer also has rpm monitor inputs 42, 43 from the first and second motors. Based on the combination of inputs, the software determines whether it is necessary to increase, decrease or maintain the present output speed. The computer sends signals to the voltage generators and variable loads 53, 54 to generate the desired output shaft rpms.

A/B assignor 47 then, according to step 103, compares the rpms of motors 11, 12 with their respective peak rpm, P. If either first motor 11 or second motor 12 are at or above P, computer 23 exchanges the assignment of motors A and B as representative of motors 11, 12. In this manner, either motor A or motor B always represents the accelerating motor. For example, motor A may always represent the accelerating motor while motor B always represents the decelerating motor. if a change of polarity of the load or power is required to match polarity of batteries 20 or motors 11, 12, computer 23 through first and second computer reversers 48, 49 to first and second drive reversers 50, 51 sends signals to motors 11, 12 to reverse the directions of either or both motors 11, 12. After completing step 103 and the possible exchange of A and B in step 104, adjustments are made in step 105. For example, a desired change in the rate of acceleration or deceleration with preferred torque read by the system in step 102 can be made.

If the rpm of motor A is outside its load limit and a deceleration is desired, step 107, applying a load to motor A, is performed. Specifically, force calculator 52 sends signals to either variable load 53 or 54, depending on which variable load_.53 or 54 corresponds to motor A which in turns draws power from motor A to rechargeable power supply 20.

When power is being applied to motor 11 or 12, force calculator 52 sends a signal to first or second comparator stage 55 or 56, depending on which motor corresponds ^'to motor A, which uses the signal of first or second triangle wave generator 57 or 58. Power is drawn from power supply 20 according to the signal provided to first or second output driver 59 or 60, through first or second current sensor 61 or 62, through first or second driver reverser 50 or 51 to first or second motor 11 or 12. Output drivers 59, 60 send voltage signals through first or second averagers 63 or 64 to first or second motor monitor 65 or 66. Current signals are also received by first and second motor monitors 65, 65 through first and second current sensors 61, 62.

Suitable circuitry for variable speed drives 21, 22 is shown in the appendix.

It will be appreciated by those of skill in the art that rpms, voltages, and current may not be exactly as programmed or expected. For this reason, computer 23 is able to adjust programmed values to compensate for such deviations. It will be appreciated by those of skill in the art that the relationship between the rpms of motors 11, 12 and differential output shaft 18 may be quite varied. It is possible that the rates of change of rpm of drive motors 11, 12 are different with respect to each other. In the vehicle drive system, both motors 11, 12 contribute to the rotational speed of differential output shaft 18. Motors 11, 12 work in conjunction with each other to result in a very efficient electrical vehicle drive system. While one motor is accelerating and therefore requires power, the other motor may indeed be decelerating, thereby providing power to the system.

APPENDIX

Claims

1. A vehicle drive system comprising: first and second electric reversible motors, each motor having an output shaft; a planetary gear system having two input shafts and one output shaft, the two input shafts being connected to the first and second motor output shafts, respectively; an electrical power source operatively connected to the first and second motors, the power source comprising electric control means, the control means comprising means for independently supplying a variable and reversible current to the first and second motors, means for defining a predetermined relationship between the rpm and rotation direction of the first and second motors, and the gear system output shaft rpm, such that when the motors are rotated in directions and at rpms according to the defining means, the gear system output shaft rotates in a predetermined direction and rpm according to the defining means, wherein the defining means includes at least one state wherein the output shaft rotates at an rpm less than the rpm of one of the two motors, and input means for designating a desired change in vehicle speed; and means for monitoring the rotational output of the first and second electric motors, the monitoring means being operatively connected to control means, such that the control means provides current to the motors to cause the motors to rotate in the direction and rpm in accordance with the defining means.

2. The vehicle drive system of claim 1 wherein the planetary gear system comprises a differential.

3. The vehicle drive system of claim 1 wherein the power source is rechargeable.

4. The vehicle drive system of claim 1 further comprising a means for recharging the electrical power source.

5. The vehicle drive system of claim 1 wherein the control means system comprises a computer.

6. The vehicle drive system of claim 1 wherein the defining means defines states for the two motors whereby the two motors change their rate of rpm at different rates.

7. A method for driving a vehicle having an output drive shaft, ^' comprising the steps of: providing a vehicle drive system comprising first and second electric reversible motors, a planetary gear system having two input shafts operatively connected to the first and second motors and an output shaft, and an electrical power source operatively connected to the first and second motors, the power source comprising control means, the control means comprising means for independently supplying a variable and reversible current to the first and second motors, and means for defining a predetermined relationship between the rpm and rotation direction of the first and second motors, and the gear system output shaft rpm; and rotating first and second electric motors in opposite directions with respect to each other such that the gear system output shaft rpm is an average of the rpms of the first and second electric motors.

8. The method for driving a vehicle of claim 7 further comprising the step of changing the rate of rpm change of each motor at different rates with respect to each other.

9. The method for driving a vehicle of claim 7 further comprising the step of recharging the power source.

10. The method for driving a vehicle of claim 7 wherein the vehicle drive system comprises the vehicle drive system of claim 1.

11. The method for driving a vehicle of claim 7 wherein the planetary gear system comprises a differential. 12. The method for driving a vehicle of claim 7 further comprising first and second motor output shafts, one from each motor, connected to the gear system input shafts. 13. The method for driving a vehicle of claim 7 wherein the control means further comprises input means for designating a desired change in vehicle speed.

14. The method for driving a vehicle of claim 7 further comprising means for monitoring the rotational output of the first and second electric motors, the monitoring means being operatively connected to control means, such that the control means provides current to the motors to cause the motors to rotate in the direction and rpm in accordance with the defining means.

AME_MDED CT-AIMS

[received by the International Bureau on 30 December 1992 (30.

12.92); original claims 7, 11 and 12 deleted; original claims 1,6, 8-10, 13 and 14 amended; new claim 15 added; remaining claims unchanged (3 pages)]

1. A vehicle drive system comprising: first and second electric reversible motors, each motor having an output shaft; a planetary gear system having two input shafts and one output shaft, the two input shafts being connected to the first and second motor output shafts, respectively; an electrical power source operatively connected to the first and second motors, the power source comprising electronic control means, the control means comprising means for Independently supply a variable and reversible current to the first and second motors, means for defining a predetermined relationship between the rpm and rotation direction of the first and second motors, and the gear system output shaft rpm, such that when the motors are rotated in directions and at rpms according to the defining means, the gear system output shaft rotates in a predetermined direction and rpm according to the defining means, wherein the defining means includes at least one state wherein the output shaft rotates at an rpm less than the rpm of one of the two motors, and input means for designating a desired change in vehicle speed; and means for monitoring the rotational output of the first and second electrical motors, the monitoring means being operatively connected to the control means, such that the control means provides current to the motors to cause the motors to rotate in the direction and rpm in accordance with the defining means, and whereby an increase in vehicle speed as designated by the input means causes the simultaneous and continuous change of the rpms of both the first and second motors according to the defining means to yield a predefined torque of the output shaft during such an increase in vehicle speed. 2. The vehicle drive system of claim 1 wherein the planetary gear system comprises a differential.

3. T e vehicle drive system of claim 1 wherein the power source is rechargeable. 4. The vehicle drive system of claim 1 further comprising a means for recharging the electrical power source.

5. The vehicle drive system of claim 1 wherein the control means system comprises a computer. 6. The vehicle drive system of claim 1 wherein the defining means defines states for the two motors whereby the two motors change their rpm at different rates.

8. The method for driving a vehicle of claim 15 wherein the step of controlling the rpm of each motor includes varying the current supplied to each motor to change the rate of rotation of each motor at different rates with respect to each other.

9. The method for driving a vehicle of claim 15 further comprising the step of recharging the power source.

10. The method for driving a vehicle of claim 15 wherein the vehicle drive system comprises the vehicle drive system of claim 1.

13. The method for driving a vehicle of claim 15 wherein the control means further comprises input means for designating a desired change in vehicle speed, the method further comprising, before controlling the rpms of the motors, the step of: designating a desired change in vehicle speed.

14. The method for driving a vehicle of claim 15 wherein the vehicle further comprises means for monitoring the rotational output of the first and second electric motors, the monitoring means being operatively connected to control means, the method further comprising the step of: monitoring the rpms of the motors.

15. A method for accelerating a vehicle having an output drive shaft, first and second electric reversible motors, a planetary gear system having two input shafts operatively connected to the first and second motors and an output shaft, and an electrical power source operatively connected to the first and second motors, the power source comprising control means, the control means comprising means for independently supplying a variable and reversible current to the first and second motors, and means for defining a predetermined relationship between the T 6 rpm and rotation direction of the first and second motors, and the gear system output shaft rpm, the method comprising the step of: simultaneously controlling the rpms of the first and second electric motors by providing variable current to both motors with the control means to thereby cause the gear system output shaft to rotate at an rpm equal to the average of the rpms of the first and second electric motors.