Electrical transmission or interconnection systems – Switching systems – Plural switches
Reexamination Certificate
2000-01-21
2001-09-04
Tso, Edward H. (Department: 2838)
Electrical transmission or interconnection systems
Switching systems
Plural switches
Reexamination Certificate
active
06285093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an electrical control circuit for providing an analog voltage signal to an electronic transmission controller for a hydrostatic transmission.
2. Description of the Prior Art
Hydrostatic transmissions are becoming increasingly common in off road work vehicles. Electronic transmission controllers have been used to control the operation of the hydrostatic transmission. These controllers receive an analog voltage signal from the operator to control the output of the transmission. In a system currently marketed by the assignee of the present invention, the system uses two levers to control the operation of the transmission. The first lever is used to control steering and the forward and reverse movement of the vehicle. The maximum desired speed of the vehicle is controlled by a separate lever.
Single lever shift levers for off road work vehicles have been proposed which have a knob that can be rotated to signal different speed ratios. The knob may also be provided with a rocker switch which is used to shift the transmission between forward and reverse, see U.S. Pat. No. 4,360,718. In addition, a steering lever for an off road work vehicle has also been proposed having keys for shifting the transmission into forward and reverse. Other keys are provided for higher or lower speed levels, see U.S. Pat. No. 5,566,586.
SUMMARY
The present invention is directed to an electrical control circuit for supplying an analog voltage signal to an electronic transmission controller for a hydrostatic transmission. The control circuit comprises two switches located on a T-bar handle of a control lever. The control lever is used to control steering and the forward and reverse operation of the vehicle. The circuit is provided with two switches a first switch for reducing the speed of the vehicle and a second switch for increasing the speed of the vehicle. The switches are normally open and depressing the first switch closes the switch and reduces the speed of the vehicle. Depressing the second switch closes that switch and increases the speed of the vehicle.
The circuit is provided with a constant direct current voltage source. A first resistor is mounted in series with the voltage source. A second resistor in turn is mounted in series with the first resistor. The first switch is mounted in parallel with second resistor. A third resistor is mounted in series with the second resistor downstream from the first resistor. The third resistor is coupled to ground. The second switch is mounted in series with the second resistor downstream from the first resistor. A fourth resistor is mounted in series with the second switch. The second switch and fourth resistor are mounted in parallel to the third resistor. A voltage signal output is located between the second and third resistors and supplies an analog voltage signal to the electronic transmission controller.
In the preferred embodiment the first and second resistors have approximately the same resistance. Both the first and second resistors individually have a smaller resistance than the third resistor. In addition, the first and second resistors combined have a smaller resistance than the third resistor. The fourth resistor is smaller than the both the first and second resistors individually. Through this arrangement of resistances the voltage output of the circuit has three distinct control bands. In the neutral band with both switches open an analog voltage signal is emitted in the neutral voltage band. In the neutral voltage band electrical current from the voltage source passes through the first, second and third resistors resulting in a voltage signal at the voltage signal output in the neutral voltage band. In response to this signal the electronic transmission controller maintains the vehicle at its current operating speed. Closing the first switch signals a desired speed reduction as an analog voltage signal is emitted in the down voltage band. The down voltage band has a higher voltage than the neutral voltage band as the closed first switch allows the current to bypass the second resistor. The electronic transmission controller uses this signal to deaccelerate the vehicle. Closing the second switch signals a desired speed increase as an analog voltage signal is emitted in the up voltage band. The up voltage band has a lower voltage than the neutral voltage band as the closed second switch allows current to pass through the fourth resistor to ground. The electronic controller uses this signal to accelerate the vehicle.
In addition to the control bands, neutral, down and up, two other bands indicating an open circuit to ground and a short circuit when both switches are depressed. In the open circuit to ground condition, current passes through the first and second resistors and then passes to ground through a fifth resistor located in the electronic transmission controller. As this fifth resistor is larger than the third resistor the open circuit analog voltage signal band is greater than the down control signal band. If both switches are depressed the second resistor is bypassed as the first switch is closed and the fourth resistor provides a current path as the second switch is depressed. This configuration results in a up/down analog signal voltage band having a voltage that is smaller than the voltage of the neutral voltage band and larger than the voltage of the up voltage band.
REFERENCES:
patent: 4095071 (1978-06-01), Chamberlain
patent: 4360718 (1982-11-01), Schobinger et al.
patent: 5244066 (1993-09-01), Mackoway et al.
patent: 5456333 (1995-10-01), Brandt et al.
patent: 5566586 (1996-10-01), Lauer et al.
Deere & Company Brochure entitled Crawler Dozers 550H, cover and pp. 2, 4-5, 10-11, and back page, printed in the U.S.A., Sep. 1999.
Deere & Company
Tso Edward H.
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