Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1991-09-27
1992-12-22
Lorence, Richard
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
74868, 74878, B60K 4106
Patent
active
051726114
DESCRIPTION:
BRIEF SUMMARY
The invention concerns an engine-rpm-dependent arrest device to prevent non-permitted down shifts (hereinafter called a "down shift arrest device" for short) in motor vehicle transmissions having at least two shiftable gears with one gear-shift valve movable by the driver, one pilot valve with two shift positions and one control valve with two shift positions, according to the preamble of claim 1.
Such a down shift arrest device has been disclosed, for instance, in German Patent 20 40 195. The arrest device in said patent consists of two independent separate arrest devices which engage depending upon the traveling speed. One of the said separate arrest devices acts upon a group transmission rear-mounted on a four-gear transmission. Both gear steps of the group transmission are changed over by a pilot valve designated as a relay valve which is pilot controlled by a gear-shift valve designated as a pilot-control valve. The actual change-over is effected by a double-acting shift cylinder which corresponds to an activation device for the low and the high gear steps, respectively. By means of a low-pressure pump that works depending on the traveling speed, a down shift from the high gear group to the low gear group is prevented when the vehicle has exceeded a specific traveling speed corresponding to a given, but still permitted, rpm of the prime mover. By means of the said down shift arrest device an overspeed of the prime mover is prevented, which would occur if the change-over transmission were down shifted from the high gear range to the low gear range when the prime mover is at high speed.
The down shift arrest device already known is successfully used in practice. When used in certain vehicles such as mobile excavators and similar working machines, however, greater importance is attached to a simple arrangement of the pressure fluid lines (for instance, on account of the guiding of the lines from the upper to the lower chassis of the mobile excavator) which are required for the control and actuation of the transmission, and of the down shift arrest device.
Therefore, the invention is based on the problem of simplifying the already known, down shift arrest device in the sense that the number of necessary pressure medium pipes can be reduced. At the same time, however, the quality and reliability of the arrest device must be maintained.
This problem is solved by the engine-rpm-dependent arrest device characterized in claim 1. The invention, however, is not limited to the combinations of features of the claims. Other logical possible combinations of claims and individual features of the claims result for the expert as the problem arises.
The solution of the problem consists of a combination of individual features. The primary individual feature is that the control valve is exclusively in contact with the pressure medium conveyed by the low-pressure pump. This means that the control valve can be designed as an easily engageable piston valve without a high-pressure seal. The low-pressure flow controlled by the control valve is fed to the pilot valve for direct activation on the large end surface or on the annular surface of the pilot-valve piston designed as a stepped piston. For shifting the low gear, the force of the low pressure acting upon the annular surface is supported or the force of the low pressure acting upon the large end surface is overdriven by means of the force of the shift pressure acting upon the small end surface of the stepped piston. In a state of operation where the high gear is engaged and the prime mover and therewith the low-pressure pump revolve at high speed at which the given value of the pressure of the low-pressure pump is exceeded, an actuation of the actuation device of the low gear with shift pressure is prevented in that the first work line connection coordinated with the low gear is connected with the activation connection for the activation device of the high gear. A non-permitted down shift to the low gear is thereby prevented.
By virtue of this design according to the inve
REFERENCES:
patent: 3937107 (1976-02-01), Lentz
patent: 4680989 (1987-07-01), Sykora et al.
patent: 4903551 (1990-02-01), Hiramatsu et al.
patent: 5005445 (1991-04-01), Gierer
patent: 5079973 (1992-01-01), Ookubo et al.
Buck Gerhard
Eymuller Helmut
Legner Jurgen
Stutzle Siegfried
Levi Benjamin
Lorence Richard
Zahnradfabrik Friedrichshafen AG
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